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Copyright copy 2010 American Scientific PublishersAll rights reservedPrinted in the United States of America

Journal ofBionanoscience

Vol 4 1ndash13 2010

Nanoncology A State-of-Art Update

V S Joo1 T G Ramasamy1 R Murugan23 and Z S Haidar145lowast1Department of Bioengineering and Regenerative Medicine Utah-Inha DDS and Advanced Therapeutics Research Center

B-404 Meet-You-All Tower Songdo TechnoPark 7-50 Songdo-Dong Yeonsu-Gu Incheon 406-840 Republic of South Korea2Faculty of Medicine National Institute of Health and Medical Research U977 University of Strasbourg Strasbourg 67085 France

3WPI-Advanced Institute for Materials Research Tohoku University Sendai 980-8577 Japan4Department of BioEngineering School of Medicine University of Utah 301 Skaggs 190D BPRB Salt Lake City UT 84112-5820 USA

5Department of Pharmaceutics and Pharmaceutical Chemistry College of Pharmacy University of Utah 30 South 2000 EastSalt Lake City UT 84112-5820 USA

Nanoscale drug delivery applications in cancer therapeutics termed as nanoncology are beingutilized to resolve recurring problems in conventional drug delivery Nanoparticles have propertiesunlike their bulk counterparts and the ongoing development of these characteristics continues toincrease the repertoire of bio-functionality in regards to interactions of oncotic cellular and molecularsystems Nanoparticles can be constructed in a manner that is tunable and targeted which givesstandard chemotherapy a new approach in terms of drug administration and lowering off-targettoxicities This work concisely discusses pivotal factors in nanoparticle characteristics for cancertherapy providing an up-to-date therapeutics platforms review

Keywords Cancer Chemotherapy Drug Delivery Nanobiotechnology NanoparticleNanoncology Oncology Polymers Therapy Tumor

CONTENTS

1 Introduction 12 Targeting Methodology and Factors 2

21 Tumor Infrastructure 222 Hypoxia and pH 223 Receptor and Antigen Directed Targeting 224 Protein Targeting 325 Carbohydrate-Directed Targeting 3

3 Advantages of Nanoncology 331 Eliminating Drug Resistance 332 Avoiding Physiological Barriers 4

4 Key Properties of Anti-Cancer Nanoparticles 441 Dimensions 442 Surface Properties 443 Intermolecular Binding 4

5 Nanobiotechnology Therapeutic DeliveryPlatforms in Cancer 551 Polymeric Nanoparticles 552 Micelles 653 Liposomes and Solid Lipid Nanoparticles 654 Dendrimers 655 Carbon Nanotubes and Nanodiamonds 656 Silicon Nanoparticles 757 Gold and Magnetic Nanoparticles 758 Viral Nanoparticles 859 RNA Interference 8510 Monoclonal Antibodies 9511 Aptamers 9

lowastAuthor to whom correspondence should be addressed

6 Current Clinical Progress of Nanoncology Therapeutics 97 Closing Remarks Future Perspective 11

Acknowledgments 11References and Notes 11

1 INTRODUCTION

Cancer therapy is one of the most extensively researchedfields in biomedical research Even so the progress inwhich novel therapeutics are developed produced testedand approved is regrettably slow Traditional chemother-apeutic agents disperse throughout the human body ina non-specific manner which affects both cancerous andindigenous cell populations producing deficient treatmentdue to excessive toxicities and limited maximum dosagewithin the tumor As a result target organs and tissuesrequire a constant administration of drugs in increasingquantities which also may result in systemic toxicity andserious adverse effects However advances in the fieldof nanobiotechnology now provide numerous alternativesin the way nano-scientists and clinicians approach can-cer therapy The use of nano-bio-inspired therapeutics intumor treatment termed lsquonanoncologyrsquo includes nano-sized particles typically comprised of therapeutic entitiessuch as small-molecule drugs nucleic acids peptidesproteins as well as components that assemble with nano-scaled delivery agents such as lipids and polymers to

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Nanoncology A State-of-Art Update Joo et al

form nanoparticles1ndash3 These formulations can have anenhanced anticancer effect compared to the therapeuticentities they contain alone This is due to more special-ized targeting to tumor tissue via improved pharmacokinet-ics pharmacodynamics and active intracellular deliveryRecent and ongoing advancements in nanotechnology havebeen able to contend with common problems associatedwith chemotherapy such as drug resistance drug degra-dation drug solubility and side effects due to systemictoxicity4 This approach could potentially eliminate suchproblems that occur during cancer therapy While drug sol-ubility and drug protection from degradation are importanttopics in nanoncology it is worth mentioning herein thatthey will not be covered in this review due to the speci-ficity in detailing their physical and chemical propertiesSeveral excellent works are available in the published lit-erature that the curious reader is encouraged to consultLikewise regarding imaging and bio-sensing applicationsSo in a traditional chemotherapy regime cancer cells maydevelop resistance to drug therapy leading to a relapseof the disease and subsequently an increased dosage ortransition to a new chemotherapeutic agent5 Two mainobjectives in the process of enhancing the effectiveness perdosage of any therapeutic constitution(a) to increase selectivity in the distinction between cancerand healthy cells and(b) to equip therapeutic delivery agents with proper mech-anisms to overcome chemical biological and physiologicalobstructions that offset target acquisition4

Those are discussed in the next few sections

2 TARGETING METHODOLOGY ANDFACTORS

Nanoparticulate drug delivery systems through the useof biodegradable and biocompatible materials provide amore efficient yet less harmful solution to overcome someof these hurdles The delivery of a drug to its target tis-sue through the use of nanoparticles can be accomplishedprimarily in two ways passive and active Passive target-ing exploits the permeability characteristic of tumor tissueAccelerated vascularization from the tumor supplying therapid growth of cancerous tissue creates a leaky and defec-tive architecture which in turn can be more easily accessi-ble to toxic therapeutics67 Passive targeting incorporatesthe delivery of the drug to the tumor bed through severalinvasive modalities On the other hand active targeting isusually achieved by conjugating the nanoparticle to a tar-geting moiety allowing preferential accumulation of drugin tumor tissue and within individual cancer cells intra-cellular organelles or molecules specific to cancer cellsThis approach can be used to direct nanoparticles towardscancer cell surface carbohydrates receptors antigens andother proteins There are a number of excellent reviewsdiscussing this subject in vast detail2ndash5

21 Tumor Infrastructure

Much of the tumor vasculature displays abnormalities dif-ferent from the surrounding tissue which enables a biodis-tribution of nanoparticles favorable for the localization oftherapeutics First described by Maeda8 enhanced perme-ability and retention (EPR) phenomenon is based on twofactors(a) capillary endothelium in malignant tissue being moredisorderly and irregular and(b) lack of tumor lymphatic drainage in the tumor bedresults in accumulation of the drug

Based on size and surface characteristics alone nanopar-ticles may concentrate within the tumor bed several foldshigher than in plasma8 Most nanotherapeutics currentlyin clinical use utilize passive targeting to reach tumorsA number of reviews cover the tumor vasculature and theEPR effect in greater detail8ndash10 A recent advancement inpenetrating the tumor infrastructure comes with the pro-tein iRGD which displays increased vascular and tissuepermeability specific to the tumor via targeting the vintegrins expressed on the tumor vessel endothelium andneuropilin-1 Indeed co-administration with doxorubicin-loaded nanoparticles has much higher intracellular concen-trations than with iRGD-free11

22 Hypoxia and pH

As tumor cells proliferate regions of deprived oxygen arecreated within the tumor microenvironment1213 Hencetumor hypoxia is related to the resistance in chemother-apy and radiotherapy as well as being characteristic ofincreased tumor aggressiveness Tumor microenvironmentalso exhibits a pH imbalance that deviates from the nor-mal extracellular pH allowing its surroundings to becomeslightly acidic The primary reason for this imbalance ofcancer pH is the high rate of glycolysis in cancer cellsThis is may be beneficial to the cancer cells by gen-erating an unfavorable environment for the surroundingnormal tissue cell and extracellular matrix1314 Also theacidic pH in endosomes and lysosomes during endocyticuptake is a possible factor to consider for pH-sensitivenanotherapeutics For example Baersquos University of Utahresearch group has recently developed pH-sensitive poly-meric micelles which destabilize below a pH of 74 Thisallowed drug release within the extracellular tumor micro-enivornment and in endosomes following folate receptor-mediated endocytosis14

23 Receptor and Antigen Directed Targeting

Overexpression of specific receptors and antigens in humancancers shows a substantially more efficient uptake viareceptor-mediated endocytosis A drug bound to a poly-mer carrier may be taken into the cell via ligand-receptor interactions Once localized at the cell surface

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the targeted drug-polymer carrier complex may exertits cytosolic action either at the plasma membrane orfollowing internalization15 Receptorantigenic expressionshould be reversible after drug delivery is complete Vascu-lar endothelial growth factor receptor and human epidermalreceptor are some of the different types of receptors that canbe targeted due to high levels of expression in tumor cellangiogenesisproliferation1516 To circumvent cell perme-ation problems and improve tumor specificity in nanopar-ticulate therapeutics folate receptor-mediated endocytosishas emerged as a potential strategy for drug delivery dueto both an overexpression of the folate receptor on can-cer cells and rapid internalization by receptor-mediatedendocytosis1617 Incidence of folate receptor expression inhuman head and neck (primary and metastatic) tumor tis-sues exists and compared with normal tissue such as bonemarrow folate receptor expression was found in 53 ofsamples whereas normal bone marrow cells did not displayany folate receptor expression Thus such receptor over-expression has indeed some great active tumor targetingpotential16

24 Protein Targeting

Matrix metalloproteinases (MMP) are zinc-dependentendopeptidases that play a major role in ECM degrada-tion as well as tissue repair morphogenesis angiogene-sis and have been shown to be overexpressed in tumortissue1819 In an effort to target MT1-MMP Fab222-1D8prime

fragments of anti-human MT1-MMP monoclonal anti-body were conjugated to doxorubicin immunoliposomescontaining approximately 40 Fabprime fragments per lipo-some Subsequently the liposomes were administered totumors 1000 to 3000 mm3 in size20 After 12 days non-targeted liposome treatment showed decreased tumor vol-ume in 16 mice and 36 mice died probably due toside effects of doxorubicin-encapsulated non-targeted lipo-somes However in the case of targeted liposomes tumorvolume decreased significantly with only 1 mouse report-ing notable body weight changes20 TNF- and v3 inte-grin are other tumor targeting proteins1520

25 Carbohydrate-Directed Targeting

Lectin-cell surface carbohydrates are used for activedrug targeting Briefly cell surface carbohydrates affecttumor cell interactions with normal cells during metastaticspread and growth21 These interactions can be mediatedthrough tumor cell carbohydrates and their binding pro-teins referred to as lectins Further cell surface mem-brane lectins are known to be overexpressed on the surfaceof numerous cancer cells and able to internalize endoge-nous sugar molecules22 Lectins affect tumor cell survivaladhesion to the endothelium as well as tumor vascular-ization and other processes crucial for metastatic spreadand growth21 This ligand-carbohydrate interaction can

be used for the development of nanoparticles containingcarbohydrate moieties that are directed to certain lectinsand incorporating lectins directed to exact cell surfacecarbohydrates2123

3 ADVANTAGES OF NANONCOLOGY

31 Eliminating Drug Resistance

Drug resistance has become a major obstacle in limit-ing the efficacy of chemotherapy The ATP-binding cas-sette (ABC) family of transporters plays a central partin the emergence of drug resistance as carrier pumpsfor influx and efflux of hydrophobic drugs among cancercells Nucleotide binding domains (NBD) for ATP bindingand hydrolysis derives energy necessary for transportingcell nutrients across membranes Three ABC transportersknown to be involved in multiple drug resistant cancer areP-glycoprotein (P-GP)2425 multi-drug resistance associ-ated protein (MRP)2425 and breast cancer resistance protein(ABCG2)25 One possible mechanism in which nanopar-ticles may help anticancer drugs avoid recognition bythe P-GP efflux pump is by means of envelopment inan endosome upon entering the cell via ligand targetedreceptor-mediated endocytosis thereby leading to higherintracellular concentrations25 As the interior of the endo-some becomes more acidic and lysozymes activated thedrug may be released from its nanoparticle conjugateand enter the cytoplasm to its target organelle avoidingthe P-DP efflux pump Kobayashi et al demonstrated abypass of the P-glycoprotein transporter with liposomesin doxorubicin-resistant SBC-3 a human small cell lungcancer cell line Transferrin ligands were attached todoxorubicin encapsulated EPC liposomes which showedsignificantly higher cytotoxicity in MDR cells than non-targeted liposomes Transferrin-bound liposomes were ableto deliver doxorubicin more closely to the nucleus allow-ing less of the drug to be affected by P-GP pump26 Non-transport based mechanisms can affect a variety of drugclasses as well This particular type of resistance may becaused by a mutation or an alteration in the activity ofenzymes such as glutathione S-transferase and topoiso-merase which decreases the cytotoxic efficiency of drugsindependent of intracellular drug concentrations Changesthat occur in the regulation of proteins that control apopto-sis and reduction in the efficacy of chemotherapeutic agentscan be attributed to the fact that most cancer drugs uti-lize cytotoxic effects by apoptotic processes25 Chen et al27

addressed this issue using mesoporous silica nanoparti-cles that simultaneously deliver doxorubicin and Bcl-2-targeting siRNA in multi-drug resistant A2780AD humanovarian cancer cells Bcl-2 overexpression is linked withinhibition of cellular apoptosis as well as being the mainnon-pump resistance protein in multi-drug resistant cancercells Cytotoxicity of doxorubicin was increased 132-foldfollowing co-delivery of Bcl-2 siRNA This shows the

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effectiveness in which a nanoparticulate system may carryboth the therapeutic agent and a small molecule inhibitor orchemo-sensitizer to disrupt the drug resistance mechanismwhile inducingenhancing chemotherapy simultaneously27

32 Avoiding Physiological Barriers

For conventional formulations the path of a therapeuticagent from the point of administration to the target ofintent is consistently subverted by obstructions and bio-logical barriers that may prevent effective treatment Onesuch example is the tight junction between epithelial cellsknown as the blood brain barrier (BBB)28 Now certainnanoparticles have shown ability in crossing the BBB dueto intrinsic properties of their constituent core materialssuch as polysorbate-coated nanoparticles In one studydoxorubicin-bound nanoparticles coated with polysorbate80 were used to target glioblastoma in rats showinghigher survival rates than non-coated doxorubicin-boundnanoparticles29 However more conclusive studies on dox-orubicin and polysorbate neuro-toxicity must be com-pleted before considering clinical use Endothelial vascularpermeability may be increased by the co-administrationof a bradykinin antagonist a cyclooxygenase inhibitoror a nitric oxide scavenger30 This is a possible strat-egy for the enhancement of tumor vasculature targetingThe combined delivery of permeation enhancers such aszonula-occludens toxin and its fragments can reversiblyopen tight junctions and allow penetration of nanopar-ticle agents31 Antagonistic oncotic and interstitial pres-sures from tumor bed as well as dissemination or cellularuptake throughout the tumor interstitium poses problemsfor the entry passage and retention of nanotherapeutics32

Phagocytes of the reticuloendothelial system (RES) actas immunological barriers against the targeting poten-tial of nanoparticle-encapsulated drugs as they sequesterinjected nanoparticles from circulation Extensive researchand experience in liposomes have demonstrated that uptakeby RES is effectively avoided by surface modification withpolyethylene glycol (PEG) to increase circulatory half-life from minutes to hours or days thereby allowing forenhanced targeting of liposomes within the tumor33 How-ever PEGylation not only prevents RES uptake but alsomasks the targeting ligand causing a reduction in thechances of bio-recognition and uptake34

4 KEY PROPERTIES OF ANTI-CANCERNANOPARTICLES

41 Dimensions

The dimensions of nanoparticles in cancer therapy arewidely debated however it is understood that the diam-eter of a nanoparticle should be in the range of 55 nmndash250 nm depending on the composition and surfacemodifications35ndash37 Lower limits have been defined due to

the threshold for filtration of particles within the glomeru-lar capillary wall of kidneys being 55 nm35 On the otherhand the upper size limits are not definite at the momenthowever increasingly larger particles or particle aggregatestend to be more prone to the RES The vasculature intumors is vulnerable to macromolecule permeation andEPR effect Nonetheless the cutoff in size for nanoparticleaccumulation in the tumor attributed to EPR effect seemsto be about 400 nm36ndash39 Particles hundreds of nanometerin size have been shown to leak out of blood vessels andaccumulate within tumors but larger macromolecules maystill have limited diffusion within the extracellular space38

Experiments from animal models suggest that particles of150 nm neutral or slightly negatively charged can movethrough tumor tissue In addition recent data shows thatnanoparticles in the 50ndash100 nm range carrying a slightpositive charge penetrate large tumors following systemicadministration40 Therefore are restricted from exiting intonormal vasculature requiring a size less than 1ndash2 nm3536

42 Surface Properties

Nanoparticles have a high surface-to-volume ratio com-pared to microparticles Control of surface properties is cru-cial for predicting behavior in the human body2341 Theultimate fate of nanoparticles can be determined by theinteractions of nanoparticles within their local environmentwhich depends largely on a combination of size and surfaceproperties Nanoparticles are sterically stabilized and havesurface charges41 In a recent study with gold nanoparti-cles positively charged nanoparticles depolarized the mem-brane to the greatest extent while nanoparticles of othercharges had a negligible effect However as the surfacecharge greatens (either positively or negatively) chancesfor macrophage uptake and clearance by RES increase39

Further therapeutic entities within nanoparticles do notimpact nanoparticle propertiesmdashdoxorubicin-loaded lipo-somes and their drug-free analogue liposomes for exam-ple can be expected to possess the same particle sizesurface charge pharmaco-dynamics-kinetics etc In con-trast molecular conjugates often strongly alter the prop-erties of the individual drug molecule with presence of acovalently attached modifier such as PEG andor antibody

43 Intermolecular Binding

The incorporation of targeting ligands provides specificnanoparticle-cell surface interactions in the selectivity ofthe nanoparticle Affinity of the ligand and its recep-tor can strongly influence the effects of multivalencyRelatively low-affinity ligands have potential to createstrong effective affinities within the context of a multi-valent nanoparticle42 For example increasing the num-ber of transferrin molecules on a 70-nm PEGylated goldnanoparticle to 144 gave a 013 nM Kd to the surface of

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Neuro2A cells (which have upregulated transferring recep-tors) compared to 64 nM for transferrin alone43 More-over molecules without sufficient binding affinity for useas a drug or individual targeting ligand can be encapsulatedwithin nanoparticles Also many drug candidates that wereineffective due to low binding of the target can be used onthe surface of nanoparticles as targeting agents A target-ing ligand increases the extent of cellular internalizationby particles that reach tumor tissue in a ligand density-dependent manner Inability of a targeting ligand to sig-nificantly increase tumor deposition is consistent with theroles of molecular size and affinity on tumor uptake44

It has been reported that intermediate-sized ligands witha molecular weight of about 25 kDa achieve the low-est tumor uptake levels while both smaller ligands (thatrequire high receptor affinity to be retained) and largerligands (that can achieve similar retention as smaller lig-ands withgt 100-fold weaker binding) showed an enhancedtumor uptake42ndash44

5 NANOBIOTECHNOLOGY THERAPEUTICDELIVERY PLATFORMS IN CANCER

A few nanoncologic systems have reached the pre-clinicaland clinical trial stage Below is a comprehensive yet pro-visional set of potential drug delivery systems examples(Fig 1) and their components being investigated in vitroand in vivo currently Other nanoparticles such as quantumdots nanowires and nanosensors are not discussed as theymainly deal with detection and imaging Yet few excitingmultifunctional systems such as iron oxide nanoparticlesare touched upon to further stress their future potential

51 Polymeric Nanoparticles

Polymers such as chitosan cyclodextrins alginate andhyaluronic acid occur naturally and have been the mate-rial of choice for the delivery of proteins DNA RNA

Fig 1 Nanoncology carrier applications in cancer therapeutics

as well as drugs Natural polymers have the advantageof being biodegradable and biocompatible more so thantheir synthetic counterparts45ndash47 Gupta and colleaguesexperimented with biologically-derived silk fibroin (SF)and chitosan (CH) blended non-covalently to encapsulatecurcumin48 Curcumin can interfere with the activity oftranscription factor NF-B and induce apoptosis in cancercells while avoiding healthy cells SF was shown to havebetter encapsulation properties and efficacy than liposomesSF-curcumin nanoparticles showed higher efficacy againstbreast cancer cells48 This demonstrates the potential totreat in vivo breast tumors by a possible sustained long-term biodegradable and therapeutic delivery system Onthe other hand synthetic polymers are not easily removedby normal clearance systems and can accumulate in tissuesHowever synthetic polymers such as PEG poly(lactic-co-glycolic acid) (PLGA) polyethylenimine (PEI) andhydroxyl propyl methacrylamide copolymer (HPMA) havecharacteristics that are more well-defined and can be finetuned to perform in a predictable manner As shown earlierchemical conjugation with PEG or PEGylation is one of themost acknowledged methods for prolonging the duration ofdrugs in the bloodstream and has also been demonstratedto contain certain targeting properties as well49 PEGyla-tion lowers plasma clearance rate by reducing receptor-mediated uptake during systemic circulation as well asmetabolic degradation by disguising the surface of theprotein49 It also reduces immunogenicity improves thesafety profile of the protein and protects the immunogenicepitopes Liu et al developed a novel nanocrystal formu-lation of Pluronic F127 for 2 anti-cancer drugs paclitaxel(PTX) and camptothecin50 Intravenously injected nano-crystals significantly inhibited tumor growth Considerabletherapeutic effects were shown via oral administration aswell In addition the targeted delivery of PTX via conju-gating a folate ligand to F127 was demonstrated50

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52 Micelles

Amphipilic nanoparticles composed of block or graft co-polymers such as N -vinylpyrrolidone and poloxamers canform polymeric micelles A hydrophobic core containshydrophobic drugs and the hydrophilic shell stabilizesthe core and makes the drug water-soluble4751 Poly-meric micelles have been shown to accumulate more read-ily in tumors than the larger liposomes mainly due totheir size51 The first polymeric micelle formulation ofPTX Genexol-PM a cremophor-free polymeric micellehas completed phase II clinical trials in the US withconsiderable anti-tumor activity in combination with cis-platin chemotherapy Cremophor EL is an excipient withcertain drugs and has been suggested to be a dose lim-iting factor in the administration of PTX52 This micel-lar nanoparticulate system allowed for higher doses of thedrug while being able to deliver and concentrate inside thetumor interstitium Another biodegradable formulation ofcationic micelles were prepared with PDMAEMA-PCL-PDMAEMA tri-block co-polymers and applied for thedual delivery of siRNA and PTX into cancer cells Combi-natorial delivery of anti-VEGF siRNA and PTX knockeddown VEGF expression53

53 Liposomes and Solid Lipid Nanoparticles

Natural liposomes a closed colloidal structure composedof a lipid bi-layer and an aqueous core are composed oflecithin phospholipids and can also be multi-laminar ratherthan uni-laminar carrying a larger payload of water- andfat-soluble constituents up to 500 nm in size5455 Lipo-somes take advantage of the overexpression of perforationsin cancer neovasculature in order to increase drug concen-trations passively at tumor sites Liposomal drug deliveryhas been the most successful nanoparticulate formulationused in the clinic as shown by liposomal-encapsulateddoxorubicin for Kaposirsquos sarcoma and more recentlybreast and ovarian cancer56 Small dimensions (lt300 nm)enables the drug to accumulate in the tumor mass by cross-ing passively into the tumor vasculature while avoiding orreducing the permeation of normal tissue55 On the otherhand solid lipid nanoparticles (SLNs) are solid lipids athuman physiological temperature with a diameter from50 to 1000 nm They are formed from a range of lipidsincluding mono- di- and tri-glycerides waxes fatty acidsand combinations of those SLNs are biodegradable bio-compatible with several human applications57 They form astrong lipophilic matrix in which water-insoluble lipophilicdrugs can be loaded for subsequent release The chemi-cal and physical properties of lipids in a heterogeneousmixture promote an imperfect crystalline structure withlarger gaps for efficient drug loading57 Use of SLNs havebeen investigated for the delivery of various anti-cancerdrugs with promising results in pre-clinical mouse trialsspecifically showing that SLNs might help overcome MDR

in cancers Serpe et al using human colon cancer cellsHT-29 demonstrated the benefits of SLNs in the deliveryof cholesteryl butyrate (chol-but) with doxorubicin Cyto-toxicity was shown to be higher in chol-but SLN loadedwith doxorubicin than free doxorubicin alone howeverPTX-loaded SLN did not show any improvement over freePTX5859 Lu et al loaded mitoxantrone a topoisomeraseinhibitor that blocks DNA replication into SLNs for alocal injection in the treatment of breast cancer and lymphnode metastases in mice60 Almost three-fold reduction inlymph node size was reported when compared to freely-administered mitoxantrone This was considered a signifi-cant improvement over existing treatment by the authors60

54 Dendrimers

Dendrimers may serve as a versatile nanoscale platformfor creating a multi-functional system capable of detect-ing cancer and delivering drugs A synthetic polymericmacromolecule of nanometer dimensions a dendrimer iscomposed of multiple highly branched monomers thatemerge radially from a central core The readily modifiablesurface characteristic enables them to be simultaneouslyconjugated with several molecules such as imaging con-trast agents targeting ligands andor therapeutic drugs61

Many commercial small molecule drugs with anti-canceractivity have been successfully conjugated with den-drimers such as polyamidoamine poly(propylene imine)and poly(etherhydroxylamine) dendrimers by means ofeither steric interactions or chemical reactions6263 Tar-geted delivery is possible via targeting moieties conju-gated to dendrimer surface or passive delivery due to theEPR effect Cationic dendrimers show cytotoxicity how-ever derivatization with fatty acid or PEG chains canreduce the overall charge density and minimize contactbetween cell surface thus reducing toxic effects6162 Patriet al demonstrated that covalently coupled methotrexate-dendrimer conjugates targeting high-affinity receptor forfolic acid have a similar activity to the free drug invitro while specifically killing receptor-expressing cells viareceptor-mediated endocytosis64

55 Carbon Nanotubes and Nanodiamonds

Carbon nanotubes are generally insoluble causing them tobe non-biocompatible however the introduction of chem-ical modification to carbon nanotubes render them water-soluble and functionalized so that they can be linked to awide variety of active molecules such as peptides proteinsnucleic acids and therapeutic agents Functionalized car-bon nanotubes also have an intrinsic capability to perme-ate cell membranes which allows endocytosis-independentinternalization of nanoparticles265 Methotrexate cova-lently linked to carbon nanotubes with a fluorescent agentwas shown to be more effectively internalized into cells

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when compared to the free unbound drug65 The multi-ple covalent functionalizations on the sidewall or tips ofcarbon nanotubes allow them to carry several moleculesat once This strategy provides a fundamental advantagein the treatment of cancer Targeted heat therapy or lsquother-mal ablationrsquo is being tested to destroy breast cancertumors using carbon nanotubes Accordingly the HER2IgY-single wall carbon nanotube (SWNT) complex specif-ically targeted HER2-expressing SK-BR-3 cells but notreceptor-negative MCF-7 cells Near-infrared irradiationwith an 808 nm laser showed extensive cell death withSWNT66 On the other hand a nanodiamond-embeddeddevice is being developed to deliver chemotherapy locallyto sites where cancerous tumors have been surgicallyremoved67 Nanodiamonds complexed with doxorubicin-hydrochloride enable a sustained release of drug for aminimum of 30 days with a significant amount of drugin reserve This shows potential for highly localized drugrelease as a complementary yet potent form of treat-ment with systemic injection Ho and group embeddedmillions of tiny drug carrying nanodiamonds into theFDA-approved parylene67ndash69 Currently used as a coatingfor implants biostable parylene is a flexible and versa-tile polymeric material Nanodiamonds placed betweenextremely thin parylene films resulted in a device that isminimally-invasive Internalization assays revealed a pri-marily endocytic uptake process High degree of nanodia-mond (sim46 nm in diameter) and endosome co-localizationas well as cytoplasmic presence of smaller nanodiamondswere observed69

56 Silicon Nanoparticles

Silicon and silica are establishing themselves as inter-esting candidate materials for injectable nanoparticles indrug delivery70 Porosified silicon is biodegradable71 withkinetics that are much more rapid than those of typicalbiodegradable polymers and as a result releases drugswith previously un-attainable time profiles Lu et al loadedhydrophobic anti-cancer drug camptothecin (CPT) ontomesoporous silica nanoparticles CPT release was mini-mal and sustained in aqueous solution This effectivelyaddressed the problem of poor water-solubility of certainanti-cancer drugs as well as sustainable release profiles71

Furthermore there are metal-based nanovectors such asnanoshells70 comprised of a gold layer over a silica coreThe thickness of the gold layer can be precisely tuned sothat the nanoshell can be selectively activated through tis-sue irradiation with near-infrared light to perform localizedtherapeutic thermal ablation This approach was recentlyused to eradicate transmissible venereal tumors in mice72

In another study nitric oxide (NO)-releasing silica nanopar-ticles exhibited enhanced growth inhibition of ovariantumor cells and showed greater inhibition of the anchorage-independent growth of tumor-derived and Ras-transformed

ovarian cels73 NO a free radical bio-regulator endoge-nously synthesized in the body impacts multiple stages oftumor development spanning cytostatic processes cellulartransformation and formation of neoplastic lesions7374 Itis worth mentioning herein that research efforts have beenimpeded by the fact that possible normal cell toxicity ofthe NO donor drug by-product and the inability to targetdelivery of the drug selectively to cancer cells

57 Gold and Magnetic Nanoparticles

Gold (Au) nanoparticles are very versatile and can beprepared with different geometries such as nanospheresnanoshells nanorods or nanocages75 Further they haveunrivaled physical and chemical properties such asexceedingly small size (less than 50 nm) large sur-face area to mass proportion heightened surface sensitiv-ity presence of characteristic surface plasmon resonancebands biocompatibility and ease of surface functionaliza-tion Au nanoparticles are also excellent conductors ofelectrical and thermal energy which allows possibilitiesfor thermal ablation treatment In photodynamic therapy(PDT) Au nanoparticles are becoming known as a photo-sensitizer with great potential due to its optimal absorptionand light scattering properties along with controllable opti-cal characteristics El-Sayed and collegues have shown thatanti-EGFR antibody conjugated gold nanoparticles selec-tively localized in malignant HOC and HSC cells andunderwent significant photothermal destruction upon nearinfrared irradiation76 However using radiofrequency irra-diation Gannon et al demonstrated that the internalizationof Au nanoparticles in gastrointestinal cancer cells releasedsubstantial heat rapidly after exposure to an external high-voltage focused radiofrequency field (RF) It is noteworthythat radiofrequency ablation has an advantage over nearinfrared ablation which is limited to superficial tumorswith minimal tissue penetration Hep3B and Panc-1 cellstreated with 67 ML Au nanoparticles had significantlyhigher rates of cell death than the control samples at alltime-points after RF exposure77 Interestingly Au nanopar-ticles about 5ndash10 nm in diameter have been shown to haveintrinsic anti-angiogenic properties78 These nanoparticlesbind to heparin-binding pro-angiogenic growth factorssuch as VEGF165 and bFGF to inhibit their activity TheAu nanoparticles themselves also reduced ascites accumu-lation in a pre-clinical model of ovarian cancer inhibitedproliferation of multiple myeloma cells and induced apop-tosis in chronic B cell leukemia78 On the other hand mag-netic nanoparticles (MNPs) have traditionally been usedfor disease imaging via magnetic resonance (MR) imagingdue to their intrinsic properties Recent advances have alsoopened the door to cellular-specific targeting drug deliv-ery and multi-modal imaging Further MNPs can be func-tionalized through coating with polymers preferentiallywith biocompatible or biodegradable polymers of synthetic

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or biological origin7980 As solid tumor develops it out-grows its blood supply which results in the formation ofa hypoxic semi-necrotic tumor core and dormant tumorcells send out chemical signals that recruit macrophagesinto the core Macrophages begin to rebuild the bloodsupply allowing the tumor to start growing again8182

Muthana et al loaded human monocytes with MNPs plac-ing magnets near the site of a human prostate tumor grownin mice82 The MNP-loaded monocytes carrying a reportergene invaded the tumor at a rate more than three timesthat of the non-loaded cells82 This demonstration of mag-netic targeting shows that MNP-loaded cells circulatingin the body can be attracted to the tumor site where anexternal magnet is placed allowing a higher proportion ofloaded cells to respond to chemical signals from the tumorcore In addition the loaded monocytes were able to reachthe poorly vascularized peri-necrotic regions of the tumorthat are normally difficult to target As the moncytes areloaded with MNPs they can then be destroyed by hyper-thermia after delivering a therapeutic drug or gene8182

Classes of MNPs include metallic bimetallic and super-paramagnetic iron oxide nanoparticles widely-knows asSPIONs SPIONS are favored because due to low toxicityprofile and their reactive surface that can be readily modi-fied with biocompatible coatings87 This flexibility has ledto SPION use in magnetic separation biosensor in vivomedical imaging drug delivery tissue repair and hyper-thermia applications84 Yu et al preciously showed thatthermally crosslinked SPIONs loaded with doxorubicinhad potential as both an imaging and therapeutic deliverysystem83 This DoxTCL-SPION was also demonstratedto efficiently reach tumor sites and release the drug withoutany active targeting from ligandsantibodies or magneticfield largely due to the EPR effect83

58 Viral Nanoparticles

A variety of viruses including cowpea mosaic viruscanine parvovirus adenovirus coxsackie virus measlesvirus along with virions and virus-like particles have beendeployed for biomedical and nanotechnology applicationsthat include tissue targeting and drug delivery84 Target-ing molecules and peptides can be produced in a bio-logically functional form on the capsid surface throughchemical conjugation or gene expression Several lig-ands including transferrin folic acid and single-chainantibodies have been conjugated to viruses for specifictumor targeting84 Further a subset of viruses such ascanine parvovirus have a natural affinity for receptors liketransferrins that are up-regulated in a variety of tumorcells85 Adenoviral vectors offer many advantages for can-cer gene therapy including high transduction efficiencyyet safety concerns related to immunogenic response haveled to a cautious approach of their use in human clini-cal trials86 To overcome these obstacles hybrid vectors

combining both viral and non-viral elements are beingdeveloped Adenovirus coated with an arginine-graftedbioreducible polymer (ABP) via electrostatic interaction isone example ABP-coated complexes were shown to havesignificantly reduced the innate immune response whileproducing higher levels of transgene expression8687 Fur-thermore herpes simplex virus (HSV) vectors are alreadyin early phase human clinical trials for recurrent malignantglioblastoma A mutant form (vIII) of epidermal growthfactor receptor (EGFR) present in glioma tumor is rec-ognized by a single-chain antibody designated MR1-1HSV virions bearing MR1-1-modified gC had five-foldincreased infectivity for EGFRvIII-bearing human gliomaU87 cells showing enhanced vector specificity and tumorcell damage88

59 RNA Interference

Since its discovery nearly two decades ago RNA inter-ference (RNAi) has been lauded as the next generation ingene therapy due to the unique pathway in which smallinterfering (siRNA) or microRNA (miRNA) can preventmRNA expression and silence- specific targeted geneseffectively89 RNAi cancer gene targets are pathways thatcontribute to tumor growth through increased tumor cellproliferation andor reduced tumor cell death RNAi canalso be used to target and silence gene products thatnegatively regulate the function of endogenous tumor sup-pressor genes as well as proteins involved in cellular senes-cence or protein stabilitydegradation However in vivostudies up until now have shown wide variation on thepotency of RNAi and its suppression activities as a resultof poor cellular uptake rapid renal clearance and nucle-ase degradation90 Also previous experiments have beenplagued with additional problems such as off-targeting andimmunogenic response9091 Nonetheless the characteri-zation of novel nanoparticle carriers and chemical mod-ifications to siRNA itself has addressed some of theseissues Suh and collegues developed a cationic lipid N N primeprime-dioleylglutamide linked by negatively charged glutamicacid to oleoylamine as a siRNA carrier92 It was ableto deliver siRNA to various cancer cells in vitro moreeffectively than other cationic liposomes and with reducedcytotoxicity Moreover results showed that it was effectivefor local in vivo siRNA delivery providing clear evidencethat target protein expression was knocked down in tumortissues92 In addition Chen et al developed a liposome-polycation-hyaluronic acid (LPH) nanoparticle formulationmodified with single-chain antibody fragment (GC4 scFv)for the systemic delivery of siRNA and miRNA in experi-mental lung metastasis of murine B16F10 melanoma Inhi-bition of c-Myc MDM2 and VEGF protein expression bysiRNA formulated with GC4 scFv modified LPH nanopar-ticles significantly suppressed B16F10 metastatic tumorgrowth while showing increased siRNA uptake within thelung tumors93

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510 Monoclonal Antibodies

Monoclonal antibodies (mAB) are monospecific antibod-ies that bind only to one particular antigenic determinantor epitope By blocking ligand binding andor signalingof growth receptors mABs have the capability to sen-sitize tumors to chemotherapeutic agents reduce growthrates and induce apoptosis Many different monoclonalantibodies are currently used in the therapy of cer-tain cancers such as Bevacizumab Imatinib BortezomibGefitinib Sorafenib Tositumomab Tamoxifen and Ritux-imab which are all FDA-approved therapies for cancer todate94 In some in vivo applications the antibody itself issufficient and once bound to its target mAB triggers theeffector cell mechanisms of the immune system An excel-lent 2010 review by Weiner et al addresses the specificimmunologic pathways in which mABs interact with can-cer cells94 mAB may also be coupled to another moleculesuch as a fluorescent molecule to aid in imaging or aradioactive isotope such as Iodine-125 to aid in killing can-cer cells with radioimmunotherapy95 However in a recentstudy of radioimmunotherapy it was concluded that a sin-gle -emitter 90Y coupled to each antibody had a signifi-cantly lower biological effective dose and was insufficientto treat non small-cell lung cancer than a single 5 nm90Y2O3 nanoparticle96 In the application of nanoparticlesmAB can be used as efficient targeting ligands Workby Park and associates shows the targeting specificityof a modified lymphocyte function-associated antigen-1domain tuned to have variable affinities for intercellularadhesion molecule (ICAM)-1 Applying this antibody totheir nanoparticle system amphiphilic urethane acrylatenonionomer (UAN) researchers were able to demonstrateefficient encapsulation of a FITC marker and a protea-some inhibitor (celastrol) as well as the targeted deliveryto HeLa cells producing a more potent cytotoxicity withequal amounts of drug than with the untargeted UAN97

511 Aptamers

Aptamers are synthetic oligonucleotide ligands or peptidesthat bear unique three-dimensional conformations capa-ble of binding to target antigens with high affinity andspecificity Aptamers bind to their targets to effectivelyillicit little or none immunogenicity and possess molecu-lar recognition properties similar to monoclonal antibod-ies They have been applied to drug delivery systems asligands to enhance selectivity98 RNA aptamer OPN-R3has been shown in an in vivo xenograft model of breastcancer with MDA-MB-231 cells to significantly decreaselocal progression and distant metastases By day 20 tumorvolume in the modified OPN-R3 treated group was 18ndash20-fold smaller than the tumor volume in mutant OPN-R3and no treatment groups99 Another aptamer SM20 iso-lated against plasminogen activator inhibitor-1 has demon-strated in vitro therapeutic potential as an antimetastatic

agent and could possibly be used as an adjuvant to tradi-tional chemotherapy for breast cancer100 Several aptamershave been recently isolated for potential treatment of othercancers such as glioblastoma T cell leukaemia and epithe-lial cancer cells in the breast colon lung ovaries andpancreas98 Finally apatmers can be used as a targetingmoiety to be conjugated to a certain drug delivery for-mulation or may act as modalities with characteristics ofintrinsic specificity100

6 CURRENT CLINICAL PROGRESS OFNANONCOLOGY THERAPEUTICS

In this section nanoparticles for cancer therapy that havealready reached the clinic are discussed A few sys-tems having been approved and many are still ongoingin human clinical trials (Table I) As described earliernon-targeting nanoparticles utilize leaky vasculature oftumors to reach via passive targeting PEGylation has beenapplied to various proteins enzymes cytokines and mon-oclonal antibody fragments to increase circulatory half-life and decrease antigenicity3349101102 Many clinicaltrials involving PEGylation of nanoparticles are in differ-ent phase trials at the moment such as PEG-InterferonAlfa-2b PEGylated recombinant human Hyaluronidase(PEGPH20) PEG conjugate of SN38 (EZN-2208) toname a few An interesting PEgylated complex is PEG-ADI 20 currently undergoing Phase II studies Argininedeiminase (ADI) is a microbial enzyme that degrades argi-nine Certain cancer cells deficient in producing argininethrough argininosuccinate synthase obtain exogenous argi-nine from circulation PEG-ADI 20 depletes arginine con-centrations in the blood thereby controlling and reducingtumor growth103 The previous phase III study was com-pleted on un-resectable hepatocellular carcinoma knownfor its poor prognosis In a study with 35 patients allpatients exhibited blood arginine levels lower than 2 uMwhile 2 patients became stable 1 patient became resectableand 28 progressed with a mean duration before progres-sion of 34 months103 On the other hand CRLX101 isa nanoparticle drug delivery system comprised of thechemotherapeutic camptothecin (CPT) conjugated to acyclodextrin-based polymer CRLX101 was designed toincrease the exposure of tumor cells to CPT while reducingside effects Anti-cancer activity of camptothecin is due inpart to the inhibition of DNA topoisomerase I but has beenprevented from use as an anti-cancer drug due to poor sol-ubility lack of activity and excessive toxicity104 HoweverCRLX101 nanoparticle was shown to have significantlyhigher antitumor activity with lower dosing while main-taining the levels of free camptothecin in the blood to aminimum It is noteworthy that it was effective in a num-ber of tumors resistant to irinotecan treatment CRLX101is currently undergoing Phase IB2A trials104 Ultimatelyactive targeting through the inclusion of a targeting lig-and on the nanoparticles is envisioned to provide the

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Table I Nanoncology in clinical development

Class Carrier Active agent Target Clinical status Indication (s) Ref

LiposomesDaunoXome Liposome Daunorubicin

citrateNA Approved Chronic myelogenous

leukemia neuroblastoma3

DOTAP Chol-FUS1 Liposome Plasmid DNA(FUS1)

NA Phase I Metastatic non-small celllung cancer

114

SGT-53 Liposome Plasmid DNAp53 W-T

Transferrinreceptor

Phase I Advanced Solid Tumors 115

MBP 426 Liposome Oxaliplatin Transferrinreceptor

Phase lbII Advanced or MetastaticSolid Tumors

105

PEGylatedDoxil PEGylaled-Liposome Doxorubicin NA Approved Ovanan cancer recurrent

breast cancer2 56

Oncospar PEGylaled-Asparagnase

L-asparagnase NA Approved Acute lymphoblasticleukemia

2

CYT-6091 PEGylaled-ThiolGold

RecombinantTNF-

Tumor necrosisfactor recepteor

Phase II Advanced solid tumors 110

ADI-PEG 20 PEGylated-ArginineDeiminase

Augininedeiminase

NA Phase II Hepatocellular carcinomaMetastatic melanomarelapsed small cell lungcancer

103

PeptideAbraxane Albumin Paclitaxel NA Approved Metastatic non-small cell

lung cancer2 3

Ontak Interkeukin-2engineered protein

Diphtheria toxin Interleukin-2receptors

Approved Cutaneous T-cell lymphoma 3

AMG 386 Peptibody Recombinantpeptide-Fcfusion protein

Angiopoietin 1and 2

Phase III Various cancers 113

PolymericCALAA-01 Cyclodextrin Small interfering

RNATransferrin

receptorPhase I Solid tumors 107 108

XMT-1001 Fleximer Camptothecin Prodrug activation Phase I Advanced solid tumors 111Genexol Polymeric micelles Paclitaxel NA Phase II Various cancers 52CT-2103 Poly-L-glutmate Paclitaxel NA Phase II Various cancers 112

Antibodya

Trastuzumab HumanizedMonoclonalantibody

Antibody CD340 receptor Approved HER2-positive metastaticbreast cancer

3 4 94

Rituximab Chimeric monoclonalAntibody

Antibody Protein CD20 Approved Leukemias and lymphomas 3 4 94

a Currently there are over 20 FDA-approved monoclonal antibodies for use in cancer therapy

most effective therapy A targeting nanoparticle in Pha-seIBII study is MbP-426 which contains the cytotoxicplatinum-based drug oxaliplatin in a transferrin-conjugatedlipopsome105 Transferrin receptors (TfR) overexpressedon tumor cells allow selective uptake via Tf-TfR interac-tion Outcome of Phase I trial with 39 patients showed that15 patients had stable disease after 2 cycles 3 patients withcolon carcinoma refractory to conventional oxaliplatin hadstable disease for 4-6 cycles and 2 patients had 12 and26 decrease in target lesions105 Further Rexin-G is amurine leukemia virus-based retrovector nanoparticle thatcontains a cytocidal dominant negative cyclin-G1 constructand allows for the functional restoration of tumor sup-pressor microRNA-122a It has been found that block-ade of cyclin G1 may restore intrinsic molecular form

of tumor suppression106 Rexin-G has been found to havelow immunogenicity with preferential selection of rapidly-dividing cells over normal non-dividing or differentiatedcells In Phase II clinical trials 88 of patients had partialresponses or stable disease while the overall survival ratewas 6 months for all 22 patients106 On a further note sometargeted nanoparticles can have active mechanisms for theintracellular release of the therapeutic moiety CALAA-01is a targeted nanoparticle that has a high drug (siRNA)payload per targeting ligand tested and proven multiva-lent binding to cancer cell surfaces and an active siRNArelease mechanism that is triggered upon the recogni-tion of intracellular localization by a pH decline belowa value of 60107108 This nanoparticle system containsa cyclodextrin-based polymer human transferring protein

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targeting ligand hydrophilic polymer (PEG) and siRNAdesigned to reduce expression of RRM2 It is currentlyundergoing Phase I clinical trials for a dose-escalatingstudy in the treatment of solid tumor cancer107 An aptamerfor potential cancer treatment is AS1411109 It binds nucle-olin on the surface of cancer cells and induces apoptosisIn a dose escalation (1 mgkgday to 10 mgkgday) clin-ical study AS1411 showed positive responses in patientswith advanced solid tumors without any adverse effects109

Recently in a randomized phase II clinical trials a10 mgkgday or 40 mgkgday dose of AS1411 com-bined with high-dose cytarabine was well tolerated andshowed promising signs of activity in patients with pri-mary refractory or relapsed acute myeloid leukaemia Itis also currently being evaluated for treatment of breastcancer110 In another example Aurimune is a colloidalAu nanoparticle which delivers recombinant TNF- tocancer tumors TNF is attached to the Au nanoparticle withthiol-derivatized PEG which allows the nanoparticle toflow through the blood stream without causing a clearanceresponse110 Clinical data to date reports that Aurimunehas no antibody or immune responses and is well-toleratedbeyond the known maximum dose for TNF-110

7 CLOSING REMARKS FUTUREPERSPECTIVE

Over the past decades nanoncology (therapeutics anddiagnostics) has evolved from nano-sized drug particlesto bio-functional nanomaterials capable of deliveringheat treatment ionizing radiation andor chemothera-peutic agents From simple liposomal formulations andconjugation of PEG to antibody-conjugated nanoparti-cle chemotherapeutic and RNAi delivery nanoncology isbecoming more intricate smart and multi-functional Fur-ther the differences between cancerous and normal cellsincluding uncontrolled proliferation insensitivity to nega-tive growth regulation and anti-growth signals angiogen-esis and metastasis can be now be effectively exploitedThere is no doubt that nanoparticle therapeutics with theincreasing multi-functionality will continue to expand inthe future Investments in research development and per-formance trials are considerably large Sponsoring agen-cies in both private and government sectors should createeconomic strategies and innovative management to makesuch biotechnologies more cost-effective and easily acces-sible for patients across Although many challenges existfor the transition of nanoparticles from bench to bed theirpotential advantages will drive successful development andemerge as a new class of undeniable anti-cancer thera-peutic Finally (i) individualizedpersonalized oncology inwhich cancer detection diagnosis and therapy can be mod-ified to best fit the tumor molecular profile of a patientand (ii) predictive oncology in which genetic biochemicaland molecular markers are orchestrated to predict disease

development progression and clinical outcomes will cer-tainly shape the nanoncologic strategies of the near future

Acknowledgments This work was supported by theSouth Korean Ministry of Knowledge and Education(MKE) and the Incheon Free Economic Zone (IFEZ) inthe framework of several funding operating grants to theUtah-Inha DDS amp Advanced Therapeutics Research Cen-ter KR

References and Notes

1 N Portney and M Ozkan Anal Bioanal Chem 3 620 (2006)2 M Ferrari Nat Rev Cancer 3 161 (2005)3 T M Allen Nat Rev Cancer 1 0750 (2002)4 J S Ross D P Schenkein and R Pietrusko Am J Clin Pathol

4 598 (2004)5 M Wang and M Thanou Drug Resist Updat 2 90 (2010)6 A Jones and A L Harris Cancer J Sci Am 4 209 (1998)7 D F Baban and L W Seymour Adv Drug Deliv 1 109 (1998)8 H Maeda Adv Enzyme Regul 41 189 (2001)9 K Greish Methods Mol Biol 624 25 (2010)10 A K Iyer K Greish T Seki S Okazaki J Fang K Takeshita

and H Maeda Drug Discov Today 11 812 (2006)11 K N Sugahara T Teesalu P P Karmali V R Kotamraju

L Agemy D R Greenwald and E Ruoslahti Science 5981 1031(2010)

12 R G Boyle and S Travess Anticancer Agents Med Chem 64 281(2006)

13 J M Brown and W R Wilson Nat Rev Cancer 4 437 (2004)14 D Kim E S Lee K Park I C Kwon and Y H Bae Pharm

Res 9 2074 (2008)15 L M Bareford and P W Swaan Adv Drug Deliv Rev 8 748

(2007)16 N F Saba X Wang S Muumlller M Tighiouart K Cho S Nie

Z Chen and D M Shin Head Neck 4 475 (2009)17 Y Lu L C Xu N Parker E Westrick J A Reddy M Vetzel

P S Low and C P Leamon Mol Cancer Ther 12 3258 (2006)18 E I Deryugina and J P Quigley Cancer Metastasis Rev 25 9

(2006)19 A M Mansour J Drevs N Esser F M Hamada O A Badary

C Unger I Fichtner and F Kratz Cancer Res 14 4062 (2003)20 H Hatakeyama H Akita E Ishida K Hashimoto H Kobayashi

T Aoki J Yasuda K Obata H Kikuchi T Ishida H Kiwadaand H Harashima Int J Pharm 1ndash2 194 (2007)

21 A Raz L Meromsky and R Lotan Cancer Res 7 3667 (1986)22 E Gorelik U Galili and A Raz Cancer Metastasis Rev 3ndash4 245

(2001)23 C Bies C M Lehr and J F Woodley Adv Drug Deliv Rev

4 425 (2004)24 H Glavinas P Krajcsi J Cserepes and B Sarkadi Curr Drug

Deliv 1 27 (2004)25 M Dean T Fojo and S Bates Nat Rev Cancer 4 275 (2005)26 T Kobayashi T Ishida Y Okada S Ise H Harashima and

H Kiwada Int J Pharm 1ndash2 94 (2007)27 A M Chen M Zhang D Wei D Stueber O Taratula T Minko

and H He Small 23 2673 (2009)28 J M Koziara P R Lockman D D Allen and R J Mumper

Pharm Res 11 1772 (2003)29 S C Steiniger J Kreuter A S Khalansky I N Skidan A I

Bobruskin Z S Smirnova S E Severin R Uhl M Kock K DGeiger and S E Gelperina Int J Cancer 5 759 (2004)

30 J Wu T Akaike and H Maeda Cancer Res 1 159 (1998)31 M A Deli Biochim Biophys Acta 4 892 (2009)

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form nanoparticles1ndash3 These formulations can have anenhanced anticancer effect compared to the therapeuticentities they contain alone This is due to more special-ized targeting to tumor tissue via improved pharmacokinet-ics pharmacodynamics and active intracellular deliveryRecent and ongoing advancements in nanotechnology havebeen able to contend with common problems associatedwith chemotherapy such as drug resistance drug degra-dation drug solubility and side effects due to systemictoxicity4 This approach could potentially eliminate suchproblems that occur during cancer therapy While drug sol-ubility and drug protection from degradation are importanttopics in nanoncology it is worth mentioning herein thatthey will not be covered in this review due to the speci-ficity in detailing their physical and chemical propertiesSeveral excellent works are available in the published lit-erature that the curious reader is encouraged to consultLikewise regarding imaging and bio-sensing applicationsSo in a traditional chemotherapy regime cancer cells maydevelop resistance to drug therapy leading to a relapseof the disease and subsequently an increased dosage ortransition to a new chemotherapeutic agent5 Two mainobjectives in the process of enhancing the effectiveness perdosage of any therapeutic constitution(a) to increase selectivity in the distinction between cancerand healthy cells and(b) to equip therapeutic delivery agents with proper mech-anisms to overcome chemical biological and physiologicalobstructions that offset target acquisition4

Those are discussed in the next few sections

2 TARGETING METHODOLOGY ANDFACTORS

Nanoparticulate drug delivery systems through the useof biodegradable and biocompatible materials provide amore efficient yet less harmful solution to overcome someof these hurdles The delivery of a drug to its target tis-sue through the use of nanoparticles can be accomplishedprimarily in two ways passive and active Passive target-ing exploits the permeability characteristic of tumor tissueAccelerated vascularization from the tumor supplying therapid growth of cancerous tissue creates a leaky and defec-tive architecture which in turn can be more easily accessi-ble to toxic therapeutics67 Passive targeting incorporatesthe delivery of the drug to the tumor bed through severalinvasive modalities On the other hand active targeting isusually achieved by conjugating the nanoparticle to a tar-geting moiety allowing preferential accumulation of drugin tumor tissue and within individual cancer cells intra-cellular organelles or molecules specific to cancer cellsThis approach can be used to direct nanoparticles towardscancer cell surface carbohydrates receptors antigens andother proteins There are a number of excellent reviewsdiscussing this subject in vast detail2ndash5

21 Tumor Infrastructure

Much of the tumor vasculature displays abnormalities dif-ferent from the surrounding tissue which enables a biodis-tribution of nanoparticles favorable for the localization oftherapeutics First described by Maeda8 enhanced perme-ability and retention (EPR) phenomenon is based on twofactors(a) capillary endothelium in malignant tissue being moredisorderly and irregular and(b) lack of tumor lymphatic drainage in the tumor bedresults in accumulation of the drug

Based on size and surface characteristics alone nanopar-ticles may concentrate within the tumor bed several foldshigher than in plasma8 Most nanotherapeutics currentlyin clinical use utilize passive targeting to reach tumorsA number of reviews cover the tumor vasculature and theEPR effect in greater detail8ndash10 A recent advancement inpenetrating the tumor infrastructure comes with the pro-tein iRGD which displays increased vascular and tissuepermeability specific to the tumor via targeting the vintegrins expressed on the tumor vessel endothelium andneuropilin-1 Indeed co-administration with doxorubicin-loaded nanoparticles has much higher intracellular concen-trations than with iRGD-free11

22 Hypoxia and pH

As tumor cells proliferate regions of deprived oxygen arecreated within the tumor microenvironment1213 Hencetumor hypoxia is related to the resistance in chemother-apy and radiotherapy as well as being characteristic ofincreased tumor aggressiveness Tumor microenvironmentalso exhibits a pH imbalance that deviates from the nor-mal extracellular pH allowing its surroundings to becomeslightly acidic The primary reason for this imbalance ofcancer pH is the high rate of glycolysis in cancer cellsThis is may be beneficial to the cancer cells by gen-erating an unfavorable environment for the surroundingnormal tissue cell and extracellular matrix1314 Also theacidic pH in endosomes and lysosomes during endocyticuptake is a possible factor to consider for pH-sensitivenanotherapeutics For example Baersquos University of Utahresearch group has recently developed pH-sensitive poly-meric micelles which destabilize below a pH of 74 Thisallowed drug release within the extracellular tumor micro-enivornment and in endosomes following folate receptor-mediated endocytosis14

23 Receptor and Antigen Directed Targeting

Overexpression of specific receptors and antigens in humancancers shows a substantially more efficient uptake viareceptor-mediated endocytosis A drug bound to a poly-mer carrier may be taken into the cell via ligand-receptor interactions Once localized at the cell surface

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the targeted drug-polymer carrier complex may exertits cytosolic action either at the plasma membrane orfollowing internalization15 Receptorantigenic expressionshould be reversible after drug delivery is complete Vascu-lar endothelial growth factor receptor and human epidermalreceptor are some of the different types of receptors that canbe targeted due to high levels of expression in tumor cellangiogenesisproliferation1516 To circumvent cell perme-ation problems and improve tumor specificity in nanopar-ticulate therapeutics folate receptor-mediated endocytosishas emerged as a potential strategy for drug delivery dueto both an overexpression of the folate receptor on can-cer cells and rapid internalization by receptor-mediatedendocytosis1617 Incidence of folate receptor expression inhuman head and neck (primary and metastatic) tumor tis-sues exists and compared with normal tissue such as bonemarrow folate receptor expression was found in 53 ofsamples whereas normal bone marrow cells did not displayany folate receptor expression Thus such receptor over-expression has indeed some great active tumor targetingpotential16

24 Protein Targeting

Matrix metalloproteinases (MMP) are zinc-dependentendopeptidases that play a major role in ECM degrada-tion as well as tissue repair morphogenesis angiogene-sis and have been shown to be overexpressed in tumortissue1819 In an effort to target MT1-MMP Fab222-1D8prime

fragments of anti-human MT1-MMP monoclonal anti-body were conjugated to doxorubicin immunoliposomescontaining approximately 40 Fabprime fragments per lipo-some Subsequently the liposomes were administered totumors 1000 to 3000 mm3 in size20 After 12 days non-targeted liposome treatment showed decreased tumor vol-ume in 16 mice and 36 mice died probably due toside effects of doxorubicin-encapsulated non-targeted lipo-somes However in the case of targeted liposomes tumorvolume decreased significantly with only 1 mouse report-ing notable body weight changes20 TNF- and v3 inte-grin are other tumor targeting proteins1520

25 Carbohydrate-Directed Targeting

Lectin-cell surface carbohydrates are used for activedrug targeting Briefly cell surface carbohydrates affecttumor cell interactions with normal cells during metastaticspread and growth21 These interactions can be mediatedthrough tumor cell carbohydrates and their binding pro-teins referred to as lectins Further cell surface mem-brane lectins are known to be overexpressed on the surfaceof numerous cancer cells and able to internalize endoge-nous sugar molecules22 Lectins affect tumor cell survivaladhesion to the endothelium as well as tumor vascular-ization and other processes crucial for metastatic spreadand growth21 This ligand-carbohydrate interaction can

be used for the development of nanoparticles containingcarbohydrate moieties that are directed to certain lectinsand incorporating lectins directed to exact cell surfacecarbohydrates2123

3 ADVANTAGES OF NANONCOLOGY

31 Eliminating Drug Resistance

Drug resistance has become a major obstacle in limit-ing the efficacy of chemotherapy The ATP-binding cas-sette (ABC) family of transporters plays a central partin the emergence of drug resistance as carrier pumpsfor influx and efflux of hydrophobic drugs among cancercells Nucleotide binding domains (NBD) for ATP bindingand hydrolysis derives energy necessary for transportingcell nutrients across membranes Three ABC transportersknown to be involved in multiple drug resistant cancer areP-glycoprotein (P-GP)2425 multi-drug resistance associ-ated protein (MRP)2425 and breast cancer resistance protein(ABCG2)25 One possible mechanism in which nanopar-ticles may help anticancer drugs avoid recognition bythe P-GP efflux pump is by means of envelopment inan endosome upon entering the cell via ligand targetedreceptor-mediated endocytosis thereby leading to higherintracellular concentrations25 As the interior of the endo-some becomes more acidic and lysozymes activated thedrug may be released from its nanoparticle conjugateand enter the cytoplasm to its target organelle avoidingthe P-DP efflux pump Kobayashi et al demonstrated abypass of the P-glycoprotein transporter with liposomesin doxorubicin-resistant SBC-3 a human small cell lungcancer cell line Transferrin ligands were attached todoxorubicin encapsulated EPC liposomes which showedsignificantly higher cytotoxicity in MDR cells than non-targeted liposomes Transferrin-bound liposomes were ableto deliver doxorubicin more closely to the nucleus allow-ing less of the drug to be affected by P-GP pump26 Non-transport based mechanisms can affect a variety of drugclasses as well This particular type of resistance may becaused by a mutation or an alteration in the activity ofenzymes such as glutathione S-transferase and topoiso-merase which decreases the cytotoxic efficiency of drugsindependent of intracellular drug concentrations Changesthat occur in the regulation of proteins that control apopto-sis and reduction in the efficacy of chemotherapeutic agentscan be attributed to the fact that most cancer drugs uti-lize cytotoxic effects by apoptotic processes25 Chen et al27

addressed this issue using mesoporous silica nanoparti-cles that simultaneously deliver doxorubicin and Bcl-2-targeting siRNA in multi-drug resistant A2780AD humanovarian cancer cells Bcl-2 overexpression is linked withinhibition of cellular apoptosis as well as being the mainnon-pump resistance protein in multi-drug resistant cancercells Cytotoxicity of doxorubicin was increased 132-foldfollowing co-delivery of Bcl-2 siRNA This shows the

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effectiveness in which a nanoparticulate system may carryboth the therapeutic agent and a small molecule inhibitor orchemo-sensitizer to disrupt the drug resistance mechanismwhile inducingenhancing chemotherapy simultaneously27

32 Avoiding Physiological Barriers

For conventional formulations the path of a therapeuticagent from the point of administration to the target ofintent is consistently subverted by obstructions and bio-logical barriers that may prevent effective treatment Onesuch example is the tight junction between epithelial cellsknown as the blood brain barrier (BBB)28 Now certainnanoparticles have shown ability in crossing the BBB dueto intrinsic properties of their constituent core materialssuch as polysorbate-coated nanoparticles In one studydoxorubicin-bound nanoparticles coated with polysorbate80 were used to target glioblastoma in rats showinghigher survival rates than non-coated doxorubicin-boundnanoparticles29 However more conclusive studies on dox-orubicin and polysorbate neuro-toxicity must be com-pleted before considering clinical use Endothelial vascularpermeability may be increased by the co-administrationof a bradykinin antagonist a cyclooxygenase inhibitoror a nitric oxide scavenger30 This is a possible strat-egy for the enhancement of tumor vasculature targetingThe combined delivery of permeation enhancers such aszonula-occludens toxin and its fragments can reversiblyopen tight junctions and allow penetration of nanopar-ticle agents31 Antagonistic oncotic and interstitial pres-sures from tumor bed as well as dissemination or cellularuptake throughout the tumor interstitium poses problemsfor the entry passage and retention of nanotherapeutics32

Phagocytes of the reticuloendothelial system (RES) actas immunological barriers against the targeting poten-tial of nanoparticle-encapsulated drugs as they sequesterinjected nanoparticles from circulation Extensive researchand experience in liposomes have demonstrated that uptakeby RES is effectively avoided by surface modification withpolyethylene glycol (PEG) to increase circulatory half-life from minutes to hours or days thereby allowing forenhanced targeting of liposomes within the tumor33 How-ever PEGylation not only prevents RES uptake but alsomasks the targeting ligand causing a reduction in thechances of bio-recognition and uptake34

4 KEY PROPERTIES OF ANTI-CANCERNANOPARTICLES

41 Dimensions

The dimensions of nanoparticles in cancer therapy arewidely debated however it is understood that the diam-eter of a nanoparticle should be in the range of 55 nmndash250 nm depending on the composition and surfacemodifications35ndash37 Lower limits have been defined due to

the threshold for filtration of particles within the glomeru-lar capillary wall of kidneys being 55 nm35 On the otherhand the upper size limits are not definite at the momenthowever increasingly larger particles or particle aggregatestend to be more prone to the RES The vasculature intumors is vulnerable to macromolecule permeation andEPR effect Nonetheless the cutoff in size for nanoparticleaccumulation in the tumor attributed to EPR effect seemsto be about 400 nm36ndash39 Particles hundreds of nanometerin size have been shown to leak out of blood vessels andaccumulate within tumors but larger macromolecules maystill have limited diffusion within the extracellular space38

Experiments from animal models suggest that particles of150 nm neutral or slightly negatively charged can movethrough tumor tissue In addition recent data shows thatnanoparticles in the 50ndash100 nm range carrying a slightpositive charge penetrate large tumors following systemicadministration40 Therefore are restricted from exiting intonormal vasculature requiring a size less than 1ndash2 nm3536

42 Surface Properties

Nanoparticles have a high surface-to-volume ratio com-pared to microparticles Control of surface properties is cru-cial for predicting behavior in the human body2341 Theultimate fate of nanoparticles can be determined by theinteractions of nanoparticles within their local environmentwhich depends largely on a combination of size and surfaceproperties Nanoparticles are sterically stabilized and havesurface charges41 In a recent study with gold nanoparti-cles positively charged nanoparticles depolarized the mem-brane to the greatest extent while nanoparticles of othercharges had a negligible effect However as the surfacecharge greatens (either positively or negatively) chancesfor macrophage uptake and clearance by RES increase39

Further therapeutic entities within nanoparticles do notimpact nanoparticle propertiesmdashdoxorubicin-loaded lipo-somes and their drug-free analogue liposomes for exam-ple can be expected to possess the same particle sizesurface charge pharmaco-dynamics-kinetics etc In con-trast molecular conjugates often strongly alter the prop-erties of the individual drug molecule with presence of acovalently attached modifier such as PEG andor antibody

43 Intermolecular Binding

The incorporation of targeting ligands provides specificnanoparticle-cell surface interactions in the selectivity ofthe nanoparticle Affinity of the ligand and its recep-tor can strongly influence the effects of multivalencyRelatively low-affinity ligands have potential to createstrong effective affinities within the context of a multi-valent nanoparticle42 For example increasing the num-ber of transferrin molecules on a 70-nm PEGylated goldnanoparticle to 144 gave a 013 nM Kd to the surface of

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Neuro2A cells (which have upregulated transferring recep-tors) compared to 64 nM for transferrin alone43 More-over molecules without sufficient binding affinity for useas a drug or individual targeting ligand can be encapsulatedwithin nanoparticles Also many drug candidates that wereineffective due to low binding of the target can be used onthe surface of nanoparticles as targeting agents A target-ing ligand increases the extent of cellular internalizationby particles that reach tumor tissue in a ligand density-dependent manner Inability of a targeting ligand to sig-nificantly increase tumor deposition is consistent with theroles of molecular size and affinity on tumor uptake44

It has been reported that intermediate-sized ligands witha molecular weight of about 25 kDa achieve the low-est tumor uptake levels while both smaller ligands (thatrequire high receptor affinity to be retained) and largerligands (that can achieve similar retention as smaller lig-ands withgt 100-fold weaker binding) showed an enhancedtumor uptake42ndash44

5 NANOBIOTECHNOLOGY THERAPEUTICDELIVERY PLATFORMS IN CANCER

A few nanoncologic systems have reached the pre-clinicaland clinical trial stage Below is a comprehensive yet pro-visional set of potential drug delivery systems examples(Fig 1) and their components being investigated in vitroand in vivo currently Other nanoparticles such as quantumdots nanowires and nanosensors are not discussed as theymainly deal with detection and imaging Yet few excitingmultifunctional systems such as iron oxide nanoparticlesare touched upon to further stress their future potential

51 Polymeric Nanoparticles

Polymers such as chitosan cyclodextrins alginate andhyaluronic acid occur naturally and have been the mate-rial of choice for the delivery of proteins DNA RNA

Fig 1 Nanoncology carrier applications in cancer therapeutics

as well as drugs Natural polymers have the advantageof being biodegradable and biocompatible more so thantheir synthetic counterparts45ndash47 Gupta and colleaguesexperimented with biologically-derived silk fibroin (SF)and chitosan (CH) blended non-covalently to encapsulatecurcumin48 Curcumin can interfere with the activity oftranscription factor NF-B and induce apoptosis in cancercells while avoiding healthy cells SF was shown to havebetter encapsulation properties and efficacy than liposomesSF-curcumin nanoparticles showed higher efficacy againstbreast cancer cells48 This demonstrates the potential totreat in vivo breast tumors by a possible sustained long-term biodegradable and therapeutic delivery system Onthe other hand synthetic polymers are not easily removedby normal clearance systems and can accumulate in tissuesHowever synthetic polymers such as PEG poly(lactic-co-glycolic acid) (PLGA) polyethylenimine (PEI) andhydroxyl propyl methacrylamide copolymer (HPMA) havecharacteristics that are more well-defined and can be finetuned to perform in a predictable manner As shown earlierchemical conjugation with PEG or PEGylation is one of themost acknowledged methods for prolonging the duration ofdrugs in the bloodstream and has also been demonstratedto contain certain targeting properties as well49 PEGyla-tion lowers plasma clearance rate by reducing receptor-mediated uptake during systemic circulation as well asmetabolic degradation by disguising the surface of theprotein49 It also reduces immunogenicity improves thesafety profile of the protein and protects the immunogenicepitopes Liu et al developed a novel nanocrystal formu-lation of Pluronic F127 for 2 anti-cancer drugs paclitaxel(PTX) and camptothecin50 Intravenously injected nano-crystals significantly inhibited tumor growth Considerabletherapeutic effects were shown via oral administration aswell In addition the targeted delivery of PTX via conju-gating a folate ligand to F127 was demonstrated50

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52 Micelles

Amphipilic nanoparticles composed of block or graft co-polymers such as N -vinylpyrrolidone and poloxamers canform polymeric micelles A hydrophobic core containshydrophobic drugs and the hydrophilic shell stabilizesthe core and makes the drug water-soluble4751 Poly-meric micelles have been shown to accumulate more read-ily in tumors than the larger liposomes mainly due totheir size51 The first polymeric micelle formulation ofPTX Genexol-PM a cremophor-free polymeric micellehas completed phase II clinical trials in the US withconsiderable anti-tumor activity in combination with cis-platin chemotherapy Cremophor EL is an excipient withcertain drugs and has been suggested to be a dose lim-iting factor in the administration of PTX52 This micel-lar nanoparticulate system allowed for higher doses of thedrug while being able to deliver and concentrate inside thetumor interstitium Another biodegradable formulation ofcationic micelles were prepared with PDMAEMA-PCL-PDMAEMA tri-block co-polymers and applied for thedual delivery of siRNA and PTX into cancer cells Combi-natorial delivery of anti-VEGF siRNA and PTX knockeddown VEGF expression53

53 Liposomes and Solid Lipid Nanoparticles

Natural liposomes a closed colloidal structure composedof a lipid bi-layer and an aqueous core are composed oflecithin phospholipids and can also be multi-laminar ratherthan uni-laminar carrying a larger payload of water- andfat-soluble constituents up to 500 nm in size5455 Lipo-somes take advantage of the overexpression of perforationsin cancer neovasculature in order to increase drug concen-trations passively at tumor sites Liposomal drug deliveryhas been the most successful nanoparticulate formulationused in the clinic as shown by liposomal-encapsulateddoxorubicin for Kaposirsquos sarcoma and more recentlybreast and ovarian cancer56 Small dimensions (lt300 nm)enables the drug to accumulate in the tumor mass by cross-ing passively into the tumor vasculature while avoiding orreducing the permeation of normal tissue55 On the otherhand solid lipid nanoparticles (SLNs) are solid lipids athuman physiological temperature with a diameter from50 to 1000 nm They are formed from a range of lipidsincluding mono- di- and tri-glycerides waxes fatty acidsand combinations of those SLNs are biodegradable bio-compatible with several human applications57 They form astrong lipophilic matrix in which water-insoluble lipophilicdrugs can be loaded for subsequent release The chemi-cal and physical properties of lipids in a heterogeneousmixture promote an imperfect crystalline structure withlarger gaps for efficient drug loading57 Use of SLNs havebeen investigated for the delivery of various anti-cancerdrugs with promising results in pre-clinical mouse trialsspecifically showing that SLNs might help overcome MDR

in cancers Serpe et al using human colon cancer cellsHT-29 demonstrated the benefits of SLNs in the deliveryof cholesteryl butyrate (chol-but) with doxorubicin Cyto-toxicity was shown to be higher in chol-but SLN loadedwith doxorubicin than free doxorubicin alone howeverPTX-loaded SLN did not show any improvement over freePTX5859 Lu et al loaded mitoxantrone a topoisomeraseinhibitor that blocks DNA replication into SLNs for alocal injection in the treatment of breast cancer and lymphnode metastases in mice60 Almost three-fold reduction inlymph node size was reported when compared to freely-administered mitoxantrone This was considered a signifi-cant improvement over existing treatment by the authors60

54 Dendrimers

Dendrimers may serve as a versatile nanoscale platformfor creating a multi-functional system capable of detect-ing cancer and delivering drugs A synthetic polymericmacromolecule of nanometer dimensions a dendrimer iscomposed of multiple highly branched monomers thatemerge radially from a central core The readily modifiablesurface characteristic enables them to be simultaneouslyconjugated with several molecules such as imaging con-trast agents targeting ligands andor therapeutic drugs61

Many commercial small molecule drugs with anti-canceractivity have been successfully conjugated with den-drimers such as polyamidoamine poly(propylene imine)and poly(etherhydroxylamine) dendrimers by means ofeither steric interactions or chemical reactions6263 Tar-geted delivery is possible via targeting moieties conju-gated to dendrimer surface or passive delivery due to theEPR effect Cationic dendrimers show cytotoxicity how-ever derivatization with fatty acid or PEG chains canreduce the overall charge density and minimize contactbetween cell surface thus reducing toxic effects6162 Patriet al demonstrated that covalently coupled methotrexate-dendrimer conjugates targeting high-affinity receptor forfolic acid have a similar activity to the free drug invitro while specifically killing receptor-expressing cells viareceptor-mediated endocytosis64

55 Carbon Nanotubes and Nanodiamonds

Carbon nanotubes are generally insoluble causing them tobe non-biocompatible however the introduction of chem-ical modification to carbon nanotubes render them water-soluble and functionalized so that they can be linked to awide variety of active molecules such as peptides proteinsnucleic acids and therapeutic agents Functionalized car-bon nanotubes also have an intrinsic capability to perme-ate cell membranes which allows endocytosis-independentinternalization of nanoparticles265 Methotrexate cova-lently linked to carbon nanotubes with a fluorescent agentwas shown to be more effectively internalized into cells

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when compared to the free unbound drug65 The multi-ple covalent functionalizations on the sidewall or tips ofcarbon nanotubes allow them to carry several moleculesat once This strategy provides a fundamental advantagein the treatment of cancer Targeted heat therapy or lsquother-mal ablationrsquo is being tested to destroy breast cancertumors using carbon nanotubes Accordingly the HER2IgY-single wall carbon nanotube (SWNT) complex specif-ically targeted HER2-expressing SK-BR-3 cells but notreceptor-negative MCF-7 cells Near-infrared irradiationwith an 808 nm laser showed extensive cell death withSWNT66 On the other hand a nanodiamond-embeddeddevice is being developed to deliver chemotherapy locallyto sites where cancerous tumors have been surgicallyremoved67 Nanodiamonds complexed with doxorubicin-hydrochloride enable a sustained release of drug for aminimum of 30 days with a significant amount of drugin reserve This shows potential for highly localized drugrelease as a complementary yet potent form of treat-ment with systemic injection Ho and group embeddedmillions of tiny drug carrying nanodiamonds into theFDA-approved parylene67ndash69 Currently used as a coatingfor implants biostable parylene is a flexible and versa-tile polymeric material Nanodiamonds placed betweenextremely thin parylene films resulted in a device that isminimally-invasive Internalization assays revealed a pri-marily endocytic uptake process High degree of nanodia-mond (sim46 nm in diameter) and endosome co-localizationas well as cytoplasmic presence of smaller nanodiamondswere observed69

56 Silicon Nanoparticles

Silicon and silica are establishing themselves as inter-esting candidate materials for injectable nanoparticles indrug delivery70 Porosified silicon is biodegradable71 withkinetics that are much more rapid than those of typicalbiodegradable polymers and as a result releases drugswith previously un-attainable time profiles Lu et al loadedhydrophobic anti-cancer drug camptothecin (CPT) ontomesoporous silica nanoparticles CPT release was mini-mal and sustained in aqueous solution This effectivelyaddressed the problem of poor water-solubility of certainanti-cancer drugs as well as sustainable release profiles71

Furthermore there are metal-based nanovectors such asnanoshells70 comprised of a gold layer over a silica coreThe thickness of the gold layer can be precisely tuned sothat the nanoshell can be selectively activated through tis-sue irradiation with near-infrared light to perform localizedtherapeutic thermal ablation This approach was recentlyused to eradicate transmissible venereal tumors in mice72

In another study nitric oxide (NO)-releasing silica nanopar-ticles exhibited enhanced growth inhibition of ovariantumor cells and showed greater inhibition of the anchorage-independent growth of tumor-derived and Ras-transformed

ovarian cels73 NO a free radical bio-regulator endoge-nously synthesized in the body impacts multiple stages oftumor development spanning cytostatic processes cellulartransformation and formation of neoplastic lesions7374 Itis worth mentioning herein that research efforts have beenimpeded by the fact that possible normal cell toxicity ofthe NO donor drug by-product and the inability to targetdelivery of the drug selectively to cancer cells

57 Gold and Magnetic Nanoparticles

Gold (Au) nanoparticles are very versatile and can beprepared with different geometries such as nanospheresnanoshells nanorods or nanocages75 Further they haveunrivaled physical and chemical properties such asexceedingly small size (less than 50 nm) large sur-face area to mass proportion heightened surface sensitiv-ity presence of characteristic surface plasmon resonancebands biocompatibility and ease of surface functionaliza-tion Au nanoparticles are also excellent conductors ofelectrical and thermal energy which allows possibilitiesfor thermal ablation treatment In photodynamic therapy(PDT) Au nanoparticles are becoming known as a photo-sensitizer with great potential due to its optimal absorptionand light scattering properties along with controllable opti-cal characteristics El-Sayed and collegues have shown thatanti-EGFR antibody conjugated gold nanoparticles selec-tively localized in malignant HOC and HSC cells andunderwent significant photothermal destruction upon nearinfrared irradiation76 However using radiofrequency irra-diation Gannon et al demonstrated that the internalizationof Au nanoparticles in gastrointestinal cancer cells releasedsubstantial heat rapidly after exposure to an external high-voltage focused radiofrequency field (RF) It is noteworthythat radiofrequency ablation has an advantage over nearinfrared ablation which is limited to superficial tumorswith minimal tissue penetration Hep3B and Panc-1 cellstreated with 67 ML Au nanoparticles had significantlyhigher rates of cell death than the control samples at alltime-points after RF exposure77 Interestingly Au nanopar-ticles about 5ndash10 nm in diameter have been shown to haveintrinsic anti-angiogenic properties78 These nanoparticlesbind to heparin-binding pro-angiogenic growth factorssuch as VEGF165 and bFGF to inhibit their activity TheAu nanoparticles themselves also reduced ascites accumu-lation in a pre-clinical model of ovarian cancer inhibitedproliferation of multiple myeloma cells and induced apop-tosis in chronic B cell leukemia78 On the other hand mag-netic nanoparticles (MNPs) have traditionally been usedfor disease imaging via magnetic resonance (MR) imagingdue to their intrinsic properties Recent advances have alsoopened the door to cellular-specific targeting drug deliv-ery and multi-modal imaging Further MNPs can be func-tionalized through coating with polymers preferentiallywith biocompatible or biodegradable polymers of synthetic

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or biological origin7980 As solid tumor develops it out-grows its blood supply which results in the formation ofa hypoxic semi-necrotic tumor core and dormant tumorcells send out chemical signals that recruit macrophagesinto the core Macrophages begin to rebuild the bloodsupply allowing the tumor to start growing again8182

Muthana et al loaded human monocytes with MNPs plac-ing magnets near the site of a human prostate tumor grownin mice82 The MNP-loaded monocytes carrying a reportergene invaded the tumor at a rate more than three timesthat of the non-loaded cells82 This demonstration of mag-netic targeting shows that MNP-loaded cells circulatingin the body can be attracted to the tumor site where anexternal magnet is placed allowing a higher proportion ofloaded cells to respond to chemical signals from the tumorcore In addition the loaded monocytes were able to reachthe poorly vascularized peri-necrotic regions of the tumorthat are normally difficult to target As the moncytes areloaded with MNPs they can then be destroyed by hyper-thermia after delivering a therapeutic drug or gene8182

Classes of MNPs include metallic bimetallic and super-paramagnetic iron oxide nanoparticles widely-knows asSPIONs SPIONS are favored because due to low toxicityprofile and their reactive surface that can be readily modi-fied with biocompatible coatings87 This flexibility has ledto SPION use in magnetic separation biosensor in vivomedical imaging drug delivery tissue repair and hyper-thermia applications84 Yu et al preciously showed thatthermally crosslinked SPIONs loaded with doxorubicinhad potential as both an imaging and therapeutic deliverysystem83 This DoxTCL-SPION was also demonstratedto efficiently reach tumor sites and release the drug withoutany active targeting from ligandsantibodies or magneticfield largely due to the EPR effect83

58 Viral Nanoparticles

A variety of viruses including cowpea mosaic viruscanine parvovirus adenovirus coxsackie virus measlesvirus along with virions and virus-like particles have beendeployed for biomedical and nanotechnology applicationsthat include tissue targeting and drug delivery84 Target-ing molecules and peptides can be produced in a bio-logically functional form on the capsid surface throughchemical conjugation or gene expression Several lig-ands including transferrin folic acid and single-chainantibodies have been conjugated to viruses for specifictumor targeting84 Further a subset of viruses such ascanine parvovirus have a natural affinity for receptors liketransferrins that are up-regulated in a variety of tumorcells85 Adenoviral vectors offer many advantages for can-cer gene therapy including high transduction efficiencyyet safety concerns related to immunogenic response haveled to a cautious approach of their use in human clini-cal trials86 To overcome these obstacles hybrid vectors

combining both viral and non-viral elements are beingdeveloped Adenovirus coated with an arginine-graftedbioreducible polymer (ABP) via electrostatic interaction isone example ABP-coated complexes were shown to havesignificantly reduced the innate immune response whileproducing higher levels of transgene expression8687 Fur-thermore herpes simplex virus (HSV) vectors are alreadyin early phase human clinical trials for recurrent malignantglioblastoma A mutant form (vIII) of epidermal growthfactor receptor (EGFR) present in glioma tumor is rec-ognized by a single-chain antibody designated MR1-1HSV virions bearing MR1-1-modified gC had five-foldincreased infectivity for EGFRvIII-bearing human gliomaU87 cells showing enhanced vector specificity and tumorcell damage88

59 RNA Interference

Since its discovery nearly two decades ago RNA inter-ference (RNAi) has been lauded as the next generation ingene therapy due to the unique pathway in which smallinterfering (siRNA) or microRNA (miRNA) can preventmRNA expression and silence- specific targeted geneseffectively89 RNAi cancer gene targets are pathways thatcontribute to tumor growth through increased tumor cellproliferation andor reduced tumor cell death RNAi canalso be used to target and silence gene products thatnegatively regulate the function of endogenous tumor sup-pressor genes as well as proteins involved in cellular senes-cence or protein stabilitydegradation However in vivostudies up until now have shown wide variation on thepotency of RNAi and its suppression activities as a resultof poor cellular uptake rapid renal clearance and nucle-ase degradation90 Also previous experiments have beenplagued with additional problems such as off-targeting andimmunogenic response9091 Nonetheless the characteri-zation of novel nanoparticle carriers and chemical mod-ifications to siRNA itself has addressed some of theseissues Suh and collegues developed a cationic lipid N N primeprime-dioleylglutamide linked by negatively charged glutamicacid to oleoylamine as a siRNA carrier92 It was ableto deliver siRNA to various cancer cells in vitro moreeffectively than other cationic liposomes and with reducedcytotoxicity Moreover results showed that it was effectivefor local in vivo siRNA delivery providing clear evidencethat target protein expression was knocked down in tumortissues92 In addition Chen et al developed a liposome-polycation-hyaluronic acid (LPH) nanoparticle formulationmodified with single-chain antibody fragment (GC4 scFv)for the systemic delivery of siRNA and miRNA in experi-mental lung metastasis of murine B16F10 melanoma Inhi-bition of c-Myc MDM2 and VEGF protein expression bysiRNA formulated with GC4 scFv modified LPH nanopar-ticles significantly suppressed B16F10 metastatic tumorgrowth while showing increased siRNA uptake within thelung tumors93

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510 Monoclonal Antibodies

Monoclonal antibodies (mAB) are monospecific antibod-ies that bind only to one particular antigenic determinantor epitope By blocking ligand binding andor signalingof growth receptors mABs have the capability to sen-sitize tumors to chemotherapeutic agents reduce growthrates and induce apoptosis Many different monoclonalantibodies are currently used in the therapy of cer-tain cancers such as Bevacizumab Imatinib BortezomibGefitinib Sorafenib Tositumomab Tamoxifen and Ritux-imab which are all FDA-approved therapies for cancer todate94 In some in vivo applications the antibody itself issufficient and once bound to its target mAB triggers theeffector cell mechanisms of the immune system An excel-lent 2010 review by Weiner et al addresses the specificimmunologic pathways in which mABs interact with can-cer cells94 mAB may also be coupled to another moleculesuch as a fluorescent molecule to aid in imaging or aradioactive isotope such as Iodine-125 to aid in killing can-cer cells with radioimmunotherapy95 However in a recentstudy of radioimmunotherapy it was concluded that a sin-gle -emitter 90Y coupled to each antibody had a signifi-cantly lower biological effective dose and was insufficientto treat non small-cell lung cancer than a single 5 nm90Y2O3 nanoparticle96 In the application of nanoparticlesmAB can be used as efficient targeting ligands Workby Park and associates shows the targeting specificityof a modified lymphocyte function-associated antigen-1domain tuned to have variable affinities for intercellularadhesion molecule (ICAM)-1 Applying this antibody totheir nanoparticle system amphiphilic urethane acrylatenonionomer (UAN) researchers were able to demonstrateefficient encapsulation of a FITC marker and a protea-some inhibitor (celastrol) as well as the targeted deliveryto HeLa cells producing a more potent cytotoxicity withequal amounts of drug than with the untargeted UAN97

511 Aptamers

Aptamers are synthetic oligonucleotide ligands or peptidesthat bear unique three-dimensional conformations capa-ble of binding to target antigens with high affinity andspecificity Aptamers bind to their targets to effectivelyillicit little or none immunogenicity and possess molecu-lar recognition properties similar to monoclonal antibod-ies They have been applied to drug delivery systems asligands to enhance selectivity98 RNA aptamer OPN-R3has been shown in an in vivo xenograft model of breastcancer with MDA-MB-231 cells to significantly decreaselocal progression and distant metastases By day 20 tumorvolume in the modified OPN-R3 treated group was 18ndash20-fold smaller than the tumor volume in mutant OPN-R3and no treatment groups99 Another aptamer SM20 iso-lated against plasminogen activator inhibitor-1 has demon-strated in vitro therapeutic potential as an antimetastatic

agent and could possibly be used as an adjuvant to tradi-tional chemotherapy for breast cancer100 Several aptamershave been recently isolated for potential treatment of othercancers such as glioblastoma T cell leukaemia and epithe-lial cancer cells in the breast colon lung ovaries andpancreas98 Finally apatmers can be used as a targetingmoiety to be conjugated to a certain drug delivery for-mulation or may act as modalities with characteristics ofintrinsic specificity100

6 CURRENT CLINICAL PROGRESS OFNANONCOLOGY THERAPEUTICS

In this section nanoparticles for cancer therapy that havealready reached the clinic are discussed A few sys-tems having been approved and many are still ongoingin human clinical trials (Table I) As described earliernon-targeting nanoparticles utilize leaky vasculature oftumors to reach via passive targeting PEGylation has beenapplied to various proteins enzymes cytokines and mon-oclonal antibody fragments to increase circulatory half-life and decrease antigenicity3349101102 Many clinicaltrials involving PEGylation of nanoparticles are in differ-ent phase trials at the moment such as PEG-InterferonAlfa-2b PEGylated recombinant human Hyaluronidase(PEGPH20) PEG conjugate of SN38 (EZN-2208) toname a few An interesting PEgylated complex is PEG-ADI 20 currently undergoing Phase II studies Argininedeiminase (ADI) is a microbial enzyme that degrades argi-nine Certain cancer cells deficient in producing argininethrough argininosuccinate synthase obtain exogenous argi-nine from circulation PEG-ADI 20 depletes arginine con-centrations in the blood thereby controlling and reducingtumor growth103 The previous phase III study was com-pleted on un-resectable hepatocellular carcinoma knownfor its poor prognosis In a study with 35 patients allpatients exhibited blood arginine levels lower than 2 uMwhile 2 patients became stable 1 patient became resectableand 28 progressed with a mean duration before progres-sion of 34 months103 On the other hand CRLX101 isa nanoparticle drug delivery system comprised of thechemotherapeutic camptothecin (CPT) conjugated to acyclodextrin-based polymer CRLX101 was designed toincrease the exposure of tumor cells to CPT while reducingside effects Anti-cancer activity of camptothecin is due inpart to the inhibition of DNA topoisomerase I but has beenprevented from use as an anti-cancer drug due to poor sol-ubility lack of activity and excessive toxicity104 HoweverCRLX101 nanoparticle was shown to have significantlyhigher antitumor activity with lower dosing while main-taining the levels of free camptothecin in the blood to aminimum It is noteworthy that it was effective in a num-ber of tumors resistant to irinotecan treatment CRLX101is currently undergoing Phase IB2A trials104 Ultimatelyactive targeting through the inclusion of a targeting lig-and on the nanoparticles is envisioned to provide the

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Table I Nanoncology in clinical development

Class Carrier Active agent Target Clinical status Indication (s) Ref

LiposomesDaunoXome Liposome Daunorubicin

citrateNA Approved Chronic myelogenous

leukemia neuroblastoma3

DOTAP Chol-FUS1 Liposome Plasmid DNA(FUS1)

NA Phase I Metastatic non-small celllung cancer

114

SGT-53 Liposome Plasmid DNAp53 W-T

Transferrinreceptor

Phase I Advanced Solid Tumors 115

MBP 426 Liposome Oxaliplatin Transferrinreceptor

Phase lbII Advanced or MetastaticSolid Tumors

105

PEGylatedDoxil PEGylaled-Liposome Doxorubicin NA Approved Ovanan cancer recurrent

breast cancer2 56

Oncospar PEGylaled-Asparagnase

L-asparagnase NA Approved Acute lymphoblasticleukemia

2

CYT-6091 PEGylaled-ThiolGold

RecombinantTNF-

Tumor necrosisfactor recepteor

Phase II Advanced solid tumors 110

ADI-PEG 20 PEGylated-ArginineDeiminase

Augininedeiminase

NA Phase II Hepatocellular carcinomaMetastatic melanomarelapsed small cell lungcancer

103

PeptideAbraxane Albumin Paclitaxel NA Approved Metastatic non-small cell

lung cancer2 3

Ontak Interkeukin-2engineered protein

Diphtheria toxin Interleukin-2receptors

Approved Cutaneous T-cell lymphoma 3

AMG 386 Peptibody Recombinantpeptide-Fcfusion protein

Angiopoietin 1and 2

Phase III Various cancers 113

PolymericCALAA-01 Cyclodextrin Small interfering

RNATransferrin

receptorPhase I Solid tumors 107 108

XMT-1001 Fleximer Camptothecin Prodrug activation Phase I Advanced solid tumors 111Genexol Polymeric micelles Paclitaxel NA Phase II Various cancers 52CT-2103 Poly-L-glutmate Paclitaxel NA Phase II Various cancers 112

Antibodya

Trastuzumab HumanizedMonoclonalantibody

Antibody CD340 receptor Approved HER2-positive metastaticbreast cancer

3 4 94

Rituximab Chimeric monoclonalAntibody

Antibody Protein CD20 Approved Leukemias and lymphomas 3 4 94

a Currently there are over 20 FDA-approved monoclonal antibodies for use in cancer therapy

most effective therapy A targeting nanoparticle in Pha-seIBII study is MbP-426 which contains the cytotoxicplatinum-based drug oxaliplatin in a transferrin-conjugatedlipopsome105 Transferrin receptors (TfR) overexpressedon tumor cells allow selective uptake via Tf-TfR interac-tion Outcome of Phase I trial with 39 patients showed that15 patients had stable disease after 2 cycles 3 patients withcolon carcinoma refractory to conventional oxaliplatin hadstable disease for 4-6 cycles and 2 patients had 12 and26 decrease in target lesions105 Further Rexin-G is amurine leukemia virus-based retrovector nanoparticle thatcontains a cytocidal dominant negative cyclin-G1 constructand allows for the functional restoration of tumor sup-pressor microRNA-122a It has been found that block-ade of cyclin G1 may restore intrinsic molecular form

of tumor suppression106 Rexin-G has been found to havelow immunogenicity with preferential selection of rapidly-dividing cells over normal non-dividing or differentiatedcells In Phase II clinical trials 88 of patients had partialresponses or stable disease while the overall survival ratewas 6 months for all 22 patients106 On a further note sometargeted nanoparticles can have active mechanisms for theintracellular release of the therapeutic moiety CALAA-01is a targeted nanoparticle that has a high drug (siRNA)payload per targeting ligand tested and proven multiva-lent binding to cancer cell surfaces and an active siRNArelease mechanism that is triggered upon the recogni-tion of intracellular localization by a pH decline belowa value of 60107108 This nanoparticle system containsa cyclodextrin-based polymer human transferring protein

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targeting ligand hydrophilic polymer (PEG) and siRNAdesigned to reduce expression of RRM2 It is currentlyundergoing Phase I clinical trials for a dose-escalatingstudy in the treatment of solid tumor cancer107 An aptamerfor potential cancer treatment is AS1411109 It binds nucle-olin on the surface of cancer cells and induces apoptosisIn a dose escalation (1 mgkgday to 10 mgkgday) clin-ical study AS1411 showed positive responses in patientswith advanced solid tumors without any adverse effects109

Recently in a randomized phase II clinical trials a10 mgkgday or 40 mgkgday dose of AS1411 com-bined with high-dose cytarabine was well tolerated andshowed promising signs of activity in patients with pri-mary refractory or relapsed acute myeloid leukaemia Itis also currently being evaluated for treatment of breastcancer110 In another example Aurimune is a colloidalAu nanoparticle which delivers recombinant TNF- tocancer tumors TNF is attached to the Au nanoparticle withthiol-derivatized PEG which allows the nanoparticle toflow through the blood stream without causing a clearanceresponse110 Clinical data to date reports that Aurimunehas no antibody or immune responses and is well-toleratedbeyond the known maximum dose for TNF-110

7 CLOSING REMARKS FUTUREPERSPECTIVE

Over the past decades nanoncology (therapeutics anddiagnostics) has evolved from nano-sized drug particlesto bio-functional nanomaterials capable of deliveringheat treatment ionizing radiation andor chemothera-peutic agents From simple liposomal formulations andconjugation of PEG to antibody-conjugated nanoparti-cle chemotherapeutic and RNAi delivery nanoncology isbecoming more intricate smart and multi-functional Fur-ther the differences between cancerous and normal cellsincluding uncontrolled proliferation insensitivity to nega-tive growth regulation and anti-growth signals angiogen-esis and metastasis can be now be effectively exploitedThere is no doubt that nanoparticle therapeutics with theincreasing multi-functionality will continue to expand inthe future Investments in research development and per-formance trials are considerably large Sponsoring agen-cies in both private and government sectors should createeconomic strategies and innovative management to makesuch biotechnologies more cost-effective and easily acces-sible for patients across Although many challenges existfor the transition of nanoparticles from bench to bed theirpotential advantages will drive successful development andemerge as a new class of undeniable anti-cancer thera-peutic Finally (i) individualizedpersonalized oncology inwhich cancer detection diagnosis and therapy can be mod-ified to best fit the tumor molecular profile of a patientand (ii) predictive oncology in which genetic biochemicaland molecular markers are orchestrated to predict disease

development progression and clinical outcomes will cer-tainly shape the nanoncologic strategies of the near future

Acknowledgments This work was supported by theSouth Korean Ministry of Knowledge and Education(MKE) and the Incheon Free Economic Zone (IFEZ) inthe framework of several funding operating grants to theUtah-Inha DDS amp Advanced Therapeutics Research Cen-ter KR

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4 598 (2004)5 M Wang and M Thanou Drug Resist Updat 2 90 (2010)6 A Jones and A L Harris Cancer J Sci Am 4 209 (1998)7 D F Baban and L W Seymour Adv Drug Deliv 1 109 (1998)8 H Maeda Adv Enzyme Regul 41 189 (2001)9 K Greish Methods Mol Biol 624 25 (2010)10 A K Iyer K Greish T Seki S Okazaki J Fang K Takeshita

and H Maeda Drug Discov Today 11 812 (2006)11 K N Sugahara T Teesalu P P Karmali V R Kotamraju

L Agemy D R Greenwald and E Ruoslahti Science 5981 1031(2010)

12 R G Boyle and S Travess Anticancer Agents Med Chem 64 281(2006)

13 J M Brown and W R Wilson Nat Rev Cancer 4 437 (2004)14 D Kim E S Lee K Park I C Kwon and Y H Bae Pharm

Res 9 2074 (2008)15 L M Bareford and P W Swaan Adv Drug Deliv Rev 8 748

(2007)16 N F Saba X Wang S Muumlller M Tighiouart K Cho S Nie

Z Chen and D M Shin Head Neck 4 475 (2009)17 Y Lu L C Xu N Parker E Westrick J A Reddy M Vetzel

P S Low and C P Leamon Mol Cancer Ther 12 3258 (2006)18 E I Deryugina and J P Quigley Cancer Metastasis Rev 25 9

(2006)19 A M Mansour J Drevs N Esser F M Hamada O A Badary

C Unger I Fichtner and F Kratz Cancer Res 14 4062 (2003)20 H Hatakeyama H Akita E Ishida K Hashimoto H Kobayashi

T Aoki J Yasuda K Obata H Kikuchi T Ishida H Kiwadaand H Harashima Int J Pharm 1ndash2 194 (2007)

21 A Raz L Meromsky and R Lotan Cancer Res 7 3667 (1986)22 E Gorelik U Galili and A Raz Cancer Metastasis Rev 3ndash4 245

(2001)23 C Bies C M Lehr and J F Woodley Adv Drug Deliv Rev

4 425 (2004)24 H Glavinas P Krajcsi J Cserepes and B Sarkadi Curr Drug

Deliv 1 27 (2004)25 M Dean T Fojo and S Bates Nat Rev Cancer 4 275 (2005)26 T Kobayashi T Ishida Y Okada S Ise H Harashima and

H Kiwada Int J Pharm 1ndash2 94 (2007)27 A M Chen M Zhang D Wei D Stueber O Taratula T Minko

and H He Small 23 2673 (2009)28 J M Koziara P R Lockman D D Allen and R J Mumper

Pharm Res 11 1772 (2003)29 S C Steiniger J Kreuter A S Khalansky I N Skidan A I

Bobruskin Z S Smirnova S E Severin R Uhl M Kock K DGeiger and S E Gelperina Int J Cancer 5 759 (2004)

30 J Wu T Akaike and H Maeda Cancer Res 1 159 (1998)31 M A Deli Biochim Biophys Acta 4 892 (2009)

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the targeted drug-polymer carrier complex may exertits cytosolic action either at the plasma membrane orfollowing internalization15 Receptorantigenic expressionshould be reversible after drug delivery is complete Vascu-lar endothelial growth factor receptor and human epidermalreceptor are some of the different types of receptors that canbe targeted due to high levels of expression in tumor cellangiogenesisproliferation1516 To circumvent cell perme-ation problems and improve tumor specificity in nanopar-ticulate therapeutics folate receptor-mediated endocytosishas emerged as a potential strategy for drug delivery dueto both an overexpression of the folate receptor on can-cer cells and rapid internalization by receptor-mediatedendocytosis1617 Incidence of folate receptor expression inhuman head and neck (primary and metastatic) tumor tis-sues exists and compared with normal tissue such as bonemarrow folate receptor expression was found in 53 ofsamples whereas normal bone marrow cells did not displayany folate receptor expression Thus such receptor over-expression has indeed some great active tumor targetingpotential16

24 Protein Targeting

Matrix metalloproteinases (MMP) are zinc-dependentendopeptidases that play a major role in ECM degrada-tion as well as tissue repair morphogenesis angiogene-sis and have been shown to be overexpressed in tumortissue1819 In an effort to target MT1-MMP Fab222-1D8prime

fragments of anti-human MT1-MMP monoclonal anti-body were conjugated to doxorubicin immunoliposomescontaining approximately 40 Fabprime fragments per lipo-some Subsequently the liposomes were administered totumors 1000 to 3000 mm3 in size20 After 12 days non-targeted liposome treatment showed decreased tumor vol-ume in 16 mice and 36 mice died probably due toside effects of doxorubicin-encapsulated non-targeted lipo-somes However in the case of targeted liposomes tumorvolume decreased significantly with only 1 mouse report-ing notable body weight changes20 TNF- and v3 inte-grin are other tumor targeting proteins1520

25 Carbohydrate-Directed Targeting

Lectin-cell surface carbohydrates are used for activedrug targeting Briefly cell surface carbohydrates affecttumor cell interactions with normal cells during metastaticspread and growth21 These interactions can be mediatedthrough tumor cell carbohydrates and their binding pro-teins referred to as lectins Further cell surface mem-brane lectins are known to be overexpressed on the surfaceof numerous cancer cells and able to internalize endoge-nous sugar molecules22 Lectins affect tumor cell survivaladhesion to the endothelium as well as tumor vascular-ization and other processes crucial for metastatic spreadand growth21 This ligand-carbohydrate interaction can

be used for the development of nanoparticles containingcarbohydrate moieties that are directed to certain lectinsand incorporating lectins directed to exact cell surfacecarbohydrates2123

3 ADVANTAGES OF NANONCOLOGY

31 Eliminating Drug Resistance

Drug resistance has become a major obstacle in limit-ing the efficacy of chemotherapy The ATP-binding cas-sette (ABC) family of transporters plays a central partin the emergence of drug resistance as carrier pumpsfor influx and efflux of hydrophobic drugs among cancercells Nucleotide binding domains (NBD) for ATP bindingand hydrolysis derives energy necessary for transportingcell nutrients across membranes Three ABC transportersknown to be involved in multiple drug resistant cancer areP-glycoprotein (P-GP)2425 multi-drug resistance associ-ated protein (MRP)2425 and breast cancer resistance protein(ABCG2)25 One possible mechanism in which nanopar-ticles may help anticancer drugs avoid recognition bythe P-GP efflux pump is by means of envelopment inan endosome upon entering the cell via ligand targetedreceptor-mediated endocytosis thereby leading to higherintracellular concentrations25 As the interior of the endo-some becomes more acidic and lysozymes activated thedrug may be released from its nanoparticle conjugateand enter the cytoplasm to its target organelle avoidingthe P-DP efflux pump Kobayashi et al demonstrated abypass of the P-glycoprotein transporter with liposomesin doxorubicin-resistant SBC-3 a human small cell lungcancer cell line Transferrin ligands were attached todoxorubicin encapsulated EPC liposomes which showedsignificantly higher cytotoxicity in MDR cells than non-targeted liposomes Transferrin-bound liposomes were ableto deliver doxorubicin more closely to the nucleus allow-ing less of the drug to be affected by P-GP pump26 Non-transport based mechanisms can affect a variety of drugclasses as well This particular type of resistance may becaused by a mutation or an alteration in the activity ofenzymes such as glutathione S-transferase and topoiso-merase which decreases the cytotoxic efficiency of drugsindependent of intracellular drug concentrations Changesthat occur in the regulation of proteins that control apopto-sis and reduction in the efficacy of chemotherapeutic agentscan be attributed to the fact that most cancer drugs uti-lize cytotoxic effects by apoptotic processes25 Chen et al27

addressed this issue using mesoporous silica nanoparti-cles that simultaneously deliver doxorubicin and Bcl-2-targeting siRNA in multi-drug resistant A2780AD humanovarian cancer cells Bcl-2 overexpression is linked withinhibition of cellular apoptosis as well as being the mainnon-pump resistance protein in multi-drug resistant cancercells Cytotoxicity of doxorubicin was increased 132-foldfollowing co-delivery of Bcl-2 siRNA This shows the

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effectiveness in which a nanoparticulate system may carryboth the therapeutic agent and a small molecule inhibitor orchemo-sensitizer to disrupt the drug resistance mechanismwhile inducingenhancing chemotherapy simultaneously27

32 Avoiding Physiological Barriers

For conventional formulations the path of a therapeuticagent from the point of administration to the target ofintent is consistently subverted by obstructions and bio-logical barriers that may prevent effective treatment Onesuch example is the tight junction between epithelial cellsknown as the blood brain barrier (BBB)28 Now certainnanoparticles have shown ability in crossing the BBB dueto intrinsic properties of their constituent core materialssuch as polysorbate-coated nanoparticles In one studydoxorubicin-bound nanoparticles coated with polysorbate80 were used to target glioblastoma in rats showinghigher survival rates than non-coated doxorubicin-boundnanoparticles29 However more conclusive studies on dox-orubicin and polysorbate neuro-toxicity must be com-pleted before considering clinical use Endothelial vascularpermeability may be increased by the co-administrationof a bradykinin antagonist a cyclooxygenase inhibitoror a nitric oxide scavenger30 This is a possible strat-egy for the enhancement of tumor vasculature targetingThe combined delivery of permeation enhancers such aszonula-occludens toxin and its fragments can reversiblyopen tight junctions and allow penetration of nanopar-ticle agents31 Antagonistic oncotic and interstitial pres-sures from tumor bed as well as dissemination or cellularuptake throughout the tumor interstitium poses problemsfor the entry passage and retention of nanotherapeutics32

Phagocytes of the reticuloendothelial system (RES) actas immunological barriers against the targeting poten-tial of nanoparticle-encapsulated drugs as they sequesterinjected nanoparticles from circulation Extensive researchand experience in liposomes have demonstrated that uptakeby RES is effectively avoided by surface modification withpolyethylene glycol (PEG) to increase circulatory half-life from minutes to hours or days thereby allowing forenhanced targeting of liposomes within the tumor33 How-ever PEGylation not only prevents RES uptake but alsomasks the targeting ligand causing a reduction in thechances of bio-recognition and uptake34

4 KEY PROPERTIES OF ANTI-CANCERNANOPARTICLES

41 Dimensions

The dimensions of nanoparticles in cancer therapy arewidely debated however it is understood that the diam-eter of a nanoparticle should be in the range of 55 nmndash250 nm depending on the composition and surfacemodifications35ndash37 Lower limits have been defined due to

the threshold for filtration of particles within the glomeru-lar capillary wall of kidneys being 55 nm35 On the otherhand the upper size limits are not definite at the momenthowever increasingly larger particles or particle aggregatestend to be more prone to the RES The vasculature intumors is vulnerable to macromolecule permeation andEPR effect Nonetheless the cutoff in size for nanoparticleaccumulation in the tumor attributed to EPR effect seemsto be about 400 nm36ndash39 Particles hundreds of nanometerin size have been shown to leak out of blood vessels andaccumulate within tumors but larger macromolecules maystill have limited diffusion within the extracellular space38

Experiments from animal models suggest that particles of150 nm neutral or slightly negatively charged can movethrough tumor tissue In addition recent data shows thatnanoparticles in the 50ndash100 nm range carrying a slightpositive charge penetrate large tumors following systemicadministration40 Therefore are restricted from exiting intonormal vasculature requiring a size less than 1ndash2 nm3536

42 Surface Properties

Nanoparticles have a high surface-to-volume ratio com-pared to microparticles Control of surface properties is cru-cial for predicting behavior in the human body2341 Theultimate fate of nanoparticles can be determined by theinteractions of nanoparticles within their local environmentwhich depends largely on a combination of size and surfaceproperties Nanoparticles are sterically stabilized and havesurface charges41 In a recent study with gold nanoparti-cles positively charged nanoparticles depolarized the mem-brane to the greatest extent while nanoparticles of othercharges had a negligible effect However as the surfacecharge greatens (either positively or negatively) chancesfor macrophage uptake and clearance by RES increase39

Further therapeutic entities within nanoparticles do notimpact nanoparticle propertiesmdashdoxorubicin-loaded lipo-somes and their drug-free analogue liposomes for exam-ple can be expected to possess the same particle sizesurface charge pharmaco-dynamics-kinetics etc In con-trast molecular conjugates often strongly alter the prop-erties of the individual drug molecule with presence of acovalently attached modifier such as PEG andor antibody

43 Intermolecular Binding

The incorporation of targeting ligands provides specificnanoparticle-cell surface interactions in the selectivity ofthe nanoparticle Affinity of the ligand and its recep-tor can strongly influence the effects of multivalencyRelatively low-affinity ligands have potential to createstrong effective affinities within the context of a multi-valent nanoparticle42 For example increasing the num-ber of transferrin molecules on a 70-nm PEGylated goldnanoparticle to 144 gave a 013 nM Kd to the surface of

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Neuro2A cells (which have upregulated transferring recep-tors) compared to 64 nM for transferrin alone43 More-over molecules without sufficient binding affinity for useas a drug or individual targeting ligand can be encapsulatedwithin nanoparticles Also many drug candidates that wereineffective due to low binding of the target can be used onthe surface of nanoparticles as targeting agents A target-ing ligand increases the extent of cellular internalizationby particles that reach tumor tissue in a ligand density-dependent manner Inability of a targeting ligand to sig-nificantly increase tumor deposition is consistent with theroles of molecular size and affinity on tumor uptake44

It has been reported that intermediate-sized ligands witha molecular weight of about 25 kDa achieve the low-est tumor uptake levels while both smaller ligands (thatrequire high receptor affinity to be retained) and largerligands (that can achieve similar retention as smaller lig-ands withgt 100-fold weaker binding) showed an enhancedtumor uptake42ndash44

5 NANOBIOTECHNOLOGY THERAPEUTICDELIVERY PLATFORMS IN CANCER

A few nanoncologic systems have reached the pre-clinicaland clinical trial stage Below is a comprehensive yet pro-visional set of potential drug delivery systems examples(Fig 1) and their components being investigated in vitroand in vivo currently Other nanoparticles such as quantumdots nanowires and nanosensors are not discussed as theymainly deal with detection and imaging Yet few excitingmultifunctional systems such as iron oxide nanoparticlesare touched upon to further stress their future potential

51 Polymeric Nanoparticles

Polymers such as chitosan cyclodextrins alginate andhyaluronic acid occur naturally and have been the mate-rial of choice for the delivery of proteins DNA RNA

Fig 1 Nanoncology carrier applications in cancer therapeutics

as well as drugs Natural polymers have the advantageof being biodegradable and biocompatible more so thantheir synthetic counterparts45ndash47 Gupta and colleaguesexperimented with biologically-derived silk fibroin (SF)and chitosan (CH) blended non-covalently to encapsulatecurcumin48 Curcumin can interfere with the activity oftranscription factor NF-B and induce apoptosis in cancercells while avoiding healthy cells SF was shown to havebetter encapsulation properties and efficacy than liposomesSF-curcumin nanoparticles showed higher efficacy againstbreast cancer cells48 This demonstrates the potential totreat in vivo breast tumors by a possible sustained long-term biodegradable and therapeutic delivery system Onthe other hand synthetic polymers are not easily removedby normal clearance systems and can accumulate in tissuesHowever synthetic polymers such as PEG poly(lactic-co-glycolic acid) (PLGA) polyethylenimine (PEI) andhydroxyl propyl methacrylamide copolymer (HPMA) havecharacteristics that are more well-defined and can be finetuned to perform in a predictable manner As shown earlierchemical conjugation with PEG or PEGylation is one of themost acknowledged methods for prolonging the duration ofdrugs in the bloodstream and has also been demonstratedto contain certain targeting properties as well49 PEGyla-tion lowers plasma clearance rate by reducing receptor-mediated uptake during systemic circulation as well asmetabolic degradation by disguising the surface of theprotein49 It also reduces immunogenicity improves thesafety profile of the protein and protects the immunogenicepitopes Liu et al developed a novel nanocrystal formu-lation of Pluronic F127 for 2 anti-cancer drugs paclitaxel(PTX) and camptothecin50 Intravenously injected nano-crystals significantly inhibited tumor growth Considerabletherapeutic effects were shown via oral administration aswell In addition the targeted delivery of PTX via conju-gating a folate ligand to F127 was demonstrated50

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52 Micelles

Amphipilic nanoparticles composed of block or graft co-polymers such as N -vinylpyrrolidone and poloxamers canform polymeric micelles A hydrophobic core containshydrophobic drugs and the hydrophilic shell stabilizesthe core and makes the drug water-soluble4751 Poly-meric micelles have been shown to accumulate more read-ily in tumors than the larger liposomes mainly due totheir size51 The first polymeric micelle formulation ofPTX Genexol-PM a cremophor-free polymeric micellehas completed phase II clinical trials in the US withconsiderable anti-tumor activity in combination with cis-platin chemotherapy Cremophor EL is an excipient withcertain drugs and has been suggested to be a dose lim-iting factor in the administration of PTX52 This micel-lar nanoparticulate system allowed for higher doses of thedrug while being able to deliver and concentrate inside thetumor interstitium Another biodegradable formulation ofcationic micelles were prepared with PDMAEMA-PCL-PDMAEMA tri-block co-polymers and applied for thedual delivery of siRNA and PTX into cancer cells Combi-natorial delivery of anti-VEGF siRNA and PTX knockeddown VEGF expression53

53 Liposomes and Solid Lipid Nanoparticles

Natural liposomes a closed colloidal structure composedof a lipid bi-layer and an aqueous core are composed oflecithin phospholipids and can also be multi-laminar ratherthan uni-laminar carrying a larger payload of water- andfat-soluble constituents up to 500 nm in size5455 Lipo-somes take advantage of the overexpression of perforationsin cancer neovasculature in order to increase drug concen-trations passively at tumor sites Liposomal drug deliveryhas been the most successful nanoparticulate formulationused in the clinic as shown by liposomal-encapsulateddoxorubicin for Kaposirsquos sarcoma and more recentlybreast and ovarian cancer56 Small dimensions (lt300 nm)enables the drug to accumulate in the tumor mass by cross-ing passively into the tumor vasculature while avoiding orreducing the permeation of normal tissue55 On the otherhand solid lipid nanoparticles (SLNs) are solid lipids athuman physiological temperature with a diameter from50 to 1000 nm They are formed from a range of lipidsincluding mono- di- and tri-glycerides waxes fatty acidsand combinations of those SLNs are biodegradable bio-compatible with several human applications57 They form astrong lipophilic matrix in which water-insoluble lipophilicdrugs can be loaded for subsequent release The chemi-cal and physical properties of lipids in a heterogeneousmixture promote an imperfect crystalline structure withlarger gaps for efficient drug loading57 Use of SLNs havebeen investigated for the delivery of various anti-cancerdrugs with promising results in pre-clinical mouse trialsspecifically showing that SLNs might help overcome MDR

in cancers Serpe et al using human colon cancer cellsHT-29 demonstrated the benefits of SLNs in the deliveryof cholesteryl butyrate (chol-but) with doxorubicin Cyto-toxicity was shown to be higher in chol-but SLN loadedwith doxorubicin than free doxorubicin alone howeverPTX-loaded SLN did not show any improvement over freePTX5859 Lu et al loaded mitoxantrone a topoisomeraseinhibitor that blocks DNA replication into SLNs for alocal injection in the treatment of breast cancer and lymphnode metastases in mice60 Almost three-fold reduction inlymph node size was reported when compared to freely-administered mitoxantrone This was considered a signifi-cant improvement over existing treatment by the authors60

54 Dendrimers

Dendrimers may serve as a versatile nanoscale platformfor creating a multi-functional system capable of detect-ing cancer and delivering drugs A synthetic polymericmacromolecule of nanometer dimensions a dendrimer iscomposed of multiple highly branched monomers thatemerge radially from a central core The readily modifiablesurface characteristic enables them to be simultaneouslyconjugated with several molecules such as imaging con-trast agents targeting ligands andor therapeutic drugs61

Many commercial small molecule drugs with anti-canceractivity have been successfully conjugated with den-drimers such as polyamidoamine poly(propylene imine)and poly(etherhydroxylamine) dendrimers by means ofeither steric interactions or chemical reactions6263 Tar-geted delivery is possible via targeting moieties conju-gated to dendrimer surface or passive delivery due to theEPR effect Cationic dendrimers show cytotoxicity how-ever derivatization with fatty acid or PEG chains canreduce the overall charge density and minimize contactbetween cell surface thus reducing toxic effects6162 Patriet al demonstrated that covalently coupled methotrexate-dendrimer conjugates targeting high-affinity receptor forfolic acid have a similar activity to the free drug invitro while specifically killing receptor-expressing cells viareceptor-mediated endocytosis64

55 Carbon Nanotubes and Nanodiamonds

Carbon nanotubes are generally insoluble causing them tobe non-biocompatible however the introduction of chem-ical modification to carbon nanotubes render them water-soluble and functionalized so that they can be linked to awide variety of active molecules such as peptides proteinsnucleic acids and therapeutic agents Functionalized car-bon nanotubes also have an intrinsic capability to perme-ate cell membranes which allows endocytosis-independentinternalization of nanoparticles265 Methotrexate cova-lently linked to carbon nanotubes with a fluorescent agentwas shown to be more effectively internalized into cells

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when compared to the free unbound drug65 The multi-ple covalent functionalizations on the sidewall or tips ofcarbon nanotubes allow them to carry several moleculesat once This strategy provides a fundamental advantagein the treatment of cancer Targeted heat therapy or lsquother-mal ablationrsquo is being tested to destroy breast cancertumors using carbon nanotubes Accordingly the HER2IgY-single wall carbon nanotube (SWNT) complex specif-ically targeted HER2-expressing SK-BR-3 cells but notreceptor-negative MCF-7 cells Near-infrared irradiationwith an 808 nm laser showed extensive cell death withSWNT66 On the other hand a nanodiamond-embeddeddevice is being developed to deliver chemotherapy locallyto sites where cancerous tumors have been surgicallyremoved67 Nanodiamonds complexed with doxorubicin-hydrochloride enable a sustained release of drug for aminimum of 30 days with a significant amount of drugin reserve This shows potential for highly localized drugrelease as a complementary yet potent form of treat-ment with systemic injection Ho and group embeddedmillions of tiny drug carrying nanodiamonds into theFDA-approved parylene67ndash69 Currently used as a coatingfor implants biostable parylene is a flexible and versa-tile polymeric material Nanodiamonds placed betweenextremely thin parylene films resulted in a device that isminimally-invasive Internalization assays revealed a pri-marily endocytic uptake process High degree of nanodia-mond (sim46 nm in diameter) and endosome co-localizationas well as cytoplasmic presence of smaller nanodiamondswere observed69

56 Silicon Nanoparticles

Silicon and silica are establishing themselves as inter-esting candidate materials for injectable nanoparticles indrug delivery70 Porosified silicon is biodegradable71 withkinetics that are much more rapid than those of typicalbiodegradable polymers and as a result releases drugswith previously un-attainable time profiles Lu et al loadedhydrophobic anti-cancer drug camptothecin (CPT) ontomesoporous silica nanoparticles CPT release was mini-mal and sustained in aqueous solution This effectivelyaddressed the problem of poor water-solubility of certainanti-cancer drugs as well as sustainable release profiles71

Furthermore there are metal-based nanovectors such asnanoshells70 comprised of a gold layer over a silica coreThe thickness of the gold layer can be precisely tuned sothat the nanoshell can be selectively activated through tis-sue irradiation with near-infrared light to perform localizedtherapeutic thermal ablation This approach was recentlyused to eradicate transmissible venereal tumors in mice72

In another study nitric oxide (NO)-releasing silica nanopar-ticles exhibited enhanced growth inhibition of ovariantumor cells and showed greater inhibition of the anchorage-independent growth of tumor-derived and Ras-transformed

ovarian cels73 NO a free radical bio-regulator endoge-nously synthesized in the body impacts multiple stages oftumor development spanning cytostatic processes cellulartransformation and formation of neoplastic lesions7374 Itis worth mentioning herein that research efforts have beenimpeded by the fact that possible normal cell toxicity ofthe NO donor drug by-product and the inability to targetdelivery of the drug selectively to cancer cells

57 Gold and Magnetic Nanoparticles

Gold (Au) nanoparticles are very versatile and can beprepared with different geometries such as nanospheresnanoshells nanorods or nanocages75 Further they haveunrivaled physical and chemical properties such asexceedingly small size (less than 50 nm) large sur-face area to mass proportion heightened surface sensitiv-ity presence of characteristic surface plasmon resonancebands biocompatibility and ease of surface functionaliza-tion Au nanoparticles are also excellent conductors ofelectrical and thermal energy which allows possibilitiesfor thermal ablation treatment In photodynamic therapy(PDT) Au nanoparticles are becoming known as a photo-sensitizer with great potential due to its optimal absorptionand light scattering properties along with controllable opti-cal characteristics El-Sayed and collegues have shown thatanti-EGFR antibody conjugated gold nanoparticles selec-tively localized in malignant HOC and HSC cells andunderwent significant photothermal destruction upon nearinfrared irradiation76 However using radiofrequency irra-diation Gannon et al demonstrated that the internalizationof Au nanoparticles in gastrointestinal cancer cells releasedsubstantial heat rapidly after exposure to an external high-voltage focused radiofrequency field (RF) It is noteworthythat radiofrequency ablation has an advantage over nearinfrared ablation which is limited to superficial tumorswith minimal tissue penetration Hep3B and Panc-1 cellstreated with 67 ML Au nanoparticles had significantlyhigher rates of cell death than the control samples at alltime-points after RF exposure77 Interestingly Au nanopar-ticles about 5ndash10 nm in diameter have been shown to haveintrinsic anti-angiogenic properties78 These nanoparticlesbind to heparin-binding pro-angiogenic growth factorssuch as VEGF165 and bFGF to inhibit their activity TheAu nanoparticles themselves also reduced ascites accumu-lation in a pre-clinical model of ovarian cancer inhibitedproliferation of multiple myeloma cells and induced apop-tosis in chronic B cell leukemia78 On the other hand mag-netic nanoparticles (MNPs) have traditionally been usedfor disease imaging via magnetic resonance (MR) imagingdue to their intrinsic properties Recent advances have alsoopened the door to cellular-specific targeting drug deliv-ery and multi-modal imaging Further MNPs can be func-tionalized through coating with polymers preferentiallywith biocompatible or biodegradable polymers of synthetic

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or biological origin7980 As solid tumor develops it out-grows its blood supply which results in the formation ofa hypoxic semi-necrotic tumor core and dormant tumorcells send out chemical signals that recruit macrophagesinto the core Macrophages begin to rebuild the bloodsupply allowing the tumor to start growing again8182

Muthana et al loaded human monocytes with MNPs plac-ing magnets near the site of a human prostate tumor grownin mice82 The MNP-loaded monocytes carrying a reportergene invaded the tumor at a rate more than three timesthat of the non-loaded cells82 This demonstration of mag-netic targeting shows that MNP-loaded cells circulatingin the body can be attracted to the tumor site where anexternal magnet is placed allowing a higher proportion ofloaded cells to respond to chemical signals from the tumorcore In addition the loaded monocytes were able to reachthe poorly vascularized peri-necrotic regions of the tumorthat are normally difficult to target As the moncytes areloaded with MNPs they can then be destroyed by hyper-thermia after delivering a therapeutic drug or gene8182

Classes of MNPs include metallic bimetallic and super-paramagnetic iron oxide nanoparticles widely-knows asSPIONs SPIONS are favored because due to low toxicityprofile and their reactive surface that can be readily modi-fied with biocompatible coatings87 This flexibility has ledto SPION use in magnetic separation biosensor in vivomedical imaging drug delivery tissue repair and hyper-thermia applications84 Yu et al preciously showed thatthermally crosslinked SPIONs loaded with doxorubicinhad potential as both an imaging and therapeutic deliverysystem83 This DoxTCL-SPION was also demonstratedto efficiently reach tumor sites and release the drug withoutany active targeting from ligandsantibodies or magneticfield largely due to the EPR effect83

58 Viral Nanoparticles

A variety of viruses including cowpea mosaic viruscanine parvovirus adenovirus coxsackie virus measlesvirus along with virions and virus-like particles have beendeployed for biomedical and nanotechnology applicationsthat include tissue targeting and drug delivery84 Target-ing molecules and peptides can be produced in a bio-logically functional form on the capsid surface throughchemical conjugation or gene expression Several lig-ands including transferrin folic acid and single-chainantibodies have been conjugated to viruses for specifictumor targeting84 Further a subset of viruses such ascanine parvovirus have a natural affinity for receptors liketransferrins that are up-regulated in a variety of tumorcells85 Adenoviral vectors offer many advantages for can-cer gene therapy including high transduction efficiencyyet safety concerns related to immunogenic response haveled to a cautious approach of their use in human clini-cal trials86 To overcome these obstacles hybrid vectors

combining both viral and non-viral elements are beingdeveloped Adenovirus coated with an arginine-graftedbioreducible polymer (ABP) via electrostatic interaction isone example ABP-coated complexes were shown to havesignificantly reduced the innate immune response whileproducing higher levels of transgene expression8687 Fur-thermore herpes simplex virus (HSV) vectors are alreadyin early phase human clinical trials for recurrent malignantglioblastoma A mutant form (vIII) of epidermal growthfactor receptor (EGFR) present in glioma tumor is rec-ognized by a single-chain antibody designated MR1-1HSV virions bearing MR1-1-modified gC had five-foldincreased infectivity for EGFRvIII-bearing human gliomaU87 cells showing enhanced vector specificity and tumorcell damage88

59 RNA Interference

Since its discovery nearly two decades ago RNA inter-ference (RNAi) has been lauded as the next generation ingene therapy due to the unique pathway in which smallinterfering (siRNA) or microRNA (miRNA) can preventmRNA expression and silence- specific targeted geneseffectively89 RNAi cancer gene targets are pathways thatcontribute to tumor growth through increased tumor cellproliferation andor reduced tumor cell death RNAi canalso be used to target and silence gene products thatnegatively regulate the function of endogenous tumor sup-pressor genes as well as proteins involved in cellular senes-cence or protein stabilitydegradation However in vivostudies up until now have shown wide variation on thepotency of RNAi and its suppression activities as a resultof poor cellular uptake rapid renal clearance and nucle-ase degradation90 Also previous experiments have beenplagued with additional problems such as off-targeting andimmunogenic response9091 Nonetheless the characteri-zation of novel nanoparticle carriers and chemical mod-ifications to siRNA itself has addressed some of theseissues Suh and collegues developed a cationic lipid N N primeprime-dioleylglutamide linked by negatively charged glutamicacid to oleoylamine as a siRNA carrier92 It was ableto deliver siRNA to various cancer cells in vitro moreeffectively than other cationic liposomes and with reducedcytotoxicity Moreover results showed that it was effectivefor local in vivo siRNA delivery providing clear evidencethat target protein expression was knocked down in tumortissues92 In addition Chen et al developed a liposome-polycation-hyaluronic acid (LPH) nanoparticle formulationmodified with single-chain antibody fragment (GC4 scFv)for the systemic delivery of siRNA and miRNA in experi-mental lung metastasis of murine B16F10 melanoma Inhi-bition of c-Myc MDM2 and VEGF protein expression bysiRNA formulated with GC4 scFv modified LPH nanopar-ticles significantly suppressed B16F10 metastatic tumorgrowth while showing increased siRNA uptake within thelung tumors93

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510 Monoclonal Antibodies

Monoclonal antibodies (mAB) are monospecific antibod-ies that bind only to one particular antigenic determinantor epitope By blocking ligand binding andor signalingof growth receptors mABs have the capability to sen-sitize tumors to chemotherapeutic agents reduce growthrates and induce apoptosis Many different monoclonalantibodies are currently used in the therapy of cer-tain cancers such as Bevacizumab Imatinib BortezomibGefitinib Sorafenib Tositumomab Tamoxifen and Ritux-imab which are all FDA-approved therapies for cancer todate94 In some in vivo applications the antibody itself issufficient and once bound to its target mAB triggers theeffector cell mechanisms of the immune system An excel-lent 2010 review by Weiner et al addresses the specificimmunologic pathways in which mABs interact with can-cer cells94 mAB may also be coupled to another moleculesuch as a fluorescent molecule to aid in imaging or aradioactive isotope such as Iodine-125 to aid in killing can-cer cells with radioimmunotherapy95 However in a recentstudy of radioimmunotherapy it was concluded that a sin-gle -emitter 90Y coupled to each antibody had a signifi-cantly lower biological effective dose and was insufficientto treat non small-cell lung cancer than a single 5 nm90Y2O3 nanoparticle96 In the application of nanoparticlesmAB can be used as efficient targeting ligands Workby Park and associates shows the targeting specificityof a modified lymphocyte function-associated antigen-1domain tuned to have variable affinities for intercellularadhesion molecule (ICAM)-1 Applying this antibody totheir nanoparticle system amphiphilic urethane acrylatenonionomer (UAN) researchers were able to demonstrateefficient encapsulation of a FITC marker and a protea-some inhibitor (celastrol) as well as the targeted deliveryto HeLa cells producing a more potent cytotoxicity withequal amounts of drug than with the untargeted UAN97

511 Aptamers

Aptamers are synthetic oligonucleotide ligands or peptidesthat bear unique three-dimensional conformations capa-ble of binding to target antigens with high affinity andspecificity Aptamers bind to their targets to effectivelyillicit little or none immunogenicity and possess molecu-lar recognition properties similar to monoclonal antibod-ies They have been applied to drug delivery systems asligands to enhance selectivity98 RNA aptamer OPN-R3has been shown in an in vivo xenograft model of breastcancer with MDA-MB-231 cells to significantly decreaselocal progression and distant metastases By day 20 tumorvolume in the modified OPN-R3 treated group was 18ndash20-fold smaller than the tumor volume in mutant OPN-R3and no treatment groups99 Another aptamer SM20 iso-lated against plasminogen activator inhibitor-1 has demon-strated in vitro therapeutic potential as an antimetastatic

agent and could possibly be used as an adjuvant to tradi-tional chemotherapy for breast cancer100 Several aptamershave been recently isolated for potential treatment of othercancers such as glioblastoma T cell leukaemia and epithe-lial cancer cells in the breast colon lung ovaries andpancreas98 Finally apatmers can be used as a targetingmoiety to be conjugated to a certain drug delivery for-mulation or may act as modalities with characteristics ofintrinsic specificity100

6 CURRENT CLINICAL PROGRESS OFNANONCOLOGY THERAPEUTICS

In this section nanoparticles for cancer therapy that havealready reached the clinic are discussed A few sys-tems having been approved and many are still ongoingin human clinical trials (Table I) As described earliernon-targeting nanoparticles utilize leaky vasculature oftumors to reach via passive targeting PEGylation has beenapplied to various proteins enzymes cytokines and mon-oclonal antibody fragments to increase circulatory half-life and decrease antigenicity3349101102 Many clinicaltrials involving PEGylation of nanoparticles are in differ-ent phase trials at the moment such as PEG-InterferonAlfa-2b PEGylated recombinant human Hyaluronidase(PEGPH20) PEG conjugate of SN38 (EZN-2208) toname a few An interesting PEgylated complex is PEG-ADI 20 currently undergoing Phase II studies Argininedeiminase (ADI) is a microbial enzyme that degrades argi-nine Certain cancer cells deficient in producing argininethrough argininosuccinate synthase obtain exogenous argi-nine from circulation PEG-ADI 20 depletes arginine con-centrations in the blood thereby controlling and reducingtumor growth103 The previous phase III study was com-pleted on un-resectable hepatocellular carcinoma knownfor its poor prognosis In a study with 35 patients allpatients exhibited blood arginine levels lower than 2 uMwhile 2 patients became stable 1 patient became resectableand 28 progressed with a mean duration before progres-sion of 34 months103 On the other hand CRLX101 isa nanoparticle drug delivery system comprised of thechemotherapeutic camptothecin (CPT) conjugated to acyclodextrin-based polymer CRLX101 was designed toincrease the exposure of tumor cells to CPT while reducingside effects Anti-cancer activity of camptothecin is due inpart to the inhibition of DNA topoisomerase I but has beenprevented from use as an anti-cancer drug due to poor sol-ubility lack of activity and excessive toxicity104 HoweverCRLX101 nanoparticle was shown to have significantlyhigher antitumor activity with lower dosing while main-taining the levels of free camptothecin in the blood to aminimum It is noteworthy that it was effective in a num-ber of tumors resistant to irinotecan treatment CRLX101is currently undergoing Phase IB2A trials104 Ultimatelyactive targeting through the inclusion of a targeting lig-and on the nanoparticles is envisioned to provide the

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Table I Nanoncology in clinical development

Class Carrier Active agent Target Clinical status Indication (s) Ref

LiposomesDaunoXome Liposome Daunorubicin

citrateNA Approved Chronic myelogenous

leukemia neuroblastoma3

DOTAP Chol-FUS1 Liposome Plasmid DNA(FUS1)

NA Phase I Metastatic non-small celllung cancer

114

SGT-53 Liposome Plasmid DNAp53 W-T

Transferrinreceptor

Phase I Advanced Solid Tumors 115

MBP 426 Liposome Oxaliplatin Transferrinreceptor

Phase lbII Advanced or MetastaticSolid Tumors

105

PEGylatedDoxil PEGylaled-Liposome Doxorubicin NA Approved Ovanan cancer recurrent

breast cancer2 56

Oncospar PEGylaled-Asparagnase

L-asparagnase NA Approved Acute lymphoblasticleukemia

2

CYT-6091 PEGylaled-ThiolGold

RecombinantTNF-

Tumor necrosisfactor recepteor

Phase II Advanced solid tumors 110

ADI-PEG 20 PEGylated-ArginineDeiminase

Augininedeiminase

NA Phase II Hepatocellular carcinomaMetastatic melanomarelapsed small cell lungcancer

103

PeptideAbraxane Albumin Paclitaxel NA Approved Metastatic non-small cell

lung cancer2 3

Ontak Interkeukin-2engineered protein

Diphtheria toxin Interleukin-2receptors

Approved Cutaneous T-cell lymphoma 3

AMG 386 Peptibody Recombinantpeptide-Fcfusion protein

Angiopoietin 1and 2

Phase III Various cancers 113

PolymericCALAA-01 Cyclodextrin Small interfering

RNATransferrin

receptorPhase I Solid tumors 107 108

XMT-1001 Fleximer Camptothecin Prodrug activation Phase I Advanced solid tumors 111Genexol Polymeric micelles Paclitaxel NA Phase II Various cancers 52CT-2103 Poly-L-glutmate Paclitaxel NA Phase II Various cancers 112

Antibodya

Trastuzumab HumanizedMonoclonalantibody

Antibody CD340 receptor Approved HER2-positive metastaticbreast cancer

3 4 94

Rituximab Chimeric monoclonalAntibody

Antibody Protein CD20 Approved Leukemias and lymphomas 3 4 94

a Currently there are over 20 FDA-approved monoclonal antibodies for use in cancer therapy

most effective therapy A targeting nanoparticle in Pha-seIBII study is MbP-426 which contains the cytotoxicplatinum-based drug oxaliplatin in a transferrin-conjugatedlipopsome105 Transferrin receptors (TfR) overexpressedon tumor cells allow selective uptake via Tf-TfR interac-tion Outcome of Phase I trial with 39 patients showed that15 patients had stable disease after 2 cycles 3 patients withcolon carcinoma refractory to conventional oxaliplatin hadstable disease for 4-6 cycles and 2 patients had 12 and26 decrease in target lesions105 Further Rexin-G is amurine leukemia virus-based retrovector nanoparticle thatcontains a cytocidal dominant negative cyclin-G1 constructand allows for the functional restoration of tumor sup-pressor microRNA-122a It has been found that block-ade of cyclin G1 may restore intrinsic molecular form

of tumor suppression106 Rexin-G has been found to havelow immunogenicity with preferential selection of rapidly-dividing cells over normal non-dividing or differentiatedcells In Phase II clinical trials 88 of patients had partialresponses or stable disease while the overall survival ratewas 6 months for all 22 patients106 On a further note sometargeted nanoparticles can have active mechanisms for theintracellular release of the therapeutic moiety CALAA-01is a targeted nanoparticle that has a high drug (siRNA)payload per targeting ligand tested and proven multiva-lent binding to cancer cell surfaces and an active siRNArelease mechanism that is triggered upon the recogni-tion of intracellular localization by a pH decline belowa value of 60107108 This nanoparticle system containsa cyclodextrin-based polymer human transferring protein

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targeting ligand hydrophilic polymer (PEG) and siRNAdesigned to reduce expression of RRM2 It is currentlyundergoing Phase I clinical trials for a dose-escalatingstudy in the treatment of solid tumor cancer107 An aptamerfor potential cancer treatment is AS1411109 It binds nucle-olin on the surface of cancer cells and induces apoptosisIn a dose escalation (1 mgkgday to 10 mgkgday) clin-ical study AS1411 showed positive responses in patientswith advanced solid tumors without any adverse effects109

Recently in a randomized phase II clinical trials a10 mgkgday or 40 mgkgday dose of AS1411 com-bined with high-dose cytarabine was well tolerated andshowed promising signs of activity in patients with pri-mary refractory or relapsed acute myeloid leukaemia Itis also currently being evaluated for treatment of breastcancer110 In another example Aurimune is a colloidalAu nanoparticle which delivers recombinant TNF- tocancer tumors TNF is attached to the Au nanoparticle withthiol-derivatized PEG which allows the nanoparticle toflow through the blood stream without causing a clearanceresponse110 Clinical data to date reports that Aurimunehas no antibody or immune responses and is well-toleratedbeyond the known maximum dose for TNF-110

7 CLOSING REMARKS FUTUREPERSPECTIVE

Over the past decades nanoncology (therapeutics anddiagnostics) has evolved from nano-sized drug particlesto bio-functional nanomaterials capable of deliveringheat treatment ionizing radiation andor chemothera-peutic agents From simple liposomal formulations andconjugation of PEG to antibody-conjugated nanoparti-cle chemotherapeutic and RNAi delivery nanoncology isbecoming more intricate smart and multi-functional Fur-ther the differences between cancerous and normal cellsincluding uncontrolled proliferation insensitivity to nega-tive growth regulation and anti-growth signals angiogen-esis and metastasis can be now be effectively exploitedThere is no doubt that nanoparticle therapeutics with theincreasing multi-functionality will continue to expand inthe future Investments in research development and per-formance trials are considerably large Sponsoring agen-cies in both private and government sectors should createeconomic strategies and innovative management to makesuch biotechnologies more cost-effective and easily acces-sible for patients across Although many challenges existfor the transition of nanoparticles from bench to bed theirpotential advantages will drive successful development andemerge as a new class of undeniable anti-cancer thera-peutic Finally (i) individualizedpersonalized oncology inwhich cancer detection diagnosis and therapy can be mod-ified to best fit the tumor molecular profile of a patientand (ii) predictive oncology in which genetic biochemicaland molecular markers are orchestrated to predict disease

development progression and clinical outcomes will cer-tainly shape the nanoncologic strategies of the near future

Acknowledgments This work was supported by theSouth Korean Ministry of Knowledge and Education(MKE) and the Incheon Free Economic Zone (IFEZ) inthe framework of several funding operating grants to theUtah-Inha DDS amp Advanced Therapeutics Research Cen-ter KR

References and Notes

1 N Portney and M Ozkan Anal Bioanal Chem 3 620 (2006)2 M Ferrari Nat Rev Cancer 3 161 (2005)3 T M Allen Nat Rev Cancer 1 0750 (2002)4 J S Ross D P Schenkein and R Pietrusko Am J Clin Pathol

4 598 (2004)5 M Wang and M Thanou Drug Resist Updat 2 90 (2010)6 A Jones and A L Harris Cancer J Sci Am 4 209 (1998)7 D F Baban and L W Seymour Adv Drug Deliv 1 109 (1998)8 H Maeda Adv Enzyme Regul 41 189 (2001)9 K Greish Methods Mol Biol 624 25 (2010)10 A K Iyer K Greish T Seki S Okazaki J Fang K Takeshita

and H Maeda Drug Discov Today 11 812 (2006)11 K N Sugahara T Teesalu P P Karmali V R Kotamraju

L Agemy D R Greenwald and E Ruoslahti Science 5981 1031(2010)

12 R G Boyle and S Travess Anticancer Agents Med Chem 64 281(2006)

13 J M Brown and W R Wilson Nat Rev Cancer 4 437 (2004)14 D Kim E S Lee K Park I C Kwon and Y H Bae Pharm

Res 9 2074 (2008)15 L M Bareford and P W Swaan Adv Drug Deliv Rev 8 748

(2007)16 N F Saba X Wang S Muumlller M Tighiouart K Cho S Nie

Z Chen and D M Shin Head Neck 4 475 (2009)17 Y Lu L C Xu N Parker E Westrick J A Reddy M Vetzel

P S Low and C P Leamon Mol Cancer Ther 12 3258 (2006)18 E I Deryugina and J P Quigley Cancer Metastasis Rev 25 9

(2006)19 A M Mansour J Drevs N Esser F M Hamada O A Badary

C Unger I Fichtner and F Kratz Cancer Res 14 4062 (2003)20 H Hatakeyama H Akita E Ishida K Hashimoto H Kobayashi

T Aoki J Yasuda K Obata H Kikuchi T Ishida H Kiwadaand H Harashima Int J Pharm 1ndash2 194 (2007)

21 A Raz L Meromsky and R Lotan Cancer Res 7 3667 (1986)22 E Gorelik U Galili and A Raz Cancer Metastasis Rev 3ndash4 245

(2001)23 C Bies C M Lehr and J F Woodley Adv Drug Deliv Rev

4 425 (2004)24 H Glavinas P Krajcsi J Cserepes and B Sarkadi Curr Drug

Deliv 1 27 (2004)25 M Dean T Fojo and S Bates Nat Rev Cancer 4 275 (2005)26 T Kobayashi T Ishida Y Okada S Ise H Harashima and

H Kiwada Int J Pharm 1ndash2 94 (2007)27 A M Chen M Zhang D Wei D Stueber O Taratula T Minko

and H He Small 23 2673 (2009)28 J M Koziara P R Lockman D D Allen and R J Mumper

Pharm Res 11 1772 (2003)29 S C Steiniger J Kreuter A S Khalansky I N Skidan A I

Bobruskin Z S Smirnova S E Severin R Uhl M Kock K DGeiger and S E Gelperina Int J Cancer 5 759 (2004)

30 J Wu T Akaike and H Maeda Cancer Res 1 159 (1998)31 M A Deli Biochim Biophys Acta 4 892 (2009)

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effectiveness in which a nanoparticulate system may carryboth the therapeutic agent and a small molecule inhibitor orchemo-sensitizer to disrupt the drug resistance mechanismwhile inducingenhancing chemotherapy simultaneously27

32 Avoiding Physiological Barriers

For conventional formulations the path of a therapeuticagent from the point of administration to the target ofintent is consistently subverted by obstructions and bio-logical barriers that may prevent effective treatment Onesuch example is the tight junction between epithelial cellsknown as the blood brain barrier (BBB)28 Now certainnanoparticles have shown ability in crossing the BBB dueto intrinsic properties of their constituent core materialssuch as polysorbate-coated nanoparticles In one studydoxorubicin-bound nanoparticles coated with polysorbate80 were used to target glioblastoma in rats showinghigher survival rates than non-coated doxorubicin-boundnanoparticles29 However more conclusive studies on dox-orubicin and polysorbate neuro-toxicity must be com-pleted before considering clinical use Endothelial vascularpermeability may be increased by the co-administrationof a bradykinin antagonist a cyclooxygenase inhibitoror a nitric oxide scavenger30 This is a possible strat-egy for the enhancement of tumor vasculature targetingThe combined delivery of permeation enhancers such aszonula-occludens toxin and its fragments can reversiblyopen tight junctions and allow penetration of nanopar-ticle agents31 Antagonistic oncotic and interstitial pres-sures from tumor bed as well as dissemination or cellularuptake throughout the tumor interstitium poses problemsfor the entry passage and retention of nanotherapeutics32

Phagocytes of the reticuloendothelial system (RES) actas immunological barriers against the targeting poten-tial of nanoparticle-encapsulated drugs as they sequesterinjected nanoparticles from circulation Extensive researchand experience in liposomes have demonstrated that uptakeby RES is effectively avoided by surface modification withpolyethylene glycol (PEG) to increase circulatory half-life from minutes to hours or days thereby allowing forenhanced targeting of liposomes within the tumor33 How-ever PEGylation not only prevents RES uptake but alsomasks the targeting ligand causing a reduction in thechances of bio-recognition and uptake34

4 KEY PROPERTIES OF ANTI-CANCERNANOPARTICLES

41 Dimensions

The dimensions of nanoparticles in cancer therapy arewidely debated however it is understood that the diam-eter of a nanoparticle should be in the range of 55 nmndash250 nm depending on the composition and surfacemodifications35ndash37 Lower limits have been defined due to

the threshold for filtration of particles within the glomeru-lar capillary wall of kidneys being 55 nm35 On the otherhand the upper size limits are not definite at the momenthowever increasingly larger particles or particle aggregatestend to be more prone to the RES The vasculature intumors is vulnerable to macromolecule permeation andEPR effect Nonetheless the cutoff in size for nanoparticleaccumulation in the tumor attributed to EPR effect seemsto be about 400 nm36ndash39 Particles hundreds of nanometerin size have been shown to leak out of blood vessels andaccumulate within tumors but larger macromolecules maystill have limited diffusion within the extracellular space38

Experiments from animal models suggest that particles of150 nm neutral or slightly negatively charged can movethrough tumor tissue In addition recent data shows thatnanoparticles in the 50ndash100 nm range carrying a slightpositive charge penetrate large tumors following systemicadministration40 Therefore are restricted from exiting intonormal vasculature requiring a size less than 1ndash2 nm3536

42 Surface Properties

Nanoparticles have a high surface-to-volume ratio com-pared to microparticles Control of surface properties is cru-cial for predicting behavior in the human body2341 Theultimate fate of nanoparticles can be determined by theinteractions of nanoparticles within their local environmentwhich depends largely on a combination of size and surfaceproperties Nanoparticles are sterically stabilized and havesurface charges41 In a recent study with gold nanoparti-cles positively charged nanoparticles depolarized the mem-brane to the greatest extent while nanoparticles of othercharges had a negligible effect However as the surfacecharge greatens (either positively or negatively) chancesfor macrophage uptake and clearance by RES increase39

Further therapeutic entities within nanoparticles do notimpact nanoparticle propertiesmdashdoxorubicin-loaded lipo-somes and their drug-free analogue liposomes for exam-ple can be expected to possess the same particle sizesurface charge pharmaco-dynamics-kinetics etc In con-trast molecular conjugates often strongly alter the prop-erties of the individual drug molecule with presence of acovalently attached modifier such as PEG andor antibody

43 Intermolecular Binding

The incorporation of targeting ligands provides specificnanoparticle-cell surface interactions in the selectivity ofthe nanoparticle Affinity of the ligand and its recep-tor can strongly influence the effects of multivalencyRelatively low-affinity ligands have potential to createstrong effective affinities within the context of a multi-valent nanoparticle42 For example increasing the num-ber of transferrin molecules on a 70-nm PEGylated goldnanoparticle to 144 gave a 013 nM Kd to the surface of

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Neuro2A cells (which have upregulated transferring recep-tors) compared to 64 nM for transferrin alone43 More-over molecules without sufficient binding affinity for useas a drug or individual targeting ligand can be encapsulatedwithin nanoparticles Also many drug candidates that wereineffective due to low binding of the target can be used onthe surface of nanoparticles as targeting agents A target-ing ligand increases the extent of cellular internalizationby particles that reach tumor tissue in a ligand density-dependent manner Inability of a targeting ligand to sig-nificantly increase tumor deposition is consistent with theroles of molecular size and affinity on tumor uptake44

It has been reported that intermediate-sized ligands witha molecular weight of about 25 kDa achieve the low-est tumor uptake levels while both smaller ligands (thatrequire high receptor affinity to be retained) and largerligands (that can achieve similar retention as smaller lig-ands withgt 100-fold weaker binding) showed an enhancedtumor uptake42ndash44

5 NANOBIOTECHNOLOGY THERAPEUTICDELIVERY PLATFORMS IN CANCER

A few nanoncologic systems have reached the pre-clinicaland clinical trial stage Below is a comprehensive yet pro-visional set of potential drug delivery systems examples(Fig 1) and their components being investigated in vitroand in vivo currently Other nanoparticles such as quantumdots nanowires and nanosensors are not discussed as theymainly deal with detection and imaging Yet few excitingmultifunctional systems such as iron oxide nanoparticlesare touched upon to further stress their future potential

51 Polymeric Nanoparticles

Polymers such as chitosan cyclodextrins alginate andhyaluronic acid occur naturally and have been the mate-rial of choice for the delivery of proteins DNA RNA

Fig 1 Nanoncology carrier applications in cancer therapeutics

as well as drugs Natural polymers have the advantageof being biodegradable and biocompatible more so thantheir synthetic counterparts45ndash47 Gupta and colleaguesexperimented with biologically-derived silk fibroin (SF)and chitosan (CH) blended non-covalently to encapsulatecurcumin48 Curcumin can interfere with the activity oftranscription factor NF-B and induce apoptosis in cancercells while avoiding healthy cells SF was shown to havebetter encapsulation properties and efficacy than liposomesSF-curcumin nanoparticles showed higher efficacy againstbreast cancer cells48 This demonstrates the potential totreat in vivo breast tumors by a possible sustained long-term biodegradable and therapeutic delivery system Onthe other hand synthetic polymers are not easily removedby normal clearance systems and can accumulate in tissuesHowever synthetic polymers such as PEG poly(lactic-co-glycolic acid) (PLGA) polyethylenimine (PEI) andhydroxyl propyl methacrylamide copolymer (HPMA) havecharacteristics that are more well-defined and can be finetuned to perform in a predictable manner As shown earlierchemical conjugation with PEG or PEGylation is one of themost acknowledged methods for prolonging the duration ofdrugs in the bloodstream and has also been demonstratedto contain certain targeting properties as well49 PEGyla-tion lowers plasma clearance rate by reducing receptor-mediated uptake during systemic circulation as well asmetabolic degradation by disguising the surface of theprotein49 It also reduces immunogenicity improves thesafety profile of the protein and protects the immunogenicepitopes Liu et al developed a novel nanocrystal formu-lation of Pluronic F127 for 2 anti-cancer drugs paclitaxel(PTX) and camptothecin50 Intravenously injected nano-crystals significantly inhibited tumor growth Considerabletherapeutic effects were shown via oral administration aswell In addition the targeted delivery of PTX via conju-gating a folate ligand to F127 was demonstrated50

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52 Micelles

Amphipilic nanoparticles composed of block or graft co-polymers such as N -vinylpyrrolidone and poloxamers canform polymeric micelles A hydrophobic core containshydrophobic drugs and the hydrophilic shell stabilizesthe core and makes the drug water-soluble4751 Poly-meric micelles have been shown to accumulate more read-ily in tumors than the larger liposomes mainly due totheir size51 The first polymeric micelle formulation ofPTX Genexol-PM a cremophor-free polymeric micellehas completed phase II clinical trials in the US withconsiderable anti-tumor activity in combination with cis-platin chemotherapy Cremophor EL is an excipient withcertain drugs and has been suggested to be a dose lim-iting factor in the administration of PTX52 This micel-lar nanoparticulate system allowed for higher doses of thedrug while being able to deliver and concentrate inside thetumor interstitium Another biodegradable formulation ofcationic micelles were prepared with PDMAEMA-PCL-PDMAEMA tri-block co-polymers and applied for thedual delivery of siRNA and PTX into cancer cells Combi-natorial delivery of anti-VEGF siRNA and PTX knockeddown VEGF expression53

53 Liposomes and Solid Lipid Nanoparticles

Natural liposomes a closed colloidal structure composedof a lipid bi-layer and an aqueous core are composed oflecithin phospholipids and can also be multi-laminar ratherthan uni-laminar carrying a larger payload of water- andfat-soluble constituents up to 500 nm in size5455 Lipo-somes take advantage of the overexpression of perforationsin cancer neovasculature in order to increase drug concen-trations passively at tumor sites Liposomal drug deliveryhas been the most successful nanoparticulate formulationused in the clinic as shown by liposomal-encapsulateddoxorubicin for Kaposirsquos sarcoma and more recentlybreast and ovarian cancer56 Small dimensions (lt300 nm)enables the drug to accumulate in the tumor mass by cross-ing passively into the tumor vasculature while avoiding orreducing the permeation of normal tissue55 On the otherhand solid lipid nanoparticles (SLNs) are solid lipids athuman physiological temperature with a diameter from50 to 1000 nm They are formed from a range of lipidsincluding mono- di- and tri-glycerides waxes fatty acidsand combinations of those SLNs are biodegradable bio-compatible with several human applications57 They form astrong lipophilic matrix in which water-insoluble lipophilicdrugs can be loaded for subsequent release The chemi-cal and physical properties of lipids in a heterogeneousmixture promote an imperfect crystalline structure withlarger gaps for efficient drug loading57 Use of SLNs havebeen investigated for the delivery of various anti-cancerdrugs with promising results in pre-clinical mouse trialsspecifically showing that SLNs might help overcome MDR

in cancers Serpe et al using human colon cancer cellsHT-29 demonstrated the benefits of SLNs in the deliveryof cholesteryl butyrate (chol-but) with doxorubicin Cyto-toxicity was shown to be higher in chol-but SLN loadedwith doxorubicin than free doxorubicin alone howeverPTX-loaded SLN did not show any improvement over freePTX5859 Lu et al loaded mitoxantrone a topoisomeraseinhibitor that blocks DNA replication into SLNs for alocal injection in the treatment of breast cancer and lymphnode metastases in mice60 Almost three-fold reduction inlymph node size was reported when compared to freely-administered mitoxantrone This was considered a signifi-cant improvement over existing treatment by the authors60

54 Dendrimers

Dendrimers may serve as a versatile nanoscale platformfor creating a multi-functional system capable of detect-ing cancer and delivering drugs A synthetic polymericmacromolecule of nanometer dimensions a dendrimer iscomposed of multiple highly branched monomers thatemerge radially from a central core The readily modifiablesurface characteristic enables them to be simultaneouslyconjugated with several molecules such as imaging con-trast agents targeting ligands andor therapeutic drugs61

Many commercial small molecule drugs with anti-canceractivity have been successfully conjugated with den-drimers such as polyamidoamine poly(propylene imine)and poly(etherhydroxylamine) dendrimers by means ofeither steric interactions or chemical reactions6263 Tar-geted delivery is possible via targeting moieties conju-gated to dendrimer surface or passive delivery due to theEPR effect Cationic dendrimers show cytotoxicity how-ever derivatization with fatty acid or PEG chains canreduce the overall charge density and minimize contactbetween cell surface thus reducing toxic effects6162 Patriet al demonstrated that covalently coupled methotrexate-dendrimer conjugates targeting high-affinity receptor forfolic acid have a similar activity to the free drug invitro while specifically killing receptor-expressing cells viareceptor-mediated endocytosis64

55 Carbon Nanotubes and Nanodiamonds

Carbon nanotubes are generally insoluble causing them tobe non-biocompatible however the introduction of chem-ical modification to carbon nanotubes render them water-soluble and functionalized so that they can be linked to awide variety of active molecules such as peptides proteinsnucleic acids and therapeutic agents Functionalized car-bon nanotubes also have an intrinsic capability to perme-ate cell membranes which allows endocytosis-independentinternalization of nanoparticles265 Methotrexate cova-lently linked to carbon nanotubes with a fluorescent agentwas shown to be more effectively internalized into cells

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when compared to the free unbound drug65 The multi-ple covalent functionalizations on the sidewall or tips ofcarbon nanotubes allow them to carry several moleculesat once This strategy provides a fundamental advantagein the treatment of cancer Targeted heat therapy or lsquother-mal ablationrsquo is being tested to destroy breast cancertumors using carbon nanotubes Accordingly the HER2IgY-single wall carbon nanotube (SWNT) complex specif-ically targeted HER2-expressing SK-BR-3 cells but notreceptor-negative MCF-7 cells Near-infrared irradiationwith an 808 nm laser showed extensive cell death withSWNT66 On the other hand a nanodiamond-embeddeddevice is being developed to deliver chemotherapy locallyto sites where cancerous tumors have been surgicallyremoved67 Nanodiamonds complexed with doxorubicin-hydrochloride enable a sustained release of drug for aminimum of 30 days with a significant amount of drugin reserve This shows potential for highly localized drugrelease as a complementary yet potent form of treat-ment with systemic injection Ho and group embeddedmillions of tiny drug carrying nanodiamonds into theFDA-approved parylene67ndash69 Currently used as a coatingfor implants biostable parylene is a flexible and versa-tile polymeric material Nanodiamonds placed betweenextremely thin parylene films resulted in a device that isminimally-invasive Internalization assays revealed a pri-marily endocytic uptake process High degree of nanodia-mond (sim46 nm in diameter) and endosome co-localizationas well as cytoplasmic presence of smaller nanodiamondswere observed69

56 Silicon Nanoparticles

Silicon and silica are establishing themselves as inter-esting candidate materials for injectable nanoparticles indrug delivery70 Porosified silicon is biodegradable71 withkinetics that are much more rapid than those of typicalbiodegradable polymers and as a result releases drugswith previously un-attainable time profiles Lu et al loadedhydrophobic anti-cancer drug camptothecin (CPT) ontomesoporous silica nanoparticles CPT release was mini-mal and sustained in aqueous solution This effectivelyaddressed the problem of poor water-solubility of certainanti-cancer drugs as well as sustainable release profiles71

Furthermore there are metal-based nanovectors such asnanoshells70 comprised of a gold layer over a silica coreThe thickness of the gold layer can be precisely tuned sothat the nanoshell can be selectively activated through tis-sue irradiation with near-infrared light to perform localizedtherapeutic thermal ablation This approach was recentlyused to eradicate transmissible venereal tumors in mice72

In another study nitric oxide (NO)-releasing silica nanopar-ticles exhibited enhanced growth inhibition of ovariantumor cells and showed greater inhibition of the anchorage-independent growth of tumor-derived and Ras-transformed

ovarian cels73 NO a free radical bio-regulator endoge-nously synthesized in the body impacts multiple stages oftumor development spanning cytostatic processes cellulartransformation and formation of neoplastic lesions7374 Itis worth mentioning herein that research efforts have beenimpeded by the fact that possible normal cell toxicity ofthe NO donor drug by-product and the inability to targetdelivery of the drug selectively to cancer cells

57 Gold and Magnetic Nanoparticles

Gold (Au) nanoparticles are very versatile and can beprepared with different geometries such as nanospheresnanoshells nanorods or nanocages75 Further they haveunrivaled physical and chemical properties such asexceedingly small size (less than 50 nm) large sur-face area to mass proportion heightened surface sensitiv-ity presence of characteristic surface plasmon resonancebands biocompatibility and ease of surface functionaliza-tion Au nanoparticles are also excellent conductors ofelectrical and thermal energy which allows possibilitiesfor thermal ablation treatment In photodynamic therapy(PDT) Au nanoparticles are becoming known as a photo-sensitizer with great potential due to its optimal absorptionand light scattering properties along with controllable opti-cal characteristics El-Sayed and collegues have shown thatanti-EGFR antibody conjugated gold nanoparticles selec-tively localized in malignant HOC and HSC cells andunderwent significant photothermal destruction upon nearinfrared irradiation76 However using radiofrequency irra-diation Gannon et al demonstrated that the internalizationof Au nanoparticles in gastrointestinal cancer cells releasedsubstantial heat rapidly after exposure to an external high-voltage focused radiofrequency field (RF) It is noteworthythat radiofrequency ablation has an advantage over nearinfrared ablation which is limited to superficial tumorswith minimal tissue penetration Hep3B and Panc-1 cellstreated with 67 ML Au nanoparticles had significantlyhigher rates of cell death than the control samples at alltime-points after RF exposure77 Interestingly Au nanopar-ticles about 5ndash10 nm in diameter have been shown to haveintrinsic anti-angiogenic properties78 These nanoparticlesbind to heparin-binding pro-angiogenic growth factorssuch as VEGF165 and bFGF to inhibit their activity TheAu nanoparticles themselves also reduced ascites accumu-lation in a pre-clinical model of ovarian cancer inhibitedproliferation of multiple myeloma cells and induced apop-tosis in chronic B cell leukemia78 On the other hand mag-netic nanoparticles (MNPs) have traditionally been usedfor disease imaging via magnetic resonance (MR) imagingdue to their intrinsic properties Recent advances have alsoopened the door to cellular-specific targeting drug deliv-ery and multi-modal imaging Further MNPs can be func-tionalized through coating with polymers preferentiallywith biocompatible or biodegradable polymers of synthetic

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or biological origin7980 As solid tumor develops it out-grows its blood supply which results in the formation ofa hypoxic semi-necrotic tumor core and dormant tumorcells send out chemical signals that recruit macrophagesinto the core Macrophages begin to rebuild the bloodsupply allowing the tumor to start growing again8182

Muthana et al loaded human monocytes with MNPs plac-ing magnets near the site of a human prostate tumor grownin mice82 The MNP-loaded monocytes carrying a reportergene invaded the tumor at a rate more than three timesthat of the non-loaded cells82 This demonstration of mag-netic targeting shows that MNP-loaded cells circulatingin the body can be attracted to the tumor site where anexternal magnet is placed allowing a higher proportion ofloaded cells to respond to chemical signals from the tumorcore In addition the loaded monocytes were able to reachthe poorly vascularized peri-necrotic regions of the tumorthat are normally difficult to target As the moncytes areloaded with MNPs they can then be destroyed by hyper-thermia after delivering a therapeutic drug or gene8182

Classes of MNPs include metallic bimetallic and super-paramagnetic iron oxide nanoparticles widely-knows asSPIONs SPIONS are favored because due to low toxicityprofile and their reactive surface that can be readily modi-fied with biocompatible coatings87 This flexibility has ledto SPION use in magnetic separation biosensor in vivomedical imaging drug delivery tissue repair and hyper-thermia applications84 Yu et al preciously showed thatthermally crosslinked SPIONs loaded with doxorubicinhad potential as both an imaging and therapeutic deliverysystem83 This DoxTCL-SPION was also demonstratedto efficiently reach tumor sites and release the drug withoutany active targeting from ligandsantibodies or magneticfield largely due to the EPR effect83

58 Viral Nanoparticles

A variety of viruses including cowpea mosaic viruscanine parvovirus adenovirus coxsackie virus measlesvirus along with virions and virus-like particles have beendeployed for biomedical and nanotechnology applicationsthat include tissue targeting and drug delivery84 Target-ing molecules and peptides can be produced in a bio-logically functional form on the capsid surface throughchemical conjugation or gene expression Several lig-ands including transferrin folic acid and single-chainantibodies have been conjugated to viruses for specifictumor targeting84 Further a subset of viruses such ascanine parvovirus have a natural affinity for receptors liketransferrins that are up-regulated in a variety of tumorcells85 Adenoviral vectors offer many advantages for can-cer gene therapy including high transduction efficiencyyet safety concerns related to immunogenic response haveled to a cautious approach of their use in human clini-cal trials86 To overcome these obstacles hybrid vectors

combining both viral and non-viral elements are beingdeveloped Adenovirus coated with an arginine-graftedbioreducible polymer (ABP) via electrostatic interaction isone example ABP-coated complexes were shown to havesignificantly reduced the innate immune response whileproducing higher levels of transgene expression8687 Fur-thermore herpes simplex virus (HSV) vectors are alreadyin early phase human clinical trials for recurrent malignantglioblastoma A mutant form (vIII) of epidermal growthfactor receptor (EGFR) present in glioma tumor is rec-ognized by a single-chain antibody designated MR1-1HSV virions bearing MR1-1-modified gC had five-foldincreased infectivity for EGFRvIII-bearing human gliomaU87 cells showing enhanced vector specificity and tumorcell damage88

59 RNA Interference

Since its discovery nearly two decades ago RNA inter-ference (RNAi) has been lauded as the next generation ingene therapy due to the unique pathway in which smallinterfering (siRNA) or microRNA (miRNA) can preventmRNA expression and silence- specific targeted geneseffectively89 RNAi cancer gene targets are pathways thatcontribute to tumor growth through increased tumor cellproliferation andor reduced tumor cell death RNAi canalso be used to target and silence gene products thatnegatively regulate the function of endogenous tumor sup-pressor genes as well as proteins involved in cellular senes-cence or protein stabilitydegradation However in vivostudies up until now have shown wide variation on thepotency of RNAi and its suppression activities as a resultof poor cellular uptake rapid renal clearance and nucle-ase degradation90 Also previous experiments have beenplagued with additional problems such as off-targeting andimmunogenic response9091 Nonetheless the characteri-zation of novel nanoparticle carriers and chemical mod-ifications to siRNA itself has addressed some of theseissues Suh and collegues developed a cationic lipid N N primeprime-dioleylglutamide linked by negatively charged glutamicacid to oleoylamine as a siRNA carrier92 It was ableto deliver siRNA to various cancer cells in vitro moreeffectively than other cationic liposomes and with reducedcytotoxicity Moreover results showed that it was effectivefor local in vivo siRNA delivery providing clear evidencethat target protein expression was knocked down in tumortissues92 In addition Chen et al developed a liposome-polycation-hyaluronic acid (LPH) nanoparticle formulationmodified with single-chain antibody fragment (GC4 scFv)for the systemic delivery of siRNA and miRNA in experi-mental lung metastasis of murine B16F10 melanoma Inhi-bition of c-Myc MDM2 and VEGF protein expression bysiRNA formulated with GC4 scFv modified LPH nanopar-ticles significantly suppressed B16F10 metastatic tumorgrowth while showing increased siRNA uptake within thelung tumors93

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510 Monoclonal Antibodies

Monoclonal antibodies (mAB) are monospecific antibod-ies that bind only to one particular antigenic determinantor epitope By blocking ligand binding andor signalingof growth receptors mABs have the capability to sen-sitize tumors to chemotherapeutic agents reduce growthrates and induce apoptosis Many different monoclonalantibodies are currently used in the therapy of cer-tain cancers such as Bevacizumab Imatinib BortezomibGefitinib Sorafenib Tositumomab Tamoxifen and Ritux-imab which are all FDA-approved therapies for cancer todate94 In some in vivo applications the antibody itself issufficient and once bound to its target mAB triggers theeffector cell mechanisms of the immune system An excel-lent 2010 review by Weiner et al addresses the specificimmunologic pathways in which mABs interact with can-cer cells94 mAB may also be coupled to another moleculesuch as a fluorescent molecule to aid in imaging or aradioactive isotope such as Iodine-125 to aid in killing can-cer cells with radioimmunotherapy95 However in a recentstudy of radioimmunotherapy it was concluded that a sin-gle -emitter 90Y coupled to each antibody had a signifi-cantly lower biological effective dose and was insufficientto treat non small-cell lung cancer than a single 5 nm90Y2O3 nanoparticle96 In the application of nanoparticlesmAB can be used as efficient targeting ligands Workby Park and associates shows the targeting specificityof a modified lymphocyte function-associated antigen-1domain tuned to have variable affinities for intercellularadhesion molecule (ICAM)-1 Applying this antibody totheir nanoparticle system amphiphilic urethane acrylatenonionomer (UAN) researchers were able to demonstrateefficient encapsulation of a FITC marker and a protea-some inhibitor (celastrol) as well as the targeted deliveryto HeLa cells producing a more potent cytotoxicity withequal amounts of drug than with the untargeted UAN97

511 Aptamers

Aptamers are synthetic oligonucleotide ligands or peptidesthat bear unique three-dimensional conformations capa-ble of binding to target antigens with high affinity andspecificity Aptamers bind to their targets to effectivelyillicit little or none immunogenicity and possess molecu-lar recognition properties similar to monoclonal antibod-ies They have been applied to drug delivery systems asligands to enhance selectivity98 RNA aptamer OPN-R3has been shown in an in vivo xenograft model of breastcancer with MDA-MB-231 cells to significantly decreaselocal progression and distant metastases By day 20 tumorvolume in the modified OPN-R3 treated group was 18ndash20-fold smaller than the tumor volume in mutant OPN-R3and no treatment groups99 Another aptamer SM20 iso-lated against plasminogen activator inhibitor-1 has demon-strated in vitro therapeutic potential as an antimetastatic

agent and could possibly be used as an adjuvant to tradi-tional chemotherapy for breast cancer100 Several aptamershave been recently isolated for potential treatment of othercancers such as glioblastoma T cell leukaemia and epithe-lial cancer cells in the breast colon lung ovaries andpancreas98 Finally apatmers can be used as a targetingmoiety to be conjugated to a certain drug delivery for-mulation or may act as modalities with characteristics ofintrinsic specificity100

6 CURRENT CLINICAL PROGRESS OFNANONCOLOGY THERAPEUTICS

In this section nanoparticles for cancer therapy that havealready reached the clinic are discussed A few sys-tems having been approved and many are still ongoingin human clinical trials (Table I) As described earliernon-targeting nanoparticles utilize leaky vasculature oftumors to reach via passive targeting PEGylation has beenapplied to various proteins enzymes cytokines and mon-oclonal antibody fragments to increase circulatory half-life and decrease antigenicity3349101102 Many clinicaltrials involving PEGylation of nanoparticles are in differ-ent phase trials at the moment such as PEG-InterferonAlfa-2b PEGylated recombinant human Hyaluronidase(PEGPH20) PEG conjugate of SN38 (EZN-2208) toname a few An interesting PEgylated complex is PEG-ADI 20 currently undergoing Phase II studies Argininedeiminase (ADI) is a microbial enzyme that degrades argi-nine Certain cancer cells deficient in producing argininethrough argininosuccinate synthase obtain exogenous argi-nine from circulation PEG-ADI 20 depletes arginine con-centrations in the blood thereby controlling and reducingtumor growth103 The previous phase III study was com-pleted on un-resectable hepatocellular carcinoma knownfor its poor prognosis In a study with 35 patients allpatients exhibited blood arginine levels lower than 2 uMwhile 2 patients became stable 1 patient became resectableand 28 progressed with a mean duration before progres-sion of 34 months103 On the other hand CRLX101 isa nanoparticle drug delivery system comprised of thechemotherapeutic camptothecin (CPT) conjugated to acyclodextrin-based polymer CRLX101 was designed toincrease the exposure of tumor cells to CPT while reducingside effects Anti-cancer activity of camptothecin is due inpart to the inhibition of DNA topoisomerase I but has beenprevented from use as an anti-cancer drug due to poor sol-ubility lack of activity and excessive toxicity104 HoweverCRLX101 nanoparticle was shown to have significantlyhigher antitumor activity with lower dosing while main-taining the levels of free camptothecin in the blood to aminimum It is noteworthy that it was effective in a num-ber of tumors resistant to irinotecan treatment CRLX101is currently undergoing Phase IB2A trials104 Ultimatelyactive targeting through the inclusion of a targeting lig-and on the nanoparticles is envisioned to provide the

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Table I Nanoncology in clinical development

Class Carrier Active agent Target Clinical status Indication (s) Ref

LiposomesDaunoXome Liposome Daunorubicin

citrateNA Approved Chronic myelogenous

leukemia neuroblastoma3

DOTAP Chol-FUS1 Liposome Plasmid DNA(FUS1)

NA Phase I Metastatic non-small celllung cancer

114

SGT-53 Liposome Plasmid DNAp53 W-T

Transferrinreceptor

Phase I Advanced Solid Tumors 115

MBP 426 Liposome Oxaliplatin Transferrinreceptor

Phase lbII Advanced or MetastaticSolid Tumors

105

PEGylatedDoxil PEGylaled-Liposome Doxorubicin NA Approved Ovanan cancer recurrent

breast cancer2 56

Oncospar PEGylaled-Asparagnase

L-asparagnase NA Approved Acute lymphoblasticleukemia

2

CYT-6091 PEGylaled-ThiolGold

RecombinantTNF-

Tumor necrosisfactor recepteor

Phase II Advanced solid tumors 110

ADI-PEG 20 PEGylated-ArginineDeiminase

Augininedeiminase

NA Phase II Hepatocellular carcinomaMetastatic melanomarelapsed small cell lungcancer

103

PeptideAbraxane Albumin Paclitaxel NA Approved Metastatic non-small cell

lung cancer2 3

Ontak Interkeukin-2engineered protein

Diphtheria toxin Interleukin-2receptors

Approved Cutaneous T-cell lymphoma 3

AMG 386 Peptibody Recombinantpeptide-Fcfusion protein

Angiopoietin 1and 2

Phase III Various cancers 113

PolymericCALAA-01 Cyclodextrin Small interfering

RNATransferrin

receptorPhase I Solid tumors 107 108

XMT-1001 Fleximer Camptothecin Prodrug activation Phase I Advanced solid tumors 111Genexol Polymeric micelles Paclitaxel NA Phase II Various cancers 52CT-2103 Poly-L-glutmate Paclitaxel NA Phase II Various cancers 112

Antibodya

Trastuzumab HumanizedMonoclonalantibody

Antibody CD340 receptor Approved HER2-positive metastaticbreast cancer

3 4 94

Rituximab Chimeric monoclonalAntibody

Antibody Protein CD20 Approved Leukemias and lymphomas 3 4 94

a Currently there are over 20 FDA-approved monoclonal antibodies for use in cancer therapy

most effective therapy A targeting nanoparticle in Pha-seIBII study is MbP-426 which contains the cytotoxicplatinum-based drug oxaliplatin in a transferrin-conjugatedlipopsome105 Transferrin receptors (TfR) overexpressedon tumor cells allow selective uptake via Tf-TfR interac-tion Outcome of Phase I trial with 39 patients showed that15 patients had stable disease after 2 cycles 3 patients withcolon carcinoma refractory to conventional oxaliplatin hadstable disease for 4-6 cycles and 2 patients had 12 and26 decrease in target lesions105 Further Rexin-G is amurine leukemia virus-based retrovector nanoparticle thatcontains a cytocidal dominant negative cyclin-G1 constructand allows for the functional restoration of tumor sup-pressor microRNA-122a It has been found that block-ade of cyclin G1 may restore intrinsic molecular form

of tumor suppression106 Rexin-G has been found to havelow immunogenicity with preferential selection of rapidly-dividing cells over normal non-dividing or differentiatedcells In Phase II clinical trials 88 of patients had partialresponses or stable disease while the overall survival ratewas 6 months for all 22 patients106 On a further note sometargeted nanoparticles can have active mechanisms for theintracellular release of the therapeutic moiety CALAA-01is a targeted nanoparticle that has a high drug (siRNA)payload per targeting ligand tested and proven multiva-lent binding to cancer cell surfaces and an active siRNArelease mechanism that is triggered upon the recogni-tion of intracellular localization by a pH decline belowa value of 60107108 This nanoparticle system containsa cyclodextrin-based polymer human transferring protein

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targeting ligand hydrophilic polymer (PEG) and siRNAdesigned to reduce expression of RRM2 It is currentlyundergoing Phase I clinical trials for a dose-escalatingstudy in the treatment of solid tumor cancer107 An aptamerfor potential cancer treatment is AS1411109 It binds nucle-olin on the surface of cancer cells and induces apoptosisIn a dose escalation (1 mgkgday to 10 mgkgday) clin-ical study AS1411 showed positive responses in patientswith advanced solid tumors without any adverse effects109

Recently in a randomized phase II clinical trials a10 mgkgday or 40 mgkgday dose of AS1411 com-bined with high-dose cytarabine was well tolerated andshowed promising signs of activity in patients with pri-mary refractory or relapsed acute myeloid leukaemia Itis also currently being evaluated for treatment of breastcancer110 In another example Aurimune is a colloidalAu nanoparticle which delivers recombinant TNF- tocancer tumors TNF is attached to the Au nanoparticle withthiol-derivatized PEG which allows the nanoparticle toflow through the blood stream without causing a clearanceresponse110 Clinical data to date reports that Aurimunehas no antibody or immune responses and is well-toleratedbeyond the known maximum dose for TNF-110

7 CLOSING REMARKS FUTUREPERSPECTIVE

Over the past decades nanoncology (therapeutics anddiagnostics) has evolved from nano-sized drug particlesto bio-functional nanomaterials capable of deliveringheat treatment ionizing radiation andor chemothera-peutic agents From simple liposomal formulations andconjugation of PEG to antibody-conjugated nanoparti-cle chemotherapeutic and RNAi delivery nanoncology isbecoming more intricate smart and multi-functional Fur-ther the differences between cancerous and normal cellsincluding uncontrolled proliferation insensitivity to nega-tive growth regulation and anti-growth signals angiogen-esis and metastasis can be now be effectively exploitedThere is no doubt that nanoparticle therapeutics with theincreasing multi-functionality will continue to expand inthe future Investments in research development and per-formance trials are considerably large Sponsoring agen-cies in both private and government sectors should createeconomic strategies and innovative management to makesuch biotechnologies more cost-effective and easily acces-sible for patients across Although many challenges existfor the transition of nanoparticles from bench to bed theirpotential advantages will drive successful development andemerge as a new class of undeniable anti-cancer thera-peutic Finally (i) individualizedpersonalized oncology inwhich cancer detection diagnosis and therapy can be mod-ified to best fit the tumor molecular profile of a patientand (ii) predictive oncology in which genetic biochemicaland molecular markers are orchestrated to predict disease

development progression and clinical outcomes will cer-tainly shape the nanoncologic strategies of the near future

Acknowledgments This work was supported by theSouth Korean Ministry of Knowledge and Education(MKE) and the Incheon Free Economic Zone (IFEZ) inthe framework of several funding operating grants to theUtah-Inha DDS amp Advanced Therapeutics Research Cen-ter KR

References and Notes

1 N Portney and M Ozkan Anal Bioanal Chem 3 620 (2006)2 M Ferrari Nat Rev Cancer 3 161 (2005)3 T M Allen Nat Rev Cancer 1 0750 (2002)4 J S Ross D P Schenkein and R Pietrusko Am J Clin Pathol

4 598 (2004)5 M Wang and M Thanou Drug Resist Updat 2 90 (2010)6 A Jones and A L Harris Cancer J Sci Am 4 209 (1998)7 D F Baban and L W Seymour Adv Drug Deliv 1 109 (1998)8 H Maeda Adv Enzyme Regul 41 189 (2001)9 K Greish Methods Mol Biol 624 25 (2010)10 A K Iyer K Greish T Seki S Okazaki J Fang K Takeshita

and H Maeda Drug Discov Today 11 812 (2006)11 K N Sugahara T Teesalu P P Karmali V R Kotamraju

L Agemy D R Greenwald and E Ruoslahti Science 5981 1031(2010)

12 R G Boyle and S Travess Anticancer Agents Med Chem 64 281(2006)

13 J M Brown and W R Wilson Nat Rev Cancer 4 437 (2004)14 D Kim E S Lee K Park I C Kwon and Y H Bae Pharm

Res 9 2074 (2008)15 L M Bareford and P W Swaan Adv Drug Deliv Rev 8 748

(2007)16 N F Saba X Wang S Muumlller M Tighiouart K Cho S Nie

Z Chen and D M Shin Head Neck 4 475 (2009)17 Y Lu L C Xu N Parker E Westrick J A Reddy M Vetzel

P S Low and C P Leamon Mol Cancer Ther 12 3258 (2006)18 E I Deryugina and J P Quigley Cancer Metastasis Rev 25 9

(2006)19 A M Mansour J Drevs N Esser F M Hamada O A Badary

C Unger I Fichtner and F Kratz Cancer Res 14 4062 (2003)20 H Hatakeyama H Akita E Ishida K Hashimoto H Kobayashi

T Aoki J Yasuda K Obata H Kikuchi T Ishida H Kiwadaand H Harashima Int J Pharm 1ndash2 194 (2007)

21 A Raz L Meromsky and R Lotan Cancer Res 7 3667 (1986)22 E Gorelik U Galili and A Raz Cancer Metastasis Rev 3ndash4 245

(2001)23 C Bies C M Lehr and J F Woodley Adv Drug Deliv Rev

4 425 (2004)24 H Glavinas P Krajcsi J Cserepes and B Sarkadi Curr Drug

Deliv 1 27 (2004)25 M Dean T Fojo and S Bates Nat Rev Cancer 4 275 (2005)26 T Kobayashi T Ishida Y Okada S Ise H Harashima and

H Kiwada Int J Pharm 1ndash2 94 (2007)27 A M Chen M Zhang D Wei D Stueber O Taratula T Minko

and H He Small 23 2673 (2009)28 J M Koziara P R Lockman D D Allen and R J Mumper

Pharm Res 11 1772 (2003)29 S C Steiniger J Kreuter A S Khalansky I N Skidan A I

Bobruskin Z S Smirnova S E Severin R Uhl M Kock K DGeiger and S E Gelperina Int J Cancer 5 759 (2004)

30 J Wu T Akaike and H Maeda Cancer Res 1 159 (1998)31 M A Deli Biochim Biophys Acta 4 892 (2009)

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Neuro2A cells (which have upregulated transferring recep-tors) compared to 64 nM for transferrin alone43 More-over molecules without sufficient binding affinity for useas a drug or individual targeting ligand can be encapsulatedwithin nanoparticles Also many drug candidates that wereineffective due to low binding of the target can be used onthe surface of nanoparticles as targeting agents A target-ing ligand increases the extent of cellular internalizationby particles that reach tumor tissue in a ligand density-dependent manner Inability of a targeting ligand to sig-nificantly increase tumor deposition is consistent with theroles of molecular size and affinity on tumor uptake44

It has been reported that intermediate-sized ligands witha molecular weight of about 25 kDa achieve the low-est tumor uptake levels while both smaller ligands (thatrequire high receptor affinity to be retained) and largerligands (that can achieve similar retention as smaller lig-ands withgt 100-fold weaker binding) showed an enhancedtumor uptake42ndash44

5 NANOBIOTECHNOLOGY THERAPEUTICDELIVERY PLATFORMS IN CANCER

A few nanoncologic systems have reached the pre-clinicaland clinical trial stage Below is a comprehensive yet pro-visional set of potential drug delivery systems examples(Fig 1) and their components being investigated in vitroand in vivo currently Other nanoparticles such as quantumdots nanowires and nanosensors are not discussed as theymainly deal with detection and imaging Yet few excitingmultifunctional systems such as iron oxide nanoparticlesare touched upon to further stress their future potential

51 Polymeric Nanoparticles

Polymers such as chitosan cyclodextrins alginate andhyaluronic acid occur naturally and have been the mate-rial of choice for the delivery of proteins DNA RNA

Fig 1 Nanoncology carrier applications in cancer therapeutics

as well as drugs Natural polymers have the advantageof being biodegradable and biocompatible more so thantheir synthetic counterparts45ndash47 Gupta and colleaguesexperimented with biologically-derived silk fibroin (SF)and chitosan (CH) blended non-covalently to encapsulatecurcumin48 Curcumin can interfere with the activity oftranscription factor NF-B and induce apoptosis in cancercells while avoiding healthy cells SF was shown to havebetter encapsulation properties and efficacy than liposomesSF-curcumin nanoparticles showed higher efficacy againstbreast cancer cells48 This demonstrates the potential totreat in vivo breast tumors by a possible sustained long-term biodegradable and therapeutic delivery system Onthe other hand synthetic polymers are not easily removedby normal clearance systems and can accumulate in tissuesHowever synthetic polymers such as PEG poly(lactic-co-glycolic acid) (PLGA) polyethylenimine (PEI) andhydroxyl propyl methacrylamide copolymer (HPMA) havecharacteristics that are more well-defined and can be finetuned to perform in a predictable manner As shown earlierchemical conjugation with PEG or PEGylation is one of themost acknowledged methods for prolonging the duration ofdrugs in the bloodstream and has also been demonstratedto contain certain targeting properties as well49 PEGyla-tion lowers plasma clearance rate by reducing receptor-mediated uptake during systemic circulation as well asmetabolic degradation by disguising the surface of theprotein49 It also reduces immunogenicity improves thesafety profile of the protein and protects the immunogenicepitopes Liu et al developed a novel nanocrystal formu-lation of Pluronic F127 for 2 anti-cancer drugs paclitaxel(PTX) and camptothecin50 Intravenously injected nano-crystals significantly inhibited tumor growth Considerabletherapeutic effects were shown via oral administration aswell In addition the targeted delivery of PTX via conju-gating a folate ligand to F127 was demonstrated50

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52 Micelles

Amphipilic nanoparticles composed of block or graft co-polymers such as N -vinylpyrrolidone and poloxamers canform polymeric micelles A hydrophobic core containshydrophobic drugs and the hydrophilic shell stabilizesthe core and makes the drug water-soluble4751 Poly-meric micelles have been shown to accumulate more read-ily in tumors than the larger liposomes mainly due totheir size51 The first polymeric micelle formulation ofPTX Genexol-PM a cremophor-free polymeric micellehas completed phase II clinical trials in the US withconsiderable anti-tumor activity in combination with cis-platin chemotherapy Cremophor EL is an excipient withcertain drugs and has been suggested to be a dose lim-iting factor in the administration of PTX52 This micel-lar nanoparticulate system allowed for higher doses of thedrug while being able to deliver and concentrate inside thetumor interstitium Another biodegradable formulation ofcationic micelles were prepared with PDMAEMA-PCL-PDMAEMA tri-block co-polymers and applied for thedual delivery of siRNA and PTX into cancer cells Combi-natorial delivery of anti-VEGF siRNA and PTX knockeddown VEGF expression53

53 Liposomes and Solid Lipid Nanoparticles

Natural liposomes a closed colloidal structure composedof a lipid bi-layer and an aqueous core are composed oflecithin phospholipids and can also be multi-laminar ratherthan uni-laminar carrying a larger payload of water- andfat-soluble constituents up to 500 nm in size5455 Lipo-somes take advantage of the overexpression of perforationsin cancer neovasculature in order to increase drug concen-trations passively at tumor sites Liposomal drug deliveryhas been the most successful nanoparticulate formulationused in the clinic as shown by liposomal-encapsulateddoxorubicin for Kaposirsquos sarcoma and more recentlybreast and ovarian cancer56 Small dimensions (lt300 nm)enables the drug to accumulate in the tumor mass by cross-ing passively into the tumor vasculature while avoiding orreducing the permeation of normal tissue55 On the otherhand solid lipid nanoparticles (SLNs) are solid lipids athuman physiological temperature with a diameter from50 to 1000 nm They are formed from a range of lipidsincluding mono- di- and tri-glycerides waxes fatty acidsand combinations of those SLNs are biodegradable bio-compatible with several human applications57 They form astrong lipophilic matrix in which water-insoluble lipophilicdrugs can be loaded for subsequent release The chemi-cal and physical properties of lipids in a heterogeneousmixture promote an imperfect crystalline structure withlarger gaps for efficient drug loading57 Use of SLNs havebeen investigated for the delivery of various anti-cancerdrugs with promising results in pre-clinical mouse trialsspecifically showing that SLNs might help overcome MDR

in cancers Serpe et al using human colon cancer cellsHT-29 demonstrated the benefits of SLNs in the deliveryof cholesteryl butyrate (chol-but) with doxorubicin Cyto-toxicity was shown to be higher in chol-but SLN loadedwith doxorubicin than free doxorubicin alone howeverPTX-loaded SLN did not show any improvement over freePTX5859 Lu et al loaded mitoxantrone a topoisomeraseinhibitor that blocks DNA replication into SLNs for alocal injection in the treatment of breast cancer and lymphnode metastases in mice60 Almost three-fold reduction inlymph node size was reported when compared to freely-administered mitoxantrone This was considered a signifi-cant improvement over existing treatment by the authors60

54 Dendrimers

Dendrimers may serve as a versatile nanoscale platformfor creating a multi-functional system capable of detect-ing cancer and delivering drugs A synthetic polymericmacromolecule of nanometer dimensions a dendrimer iscomposed of multiple highly branched monomers thatemerge radially from a central core The readily modifiablesurface characteristic enables them to be simultaneouslyconjugated with several molecules such as imaging con-trast agents targeting ligands andor therapeutic drugs61

Many commercial small molecule drugs with anti-canceractivity have been successfully conjugated with den-drimers such as polyamidoamine poly(propylene imine)and poly(etherhydroxylamine) dendrimers by means ofeither steric interactions or chemical reactions6263 Tar-geted delivery is possible via targeting moieties conju-gated to dendrimer surface or passive delivery due to theEPR effect Cationic dendrimers show cytotoxicity how-ever derivatization with fatty acid or PEG chains canreduce the overall charge density and minimize contactbetween cell surface thus reducing toxic effects6162 Patriet al demonstrated that covalently coupled methotrexate-dendrimer conjugates targeting high-affinity receptor forfolic acid have a similar activity to the free drug invitro while specifically killing receptor-expressing cells viareceptor-mediated endocytosis64

55 Carbon Nanotubes and Nanodiamonds

Carbon nanotubes are generally insoluble causing them tobe non-biocompatible however the introduction of chem-ical modification to carbon nanotubes render them water-soluble and functionalized so that they can be linked to awide variety of active molecules such as peptides proteinsnucleic acids and therapeutic agents Functionalized car-bon nanotubes also have an intrinsic capability to perme-ate cell membranes which allows endocytosis-independentinternalization of nanoparticles265 Methotrexate cova-lently linked to carbon nanotubes with a fluorescent agentwas shown to be more effectively internalized into cells

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when compared to the free unbound drug65 The multi-ple covalent functionalizations on the sidewall or tips ofcarbon nanotubes allow them to carry several moleculesat once This strategy provides a fundamental advantagein the treatment of cancer Targeted heat therapy or lsquother-mal ablationrsquo is being tested to destroy breast cancertumors using carbon nanotubes Accordingly the HER2IgY-single wall carbon nanotube (SWNT) complex specif-ically targeted HER2-expressing SK-BR-3 cells but notreceptor-negative MCF-7 cells Near-infrared irradiationwith an 808 nm laser showed extensive cell death withSWNT66 On the other hand a nanodiamond-embeddeddevice is being developed to deliver chemotherapy locallyto sites where cancerous tumors have been surgicallyremoved67 Nanodiamonds complexed with doxorubicin-hydrochloride enable a sustained release of drug for aminimum of 30 days with a significant amount of drugin reserve This shows potential for highly localized drugrelease as a complementary yet potent form of treat-ment with systemic injection Ho and group embeddedmillions of tiny drug carrying nanodiamonds into theFDA-approved parylene67ndash69 Currently used as a coatingfor implants biostable parylene is a flexible and versa-tile polymeric material Nanodiamonds placed betweenextremely thin parylene films resulted in a device that isminimally-invasive Internalization assays revealed a pri-marily endocytic uptake process High degree of nanodia-mond (sim46 nm in diameter) and endosome co-localizationas well as cytoplasmic presence of smaller nanodiamondswere observed69

56 Silicon Nanoparticles

Silicon and silica are establishing themselves as inter-esting candidate materials for injectable nanoparticles indrug delivery70 Porosified silicon is biodegradable71 withkinetics that are much more rapid than those of typicalbiodegradable polymers and as a result releases drugswith previously un-attainable time profiles Lu et al loadedhydrophobic anti-cancer drug camptothecin (CPT) ontomesoporous silica nanoparticles CPT release was mini-mal and sustained in aqueous solution This effectivelyaddressed the problem of poor water-solubility of certainanti-cancer drugs as well as sustainable release profiles71

Furthermore there are metal-based nanovectors such asnanoshells70 comprised of a gold layer over a silica coreThe thickness of the gold layer can be precisely tuned sothat the nanoshell can be selectively activated through tis-sue irradiation with near-infrared light to perform localizedtherapeutic thermal ablation This approach was recentlyused to eradicate transmissible venereal tumors in mice72

In another study nitric oxide (NO)-releasing silica nanopar-ticles exhibited enhanced growth inhibition of ovariantumor cells and showed greater inhibition of the anchorage-independent growth of tumor-derived and Ras-transformed

ovarian cels73 NO a free radical bio-regulator endoge-nously synthesized in the body impacts multiple stages oftumor development spanning cytostatic processes cellulartransformation and formation of neoplastic lesions7374 Itis worth mentioning herein that research efforts have beenimpeded by the fact that possible normal cell toxicity ofthe NO donor drug by-product and the inability to targetdelivery of the drug selectively to cancer cells

57 Gold and Magnetic Nanoparticles

Gold (Au) nanoparticles are very versatile and can beprepared with different geometries such as nanospheresnanoshells nanorods or nanocages75 Further they haveunrivaled physical and chemical properties such asexceedingly small size (less than 50 nm) large sur-face area to mass proportion heightened surface sensitiv-ity presence of characteristic surface plasmon resonancebands biocompatibility and ease of surface functionaliza-tion Au nanoparticles are also excellent conductors ofelectrical and thermal energy which allows possibilitiesfor thermal ablation treatment In photodynamic therapy(PDT) Au nanoparticles are becoming known as a photo-sensitizer with great potential due to its optimal absorptionand light scattering properties along with controllable opti-cal characteristics El-Sayed and collegues have shown thatanti-EGFR antibody conjugated gold nanoparticles selec-tively localized in malignant HOC and HSC cells andunderwent significant photothermal destruction upon nearinfrared irradiation76 However using radiofrequency irra-diation Gannon et al demonstrated that the internalizationof Au nanoparticles in gastrointestinal cancer cells releasedsubstantial heat rapidly after exposure to an external high-voltage focused radiofrequency field (RF) It is noteworthythat radiofrequency ablation has an advantage over nearinfrared ablation which is limited to superficial tumorswith minimal tissue penetration Hep3B and Panc-1 cellstreated with 67 ML Au nanoparticles had significantlyhigher rates of cell death than the control samples at alltime-points after RF exposure77 Interestingly Au nanopar-ticles about 5ndash10 nm in diameter have been shown to haveintrinsic anti-angiogenic properties78 These nanoparticlesbind to heparin-binding pro-angiogenic growth factorssuch as VEGF165 and bFGF to inhibit their activity TheAu nanoparticles themselves also reduced ascites accumu-lation in a pre-clinical model of ovarian cancer inhibitedproliferation of multiple myeloma cells and induced apop-tosis in chronic B cell leukemia78 On the other hand mag-netic nanoparticles (MNPs) have traditionally been usedfor disease imaging via magnetic resonance (MR) imagingdue to their intrinsic properties Recent advances have alsoopened the door to cellular-specific targeting drug deliv-ery and multi-modal imaging Further MNPs can be func-tionalized through coating with polymers preferentiallywith biocompatible or biodegradable polymers of synthetic

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or biological origin7980 As solid tumor develops it out-grows its blood supply which results in the formation ofa hypoxic semi-necrotic tumor core and dormant tumorcells send out chemical signals that recruit macrophagesinto the core Macrophages begin to rebuild the bloodsupply allowing the tumor to start growing again8182

Muthana et al loaded human monocytes with MNPs plac-ing magnets near the site of a human prostate tumor grownin mice82 The MNP-loaded monocytes carrying a reportergene invaded the tumor at a rate more than three timesthat of the non-loaded cells82 This demonstration of mag-netic targeting shows that MNP-loaded cells circulatingin the body can be attracted to the tumor site where anexternal magnet is placed allowing a higher proportion ofloaded cells to respond to chemical signals from the tumorcore In addition the loaded monocytes were able to reachthe poorly vascularized peri-necrotic regions of the tumorthat are normally difficult to target As the moncytes areloaded with MNPs they can then be destroyed by hyper-thermia after delivering a therapeutic drug or gene8182

Classes of MNPs include metallic bimetallic and super-paramagnetic iron oxide nanoparticles widely-knows asSPIONs SPIONS are favored because due to low toxicityprofile and their reactive surface that can be readily modi-fied with biocompatible coatings87 This flexibility has ledto SPION use in magnetic separation biosensor in vivomedical imaging drug delivery tissue repair and hyper-thermia applications84 Yu et al preciously showed thatthermally crosslinked SPIONs loaded with doxorubicinhad potential as both an imaging and therapeutic deliverysystem83 This DoxTCL-SPION was also demonstratedto efficiently reach tumor sites and release the drug withoutany active targeting from ligandsantibodies or magneticfield largely due to the EPR effect83

58 Viral Nanoparticles

A variety of viruses including cowpea mosaic viruscanine parvovirus adenovirus coxsackie virus measlesvirus along with virions and virus-like particles have beendeployed for biomedical and nanotechnology applicationsthat include tissue targeting and drug delivery84 Target-ing molecules and peptides can be produced in a bio-logically functional form on the capsid surface throughchemical conjugation or gene expression Several lig-ands including transferrin folic acid and single-chainantibodies have been conjugated to viruses for specifictumor targeting84 Further a subset of viruses such ascanine parvovirus have a natural affinity for receptors liketransferrins that are up-regulated in a variety of tumorcells85 Adenoviral vectors offer many advantages for can-cer gene therapy including high transduction efficiencyyet safety concerns related to immunogenic response haveled to a cautious approach of their use in human clini-cal trials86 To overcome these obstacles hybrid vectors

combining both viral and non-viral elements are beingdeveloped Adenovirus coated with an arginine-graftedbioreducible polymer (ABP) via electrostatic interaction isone example ABP-coated complexes were shown to havesignificantly reduced the innate immune response whileproducing higher levels of transgene expression8687 Fur-thermore herpes simplex virus (HSV) vectors are alreadyin early phase human clinical trials for recurrent malignantglioblastoma A mutant form (vIII) of epidermal growthfactor receptor (EGFR) present in glioma tumor is rec-ognized by a single-chain antibody designated MR1-1HSV virions bearing MR1-1-modified gC had five-foldincreased infectivity for EGFRvIII-bearing human gliomaU87 cells showing enhanced vector specificity and tumorcell damage88

59 RNA Interference

Since its discovery nearly two decades ago RNA inter-ference (RNAi) has been lauded as the next generation ingene therapy due to the unique pathway in which smallinterfering (siRNA) or microRNA (miRNA) can preventmRNA expression and silence- specific targeted geneseffectively89 RNAi cancer gene targets are pathways thatcontribute to tumor growth through increased tumor cellproliferation andor reduced tumor cell death RNAi canalso be used to target and silence gene products thatnegatively regulate the function of endogenous tumor sup-pressor genes as well as proteins involved in cellular senes-cence or protein stabilitydegradation However in vivostudies up until now have shown wide variation on thepotency of RNAi and its suppression activities as a resultof poor cellular uptake rapid renal clearance and nucle-ase degradation90 Also previous experiments have beenplagued with additional problems such as off-targeting andimmunogenic response9091 Nonetheless the characteri-zation of novel nanoparticle carriers and chemical mod-ifications to siRNA itself has addressed some of theseissues Suh and collegues developed a cationic lipid N N primeprime-dioleylglutamide linked by negatively charged glutamicacid to oleoylamine as a siRNA carrier92 It was ableto deliver siRNA to various cancer cells in vitro moreeffectively than other cationic liposomes and with reducedcytotoxicity Moreover results showed that it was effectivefor local in vivo siRNA delivery providing clear evidencethat target protein expression was knocked down in tumortissues92 In addition Chen et al developed a liposome-polycation-hyaluronic acid (LPH) nanoparticle formulationmodified with single-chain antibody fragment (GC4 scFv)for the systemic delivery of siRNA and miRNA in experi-mental lung metastasis of murine B16F10 melanoma Inhi-bition of c-Myc MDM2 and VEGF protein expression bysiRNA formulated with GC4 scFv modified LPH nanopar-ticles significantly suppressed B16F10 metastatic tumorgrowth while showing increased siRNA uptake within thelung tumors93

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510 Monoclonal Antibodies

Monoclonal antibodies (mAB) are monospecific antibod-ies that bind only to one particular antigenic determinantor epitope By blocking ligand binding andor signalingof growth receptors mABs have the capability to sen-sitize tumors to chemotherapeutic agents reduce growthrates and induce apoptosis Many different monoclonalantibodies are currently used in the therapy of cer-tain cancers such as Bevacizumab Imatinib BortezomibGefitinib Sorafenib Tositumomab Tamoxifen and Ritux-imab which are all FDA-approved therapies for cancer todate94 In some in vivo applications the antibody itself issufficient and once bound to its target mAB triggers theeffector cell mechanisms of the immune system An excel-lent 2010 review by Weiner et al addresses the specificimmunologic pathways in which mABs interact with can-cer cells94 mAB may also be coupled to another moleculesuch as a fluorescent molecule to aid in imaging or aradioactive isotope such as Iodine-125 to aid in killing can-cer cells with radioimmunotherapy95 However in a recentstudy of radioimmunotherapy it was concluded that a sin-gle -emitter 90Y coupled to each antibody had a signifi-cantly lower biological effective dose and was insufficientto treat non small-cell lung cancer than a single 5 nm90Y2O3 nanoparticle96 In the application of nanoparticlesmAB can be used as efficient targeting ligands Workby Park and associates shows the targeting specificityof a modified lymphocyte function-associated antigen-1domain tuned to have variable affinities for intercellularadhesion molecule (ICAM)-1 Applying this antibody totheir nanoparticle system amphiphilic urethane acrylatenonionomer (UAN) researchers were able to demonstrateefficient encapsulation of a FITC marker and a protea-some inhibitor (celastrol) as well as the targeted deliveryto HeLa cells producing a more potent cytotoxicity withequal amounts of drug than with the untargeted UAN97

511 Aptamers

Aptamers are synthetic oligonucleotide ligands or peptidesthat bear unique three-dimensional conformations capa-ble of binding to target antigens with high affinity andspecificity Aptamers bind to their targets to effectivelyillicit little or none immunogenicity and possess molecu-lar recognition properties similar to monoclonal antibod-ies They have been applied to drug delivery systems asligands to enhance selectivity98 RNA aptamer OPN-R3has been shown in an in vivo xenograft model of breastcancer with MDA-MB-231 cells to significantly decreaselocal progression and distant metastases By day 20 tumorvolume in the modified OPN-R3 treated group was 18ndash20-fold smaller than the tumor volume in mutant OPN-R3and no treatment groups99 Another aptamer SM20 iso-lated against plasminogen activator inhibitor-1 has demon-strated in vitro therapeutic potential as an antimetastatic

agent and could possibly be used as an adjuvant to tradi-tional chemotherapy for breast cancer100 Several aptamershave been recently isolated for potential treatment of othercancers such as glioblastoma T cell leukaemia and epithe-lial cancer cells in the breast colon lung ovaries andpancreas98 Finally apatmers can be used as a targetingmoiety to be conjugated to a certain drug delivery for-mulation or may act as modalities with characteristics ofintrinsic specificity100

6 CURRENT CLINICAL PROGRESS OFNANONCOLOGY THERAPEUTICS

In this section nanoparticles for cancer therapy that havealready reached the clinic are discussed A few sys-tems having been approved and many are still ongoingin human clinical trials (Table I) As described earliernon-targeting nanoparticles utilize leaky vasculature oftumors to reach via passive targeting PEGylation has beenapplied to various proteins enzymes cytokines and mon-oclonal antibody fragments to increase circulatory half-life and decrease antigenicity3349101102 Many clinicaltrials involving PEGylation of nanoparticles are in differ-ent phase trials at the moment such as PEG-InterferonAlfa-2b PEGylated recombinant human Hyaluronidase(PEGPH20) PEG conjugate of SN38 (EZN-2208) toname a few An interesting PEgylated complex is PEG-ADI 20 currently undergoing Phase II studies Argininedeiminase (ADI) is a microbial enzyme that degrades argi-nine Certain cancer cells deficient in producing argininethrough argininosuccinate synthase obtain exogenous argi-nine from circulation PEG-ADI 20 depletes arginine con-centrations in the blood thereby controlling and reducingtumor growth103 The previous phase III study was com-pleted on un-resectable hepatocellular carcinoma knownfor its poor prognosis In a study with 35 patients allpatients exhibited blood arginine levels lower than 2 uMwhile 2 patients became stable 1 patient became resectableand 28 progressed with a mean duration before progres-sion of 34 months103 On the other hand CRLX101 isa nanoparticle drug delivery system comprised of thechemotherapeutic camptothecin (CPT) conjugated to acyclodextrin-based polymer CRLX101 was designed toincrease the exposure of tumor cells to CPT while reducingside effects Anti-cancer activity of camptothecin is due inpart to the inhibition of DNA topoisomerase I but has beenprevented from use as an anti-cancer drug due to poor sol-ubility lack of activity and excessive toxicity104 HoweverCRLX101 nanoparticle was shown to have significantlyhigher antitumor activity with lower dosing while main-taining the levels of free camptothecin in the blood to aminimum It is noteworthy that it was effective in a num-ber of tumors resistant to irinotecan treatment CRLX101is currently undergoing Phase IB2A trials104 Ultimatelyactive targeting through the inclusion of a targeting lig-and on the nanoparticles is envisioned to provide the

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Table I Nanoncology in clinical development

Class Carrier Active agent Target Clinical status Indication (s) Ref

LiposomesDaunoXome Liposome Daunorubicin

citrateNA Approved Chronic myelogenous

leukemia neuroblastoma3

DOTAP Chol-FUS1 Liposome Plasmid DNA(FUS1)

NA Phase I Metastatic non-small celllung cancer

114

SGT-53 Liposome Plasmid DNAp53 W-T

Transferrinreceptor

Phase I Advanced Solid Tumors 115

MBP 426 Liposome Oxaliplatin Transferrinreceptor

Phase lbII Advanced or MetastaticSolid Tumors

105

PEGylatedDoxil PEGylaled-Liposome Doxorubicin NA Approved Ovanan cancer recurrent

breast cancer2 56

Oncospar PEGylaled-Asparagnase

L-asparagnase NA Approved Acute lymphoblasticleukemia

2

CYT-6091 PEGylaled-ThiolGold

RecombinantTNF-

Tumor necrosisfactor recepteor

Phase II Advanced solid tumors 110

ADI-PEG 20 PEGylated-ArginineDeiminase

Augininedeiminase

NA Phase II Hepatocellular carcinomaMetastatic melanomarelapsed small cell lungcancer

103

PeptideAbraxane Albumin Paclitaxel NA Approved Metastatic non-small cell

lung cancer2 3

Ontak Interkeukin-2engineered protein

Diphtheria toxin Interleukin-2receptors

Approved Cutaneous T-cell lymphoma 3

AMG 386 Peptibody Recombinantpeptide-Fcfusion protein

Angiopoietin 1and 2

Phase III Various cancers 113

PolymericCALAA-01 Cyclodextrin Small interfering

RNATransferrin

receptorPhase I Solid tumors 107 108

XMT-1001 Fleximer Camptothecin Prodrug activation Phase I Advanced solid tumors 111Genexol Polymeric micelles Paclitaxel NA Phase II Various cancers 52CT-2103 Poly-L-glutmate Paclitaxel NA Phase II Various cancers 112

Antibodya

Trastuzumab HumanizedMonoclonalantibody

Antibody CD340 receptor Approved HER2-positive metastaticbreast cancer

3 4 94

Rituximab Chimeric monoclonalAntibody

Antibody Protein CD20 Approved Leukemias and lymphomas 3 4 94

a Currently there are over 20 FDA-approved monoclonal antibodies for use in cancer therapy

most effective therapy A targeting nanoparticle in Pha-seIBII study is MbP-426 which contains the cytotoxicplatinum-based drug oxaliplatin in a transferrin-conjugatedlipopsome105 Transferrin receptors (TfR) overexpressedon tumor cells allow selective uptake via Tf-TfR interac-tion Outcome of Phase I trial with 39 patients showed that15 patients had stable disease after 2 cycles 3 patients withcolon carcinoma refractory to conventional oxaliplatin hadstable disease for 4-6 cycles and 2 patients had 12 and26 decrease in target lesions105 Further Rexin-G is amurine leukemia virus-based retrovector nanoparticle thatcontains a cytocidal dominant negative cyclin-G1 constructand allows for the functional restoration of tumor sup-pressor microRNA-122a It has been found that block-ade of cyclin G1 may restore intrinsic molecular form

of tumor suppression106 Rexin-G has been found to havelow immunogenicity with preferential selection of rapidly-dividing cells over normal non-dividing or differentiatedcells In Phase II clinical trials 88 of patients had partialresponses or stable disease while the overall survival ratewas 6 months for all 22 patients106 On a further note sometargeted nanoparticles can have active mechanisms for theintracellular release of the therapeutic moiety CALAA-01is a targeted nanoparticle that has a high drug (siRNA)payload per targeting ligand tested and proven multiva-lent binding to cancer cell surfaces and an active siRNArelease mechanism that is triggered upon the recogni-tion of intracellular localization by a pH decline belowa value of 60107108 This nanoparticle system containsa cyclodextrin-based polymer human transferring protein

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targeting ligand hydrophilic polymer (PEG) and siRNAdesigned to reduce expression of RRM2 It is currentlyundergoing Phase I clinical trials for a dose-escalatingstudy in the treatment of solid tumor cancer107 An aptamerfor potential cancer treatment is AS1411109 It binds nucle-olin on the surface of cancer cells and induces apoptosisIn a dose escalation (1 mgkgday to 10 mgkgday) clin-ical study AS1411 showed positive responses in patientswith advanced solid tumors without any adverse effects109

Recently in a randomized phase II clinical trials a10 mgkgday or 40 mgkgday dose of AS1411 com-bined with high-dose cytarabine was well tolerated andshowed promising signs of activity in patients with pri-mary refractory or relapsed acute myeloid leukaemia Itis also currently being evaluated for treatment of breastcancer110 In another example Aurimune is a colloidalAu nanoparticle which delivers recombinant TNF- tocancer tumors TNF is attached to the Au nanoparticle withthiol-derivatized PEG which allows the nanoparticle toflow through the blood stream without causing a clearanceresponse110 Clinical data to date reports that Aurimunehas no antibody or immune responses and is well-toleratedbeyond the known maximum dose for TNF-110

7 CLOSING REMARKS FUTUREPERSPECTIVE

Over the past decades nanoncology (therapeutics anddiagnostics) has evolved from nano-sized drug particlesto bio-functional nanomaterials capable of deliveringheat treatment ionizing radiation andor chemothera-peutic agents From simple liposomal formulations andconjugation of PEG to antibody-conjugated nanoparti-cle chemotherapeutic and RNAi delivery nanoncology isbecoming more intricate smart and multi-functional Fur-ther the differences between cancerous and normal cellsincluding uncontrolled proliferation insensitivity to nega-tive growth regulation and anti-growth signals angiogen-esis and metastasis can be now be effectively exploitedThere is no doubt that nanoparticle therapeutics with theincreasing multi-functionality will continue to expand inthe future Investments in research development and per-formance trials are considerably large Sponsoring agen-cies in both private and government sectors should createeconomic strategies and innovative management to makesuch biotechnologies more cost-effective and easily acces-sible for patients across Although many challenges existfor the transition of nanoparticles from bench to bed theirpotential advantages will drive successful development andemerge as a new class of undeniable anti-cancer thera-peutic Finally (i) individualizedpersonalized oncology inwhich cancer detection diagnosis and therapy can be mod-ified to best fit the tumor molecular profile of a patientand (ii) predictive oncology in which genetic biochemicaland molecular markers are orchestrated to predict disease

development progression and clinical outcomes will cer-tainly shape the nanoncologic strategies of the near future

Acknowledgments This work was supported by theSouth Korean Ministry of Knowledge and Education(MKE) and the Incheon Free Economic Zone (IFEZ) inthe framework of several funding operating grants to theUtah-Inha DDS amp Advanced Therapeutics Research Cen-ter KR

References and Notes

1 N Portney and M Ozkan Anal Bioanal Chem 3 620 (2006)2 M Ferrari Nat Rev Cancer 3 161 (2005)3 T M Allen Nat Rev Cancer 1 0750 (2002)4 J S Ross D P Schenkein and R Pietrusko Am J Clin Pathol

4 598 (2004)5 M Wang and M Thanou Drug Resist Updat 2 90 (2010)6 A Jones and A L Harris Cancer J Sci Am 4 209 (1998)7 D F Baban and L W Seymour Adv Drug Deliv 1 109 (1998)8 H Maeda Adv Enzyme Regul 41 189 (2001)9 K Greish Methods Mol Biol 624 25 (2010)10 A K Iyer K Greish T Seki S Okazaki J Fang K Takeshita

and H Maeda Drug Discov Today 11 812 (2006)11 K N Sugahara T Teesalu P P Karmali V R Kotamraju

L Agemy D R Greenwald and E Ruoslahti Science 5981 1031(2010)

12 R G Boyle and S Travess Anticancer Agents Med Chem 64 281(2006)

13 J M Brown and W R Wilson Nat Rev Cancer 4 437 (2004)14 D Kim E S Lee K Park I C Kwon and Y H Bae Pharm

Res 9 2074 (2008)15 L M Bareford and P W Swaan Adv Drug Deliv Rev 8 748

(2007)16 N F Saba X Wang S Muumlller M Tighiouart K Cho S Nie

Z Chen and D M Shin Head Neck 4 475 (2009)17 Y Lu L C Xu N Parker E Westrick J A Reddy M Vetzel

P S Low and C P Leamon Mol Cancer Ther 12 3258 (2006)18 E I Deryugina and J P Quigley Cancer Metastasis Rev 25 9

(2006)19 A M Mansour J Drevs N Esser F M Hamada O A Badary

C Unger I Fichtner and F Kratz Cancer Res 14 4062 (2003)20 H Hatakeyama H Akita E Ishida K Hashimoto H Kobayashi

T Aoki J Yasuda K Obata H Kikuchi T Ishida H Kiwadaand H Harashima Int J Pharm 1ndash2 194 (2007)

21 A Raz L Meromsky and R Lotan Cancer Res 7 3667 (1986)22 E Gorelik U Galili and A Raz Cancer Metastasis Rev 3ndash4 245

(2001)23 C Bies C M Lehr and J F Woodley Adv Drug Deliv Rev

4 425 (2004)24 H Glavinas P Krajcsi J Cserepes and B Sarkadi Curr Drug

Deliv 1 27 (2004)25 M Dean T Fojo and S Bates Nat Rev Cancer 4 275 (2005)26 T Kobayashi T Ishida Y Okada S Ise H Harashima and

H Kiwada Int J Pharm 1ndash2 94 (2007)27 A M Chen M Zhang D Wei D Stueber O Taratula T Minko

and H He Small 23 2673 (2009)28 J M Koziara P R Lockman D D Allen and R J Mumper

Pharm Res 11 1772 (2003)29 S C Steiniger J Kreuter A S Khalansky I N Skidan A I

Bobruskin Z S Smirnova S E Severin R Uhl M Kock K DGeiger and S E Gelperina Int J Cancer 5 759 (2004)

30 J Wu T Akaike and H Maeda Cancer Res 1 159 (1998)31 M A Deli Biochim Biophys Acta 4 892 (2009)

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52 Micelles

Amphipilic nanoparticles composed of block or graft co-polymers such as N -vinylpyrrolidone and poloxamers canform polymeric micelles A hydrophobic core containshydrophobic drugs and the hydrophilic shell stabilizesthe core and makes the drug water-soluble4751 Poly-meric micelles have been shown to accumulate more read-ily in tumors than the larger liposomes mainly due totheir size51 The first polymeric micelle formulation ofPTX Genexol-PM a cremophor-free polymeric micellehas completed phase II clinical trials in the US withconsiderable anti-tumor activity in combination with cis-platin chemotherapy Cremophor EL is an excipient withcertain drugs and has been suggested to be a dose lim-iting factor in the administration of PTX52 This micel-lar nanoparticulate system allowed for higher doses of thedrug while being able to deliver and concentrate inside thetumor interstitium Another biodegradable formulation ofcationic micelles were prepared with PDMAEMA-PCL-PDMAEMA tri-block co-polymers and applied for thedual delivery of siRNA and PTX into cancer cells Combi-natorial delivery of anti-VEGF siRNA and PTX knockeddown VEGF expression53

53 Liposomes and Solid Lipid Nanoparticles

Natural liposomes a closed colloidal structure composedof a lipid bi-layer and an aqueous core are composed oflecithin phospholipids and can also be multi-laminar ratherthan uni-laminar carrying a larger payload of water- andfat-soluble constituents up to 500 nm in size5455 Lipo-somes take advantage of the overexpression of perforationsin cancer neovasculature in order to increase drug concen-trations passively at tumor sites Liposomal drug deliveryhas been the most successful nanoparticulate formulationused in the clinic as shown by liposomal-encapsulateddoxorubicin for Kaposirsquos sarcoma and more recentlybreast and ovarian cancer56 Small dimensions (lt300 nm)enables the drug to accumulate in the tumor mass by cross-ing passively into the tumor vasculature while avoiding orreducing the permeation of normal tissue55 On the otherhand solid lipid nanoparticles (SLNs) are solid lipids athuman physiological temperature with a diameter from50 to 1000 nm They are formed from a range of lipidsincluding mono- di- and tri-glycerides waxes fatty acidsand combinations of those SLNs are biodegradable bio-compatible with several human applications57 They form astrong lipophilic matrix in which water-insoluble lipophilicdrugs can be loaded for subsequent release The chemi-cal and physical properties of lipids in a heterogeneousmixture promote an imperfect crystalline structure withlarger gaps for efficient drug loading57 Use of SLNs havebeen investigated for the delivery of various anti-cancerdrugs with promising results in pre-clinical mouse trialsspecifically showing that SLNs might help overcome MDR

in cancers Serpe et al using human colon cancer cellsHT-29 demonstrated the benefits of SLNs in the deliveryof cholesteryl butyrate (chol-but) with doxorubicin Cyto-toxicity was shown to be higher in chol-but SLN loadedwith doxorubicin than free doxorubicin alone howeverPTX-loaded SLN did not show any improvement over freePTX5859 Lu et al loaded mitoxantrone a topoisomeraseinhibitor that blocks DNA replication into SLNs for alocal injection in the treatment of breast cancer and lymphnode metastases in mice60 Almost three-fold reduction inlymph node size was reported when compared to freely-administered mitoxantrone This was considered a signifi-cant improvement over existing treatment by the authors60

54 Dendrimers

Dendrimers may serve as a versatile nanoscale platformfor creating a multi-functional system capable of detect-ing cancer and delivering drugs A synthetic polymericmacromolecule of nanometer dimensions a dendrimer iscomposed of multiple highly branched monomers thatemerge radially from a central core The readily modifiablesurface characteristic enables them to be simultaneouslyconjugated with several molecules such as imaging con-trast agents targeting ligands andor therapeutic drugs61

Many commercial small molecule drugs with anti-canceractivity have been successfully conjugated with den-drimers such as polyamidoamine poly(propylene imine)and poly(etherhydroxylamine) dendrimers by means ofeither steric interactions or chemical reactions6263 Tar-geted delivery is possible via targeting moieties conju-gated to dendrimer surface or passive delivery due to theEPR effect Cationic dendrimers show cytotoxicity how-ever derivatization with fatty acid or PEG chains canreduce the overall charge density and minimize contactbetween cell surface thus reducing toxic effects6162 Patriet al demonstrated that covalently coupled methotrexate-dendrimer conjugates targeting high-affinity receptor forfolic acid have a similar activity to the free drug invitro while specifically killing receptor-expressing cells viareceptor-mediated endocytosis64

55 Carbon Nanotubes and Nanodiamonds

Carbon nanotubes are generally insoluble causing them tobe non-biocompatible however the introduction of chem-ical modification to carbon nanotubes render them water-soluble and functionalized so that they can be linked to awide variety of active molecules such as peptides proteinsnucleic acids and therapeutic agents Functionalized car-bon nanotubes also have an intrinsic capability to perme-ate cell membranes which allows endocytosis-independentinternalization of nanoparticles265 Methotrexate cova-lently linked to carbon nanotubes with a fluorescent agentwas shown to be more effectively internalized into cells

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when compared to the free unbound drug65 The multi-ple covalent functionalizations on the sidewall or tips ofcarbon nanotubes allow them to carry several moleculesat once This strategy provides a fundamental advantagein the treatment of cancer Targeted heat therapy or lsquother-mal ablationrsquo is being tested to destroy breast cancertumors using carbon nanotubes Accordingly the HER2IgY-single wall carbon nanotube (SWNT) complex specif-ically targeted HER2-expressing SK-BR-3 cells but notreceptor-negative MCF-7 cells Near-infrared irradiationwith an 808 nm laser showed extensive cell death withSWNT66 On the other hand a nanodiamond-embeddeddevice is being developed to deliver chemotherapy locallyto sites where cancerous tumors have been surgicallyremoved67 Nanodiamonds complexed with doxorubicin-hydrochloride enable a sustained release of drug for aminimum of 30 days with a significant amount of drugin reserve This shows potential for highly localized drugrelease as a complementary yet potent form of treat-ment with systemic injection Ho and group embeddedmillions of tiny drug carrying nanodiamonds into theFDA-approved parylene67ndash69 Currently used as a coatingfor implants biostable parylene is a flexible and versa-tile polymeric material Nanodiamonds placed betweenextremely thin parylene films resulted in a device that isminimally-invasive Internalization assays revealed a pri-marily endocytic uptake process High degree of nanodia-mond (sim46 nm in diameter) and endosome co-localizationas well as cytoplasmic presence of smaller nanodiamondswere observed69

56 Silicon Nanoparticles

Silicon and silica are establishing themselves as inter-esting candidate materials for injectable nanoparticles indrug delivery70 Porosified silicon is biodegradable71 withkinetics that are much more rapid than those of typicalbiodegradable polymers and as a result releases drugswith previously un-attainable time profiles Lu et al loadedhydrophobic anti-cancer drug camptothecin (CPT) ontomesoporous silica nanoparticles CPT release was mini-mal and sustained in aqueous solution This effectivelyaddressed the problem of poor water-solubility of certainanti-cancer drugs as well as sustainable release profiles71

Furthermore there are metal-based nanovectors such asnanoshells70 comprised of a gold layer over a silica coreThe thickness of the gold layer can be precisely tuned sothat the nanoshell can be selectively activated through tis-sue irradiation with near-infrared light to perform localizedtherapeutic thermal ablation This approach was recentlyused to eradicate transmissible venereal tumors in mice72

In another study nitric oxide (NO)-releasing silica nanopar-ticles exhibited enhanced growth inhibition of ovariantumor cells and showed greater inhibition of the anchorage-independent growth of tumor-derived and Ras-transformed

ovarian cels73 NO a free radical bio-regulator endoge-nously synthesized in the body impacts multiple stages oftumor development spanning cytostatic processes cellulartransformation and formation of neoplastic lesions7374 Itis worth mentioning herein that research efforts have beenimpeded by the fact that possible normal cell toxicity ofthe NO donor drug by-product and the inability to targetdelivery of the drug selectively to cancer cells

57 Gold and Magnetic Nanoparticles

Gold (Au) nanoparticles are very versatile and can beprepared with different geometries such as nanospheresnanoshells nanorods or nanocages75 Further they haveunrivaled physical and chemical properties such asexceedingly small size (less than 50 nm) large sur-face area to mass proportion heightened surface sensitiv-ity presence of characteristic surface plasmon resonancebands biocompatibility and ease of surface functionaliza-tion Au nanoparticles are also excellent conductors ofelectrical and thermal energy which allows possibilitiesfor thermal ablation treatment In photodynamic therapy(PDT) Au nanoparticles are becoming known as a photo-sensitizer with great potential due to its optimal absorptionand light scattering properties along with controllable opti-cal characteristics El-Sayed and collegues have shown thatanti-EGFR antibody conjugated gold nanoparticles selec-tively localized in malignant HOC and HSC cells andunderwent significant photothermal destruction upon nearinfrared irradiation76 However using radiofrequency irra-diation Gannon et al demonstrated that the internalizationof Au nanoparticles in gastrointestinal cancer cells releasedsubstantial heat rapidly after exposure to an external high-voltage focused radiofrequency field (RF) It is noteworthythat radiofrequency ablation has an advantage over nearinfrared ablation which is limited to superficial tumorswith minimal tissue penetration Hep3B and Panc-1 cellstreated with 67 ML Au nanoparticles had significantlyhigher rates of cell death than the control samples at alltime-points after RF exposure77 Interestingly Au nanopar-ticles about 5ndash10 nm in diameter have been shown to haveintrinsic anti-angiogenic properties78 These nanoparticlesbind to heparin-binding pro-angiogenic growth factorssuch as VEGF165 and bFGF to inhibit their activity TheAu nanoparticles themselves also reduced ascites accumu-lation in a pre-clinical model of ovarian cancer inhibitedproliferation of multiple myeloma cells and induced apop-tosis in chronic B cell leukemia78 On the other hand mag-netic nanoparticles (MNPs) have traditionally been usedfor disease imaging via magnetic resonance (MR) imagingdue to their intrinsic properties Recent advances have alsoopened the door to cellular-specific targeting drug deliv-ery and multi-modal imaging Further MNPs can be func-tionalized through coating with polymers preferentiallywith biocompatible or biodegradable polymers of synthetic

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or biological origin7980 As solid tumor develops it out-grows its blood supply which results in the formation ofa hypoxic semi-necrotic tumor core and dormant tumorcells send out chemical signals that recruit macrophagesinto the core Macrophages begin to rebuild the bloodsupply allowing the tumor to start growing again8182

Muthana et al loaded human monocytes with MNPs plac-ing magnets near the site of a human prostate tumor grownin mice82 The MNP-loaded monocytes carrying a reportergene invaded the tumor at a rate more than three timesthat of the non-loaded cells82 This demonstration of mag-netic targeting shows that MNP-loaded cells circulatingin the body can be attracted to the tumor site where anexternal magnet is placed allowing a higher proportion ofloaded cells to respond to chemical signals from the tumorcore In addition the loaded monocytes were able to reachthe poorly vascularized peri-necrotic regions of the tumorthat are normally difficult to target As the moncytes areloaded with MNPs they can then be destroyed by hyper-thermia after delivering a therapeutic drug or gene8182

Classes of MNPs include metallic bimetallic and super-paramagnetic iron oxide nanoparticles widely-knows asSPIONs SPIONS are favored because due to low toxicityprofile and their reactive surface that can be readily modi-fied with biocompatible coatings87 This flexibility has ledto SPION use in magnetic separation biosensor in vivomedical imaging drug delivery tissue repair and hyper-thermia applications84 Yu et al preciously showed thatthermally crosslinked SPIONs loaded with doxorubicinhad potential as both an imaging and therapeutic deliverysystem83 This DoxTCL-SPION was also demonstratedto efficiently reach tumor sites and release the drug withoutany active targeting from ligandsantibodies or magneticfield largely due to the EPR effect83

58 Viral Nanoparticles

A variety of viruses including cowpea mosaic viruscanine parvovirus adenovirus coxsackie virus measlesvirus along with virions and virus-like particles have beendeployed for biomedical and nanotechnology applicationsthat include tissue targeting and drug delivery84 Target-ing molecules and peptides can be produced in a bio-logically functional form on the capsid surface throughchemical conjugation or gene expression Several lig-ands including transferrin folic acid and single-chainantibodies have been conjugated to viruses for specifictumor targeting84 Further a subset of viruses such ascanine parvovirus have a natural affinity for receptors liketransferrins that are up-regulated in a variety of tumorcells85 Adenoviral vectors offer many advantages for can-cer gene therapy including high transduction efficiencyyet safety concerns related to immunogenic response haveled to a cautious approach of their use in human clini-cal trials86 To overcome these obstacles hybrid vectors

combining both viral and non-viral elements are beingdeveloped Adenovirus coated with an arginine-graftedbioreducible polymer (ABP) via electrostatic interaction isone example ABP-coated complexes were shown to havesignificantly reduced the innate immune response whileproducing higher levels of transgene expression8687 Fur-thermore herpes simplex virus (HSV) vectors are alreadyin early phase human clinical trials for recurrent malignantglioblastoma A mutant form (vIII) of epidermal growthfactor receptor (EGFR) present in glioma tumor is rec-ognized by a single-chain antibody designated MR1-1HSV virions bearing MR1-1-modified gC had five-foldincreased infectivity for EGFRvIII-bearing human gliomaU87 cells showing enhanced vector specificity and tumorcell damage88

59 RNA Interference

Since its discovery nearly two decades ago RNA inter-ference (RNAi) has been lauded as the next generation ingene therapy due to the unique pathway in which smallinterfering (siRNA) or microRNA (miRNA) can preventmRNA expression and silence- specific targeted geneseffectively89 RNAi cancer gene targets are pathways thatcontribute to tumor growth through increased tumor cellproliferation andor reduced tumor cell death RNAi canalso be used to target and silence gene products thatnegatively regulate the function of endogenous tumor sup-pressor genes as well as proteins involved in cellular senes-cence or protein stabilitydegradation However in vivostudies up until now have shown wide variation on thepotency of RNAi and its suppression activities as a resultof poor cellular uptake rapid renal clearance and nucle-ase degradation90 Also previous experiments have beenplagued with additional problems such as off-targeting andimmunogenic response9091 Nonetheless the characteri-zation of novel nanoparticle carriers and chemical mod-ifications to siRNA itself has addressed some of theseissues Suh and collegues developed a cationic lipid N N primeprime-dioleylglutamide linked by negatively charged glutamicacid to oleoylamine as a siRNA carrier92 It was ableto deliver siRNA to various cancer cells in vitro moreeffectively than other cationic liposomes and with reducedcytotoxicity Moreover results showed that it was effectivefor local in vivo siRNA delivery providing clear evidencethat target protein expression was knocked down in tumortissues92 In addition Chen et al developed a liposome-polycation-hyaluronic acid (LPH) nanoparticle formulationmodified with single-chain antibody fragment (GC4 scFv)for the systemic delivery of siRNA and miRNA in experi-mental lung metastasis of murine B16F10 melanoma Inhi-bition of c-Myc MDM2 and VEGF protein expression bysiRNA formulated with GC4 scFv modified LPH nanopar-ticles significantly suppressed B16F10 metastatic tumorgrowth while showing increased siRNA uptake within thelung tumors93

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510 Monoclonal Antibodies

Monoclonal antibodies (mAB) are monospecific antibod-ies that bind only to one particular antigenic determinantor epitope By blocking ligand binding andor signalingof growth receptors mABs have the capability to sen-sitize tumors to chemotherapeutic agents reduce growthrates and induce apoptosis Many different monoclonalantibodies are currently used in the therapy of cer-tain cancers such as Bevacizumab Imatinib BortezomibGefitinib Sorafenib Tositumomab Tamoxifen and Ritux-imab which are all FDA-approved therapies for cancer todate94 In some in vivo applications the antibody itself issufficient and once bound to its target mAB triggers theeffector cell mechanisms of the immune system An excel-lent 2010 review by Weiner et al addresses the specificimmunologic pathways in which mABs interact with can-cer cells94 mAB may also be coupled to another moleculesuch as a fluorescent molecule to aid in imaging or aradioactive isotope such as Iodine-125 to aid in killing can-cer cells with radioimmunotherapy95 However in a recentstudy of radioimmunotherapy it was concluded that a sin-gle -emitter 90Y coupled to each antibody had a signifi-cantly lower biological effective dose and was insufficientto treat non small-cell lung cancer than a single 5 nm90Y2O3 nanoparticle96 In the application of nanoparticlesmAB can be used as efficient targeting ligands Workby Park and associates shows the targeting specificityof a modified lymphocyte function-associated antigen-1domain tuned to have variable affinities for intercellularadhesion molecule (ICAM)-1 Applying this antibody totheir nanoparticle system amphiphilic urethane acrylatenonionomer (UAN) researchers were able to demonstrateefficient encapsulation of a FITC marker and a protea-some inhibitor (celastrol) as well as the targeted deliveryto HeLa cells producing a more potent cytotoxicity withequal amounts of drug than with the untargeted UAN97

511 Aptamers

Aptamers are synthetic oligonucleotide ligands or peptidesthat bear unique three-dimensional conformations capa-ble of binding to target antigens with high affinity andspecificity Aptamers bind to their targets to effectivelyillicit little or none immunogenicity and possess molecu-lar recognition properties similar to monoclonal antibod-ies They have been applied to drug delivery systems asligands to enhance selectivity98 RNA aptamer OPN-R3has been shown in an in vivo xenograft model of breastcancer with MDA-MB-231 cells to significantly decreaselocal progression and distant metastases By day 20 tumorvolume in the modified OPN-R3 treated group was 18ndash20-fold smaller than the tumor volume in mutant OPN-R3and no treatment groups99 Another aptamer SM20 iso-lated against plasminogen activator inhibitor-1 has demon-strated in vitro therapeutic potential as an antimetastatic

agent and could possibly be used as an adjuvant to tradi-tional chemotherapy for breast cancer100 Several aptamershave been recently isolated for potential treatment of othercancers such as glioblastoma T cell leukaemia and epithe-lial cancer cells in the breast colon lung ovaries andpancreas98 Finally apatmers can be used as a targetingmoiety to be conjugated to a certain drug delivery for-mulation or may act as modalities with characteristics ofintrinsic specificity100

6 CURRENT CLINICAL PROGRESS OFNANONCOLOGY THERAPEUTICS

In this section nanoparticles for cancer therapy that havealready reached the clinic are discussed A few sys-tems having been approved and many are still ongoingin human clinical trials (Table I) As described earliernon-targeting nanoparticles utilize leaky vasculature oftumors to reach via passive targeting PEGylation has beenapplied to various proteins enzymes cytokines and mon-oclonal antibody fragments to increase circulatory half-life and decrease antigenicity3349101102 Many clinicaltrials involving PEGylation of nanoparticles are in differ-ent phase trials at the moment such as PEG-InterferonAlfa-2b PEGylated recombinant human Hyaluronidase(PEGPH20) PEG conjugate of SN38 (EZN-2208) toname a few An interesting PEgylated complex is PEG-ADI 20 currently undergoing Phase II studies Argininedeiminase (ADI) is a microbial enzyme that degrades argi-nine Certain cancer cells deficient in producing argininethrough argininosuccinate synthase obtain exogenous argi-nine from circulation PEG-ADI 20 depletes arginine con-centrations in the blood thereby controlling and reducingtumor growth103 The previous phase III study was com-pleted on un-resectable hepatocellular carcinoma knownfor its poor prognosis In a study with 35 patients allpatients exhibited blood arginine levels lower than 2 uMwhile 2 patients became stable 1 patient became resectableand 28 progressed with a mean duration before progres-sion of 34 months103 On the other hand CRLX101 isa nanoparticle drug delivery system comprised of thechemotherapeutic camptothecin (CPT) conjugated to acyclodextrin-based polymer CRLX101 was designed toincrease the exposure of tumor cells to CPT while reducingside effects Anti-cancer activity of camptothecin is due inpart to the inhibition of DNA topoisomerase I but has beenprevented from use as an anti-cancer drug due to poor sol-ubility lack of activity and excessive toxicity104 HoweverCRLX101 nanoparticle was shown to have significantlyhigher antitumor activity with lower dosing while main-taining the levels of free camptothecin in the blood to aminimum It is noteworthy that it was effective in a num-ber of tumors resistant to irinotecan treatment CRLX101is currently undergoing Phase IB2A trials104 Ultimatelyactive targeting through the inclusion of a targeting lig-and on the nanoparticles is envisioned to provide the

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Table I Nanoncology in clinical development

Class Carrier Active agent Target Clinical status Indication (s) Ref

LiposomesDaunoXome Liposome Daunorubicin

citrateNA Approved Chronic myelogenous

leukemia neuroblastoma3

DOTAP Chol-FUS1 Liposome Plasmid DNA(FUS1)

NA Phase I Metastatic non-small celllung cancer

114

SGT-53 Liposome Plasmid DNAp53 W-T

Transferrinreceptor

Phase I Advanced Solid Tumors 115

MBP 426 Liposome Oxaliplatin Transferrinreceptor

Phase lbII Advanced or MetastaticSolid Tumors

105

PEGylatedDoxil PEGylaled-Liposome Doxorubicin NA Approved Ovanan cancer recurrent

breast cancer2 56

Oncospar PEGylaled-Asparagnase

L-asparagnase NA Approved Acute lymphoblasticleukemia

2

CYT-6091 PEGylaled-ThiolGold

RecombinantTNF-

Tumor necrosisfactor recepteor

Phase II Advanced solid tumors 110

ADI-PEG 20 PEGylated-ArginineDeiminase

Augininedeiminase

NA Phase II Hepatocellular carcinomaMetastatic melanomarelapsed small cell lungcancer

103

PeptideAbraxane Albumin Paclitaxel NA Approved Metastatic non-small cell

lung cancer2 3

Ontak Interkeukin-2engineered protein

Diphtheria toxin Interleukin-2receptors

Approved Cutaneous T-cell lymphoma 3

AMG 386 Peptibody Recombinantpeptide-Fcfusion protein

Angiopoietin 1and 2

Phase III Various cancers 113

PolymericCALAA-01 Cyclodextrin Small interfering

RNATransferrin

receptorPhase I Solid tumors 107 108

XMT-1001 Fleximer Camptothecin Prodrug activation Phase I Advanced solid tumors 111Genexol Polymeric micelles Paclitaxel NA Phase II Various cancers 52CT-2103 Poly-L-glutmate Paclitaxel NA Phase II Various cancers 112

Antibodya

Trastuzumab HumanizedMonoclonalantibody

Antibody CD340 receptor Approved HER2-positive metastaticbreast cancer

3 4 94

Rituximab Chimeric monoclonalAntibody

Antibody Protein CD20 Approved Leukemias and lymphomas 3 4 94

a Currently there are over 20 FDA-approved monoclonal antibodies for use in cancer therapy

most effective therapy A targeting nanoparticle in Pha-seIBII study is MbP-426 which contains the cytotoxicplatinum-based drug oxaliplatin in a transferrin-conjugatedlipopsome105 Transferrin receptors (TfR) overexpressedon tumor cells allow selective uptake via Tf-TfR interac-tion Outcome of Phase I trial with 39 patients showed that15 patients had stable disease after 2 cycles 3 patients withcolon carcinoma refractory to conventional oxaliplatin hadstable disease for 4-6 cycles and 2 patients had 12 and26 decrease in target lesions105 Further Rexin-G is amurine leukemia virus-based retrovector nanoparticle thatcontains a cytocidal dominant negative cyclin-G1 constructand allows for the functional restoration of tumor sup-pressor microRNA-122a It has been found that block-ade of cyclin G1 may restore intrinsic molecular form

of tumor suppression106 Rexin-G has been found to havelow immunogenicity with preferential selection of rapidly-dividing cells over normal non-dividing or differentiatedcells In Phase II clinical trials 88 of patients had partialresponses or stable disease while the overall survival ratewas 6 months for all 22 patients106 On a further note sometargeted nanoparticles can have active mechanisms for theintracellular release of the therapeutic moiety CALAA-01is a targeted nanoparticle that has a high drug (siRNA)payload per targeting ligand tested and proven multiva-lent binding to cancer cell surfaces and an active siRNArelease mechanism that is triggered upon the recogni-tion of intracellular localization by a pH decline belowa value of 60107108 This nanoparticle system containsa cyclodextrin-based polymer human transferring protein

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targeting ligand hydrophilic polymer (PEG) and siRNAdesigned to reduce expression of RRM2 It is currentlyundergoing Phase I clinical trials for a dose-escalatingstudy in the treatment of solid tumor cancer107 An aptamerfor potential cancer treatment is AS1411109 It binds nucle-olin on the surface of cancer cells and induces apoptosisIn a dose escalation (1 mgkgday to 10 mgkgday) clin-ical study AS1411 showed positive responses in patientswith advanced solid tumors without any adverse effects109

Recently in a randomized phase II clinical trials a10 mgkgday or 40 mgkgday dose of AS1411 com-bined with high-dose cytarabine was well tolerated andshowed promising signs of activity in patients with pri-mary refractory or relapsed acute myeloid leukaemia Itis also currently being evaluated for treatment of breastcancer110 In another example Aurimune is a colloidalAu nanoparticle which delivers recombinant TNF- tocancer tumors TNF is attached to the Au nanoparticle withthiol-derivatized PEG which allows the nanoparticle toflow through the blood stream without causing a clearanceresponse110 Clinical data to date reports that Aurimunehas no antibody or immune responses and is well-toleratedbeyond the known maximum dose for TNF-110

7 CLOSING REMARKS FUTUREPERSPECTIVE

Over the past decades nanoncology (therapeutics anddiagnostics) has evolved from nano-sized drug particlesto bio-functional nanomaterials capable of deliveringheat treatment ionizing radiation andor chemothera-peutic agents From simple liposomal formulations andconjugation of PEG to antibody-conjugated nanoparti-cle chemotherapeutic and RNAi delivery nanoncology isbecoming more intricate smart and multi-functional Fur-ther the differences between cancerous and normal cellsincluding uncontrolled proliferation insensitivity to nega-tive growth regulation and anti-growth signals angiogen-esis and metastasis can be now be effectively exploitedThere is no doubt that nanoparticle therapeutics with theincreasing multi-functionality will continue to expand inthe future Investments in research development and per-formance trials are considerably large Sponsoring agen-cies in both private and government sectors should createeconomic strategies and innovative management to makesuch biotechnologies more cost-effective and easily acces-sible for patients across Although many challenges existfor the transition of nanoparticles from bench to bed theirpotential advantages will drive successful development andemerge as a new class of undeniable anti-cancer thera-peutic Finally (i) individualizedpersonalized oncology inwhich cancer detection diagnosis and therapy can be mod-ified to best fit the tumor molecular profile of a patientand (ii) predictive oncology in which genetic biochemicaland molecular markers are orchestrated to predict disease

development progression and clinical outcomes will cer-tainly shape the nanoncologic strategies of the near future

Acknowledgments This work was supported by theSouth Korean Ministry of Knowledge and Education(MKE) and the Incheon Free Economic Zone (IFEZ) inthe framework of several funding operating grants to theUtah-Inha DDS amp Advanced Therapeutics Research Cen-ter KR

References and Notes

1 N Portney and M Ozkan Anal Bioanal Chem 3 620 (2006)2 M Ferrari Nat Rev Cancer 3 161 (2005)3 T M Allen Nat Rev Cancer 1 0750 (2002)4 J S Ross D P Schenkein and R Pietrusko Am J Clin Pathol

4 598 (2004)5 M Wang and M Thanou Drug Resist Updat 2 90 (2010)6 A Jones and A L Harris Cancer J Sci Am 4 209 (1998)7 D F Baban and L W Seymour Adv Drug Deliv 1 109 (1998)8 H Maeda Adv Enzyme Regul 41 189 (2001)9 K Greish Methods Mol Biol 624 25 (2010)10 A K Iyer K Greish T Seki S Okazaki J Fang K Takeshita

and H Maeda Drug Discov Today 11 812 (2006)11 K N Sugahara T Teesalu P P Karmali V R Kotamraju

L Agemy D R Greenwald and E Ruoslahti Science 5981 1031(2010)

12 R G Boyle and S Travess Anticancer Agents Med Chem 64 281(2006)

13 J M Brown and W R Wilson Nat Rev Cancer 4 437 (2004)14 D Kim E S Lee K Park I C Kwon and Y H Bae Pharm

Res 9 2074 (2008)15 L M Bareford and P W Swaan Adv Drug Deliv Rev 8 748

(2007)16 N F Saba X Wang S Muumlller M Tighiouart K Cho S Nie

Z Chen and D M Shin Head Neck 4 475 (2009)17 Y Lu L C Xu N Parker E Westrick J A Reddy M Vetzel

P S Low and C P Leamon Mol Cancer Ther 12 3258 (2006)18 E I Deryugina and J P Quigley Cancer Metastasis Rev 25 9

(2006)19 A M Mansour J Drevs N Esser F M Hamada O A Badary

C Unger I Fichtner and F Kratz Cancer Res 14 4062 (2003)20 H Hatakeyama H Akita E Ishida K Hashimoto H Kobayashi

T Aoki J Yasuda K Obata H Kikuchi T Ishida H Kiwadaand H Harashima Int J Pharm 1ndash2 194 (2007)

21 A Raz L Meromsky and R Lotan Cancer Res 7 3667 (1986)22 E Gorelik U Galili and A Raz Cancer Metastasis Rev 3ndash4 245

(2001)23 C Bies C M Lehr and J F Woodley Adv Drug Deliv Rev

4 425 (2004)24 H Glavinas P Krajcsi J Cserepes and B Sarkadi Curr Drug

Deliv 1 27 (2004)25 M Dean T Fojo and S Bates Nat Rev Cancer 4 275 (2005)26 T Kobayashi T Ishida Y Okada S Ise H Harashima and

H Kiwada Int J Pharm 1ndash2 94 (2007)27 A M Chen M Zhang D Wei D Stueber O Taratula T Minko

and H He Small 23 2673 (2009)28 J M Koziara P R Lockman D D Allen and R J Mumper

Pharm Res 11 1772 (2003)29 S C Steiniger J Kreuter A S Khalansky I N Skidan A I

Bobruskin Z S Smirnova S E Severin R Uhl M Kock K DGeiger and S E Gelperina Int J Cancer 5 759 (2004)

30 J Wu T Akaike and H Maeda Cancer Res 1 159 (1998)31 M A Deli Biochim Biophys Acta 4 892 (2009)

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when compared to the free unbound drug65 The multi-ple covalent functionalizations on the sidewall or tips ofcarbon nanotubes allow them to carry several moleculesat once This strategy provides a fundamental advantagein the treatment of cancer Targeted heat therapy or lsquother-mal ablationrsquo is being tested to destroy breast cancertumors using carbon nanotubes Accordingly the HER2IgY-single wall carbon nanotube (SWNT) complex specif-ically targeted HER2-expressing SK-BR-3 cells but notreceptor-negative MCF-7 cells Near-infrared irradiationwith an 808 nm laser showed extensive cell death withSWNT66 On the other hand a nanodiamond-embeddeddevice is being developed to deliver chemotherapy locallyto sites where cancerous tumors have been surgicallyremoved67 Nanodiamonds complexed with doxorubicin-hydrochloride enable a sustained release of drug for aminimum of 30 days with a significant amount of drugin reserve This shows potential for highly localized drugrelease as a complementary yet potent form of treat-ment with systemic injection Ho and group embeddedmillions of tiny drug carrying nanodiamonds into theFDA-approved parylene67ndash69 Currently used as a coatingfor implants biostable parylene is a flexible and versa-tile polymeric material Nanodiamonds placed betweenextremely thin parylene films resulted in a device that isminimally-invasive Internalization assays revealed a pri-marily endocytic uptake process High degree of nanodia-mond (sim46 nm in diameter) and endosome co-localizationas well as cytoplasmic presence of smaller nanodiamondswere observed69

56 Silicon Nanoparticles

Silicon and silica are establishing themselves as inter-esting candidate materials for injectable nanoparticles indrug delivery70 Porosified silicon is biodegradable71 withkinetics that are much more rapid than those of typicalbiodegradable polymers and as a result releases drugswith previously un-attainable time profiles Lu et al loadedhydrophobic anti-cancer drug camptothecin (CPT) ontomesoporous silica nanoparticles CPT release was mini-mal and sustained in aqueous solution This effectivelyaddressed the problem of poor water-solubility of certainanti-cancer drugs as well as sustainable release profiles71

Furthermore there are metal-based nanovectors such asnanoshells70 comprised of a gold layer over a silica coreThe thickness of the gold layer can be precisely tuned sothat the nanoshell can be selectively activated through tis-sue irradiation with near-infrared light to perform localizedtherapeutic thermal ablation This approach was recentlyused to eradicate transmissible venereal tumors in mice72

In another study nitric oxide (NO)-releasing silica nanopar-ticles exhibited enhanced growth inhibition of ovariantumor cells and showed greater inhibition of the anchorage-independent growth of tumor-derived and Ras-transformed

ovarian cels73 NO a free radical bio-regulator endoge-nously synthesized in the body impacts multiple stages oftumor development spanning cytostatic processes cellulartransformation and formation of neoplastic lesions7374 Itis worth mentioning herein that research efforts have beenimpeded by the fact that possible normal cell toxicity ofthe NO donor drug by-product and the inability to targetdelivery of the drug selectively to cancer cells

57 Gold and Magnetic Nanoparticles

Gold (Au) nanoparticles are very versatile and can beprepared with different geometries such as nanospheresnanoshells nanorods or nanocages75 Further they haveunrivaled physical and chemical properties such asexceedingly small size (less than 50 nm) large sur-face area to mass proportion heightened surface sensitiv-ity presence of characteristic surface plasmon resonancebands biocompatibility and ease of surface functionaliza-tion Au nanoparticles are also excellent conductors ofelectrical and thermal energy which allows possibilitiesfor thermal ablation treatment In photodynamic therapy(PDT) Au nanoparticles are becoming known as a photo-sensitizer with great potential due to its optimal absorptionand light scattering properties along with controllable opti-cal characteristics El-Sayed and collegues have shown thatanti-EGFR antibody conjugated gold nanoparticles selec-tively localized in malignant HOC and HSC cells andunderwent significant photothermal destruction upon nearinfrared irradiation76 However using radiofrequency irra-diation Gannon et al demonstrated that the internalizationof Au nanoparticles in gastrointestinal cancer cells releasedsubstantial heat rapidly after exposure to an external high-voltage focused radiofrequency field (RF) It is noteworthythat radiofrequency ablation has an advantage over nearinfrared ablation which is limited to superficial tumorswith minimal tissue penetration Hep3B and Panc-1 cellstreated with 67 ML Au nanoparticles had significantlyhigher rates of cell death than the control samples at alltime-points after RF exposure77 Interestingly Au nanopar-ticles about 5ndash10 nm in diameter have been shown to haveintrinsic anti-angiogenic properties78 These nanoparticlesbind to heparin-binding pro-angiogenic growth factorssuch as VEGF165 and bFGF to inhibit their activity TheAu nanoparticles themselves also reduced ascites accumu-lation in a pre-clinical model of ovarian cancer inhibitedproliferation of multiple myeloma cells and induced apop-tosis in chronic B cell leukemia78 On the other hand mag-netic nanoparticles (MNPs) have traditionally been usedfor disease imaging via magnetic resonance (MR) imagingdue to their intrinsic properties Recent advances have alsoopened the door to cellular-specific targeting drug deliv-ery and multi-modal imaging Further MNPs can be func-tionalized through coating with polymers preferentiallywith biocompatible or biodegradable polymers of synthetic

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or biological origin7980 As solid tumor develops it out-grows its blood supply which results in the formation ofa hypoxic semi-necrotic tumor core and dormant tumorcells send out chemical signals that recruit macrophagesinto the core Macrophages begin to rebuild the bloodsupply allowing the tumor to start growing again8182

Muthana et al loaded human monocytes with MNPs plac-ing magnets near the site of a human prostate tumor grownin mice82 The MNP-loaded monocytes carrying a reportergene invaded the tumor at a rate more than three timesthat of the non-loaded cells82 This demonstration of mag-netic targeting shows that MNP-loaded cells circulatingin the body can be attracted to the tumor site where anexternal magnet is placed allowing a higher proportion ofloaded cells to respond to chemical signals from the tumorcore In addition the loaded monocytes were able to reachthe poorly vascularized peri-necrotic regions of the tumorthat are normally difficult to target As the moncytes areloaded with MNPs they can then be destroyed by hyper-thermia after delivering a therapeutic drug or gene8182

Classes of MNPs include metallic bimetallic and super-paramagnetic iron oxide nanoparticles widely-knows asSPIONs SPIONS are favored because due to low toxicityprofile and their reactive surface that can be readily modi-fied with biocompatible coatings87 This flexibility has ledto SPION use in magnetic separation biosensor in vivomedical imaging drug delivery tissue repair and hyper-thermia applications84 Yu et al preciously showed thatthermally crosslinked SPIONs loaded with doxorubicinhad potential as both an imaging and therapeutic deliverysystem83 This DoxTCL-SPION was also demonstratedto efficiently reach tumor sites and release the drug withoutany active targeting from ligandsantibodies or magneticfield largely due to the EPR effect83

58 Viral Nanoparticles

A variety of viruses including cowpea mosaic viruscanine parvovirus adenovirus coxsackie virus measlesvirus along with virions and virus-like particles have beendeployed for biomedical and nanotechnology applicationsthat include tissue targeting and drug delivery84 Target-ing molecules and peptides can be produced in a bio-logically functional form on the capsid surface throughchemical conjugation or gene expression Several lig-ands including transferrin folic acid and single-chainantibodies have been conjugated to viruses for specifictumor targeting84 Further a subset of viruses such ascanine parvovirus have a natural affinity for receptors liketransferrins that are up-regulated in a variety of tumorcells85 Adenoviral vectors offer many advantages for can-cer gene therapy including high transduction efficiencyyet safety concerns related to immunogenic response haveled to a cautious approach of their use in human clini-cal trials86 To overcome these obstacles hybrid vectors

combining both viral and non-viral elements are beingdeveloped Adenovirus coated with an arginine-graftedbioreducible polymer (ABP) via electrostatic interaction isone example ABP-coated complexes were shown to havesignificantly reduced the innate immune response whileproducing higher levels of transgene expression8687 Fur-thermore herpes simplex virus (HSV) vectors are alreadyin early phase human clinical trials for recurrent malignantglioblastoma A mutant form (vIII) of epidermal growthfactor receptor (EGFR) present in glioma tumor is rec-ognized by a single-chain antibody designated MR1-1HSV virions bearing MR1-1-modified gC had five-foldincreased infectivity for EGFRvIII-bearing human gliomaU87 cells showing enhanced vector specificity and tumorcell damage88

59 RNA Interference

Since its discovery nearly two decades ago RNA inter-ference (RNAi) has been lauded as the next generation ingene therapy due to the unique pathway in which smallinterfering (siRNA) or microRNA (miRNA) can preventmRNA expression and silence- specific targeted geneseffectively89 RNAi cancer gene targets are pathways thatcontribute to tumor growth through increased tumor cellproliferation andor reduced tumor cell death RNAi canalso be used to target and silence gene products thatnegatively regulate the function of endogenous tumor sup-pressor genes as well as proteins involved in cellular senes-cence or protein stabilitydegradation However in vivostudies up until now have shown wide variation on thepotency of RNAi and its suppression activities as a resultof poor cellular uptake rapid renal clearance and nucle-ase degradation90 Also previous experiments have beenplagued with additional problems such as off-targeting andimmunogenic response9091 Nonetheless the characteri-zation of novel nanoparticle carriers and chemical mod-ifications to siRNA itself has addressed some of theseissues Suh and collegues developed a cationic lipid N N primeprime-dioleylglutamide linked by negatively charged glutamicacid to oleoylamine as a siRNA carrier92 It was ableto deliver siRNA to various cancer cells in vitro moreeffectively than other cationic liposomes and with reducedcytotoxicity Moreover results showed that it was effectivefor local in vivo siRNA delivery providing clear evidencethat target protein expression was knocked down in tumortissues92 In addition Chen et al developed a liposome-polycation-hyaluronic acid (LPH) nanoparticle formulationmodified with single-chain antibody fragment (GC4 scFv)for the systemic delivery of siRNA and miRNA in experi-mental lung metastasis of murine B16F10 melanoma Inhi-bition of c-Myc MDM2 and VEGF protein expression bysiRNA formulated with GC4 scFv modified LPH nanopar-ticles significantly suppressed B16F10 metastatic tumorgrowth while showing increased siRNA uptake within thelung tumors93

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510 Monoclonal Antibodies

Monoclonal antibodies (mAB) are monospecific antibod-ies that bind only to one particular antigenic determinantor epitope By blocking ligand binding andor signalingof growth receptors mABs have the capability to sen-sitize tumors to chemotherapeutic agents reduce growthrates and induce apoptosis Many different monoclonalantibodies are currently used in the therapy of cer-tain cancers such as Bevacizumab Imatinib BortezomibGefitinib Sorafenib Tositumomab Tamoxifen and Ritux-imab which are all FDA-approved therapies for cancer todate94 In some in vivo applications the antibody itself issufficient and once bound to its target mAB triggers theeffector cell mechanisms of the immune system An excel-lent 2010 review by Weiner et al addresses the specificimmunologic pathways in which mABs interact with can-cer cells94 mAB may also be coupled to another moleculesuch as a fluorescent molecule to aid in imaging or aradioactive isotope such as Iodine-125 to aid in killing can-cer cells with radioimmunotherapy95 However in a recentstudy of radioimmunotherapy it was concluded that a sin-gle -emitter 90Y coupled to each antibody had a signifi-cantly lower biological effective dose and was insufficientto treat non small-cell lung cancer than a single 5 nm90Y2O3 nanoparticle96 In the application of nanoparticlesmAB can be used as efficient targeting ligands Workby Park and associates shows the targeting specificityof a modified lymphocyte function-associated antigen-1domain tuned to have variable affinities for intercellularadhesion molecule (ICAM)-1 Applying this antibody totheir nanoparticle system amphiphilic urethane acrylatenonionomer (UAN) researchers were able to demonstrateefficient encapsulation of a FITC marker and a protea-some inhibitor (celastrol) as well as the targeted deliveryto HeLa cells producing a more potent cytotoxicity withequal amounts of drug than with the untargeted UAN97

511 Aptamers

Aptamers are synthetic oligonucleotide ligands or peptidesthat bear unique three-dimensional conformations capa-ble of binding to target antigens with high affinity andspecificity Aptamers bind to their targets to effectivelyillicit little or none immunogenicity and possess molecu-lar recognition properties similar to monoclonal antibod-ies They have been applied to drug delivery systems asligands to enhance selectivity98 RNA aptamer OPN-R3has been shown in an in vivo xenograft model of breastcancer with MDA-MB-231 cells to significantly decreaselocal progression and distant metastases By day 20 tumorvolume in the modified OPN-R3 treated group was 18ndash20-fold smaller than the tumor volume in mutant OPN-R3and no treatment groups99 Another aptamer SM20 iso-lated against plasminogen activator inhibitor-1 has demon-strated in vitro therapeutic potential as an antimetastatic

agent and could possibly be used as an adjuvant to tradi-tional chemotherapy for breast cancer100 Several aptamershave been recently isolated for potential treatment of othercancers such as glioblastoma T cell leukaemia and epithe-lial cancer cells in the breast colon lung ovaries andpancreas98 Finally apatmers can be used as a targetingmoiety to be conjugated to a certain drug delivery for-mulation or may act as modalities with characteristics ofintrinsic specificity100

6 CURRENT CLINICAL PROGRESS OFNANONCOLOGY THERAPEUTICS

In this section nanoparticles for cancer therapy that havealready reached the clinic are discussed A few sys-tems having been approved and many are still ongoingin human clinical trials (Table I) As described earliernon-targeting nanoparticles utilize leaky vasculature oftumors to reach via passive targeting PEGylation has beenapplied to various proteins enzymes cytokines and mon-oclonal antibody fragments to increase circulatory half-life and decrease antigenicity3349101102 Many clinicaltrials involving PEGylation of nanoparticles are in differ-ent phase trials at the moment such as PEG-InterferonAlfa-2b PEGylated recombinant human Hyaluronidase(PEGPH20) PEG conjugate of SN38 (EZN-2208) toname a few An interesting PEgylated complex is PEG-ADI 20 currently undergoing Phase II studies Argininedeiminase (ADI) is a microbial enzyme that degrades argi-nine Certain cancer cells deficient in producing argininethrough argininosuccinate synthase obtain exogenous argi-nine from circulation PEG-ADI 20 depletes arginine con-centrations in the blood thereby controlling and reducingtumor growth103 The previous phase III study was com-pleted on un-resectable hepatocellular carcinoma knownfor its poor prognosis In a study with 35 patients allpatients exhibited blood arginine levels lower than 2 uMwhile 2 patients became stable 1 patient became resectableand 28 progressed with a mean duration before progres-sion of 34 months103 On the other hand CRLX101 isa nanoparticle drug delivery system comprised of thechemotherapeutic camptothecin (CPT) conjugated to acyclodextrin-based polymer CRLX101 was designed toincrease the exposure of tumor cells to CPT while reducingside effects Anti-cancer activity of camptothecin is due inpart to the inhibition of DNA topoisomerase I but has beenprevented from use as an anti-cancer drug due to poor sol-ubility lack of activity and excessive toxicity104 HoweverCRLX101 nanoparticle was shown to have significantlyhigher antitumor activity with lower dosing while main-taining the levels of free camptothecin in the blood to aminimum It is noteworthy that it was effective in a num-ber of tumors resistant to irinotecan treatment CRLX101is currently undergoing Phase IB2A trials104 Ultimatelyactive targeting through the inclusion of a targeting lig-and on the nanoparticles is envisioned to provide the

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Table I Nanoncology in clinical development

Class Carrier Active agent Target Clinical status Indication (s) Ref

LiposomesDaunoXome Liposome Daunorubicin

citrateNA Approved Chronic myelogenous

leukemia neuroblastoma3

DOTAP Chol-FUS1 Liposome Plasmid DNA(FUS1)

NA Phase I Metastatic non-small celllung cancer

114

SGT-53 Liposome Plasmid DNAp53 W-T

Transferrinreceptor

Phase I Advanced Solid Tumors 115

MBP 426 Liposome Oxaliplatin Transferrinreceptor

Phase lbII Advanced or MetastaticSolid Tumors

105

PEGylatedDoxil PEGylaled-Liposome Doxorubicin NA Approved Ovanan cancer recurrent

breast cancer2 56

Oncospar PEGylaled-Asparagnase

L-asparagnase NA Approved Acute lymphoblasticleukemia

2

CYT-6091 PEGylaled-ThiolGold

RecombinantTNF-

Tumor necrosisfactor recepteor

Phase II Advanced solid tumors 110

ADI-PEG 20 PEGylated-ArginineDeiminase

Augininedeiminase

NA Phase II Hepatocellular carcinomaMetastatic melanomarelapsed small cell lungcancer

103

PeptideAbraxane Albumin Paclitaxel NA Approved Metastatic non-small cell

lung cancer2 3

Ontak Interkeukin-2engineered protein

Diphtheria toxin Interleukin-2receptors

Approved Cutaneous T-cell lymphoma 3

AMG 386 Peptibody Recombinantpeptide-Fcfusion protein

Angiopoietin 1and 2

Phase III Various cancers 113

PolymericCALAA-01 Cyclodextrin Small interfering

RNATransferrin

receptorPhase I Solid tumors 107 108

XMT-1001 Fleximer Camptothecin Prodrug activation Phase I Advanced solid tumors 111Genexol Polymeric micelles Paclitaxel NA Phase II Various cancers 52CT-2103 Poly-L-glutmate Paclitaxel NA Phase II Various cancers 112

Antibodya

Trastuzumab HumanizedMonoclonalantibody

Antibody CD340 receptor Approved HER2-positive metastaticbreast cancer

3 4 94

Rituximab Chimeric monoclonalAntibody

Antibody Protein CD20 Approved Leukemias and lymphomas 3 4 94

a Currently there are over 20 FDA-approved monoclonal antibodies for use in cancer therapy

most effective therapy A targeting nanoparticle in Pha-seIBII study is MbP-426 which contains the cytotoxicplatinum-based drug oxaliplatin in a transferrin-conjugatedlipopsome105 Transferrin receptors (TfR) overexpressedon tumor cells allow selective uptake via Tf-TfR interac-tion Outcome of Phase I trial with 39 patients showed that15 patients had stable disease after 2 cycles 3 patients withcolon carcinoma refractory to conventional oxaliplatin hadstable disease for 4-6 cycles and 2 patients had 12 and26 decrease in target lesions105 Further Rexin-G is amurine leukemia virus-based retrovector nanoparticle thatcontains a cytocidal dominant negative cyclin-G1 constructand allows for the functional restoration of tumor sup-pressor microRNA-122a It has been found that block-ade of cyclin G1 may restore intrinsic molecular form

of tumor suppression106 Rexin-G has been found to havelow immunogenicity with preferential selection of rapidly-dividing cells over normal non-dividing or differentiatedcells In Phase II clinical trials 88 of patients had partialresponses or stable disease while the overall survival ratewas 6 months for all 22 patients106 On a further note sometargeted nanoparticles can have active mechanisms for theintracellular release of the therapeutic moiety CALAA-01is a targeted nanoparticle that has a high drug (siRNA)payload per targeting ligand tested and proven multiva-lent binding to cancer cell surfaces and an active siRNArelease mechanism that is triggered upon the recogni-tion of intracellular localization by a pH decline belowa value of 60107108 This nanoparticle system containsa cyclodextrin-based polymer human transferring protein

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targeting ligand hydrophilic polymer (PEG) and siRNAdesigned to reduce expression of RRM2 It is currentlyundergoing Phase I clinical trials for a dose-escalatingstudy in the treatment of solid tumor cancer107 An aptamerfor potential cancer treatment is AS1411109 It binds nucle-olin on the surface of cancer cells and induces apoptosisIn a dose escalation (1 mgkgday to 10 mgkgday) clin-ical study AS1411 showed positive responses in patientswith advanced solid tumors without any adverse effects109

Recently in a randomized phase II clinical trials a10 mgkgday or 40 mgkgday dose of AS1411 com-bined with high-dose cytarabine was well tolerated andshowed promising signs of activity in patients with pri-mary refractory or relapsed acute myeloid leukaemia Itis also currently being evaluated for treatment of breastcancer110 In another example Aurimune is a colloidalAu nanoparticle which delivers recombinant TNF- tocancer tumors TNF is attached to the Au nanoparticle withthiol-derivatized PEG which allows the nanoparticle toflow through the blood stream without causing a clearanceresponse110 Clinical data to date reports that Aurimunehas no antibody or immune responses and is well-toleratedbeyond the known maximum dose for TNF-110

7 CLOSING REMARKS FUTUREPERSPECTIVE

Over the past decades nanoncology (therapeutics anddiagnostics) has evolved from nano-sized drug particlesto bio-functional nanomaterials capable of deliveringheat treatment ionizing radiation andor chemothera-peutic agents From simple liposomal formulations andconjugation of PEG to antibody-conjugated nanoparti-cle chemotherapeutic and RNAi delivery nanoncology isbecoming more intricate smart and multi-functional Fur-ther the differences between cancerous and normal cellsincluding uncontrolled proliferation insensitivity to nega-tive growth regulation and anti-growth signals angiogen-esis and metastasis can be now be effectively exploitedThere is no doubt that nanoparticle therapeutics with theincreasing multi-functionality will continue to expand inthe future Investments in research development and per-formance trials are considerably large Sponsoring agen-cies in both private and government sectors should createeconomic strategies and innovative management to makesuch biotechnologies more cost-effective and easily acces-sible for patients across Although many challenges existfor the transition of nanoparticles from bench to bed theirpotential advantages will drive successful development andemerge as a new class of undeniable anti-cancer thera-peutic Finally (i) individualizedpersonalized oncology inwhich cancer detection diagnosis and therapy can be mod-ified to best fit the tumor molecular profile of a patientand (ii) predictive oncology in which genetic biochemicaland molecular markers are orchestrated to predict disease

development progression and clinical outcomes will cer-tainly shape the nanoncologic strategies of the near future

Acknowledgments This work was supported by theSouth Korean Ministry of Knowledge and Education(MKE) and the Incheon Free Economic Zone (IFEZ) inthe framework of several funding operating grants to theUtah-Inha DDS amp Advanced Therapeutics Research Cen-ter KR

References and Notes

1 N Portney and M Ozkan Anal Bioanal Chem 3 620 (2006)2 M Ferrari Nat Rev Cancer 3 161 (2005)3 T M Allen Nat Rev Cancer 1 0750 (2002)4 J S Ross D P Schenkein and R Pietrusko Am J Clin Pathol

4 598 (2004)5 M Wang and M Thanou Drug Resist Updat 2 90 (2010)6 A Jones and A L Harris Cancer J Sci Am 4 209 (1998)7 D F Baban and L W Seymour Adv Drug Deliv 1 109 (1998)8 H Maeda Adv Enzyme Regul 41 189 (2001)9 K Greish Methods Mol Biol 624 25 (2010)10 A K Iyer K Greish T Seki S Okazaki J Fang K Takeshita

and H Maeda Drug Discov Today 11 812 (2006)11 K N Sugahara T Teesalu P P Karmali V R Kotamraju

L Agemy D R Greenwald and E Ruoslahti Science 5981 1031(2010)

12 R G Boyle and S Travess Anticancer Agents Med Chem 64 281(2006)

13 J M Brown and W R Wilson Nat Rev Cancer 4 437 (2004)14 D Kim E S Lee K Park I C Kwon and Y H Bae Pharm

Res 9 2074 (2008)15 L M Bareford and P W Swaan Adv Drug Deliv Rev 8 748

(2007)16 N F Saba X Wang S Muumlller M Tighiouart K Cho S Nie

Z Chen and D M Shin Head Neck 4 475 (2009)17 Y Lu L C Xu N Parker E Westrick J A Reddy M Vetzel

P S Low and C P Leamon Mol Cancer Ther 12 3258 (2006)18 E I Deryugina and J P Quigley Cancer Metastasis Rev 25 9

(2006)19 A M Mansour J Drevs N Esser F M Hamada O A Badary

C Unger I Fichtner and F Kratz Cancer Res 14 4062 (2003)20 H Hatakeyama H Akita E Ishida K Hashimoto H Kobayashi

T Aoki J Yasuda K Obata H Kikuchi T Ishida H Kiwadaand H Harashima Int J Pharm 1ndash2 194 (2007)

21 A Raz L Meromsky and R Lotan Cancer Res 7 3667 (1986)22 E Gorelik U Galili and A Raz Cancer Metastasis Rev 3ndash4 245

(2001)23 C Bies C M Lehr and J F Woodley Adv Drug Deliv Rev

4 425 (2004)24 H Glavinas P Krajcsi J Cserepes and B Sarkadi Curr Drug

Deliv 1 27 (2004)25 M Dean T Fojo and S Bates Nat Rev Cancer 4 275 (2005)26 T Kobayashi T Ishida Y Okada S Ise H Harashima and

H Kiwada Int J Pharm 1ndash2 94 (2007)27 A M Chen M Zhang D Wei D Stueber O Taratula T Minko

and H He Small 23 2673 (2009)28 J M Koziara P R Lockman D D Allen and R J Mumper

Pharm Res 11 1772 (2003)29 S C Steiniger J Kreuter A S Khalansky I N Skidan A I

Bobruskin Z S Smirnova S E Severin R Uhl M Kock K DGeiger and S E Gelperina Int J Cancer 5 759 (2004)

30 J Wu T Akaike and H Maeda Cancer Res 1 159 (1998)31 M A Deli Biochim Biophys Acta 4 892 (2009)

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or biological origin7980 As solid tumor develops it out-grows its blood supply which results in the formation ofa hypoxic semi-necrotic tumor core and dormant tumorcells send out chemical signals that recruit macrophagesinto the core Macrophages begin to rebuild the bloodsupply allowing the tumor to start growing again8182

Muthana et al loaded human monocytes with MNPs plac-ing magnets near the site of a human prostate tumor grownin mice82 The MNP-loaded monocytes carrying a reportergene invaded the tumor at a rate more than three timesthat of the non-loaded cells82 This demonstration of mag-netic targeting shows that MNP-loaded cells circulatingin the body can be attracted to the tumor site where anexternal magnet is placed allowing a higher proportion ofloaded cells to respond to chemical signals from the tumorcore In addition the loaded monocytes were able to reachthe poorly vascularized peri-necrotic regions of the tumorthat are normally difficult to target As the moncytes areloaded with MNPs they can then be destroyed by hyper-thermia after delivering a therapeutic drug or gene8182

Classes of MNPs include metallic bimetallic and super-paramagnetic iron oxide nanoparticles widely-knows asSPIONs SPIONS are favored because due to low toxicityprofile and their reactive surface that can be readily modi-fied with biocompatible coatings87 This flexibility has ledto SPION use in magnetic separation biosensor in vivomedical imaging drug delivery tissue repair and hyper-thermia applications84 Yu et al preciously showed thatthermally crosslinked SPIONs loaded with doxorubicinhad potential as both an imaging and therapeutic deliverysystem83 This DoxTCL-SPION was also demonstratedto efficiently reach tumor sites and release the drug withoutany active targeting from ligandsantibodies or magneticfield largely due to the EPR effect83

58 Viral Nanoparticles

A variety of viruses including cowpea mosaic viruscanine parvovirus adenovirus coxsackie virus measlesvirus along with virions and virus-like particles have beendeployed for biomedical and nanotechnology applicationsthat include tissue targeting and drug delivery84 Target-ing molecules and peptides can be produced in a bio-logically functional form on the capsid surface throughchemical conjugation or gene expression Several lig-ands including transferrin folic acid and single-chainantibodies have been conjugated to viruses for specifictumor targeting84 Further a subset of viruses such ascanine parvovirus have a natural affinity for receptors liketransferrins that are up-regulated in a variety of tumorcells85 Adenoviral vectors offer many advantages for can-cer gene therapy including high transduction efficiencyyet safety concerns related to immunogenic response haveled to a cautious approach of their use in human clini-cal trials86 To overcome these obstacles hybrid vectors

combining both viral and non-viral elements are beingdeveloped Adenovirus coated with an arginine-graftedbioreducible polymer (ABP) via electrostatic interaction isone example ABP-coated complexes were shown to havesignificantly reduced the innate immune response whileproducing higher levels of transgene expression8687 Fur-thermore herpes simplex virus (HSV) vectors are alreadyin early phase human clinical trials for recurrent malignantglioblastoma A mutant form (vIII) of epidermal growthfactor receptor (EGFR) present in glioma tumor is rec-ognized by a single-chain antibody designated MR1-1HSV virions bearing MR1-1-modified gC had five-foldincreased infectivity for EGFRvIII-bearing human gliomaU87 cells showing enhanced vector specificity and tumorcell damage88

59 RNA Interference

Since its discovery nearly two decades ago RNA inter-ference (RNAi) has been lauded as the next generation ingene therapy due to the unique pathway in which smallinterfering (siRNA) or microRNA (miRNA) can preventmRNA expression and silence- specific targeted geneseffectively89 RNAi cancer gene targets are pathways thatcontribute to tumor growth through increased tumor cellproliferation andor reduced tumor cell death RNAi canalso be used to target and silence gene products thatnegatively regulate the function of endogenous tumor sup-pressor genes as well as proteins involved in cellular senes-cence or protein stabilitydegradation However in vivostudies up until now have shown wide variation on thepotency of RNAi and its suppression activities as a resultof poor cellular uptake rapid renal clearance and nucle-ase degradation90 Also previous experiments have beenplagued with additional problems such as off-targeting andimmunogenic response9091 Nonetheless the characteri-zation of novel nanoparticle carriers and chemical mod-ifications to siRNA itself has addressed some of theseissues Suh and collegues developed a cationic lipid N N primeprime-dioleylglutamide linked by negatively charged glutamicacid to oleoylamine as a siRNA carrier92 It was ableto deliver siRNA to various cancer cells in vitro moreeffectively than other cationic liposomes and with reducedcytotoxicity Moreover results showed that it was effectivefor local in vivo siRNA delivery providing clear evidencethat target protein expression was knocked down in tumortissues92 In addition Chen et al developed a liposome-polycation-hyaluronic acid (LPH) nanoparticle formulationmodified with single-chain antibody fragment (GC4 scFv)for the systemic delivery of siRNA and miRNA in experi-mental lung metastasis of murine B16F10 melanoma Inhi-bition of c-Myc MDM2 and VEGF protein expression bysiRNA formulated with GC4 scFv modified LPH nanopar-ticles significantly suppressed B16F10 metastatic tumorgrowth while showing increased siRNA uptake within thelung tumors93

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510 Monoclonal Antibodies

Monoclonal antibodies (mAB) are monospecific antibod-ies that bind only to one particular antigenic determinantor epitope By blocking ligand binding andor signalingof growth receptors mABs have the capability to sen-sitize tumors to chemotherapeutic agents reduce growthrates and induce apoptosis Many different monoclonalantibodies are currently used in the therapy of cer-tain cancers such as Bevacizumab Imatinib BortezomibGefitinib Sorafenib Tositumomab Tamoxifen and Ritux-imab which are all FDA-approved therapies for cancer todate94 In some in vivo applications the antibody itself issufficient and once bound to its target mAB triggers theeffector cell mechanisms of the immune system An excel-lent 2010 review by Weiner et al addresses the specificimmunologic pathways in which mABs interact with can-cer cells94 mAB may also be coupled to another moleculesuch as a fluorescent molecule to aid in imaging or aradioactive isotope such as Iodine-125 to aid in killing can-cer cells with radioimmunotherapy95 However in a recentstudy of radioimmunotherapy it was concluded that a sin-gle -emitter 90Y coupled to each antibody had a signifi-cantly lower biological effective dose and was insufficientto treat non small-cell lung cancer than a single 5 nm90Y2O3 nanoparticle96 In the application of nanoparticlesmAB can be used as efficient targeting ligands Workby Park and associates shows the targeting specificityof a modified lymphocyte function-associated antigen-1domain tuned to have variable affinities for intercellularadhesion molecule (ICAM)-1 Applying this antibody totheir nanoparticle system amphiphilic urethane acrylatenonionomer (UAN) researchers were able to demonstrateefficient encapsulation of a FITC marker and a protea-some inhibitor (celastrol) as well as the targeted deliveryto HeLa cells producing a more potent cytotoxicity withequal amounts of drug than with the untargeted UAN97

511 Aptamers

Aptamers are synthetic oligonucleotide ligands or peptidesthat bear unique three-dimensional conformations capa-ble of binding to target antigens with high affinity andspecificity Aptamers bind to their targets to effectivelyillicit little or none immunogenicity and possess molecu-lar recognition properties similar to monoclonal antibod-ies They have been applied to drug delivery systems asligands to enhance selectivity98 RNA aptamer OPN-R3has been shown in an in vivo xenograft model of breastcancer with MDA-MB-231 cells to significantly decreaselocal progression and distant metastases By day 20 tumorvolume in the modified OPN-R3 treated group was 18ndash20-fold smaller than the tumor volume in mutant OPN-R3and no treatment groups99 Another aptamer SM20 iso-lated against plasminogen activator inhibitor-1 has demon-strated in vitro therapeutic potential as an antimetastatic

agent and could possibly be used as an adjuvant to tradi-tional chemotherapy for breast cancer100 Several aptamershave been recently isolated for potential treatment of othercancers such as glioblastoma T cell leukaemia and epithe-lial cancer cells in the breast colon lung ovaries andpancreas98 Finally apatmers can be used as a targetingmoiety to be conjugated to a certain drug delivery for-mulation or may act as modalities with characteristics ofintrinsic specificity100

6 CURRENT CLINICAL PROGRESS OFNANONCOLOGY THERAPEUTICS

In this section nanoparticles for cancer therapy that havealready reached the clinic are discussed A few sys-tems having been approved and many are still ongoingin human clinical trials (Table I) As described earliernon-targeting nanoparticles utilize leaky vasculature oftumors to reach via passive targeting PEGylation has beenapplied to various proteins enzymes cytokines and mon-oclonal antibody fragments to increase circulatory half-life and decrease antigenicity3349101102 Many clinicaltrials involving PEGylation of nanoparticles are in differ-ent phase trials at the moment such as PEG-InterferonAlfa-2b PEGylated recombinant human Hyaluronidase(PEGPH20) PEG conjugate of SN38 (EZN-2208) toname a few An interesting PEgylated complex is PEG-ADI 20 currently undergoing Phase II studies Argininedeiminase (ADI) is a microbial enzyme that degrades argi-nine Certain cancer cells deficient in producing argininethrough argininosuccinate synthase obtain exogenous argi-nine from circulation PEG-ADI 20 depletes arginine con-centrations in the blood thereby controlling and reducingtumor growth103 The previous phase III study was com-pleted on un-resectable hepatocellular carcinoma knownfor its poor prognosis In a study with 35 patients allpatients exhibited blood arginine levels lower than 2 uMwhile 2 patients became stable 1 patient became resectableand 28 progressed with a mean duration before progres-sion of 34 months103 On the other hand CRLX101 isa nanoparticle drug delivery system comprised of thechemotherapeutic camptothecin (CPT) conjugated to acyclodextrin-based polymer CRLX101 was designed toincrease the exposure of tumor cells to CPT while reducingside effects Anti-cancer activity of camptothecin is due inpart to the inhibition of DNA topoisomerase I but has beenprevented from use as an anti-cancer drug due to poor sol-ubility lack of activity and excessive toxicity104 HoweverCRLX101 nanoparticle was shown to have significantlyhigher antitumor activity with lower dosing while main-taining the levels of free camptothecin in the blood to aminimum It is noteworthy that it was effective in a num-ber of tumors resistant to irinotecan treatment CRLX101is currently undergoing Phase IB2A trials104 Ultimatelyactive targeting through the inclusion of a targeting lig-and on the nanoparticles is envisioned to provide the

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Nanoncology A State-of-Art Update Joo et al

Table I Nanoncology in clinical development

Class Carrier Active agent Target Clinical status Indication (s) Ref

LiposomesDaunoXome Liposome Daunorubicin

citrateNA Approved Chronic myelogenous

leukemia neuroblastoma3

DOTAP Chol-FUS1 Liposome Plasmid DNA(FUS1)

NA Phase I Metastatic non-small celllung cancer

114

SGT-53 Liposome Plasmid DNAp53 W-T

Transferrinreceptor

Phase I Advanced Solid Tumors 115

MBP 426 Liposome Oxaliplatin Transferrinreceptor

Phase lbII Advanced or MetastaticSolid Tumors

105

PEGylatedDoxil PEGylaled-Liposome Doxorubicin NA Approved Ovanan cancer recurrent

breast cancer2 56

Oncospar PEGylaled-Asparagnase

L-asparagnase NA Approved Acute lymphoblasticleukemia

2

CYT-6091 PEGylaled-ThiolGold

RecombinantTNF-

Tumor necrosisfactor recepteor

Phase II Advanced solid tumors 110

ADI-PEG 20 PEGylated-ArginineDeiminase

Augininedeiminase

NA Phase II Hepatocellular carcinomaMetastatic melanomarelapsed small cell lungcancer

103

PeptideAbraxane Albumin Paclitaxel NA Approved Metastatic non-small cell

lung cancer2 3

Ontak Interkeukin-2engineered protein

Diphtheria toxin Interleukin-2receptors

Approved Cutaneous T-cell lymphoma 3

AMG 386 Peptibody Recombinantpeptide-Fcfusion protein

Angiopoietin 1and 2

Phase III Various cancers 113

PolymericCALAA-01 Cyclodextrin Small interfering

RNATransferrin

receptorPhase I Solid tumors 107 108

XMT-1001 Fleximer Camptothecin Prodrug activation Phase I Advanced solid tumors 111Genexol Polymeric micelles Paclitaxel NA Phase II Various cancers 52CT-2103 Poly-L-glutmate Paclitaxel NA Phase II Various cancers 112

Antibodya

Trastuzumab HumanizedMonoclonalantibody

Antibody CD340 receptor Approved HER2-positive metastaticbreast cancer

3 4 94

Rituximab Chimeric monoclonalAntibody

Antibody Protein CD20 Approved Leukemias and lymphomas 3 4 94

a Currently there are over 20 FDA-approved monoclonal antibodies for use in cancer therapy

most effective therapy A targeting nanoparticle in Pha-seIBII study is MbP-426 which contains the cytotoxicplatinum-based drug oxaliplatin in a transferrin-conjugatedlipopsome105 Transferrin receptors (TfR) overexpressedon tumor cells allow selective uptake via Tf-TfR interac-tion Outcome of Phase I trial with 39 patients showed that15 patients had stable disease after 2 cycles 3 patients withcolon carcinoma refractory to conventional oxaliplatin hadstable disease for 4-6 cycles and 2 patients had 12 and26 decrease in target lesions105 Further Rexin-G is amurine leukemia virus-based retrovector nanoparticle thatcontains a cytocidal dominant negative cyclin-G1 constructand allows for the functional restoration of tumor sup-pressor microRNA-122a It has been found that block-ade of cyclin G1 may restore intrinsic molecular form

of tumor suppression106 Rexin-G has been found to havelow immunogenicity with preferential selection of rapidly-dividing cells over normal non-dividing or differentiatedcells In Phase II clinical trials 88 of patients had partialresponses or stable disease while the overall survival ratewas 6 months for all 22 patients106 On a further note sometargeted nanoparticles can have active mechanisms for theintracellular release of the therapeutic moiety CALAA-01is a targeted nanoparticle that has a high drug (siRNA)payload per targeting ligand tested and proven multiva-lent binding to cancer cell surfaces and an active siRNArelease mechanism that is triggered upon the recogni-tion of intracellular localization by a pH decline belowa value of 60107108 This nanoparticle system containsa cyclodextrin-based polymer human transferring protein

10 J Bionanosci 4 1ndash13 2010

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Joo et al Nanoncology A State-of-Art Update

targeting ligand hydrophilic polymer (PEG) and siRNAdesigned to reduce expression of RRM2 It is currentlyundergoing Phase I clinical trials for a dose-escalatingstudy in the treatment of solid tumor cancer107 An aptamerfor potential cancer treatment is AS1411109 It binds nucle-olin on the surface of cancer cells and induces apoptosisIn a dose escalation (1 mgkgday to 10 mgkgday) clin-ical study AS1411 showed positive responses in patientswith advanced solid tumors without any adverse effects109

Recently in a randomized phase II clinical trials a10 mgkgday or 40 mgkgday dose of AS1411 com-bined with high-dose cytarabine was well tolerated andshowed promising signs of activity in patients with pri-mary refractory or relapsed acute myeloid leukaemia Itis also currently being evaluated for treatment of breastcancer110 In another example Aurimune is a colloidalAu nanoparticle which delivers recombinant TNF- tocancer tumors TNF is attached to the Au nanoparticle withthiol-derivatized PEG which allows the nanoparticle toflow through the blood stream without causing a clearanceresponse110 Clinical data to date reports that Aurimunehas no antibody or immune responses and is well-toleratedbeyond the known maximum dose for TNF-110

7 CLOSING REMARKS FUTUREPERSPECTIVE

Over the past decades nanoncology (therapeutics anddiagnostics) has evolved from nano-sized drug particlesto bio-functional nanomaterials capable of deliveringheat treatment ionizing radiation andor chemothera-peutic agents From simple liposomal formulations andconjugation of PEG to antibody-conjugated nanoparti-cle chemotherapeutic and RNAi delivery nanoncology isbecoming more intricate smart and multi-functional Fur-ther the differences between cancerous and normal cellsincluding uncontrolled proliferation insensitivity to nega-tive growth regulation and anti-growth signals angiogen-esis and metastasis can be now be effectively exploitedThere is no doubt that nanoparticle therapeutics with theincreasing multi-functionality will continue to expand inthe future Investments in research development and per-formance trials are considerably large Sponsoring agen-cies in both private and government sectors should createeconomic strategies and innovative management to makesuch biotechnologies more cost-effective and easily acces-sible for patients across Although many challenges existfor the transition of nanoparticles from bench to bed theirpotential advantages will drive successful development andemerge as a new class of undeniable anti-cancer thera-peutic Finally (i) individualizedpersonalized oncology inwhich cancer detection diagnosis and therapy can be mod-ified to best fit the tumor molecular profile of a patientand (ii) predictive oncology in which genetic biochemicaland molecular markers are orchestrated to predict disease

development progression and clinical outcomes will cer-tainly shape the nanoncologic strategies of the near future

Acknowledgments This work was supported by theSouth Korean Ministry of Knowledge and Education(MKE) and the Incheon Free Economic Zone (IFEZ) inthe framework of several funding operating grants to theUtah-Inha DDS amp Advanced Therapeutics Research Cen-ter KR

References and Notes

1 N Portney and M Ozkan Anal Bioanal Chem 3 620 (2006)2 M Ferrari Nat Rev Cancer 3 161 (2005)3 T M Allen Nat Rev Cancer 1 0750 (2002)4 J S Ross D P Schenkein and R Pietrusko Am J Clin Pathol

4 598 (2004)5 M Wang and M Thanou Drug Resist Updat 2 90 (2010)6 A Jones and A L Harris Cancer J Sci Am 4 209 (1998)7 D F Baban and L W Seymour Adv Drug Deliv 1 109 (1998)8 H Maeda Adv Enzyme Regul 41 189 (2001)9 K Greish Methods Mol Biol 624 25 (2010)10 A K Iyer K Greish T Seki S Okazaki J Fang K Takeshita

and H Maeda Drug Discov Today 11 812 (2006)11 K N Sugahara T Teesalu P P Karmali V R Kotamraju

L Agemy D R Greenwald and E Ruoslahti Science 5981 1031(2010)

12 R G Boyle and S Travess Anticancer Agents Med Chem 64 281(2006)

13 J M Brown and W R Wilson Nat Rev Cancer 4 437 (2004)14 D Kim E S Lee K Park I C Kwon and Y H Bae Pharm

Res 9 2074 (2008)15 L M Bareford and P W Swaan Adv Drug Deliv Rev 8 748

(2007)16 N F Saba X Wang S Muumlller M Tighiouart K Cho S Nie

Z Chen and D M Shin Head Neck 4 475 (2009)17 Y Lu L C Xu N Parker E Westrick J A Reddy M Vetzel

P S Low and C P Leamon Mol Cancer Ther 12 3258 (2006)18 E I Deryugina and J P Quigley Cancer Metastasis Rev 25 9

(2006)19 A M Mansour J Drevs N Esser F M Hamada O A Badary

C Unger I Fichtner and F Kratz Cancer Res 14 4062 (2003)20 H Hatakeyama H Akita E Ishida K Hashimoto H Kobayashi

T Aoki J Yasuda K Obata H Kikuchi T Ishida H Kiwadaand H Harashima Int J Pharm 1ndash2 194 (2007)

21 A Raz L Meromsky and R Lotan Cancer Res 7 3667 (1986)22 E Gorelik U Galili and A Raz Cancer Metastasis Rev 3ndash4 245

(2001)23 C Bies C M Lehr and J F Woodley Adv Drug Deliv Rev

4 425 (2004)24 H Glavinas P Krajcsi J Cserepes and B Sarkadi Curr Drug

Deliv 1 27 (2004)25 M Dean T Fojo and S Bates Nat Rev Cancer 4 275 (2005)26 T Kobayashi T Ishida Y Okada S Ise H Harashima and

H Kiwada Int J Pharm 1ndash2 94 (2007)27 A M Chen M Zhang D Wei D Stueber O Taratula T Minko

and H He Small 23 2673 (2009)28 J M Koziara P R Lockman D D Allen and R J Mumper

Pharm Res 11 1772 (2003)29 S C Steiniger J Kreuter A S Khalansky I N Skidan A I

Bobruskin Z S Smirnova S E Severin R Uhl M Kock K DGeiger and S E Gelperina Int J Cancer 5 759 (2004)

30 J Wu T Akaike and H Maeda Cancer Res 1 159 (1998)31 M A Deli Biochim Biophys Acta 4 892 (2009)

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Joo et al Nanoncology A State-of-Art Update

510 Monoclonal Antibodies

Monoclonal antibodies (mAB) are monospecific antibod-ies that bind only to one particular antigenic determinantor epitope By blocking ligand binding andor signalingof growth receptors mABs have the capability to sen-sitize tumors to chemotherapeutic agents reduce growthrates and induce apoptosis Many different monoclonalantibodies are currently used in the therapy of cer-tain cancers such as Bevacizumab Imatinib BortezomibGefitinib Sorafenib Tositumomab Tamoxifen and Ritux-imab which are all FDA-approved therapies for cancer todate94 In some in vivo applications the antibody itself issufficient and once bound to its target mAB triggers theeffector cell mechanisms of the immune system An excel-lent 2010 review by Weiner et al addresses the specificimmunologic pathways in which mABs interact with can-cer cells94 mAB may also be coupled to another moleculesuch as a fluorescent molecule to aid in imaging or aradioactive isotope such as Iodine-125 to aid in killing can-cer cells with radioimmunotherapy95 However in a recentstudy of radioimmunotherapy it was concluded that a sin-gle -emitter 90Y coupled to each antibody had a signifi-cantly lower biological effective dose and was insufficientto treat non small-cell lung cancer than a single 5 nm90Y2O3 nanoparticle96 In the application of nanoparticlesmAB can be used as efficient targeting ligands Workby Park and associates shows the targeting specificityof a modified lymphocyte function-associated antigen-1domain tuned to have variable affinities for intercellularadhesion molecule (ICAM)-1 Applying this antibody totheir nanoparticle system amphiphilic urethane acrylatenonionomer (UAN) researchers were able to demonstrateefficient encapsulation of a FITC marker and a protea-some inhibitor (celastrol) as well as the targeted deliveryto HeLa cells producing a more potent cytotoxicity withequal amounts of drug than with the untargeted UAN97

511 Aptamers

Aptamers are synthetic oligonucleotide ligands or peptidesthat bear unique three-dimensional conformations capa-ble of binding to target antigens with high affinity andspecificity Aptamers bind to their targets to effectivelyillicit little or none immunogenicity and possess molecu-lar recognition properties similar to monoclonal antibod-ies They have been applied to drug delivery systems asligands to enhance selectivity98 RNA aptamer OPN-R3has been shown in an in vivo xenograft model of breastcancer with MDA-MB-231 cells to significantly decreaselocal progression and distant metastases By day 20 tumorvolume in the modified OPN-R3 treated group was 18ndash20-fold smaller than the tumor volume in mutant OPN-R3and no treatment groups99 Another aptamer SM20 iso-lated against plasminogen activator inhibitor-1 has demon-strated in vitro therapeutic potential as an antimetastatic

agent and could possibly be used as an adjuvant to tradi-tional chemotherapy for breast cancer100 Several aptamershave been recently isolated for potential treatment of othercancers such as glioblastoma T cell leukaemia and epithe-lial cancer cells in the breast colon lung ovaries andpancreas98 Finally apatmers can be used as a targetingmoiety to be conjugated to a certain drug delivery for-mulation or may act as modalities with characteristics ofintrinsic specificity100

6 CURRENT CLINICAL PROGRESS OFNANONCOLOGY THERAPEUTICS

In this section nanoparticles for cancer therapy that havealready reached the clinic are discussed A few sys-tems having been approved and many are still ongoingin human clinical trials (Table I) As described earliernon-targeting nanoparticles utilize leaky vasculature oftumors to reach via passive targeting PEGylation has beenapplied to various proteins enzymes cytokines and mon-oclonal antibody fragments to increase circulatory half-life and decrease antigenicity3349101102 Many clinicaltrials involving PEGylation of nanoparticles are in differ-ent phase trials at the moment such as PEG-InterferonAlfa-2b PEGylated recombinant human Hyaluronidase(PEGPH20) PEG conjugate of SN38 (EZN-2208) toname a few An interesting PEgylated complex is PEG-ADI 20 currently undergoing Phase II studies Argininedeiminase (ADI) is a microbial enzyme that degrades argi-nine Certain cancer cells deficient in producing argininethrough argininosuccinate synthase obtain exogenous argi-nine from circulation PEG-ADI 20 depletes arginine con-centrations in the blood thereby controlling and reducingtumor growth103 The previous phase III study was com-pleted on un-resectable hepatocellular carcinoma knownfor its poor prognosis In a study with 35 patients allpatients exhibited blood arginine levels lower than 2 uMwhile 2 patients became stable 1 patient became resectableand 28 progressed with a mean duration before progres-sion of 34 months103 On the other hand CRLX101 isa nanoparticle drug delivery system comprised of thechemotherapeutic camptothecin (CPT) conjugated to acyclodextrin-based polymer CRLX101 was designed toincrease the exposure of tumor cells to CPT while reducingside effects Anti-cancer activity of camptothecin is due inpart to the inhibition of DNA topoisomerase I but has beenprevented from use as an anti-cancer drug due to poor sol-ubility lack of activity and excessive toxicity104 HoweverCRLX101 nanoparticle was shown to have significantlyhigher antitumor activity with lower dosing while main-taining the levels of free camptothecin in the blood to aminimum It is noteworthy that it was effective in a num-ber of tumors resistant to irinotecan treatment CRLX101is currently undergoing Phase IB2A trials104 Ultimatelyactive targeting through the inclusion of a targeting lig-and on the nanoparticles is envisioned to provide the

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Nanoncology A State-of-Art Update Joo et al

Table I Nanoncology in clinical development

Class Carrier Active agent Target Clinical status Indication (s) Ref

LiposomesDaunoXome Liposome Daunorubicin

citrateNA Approved Chronic myelogenous

leukemia neuroblastoma3

DOTAP Chol-FUS1 Liposome Plasmid DNA(FUS1)

NA Phase I Metastatic non-small celllung cancer

114

SGT-53 Liposome Plasmid DNAp53 W-T

Transferrinreceptor

Phase I Advanced Solid Tumors 115

MBP 426 Liposome Oxaliplatin Transferrinreceptor

Phase lbII Advanced or MetastaticSolid Tumors

105

PEGylatedDoxil PEGylaled-Liposome Doxorubicin NA Approved Ovanan cancer recurrent

breast cancer2 56

Oncospar PEGylaled-Asparagnase

L-asparagnase NA Approved Acute lymphoblasticleukemia

2

CYT-6091 PEGylaled-ThiolGold

RecombinantTNF-

Tumor necrosisfactor recepteor

Phase II Advanced solid tumors 110

ADI-PEG 20 PEGylated-ArginineDeiminase

Augininedeiminase

NA Phase II Hepatocellular carcinomaMetastatic melanomarelapsed small cell lungcancer

103

PeptideAbraxane Albumin Paclitaxel NA Approved Metastatic non-small cell

lung cancer2 3

Ontak Interkeukin-2engineered protein

Diphtheria toxin Interleukin-2receptors

Approved Cutaneous T-cell lymphoma 3

AMG 386 Peptibody Recombinantpeptide-Fcfusion protein

Angiopoietin 1and 2

Phase III Various cancers 113

PolymericCALAA-01 Cyclodextrin Small interfering

RNATransferrin

receptorPhase I Solid tumors 107 108

XMT-1001 Fleximer Camptothecin Prodrug activation Phase I Advanced solid tumors 111Genexol Polymeric micelles Paclitaxel NA Phase II Various cancers 52CT-2103 Poly-L-glutmate Paclitaxel NA Phase II Various cancers 112

Antibodya

Trastuzumab HumanizedMonoclonalantibody

Antibody CD340 receptor Approved HER2-positive metastaticbreast cancer

3 4 94

Rituximab Chimeric monoclonalAntibody

Antibody Protein CD20 Approved Leukemias and lymphomas 3 4 94

a Currently there are over 20 FDA-approved monoclonal antibodies for use in cancer therapy

most effective therapy A targeting nanoparticle in Pha-seIBII study is MbP-426 which contains the cytotoxicplatinum-based drug oxaliplatin in a transferrin-conjugatedlipopsome105 Transferrin receptors (TfR) overexpressedon tumor cells allow selective uptake via Tf-TfR interac-tion Outcome of Phase I trial with 39 patients showed that15 patients had stable disease after 2 cycles 3 patients withcolon carcinoma refractory to conventional oxaliplatin hadstable disease for 4-6 cycles and 2 patients had 12 and26 decrease in target lesions105 Further Rexin-G is amurine leukemia virus-based retrovector nanoparticle thatcontains a cytocidal dominant negative cyclin-G1 constructand allows for the functional restoration of tumor sup-pressor microRNA-122a It has been found that block-ade of cyclin G1 may restore intrinsic molecular form

of tumor suppression106 Rexin-G has been found to havelow immunogenicity with preferential selection of rapidly-dividing cells over normal non-dividing or differentiatedcells In Phase II clinical trials 88 of patients had partialresponses or stable disease while the overall survival ratewas 6 months for all 22 patients106 On a further note sometargeted nanoparticles can have active mechanisms for theintracellular release of the therapeutic moiety CALAA-01is a targeted nanoparticle that has a high drug (siRNA)payload per targeting ligand tested and proven multiva-lent binding to cancer cell surfaces and an active siRNArelease mechanism that is triggered upon the recogni-tion of intracellular localization by a pH decline belowa value of 60107108 This nanoparticle system containsa cyclodextrin-based polymer human transferring protein

10 J Bionanosci 4 1ndash13 2010

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Joo et al Nanoncology A State-of-Art Update

targeting ligand hydrophilic polymer (PEG) and siRNAdesigned to reduce expression of RRM2 It is currentlyundergoing Phase I clinical trials for a dose-escalatingstudy in the treatment of solid tumor cancer107 An aptamerfor potential cancer treatment is AS1411109 It binds nucle-olin on the surface of cancer cells and induces apoptosisIn a dose escalation (1 mgkgday to 10 mgkgday) clin-ical study AS1411 showed positive responses in patientswith advanced solid tumors without any adverse effects109

Recently in a randomized phase II clinical trials a10 mgkgday or 40 mgkgday dose of AS1411 com-bined with high-dose cytarabine was well tolerated andshowed promising signs of activity in patients with pri-mary refractory or relapsed acute myeloid leukaemia Itis also currently being evaluated for treatment of breastcancer110 In another example Aurimune is a colloidalAu nanoparticle which delivers recombinant TNF- tocancer tumors TNF is attached to the Au nanoparticle withthiol-derivatized PEG which allows the nanoparticle toflow through the blood stream without causing a clearanceresponse110 Clinical data to date reports that Aurimunehas no antibody or immune responses and is well-toleratedbeyond the known maximum dose for TNF-110

7 CLOSING REMARKS FUTUREPERSPECTIVE

Over the past decades nanoncology (therapeutics anddiagnostics) has evolved from nano-sized drug particlesto bio-functional nanomaterials capable of deliveringheat treatment ionizing radiation andor chemothera-peutic agents From simple liposomal formulations andconjugation of PEG to antibody-conjugated nanoparti-cle chemotherapeutic and RNAi delivery nanoncology isbecoming more intricate smart and multi-functional Fur-ther the differences between cancerous and normal cellsincluding uncontrolled proliferation insensitivity to nega-tive growth regulation and anti-growth signals angiogen-esis and metastasis can be now be effectively exploitedThere is no doubt that nanoparticle therapeutics with theincreasing multi-functionality will continue to expand inthe future Investments in research development and per-formance trials are considerably large Sponsoring agen-cies in both private and government sectors should createeconomic strategies and innovative management to makesuch biotechnologies more cost-effective and easily acces-sible for patients across Although many challenges existfor the transition of nanoparticles from bench to bed theirpotential advantages will drive successful development andemerge as a new class of undeniable anti-cancer thera-peutic Finally (i) individualizedpersonalized oncology inwhich cancer detection diagnosis and therapy can be mod-ified to best fit the tumor molecular profile of a patientand (ii) predictive oncology in which genetic biochemicaland molecular markers are orchestrated to predict disease

development progression and clinical outcomes will cer-tainly shape the nanoncologic strategies of the near future

Acknowledgments This work was supported by theSouth Korean Ministry of Knowledge and Education(MKE) and the Incheon Free Economic Zone (IFEZ) inthe framework of several funding operating grants to theUtah-Inha DDS amp Advanced Therapeutics Research Cen-ter KR

References and Notes

1 N Portney and M Ozkan Anal Bioanal Chem 3 620 (2006)2 M Ferrari Nat Rev Cancer 3 161 (2005)3 T M Allen Nat Rev Cancer 1 0750 (2002)4 J S Ross D P Schenkein and R Pietrusko Am J Clin Pathol

4 598 (2004)5 M Wang and M Thanou Drug Resist Updat 2 90 (2010)6 A Jones and A L Harris Cancer J Sci Am 4 209 (1998)7 D F Baban and L W Seymour Adv Drug Deliv 1 109 (1998)8 H Maeda Adv Enzyme Regul 41 189 (2001)9 K Greish Methods Mol Biol 624 25 (2010)10 A K Iyer K Greish T Seki S Okazaki J Fang K Takeshita

and H Maeda Drug Discov Today 11 812 (2006)11 K N Sugahara T Teesalu P P Karmali V R Kotamraju

L Agemy D R Greenwald and E Ruoslahti Science 5981 1031(2010)

12 R G Boyle and S Travess Anticancer Agents Med Chem 64 281(2006)

13 J M Brown and W R Wilson Nat Rev Cancer 4 437 (2004)14 D Kim E S Lee K Park I C Kwon and Y H Bae Pharm

Res 9 2074 (2008)15 L M Bareford and P W Swaan Adv Drug Deliv Rev 8 748

(2007)16 N F Saba X Wang S Muumlller M Tighiouart K Cho S Nie

Z Chen and D M Shin Head Neck 4 475 (2009)17 Y Lu L C Xu N Parker E Westrick J A Reddy M Vetzel

P S Low and C P Leamon Mol Cancer Ther 12 3258 (2006)18 E I Deryugina and J P Quigley Cancer Metastasis Rev 25 9

(2006)19 A M Mansour J Drevs N Esser F M Hamada O A Badary

C Unger I Fichtner and F Kratz Cancer Res 14 4062 (2003)20 H Hatakeyama H Akita E Ishida K Hashimoto H Kobayashi

T Aoki J Yasuda K Obata H Kikuchi T Ishida H Kiwadaand H Harashima Int J Pharm 1ndash2 194 (2007)

21 A Raz L Meromsky and R Lotan Cancer Res 7 3667 (1986)22 E Gorelik U Galili and A Raz Cancer Metastasis Rev 3ndash4 245

(2001)23 C Bies C M Lehr and J F Woodley Adv Drug Deliv Rev

4 425 (2004)24 H Glavinas P Krajcsi J Cserepes and B Sarkadi Curr Drug

Deliv 1 27 (2004)25 M Dean T Fojo and S Bates Nat Rev Cancer 4 275 (2005)26 T Kobayashi T Ishida Y Okada S Ise H Harashima and

H Kiwada Int J Pharm 1ndash2 94 (2007)27 A M Chen M Zhang D Wei D Stueber O Taratula T Minko

and H He Small 23 2673 (2009)28 J M Koziara P R Lockman D D Allen and R J Mumper

Pharm Res 11 1772 (2003)29 S C Steiniger J Kreuter A S Khalansky I N Skidan A I

Bobruskin Z S Smirnova S E Severin R Uhl M Kock K DGeiger and S E Gelperina Int J Cancer 5 759 (2004)

30 J Wu T Akaike and H Maeda Cancer Res 1 159 (1998)31 M A Deli Biochim Biophys Acta 4 892 (2009)

J Bionanosci 4 1ndash13 2010 11

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REVIEW

Nanoncology A State-of-Art Update Joo et al

Table I Nanoncology in clinical development

Class Carrier Active agent Target Clinical status Indication (s) Ref

LiposomesDaunoXome Liposome Daunorubicin

citrateNA Approved Chronic myelogenous

leukemia neuroblastoma3

DOTAP Chol-FUS1 Liposome Plasmid DNA(FUS1)

NA Phase I Metastatic non-small celllung cancer

114

SGT-53 Liposome Plasmid DNAp53 W-T

Transferrinreceptor

Phase I Advanced Solid Tumors 115

MBP 426 Liposome Oxaliplatin Transferrinreceptor

Phase lbII Advanced or MetastaticSolid Tumors

105

PEGylatedDoxil PEGylaled-Liposome Doxorubicin NA Approved Ovanan cancer recurrent

breast cancer2 56

Oncospar PEGylaled-Asparagnase

L-asparagnase NA Approved Acute lymphoblasticleukemia

2

CYT-6091 PEGylaled-ThiolGold

RecombinantTNF-

Tumor necrosisfactor recepteor

Phase II Advanced solid tumors 110

ADI-PEG 20 PEGylated-ArginineDeiminase

Augininedeiminase

NA Phase II Hepatocellular carcinomaMetastatic melanomarelapsed small cell lungcancer

103

PeptideAbraxane Albumin Paclitaxel NA Approved Metastatic non-small cell

lung cancer2 3

Ontak Interkeukin-2engineered protein

Diphtheria toxin Interleukin-2receptors

Approved Cutaneous T-cell lymphoma 3

AMG 386 Peptibody Recombinantpeptide-Fcfusion protein

Angiopoietin 1and 2

Phase III Various cancers 113

PolymericCALAA-01 Cyclodextrin Small interfering

RNATransferrin

receptorPhase I Solid tumors 107 108

XMT-1001 Fleximer Camptothecin Prodrug activation Phase I Advanced solid tumors 111Genexol Polymeric micelles Paclitaxel NA Phase II Various cancers 52CT-2103 Poly-L-glutmate Paclitaxel NA Phase II Various cancers 112

Antibodya

Trastuzumab HumanizedMonoclonalantibody

Antibody CD340 receptor Approved HER2-positive metastaticbreast cancer

3 4 94

Rituximab Chimeric monoclonalAntibody

Antibody Protein CD20 Approved Leukemias and lymphomas 3 4 94

a Currently there are over 20 FDA-approved monoclonal antibodies for use in cancer therapy

most effective therapy A targeting nanoparticle in Pha-seIBII study is MbP-426 which contains the cytotoxicplatinum-based drug oxaliplatin in a transferrin-conjugatedlipopsome105 Transferrin receptors (TfR) overexpressedon tumor cells allow selective uptake via Tf-TfR interac-tion Outcome of Phase I trial with 39 patients showed that15 patients had stable disease after 2 cycles 3 patients withcolon carcinoma refractory to conventional oxaliplatin hadstable disease for 4-6 cycles and 2 patients had 12 and26 decrease in target lesions105 Further Rexin-G is amurine leukemia virus-based retrovector nanoparticle thatcontains a cytocidal dominant negative cyclin-G1 constructand allows for the functional restoration of tumor sup-pressor microRNA-122a It has been found that block-ade of cyclin G1 may restore intrinsic molecular form

of tumor suppression106 Rexin-G has been found to havelow immunogenicity with preferential selection of rapidly-dividing cells over normal non-dividing or differentiatedcells In Phase II clinical trials 88 of patients had partialresponses or stable disease while the overall survival ratewas 6 months for all 22 patients106 On a further note sometargeted nanoparticles can have active mechanisms for theintracellular release of the therapeutic moiety CALAA-01is a targeted nanoparticle that has a high drug (siRNA)payload per targeting ligand tested and proven multiva-lent binding to cancer cell surfaces and an active siRNArelease mechanism that is triggered upon the recogni-tion of intracellular localization by a pH decline belowa value of 60107108 This nanoparticle system containsa cyclodextrin-based polymer human transferring protein

10 J Bionanosci 4 1ndash13 2010

Delivered by Ingenta toGuest User

IP 6284916Tue 09 Oct 2012 122526

REVIEW

Joo et al Nanoncology A State-of-Art Update

targeting ligand hydrophilic polymer (PEG) and siRNAdesigned to reduce expression of RRM2 It is currentlyundergoing Phase I clinical trials for a dose-escalatingstudy in the treatment of solid tumor cancer107 An aptamerfor potential cancer treatment is AS1411109 It binds nucle-olin on the surface of cancer cells and induces apoptosisIn a dose escalation (1 mgkgday to 10 mgkgday) clin-ical study AS1411 showed positive responses in patientswith advanced solid tumors without any adverse effects109

Recently in a randomized phase II clinical trials a10 mgkgday or 40 mgkgday dose of AS1411 com-bined with high-dose cytarabine was well tolerated andshowed promising signs of activity in patients with pri-mary refractory or relapsed acute myeloid leukaemia Itis also currently being evaluated for treatment of breastcancer110 In another example Aurimune is a colloidalAu nanoparticle which delivers recombinant TNF- tocancer tumors TNF is attached to the Au nanoparticle withthiol-derivatized PEG which allows the nanoparticle toflow through the blood stream without causing a clearanceresponse110 Clinical data to date reports that Aurimunehas no antibody or immune responses and is well-toleratedbeyond the known maximum dose for TNF-110

7 CLOSING REMARKS FUTUREPERSPECTIVE

Over the past decades nanoncology (therapeutics anddiagnostics) has evolved from nano-sized drug particlesto bio-functional nanomaterials capable of deliveringheat treatment ionizing radiation andor chemothera-peutic agents From simple liposomal formulations andconjugation of PEG to antibody-conjugated nanoparti-cle chemotherapeutic and RNAi delivery nanoncology isbecoming more intricate smart and multi-functional Fur-ther the differences between cancerous and normal cellsincluding uncontrolled proliferation insensitivity to nega-tive growth regulation and anti-growth signals angiogen-esis and metastasis can be now be effectively exploitedThere is no doubt that nanoparticle therapeutics with theincreasing multi-functionality will continue to expand inthe future Investments in research development and per-formance trials are considerably large Sponsoring agen-cies in both private and government sectors should createeconomic strategies and innovative management to makesuch biotechnologies more cost-effective and easily acces-sible for patients across Although many challenges existfor the transition of nanoparticles from bench to bed theirpotential advantages will drive successful development andemerge as a new class of undeniable anti-cancer thera-peutic Finally (i) individualizedpersonalized oncology inwhich cancer detection diagnosis and therapy can be mod-ified to best fit the tumor molecular profile of a patientand (ii) predictive oncology in which genetic biochemicaland molecular markers are orchestrated to predict disease

development progression and clinical outcomes will cer-tainly shape the nanoncologic strategies of the near future

Acknowledgments This work was supported by theSouth Korean Ministry of Knowledge and Education(MKE) and the Incheon Free Economic Zone (IFEZ) inthe framework of several funding operating grants to theUtah-Inha DDS amp Advanced Therapeutics Research Cen-ter KR

References and Notes

1 N Portney and M Ozkan Anal Bioanal Chem 3 620 (2006)2 M Ferrari Nat Rev Cancer 3 161 (2005)3 T M Allen Nat Rev Cancer 1 0750 (2002)4 J S Ross D P Schenkein and R Pietrusko Am J Clin Pathol

4 598 (2004)5 M Wang and M Thanou Drug Resist Updat 2 90 (2010)6 A Jones and A L Harris Cancer J Sci Am 4 209 (1998)7 D F Baban and L W Seymour Adv Drug Deliv 1 109 (1998)8 H Maeda Adv Enzyme Regul 41 189 (2001)9 K Greish Methods Mol Biol 624 25 (2010)10 A K Iyer K Greish T Seki S Okazaki J Fang K Takeshita

and H Maeda Drug Discov Today 11 812 (2006)11 K N Sugahara T Teesalu P P Karmali V R Kotamraju

L Agemy D R Greenwald and E Ruoslahti Science 5981 1031(2010)

12 R G Boyle and S Travess Anticancer Agents Med Chem 64 281(2006)

13 J M Brown and W R Wilson Nat Rev Cancer 4 437 (2004)14 D Kim E S Lee K Park I C Kwon and Y H Bae Pharm

Res 9 2074 (2008)15 L M Bareford and P W Swaan Adv Drug Deliv Rev 8 748

(2007)16 N F Saba X Wang S Muumlller M Tighiouart K Cho S Nie

Z Chen and D M Shin Head Neck 4 475 (2009)17 Y Lu L C Xu N Parker E Westrick J A Reddy M Vetzel

P S Low and C P Leamon Mol Cancer Ther 12 3258 (2006)18 E I Deryugina and J P Quigley Cancer Metastasis Rev 25 9

(2006)19 A M Mansour J Drevs N Esser F M Hamada O A Badary

C Unger I Fichtner and F Kratz Cancer Res 14 4062 (2003)20 H Hatakeyama H Akita E Ishida K Hashimoto H Kobayashi

T Aoki J Yasuda K Obata H Kikuchi T Ishida H Kiwadaand H Harashima Int J Pharm 1ndash2 194 (2007)

21 A Raz L Meromsky and R Lotan Cancer Res 7 3667 (1986)22 E Gorelik U Galili and A Raz Cancer Metastasis Rev 3ndash4 245

(2001)23 C Bies C M Lehr and J F Woodley Adv Drug Deliv Rev

4 425 (2004)24 H Glavinas P Krajcsi J Cserepes and B Sarkadi Curr Drug

Deliv 1 27 (2004)25 M Dean T Fojo and S Bates Nat Rev Cancer 4 275 (2005)26 T Kobayashi T Ishida Y Okada S Ise H Harashima and

H Kiwada Int J Pharm 1ndash2 94 (2007)27 A M Chen M Zhang D Wei D Stueber O Taratula T Minko

and H He Small 23 2673 (2009)28 J M Koziara P R Lockman D D Allen and R J Mumper

Pharm Res 11 1772 (2003)29 S C Steiniger J Kreuter A S Khalansky I N Skidan A I

Bobruskin Z S Smirnova S E Severin R Uhl M Kock K DGeiger and S E Gelperina Int J Cancer 5 759 (2004)

30 J Wu T Akaike and H Maeda Cancer Res 1 159 (1998)31 M A Deli Biochim Biophys Acta 4 892 (2009)

J Bionanosci 4 1ndash13 2010 11

Delivered by Ingenta toGuest User

IP 6284916Tue 09 Oct 2012 122526

REVIEW

Joo et al Nanoncology A State-of-Art Update

targeting ligand hydrophilic polymer (PEG) and siRNAdesigned to reduce expression of RRM2 It is currentlyundergoing Phase I clinical trials for a dose-escalatingstudy in the treatment of solid tumor cancer107 An aptamerfor potential cancer treatment is AS1411109 It binds nucle-olin on the surface of cancer cells and induces apoptosisIn a dose escalation (1 mgkgday to 10 mgkgday) clin-ical study AS1411 showed positive responses in patientswith advanced solid tumors without any adverse effects109

Recently in a randomized phase II clinical trials a10 mgkgday or 40 mgkgday dose of AS1411 com-bined with high-dose cytarabine was well tolerated andshowed promising signs of activity in patients with pri-mary refractory or relapsed acute myeloid leukaemia Itis also currently being evaluated for treatment of breastcancer110 In another example Aurimune is a colloidalAu nanoparticle which delivers recombinant TNF- tocancer tumors TNF is attached to the Au nanoparticle withthiol-derivatized PEG which allows the nanoparticle toflow through the blood stream without causing a clearanceresponse110 Clinical data to date reports that Aurimunehas no antibody or immune responses and is well-toleratedbeyond the known maximum dose for TNF-110

7 CLOSING REMARKS FUTUREPERSPECTIVE

Over the past decades nanoncology (therapeutics anddiagnostics) has evolved from nano-sized drug particlesto bio-functional nanomaterials capable of deliveringheat treatment ionizing radiation andor chemothera-peutic agents From simple liposomal formulations andconjugation of PEG to antibody-conjugated nanoparti-cle chemotherapeutic and RNAi delivery nanoncology isbecoming more intricate smart and multi-functional Fur-ther the differences between cancerous and normal cellsincluding uncontrolled proliferation insensitivity to nega-tive growth regulation and anti-growth signals angiogen-esis and metastasis can be now be effectively exploitedThere is no doubt that nanoparticle therapeutics with theincreasing multi-functionality will continue to expand inthe future Investments in research development and per-formance trials are considerably large Sponsoring agen-cies in both private and government sectors should createeconomic strategies and innovative management to makesuch biotechnologies more cost-effective and easily acces-sible for patients across Although many challenges existfor the transition of nanoparticles from bench to bed theirpotential advantages will drive successful development andemerge as a new class of undeniable anti-cancer thera-peutic Finally (i) individualizedpersonalized oncology inwhich cancer detection diagnosis and therapy can be mod-ified to best fit the tumor molecular profile of a patientand (ii) predictive oncology in which genetic biochemicaland molecular markers are orchestrated to predict disease

development progression and clinical outcomes will cer-tainly shape the nanoncologic strategies of the near future

Acknowledgments This work was supported by theSouth Korean Ministry of Knowledge and Education(MKE) and the Incheon Free Economic Zone (IFEZ) inthe framework of several funding operating grants to theUtah-Inha DDS amp Advanced Therapeutics Research Cen-ter KR

References and Notes

1 N Portney and M Ozkan Anal Bioanal Chem 3 620 (2006)2 M Ferrari Nat Rev Cancer 3 161 (2005)3 T M Allen Nat Rev Cancer 1 0750 (2002)4 J S Ross D P Schenkein and R Pietrusko Am J Clin Pathol

4 598 (2004)5 M Wang and M Thanou Drug Resist Updat 2 90 (2010)6 A Jones and A L Harris Cancer J Sci Am 4 209 (1998)7 D F Baban and L W Seymour Adv Drug Deliv 1 109 (1998)8 H Maeda Adv Enzyme Regul 41 189 (2001)9 K Greish Methods Mol Biol 624 25 (2010)10 A K Iyer K Greish T Seki S Okazaki J Fang K Takeshita

and H Maeda Drug Discov Today 11 812 (2006)11 K N Sugahara T Teesalu P P Karmali V R Kotamraju

L Agemy D R Greenwald and E Ruoslahti Science 5981 1031(2010)

12 R G Boyle and S Travess Anticancer Agents Med Chem 64 281(2006)

13 J M Brown and W R Wilson Nat Rev Cancer 4 437 (2004)14 D Kim E S Lee K Park I C Kwon and Y H Bae Pharm

Res 9 2074 (2008)15 L M Bareford and P W Swaan Adv Drug Deliv Rev 8 748

(2007)16 N F Saba X Wang S Muumlller M Tighiouart K Cho S Nie

Z Chen and D M Shin Head Neck 4 475 (2009)17 Y Lu L C Xu N Parker E Westrick J A Reddy M Vetzel

P S Low and C P Leamon Mol Cancer Ther 12 3258 (2006)18 E I Deryugina and J P Quigley Cancer Metastasis Rev 25 9

(2006)19 A M Mansour J Drevs N Esser F M Hamada O A Badary

C Unger I Fichtner and F Kratz Cancer Res 14 4062 (2003)20 H Hatakeyama H Akita E Ishida K Hashimoto H Kobayashi

T Aoki J Yasuda K Obata H Kikuchi T Ishida H Kiwadaand H Harashima Int J Pharm 1ndash2 194 (2007)

21 A Raz L Meromsky and R Lotan Cancer Res 7 3667 (1986)22 E Gorelik U Galili and A Raz Cancer Metastasis Rev 3ndash4 245

(2001)23 C Bies C M Lehr and J F Woodley Adv Drug Deliv Rev

4 425 (2004)24 H Glavinas P Krajcsi J Cserepes and B Sarkadi Curr Drug

Deliv 1 27 (2004)25 M Dean T Fojo and S Bates Nat Rev Cancer 4 275 (2005)26 T Kobayashi T Ishida Y Okada S Ise H Harashima and

H Kiwada Int J Pharm 1ndash2 94 (2007)27 A M Chen M Zhang D Wei D Stueber O Taratula T Minko

and H He Small 23 2673 (2009)28 J M Koziara P R Lockman D D Allen and R J Mumper

Pharm Res 11 1772 (2003)29 S C Steiniger J Kreuter A S Khalansky I N Skidan A I

Bobruskin Z S Smirnova S E Severin R Uhl M Kock K DGeiger and S E Gelperina Int J Cancer 5 759 (2004)

30 J Wu T Akaike and H Maeda Cancer Res 1 159 (1998)31 M A Deli Biochim Biophys Acta 4 892 (2009)

J Bionanosci 4 1ndash13 2010 11

Delivered by Ingenta toGuest User

IP 6284916Tue 09 Oct 2012 122526

REVIEW

Nanoncology A State-of-Art Update Joo et al

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Joo et al Nanoncology A State-of-Art Update

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Received 7 March 2011 Accepted 9 April 2011

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