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Original article

Catalytic nanomedicine: A new field in antitumor treatment using supportedplatinum nanoparticles. In vitro DNA degradation and in vivo tests with C6 animalmodel on Wistar rats

T. Lopez a,b,d,*, F. Figueras e, J. Manjarrez c, J. Bustos a, M. Alvarez b, J. Silvestre-Albero f,F. Rodrıguez-Reinoso f, A. Martınez-Ferre g, E. Martınez a,b

a Departamento de Atencion a la Salud, Universidad Autonoma Metropolitana-Xochimilco, Calz. Del Hueso 1100, Col. Villa Quietud, Coyoacan 04960, D.F., Mexicob Laboratorio de Nanotecnologıa, Mexico, Instituto Nacional de Neurologıa ‘‘MVS’’, Insurgentes Sur 3877, La Fama, Tlalpan 14269, D.F., Mexicoc Laboratorio de Fisiologıa de la Formacion Reticular, Instituto Nacional de Neurologıa ‘‘MVS’’, Insurgentes Sur 3877, La Fama, Tlalpan 14269, D.F., Mexicod Department of Chemical Engineering, Tulane University New Orleans, LA 70118, USAe Institut de Recherches sur la Catalyse et l’environnement de Lyon UMR 5256, Universite Lyon 1-CNRS, 2 Avenue Albert Einstein, F69626 Villeurbanne, Francef Laboratorio de Materiales Avanzados, Universidad de Alicante, Ap. 99, E-03080 Alicante, Spaing Experimental Embriology Laboratory, Instituto de Neurociencias, UMH-CSIC, E-03550 San Juan-Alicante, Spain

a r t i c l e i n f o

Article history:Received 1 May 2009Received in revised form29 December 2009Accepted 19 January 2010Available online 28 January 2010

Keywords:C6NanomedicineTitania sol–gelSilica sol–gelChloroplatinic acidGBM

a b s t r a c t

Novel nanostructured TiO2 and SiO2 based biocatalysts, with 3–4 wt. % of Pt have been developed. Theobtained materials exhibit a high surface area together with a broad pore size distribution. The methodof synthesis allowed obtaining high dispersed platinum metal nanoparticles. In vitro DNA reactivity testof the biocatalysts were carried out by electrophoresis and formation of DNA adducts was observed. Themost active biocatalyst was H2PtCl6/SiO2. These biocatalysts were also tested in an experimental model ofC6 brain tumours in Wistar rats. Administration of the material was made by stereotactic brain surgery toplace it directly in the malignant tissue. A significant decrease in tumour size and weight as well asmorphologic changes in cancer cells were observed.

� 2010 Elsevier Masson SAS. All rights reserved.

1. Introduction

Glioblastoma multiforme (GBM) is a grade IV astrocytoma thatconstitutes 25% of all malignant nervous system tumours [1,2] andit is associated to a poor prognosis. Surgery is commonly the firsttherapeutic modality and the optimal goal is complete resection.However, as GBM is infiltrative, complete resection is virtuallyimpossible and relapse is almost inevitable. Since curative surgeryis not possible, bulk reduction and consequent decompression ofthe brain with alleviation of the symptoms of cranial hypertensionis the only feasible achievement in most patients, the aim being toimprove quality of life and make possible that life of the patient willbe longer. Since the late 1970s, several randomized clinical trials [3]

have examined the role of adjuvant chemotherapy in improving thesurvival of brain tumor patients. Chemotherapeutic agents havebeen administered before, during or after radiotherapy [4–7] inorder to improve therapy results. Nevertheless, effectiveness of thisstrategy is very low. In the search of new alternatives for cancertreatment, the role of DNA in the control of cellular functionsbecomes an excellent target for chemotherapy. Although there aresome systemic chemotherapeutical agents available in the marketfor GBM treatment, (alkylating agents and platinum based drugs[8]), most of them are unable to cross the blood brain barrier (BBB).Temozolomide is the first drug that posses this ability. Despite this,systemic administration of temozolomide produces undesirableadverse effects. This is one of the main reasons to develop newalternatives for the treatment of this illness.

Since the pioneer work of Rosenberg in 1965, Pt complexes havebeen widely used in cancer therapy [9,10]. From then on, numerousattempts to obtain new platinum complexes with better thera-peutic performances than cis-platin have been made [11,12].

* Corresponding author at: Laboratorio de Nanotecnologıa, Insurgentes Sur 3877,La Fama, Tlalpan 14269, D.F., Mexico. Fax: þ52 55 55288036.

E-mail address: tessy3@prodigy.net.mx (T. Lopez).

Contents lists available at ScienceDirect

European Journal of Medicinal Chemistry

journal homepage: ht tp: / /www.elsevier .com/locate/e jmech

0223-5234/$ – see front matter � 2010 Elsevier Masson SAS. All rights reserved.doi:10.1016/j.ejmech.2010.01.043

European Journal of Medicinal Chemistry 45 (2010) 1982–1990

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Although the mechanism of action of these compounds at molec-ular level is still unclear [13–15], it is widely accepted that Ptcoordinates to N7 sites of DNA guanine bases to form adducts withboth DNA helixes after hydrolysis of the Pt–Cl bonds [16]. Thiswould block the cell replication [17–19]. In this study, novelnanostructured TiO2 and SiO2 based biocatalysts with a smallloading of platinum nanoparticles (w3–4 wt. % of Pt) were devel-oped. In order to stabilize structural defects like oxygen vacanciesand free electrons and to obtain high dispersion of Pt salt on theoxide, sol–gel parameters were controlled. Biocatalysts have neverbeen applied to treat solid tumours. It is shown here that this kindof compounds exhibit a significant cytotoxic activity over malig-nant cells by means of interaction with DNA. In these novel nano-structured biocatalysts cis conformation of platinum complex is notessential to be active over DNA. They were tested in an experi-mental animal brain model, placing the supported Pt biocatalyst inthe malignant tissue using stereotactic surgery. A complementaryexperience was made to visualize the DNA fragmentation by meansof electrophoresis.

2. Experimental

2.1. Materials synthesis

H2PtCl6/TiO2 and H2PtCl6/SiO2 were prepared by a sol-gelprocess, as previously reported [20,21], using TEOS (Sigma 99%)and Titanium butoxide (Sigma, 98.5%) as precursors. Hydrolysiswas carried out at neutral pH and H2PtCl6.6H2O (Sigma, 99.999%)was used as platinum precursor. Titania was further functionalizedwith a neurotransmitter in order to develop an analogy with cells[22]. The obtained gels were dried to form solid nanoparticles.

2.2. Characterization

Textural characterization of the samples was performed usingN2 adsorption–desorption isotherms at �196 �C on a home-madefully automated manometric equipment. Prior to the analysis,samples were outgassed at 30 �C until a vacuum around 10�5 Torrwas attained. Specific surface area was calculated using the Bru-nauer–Emmett–Teller (BET) method. Micropore volume (V0) wascalculated by applying the Dubinin–Raduskevitch equation to thenitrogen adsorption data whereas the mesopore volume (Vmeso)was calculated by subtracting the micropore volume from the totalpore volume (V0.99), i.e. total amount of nitrogen uptake at p/pow0.99. The micro-Raman spectra were recorded in a nearly back-scattering geometry with a Jobin–Yvon Labram apparatus, equip-ped with xy motorized stage and autofocus. The excitation lineswere the 632.8 nm line of a He–Ne laser and the 784.8 nm line ofa laser diode. The laser power on the samples was kept low by usingneutral density filters. Due to the possible electronegative characterof the samples, different measurements were performed on eachsample. X-ray photoelectron spectra (XPS) were acquired witha VG-Microtech Multilab 3000 spectrometer equipped witha hemispherical electron analyzer and a Mg Ka (h¼ 1253.6 eV,1 eV¼ 1.6302�10�19 J) 300-W X-ray source. The powdersamples were pressed into small Inox cylinders and then mountedon a sample rod placed in a pre-treatment chamber. Beforerecording the spectrum, the sample was maintained in the analysischamber until a residual pressure of ca. 4�10�9 Torr was reached.The spectra were collected at pass energy of 50 eV. The intensitieswere estimated by calculating the integral of each peak, aftersubtraction of the S-shaped background, and by fitting the exper-imental curve to a combination of Lorentzian (30%) and Gaussian(70%) lines. All binding energies (B.E.) were referenced to the C 1sline at 284.6 eV, which provided binding energy values with an

accuracy of �0.2 eV. TEM observations were carried out on a JEOLmodel JEM-2010 electron microscope working at 200 kV, equippedwith an INCA Energy TEM 100 analytical system and a SIS Mega-View II camera. Samples for analysis were suspended in methanoland placed on copper grids with a holey-carbon film support. Acidproperties were evaluated using infrared analysis of acetonitrileadsorption on self supported wafers. The experiments were carriedout on a NICOLET FTIR spectrometer model MAGNA 560 withresolution of 4 cm�1, equipped with DTGS detector. An average of100 scans was accumulated.

2.3. Reagents and materials for biological studies

Total DNA was extracted from human blood cells by the WizardGenomic DNA purification kit (Promega). DNA concentration wasmeasured with the BioPhotometer (Eppendorf).

2.4. In vitro DNA test

2 mL of DNA solution (500 mg/mL) were mixed with 2 mL ofa suspension containing the nanoparticles (200 mg/mL) and incu-bated at 37 �C for different times (0, 15, 30, 45, 60, 180, 720 and1440 minutes). After incubation, an aliquot was sampled andanalyzed by electrophoresis run at 120 V for 1 h in 1% agarose gel.The gels were stained with ethidium bromide and images wereacquired with a Bio-Rad GelDoc.

2.5. In vivo test

C6 glioma cells [23] obtained from the American Tissue CultureCollection (Rockville, MD) were cultured in standard conditions[24] and 1�106 C6 cells were inoculated into the brain of 25 maleWistar rats by means of minimal invasion stereotactic surgery(AP¼ 1.6 (A), L¼ 3.0 y V¼ 2.0). 2 weeks later a tumor was devel-oped in all animals and they were randomly separated into two

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biocatalysts.

Table 1Textural parameters obtained from the N2 adsorption data at 77 K for the differentbiocatalysts.

Sample N2 adsorption

SBET (m2/g) V0 (cm3/g) Vmeso (cm3/g) Vt (cm3/g)

H2PtCl6/SiO2 416 0.14 0.06 0.20H2PtCl6/TiO2 250 0.08 0.10 0.18

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groups: a control group A (n¼ 10), group B (n¼ 8) with a Pt-TiO2

device of 10 mg placed in the same microinjection coordinates. Ratswithout treatment died during the following three months, and thebrains were removed and processed for histological tests. Theanimals of the B group survived until they were sacrificed eight toten months after inoculation. Brains were removed and processedsections were stained with Hematoxiline–Eosine (H–E) for micro-scopic analysis. Terminal Uridine Nucleotide End Labeling assay(TUNEL) was performed to evaluate apoptosis.

3. Results and discussion

3.1. Textural characterization

N2 adsorption–desorption isotherms at 77 K for both bio-catalysts are shown in Fig. 1. H2PtCl6/SiO2 biocatalysts exhibit a typeI isotherm, according to the IUPAC classification, characteristic ofmicroporous materials [25]. However, the presence of a broad kneeat low relative pressures (below p/p0< 0.4) clearly reflects thepresence of a wide micropore size distribution. On the other hand,H2PtCl6/TiO2 biocatalyst exhibits a type IV isotherm, characteristicof porous materials with bimodal pore size distribution (presenceof both micro and mesopores). The presence of a hysteresis loop on

the H2PtCl6/TiO2 biocatalysts above p/p0w0.4 reflects the capillarycondensation of nitrogen molecules in the mesopores.

The hysteresis loop of the H2PtCl6/TiO2 biocatalyst is a type H2,which characterizes solids with interconnected networks of poreswith different size and shape (usually cylindrical mesopores withconstrictions in the pore mouth). Interestingly, the absence ofa sharp step, i.e. there is a continuous increase in the amountadsorbed, between the micropore filling region and the capillarycondensation in the mesopores confirms the presence of a contin-uous range of pore sizes covering from the microporous to themesoporous region. Textural parameters obtained from thenitrogen adsorption data are reported on Table 1.

The BET surface area for both samples was 416 m2/g and 250 m2/g, for H2PtCl6/SiO2 and H2PtCl6/TiO2, respectively, whilst themicropore volume (V0) was 0.14 and 0.08 cc/g, respectively. Theaverage pore size obtained was 1.7 for H2PtCl6/SiO2 and 3.1 nm forH2PtCl6/TiO2, as determined by BJH method, which is in agreementwith the analysis done on their corresponding isotherms.

3.2. Spectroscopic analysis

FTIR spectra of H2PtCl6/TiO2 and H2PtCl6/SiO2 under KBr weretaken in order to analyze the structure of the materials. The

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Fig. 3. FTIR spectra of pyridine adsorbed on H2PtCl6/TiO2 (left) and H2PtCl6/SiO2 (right) a) before adsorption, b) adsorption of pyridine at room temperature under vacuumconditions, c) desorption at 100 �C and d) desorption at 150 �C.

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spectrum of H2PtCl6/SiO2 (Fig. 2) shows characteristic bands ofsilicon dioxide with high hydration grade. An intense and widesignal at 3300 cm�1 (O–H stretching mode vibration) associatedwith a sharp band of moderated intensity located at 1630 cm�1 canbe observed. This band is generated by the scissors deformationvibration of protons. In the low-energy zone of the spectrum thefingerprints bands of silica can be seen: 1085, 940, 800 and450 cm�1. All of these bands are related to the structure of silicondioxide and the presence of a large amount of silanol groups (Si–OH) supported by the intensity of the band at 940 cm�1. In the mid-energy zone of the spectrum, several small bands due to thepresence of organic material (solvent and byproducts of the reac-tion synthesis) can be observed.

The high-energy region of FTIR H2PtCl6/TiO2 spectrum exhibitsbands similar to those observed in H2PtCl6/SiO2. In the low-energyregion we can observe an intense and wide band at 450 related tothe stretching vibration of Ti-O and Ti–O–Ti bonds, typical of tita-nium dioxide. Hydration grade in H2PtCl6/TiO2 is lower than insilica sample.

No peaks attributable to vibrational modes directly involving Ptatoms were observed. The Raman features observed in the spectraof H2PtCl6/TiO2 sample (Fig. 2) are close to those in the bulk anatasephase [26,27] thus confirming that the sample is not amorphous.The absence of characteristic peaks of the rutile crystal phase at 446and 609 cm�1, suggests that the powders are composed of pureanatase phase. The broad band at about 425 cm�1 can be assignedto symmetric stretching u1 mode of TiO2 [28,29]. Defect peaks at480 and 607 cm�1 named D1 and D2, attributed to symmetricstretching modes of SiO2 tetrahedra [30,31] can be observed. Thevibrations of these two bands involve pure oxygen motion [32]. Theweak bands observed in the 900–1000 cm�1 range are assigned toOH impurity content. The observed peak at 962 cm�1 is assigned toSi–OH stretching mode [33,34].

Fig. 3 shows pyridine adsorption spectra over both biocatalysts.Due to the presence of bands in the mid-energy region of the

spectra generated by water, acetonitrile adsorption experimentswere carried out to complement information regarding the acidproperties of the biocatalysts. In H2PtCl6/TiO2 spectra (Fig. 3), thereis a band located at 1490 cm�1, associated to pyridine coor-dinatively bonded to Lewis acid sites, in this case titania cations(Ti4þ and Ti3þ). These electron-acceptor centers are incompletelycoordinated titanium atoms, which can therefore fix either water-molecules, or ammonia molecules. In the case of H2PtCl6/SiO2

biocatalyst, the acidity is weaker than H2PtCl6/TiO2 since theintensity of the band located at 1610 cm�1 diminishes as temper-ature increases.

As it can be seen in Fig. 4, the spectra of acetonitrile adsorbed onH2PtCl6/TiO2 shows three bands. The band at 2252 cm�1 is relatedto physisorbed acetonitrile at the surface while the bands shifted tothe blue (2285 and 2311 cm�1) are generated by the interactionwith acid coordination and protonation sites of Pt/TiO2, respec-tively. On the other hand, FTIR spectra of H2PtCl6/SiO2, exhibit onlytwo bands located at 2261 and 2296 cm�1. These bands can beassigned to physisorbed and coordinated acetonitrile. In this caseno protonation of the probe molecule occurs, as is expected for lowacidity of silica. These results are in consistent with those obtainedby pyridine adsorption.

Table 2 reports the characterization results obtained using X-ray fluorescence spectroscopy (XRF) and X-ray photoelectronspectroscopy (XPS). As it can be observed, the percentage of Ptobtained from XRF analysis on both biocatalysts is quite close tothe nominal value 3–4 wt. % used in the initial sol-gel solution.According to the XPS spectra, Pt nanoparticles are well-dispersed

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Table 2X-ray fluorescence spectroscopy and X-ray photoelectron spectroscopy results onthe fresh biocatalysts.

Sample Weight percent(%)

Pt/Tiatomic ratio

B.E (eV)Pt 4f

Pt content(%) (XFR)

Pt Cl N

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Pt 4f5/2

Fig. 5. XPS spectra corresponding to the Pt 4f level for H2PtCl6/TiO2 biocatalysts.

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on the surface of the TiO2 support, as it can be inferred from thePt/Ti atomic ratio (this ratio can be used as a rough estimation ofthe Pt dispersion on the surface of the catalyst). The Pt 4f level X-ray photoelectron spectrum for H2PtCl6/TiO2 biocatalyst showsthe presence of two broad bands which corresponds to the Pt 4f7/2

and Pt 4f5/2 levels (Fig. 5). The binding energy (B.E., eV) corre-sponding to these two levels are 72.2 eV and 75.5 eV, respectively.According to the literature, the 4f7/2 level of platinum in differentoxidation states appears as follow: Pt0, 71.0–71.3 eV; K2PtIICl4,

72.8–73.4 eV; K2PtIVCl6, 74.1–74.3 eV [35]. Thus, the absence ofany peak in the catalysts at a low binding energy (approx. 71.0 eV)clearly rules out the presence of metallic platinum. This obser-vation confirms that the metal precursor and, more specifically,the oxidation state of the platinum precursor is preserved.Consequently, Pt(II) should be considered as the active compoundfor any further application.

Unfortunately, XPS analysis of H2PtCl6/SiO2 biocatalyst providesno signal attributed to Pt. The absence of any signal could be

Fig. 6. Scanning electron image of H2PtCl6/TiO2 biocatalyst.

Fig. 7. TEM micrographs of H2PtCl6/TiO2 (a,b) and H2PtCl6/SiO2 (c,d).

T. Lopez et al. / European Journal of Medicinal Chemistry 45 (2010) 1982–19901986

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explained on the basis of a low Pt dispersion. However, visualinspection of the biocatalyst clearly confirms the presence ofmetallic platinum (grey colour of the powder sample).

One of the features of these biocatalysts is their nanometric size.In this sense, scanning electron micrographs clearly show the pres-ence of small particles agglomerates, each individual agglomeratehaving a diameter ranging from approximately 0.2 to 1.0 mm (Fig. 6).

The morphology of the Pt nanoparticles and the oxide supportwas analyzed using transmission electron microscopy. Fig. 7 showsTEM images of both (a) H2PtCl6/TiO2 and (b) H2PtCl6/SiO2 bio-catalysts. As expected, TiO2 support (Fig. 7b) exhibits a high degreeof crystallinity in accordance with previous observations usingRaman. Interestingly, a close inspection through the whole bio-catalyst does not allow discerning any spot attributed to Pt nano-particles. The absence of any observation attributed to the platinumnanoparticles is usually attributed to the lower density of the oxidenanoparticles (compared to the pure metal), together with thepresence of spectators (organic precursor). In the case of theH2PtCl6/SiO2 biocatalyst, the situation is different. TEM imagesclearly show the presence of Pt nanoparticles, thus confirming thepresence of reduced metal species (Pt(0)). Additionally, althoughisolated Pt nanoparticles of around 8–10 nm can be observed, the

main proportion of Pt is associated forming agglomerates of smallnanoparticles (Fig. 7c and d). These agglomerates are responsiblefor the low Pt dispersion anticipated from the XPS measurements.

3.3. In vitro DNA degradation test

The results of this experiment are reported in Fig. 8. From thisstudy it was observed that after 30 minutes DNA and nanoparticleswere mixed, some DNA-Pt adducts were formed, as the smalldisplacement of the bands regarding to the control indicates (lanes2,4 and 6). The intensity of the bands in lanes 5 and 6 diminishesafter 45 minutes. This fact is related to the interaction between thebiocatalysts and DNA. After 60 minutes of incubation H2PtCl6/SiO2

totally degrades DNA (lane 6 disappears). When incubation time was180 minutes, we observed that cis-platin alone (lane 2) totallydegrades DNA. In these experimental conditions, H2PtCl6/SiO2,showed higher activity than cis-platin alone. DNA degradation withcisplatin/TiO2 and with H2PtCl6/TiO2 occurs after 720 minutes(Fig. 8). Finally, TiO2 degradated DNA at incubation time of 24 hours.This can be explained as due to presence of Lewis acid sites on titaniasurface linking this surface sites to DNA. The outcome of the test

Fig. 8. Electrophoresis of the samples of DNAþ nanoparticles as a function of time; lanes 1) Control (DNAþH2O); 2) cisplatin; 3) TiO2; 4) cisplatin/TiO2; 5) H2PtCl6/TiO2; 6) H2PtCl6/SiO2.

Fig. 9. Platinum complexes formed during chloroplatinic acid hydrolysis.

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reveals that all tested biocatalyst are active over DNA, H2PtCl6/SiO2

being the most active under experimental in vitro conditions.In the interaction with cis-platin or H2PtCl6/SiO2, the structure of

DNA is first modified, as evidenced by the lower mobility in elec-trophoresis (lanes 2 and 6) and then cleaved, since the corre-sponding spot disappears. This process is slower in the absence ofPt (lane 3, TiO2), or with cis-platin/TiO2 (lane 4). Compared to cis-platin, the reaction is remarkably faster on H2PtCl6/SiO2 biocatalyst.

In the case of H2PtCl6/SiO2, the chloroplatinic acid is mainlyadsorbed physically and can be released fast by dissolution. InH2PtCl6/TiO2, the PtCl6

2- anions are exchanged on the titania surfaceand have to be back-exchanged to go into the solution. Hydrogenhexachloroplatinate(IV) or hexachloroplatinic acid, is one of themost used compounds in preparation of heterogeneous supportedcatalysts. In aqueous solution, Pt–Cl bonds undergo a series ofhydrolysis reactions under certain conditions [36]. In dilutedsolutions, the initial rapid hydrolysis of Pt–Cl bonds seems to bedue to ligand exchange by H2O (Fig. 9), leading to chloroaquohy-droxo species [37,38].

3.4. C6 experimental brain model

GBM is the most aggressive tumor of the Central NervousSystem. It is characterized by cellular polymorphism, nuclear aty-pia, mitotic activity, vascular thrombosis, microvascular prolifera-tion and necrosis [39]. Regional heterogeneity and highly invasive

growth are typical. The progression of tumor was evaluated fromthe weight of the animals, conduct test, effort as well as histopa-thology of a representative rat of this group. H–E stain of tumorcells is shown in Fig. 10c. The characteristic GBM features abovementioned are observed. When the animals were treated withH2PtCl6/TiO2, a reduction in tumor size and a decrease in theaggressiveness (Fig. 10d) were observed. An apoptotic process canbe inferred as nuclear morphological changes are observed; thesechanges include nuclear fragmentation, nuclear condensation orperipheral chromatin condensation. Using the TUNEL technique itwas found that the death of cancerous cells was by an apoptoticmechanism instead of necrosis (Fig. 10f). This investigation provesthat there is a good response against damaged cells usinga minimum platinum dose.

Because of their capability to interact with DNA at physiologicalpH [40] chloromonoaquo species are the most interesting. Whenchloroplatinic acid is added in situ during silica sol-gel synthesis,the platinum interacts with the silanol groups before silicaformation [41] and platinum ions can be incorporated into the silicanetwork. A similar behavior can be observed in Pt/TiO2 materials[21]. The addition of a neurotransmitter gives a functionalizedsurface able to be recognized by neurons.

In the case of Co salts, the hydrolysis of alkaline phosphates orphosphoesters at pH¼ 7, and low temperature, has been reportedto be catalyzed by Cobalt (II) hydroxide through a mechanisminvolving the attack of the phosphate by an OH [42]. Artificial

Fig. 10. Photographs from a) resected tumour after 30 days of cell inoculation, b) stereotactic brain surgery for biocatalyst administration, in the same coordinates of inoculationc) H–E stained section of tumour tissue from control group (without treatment), d) H–E stained section of tumour tissue after treatment with H2PtCl6/TiO2, e) H–E stained section oftumour after treatment 10�, f) Detection of fragmented DNA (apoptotic process) by TUNEL assay.

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nucleases [43,44] also split the phosphodiester bonds of DNA bya similar mechanism [45]. So, it can be proposed that the pathleading to DNA fragmentation also starts by an attack of an OHlinked to Pt (Fig. 11). These results show that activity is notrestricted to complexes with cis structure. Indeed these supportedPt catalysts are more effective than cisplatin using a lower dose ofthe metal, since DNA degradation occurs in 60 min with H2PtCl6/SiO2 and requires 180 min on cisplatin alone. In our hypothesis ofa hydrolytic mechanism, the higher activity of chloroplatinic acidcould be related to the higher number of Cl ligands.

4. Conclusions

Nanostructured TiO2 and SiO2 based biocatalysts with platinumwere designed in order to obtain novel nanomaterials that caninteract with DNA to be used as an alternative in local cancer therapy.

Because of its strong acidity, chloroplatinic acid undergoes rapidand extensive hydrolysis that allows easily anchoring of hydroxy-species over the titania and silica surface. Moreover, platinumions can be incorporated into titania and silica matrices, improvingplatinum DNA-reactivity due to the presence of defects in thenetwork and surface OH groups. This low concentration is neces-sary to obtain highly dispersed platinum-titania and platinum-silica surface. The Platinum compound coordinates to DNA, prob-ably by forming bonds with DNA through hydrolysis of the phos-phate group. The success of the in vivo treatment is related to themodification of the surface properties of the titania support

enhancing the contact of the solid with the cell membrane, whichpermits to deliver the Pt compounds at the damaged site. Theseparticular features, besides the high surface area of sol gel mate-rials, lead to a major availability of platinum, making possible to uselower platinum doses than systemic administration.

Acknowledgements

Authors want to thank to FONCICYT-CONACyT-Mexico Project95095, INNN and UAM for financial support. Also thank to Dr. J.Sanchez and Dr. J. Navarrete for their invaluable contributions tothe present work and to A. Hamdan and G. Ramırez for theirtechnical assistance.

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