Absolute cross sections for chemoradiation therapy: Damages to cisplatin-DNA complexes induced by 10 eV electrons.

In chemoradiation therapy, the synergy between the radiation and the chemotherapeutic agent (CA) can result in a super-additive treatment. A priori, this increased effectiveness could be estimated from model calculations, if absolute cross sections (ACSs) involved in cellular damage are substantially higher, when the CA binds to DNA. We measure ACSs for damages induced by 10 eV electrons, when DNA binds to the CA cisplatin as in chemotherapy. At this energy, DNA is damaged essentially by the decay of core-excited transient anions into bond-breaking channels. Films of cisplatin-DNA complexes of ratio 5:1 with thicknesses 10, 15, and 20 nm were irradiated in vacuum during 5-30 s. Conformation changes were quantified by electrophoresis and yields extrapolated from exposure-response curves. Base damages (BDs) were revealed and quantified by enzymatic treatment. The ACSs were generated from these yields by two mathematical models. For 3197 base-pair plasmid DNA, ACS for single strand breaks, double strand breaks (DSBs), crosslinks, non-DSB cluster damages, and total BDs is 71 ± 2, 9.3 ± 0.4, 10.1 ± 0.3, 8.2 ± 0.3, and 115 ± 2 ×10-15 cm2, respectively. These ACSs are higher than those of nonmodified DNA by factors of 1.6 ± 0.1, 2.2 ± 0.1, 1.3 ± 0.1, 1.3 ± 0.3, and 2.1 ± 0.4, respectively. Since LEEs are produced in large quantities by radiolysis and strongly interact with biomolecules, we expect such enhancements to produce substantial additional damages in the DNA of the nucleus of cancer cells during concomitant chemoradiation therapy. The increase damage appears sufficiently large to justify more elaborate simulations, which could provide a quantitative evaluation of molecular sensitization by Pt-CAs.

Anticancer potential of a photoactivated transplatin derivative containing the methylazaindole ligand mediated by ROS generation and DNA cleavage.

The limitations associated with the clinical utility of conventional platinum anticancer drugs have stimulated research leading to the design of new metallodrugs with improved pharmacological properties, particularly with increased selectivity for cancer cells. Very recent research has demonstrated that photoactivation or photopotentiation of platinum drugs can be one of the promising approaches to tackle this challenge. This is so because the application of irradiation can be targeted exclusively to the tumor tissue so that the resulting effects could be much more selective and targeted to the tumor. We show in this work that the presence of 1-methyl-7-azaindole in trans-[PtCl2(NH3)(L)] (L = 1-methyl-7-azaindole, compound 1) markedly potentiated the DNA binding ability of 1 when irradiated by UVA light in a cell-free medium. Concomitantly, the formation of cytotoxic bifunctional cross-links was markedly enhanced. In addition, 1, when irradiated with UVA, was able to effectively cleave the DNA backbone also in living cells. The incorporation of 1-methyl-7-azaindole moiety had also a profound effect on the photophysical properties of 1, which can generate singlet oxygen responsible for the DNA cleavage reaction. Finally, we found that 1, upon irradiation with UVA light, exhibited a pronounced dose-dependent decrease in viability of A2780 cells whereas it was markedly less cytotoxic if the cells were treated in the absence of light. Hence, it is possible to conclude that 1 is amenable to photodynamic therapy.

Real-time in situ monitoring via europium emission of the photo-release of antitumor cisplatin from a Eu-Pt complex.

A water-soluble light-responsive antitumor agent, PtEuL, based on a cisplatin-linked europium-cyclen complex has been synthesized and evaluated for controlled cisplatin release by linear/two-photon excitation in vitro with concomitant turn-on and long-lived europium emission as a responsive traceable signal.

Non-DSB clustered DNA lesions induced by ionizing radiation are largely responsible for the loss of plasmid DNA functionality in the presence of cisplatin.

The combination of cisplatin and ionizing radiation (IR) increases cell toxicity by both enhancing DNA damage and inhibiting repair mechanisms. Although the formation of cluster DNA lesions, particularly double-strand breaks (DSB) at the site of cisplatin-DNA-adducts has been reported to induce cell death, the contribution of DSB and non-DSB cluster lesions to the cellular toxicity is still unknown. Although both lesions are toxic, it is not always possible to measure their frequency and cell survival in the same model system. To overcome this problem, here, we investigate the effect of cisplatin-adducts on the induction of DSB and non-DSB cluster DNA lesions by IR and determine the impact of such lesions on plasmid functionality. Cluster lesions are two or more lesions on opposite DNA strands with a short distance such that error free repair is difficult or impossible. At a ratio of two cisplatin per plasmid, irradiation of platinated DNA in solution with (137)Cs γ-rays shows enhancements in the formation of DNA DSB and non-DSB cluster lesions by factors of 2.6 and 2.1, respectively, compared to unmodified DNA. However, in absolute terms, the yield for non-DSB cluster lesions is far larger than that for DSB, by a factor of 26. Unmodified and cisplatin-modified DNA were irradiated and subsequently transformed into Escherichia coli to give survival curves representing the functionality of the plasmid DNA as a function of radiation dose. Our results demonstrate that non-DSB cluster lesions are the only toxic lesions present at a sufficient frequency to account for the loss of DNA functionality. Our data also show that Frank-DSB lesions are simply too infrequent to account for the loss of DNA functionality. In conclusion, non-DSB cluster DNA damage is known to be difficult to repair and is probably the lesion responsible for the loss of functionality of DNA modified by cisplatin.

The crystal structure analysis of the relative binding of cisplatin and carboplatin in a mixture with histidine in a protein studied at 100 and 300 K with repeated X-ray irradiation.

The anticancer agents cisplatin and carboplatin bind to histidine in a protein. This crystal structure study at data-collection temperatures of 100 and 300 K examines their relative binding affinities to a histidine side chain and the effect of a high X-ray radiation dose of up to ∼1.8 MGy on the stability of the subsequent protein-Pt adducts. Cisplatin binding is visible at the histidine residue, but carboplatin binding is not. Five refined X-ray crystal structures are presented: one at 100 K as a reference and four at 300 K. The diffraction resolutions are 1.8, 2.0, 2.8, 2.9 and 3.5 Å.

Production of the radioactive antitumoral cisplatin.

This work presents the preparation of radiolabelled cis-dichlorodiammineplatinum (II), CDDP*, sealed in a cadmium capsule. The irradiation of CDDP covered by cadmium, employing exposure times longer than 2 h, demonstrated good chemical purity and high specific activity. This finding allowed a better detection of in vivo CDDP* and suggests that it may be a good tool for studies of long-term biodistribution of pharmaceutical formulations containing this drug.

'Photocisplatin' reagents.

Owing to the effectiveness of cisplatin in cancer chemotherapy, there is a growing interest in the development of other metal complex-based drugs. Similarly, the approval of photodynamic therapy and extracorporeal photopheresis in clinical practice, and the general advantages of temporal and spatial specificity inherent in phototherapy have generated a general interest in the development of other light-dependent treatment modalities. Over a decade ago it was demonstrated that the thermally inert octahedral bisbipyridyl complex cis-dichlorobis(1,10-phenanthroline)-rhodium(Ill) chloride (BISPHEN) could be activated by light and could then mimic the thermal chemistry between cisplatin and calf thymus-DNA. Thus, the term 'photocisplatin reagents' was coined for rhodium (and related) metal complexes that are thermally inert, but which form covalent bonds with DNA upon irradiation with ultraviolet/visible light. This review discusses recent developments in the elaboration of such photocisplatin reagents.

Synchrotron photoactivation of cisplatin elicits an extra number of DNA breaks that stimulate RAD51-mediated repair pathways.

Combination of cis-platinum with ionizing radiation is one of the most promising anticancer treatments that appears to be more efficient than radiotherapy alone. Unlike conventional X-ray emitters, accelerators of high energy particles like synchrotrons display powerful and monochromatizable radiation that makes the induction of an Auger electron cascade in cis-platinum molecules [also called photoactivation of cis-platinum (PAT-Plat)] theoretically possible. Here, we examined the molecular consequences of one of the first attempts of synchrotron PAT-Plat, performed at the European Synchrotron Research Facility (Grenoble-France). PAT-Plat was found to result in an extra number of slowly repairable DNA double-strand breaks, inhibition of DNA-protein kinase activity, dramatic nuclear relocalization of RAD51, hyperphosphorylation of the BRCA1 protein, and activation of proto-oncogenic c-Abl tyrosine kinase.

Influence of 1 and 25 Hz, 1.5 mT magnetic fields on antitumor drug potency in a human adenocarcinoma cell line.

The resistance of tumor cells to antineoplastic agents is a major obstacle during cancer chemotherapy. Many authors have observed that some exposure protocols to pulsed electromagnetic fields (PEMF) can alter the efficacy of anticancer drugs; nevertheless, the observations are not clear. We have evaluated whether a group of PEMF pulses (1.5 mT peak, repeated at 1 and 25 Hz) produces alterations of drug potency on a multidrug resistant human colon adenocarcinoma (HCA) cell line, HCA-2/1(cch). The experiments were performed including (a) exposures to drug and PEMF exposure for 1 h at the same time, (b) drug exposure for 1 h, and then exposure to PEMF for the next 2 days (2 h/day). Drugs used were vincristine (VCR), mitomycin C (MMC), and cisplatin. Cell viability was measured by the neutral red stain cytotoxicity test. The results obtained were: (a) The 1 Hz PEMF increased VCR cytotoxicity (P < 0.01), exhibiting 6.1% of survival at 47.5 microg/ml, the highest dose for which sham exposed groups showed a 19.8% of survival. For MMC at 47.5 microg/ml, the % of survival changed significantly from 19.2% in sham exposed groups to 5.3% using 25 Hz (P < 0.001). Cisplatin showed a significant reduction in the % of survival (44.2-39.1%, P < 0.05) at 25 Hz and 47.5 microg/ml, and (b) Minor significant alterations were observed after nonsimultaneous exposure of cells to PEMF and drug. The data indicate that PEMF can induce modulation of cytostatic agents in HCA-2/1(cch), with an increased effect when PEMF was applied at the same time as the drug. The type of drug, dose, frequency, and duration of PEMF exposure could influence this modulation.

Formation of tryptophan radicals in irradiated aqueous solutions of hexachloroplatinate(IV): a flash photolysis study.

The oxidation of tryptophan photosensitized by PtCl6(2-) has been investigated in aqueous solutions at different pH using nanosecond laser flash photolysis. Cationic and neutral radicals of tryptophan were detected at pH 2.8 and 8.5, respectively. The generation of the radical was attributed to oxidation by Cl2- that was formed from the homolytic bond cleavage in the excited state of PtCl6(2-). The bimolecular rate constant derived from the kinetics analysis, 2.8 +/- 0.2 x 10(9) M-1 s-1, is in good agreement with the value obtained in earlier pulse radiolysis studies. Both the cationic and neutral radicals decayed by second-order kinetics, consistent with the dimerization process.

Decomposition of cisplatin in aqueous solutions containing chlorides by ultrasonic energy and light.

Decomposition of cisplatin in an aqueous 0.15 M chloride solution by diffuse daylight, by monochromatic light, and by ultrasonic energy was studied using a new HPLC method. The relative sensitivity of cisplatin to light copies the curve of the absorption spectrum of cisplatin with maximum at ca. 300 nm; however, any light below 500 nm must be avoided. Sonication also leads to a rapid decomposition of cisplatin. Irradiation by diffuse daylight or sonication of the cisplatin solutions for 5 min leads to ca. 1% amminetrichloroplatinate(II). Using HPLC analysis with diode-array spectrophotometric detection, the main decomposition product was identified as amminetrichloroplatinate(II).

Radiation chemistry of cis-platinum-nucleotide complexes.

The mechanism of gamma-radiolysis of cis-dichlorodiammineplatinum (II) (cis-Platinum) with guanosine-5'-monophosphate (L) complexes in aqueous solutions was investigated. The decomposition limiting yield G (-cis-Pt (NH3)2L2) in deaerated and nitrous oxide saturated solutions, determined by measuring the absorbance at 254 nm, was found to be 0.8 and 1.2, respectively. It was found from HPLC that, upon irradiation of the complexes, guanosine-5'-monophosphate, guanosine and guanine were released. Other products, such as sugarphosphate and sugar, could not be detected with this UV-method.

The radiation chemistry of some platinum-containing radiosensitizers and related compounds.

Oxidation and reduction of cis- and trans-dichlorodiammine platinum II (cis- and trans-PDD), cis-dichlorobis(1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole-N3)-p latinum II (cis-Flap), and cis-dichlorobis(isopropylamine)-trans-dihydroxyplatinum IV (Chip) have been studied using pulse radiolysis. Spectra corresponding to platinum in various oxidation states have been observed and several rate constants have been obtained. Reduction of all the compounds, except cis-Flap, produces species of a lower oxidation state of platinum which subsequently have both chloride ligands replaced. Ultimately, these products disproportionate. In the case of cis-Flap, reduction occurred on the nitroimidazole ligand. This was verified by the absence of platinum metal after disproportionation. Oxidation of all four compounds consists of production of a higher oxidation state of platinum followed by replacement of chloride ligands and finally disproportionation of the products. Only cis-Flap and Chip could be reduced by oxidized DNA bases. The one-electron reduction potential of cis-Flap was found to be -370 +/- 10 mV. trans-Flap had almost the same value. It was not possible to measure the potentials of the other compounds since their ligands were replaced rapidly but it is estimated that the one-electron reduction potentials decrease in the order cis- or trans-Flap greater than Chip greater than cis-PDD greater than trans-PDD.

Effect of radiation on cis-dichlorodiammineplatinum (II) and DNA in aqueous solution.

The radiolysis of cis-dichlorodiammineplatinum (II) (cis-PDD) was studied in order to better understand the mechanisms by which it acts as a radiation sensitizer. The Pt(I) intermediate formed by e- aq reduction of cis-PDD loses both chlorides rapidly, interacts with O2 to form a Pt-oxygen adduct, reacts with the hydroxyl radical adduct of thymine and the peroxy radical of t-butanol, and disproportionates to platinum metal and trans-PDD. The Pt (III) intermediate formed by OH oxidation of cis-PDD likely disproportionates to cis-PDD and Pt(IV) complexes. In a biological model, radiation-induced 3H-thymine base residue release from DNA is found to be inhibited by cis-PDD.