CDDP-DNA Adducts Research Articles

Anti-Quenching NIR-II Excitation Phenylboronic Acid Modified Conjugated Polyelectrolyte for Intracellular Peroxynitrite-Enhanced Chemo-Photothermal Therapy.

Multidrug resistance to clinical chemotherapeutic drugs severely limits antitumor efficacy and patient survival. The integration of chemotherapy with photothermal therapy (PTT) and reactive nitrogen species has become a major strategy to enhance cancer treatment efficacy. Herein, a multifunctional peroxynitrite (ONOO-) nanogenerator (PBT/NO/Pt) for NIR-II fluorescence (NIR-II FL)/NIR-II photoacoustic (NIR-II PA) imaging-guided chemo/NIR-II PTT/ONOO- combination therapy is reported. The multifunction nanogenerator is developed by co-loading a pH-sensitive nitric oxide donor (DETA NONOate) and nicotinamide adenine dinucleotide phosphate oxidases trigger superoxide (O2 •-) generator chemotherapy drug (CDDP) to an NIR-II excitation-conjugated polyelectrolyte (PNC11BA). PNC11BA has non-conjugated alkyl chain segments in the polymer backbone and abundant positively charged phenylboronic acid in its side chains, which support the anti-quenching of NIR-II FL and the integration of DETA NONOate and CDDP into PBT/NO/Pt. In the acidic tumor microenvironment, the coordination bonds between CDDP and PNC11BA are cleaved, releasing CDDP for chemotherapeutic activity. The simultaneous release of nitric oxide (NO) and O2 •- rapidly leads to the in situ generation of the more cytotoxic reactive physiological nitrogen species ONOO-. In vitro and in vivo results prove that PBT/NO/Pt exhibited a markedly ONOO- enhanced chemo-photothermal synergistic therapy for SKOV3/DDP tumor by downregulating the intracellular glutathione and increasing CDDP-DNA adducts.

P22phox confers resistance to cisplatin, by blocking its entry into the nucleus.

Cisplatin (CDDP) is a potent chemotherapeutic agent but resistance to the drug remains a major challenge in cancer treatment. To evaluate the efficacy of CDDP in oral squamous cell carcinoma (OSCC), we found that p22phox was highly expressed in CDDP-resistant OSCC specimens. Knockdown of p22phox sensitized OSCC cell lines to CDDP (P < 0.05). Stable overexpression of p22phox augmented CDDP resistance, as evidenced by the significantly higher IC50 values. This cytoprotective effect was attributed to the abrogation of CDDP-induced apoptosis. Akt phosphorylation was increased in p22phox stable lines. However, blocking PI3K/Akt pathway only partially restored CDDP-induced apoptosis. In addition, the overexpressed p22phox in OSCC cells exhibited cytoplasmic localization with enhanced perinuclear expression, consistent with the localization pattern in OSCC specimens. Remarkably, CDDP entry into the nucleus was severely impaired in p22phox-overexpressing cells (P < 0.001), and cytoplasmically accumulated CDDP was co-localized with overexpressed p22phox. This was supported by decreased CDDP-DNA adduct formation and delayed chk1-p53 signaling activation. Together, overexpression of p22phox sequestered CDDP and caused defective CDDP entry into the nucleus, significantly attenuating CDDP-induced apoptosis. Such diminished apoptosis was further abolished by p22phox-activating PI3K/Akt pathway. Our work has suggested a novel biomarker and insight into the mechanism of CDDP resistance.

Integrin αV modulates the cellular pharmacology of copper and cisplatin by regulating expression of the influx transporter CTR1.

The αV integrin is expressed in most cancer cells where it regulates a diverse array of cellular functions essential to the initiation, progression and metastasis of solid tumors. However, little is known about how αV integrin modulates cellular sensitivity to chemotherapeutic agents, particularly the platinum drugs. In this study, we found that down-regulation of αV sensitized human M21 cells to cisplatin (cDDP) through up-regulation of the copper influx transporter CTR1. Cells selected for low αV integrin expression (M21L) were more sensitive to cDDP, accompanied by increase in CTR1 mRNA and CTR1 protein levels, more intracellular cDDP accumulation and cDDP DNA adduct formation. Basal copper (Cu) content, Cu uptake, and Cu cytotoxicity were also increased. Transfection of a luciferase reporter construct containing the hCTR1 promoter sequence revealed an increase of the hCTR1 transcription activity in M21L cells. The basis for the increased hCTR1 transcription was related to an increase in the steady-state level of Sp1, a transcription factor known to drive hCTR1 expression. These results indicate that the αV integrin modulates sensitivity of human cells to the cytotoxic effect of cDDP by regulating expression of the Cu transporter CTR1, and introduce the concept that αV expression is linked to Cu homeostasis.

Vitamin B6 metabolism influences the intracellular accumulation of cisplatin

Vitamin B6 metabolism influences the adaptive response of non-small lung carcinoma (NSCLC) cells to distinct, potentially lethal perturbations in homeostasis, encompassing nutrient deprivation, hyperthermia, hypoxia, irradiation as well as the exposure to cytotoxic chemicals, including the DNA-damaging agent cisplatin (CDDP). Thus, the siRNA-mediated downregulation of pyridoxal kinase (PDXK), the enzyme that generates the bioactive form of vitamin B6, protects NSCLC cells (as well as a large collection of human and murine malignant cells of distinct histological derivation) from the cytotoxic effects of CDDP. Accordingly, the administration of pyridoxine, one of the inactive precursors of vitamin B6, exacerbates cisplatin-induced cell death, in vitro and in vivo, but only when PDXK is expressed. Conversely, antioxidants such as non-oxidized glutathione (GSH) are known to protect cancer cells from CDDP toxicity. Pyridoxine increases the amount of CDDP-DNA adducts formed upon the exposure of NSCLC cells to CDDP and aggravates the consequent DNA damage response. On the contrary, in the presence of GSH, NSCLC cells exhibit near-to-undetectable levels of CDDP-DNA adducts and a small fraction of the cell population activates the DNA damage response. We therefore wondered whether vitamin B6 metabolism and GSH might interact with CDDP in a pharmacokinetic fashion. In this short communication, we demonstrate that GSH inhibits the intracellular accumulation of CDDP, while pyridoxine potentiates it in a PDXK-dependent fashion. Importantly, such pharmacokinetic effects do not involve plasma membrane transporters that mediate a prominent fraction of CDDP influx, i.e., solute carrier family 31, member 1 (SLC31A1, best known as copper transporter 1, CTR1) and efflux, i.e., ATPase, Cu2+ transporting, β polypeptide (ATP7B).

Protective effect of cactus cladode extract against cisplatin induced oxidative stress, genotoxicity and apoptosis in balb/c mice: combination with phytochemical composition.

BackgroundCis-Platinum (II) (cis-diammine dichloroplatinum; CDDP) is a potent antitumor compound widely used for the treatment of many malignancies. An important side-effect of CDDP is nephrotoxicity. The cytotoxic action of this drug is often thought to induce oxidative stress and be associated with its ability to bind DNA to form CDDP–DNA adducts and apoptosis in kidney cells. In this study, the protective effect of cactus cladode extract (CCE) against CDDP-induced oxidative stress and genotoxicity were investigated in mice. We also looked for levels of malondialdehyde (MDA), catalase activity, superoxide dismutase (SOD) activity, chromosome aberrations (CA) test, SOS Chromotest, expressions of p53, bax and bcl2 in kidney and we also analyzed several parameters of renal function markers toxicity such as serum biochemical analysis.MethodsAdult, healthy balb/c (20–25 g) male mice aged of 4–5 weeks were pre-treated by intraperitonial administration of CCE (50 mg/Kg.b.w) for 2 weeks. Control animals were treated 3 days a week for 4 weeks by intraperitonial administration of 100 μg/Kg.b.w CDDP. Animals which treated by CDDP and CCE were divided into two groups: the first group was administrated CCE 2 hours before each treatment with CDDP 3 days a week for 4 weeks. The second group was administrated without pre-treatment with CCE but this extract was administrated 24 hours after each treatment with CDDP 3 days a week for 4 weeks.ResultsOur results showed that CDDP induced significant alterations in all tested oxidative stress markers. In addition it induced CA in bone morrow cells, increased the expression of pro-apoptotic proteins p53 and bax and decreased the expression of anti-apoptotic protein bcl2 in kidney. On the other hand, CDDP significantly increased the levels of urea and creatinine and decreased the levels of albumin and total protein.The treatment of CCE before or after treatment with CDDP showed, (i) a total reduction of CDDP induced oxidative damage for all tested markers, (ii) an anti-genotoxic effect resulting in an efficient prevention of chromosomal aberrations compared to the group treated with CDDP alone (iii) restriction of the effect of CDDP by differential modulation of the expression of p53 which is decreased as well as its associated genes such as bax and bcl2, (iiii) restriction of serums levels of creatinine, urea, albumin and total protein resuming its values towards near normal levels of control.ConclusionWe concluded that CCE is beneficial in CDDP-induced kidney dysfunction in mice via its anti-oxidant anti-genotoxic and anti-apoptotic properties against CDDP.

Mismatch Repair Protein Deficiency Compromises Cisplatin-induced Apoptotic Signaling

Mismatch repair (MMR) proteins participate in cytotoxicity induced by certain DNA damage-inducing agents, including cisplatin (cis-diamminedichloroplatinum(II), CDDP), a cancer chemotherapeutic drug utilized clinically to treat a variety of malignancies. MMR proteins have been demonstrated to bind to CDDP-DNA adducts and initiate MMR protein-dependent cell death in cells treated with CDDP; however, the molecular events underlying this death remain unclear. As MMR proteins have been suggested to be important in clinical responses to CDDP, a clear understanding of MMR protein-dependent, CDDP-induced cell death is critical. In this report, we demonstrate MMR protein-dependent relocalization of cytochrome c to the cytoplasm and cleavage of caspase-9, caspase-3, and poly(ADP-ribose) polymerase upon treatment of cells with CDDP. Chemical inhibition of caspases specifically attenuates CDDP/MMR protein-dependent cytotoxicity, suggesting that a caspase-dependent signaling mechanism is required for the execution of this cell death. p53 protein levels were up-regulated independently of MMR protein status, suggesting that p53 is not a mediator of MMR-dependent, CDDP-induced death. This work is the first indication of a required signaling mechanism in CDDP-induced, MMR protein-dependent cytotoxicity, which can be uncoupled from other CDDP response pathways, and defines a critical contribution of MMR proteins to the control of cell death.

Combined modalities of resistance in an oxaliplatin-resistant human gastric cancer cell line with enhanced sensitivity to 5-fluorouracil

To identify mechanisms underlying oxaliplatin resistance, a subline of the human gastric adenocarcinoma TSGH cell line, S3, was made resistant to oxaliplatin by continuous selection against increasing drug concentrations. Compared with the parental TSGH cells, the S3 subline showed 58-fold resistance to oxaliplatin; it also displayed 11-, 2-, and 4.7-fold resistance to cis-diammine-dichloroplatinum (II) (CDDP), copper sulphate, and arsenic trioxide, respectively. Interestingly, S3 cells were fourfold more susceptible to 5-fluorouracil-induced cytotoxicity due to downregulation of thymidylate synthase. Despite elevated glutathione levels in S3 cells, there was no alteration of resistant phenotype to oxaliplatin or CDDP when cells were co-treated with glutathione-depleting agent, l-buthionine-(S,R)-sulphoximine. Cellular CDDP and oxaliplatin accumulation was decreased in S3 cells. In addition, amounts of oxaliplatin- and CDDP–DNA adducts in S3 cells were about 15 and 40% of those seen with TSGH cells, respectively. Western blot analysis showed increased the expression level of copper transporter ATP7A in S3 cells compared with TSGH cells. Partial reversal of the resistance of S3 cells to oxaliplatin and CDDP was observed by treating cell with ATP7A-targeted siRNA oligonucleotides or P-type ATPase-inhibitor sodium orthovanadate. Besides, host reactivation assay revealed enhanced repair of oxaliplatin- or CDDP-damaged DNA in S3 cells compared with TSGH cells. Together, our results show that the mechanism responsible for oxaliplatin and CDDP resistance in S3 cells is the combination of increased DNA repair and overexpression of ATP7A. Downregulation of thymidylate synthase in S3 cells renders them more susceptible to 5-fluorouracil-induced cytotoxicity. These findings could pave ways for future efforts to overcome oxaliplatin resistance.

Synergistic effect and possible mechanisms of tumor necrosis factor and cisplatin cytotoxicity under moderate hyperthermia against gastric cancer cells.

Peritoneal carcinomatosis is a difficult management problem, and intraperitoneal treatment approaches may provide an opportunity to intensify dose and minimize toxicity. The current experiments were conducted to characterize the cytotoxic effects of cisplatin (cDDP), tumor necrosis factor (TNF), and hyperthermia (HT) on a gastric cancer cell line in vitro under conditions achievable with intraperitoneal treatment. Seoul National University gastric cancer cell line (SNU-5), a poorly differentiated gastric cancer cell line, was tested for sensitivity to various doses of cDDP, TNF, or combinations of the two at normothermia (37 degrees C) or HT (42.5 degrees C). The effect of TNF on cellular rates of cDDP accumulation, efflux, and cDDP-DNA adduct formation were evaluated using atomic absorbance spectrometry with Zeemen background correction. During a 2-h exposure to various doses of cDDP HT, we observed a supraadditive cytotoxicity of SNU-5 with 1 to 50 micrograms/ml of TNF (p2 = 0.0001). In the presence of the three-agent combination (HT, TNF, and cDDP) we observed statistically significant increases in total cellular accumulation of cisplatin (p2 = 0.016); a nonsignificant decrease in cellular efflux of drug (p2 = 0.098); and a 40% increase in persistent cisplatin DNA damage as measured by atomic absorption spectrophotometry (p2 = 0.06). These patterns were specifically not seen with the combinations of cDDP and HT, or cDDP and TNF. These data provide the experimental basis for the use of TNF and cDDP with HT in the treatment of gastric cancer and support the investigation of these agents in vivo in the regional treatment of peritoneal carcinomatosis.

Response of sensitive and resistant IgM immunocytomas to cis -diamminedichloroplatinum(II) does not correlate with the platination level or with the formation or removal of DNA adducts

An IgM immunocytoma cell line sensitive to cis-diamminedichloroplatinum(II) (CDDP) and a subline with acquired resistance were grown in LOU/M rats. In a previous study with such rats that had been treated with a high dose of CDDP (10 mg/kg) the tumors did not show differences in cellular platinum content or DNA-adduct levels, either immediately after treatment or 24 h later. Recently, this high dose was found to overcome resistance. Therefore, the study was repeated with a 10-fold lower dose (1 mg/kg, i.v.). At 1 and 24 h after treatment, tumor and kidney tissue were assayed for cellular platinum (atomic absorption spectroscopy, AAS) and DNA platination (immunochemical detection of the four CDDP-DNA adducts). The results were compared with previous data. All tissues showed a linear response to dose with regard to platinum uptake as well as adduct formation, with no quantitative difference being seen between the tumors. Also the relative occurrence of the four adducts was very similar. Between 1 and 24 h, in tumors a substantial decrease occurred in both platinum content and adduct level; the kidneys showed little reduction, if any. At the lower CDDP dose a somewhat larger loss of platinum and removal of DNA adducts was observed for the resistant tumor, but these differences could be explained by "dilution", as this tumor continues to grow after low-dose treatment (about 20% within 24 h). Since the strong difference observed between the tumors in sensitivity to CDDP cannot be attributed to differences in CDDP uptake, efficiency of adduct formation, or repair capability, other mechanisms are held responsible.

Correlation of the response to cisplatin of human ovarian cancer cell lines, originating from one tumor but with different sensitivity, with the recovery of DNA adducts.

Cis-Diamminedichloroplatinum(II) (CDDP) is used in the treatment of various cancers, with or without ionizing radiation. During treatment, resistance may develop, and cross-resistance can also occur. DNA is the main target for CDDP and ionizing radiation, and we therefore evaluated the correlation between the amount of CDDP-DNA adducts and the cytotoxic activity of CDDP in human ovarian cancer cell lines with different platinum sensitivities. DNA-adduct levels were investigated 18 hr after CDDP exposure in three cell lines originating from the same human ovarian cancer. The least sensitive cells appeared to have the largest amounts of CDDP-DNA adducts, while the most sensitive had higher adduct levels than the parental cells. The proportion of the four adducts measured (i.e., Pt-G, Pt-AG, Pt-GG, and G-Pt-G) was comparable in all cell lines, with a preference for Pt-GG adduct formation (> 50% of the adducts). Intracellular CDDP concentrations were higher in sensitive than in resistant cells, in contrast to the degree of CDDP adduct formation. Data obtained following continuous exposure of CDDP-resistant cells to CDDP suggest that DNA repair is partly responsible for resistance to CDDP. We conclude that the amount of CDDP-DNA adduct formation in cancer cells is not a predictor of CDDP cytotoxicity.

PARTIAL CHARACTERIZATION OF A CISPLATIN-RESISTANT SUBLINE OF MURINE RIF-1 TUMOR-CELLS

We have developed a drug-resistant cell line (RIF/Ptr1) (R) from the murine radiation-induced fibrosarcoma (RIF-1) also designated Pts or (S). This subline has been characterized previously by an increased resistance to cisplatin (cis-diamminedichloroplatinum(II) or CDDP), lowered intracellular CDDP concentrations, and elevated intracellular glutathione (GSH) levels (1.4-2.5-fold) but unaltered formation of CDDP-DNA interstrand cross-links. In this work, we have shown that RIF/Ptr1 cells were also resistant to carmustine (BCNU) and X-irradiation. Neither cell line had P-glycoprotein 170. The intrastrand CDDP-DNA adduct level was proportional to the concentration of intracellular CDDP. The oxygen consumption, ATP level, and glycolysis were similar in both cell lines. The cisplatin influx and efflux showed that the RIF/Ptr1 cells had lower drug influx and higher drug efflux compared to RIF-1. We conclude that the major difference between the cisplatin sensitive and cisplatin-resistant cells in this model is the regulation of cisplatin transport probably at the cell membrane level suggesting that a membrane active transport system other than P-glycoprotein 170 is involved. Whether glutathione is linked to the putative membrane transporter needs further investigation.

Pharmacokinetics and tissue distribution of cisplatin in nude mice: platinum levels and cisplatin-DNA adducts.

The pharmacokinetics of platinum (Pt) and cisplatin (CDDP)-DNA adducts were studied in nude mice after single-dose CDDP treatments. Whole blood, serum, kidney, lever, testis, brain, and tumor were collected at different intervals after injection of CDP at different dose levels. Pt was measured with flameless atomic absorption spectrometry (FAAS) or adsorptive voltammetry (AdV) and CDDP-DNA adducts with quantitative immunohistochemistry. The drug was immediately absorbed into the blood circulation (peak serum Pt levels were reached within 5 min) after i.p. CDDP administration, and distribution into most tissues also occurred rapidly (tissue Pt levels peaked at 15 min). With a sampling period of 7 days there was a biphasic elimination of Pt from blood, serum, and tissues. In the brain the pharmacokinetics differed with a gradual accumulation of Pt occurring during the 1st week. Formation of CDDP-DNA adducts in tissues was a slower process, with maximal levels being achieved at between 30 min and 4 h after drug administration, followed by a steady state lasting for at least 24 h. Each tissue type had its specific immunohistochemical staining pattern of adducts. With escalating CDDP doses there was a linear, or almost linear, increase in Pt concentrations and CDDP-DNA adduct levels in all sample types examined. These results suggest that a fair estimation of the amount of drug in tumor and normal tissues can be made from analysis of serum Pt at a fixed time point after a single dose of CDDP.

Evaluation of a method for quantitative immunohistochemical analysis of cisplatin‐DNA adducts in tissues from nude mice

The reproducibility of an immunohistochemical method for visualization and quantitation of the cytotoxic drug cisplatin (CDDP) in its active position, bound to nuclear DNA, was investigated in tissues from CDDP-treated nude mice. Kidney, liver, and tumor sections were stained with a PAP technique using an antiserum elicited against CDDP-DNA adducts. The resulting brown nuclear precipitate was quantitated using a CAS 200 image analyzer. The variance components of the errors in the staining procedure and in the image analysis were estimated. The method was found to be feasible for comparisons between slides of the same type of tissue, stained in the same batch, and measured by one observer on one occasion. The method should be a valuable tool for studies of CDDP pharmacodynamics, sensitivity prediction, and the effects of interactions between CDDP and other drugs and chemomodulators.

DNA CROSS-LINKING AND REPAIR IN CISPLATIN-RESISTANT HUMAN TUMOR-CELLS FOLLOWING EXPOSURE TO A NEW CISPLATIN ANALOG, CI-973

cis-1, 1-Cyclobutanedicarboxylato(2R)-2-methyl-1 4-butanediammineplatinum(II) (CI-973; NK121) is a second generation analogue of cisplatin (CDDP). This analogue caused fewer undesirable side effects in vivo than CDDP and produced a tumoricidal effect superior to that of CDDP against CDDP-resistant human tumor cells in vitro. However, the mechanisms responsible for the cross-sensitivity to CI-973 in these resistant cells have not been determined. Using a human colon carcinoma cell line (LoVo) and its CDDP-resistant counterpart (CP2.0) as study models, we found that although, on a molar basis, CI-973 was less cytotoxic than CDDP in LoVo, it partially reversed the resistance of CP2.0 cells, i.e., the magnitude of resistance was reduced from 13-fold for CDDP to 3-fold for CI-973. We investigated DNA repair as a possible mechanism for the different magnitudes of resistance of these two agents. The repair efficiency was measured by the rate of removal of drug-induced DNA interstrand cross-links (determined with the ethidium bromide fluorescence binding assay) and by unscheduled DNA synthesis. Our results showed that although the resistant CP2.0 cells were more efficient at repairing CDDP-induced DNA cross-links than LoVo cells, the rate of repair of CI-973-induced DNA adducts in CP2.0 was significantly lower than that for CDDP-DNA adducts at equi-cross-linking drug concentrations. This difference was not observed in the sensitive LoVo cells. The concomitant association of a slower rate of removal of CI-973-induced adducts with a lower magnitude of resistance to CI-973 suggests that a reduced efficiency in repairing the CI-973-induced DNA damage in CDDP-resistant CP2.0 cells may in part contribute to the sensitivity of the resistant cells to this novel CDDP analogue.

Pharmacokinetic-dynamic relationship of cisplatin in vitro: simulation of an i.v. bolus and 3 h and 20 h infusion.

The profiles of an i.v. bolus and 3 h and 20 h infusion of cisplatin (CDDP) were simulated in vitro by using a culture of the IGROV1 human ovarian cancer cell line. Disappearance of pharmacologically active unbound CDDP was accomplished by adding human albumin to the medium. Total and unbound CDDP and CDDP-DNA adduct levels were quantitated by atomic absorption spectroscopy (AAS), and tumour cell survival was measured by the clonogenic assay. The design of the experiment resulted in non-significant differences in the magnitude of the area under the concentration-time curve (AUC) of unbound CDDP between the three dose-input functions (AUC i.v. bolus, 6.34 +/- 0.36; 3 h infusion, 6.35 +/- 0.59; and 20 h infusion, 6.76 +/- 0.40 micrograms h ml-1). Also, the differences between the area under the CDDP-DNA adduct-time curves (AUA) of the three dose-input functions were not significant. The initial rate of decline of the CDDP-DNA adduct-time curve was significantly higher for the i.v. bolus and 3 h infusion than for the 20 h infusion. There was a log-linear relationship between the AUC of unbound CDDP and cell survival. These relationships were not significantly different between the three dose-input functions. Variation in the rate of input of CDDP leads to differences in the shape of the AUC and AUA without significant effects on cell survival.

Response of peritoneal solid tumours after intraperitoneal chemohyperthermia treatment with cisplatin or carboplatin.

The combination of heat and chemotherapy was studied in an intraperitoneal tumour model. Rats bearing peritoneal CC531 tumours (2-6 mm) were treated i.p. with cDDP or CBDCA [maximal tolerated dose (MTD)] in combination with regional hyperthermia (41.5 degrees C, 1 h) of the peritoneal cavity. The addition of hyperthermia to the i.p. treatment led to a decrease in the MTD of cDDP by 33.3% at 41.5 degrees C. This was due to increased nephrotoxicity. The MTD of CBDCA did not change as a result of hyperthermia treatment. The chemo-hyperthermia treatment resulted in more cDDP or CBDCA DNA adducts in peritoneal tumours after the combined treatment than after chemotherapy alone. The increased tumour platinum concentrations, rising from 1.3 micrograms Pt g-1 tumour at 37 degrees C to 5.4 micrograms Pt g-1 tumour at 41.5 degrees C for cDDP and from 0.2 microgram Pt g-1 tumor to 0.7 microgram Pt g-1 tumour at 41.5 degrees C for CBDCA, contributed considerably to the enhanced numbers of cDDP or CBDCA DNA adducts. As a result of the latter, i.p. chemotherapy combined with regional hyperthermia led to an increase in tumour growth delay (TGD) after increasing the temperature to 41.5 degrees C for cDDP and CBDCA (by 40 days for cDDP, 22 days for CBDCA). These data were in agreement with the in vitro findings, i.e. that higher temperatures led to increased cytotoxicity.

Effects of temperature on the interaction of cisplatin and carboplatin with cellular DNA

Increased levels of cisplatin (cDDP)- and carboplatin (CBDCA)-DNA adducts were detected in cDDP (10 μM)- and CBDCA (6 mM)-treated CC531 cells when the temperature was raised from 37° to 43°. In the case of cDDP, increased DNA adduct formation was already detectable at 38.5°; additional temperature steps led to further increases in DNA modification. Increased CBDCA-DNA adduct formation was observed only at temperatures higher than 40°. In vitro studies on the interaction of CDDP and CBDCA with isolated salmon sperm DNA, however, demonstrated no significant differences in the DNA binding rate between 37° and 43° for cDDP and a minor effect for CBDCA only at 43°, almost totally excluding a direct temperature effect on DNA platination in this temperature range. Furthermore, neither the stability of the formed platinum-DNA adducts nor the rate of adduct loss in CCS31 cells was changed at higher temperatures. The observed difference in cellular adduct formation, however, could be related to increased uptake of cDDP and CBDCA into CC531 cells at higher temperatures. In the case of cDDP, a temperature shift from 37° to 38.5° resulted in a significantly higher intracellular platinum concentration (0.03± 0.01 vs 0.071± 0.021 μg platinum/10 6 cells, respectively); for CBDCA, temperatures 3 ⩾ 41.5° were needed to increase the platinum concentration significantly above 37° values (0.3± 0.1 vs 0.6± 0.1 μg platinum/10 6 cells, respectively). In addition, the increase in DNA adduct formation of cDDP and CBDCA at elevated temperatures was comparable with the increase in cDDP-DNA adducts after a cDDP concentration escalation at 37°, indicating a concentration-dependent increase in cDDP-DNA adducts. It seems that heat affects primarily the cellular uptake of cDDP and CBDCA and not their covalent binding to DNA.

Effects of the modulating agent WR2721 and its main metabolites on the formation and stability of cisplatin-DNA adducts in vitro in comparison to the effects of thiosulphate and diethyldithiocarbamate

The influence of the modulating agent WR2721, its active thiol-metabolite WR1065 and the symmetrical disulphide WR33278 on the in vitro formation and stability of cis-diamminedichloroplatinum(II) (cisplatin, CDDP)-DNA adducts was investigated and compared with the effects of the highly nucleophilic modulating agents diethyldithiocarbamate (DDTC) and thiosulphate (TS). Salmon sperm DNA (0.5 mg/mL) was incubated with 25 μg/mL (83 μM) cisplatin for 1 hr in 50 mM phosphate buffer, pH7.2 at 37° in the absence or presence of modulating agent. DDTC and TS were potent inhibitors of the platination of the DNA (95 and 89%, respectively, with 4.2 mM of modulating agent). The WR-compounds were also remarkably active in the inhibition of DNA platination. Prevention of adduct formation in the presence of 4.2 mM WR-compound decreased in the order WR1065 (74%) > WR33278 (63%) > WR2721 (51%). The prevention of CDDP-DNA adduct formation by WR1065 was strongly concentration-dependent up to 4.2 mM but at higher concentrations this protection hardly increased at all. In the presence of the modulating agents, increased levels of CDDP monofunctionally bound to a guanine residue were observed with a simultaneous decrease in the relative abundance of bifunctional adducts. All modulators were also able to reverse part of the CDDP-DNA adducts formed. After a 2-hr incubation of already platinated salmon sperm DNA with 4.2 mM of modulating agent, the removal of Pt from DNA amounted to about 43% with DDTC, 28% with WR1065 and 13–14% with TS, WR2721 and WR33278. Even CDDP bifunctionally bound to two adjacent guanines in the same DNA strand, which is considered to be a very stable adduct, was partly reversed. Our observations suggest that WR2721, especially when administered prior to or concomitantly with CDDP, can be expected to protect those tissues from CDDP-induced damage to DNA that are able to efficiently dephosphorylate WR2721 followed by uptake of the thiol metabolite WR1065. This stresses the importance of a selective formation and uptake of WR1065 by non-tumour tissues for the successful use of WR2721 as a protective agent in combination with platinum-based cancer chemotherapy.

Cellular pharmacokinetics of carboplatin and cisplatin in relation to their cytotoxic action

We have studied the cellular pharmacokinetics of carboplatin (CBDCA), as part of the evaluation of the antitumor activity of CBDCA in cancers limited to the peritoneal cavity in comparison with cisplatin (cDDP). The uptake of CBDCA into L1210 (lymphosarcoma), CC531 (colonic carcinoma), COV413.B (human ovarian carcinoma) and NB1 (human neuroblastoma) cells was 1.5 to 13 times lower than the uptake of cDDP. The uptake of CBDCA into human ovarian carcinoma cells, taken directly from patients, was also 8–20 times lower than cDDP. Platinum concentrations, expressed as a percentage of the total intracellular Pt concentration, were similar for CBDCA and cDDP in cytosol and nucleus/membrane fractions. A second major difference between the drugs was their binding to DNA. Less CBDCA-DNA than cDDP-DNA adducts were formed after incubation at equimolar amounts of drug with isolated salmon sperm DNA (5–25 times less). A 16–69 times higher concentration of CBDCA than cDDP was needed to induce similar changes in cell growth activity (50% [ 3H]thymidine inhibition) in CC531 and COV413.B cells, indicating that equitoxicity can only be achieved when tumor cells are exposed to higher concentrations of CBDCA than cDDP. Similar toxicity was achieved in CC531 cells after incubation with a 16-fold higher CBDCA dose than cDDP. Comparable intracellular platinum concentrations, however, were obtained with a 10-fold higher CBDCA dose, suggesting that cellular pharmacokinetics of the drugs are different. Regarding drug uptake and pharmacokinetics the mechanism of action of CBDCA differed from cDDP at a cellular level.