ABSTRACT
Damage to cellular DNA is believed to determine the antiproliferative properties of platinum (Pt) drugs. This study characterized DNA damage by oxaliplatin, a diaminocyclohexane Pt drug with clinical antitumor activity. Compared with cisplatin, oxaliplatin formed significantly fewer Pt-DNA adducts (e.g., 0.86+/-0.04 versus 1.36+/- 0.01 adducts/10(6) base pairs/10 microM drug/1 h, respectively, in CEM cells, P<.01). Oxaliplatin was found to induce potentially lethal bifunctional lesions, such as interstrand DNA cross-links (ISC) and DNA-protein cross-links (DPC) in CEM cells. As with total adducts, however, oxaliplatin produced fewer (P<.05) bifunctional lesions than did cisplatin: 0.7+/-0.2 and 1.8+/-0.3 ISC and 0.8+/-0.1 and 1.5+/-0.3 DPC/10(6) base pairs/10 microM drug, respectively, after a 4-h treatment. Extended postincubation (up to 12 h) did not compensate the lower DPC and ISC levels by oxaliplatin. ISC and DPC determinations in isolated CEM nuclei unequivocally verified that oxaliplatin is inherently less able than cisplatin to form these lesions. Reactivation of drug-treated plasmids, observed in four cell lines, suggests that oxaliplatin adducts are repaired with similar kinetics as cisplatin adducts. Oxaliplatin, however, was more efficient than cisplatin per equal number of DNA adducts in inhibiting DNA chain elongation ( approximately 7-fold in CEM cells). Despite lower DNA reactivity, oxaliplatin exhibited similar or greater cytotoxicity in several other human tumor cell lines (50% growth inhibition in CEM cells at 1.1/1.2 microM, respectively). The results demonstrate that oxaliplatin-induced DNA lesions, including ISC and DPC, are likely to contribute to the drug's biological properties. However, oxaliplatin requires fewer DNA lesions than does cisplatin to achieve cell growth inhibition.
Subject(s)
Antineoplastic Agents/pharmacology , Cell Nucleus/drug effects , DNA Damage , DNA/drug effects , Organoplatinum Compounds/pharmacology , Cell Nucleus/metabolism , Cisplatin/pharmacology , DNA/metabolism , DNA Adducts/metabolism , HT29 Cells , Humans , Oxaliplatin , Tumor Cells, CulturedABSTRACT
Defects in mismatch repair are associated with cisplatin resistance, and several mechanisms have been proposed to explain this correlation. It is hypothesized that futile cycles of translesion synthesis past cisplatin-DNA adducts followed by removal of the newly synthesized DNA by an active mismatch repair system may lead to cell death. Thus, resistance to platinum-DNA adducts could arise through loss of the mismatch repair pathway. However, no direct link between mismatch repair status and replicative bypass ability has been reported. In this study, cytotoxicity and steady-state chain elongation assays indicate that hMLH1 or hMSH6 defects result in 1.5-4.8-fold increased cisplatin resistance and 2.5-6-fold increased replicative bypass of cisplatin adducts. Oxaliplatin adducts are not recognized by the mismatch repair complex, and no significant differences in bypass of oxaliplatin adducts in mismatch repair-proficient and -defective cells were found. Defects in hMSH3 did not alter sensitivity to, or replicative bypass of, either cisplatin or oxaliplatin adducts. These observations support the hypothesis that mismatch repair defects in hMutL alpha and hMutS alpha, but not in hMutS beta, contribute to increased net replicative bypass of cisplatin adducts and therefore to drug resistance by preventing futile cycles of translesion synthesis and mismatch correction.
Subject(s)
Antineoplastic Agents/pharmacology , Cisplatin/metabolism , Cisplatin/pharmacology , DNA Adducts/metabolism , DNA Repair , DNA, Neoplasm/drug effects , DNA-Binding Proteins/metabolism , Multidrug Resistance-Associated Proteins , Neoplasm Proteins/metabolism , Organoplatinum Compounds/pharmacology , Adaptor Proteins, Signal Transducing , Antineoplastic Agents/metabolism , Carrier Proteins , Chromosomes, Human, Pair 2/genetics , Colonic Neoplasms/genetics , Colonic Neoplasms/metabolism , DNA Damage , DNA Repair/genetics , DNA Replication , DNA, Neoplasm/genetics , DNA, Neoplasm/metabolism , Drug Resistance, Neoplasm , Female , Genetic Complementation Test , Humans , MutL Protein Homolog 1 , MutS Homolog 3 Protein , Nuclear Proteins , Organoplatinum Compounds/metabolism , Ovarian Neoplasms/genetics , Ovarian Neoplasms/metabolism , Oxaliplatin , Tumor Cells, Cultured/drug effectsABSTRACT
Oxaliplatin (4 mg/kg), cisplatin (2 mg/kg with 20 mg/kg mannitol) and ormaplatin (2 mg/kg) were administered i.p. twice weekly for 4.5 weeks. Lactose injections (0.9%) were used as a control for oxaliplatin and 0.9% saline injections were used as a control for cisplatin and ormaplatin. Morphometric changes to dorsal root ganglia L4-L6 were quantitated as a measure of neurotoxicity. Drug treatment resulted in a decrease in cell and nuclear area and an increase in the percentage of cells with eccentric nucleoli for neuronal cell bodies in the DRG. Immediately following treatment the order of morphometric changes was ormaplatin > cisplatin > or = oxaliplatin. The accumulation of platinum in the DRG was measured by inductively coupled plasma mass spectrometry. The order of accumulation was cisplatin > oxaliplatin > ormaplatin. Following an 8-week recovery period the order of morphometric changes to the DRG was ormaplatin approximately equal to oxaliplatin > cisplatin. This correlated with a greater retention of platinum by the DRG for ormaplatin and oxaliplatin than for cisplatin. The results suggest that ormaplatin is uniquely neurotoxic immediately following treatment in the Wistar rat model. However, following an 8-week recovery period both ormaplatin and oxaliplatin are more neurotoxic than cisplatin and this neurotoxicity correlates with a greater retention of platinum by the DRG.
Subject(s)
Antineoplastic Agents/toxicity , Cisplatin/toxicity , Ganglia, Spinal/drug effects , Organoplatinum Compounds/toxicity , Animals , Antineoplastic Agents/metabolism , Body Weight/drug effects , Cisplatin/pharmacokinetics , Ganglia, Spinal/ultrastructure , Kidney/metabolism , Liver/metabolism , Male , Organoplatinum Compounds/pharmacokinetics , Oxaliplatin , Rats , Rats, WistarABSTRACT
The possible correlation between alterations in cytokinetic response to cisplatin (CP) treatment and drug resistance in human ovarian carcinoma cell lines was examined. Using dual parameter flow cytometry, we performed detailed time-course and dose-response analysis of cell cycle modifications in the parental A2780 and resistant A2780/CP cells exposed to CP. The data suggested that drug treatment resulted in similar types of cell cycle alterations in cells with different CP sensitivity. Rapid normalization of the cytokinetic pattern in both cell lines at low doses of CP was observed. At higher drug concentrations reversible S phase delay predominated, accompanied by blocks in both G1/S and G2/M and followed by complete normalization of cytokinetic patterns in the surviving cells. CP treatment by lethal doses resulted in almost complete S phase block. The surviving cells at 72 h accumulated in G2 phase. CP-induced cell cycle perturbations, among which the most pronounced were alterations in the S phase populations, correlated with the level of DNA damage, but not with cell survival in these cell lines. However, at identical levels of DNA damage, the resistant A2780/CP cell line demonstrated decreased p53 induction and decreased apoptosis compared to the parental cell line. Thus, at equivalent levels of DNA damage, resistance in this model system correlated with a diminished p53-dependent apoptotic pathway rather than with differences in cell cycle response.
