title: DNA damage, cytotoxicity and free radical formation by mitomycin C in human cells.
abstract: Mitomycin C (MMC), a quinone-containing antitumor drug, has been shown to alkylate DNA and to form DNA cross-links. The ability of MMC to alkylate O6-guanine and to form interstrand cross-links (ISC) has been studied using Mer+ and Mer- human embryonic cells. Mer+ (IMR-90) cells have been reported to contain an O6-alkylguanine transferase enzyme and are, in general, more resistant to alkylating agents than the Mer- (VA-13) cell line, which is deficient in the repair of O6-lesions in DNA. Studies reported here show that MMC is more cytotoxic to VA-13 cells compared to IMR-90 cells. The alkaline elution technique was used to quantify MMC-induced ISC, and double strand breaks (DSB) in these cells. The drug-dependent formation of DSB was significantly lower in IMR-90 cells than in VA-13 cells. In contrast, no significant difference in cross-linking could be detected at the end of 2-h drug treatment. Although a small increase in cross-link frequency was observed in the VA-13 cell line relative to the IMR-90 cell line 6 h post drug treatment, it is not clear whether monoalkylated adducts at the O6-position are formed, and contribute to cross-link formation for differential cytotoxicity in VA-13 cells. Electron spin resonance and spin-trapping technique were used to detect the formation of hydroxyl radical from MMC-treated cells. Our studies show that MMC significantly stimulated the formation of hydroxyl radical in VA-13 cells, but not in the IMR-90 cells. The formation of the hydroxyl radical was inhibited by superoxide dismutase (SOD) and catalase. In addition, the presence of these enzymes partially protected VA-13 cells from MMC toxicity but not IMR-90 cells. Further studies indicated that the decreased free radical formation and resistance to MMC may be due to the increased activities of catalase and glutathione transferase in the IMR-90 cell line. These results suggest that MMC-dependent DNA damage (alkylation and DNA DSB) and the stimulation of oxy-radical formation may play critical roles in the determination of MMC-induced cell killing.
authors.affiliation: Clinical Pharmacology Branch, National Cancer Institute, Bethesda, MD 20892.
authors.forename: L
authors.initials: L
authors.lastname: Dusre
authors.forename: J M
authors.initials: JM
authors.lastname: Covey
authors.forename: C
authors.initials: C
authors.lastname: Collins
authors.forename: B K
authors.initials: BK
authors.lastname: Sinha
mesh_terms: D002374:Catalase / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects*; D004247:DNA / Q000187:drug effects; D004249:DNA Damage; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D006801:Humans; D007700:Kinetics; D016685:Mitomycin; D008937:Mitomycins / Q000494:pharmacology* / Q000633:toxicity; D013482:Superoxide Dismutase / Q000494:pharmacology
chemical_list: D005609:Free Radicals; D008937:Mitomycins; D016685:Mitomycin; D004247:DNA; D002374:Catalase; D013482:Superoxide Dismutase