ROLE OF NADPH-CYTOCHROME-C REDUCTASE AND DT-DIAPHORASE IN THE BIOTRANSFORMATION OF MITOMYCIN-C

  • 1 January 1984
    • journal article
    • research article
    • Vol. 44  (12) , 5638-5643
Abstract
Hypoxic cells of solid tumors are difficult to eradicate by X-irradiation or chemotherapy; as an approach to this problem, the effects of the bioreductive alkylating agent mitomycin C (MC) on hypoxic cells were investigated. This antibiotic was preferentially toxic to EMT6 mouse mammary tumor cells and V79 Chinese hamster lung fibroblasts under hypoxic conditions, but it was equitoxic to Chinese hamster overy cells in the presence and absence of O2. All cell lines catalyzed the formation of reactive metabolites under hypoxic conditions and contained NADPH:cytochrome c reductase and DT-diaphorase, 2 enzymes which may be responsible for the cellular activation of MC. Although a correlation existed between enzymatic activities and the formation of reactive metabolites from MC, there was no correspondence between these parameters and the degree of cytotoxicity expressed by MC under hypoxic conditions. Purified NADPH:cytochrome c reductase reduced MC in the absence of O2, with addition of cytochrome P-450 enhancing, but not participating directly in, the reduction reaction. Addition of NADP+ to cell sonicates substantially reduced NADPH:cytochrome c reductase activity, while the formation of reactive metabolites was affected only slightly; converse results were observed using mersalyl. Exposure of cell sonicates to dicumarol inhibited DT-diaphorase activity, while the rate of formation of reactive metabolites of MC was enhanced. NADPH:cytochrome c reductase and some as yet to be identified enzyme(s) evidently are important for the reductive activation of MC. DT-diaphorase and cytochrome P-450 are not directly involved in the activation of MC, but they appear to modulate the degree of activation to reactive species, which are presumably responsible for the observed cytotoxicity.