Role of NAD(P)H:(quinone acceptor) oxidoreductase (DT-diaphorase) in activation of mitomycin C under hypoxia.

The role of the two-electron reducing enzyme DT-diaphorase in the activation of mitomycin C under hypoxic conditions was investigated. Mitomycin C activity was compared in L5178Y murine lymphoblasts, which have low levels of DT-diaphorase activity, and L5178Y/HBM10 cells, which have elevated levels of enzyme activity. The cytotoxic and DNA cross-linking activities of mitomycin C were greater in L5178Y/HBM10 cells than in L5178Y cells. In L5178Y/HBM10 cells, dicoumarol, an inhibitor of DT-diaphorase, decreased cell kill and DNA cross-linking by mitomycin C in air but had no significant effect on these activities under hypoxia. By comparison, in L5178Y cells, dicoumarol had no effect on drug activity under either aerobic or hypoxic conditions. A model for the activation of mitomycin C by both one-electron and two-electron reduction is proposed. Our findings suggest that two-electron reduction by DT-diaphorase has only a limited role in the activation of mitomycin C under hypoxic conditions, although this enzyme appears to be an important contributor to drug activation under aerobic conditions.