BIOACTIVATION OF MITOMYCIN ANTIBIOTICS BY AEROBIC AND HYPOXIC CHINESE-HAMSTER OVARY CELLS OVEREXPRESSING DT-DIAPHORASE

DT-Diaphorase catalyzes a two-electron reduction of mitomycin C (MC) a nd porfiromycin (FOR) to reactive species. Many cell lines that overex press DT diaphorase and are sensitive to the mitomycins are protected from the aerobic cytotoxicity of these drugs by the DT-diaphorase inhi bitor dicumarol. The cytoprotective properties of this relatively non- specific inhibitor, however, vanish under hypoxic conditions. To ascer tain the role of DT-diaphorase in mitomycin bioactivation and cytotoxi city in living cells, a rat liver DT-diaphorase cDNA was transfected i nto Chinese hamster ovary cells. MC was equitoxic to the parental cell s under oxygenated and hypoxic conditions. In contrast, FOR was less t oxic than MC to these cells under aerobic conditions, but significantl y more toxic than MC under hypoxia. Two DT-diaphorase-transfected clon es displayed increases in DT-diaphorase activity of 126- and 133-fold over parental cells. The activities of other oxidoreductases implicate d in mitomycin bioreduction were unchanged. MC was more toxic to both DT-diaphorase-transfected lines than to parental cells; the toxicity o f MC to the transfected lines was similar in air and hypoxia. FOR was also more toxic to the DT-diaphorase-elevated clones than to parental cells under oxygenated conditions. Under hypoxia, however, the toxicit y of FOR to the transfected clones was unchanged from that of parental cells. The findings implicate DT-diaphorase in mitomycin bioactivatio n in living cells, but suggest that this enzyme does nor: contribute t o the differential toxicity of MC or FOR in air and hypoxia.