DIFFERENTIAL TOXICITY OF MITOMYCIN-C AND PORFIROMYCIN TO AEROBIC AND HYPOXIC CHINESE-HAMSTER OVARY CELLS OVEREXPRESSING HUMAN NADPH-CYTOCHROME-C (P-450) REDUCTASE

Purified NADPH:cytochrome c (P-450) reductase (FpT; NADPH-ferrihemopro tein oxidoreductase, EC 1.6.2.4) can reductively activate mitomycin an tibiotics through a one-electron reduction to species that alkylate DN A, To assess the involvement of FpT in the intracellular activation of the mitomycins, transfectants overexpressing a human FpT cDNA were es tablished from a Chinese hamster ovary cell line deficient in dihydrof olate reductase (CHO-K1/dhfr(-)). The parental cell line was equisensi tive to the cytotoxic action of mitomycin C under oxygenated and hypox ic conditions, In contrast, porfiromycin cin was considerably less cyt otoxic to wild-type parental cells than was mitomycin C in air and mar kedly more cytotoxic under hypoxia. Two FpT-transfected clones were se lected that expressed 19- and 27-fold more FpT activity than the paren tal line, Levels of other oxidoreductases implicated in the activation of the mitomycins were unchanged, Significant increases in sensitivit y to mitomycin C and porfiromycin in the two FpT-transfected clones we re seen under both oxygenated and hypoxic conditions, with the increas es in toxicity being greater under hypoxia than in air, These findings demonstrate that FpT can bioreductively activate the mitomycins in li ving cells and implicate FpT in the differential aerobic/hypoxic toxic ity of the mitomycins.