EXPRESSION OF HUMAN NAD(P)H-QUINONE OXIDOREDUCTASE (DT-DIAPHORASE) INCHINESE-HAMSTER OVARY CELLS - EFFECT ON THE TOXICITY OF ANTITUMOR QUINONES

Previous studies have indicated that NAD(P)H:quinone oxidoreductase [D T-diaphorase (NQO1)] plays an important role in the bioreductive activ ation of quinone-containing antitumor agents, Although these studies d emonstrated that purified NQO1 can reduce these compounds in vitro, th e importance of NQO1 in the intracellular activation of quinone-contai ning antitumor agents remains controversial. In our study, we transfec ted human NQO1 into Chinese hamster ovary cells that do not normally e xpress NQO1 activity and obtained stable clones that expressed NQO1 ac tivity of 19-3527 nmol of 2,6-dichlorophenolindophenol reduced/min/mg of protein. The level of NQO1 expression correlated with an increased killing by streptonigrin, EO9 idinyl-1-methyl-2-(1H-indole-4,7-dione)- propenol), and 2,5-diaziridinyl-3,6-dimethyl-1,4-benzoquinone, but mit omycin C sensitivity was independent of this activity. NQO1 expression also led to a slight decrease in the sensitivity of cells to menadion e. Our data demonstrate that compounds that are efficient substrates f or NQO1 in vitro are also bioactivated in cultured mammalian cells whe n they are transfected with human NQO1. These results are consistent w ith the relative abilities of mitomycin C, streptonigrin, EO9, and 2,5 -diaziridinyl-3,6-dimethyl-l,4-benzoquinone to serve as substrates for bioreduction by human NQO1, and show that NQO1 levels are not necessa riiy predictive in terms of sensitivity to mitomycin C.