quinone oxidoreductase (NQO1), an obligatory two-electron
reductase, is a ubiquitous cytosolic
enzyme that catalyzes the reduction of
quinone substrates. The NQO1- mediated two-electron reduction of
quinones can be either chemoprotection/detoxification or a chemotherapeutic response, depending on the target
quinones. When toxic
quinones are reduced by NQO1, they are conjugated with
glutathione or
glucuronic acid and excreted from the cells. Based on this protective effect of NQO1, the use of dietary compounds to induce the expression of NQO1 has emerged as a promising strategy for
cancer prevention. On the other hand, NQO1-mediated two-electron reduction converts certain
quinone compounds (such as
mitomycin C, E09, RH1 and -
lapachone) to
cytotoxic agents, leading to cell death. It has been known that NQO1 is expressed at high levels in numerous human
cancers, including breast, colon, cervix, lung, and pancreas, as compared with normal tissues. This implies that
tumors can be preferentially damaged relative to normal tissue by cytotoxic
quinone drugs. Importantly, NQO1 has been shown to stabilize many
proteins, including p53 and p33ING1b, by inhibiting their proteasomal degradation. This review will summarize the
biological roles of NQO1 in
cancer, with emphasis on recent findings and the potential of NQO1 as a therapeutic target for the
cancer therapy.