Quinone reductase and

The sulfur compound sulfuraphane, extracted from fresh broccoli, has received attention in recent years because of its strong action in inducing synthesis of quinone reductase and glutathione S-transferases that help detoxify xenobiotics and may have significant anticancer activity/... 

Tirapazamine is inactivated by two-electron reduction steps catalyzed by quinone reductase, yielding first the mono-N-oxide (reaction a and compound 18). In contrast, it is activated to a cytotoxic nitroxide (16) by a one-electron reduction catalyzed by NADPH-cytochrome P450 reductase (reaction b). This delocalized radical loses one molecule of water to yield a reactive radical (reaction c and compound 17). Radical 17 can then abstract one hydrogen radical from DNA (reaction d and compound 18), leading to DNA breaks and cytotoxicity. In summary, both inactivation and activation involve reduction reactions, but cytotoxicity will depend on the relative levels of quinone reductase and CYP reductase in hypoxic cells. 

Munday R, Munday CM. Relative activities of organosulfur compounds derived from onions and garlic in increasing tissue activities of quinone reductase and glutathione transferase in rat tissues. Nutr Cancer 2001 40 205-210. 

Zhu, C.Y., and Loft, S. 2003. Effect of chemopreventive compounds from Brassica vegetables on NAD(P)H quinone reductase and induction of DNA sirand breaks in murine hepalclc7 cells. 

Isothiocyanates are potent inducers of Phase II detoxification enzymes, such as quinone reductase and glutathione transferase (Faulkner et al. 1998 Fahey and Talalay 1999 Rose et al. 2000 Basten et al. 2002 Munday and Munday 2004). The induction of these enzymes enables the excretion of potential carcinogens prior to harmftil effects and is thought to be an effective mechanism to reduce the risk of carcinogenesis. The mechanism by which this occurs is likely to be by the activation of the transcription factors Nrl2. Upon exposure to... 

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