Structurally diverse phytochemicals block xenobiotic-induced oxidative stress in prostate tumor cells by inhibiting flavin-containing NADPH oxidases

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Prostate cancer is the second leading cause of cancer death in men. Recent evidence suggests that dietary supplements including polyphenols from green tea reduce the incidence and progression of pre-cancerous prostate cells. These compounds act directly by scavenging reactive oxygen intermediates (ROI) or by inhibiting enzymatic activities important for the generation of oxidative stress in prostate cells. ROI play important roles in carcinogenesis mediating responses including mitogenesis and the expression of enzymes that produce additional ROI. In this regard, induction of the NADPH oxidases Nox1 and NQO1 is regulated by ROI. In the present studies we characterized ROI production by NADPH oxidases in two prostate cancer cell lines, PC3 and MLL cells. Lysates from both cell types readily generated basal levels of hydrogen peroxide and, in the presence of redox active iron, hydroxyl radicals. Formation of ROI was dependent on NADPH and abolished by catalase. Accumulation of hydroxyl radicals was also prevented by the hydroxyl radical scavenger dimethylsulfoxide. Addition of redox cycling chemicals including menadione and paraquat markedly enhanced the formation of both hydrogen peroxide and hydroxyl radicals. The non-specific flavoprotein inhibitor diphenylene iodonium (10 μM) suppressed the production of ROI confirming the involvement of FAD-dependent redox-active enzymes within these cells. We found that vanillic and ferulic acids readily blocked both basal and menadione-stimulated formation of ROI in lysates of PC3 and MLL cells. Resveratrol and epigallocatechin gallate also inhibited hydroxyl radical formation. The effects of each compound were time- and concentration-dependent (10-1000 μM). Taken together, these data demonstrate that interaction of NADPH oxidases by diverse phytochemicals inhibits ROI formation in prostate tumor cells. Inhibition of these enzymes may be important in protecting prostate cells against oxidative stress. (Supported by CA93798 and CA100994.)