Low-dose genistein induces cyclin-dependent kinase inhibitors and G(1) cell-cycle arrest in human prostate cancer cells

Genistein, a naturally occurring isoflavone found chiefly in soy products, reportedly has antiprostate cancer effects, but the mechanisms underlying t hese effects are unknown. We studied the antiproliferative and apoptosis-in ducing effects of genistein in the androgen-sensitive human prostate cancer cell line LNCaP. Viable cell number was assessed by the 3-(4,5-dimethylthi azol-2-yl)-2,5-diphenyltetrazolium bromide assay; cell-cycle progression an d apoptosis were evaluated by flow cytometry; apoptosis was also assessed b y a histone enzyme-linked immunosorbent assay; and the expression of severa l cell-cycle- and apoptosis-related genes and their gene products was deter mined by northern blot analysis, western blot analysis, and/or assays based on polymerase chain reaction. Physiologic concentrations of genistein (les s than or equal to 20 muM) decreased LNCaP viable cell number in a dose-dep endent manner, induced a G(1) cell-cycle block, decreased prostate-specific antigen mRNA expression, and increased p27(KIP1) and p21(WAF1) (mRNA and p rotein) but had no effect on apoptosis or the mRNA expression of the apopto sis- and cell-cycle-related markers bcl-2, bax, Rb, and proliferating cell nuclear antigen. Higher concentrations of genistein (>20 muM) did induce ap optosis. We conclude that genistein (at physiologic concentrations) exerts potent antiproliferative effects on LNCaP cells by inducing a G(1) cell-cyc le block. The antiproliferative effects of genistein may be mediated by inc reased levels of p27(KIP1) and p21(WAF1), which are negative cell-cycle reg ulators that act as cyclin-dependent kinase inhibitors and that have been r ecently linked with prostate carcinogenesis. These findings may provide ins ights into the mechanisms underlying the apparent antiprostate cancer effec ts of soy consumption observed in epidemiologic studies. Mol. Carcinog. 29: 92-102, 2000. (C) 2000 Wiley-Liss. Inc.