Isoflavones inhibit proliferation of ovarian cancer cells in vitro via an estrogen receptor-dependent pathway.

Incidence rates of ovarian cancer remain lowest in Asian nations, which consume diets rich in soy products, whereas they remain among the highest in the United States and other Western nations, which consume low amounts of soy foods. The hypothesis of this study is that soy-derived isoflavones inhibit the proliferation of ovarian cancer cells in vitro by regulating cytokine synthesis. Cell proliferation was evaluated by bromodeoxyuridine and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. DNA synthesis of Caov-3 and NIH:OVCAR-3, two ovarian cancer cell lines, was significantly inhibited by genistein or daidzein at dietarily relevant concentrations (10(-8)-10(-10) M). Also, the number of viable cells was significantly lower (45-75%) in all isoflavone-treated groups than in the control group (P < 0.01). The addition of ICI-182780, an estrogen antagonist, blocked these inhibitory effects. In addition, interleukin-6 synthesis by these two cell lines was inhibited by genistein or daidzein; production was decreased by approximately 20% compared with the control group (P < 0.05). In contrast, transforming growth factor-beta 1 production in ovarian cancer cells incubated with genistein or daidzein was significantly greater, i.e., by approximately 30%, than in the control group (P < 0.05). Addition of ICI-182780 also neutralized the effects of isoflavones on the production of these two cytokines by ovarian cancer cells. In summary, genistein and daidzein independently modify cytokine production and reduce ovarian cancer cell proliferation via, at least in part, an estrogen receptor-dependent pathway.