Phytoestrogens have agonistic and combinatorial effects on estrogen-responsive gene expression in MCF-7 human breast cancer cells.

Phytoestrogens can exhibit agonistic actions on estrogen-dependent gene expression in breast cancer cells. Since several different phytoestrogens may be found within a single dietary plant source, we sought to investigate whether estrogen-dependent gene expression may be further influenced by the collective treatment of breast cancer cells with multiple phytoestrogens. Accordingly, we transfected MCF-7 breast cancer cells with estrogen-responsive reporters followed by treatment with one of four phytoestrogens (genistein, daidzein, formononetin, and equol) or a combination of these in the absence of estradiol. Our results demonstrated clear-cut agonistic effects of phytoestrogens on estrogen-dependent gene expression. Moreover, combinatorial treatment consistently stimulated reporter activity above that observed for individual phytoestrogens. Inasmuch as the phytoestrogens tested are frequently found together in food sources, these combinatorial responses may more accurately reflect the consequences of in vivo exposure.