Phytoestrogens May Inhibit Proliferation of MCF-7 Cells, an Estrogen-Responsive Breast Adenocarcinoma Cell Line

After menopause, a woman\u27s production of 17-estradiol, the predominant female sex hormone, declines. This change is associated with increased risk of osteoporosis/osteopenia and atraumatic bone fracture, cardiovascular disease, and breast and ovarian cancers. Phytoestrogens are non-steroidal compounds isolated from plants that have antagonistic, weak agonistic, or super-agonistic estrogenic effects in mammalian tissues; they have emerged as a potential therapeutic to alleviate post-menopausal symptoms. While some epidemiological evidence indicates that dietary consumption of phytoestrogens can alleviate post-menopausal health risks, other research suggests that phytoestrogens may not be completely safe. The research presented in this thesis indicates that a high concentration and sustained dose of phytoestrogens may be necessary to achieve antiestrogenic effects. MCF-7 cells, an estrogen-sensitive breast adenocarcinoma cell line, were used as a model system, and proliferating cell nuclear antigen (PCNA) was used as a marker of cell proliferation. Immunoblotting shows that genistein, a commercially purified phytoestrogen, promotes cell proliferation when administered for 24 hours, but may reduce proliferation when cells were treated for 48 hours. Genistein and estrogen have an additive effect on cells that were treated simultaneously with both hormones for 24 hours. In contrast, Promensilâ„¢, an over-the-counter phytoestrogen dietary supplement, was able to abolish expression of PCNA after 48 hours, and at high concentrations prevented estrogen-induced upregulation of PCNA after 48 hours. The clinical significance of these findings is that phytoestrogens may reduce the risk of breast cancer, but only after sustained high doses, which may be difficult if patient non-compliance is at issue. Additionally, because cell proliferation and not cell survival was investigated, we cannot say whether phytoestrogens are cytotoxic to breast cancer cells, only that they reduce proliferation