Bioactive Dietary Supplements Reactivate ER Expression in ER-Negative Breast Cancer Cells by Active Chromatin Modifications

Breast cancer is the most common cancer and the leading cause of cancer death in women. Although tamoxifen therapy is successful for some patients, it does not provide adequate benefit for those who have estrogen receptor (ER)-negative cancers. Therefore, we approached novel treatment strategies by combining two potential bioactive dietary supplements for the reactivation of ER alpha expression for effective treatment of ER alpha-negative breast cancer with tamoxifen. Bioactive dietary supplements such as green tea polyphenols (GTPs) and sulforaphane (SFN) inhibit DNA methyltransferases (DNMTs) and histone deacetylases (HDACs), respectively, which are of central importance to cancer prevention. In the present study, we have observed that treatment of ER alpha-negative breast cancer cells with GTPs and SFN alone or in combination leads to the reactivation of ER alpha expression. The combination of 20 mu g/mL GTPs and 5 mu M SFN was found to be the optimal dose of ER alpha-reactivation at 3 days in MDA-MB-231 cells. The reactivation of ER alpha expression was consistently correlated with ER alpha promoter hypomethylation and hyperacetylation. Chromatin immunoprecipitation (ChIP) analysis of the ER alpha promoter revealed that GTPs and SFN altered the binding of ER alpha-transcriptional co-repressor complex thereby contributing to ER alpha-activation. In addition, treatment with tamoxifen in combination with GTPs and SFN significantly increased both cell death and inhibition of cellular proliferation in MDA-MB-231 cells in comparison to treatment with tamoxifen alone. Collectively, our findings suggest that a novel combination of bioactive-HDAC inhibitors with bioactive-demethylating agents is a promising strategy for the effective treatment of hormonal refractory breast cancer with available anti-estrogens.