Breast cancer is the second leading cause of cancer-related death among women in the United States. One of the important classifications of breast tumors is based on the presence or absence of the estrogen receptor (ER). While the majority of breast cancers are ER-positive, approximately 30% are ER-negative. Patients with ER-positive breast cancer receive hormonal therapy using either tamoxifen or aromatase inhibitors, and have a better prognosis. However, treatment of patients with ER-negative tumor is challenging due to the poor response to hormonal therapies in the absence ER expression. Many studies have demonstrated the chemopreventive properties of green tea polyphenols (GTPs) and sulforaphane (SFN) through inhibition of DNA methyltransferase (DNMT) and histone deacetylase (HDAC) activity, respectively. In the present study, we have observed that GTPs and SFN dose-dependently inhibit the cellular proliferation in both ER-positive and ER-negative human breast carcinoma MCF-7 and MDA-MB-231 cells, respectively. Treatment of ER-negative breast cancer cells with GTPs and SFN alone or in combination leads to the reactivation of ER mRNA expression. The combination of 20 µg/mL GTPs and 5 µM SFN was found to be the optimal dose of ER reactivation at 3 days in MDA-MB-231 cells. The reactivation of ER expression was consistently correlated with ER promoter hypomethylation and hyperacetylation. Chromatin immunoprecipitation (ChIP) analysis of the ER promoter revealed that GTPs and SFN decreased the level of dimethyl H3K9, but increased the acetylation by increasing the level of acetyl H3, acetyl H4 and acetyl H3K9. In addition, a combination of GTPs and SFN significantly inhibited DNMT and HDAC activity, which might have an important role in the reactivation of ER expression in MDA-MB-231 cells. The combination of GTPs- and SFN-mediated inhibition of DNMT activity and increase of acetylation underscores the importance of DNMTs and HDACs in maintaining the repressive environment at target genes such as ER. 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 HDAC inhibitors combined with demethylating agents are a promising strategy for the epigenetic reactivation of ER expression for the effective treatment of ER-negative breast cancer.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4878.