Abstract 4318: Reversal of BRCA-1 CpG hyperthylation by genistein and (-)-epigallocatechin-3-gallate in human breast cancer cells with activated AhR

Abstract

Abstract Sporadic breast cancers, which represent the vast majority (∼90%) of breast tumor cases, do not have mutations in the tumor suppressor gene, BRCA-1 but have absent or markedly reduced levels of BRCA-1 similar to those observed in hereditary BRCA-1 tumors. Therefore, understanding the non-mutational mechanisms that contribute to repression of BRCA-1 has important implications for the prevention of both hereditary and sporadic breast tumors. Agonists of the aromatic hydrocarbon receptor (AhR) are ubiquitous in the environment and include dietary compounds, metabolites of fatty acids, industrial pollution, and photoproducts generated in the skin from ultraviolet radiation. In cultured estrogen-receptor (ER)α-positive MCF-7 breast cancer cells, we found that activation of the AhR with the prototype ligand 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) repressed by 50% estradiol-induced BRCA-1 expression. Conversely, the post-treatment with the soy isoflavone genistein and tea (-)-epigallocatechin-3-gallate (EGCG) at physiological doses (1 μM) rescued within 24 to 48 h BRCA-1 expression to levels ∼2.0 to 3.0-fold higher than those measured in cells treated with estradiol alone. Genistein and EGCG reversed BRCA-1 promoter hypermethylation in AhR-activated MCF-7 cells. In ERα-negative and AhR-overexpressing UACC-3199 breast cancer cells, genistein (1 μM) reactivated BRCA-1 expression. The post-treatment of AhR-activated MCF-7 cells with genistein and EGCG antagonized the recruitment of DNA-methyl transferase-1 (DNMT-1) enzyme to the BRCA-1 promoter. These results suggest the involvement of epigenetic mechanisms in the repression of BRCA-1 and reversal effects of genistein and EGCG against breast tumorigenesis associated with activation of the AhR. Citation Format: Ornella I. Selmin, Andreas J. Papoutsis, Donato F. Romagnolo. Reversal of BRCA-1 CpG hyperthylation by genistein and (-)-epigallocatechin-3-gallate in human breast cancer cells with activated AhR. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4318.