Anacardic Acid Inhibits Estrogen Receptor α-DNA Binding and Reduces Target Gene Transcription and Breast Cancer Cell Proliferation

Anacardic acid (AnAc; 2-hydroxy-6-alkylbenzoic acid) is a dietary and medicinal phytochemical with established anticancer activity in cell and animal models. The mechanisms by which AnAc inhibits cancer cell proliferation remain undefined. AnAc 24:1(omega 5) was purified from geranium (Pelargonium x hortorum) and shown to inhibit the proliferation of estrogen receptor alpha (ER alpha)-positive MCF-7 and endocrine-resistant LCC9 and LY2 breast cancer cells with greater efficacy than ER alpha-negative primary human breast epithelial cells, MCF-10A normal breast epithelial cells, and MDA-MB-231 basal-like breast cancer cells. AnAc 24:1(omega 5) inhibited cell cycle progression and induced apoptosis in a cell-specific manner. AnAc 24:1(omega 5) inhibited estradiol (E-2)-induced estrogen response element (ERE) reporter activity and transcription of the endogenous E-2 target genes pS2, cyclin D1, and cathepsin D in MCF-7 cells. AnAc 24:1(omega 5) did not compete with E-2 for ER alpha or ER beta binding, nor did AnAc 24:1(omega 5) reduce ER alpha or ER beta steady-state protein levels in MCF-7 cells; rather, AnAc 24:1(omega 5) inhibited ER-ERE binding in vitro. Virtual screening with the molecular docking software Surflex evaluated AnAc 24:1(omega 5) interaction with ERa ligand binding (LBD) and DNA binding (DBD) domains in conjunction with experimental validation. Molecular modeling revealed AnAc 24:1(omega 5) interaction with the ER alpha DBD but not the LBD. Chromatin immunoprecipitation experiments revealed that AnAc 24:1(omega 5) inhibited E-2-ER alpha interaction with the endogenous pS2 gene promoter region containing an ERE. These data indicate that AnAc 24:1(omega 5) inhibits cell proliferation, cell cycle progression, and apoptosis in an ER-dependent manner by reducing ER-DNA interaction and inhibiting ER-mediated transcriptional responses. Mol Cancer Ther; 9(3); 594-605. (C) 2010 AACR.