Anacardic acid inhibits estrogen receptor alpha-DNA binding and reduces target gene transcription and breast cancer cell proliferation

摘要

Anacardic acid (2-hydroxy-6-alkylbenzoic acid) is a dietary and medicinal phytochemical with established anticancer activity in cell and animal models. The mechanisms by which anacardic acid inhibits cancer cell proliferation remain undefined. Anacardic acid 24:1^ω5 (AnAc 24:1^ω5) was purified from geranium (Pelargonium × hortorum) and shown to inhibit the proliferation of estrogen receptor α (ERα)-positive MCF-7 and endocrine-resistant LCC9 and LY2 breast cancer cells with greater efficacy than ERα-negative primary human breast epithelial cells, MCF-10A normal breast epithelial cells, and MDA-MB-231 basal-like breast cancer cells. AnAc 24:1^ω5 inhibited cell cycle progression and induced apoptosis in a cell-specific manner. AnAc 24:1^ω5 inhibited estradiol (E2)-induced estrogen response element (ERE) reporter activity and transcription of the endogenous E2-target genes: pS2, cyclin D1, and cathepsin D in MCF-7 cells. AnAc 24:1^ω5 did not compete with E2 for ERα or ERβ binding, nor did AnAc 24:1^ω5 reduce ERα or ERβ steady state protein levels in MCF-7 cells; rather, AnAc 24:1^ω5 inhibited ER-ERE binding in vitro. Virtual Screening with the molecular docking software Surflex evaluated AnAc 24:1^ω5 interaction with ERα ligand binding and DNA binding domains (LBD and DBD) in conjunction with experimental validation. Molecular modeling revealed AnAc 24:1^ω5 interaction with the ERα DBD but not the LBD. Chromatin immunoprecipitation (ChIP) experiments revealed that AnAc 24:1^ω5 inhibited E2-ERα interaction with the endogenous pS2 gene promoter region containing an ERE. These data indicate that AnAc 24:1^ω5 inhibits cell proliferation, cell cycle progression and apoptosis in an ER-dependent manner by reducing ER-DNA interaction and inhibiting ER-mediated transcriptional responses.