BHPI is an antagonist of estrogen receptor α (ERα) that blocks 17β-estradiol-induced proliferation of drug-resistant breast, endometrial, and ovarian cancer cell lines at concentrations ranging from 10 to 1,000 nM. It is effective in vivo, driving tumor regression in mice bearing MCF-7 xenografts at a dose of 15 mg/kg daily. BHPI specifically inhibits ERα-dependent gene expression and protein synthesis by activating the unfolded protein response in cells.
