BHPI (E4621-GRP)

BHPI is a potent noncompetitive inhibitor of estrogen receptor α (ERα), which disrupts the protective estrogen–ERα-mediated activation of the unfolded protein response (UPR), leading to sustained UPR activation. It specifically inhibits the growth of drug-resistant ERα-positive breast and ovarian cancer cells and induces significant tumor regression in a mouse xenograft model of breast cancer.