Endocrine therapy induces oxidative stress in ER+ breast cancer that sensitizes persister cells to ferroptosis

Despite endocrine therapy, recurrence and progression of estrogen receptor alpha (ER)-positive breast cancer remain significant clinical problems. We therefore sought to identify mechanisms underlying endocrine-tolerant persistence. Endocrine-tolerant persister ER+ breast cancer cells were oxidatively stressed during endocrine therapy. Proteomic analysis revealed upregulation of antioxidant-driving enzymes including glutathione peroxidase 4 (GPX4) in persisters. Relief of oxidative stress enhanced persister fitness. The increased oxidative state of persisters enabled lipid peroxidation and ferroptosis. Persisters had an altered lipidome with increased levels of polyunsaturated fatty acids prone to peroxidation, which was attributable in part to increased lysophosphatidylcholine acyltyransferase 3 (LPCAT3, MBOAT5) expression via loss of ER-mediated repression during endocrine therapy. Treatment with the GPX4 inhibitor RSL3 enhanced the anti-persister effects of endocrine-based therapies in xenograft-bearing mice. These findings supporting the development of therapeutic strategies to leverage the oxidative stress induced by endocrine-based therapies and drive ferroptosis as a treatment for ER+ breast cancer.