AT402E

AT402E is a novel, small molecule, (Z)-endoxifen-related new chemical entity (NCE) being developed by Atossa Therapeutics, in collaboration with the Mayo Clinic, for the treatment of estrogen receptor-alpha positive (ERα+) breast cancer. Generated as a byproduct during the synthesis of (Z)-endoxifen, AT402E acts as a selective estrogen receptor modulator (SERM) that targets and inhibits estrogen receptor alpha (ERα). In preclinical studies, AT402E has demonstrated potent anti-estrogenic and anti-proliferative activity in various ERα+ breast cancer cell lines, including those harboring activating ESR1 mutations (such as Y537S and D538G) that are associated with endocrine resistance. It has also shown potential for combination therapy with CDK4/6 inhibitors like abemaciclib.