AT416E

AT416E is a novel, small molecule, selective estrogen receptor modulator (SERM) and new chemical entity (NCE) generated as a byproduct during the synthesis of (Z)-endoxifen. Developed by Atossa Therapeutics in collaboration with the Mayo Clinic, AT416E is being evaluated for the treatment of estrogen receptor-alpha positive (ERα+) breast cancer, including endocrine-resistant tumors harboring ESR1 mutations (such as Y537S and D538G). In preclinical studies, AT416E has demonstrated potent anti-proliferative and anti-estrogenic activity in ERα+ breast cancer cell lines, as well as enhanced inhibition of cell migration and invasion compared to (Z)-endoxifen. It is currently undergoing preclinical evaluation to determine its potential for in vivo efficacy and clinical translation.