Abstract A133: A novel class of selective estrogen receptor degraders regresses tumors in preclinical models of endocrine-resistant breast cancer.

Abstract 60–75% of all breast cancers express the estrogen receptor (ER) and thus are treated with anti-hormonal therapies that directly block ER function (e.g. Tamoxifen) or hormone synthesis (Aromatase Inhibitors). While these therapies are initially effective, acquired resistance invariably emerges. Importantly, the majority of these tumors continue to express and depend on ER for growth and survival, suggesting that novel approaches to target ER signaling have tremendous potential to treat endocrine-resistant disease. We have identified novel ER antagonists that induce degradation of ER at picomolar concentrations resulting in significant reduction in steady state ER protein levels in breast cancer cell lines. These compounds yield regression in both Tamoxifen-sensitive and - resistant models of breast cancer in vivo. Based on their unique in vitro profile, good pharmacokinetics and oral bioavailability, these compounds represent a novel class of Selective Estrogen Receptor Degraders (SERDs) that hold tremendous promise as a next generation therapy for the treatment of ER+ breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A133.