Abstract 5674: Discovery of AZD9833, an oral small molecule selective degrader of the estrogen receptor (SERD)

Abstract

Abstract The estrogen receptor alpha (ERα) is expressed in >70% of breast cancers and is a clinically validated target in oncology. Anti-hormonal therapies that block ER function directly (e.g. tamoxifen) or therapies that block the production of estrogen itself (e.g., aromatase inhibitors) have proven to be effective treatments of the disease. Further advances in disease control have been made with the development of the Selective Estrogen Receptor Degrader (SERD) fulvestrant, which both antagonizes ERα-driven tumor cell growth and causes degradation of the ERα receptor. The first-generation oral SERDs, including AZD9496, showed full ER degradation in MCF-7 cells but incomplete ER degradation in other cell lines, and partial agonism. Building on that learning, extensive structure-enabled chemical optimization has resulted in the identification of a next generation oral SERD AZD9833, a potent degrader and antagonist of the ERα receptor (both EC50 <1 nM in MCF7 cells) with favorable physicochemical properties (logD7.4 <3). AZD9833 delivers maximal ERα degradation equivalent to fulvestrant in all ER+ cell lines tested, including MCF7, CAMA1, T47D and BT474. In addition, and in contrast to AZD9496, AZD9833 does not cause ER agonism in the endometrial carcinoma cell line Ishikawa in vitro and does not cause an increase in the thickness of the endometrium in juvenile rats. In several patient-derived and cell line xenograft models, including models with clinically relevant ESR1 mutations, AZD9833 completely suppresses tumor growth and gives equivalent pharmacodynamic activity to supra-clinical levels of fulvestrant. Furthermore, in an ESR1 wild-type and an ESR1 D538G PDX model, AZD9833 demonstrated combinatorial benefit with palbociclib. Based on this preclinical data AZD9833 has progressed into a multi-stage monotherapy and palbociclib combination First Time in Patient clinical trial, SERENA-1 (NCT03616587). Citation Format: James S. Scott, Thomas Moss, Steve Stokes, Willem M. Nissink, Christopher J. Morrow, Mandy Lawson, Natalie Cureton, Eric Gangl, Pablo Morentin Gutierrez, Richard Mather, Justin P. Lindemann, Andrew Sykes, David Fisher, Radoslaw Polanski, Danielle Carroll, Aisling Barton Twomey, Teresa Klinowska. Discovery of AZD9833, an oral small molecule selective degrader of the estrogen receptor (SERD) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5674.