Abstract 6064: Discovery of potent and selective EP300 degraders with anti-cancer activity

Abstract E1A binding protein (EP300) and CREB binding protein (CBP) are paralog histone acetyltransferases involved in many cellular processes via their activity as transcriptional co-activators. Dysregulation of one or both proteins has been implicated in various cancers, and functional genomic screens have demonstrated a bidirectional synthetic lethal relationship between the two genes in tumor cells. Due to the high homology between EP300 and CBP, identifying chemical matter that selectively targets EP300 or CBP has proven challenging. Here, we describe a potent, highly selective heterobifunctional degrader of EP300 with biological activity in CBP-deficient and EP300-dependent tumor cells. Targeted degradation of EP300 protein resulted in a stronger suppression of cell growth and survival than targeting the bromodomain or HAT activity of EP300/CBP with small molecule inhibitors. Anti-proliferative effects have been demonstrated in multiple cancer types, including malignant lymphomas and castration-resistant prostate tumors, highlighting the essential role of EP300 in mediating oncogenic transcription required for tumor cell growth and survival. Degradation of EP300 in vivo attenuated androgen-driven transcription and inhibited tumor growth in VCAP (AR+) prostate tumor xenografts. Importantly, no evidence of overt toxicity or thrombocytopenia was observed at therapeutically efficacious doses. These findings indicate that selective targeting of EP300 with targeted protein degradation is a safe and effective treatment strategy for advanced tumors. Citation Format: Mark Zimmerman, Ammar Adam, Hafiz Ahmad, Benjamin Adams, Ketaki Adhikari, Wesley Austin, Breanna Bullock, Julie Di Bernardo, Thomas Dixon, Danette Daniels, Claudia Dominici, GiNell Elliot, Brian Ethell, Anais Gervais, Md Imran Hossain, David Huang, Dave Lahr, Mei Yun Lin, David Mayhew, Karolina Mizeracka, Solymar Negretti, Tyler Nguyen, Olga Prifti, Darshan Sappal, Shawn Schiller, Brenna Sherbanee, David Terry, Nihan Ucisik, Elizabeth Wittenborn, Qianhe Zhou, Laura La Bonte. Discovery of potent and selective EP300 degraders with anti-cancer activity abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 6064.