Abstract 6067: Identification of selective CBP degraders with robust preclinical PK, PD, efficacy and safety across solid tumor indications

Abstract CREB binding protein (CBP) and E1A binding protein (EP300) are paralog histone acetyltransferases involved in many cellular processes via their activity as transcription factor co-activators. Dysregulation of one or both proteins has been implicated in various cancer types, and functional genomic screens have revealed a bidirectional synthetic lethal relationship between these two paralogs in tumor cells. Due to the high homology between CBP and EP300, identifying selective chemical matter that selectively disrupts the activity of CBP has proven challenging. Small molecule inhibitors targeting the HAT or bromodomain of CBP/EP300 have been developed, however these agents exhibit hematopoietic toxicity resulting from dual inhibition, which limits their therapeutic window. Herein, we describe the PK, PD, and efficacy of selective, potent CBP degraders across various EP300-mutant cancer xenograft models. Our results show deep and sustained CBP degradation, leading to significant tumor growth inhibition in solid tumors. This anti-tumor activity was not associated with significant body weight loss or hematopoietic toxicity. Our CBP-selective protein degraders have the potential to be a first-in-class therapeutic option for patients with tumors harboring EP300 mutations. Citation Format: Darshan Sappal, 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, Shawn Schiller, Brenna Sherbanee, David Terry, Nihan Ucisik, Elizabeth Wittenborn, Qianhe Zhou, Mark Zimmerman, Laura La Bonte. Identification of selective CBP degraders with robust preclinical PK, PD, efficacy and safety across solid tumor indications 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 6067.