Targeting Histone Acetyltransferases EP300/CBP by Novel Proline-Based PROTAC Degraders

E1A-binding proteins p300 (EP300) and CREB-binding protein (CBP) are two homologous multidomain enzymes that have emerged as promising therapeutic targets in oncology. Recent drug discovery efforts have yielded degraders that target EP300/CBP by engaging either the bromodomain or the histone acetyltransferase (HAT) domain, with the latter potentially leading to preferential or selective degradation of one paralog. Building on a potent proline-based EP300/CBP HAT domain inhibitor, we designed, synthesized, and characterized a series of novel HAT-targeting and cereblon-recruiting proteolysis-targeting chimeras (PROTACs). In particular, compound 25a was identified as a PROTAC that promotes preferential degradation of EP300 over CBP, highlighting the potential of HAT domain engagement to modulate paralog selectivity. Functional studies in REH cells showed that preferential EP300 degradation by 25a resulted in impaired proliferation, G1 cell cycle arrest, and induction of apoptosis. Thus, HAT-targeting degrader 25a provides a promising foundation for further optimization toward therapeutic applications in EP300-dependent malignancies.