Wen-Hao Guo, Xiaoli Qi, Yang Liu, Chan-I Chung, Fang Bai, Xingcheng Lin, Lingfei Wang, Jianwei Chen, Krystle J. Nomie, Feng Li, Meng C. Wang, Xiaokun Shu, José N. Onuchic, Jennifer A. Woyach, Michael L. Wang, Jin Wang
bioRxiv 2019
Current efforts in the proteolysis targeting chimera (PROTAC) field mostly focus on choosing the appropriate E3 ligase for a certain targeted protein, improving the binding affinities towards the target protein and the E3 ligase, and optimizing the PROTAC linker. However, it is well known that due to the large sizes of PROTAC molecules, their cellular uptake level remains an issue, posing a challenge to translate PROTACs into therapeutics. Driven by our fundamental investigation to compare how different warhead chemistry, reversible noncovalent (RNC), reversible covalent (RC), and irreversible covalent (IRC) binders, may affect the degradation of a model protein Bruton’s Tyrosine Kinase (BTK), we serendipitously discovered that cyano-acrylamide-based reversible covalent chemistry can significantly enhance the intracellular concentration and target engagement of the PROTAC. Building on this discovery, we developed RC-1 as the first reversible covalent BTK PROTAC, which has high target occupancy and is effective as both an inhibitor and a degrader. Molecular dynamics calculations and phase-separation based ternary complex assays support that RC-1 forms a stable ternary complex with BTK and Cereblon (CRBN). Additionally, RC-1 compares favorably with other reported BTK degraders in cell viability and target engagement assays and has a reasonable plasma half-life for in vivo applications. Importantly, this reversible covalent strategy can be generalized and applied to improve other PROTACs. This work can not only help to develop optimal BTK degraders for clinical applications but also provide a new strategy to improve PROTAC efficacy.
