Exploring Effectiveness of KEAP1-based PROTAC Strategy

Targeted protein degradation (TPD) uses small molecules to recruit E3 ubiquitin ligases into proximity of proteins of interest, inducing ubiquitination-dependent degradation. A major bottleneck in the TPD field is the lack of accessible E3 ligase ligands for developing degraders. To expand the E3 ligase toolbox, we sought to convert the KEAP1 inhibitor KI696 into a recruitment handle for several targets. While we were able to generate KEAP1-recruiting degraders of BET family and murine FAK we discovered that the target scope of KEAP1 was narrow, as targets easily degraded by a cereblon (CRBN)-recruiting degrader were refractory to KEAP1-mediated degradation. Linking the KEAP1-binding ligand to a CRBN-binding ligand resulted in a molecule that induced degradation of KEAP1 but not CRBN. In sum, we characterize tool compounds to explore KEAP1-mediated ubiquitination and delineate the challenges of exploiting new E3 ligases for generating bivalent degraders.