Small-molecule degraders of SUMO1 induce the protein ubiquitination and degradation through CAPRIN1-CUL1-FBXO42 ubiquitin ligase for cancer therapySmall-molecule degraders of SUMO1 induce the protein ubiquitination and degradation through CAPRIN1-CUL1-FBXO42 ubiquitin ligase for cancer therapy

Targeted protein degradation has been a long sought, but elusive, strategy for discovery of small-molecule degraders that activate E3 ubiquitin ligase-mediated ubiquitination and degradation of targeted proteins in cancer cells. Here, we report a cancer cell-based drug screen in the discovery of small-molecule degraders of SUMO1 that has been an otherwise undruggable protein. Genome-scale CRISPR-CAS9 screen combined with compound pulldown proteomics identified the binding partner CAPRIN1 and the SUMO1 substrate receptor FBXO42 of CUL1 E3 ligase. Upon binding of CAPRIN1, SUMO1 degraders induce CAPRIN1-FBXO42 interaction and recruitment of SUMO1 to the CAPRIN1-CUL1-FBXO42 E3 ligase for SUMO1 ubiquitination and degradation in cancer but not normal cells. SUMO1 degraders exhibit drug-like pharmacokinetics and profound anticancer activity against various cancer models. This cancer cell-based drug screen provides an alternative approach for the discovery of new small-molecule degraders of oncoproteins as a new generation of anticancer drugs.