Expanding the targeted protein degradation approach with small molecule chimeras directed to the 26S proteasome

Classical proteolysis targeting chimeras (Protacs) bind specific targets and E3 ubiquitin-ligases, promoting ubiquitination and degradation of targets by the proteasome. Multiple chimeras that degrade proteins relevant in several diseases have been developed, and the number is quickly increasing, indicating their therapeutic projection. Given the specificities of proteolytic pathways and limitations in E3-based Protacs, alternative strategies in targeted protein degradation are pursued. Herein, using two targets relevant in oncology as models (IMPDH2 and CERT1), we provide proof of concept for 26S-oriented compounds based on small-molecule ligands of USP14, a 26S-associated deubiquitinase involved in substrate processing and allosteric regulation of 26S activity. Our findings will expand the potential of targeted protein degradation. Targeted Protein Degradation (TPD) relies on the binding of specific targets and E3 ubiquitin-ligases to promote ubiquitination and degradation of targets by the proteasome. Here, by designing chimeras that bind the proteasome-associated factor Usp14, the authors present a generalizable TPD approach based on proteasome-dependent and E3 ligase-independent small-molecule compounds.