Direct-to-Biology Enables Rapid Identification of Potent FBXO22 Degraders

ABSTRACT Proteolysis Targeting Chimeras (PROTACs) are heterobifunctional molecules that bring a ubiquitin E3 ligase into proximity of a target protein to polyubiquitinate and degrade the target. PROTACs act catalytically, offering distinct advantages over conventional inhibitors and are the subject of intense study. The development of PROTACs involves extensive optimization of the chemical moiety linking two different protein-binding chemotypes, often requiring the synthesis, purification and testing of hundreds of PROTAC candidates. We used this approach to rapidly explore the landscape of targeted degradation of four different targets in parallel, combining and comparing a recently reported FBXO22-recruiting chemical warhead with warheads for the commonly used CRBN and VHL E3 ligases. Using a limited number of compounds (175 compounds in total) we observed no FBXO22-dependent degradation of these four targets. However, our libraries generated potent FBXO22 homo-PROTACs inducing self-degradation, as well as CRBN- and VHL-mediated degraders of FBXO22.