New Frontiers in the Discovery and Development of PROTACs

Proteolysis targeting chimeras (PROTACs) are an emerging class of targeted protein degraders that coopt the intracellular degradation machinery to selectively deplete their respective targets. PROTACs act as bifunctional degraders that comprise ubiquitin E3 ligase- and target-binding moieties connected by chemical linkers with appropriate physicochemical properties. Through this bivalent structure, PROTACs induce the degradation of their targets via proximity-based pharmacology. Compared to conventional inhibitors, PROTACs exhibit superior pharmacologic properties in terms of efficacy, potency, selectivity, the durability of response, and efficacy against undruggable proteins. Over the last few years, the scientific community has witnessed significant endeavors to advance this field and expand the armamentarium of PROTACs. In this perspective, we highlight these advances with an emphasis on emerging PROTAC variants, PROTACtability and degradability of protein targets, expression-guided PROTACs, multivalent PROTACs, preclinical resistance, candidates evaluated in clinical trials, and prospects for the use of PROTACs as a therapeutic modality.