For decades, roughly 80% of the human proteome was considered undruggable — proteins that conventional small molecules simply cannot inhibit effectively. A new class of molecular tools is fundamentally challenging that assumption, with implications for cancer, neurodegeneration, and aging-related disease that extend well beyond current pharmaceutical approaches.
Targeted protein degradation (TPD) encompasses a growing toolkit — most prominently PROTACs (proteolysis-targeting chimeras) and molecular glues — that redirect the cell's own ubiquitin-proteasome machinery to selectively destroy disease-causing proteins rather than merely inhibit them. This review in Acta Pharmacologica Sinica maps the conceptual arc from foundational chemical biology to active clinical translation, examining how bifunctional degraders recruit E3 ubiquitin ligases such as CRBN and VHL to tag pathogenic targets for proteasomal elimination. The catalytic mechanism means a single degrader molecule can sequentially destroy multiple copies of a target protein, offering substoichiometric potency that conventional occupancy-based drugs cannot match.
From a longevity and healthspan perspective, TPD is particularly compelling because many proteins implicated in aging — misfolded aggregates, senescence-associated secretory factors, and oncoproteins — have historically resisted drug development precisely because they lack clean binding pockets. The ability to degrade rather than inhibit opens therapeutic windows that were previously theoretical. That said, several critical limitations deserve emphasis: oral bioavailability of large bifunctional molecules remains a formidable challenge, the human E3 ligase landscape (over 600 known) is incompletely mapped for therapeutic exploitation, and most clinical-stage degraders are still in early Phase I/II trials with efficacy data maturing slowly. Off-target degradation also poses safety questions not yet fully characterized at scale. This review reads as confirmatory of field momentum rather than paradigm-shifting on its own — but the trajectory it documents is genuinely consequential for precision medicine in age-related disease.