For decades, roughly 80% of disease-causing proteins have been considered undruggable because conventional small molecules cannot block them effectively. A class of engineered molecules called PROTACs — Proteolysis Targeting Chimeras — may fundamentally change that calculus, and the challenge now is getting them where they need to go inside the body without degradation or off-target effects.
This review in Acta Pharmacologica Sinica examines how chemistry-guided principles are being applied to engineer smarter PROTAC delivery vehicles. PROTACs work by hijacking the cell's own ubiquitin-proteasome system: a bifunctional molecule simultaneously binds a target protein and an E3 ubiquitin ligase, flagging the target for destruction rather than merely inhibiting it. The review analyzes how delivery challenges — poor membrane permeability, molecular size exceeding typical drug-likeness parameters, and rapid systemic clearance — are being addressed through nanoparticle encapsulation, prodrug strategies, antibody-conjugated carriers, and stimuli-responsive release mechanisms triggered by tumor microenvironment conditions such as low pH or elevated glutathione.
PROTAC science sits at an unusually productive intersection of chemical biology and translational medicine. Several candidates are already in Phase I and II clinical trials for cancers and neurodegenerative diseases, yet delivery remains the central bottleneck separating laboratory elegance from clinical utility. The chemistry-guided framing here is meaningful: rather than adapting generic drug delivery platforms, researchers are designing carriers informed by PROTAC's unique molecular architecture and catalytic mode of action — one molecule can degrade multiple protein copies, a substoichiometric advantage over occupancy-based inhibitors. Key limitations of the current landscape include a heavy reliance on oncology models, limited in vivo pharmacokinetic data for complex delivery constructs, and the substantial manufacturing complexity these systems introduce. Still, the trajectory is compelling — this represents genuinely paradigm-shifting pharmacology if delivery hurdles are systematically resolved over the next five to ten years.