Photo‐click Proteolysis‐Targeting Chimeras Enable Intracellular Generation of PROTACs for Precise Dual Protein Degradation

Proteolysis-targeting chimeras (PROTACs) are an emerging therapeutic modality via targeted protein degradation, but plagued by concerns about systemic toxicity and a poor pharmacokinetic profile. To tackle the issues, we have devised a photo-click proteolysis targeting chimera (PCPTAC) that enables spatiotemporally controllable intracellular synthesis of PROTACs by photo-triggered bioorthogonal ligation. A photocaged dibenzosilacycloheptyne (photo-DBSH) and the complementary azide were deployed to tag the oncoprotein ligands (i.e., (+)-JQ1 for BRD4 and Olaparib for PARP1) and the E3 ligase ligand (i.e., Pomalidomide for CRBN), respectively, for a proof-of-concept study and potential treatment for triple-negative breast cancer (TNBC). Upon light irradiation, photo-DBSH-JQ1/-Olap was rapidly uncaged to give the reactive cycloalkyne-JQ1/-Olap, which immediately underwent a strain-promoted azide-alkyne cycloaddition with azide-Pomalidomide, in situ generating dual PROTACs for simultaneous degradation of BRD4 and PARP1 in TNBC MDA-MB-231 cells, with 25- and 2.4-fold more potent antiproliferative activity than the un-irradiated inhibitors and the corresponding PROTAC combination, respectively (IC₅₀ = 0.032 µM vs. 0.846 µM and 0.075 µM). Further in zebrafish models, PCPTAC promoted BRD4 degradation leading to thinner yolk sac extension and achieved 94% tumor inhibition in HeLa xenografts. This split-and-photoclick strategy paves a new avenue for developing safer and more efficacious PROTACs with synergistic antitumor effects.