In Situ Bioorthogonal Synthesis of PROTACs via Dual‐Responsive Cleavage for Synergistic Photo‐Immunotherapy

Limited aqueous dispersibility and potential off-target toxicity hinder the development and clinical translation of proteolysis-targeting chimeras (PROTACs). Herein, a bioactive self-delivering "Split Nano-Assembly of Photosensitizers and Targeting Chimeras" (SNAP-TAC) theranostic platform is developed to address these challenges and enable tumor-selective synergistic photo-immunotherapy. To ensure synchronized in vivo delivery, an intact BRD4 degrader is chemically split into a hydrophobic targeting precursor and an amphiphilic photosensitizer-conjugated peptide, which spontaneously co-assemble into discrete nanoparticles. Within the tumor microenvironment (TME), elevated cathepsin B and glutathione trigger dual-responsive peptide cleavage and disulfide reduction. This unloads the bulky photosensitizer and exposes the reactive 1,2-aminothiol motifs, driving the in situ bioorthogonal synthesis of the active PROTAC via metal-free CBT-Cys click condensation. Consequently, active degraders are preferentially generated in tumor-associated environments. Additionally, the intrinsic fluorescence of the photosensitizer enables real-time fluorescence tracking in vivo to guide localized therapy. Therapeutically, upon localized irradiation, the released photosensitizer induces immunogenic cell death, which synergizes with BRD4 depletion-mediated PD-L1 downregulation and immune-pathway modulation to activate anti-tumor immunity. In vivo evaluations demonstrate that this synergy effectively remodels the suppressive "cold" TME into a cytolytic "hot" phenotype. Ultimately, this chemical biology approach effectively addresses the intrinsic selectivity and delivery limitations of conventional PROTACs.