pH-Triggered Copper-Free Click Reaction-Mediated Micelle Aggregation for Enhanced Tumor Retention and Elevated Immuno–Chemotherapy against Melanoma

Natural killer (NK) cell-based immunotherapy presents a promising antitumor strategy and holds potential for combination with chemotherapy. However, the suppressed NK cell activity and poor tumor retention of therapeutics hinder the efficacy. To activate NK cell-based immuno–chemotherapy and enhance the tumor retention, we proposed a pH-responsive self-aggregated nanoparticle for the codelivery of chemotherapeutic doxorubicin (DOX) and the transforming growth factor-β (TGF-β)/Smad3 signaling pathway inhibitor SIS3. Polycaprolactone-poly(ethylene glycol) (PCL-PEG2000) micelles modified with dibenzylcyclooctyne (DBCO) or azido (N3) and coated with acid-cleavable PEG5000 were established. This nanoplatform, namely, M-DN@DOX/SIS3, could remain well dispersed in the neutral systemic circulation, while quickly respond to the acidic tumor microenvironment and intracellular lysosomes, triggering copper-free click reaction-mediated aggregation, leading to the increased tumor accumulation and reduced cellular efflux. In addition, the combination of DOX with SIS3 facilitated by the aggregation strategy resulted in potent inhibition of melanoma tumor growth and significantly increased NK cells, NK cell cytokines, and antitumor T cells in the tumor. Taken together, our study offered a new concept of applying copper-free click chemistry to achieve nanoparticle aggregation and enhance tumor retention, as well as a promising new combined tumor treatment approach of chemotherapy and immunotherapy.