pH-responsive polymeric nanoparticles for peptide delivery: Synergistic STING pathway activation enhances tumor immunotherapy.

Peptides hold great promise in tumor immunotherapy, but suffer from poor stability and short systemic circulation. To overcome these challenges, we developed a pH-responsive nanodelivery systems (P-NPs) based on the amphiphilic block polymer PEO-PC7A. In addition to its role in peptide encapsulation and protection, PEO-PC7A intrinsically acted as a stimulator of the interferon genes (STING) agonist, activating the cGAS-STING signaling pathway and remodeling the immunosuppressive tumor microenvironment. P-NPs were successfully prepared via a self-assembly technique, yielding nanoparticles with a uniform diameter of 91.2 ± 3.5 nm. Their pH-responsive behavior was confirmed by significant change in particle size and accelerated peptide release under acidic conditions. In vitro, P-NPs effectively increased the cytotoxic activity of T cells and induced higher interleukin-2 (IL-2) secretion compared to free peptide. In a 4 T1 tumor-bearing mouse model, intravenous administration of P-NPs achieved greater tumor growth inhibition and higher intratumoral interferon-γ (IFN-γ) levels than free peptide, with minimal systemic toxicity and no significant impact on body weight. Overall, our study presented a novel multifunctional peptide nanocarrier that enhanced tumor immunotherapy efficacy by concurrently improving peptide delivery and stimulating innate immunity, providing a promising foundation for the further development of innovative combination cancer immunotherapy strategies.