Targeted co-delivery of SPAG5 siRNA and a PD-L1 inhibitor using nanoliposomes enhances antitumor immunity in a murine prostate cancer model

Objective To investigate the role of SPAG5 in immune evasion of prostate cancer and to evaluate the anti-tumor and immunomodulatory effects of a PSMA-targeted liposome co-loading si-SPAG5 and BMS-202 (PSMA-Lipo@BMS/si-SPAG5). Methods PSMA-Lipo@BMS/si-SPAG5 was prepared by the thin-film hydration followed by post-insertion method and its physicochemical properties were characterized. In vitro, the effects of the nanoparticles on PC-3 cell uptake, SPAG5 silencing efficiency, inhibition of the PI3K/AKT/PD-L1 pathway, immunogenic cell death (ICD), apoptosis, and immune cell functions were evaluated. An RM1-hPSMA syngeneic subcutaneous tumor model was established in immunocompetent C57BL/6 mice to assess the anti-tumor efficacy, immune microenvironment modulation, and safety of the nanoparticles. Results PSMA-Lipo@BMS/si-SPAG5 exhibited a size of 126.65 ± 7.9 nm and acid-responsive release characteristics. PSMA modification enhanced cellular accumulation in vitro and significantly improved tumor targeting in vivo. SPAG5 silencing inhibited the PI3K/AKT/PD-L1 axis, and together with BMS-202 contributing to PD-L1 inhibition, synergistically induced ICD-associated marker release and apoptosis. In immune cell co-cultures, the nanoparticles promoted CD8 + T-cell activation, NK cell cytotoxicity, and induced macrophage polarization toward the M1 phenotype. In vivo, the PSMA-Lipo@BMS/si-SPAG5 group showed the most significant tumor growth inhibition. After treatment, tumor tissues exhibited decreased Th2 cells, increased NK and Th17 cells, elevated CD8 + T-cell infiltration, reduced Tregs, a pro-inflammatory shift in cytokine profile, and no obvious toxicity. Conclusion PSMA-Lipo@BMS/si-SPAG5 modulated the tumor immune microenvironment by silencing SPAG5 and inhibiting PD-L1, increasing antitumor immune cell infiltration and pro-inflammatory cytokines, and inhibiting prostate cancer growth.