High-dose treatment of cathepsin B-activatable doxorubicin prodrug nanoparticles that induce tumor-specific immunogenic cell death for immunotherapy of melanoma with minimal systemic toxicity.

π stacking. In melanoma cells overexpressing cathepsin B, CatB-NPs effectively induced cancer cell-specific ICD, while sparing normal cells and immune cells. When CatB-NPs-treated B16F10 cells were co-cultured with immune cells, CatB-NPs enhanced the phagocytic activity of macrophages and induced the maturation of dendritic cells (DCs). In melanoma models, CatB-NPs passively accumulated at tumor tissues through the enhanced permeability and retention effect and were selectively activated by intratumoral cathepsin B, enabling high-dose treatment that induced robust ICD. Importantly, combination therapy with CatB-NPs and anti-PD-L1 antibody enhanced ICD, DC maturation and T-cell activation, resulting in complete tumor regression in 50% of treated mice by converting the immunosuppressive tumor environment into an immune-responsive state. In a lung metastasis model, high-dose CatB-NPs with anti-PD-L1 also suppressed metastatic burden without systemic toxicity, supporting their potential as a safe and effective chemo-immunotherapy for melanoma.