A carrier-within-a-carrier system with calcium nanoparticles encapsulated in β-cyclodextrin-polysaccharide hydrogel for verteporfin delivery and radiosensitization in orthotopic osteosarcoma.

Osteosarcoma remains a clinical challenge due to its high invasiveness, early metastasis, and intrinsic radioresistance, which collectively limit the efficacy of conventional treatments and immunotherapy. Here, we developed a pH-responsive hydrogel reservoir, referred to as VP/CaNPs@Gel, by integrating verteporfin (VP)-loaded CaCO3 nanoparticles (CaNPs) into a β-cyclodextrin-crosslinked polysaccharide hydrogel to achieve precise radiosensitization and immunomodulation. The hydrogel undergoes rapid in-situ crosslinking to form a robust scaffold, ensuring the sustained and pH-triggered release of VP and Ca2+ within the tumor microenvironment. In vitro assays demonstrated that VP/CaNPs@Gel significantly amplifies radiation-induced reactive oxygen species (ROS) production and triggers robust pyroptotic cell death. In an in vivo orthotopic osteosarcoma model, VP/CaNPs@Gel effectively suppressed tumor growth and markedly enhanced the efficacy of immune checkpoint blockade under X-ray. Mechanistically, treatment induced PD-L1 upregulation, elevated systemic IL-1β, IL-18, and IFN-γ levels, promoted dendritic cell maturation and CD8+ T cell infiltration, increased M1 macrophage polarization, and reduced regulatory T cells and M2 macrophages. These shifts effectively converted the immunologically "cold" tumor into a "hot" state responsive to immune checkpoint inhibitors. This carrier-within-a-carrier strategy provides a multifunctional platform that couples potent radiosensitization with immunomodulation, offering a promising approach to overcoming radioresistance and improving therapeutic outcomes in osteosarcoma.