Ultrasound-Triggered O2 Bombs: Perfluorobromooctane-Loaded Defect-Rich Metal-Organic framework for enhanced Sono-Immunotherapy.

• MOF-based nanosonosensitizers was fabricated with defect-rich Ti-based MOF, platinum nanoparticles and the O 2 carrier PFOB. • MOF-based nanosonosensitizers produced high levels of 1O 2 and induced ICD. • MOF-based nanosonosensitizers enhanced sono-immunotherapy against both primary tumors and metastatic tumors. Sonodynamic therapy (SDT) has emerged as a promising strategy for treating tumors owing to its non-invasiveness and high tissue-penetrating depth. Improving the efficiency of electron-hole separation of sonosensitizers and alleviation of the hypoxic tumor microenvironment remain major challenges. Metal-organic frameworks (MOFs) have greatly potential in SDT application, however, exploring new sonosensitizers with high reactive oxygen species (ROS) generation and improving the efficacy through a synergistic effect in combination with other therapeutic modalities remain major challenges. Furthermore, the immunosuppressive tumor microenvironment (TME) is characterized by hypoxia, which limit the efficacy of O 2 -dependent cancer treatments including SDT and immunotherapy. Herein, we fabricated a defect-rich titanium-based MOFs using propionic acid-mediated self-templated hierarchical etching. Reductive platinum nanoparticles were embedded onto the surface of MOFs to enhance the spatial separation of electron-hole pairs and improve the quantum yield of ultrasound-generated singlet oxygen (1O 2). Finally, perfluorobromooctane was encapsulated in the MOFs to function as an oxygen carrier to develop an oxygen self-feeding nanosensitizer. In vitro and in vivo assays demonstrated that this nanoplatform could produce high levels of 1O 2 under ultrasound irradiation, which led to enhanced SDT. Moreover, this nanoplatform also relieved the immunosuppressive TME by overcoming hypoxia and enhancing immunogenic cell death to promote the infiltration of tumor-specific cytotoxic T cells into the immunologically "cold" tumor. Therefore, combination of nanoplatform-mediated SDT with anti-PDL1 antibodies effectively inhibited the primary tumors, as well as the metastatic tumors. This study provides an insightful strategy for improving SDT and broadens the application of MOF-based sonosensitizers for sono-immunotherapy. [ABSTRACT FROM AUTHOR]