TLR7 Agonist Nanomedicine Suppresses Lung Metastasis of Osteosarcoma by Remodeling the Immune Microenvironment

ABSTRACT Osteosarcoma (OS) is an aggressive malignancy with high pulmonary metastatic potential, and effective therapies targeting metastasis and modulating the immunosuppressive tumor microenvironment are urgently needed. This study aimed to evaluate a TLR7 agonist liposome (1V209‐Cho‐Lip) for its anti‐metastatic effects and mechanisms in OS. In both the OS tail‐vein transplantation mouse model and orthotopic transplantation mouse model, 1V209‐Cho‐Lip significantly reduced the pulmonary metastatic burden and prolonged overall survival. Flow cytometry analysis revealed that 1V209‐Cho‐Lip intervention reshaped both pre‐metastatic niche (PMN) and the immune microenvironment (IME) in lung tissue, and enhanced germinal center responses in tumor‐drained lymph nodes, suggesting its ability to induce systemic anti‐tumor immunity. Single‐cell transcriptomics analysis further demonstrated that treatment with 1V209‐Cho‐Lip alleviates myeloid‐mediated immunosuppression, promotes CD8 + T‐cell activation and clonal expansion, and improves intercellular communication between tumor cells and immune cells. Moreover, 1V209‐Cho‐Lip showed significant synergistic effects when combined with anti‐PD‐1 antibodies or methotrexate (MTX), significantly enhancing the inhibition of metastatic progression and primary tumor growth. Taken together, comprehensive data indicate that 1V209‐Cho‐Lip acts as an immunomodulator with considerable translational potential, suitable for adjuvant therapy or combination regimens in the treatment of OS.