Aberrant activation of wound healing programs within the metastatic niche facilitates lung colonization by osteosarcoma cells.

Purpose: Lung metastasis is responsible for most deaths caused by osteosarcoma. How malignant bone cells coerce the lung microenvironment to support metastatic growth remains unclear. We sought to identify metastasis-specific therapeutic vulnerabilities by delineating the cellular and molecular mechanisms essential to metastatic niche formation in the lung.

Experimental Design: We used single-cell transcriptomics (scRNA-seq) to characterize molecular changes induced within lung tissues by disseminated osteosarcoma cells. We then evaluated the ability of nintedanib to reverse metastasis-specific changes in both immunocompetent mouse and immunodeficient xenograft models. Molecular pharmacodynamic studies used single-nucleus and spatial transcriptomics to define the tumor-intrinsic and -extrinsic changes induced by the drug.

Results: Osteosarcoma cells induced acute alveolar epithelial injury upon lung dissemination. scRNA-seq demonstrated that the surrounding lung stroma adopts a chronic, non-resolving wound-healing phenotype similar to diseases associated with lung injury. Accordingly, metastasis-associated lung demonstrated marked fibrosis, likely due to the accumulation of pathogenic, pro-fibrotic, partially differentiated epithelial intermediates and macrophages. Our data suggested that nintedanib prevented metastatic progression in multiple murine and human xenograft models by inhibiting osteosarcoma-induced fibrosis.

Conclusions: Fibrosis is essential to osteosarcoma lung metastasis and represents a targetable vulnerability. Our data support a model where interactions between osteosarcoma and epithelial cells induce the deposition of extracellular matrix proteins-a reaction disrupted by the anti-fibrotic TKI nintedanib. Our data shed light on the non-cell autonomous effects of TKIs on metastasis and provide a roadmap for using single-cell and spatial transcriptomics to define the mechanism of action of TKIs on metastases in animal models.