(P 258) INVESTIGATING THE ROLE OF ALVEOLAR PNEUMOCYTES IN THE LUNG MICROENVIRONMENT OF OSTEOSARCOMA METASTASES

Objective: Pulmonary metastasis is the leading cause of mortality in human and canine osteosarcoma (OS) patients. However, the contribution of lung-resident epithelial cells—particularly surfactant protein C (SPC) expressing type II alveolar pneumocytes (TIIPs)—to metastatic progression remains undefined. This study investigates the transcriptional as well as spatial changes in pneumocytes in OS lung metastases and explores their interactions with tumor cells across human, canine, and murine models.

Methods: Firstly, spatial transcriptomics was used to determine alveolar TIIPs’ abundance and location in the tumor microenvironment of human lung tissue of varying OS histological subtypes (n=7). Further, immunohistochemistry staining for SPC+ cells was carried out in both canine (n=14) and murine (n=18; orthotopic injection of K7M2 murine OS cell line) models of OS lung metastases. HALO quantitative image analysis was used to quantify SPC+ cells, and a paired t-test was performed for statistical analysis. To assess direct OS cell–pneumocyte crosstalk, primary in TIIPs alone compared to those co-cultured with OS cells.

Results: Spatial transcriptomics of human specimens showed an accumulation of TIIPs in the region immediately adjacent to the tumor. These findings were validated through observation of SPC+ staining of TIIPs surrounding OS metastases in murine and canine lung tissue. Quantification of SPC+ cells showed a significant increase of TIIPs located around the tumor margin versus the non-tumor associated lung in both canine and murine tissue. RNA sequencing revealed an increase in expression of MYC targets involved in cell proliferation and a decrease in inflammatory response gene signatures in TIIPs co-cultured with OS cells.

Conclusion: This multi-species investigation reveals that pneumocytes play an active role in the lung metastatic niche of OS. These findings highlight a previously under-recognized epithelial component of the metastatic microenvironment and identify new approaches for targeting host–tumor interactions to limit metastatic progression of OS in both human and canine patients.