Abstract B016: Cytokines derived from tumor-initiating osteosarcoma cells mediate a novel self-seeding mechanism relevant to growth of primary and metastatic tumors

Abstract Osteosarcoma is the most common pediatric bone tumor. Death from osteosarcoma is almost always due to metastatic spread to the lungs, which largely occurs after the primary tumor has been resected and treated with chemotherapy. Others have suggested that the primary tumor elaborates factors that suppress metastasis, though mechanisms explaining this phenomenon have not been well-validated suggested that primary osteosarcoma tumors suppress metastasis by recruiting circulating tumor cells back to the tumor via self-seeding, though the mechanism(s) of recruitment remained poorly defined. We found that osteosarcoma cells induce chemotaxis of other osteosarcoma cells in vitro. We previously demonstrated that osteosarcoma cells produce IL6 and CXCL8. Here, we found that both cytokines induced chemotaxis of osteosarcoma cells. Conversely, inhibition of both cytokines prevented osteosarcoma-induced osteosarcoma chemotaxis. These results suggested a model wherein tumor cells attract other tumor cells via inflammatory cytokine signaling. Within a living organism, such mechanisms might have implications for therapy. We wondered whether resection of a primary osteosarcoma tumor might redirect circulating tumor cells from the primary tumor to the lung (the “next best” site). To test this hypothesis, we generated orthotopic tibial tumors in mice. One cohort of mice underwent amputation of the primary tumor while another retained their primary tumors. At euthanasia, mice that underwent amputation had significantly increased tumor cell burden in the lungs. In separate experiments, lungs from mice with established primary tumors showed significantly less osteosarcoma lung burden than was seen in mice that did not have a primary tumor. Many infiltrating (labeled) tumor cells were subsequently identified within the primary tumor, strongly supporting the self-seeding model. Finally, we asked whether this same self-seeding mechanism might drive events important to lung metastasis. To test this hypothesis, mice were first inoculated with green-labeled osteosarcoma cells to induce lung metastasis. Fourteen days later, the same mice received inoculation with red labeled osteosarcoma cells. Strikingly, we found that lesions contained many more red- than green-labeled osteosarcoma cells. In addition, we have demonstrated that inhibition of IL6/CXCL8 blocks circulating tumor cell recruitment to established lung niches. This suggests circulating tumor cells preferentially target an established niche within the lung in an IL6/CXCL8 dependent manner in the absence of a primary tumor. Collectively, our data suggest that a loss of self-seeding in osteosarcoma on the excision of the primary tumor increases the metastatic burden. We are now exploring ways to leverage this biology in the development of novel therapies that prevent metastatic disease. Citation Format: Ryan D. Roberts, Amy C. Gross, James B Reinecke, Amanda Saraf. Cytokines derived from tumor-initiating osteosarcoma cells mediate a novel self-seeding mechanism relevant to growth of primary and metastatic tumors [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr B016.