Abstract 416: Regulation of osteosarcoma cell metastasis by FGFR and mTOR signaling

Osteosarcoma (OS) is the most common primary malignancy of the skeleton, occurring primarily in children and adolescents. Metastatic disease is the single most important prognostic factor with survival dropping to 15-20% in patients with lung metastases. We have recently demonstrated that high FGFR1 signaling in an oncogene-induced murine model of OS as well as in human OS samples contributes to the pathogenesis and metastasis of OS. Significantly, xenograft studies showed that genetic or pharmacological inhibition of FGFR1 decreased lung metastasis. We have identified the mTOR signaling pathway as a cooperating pathway with FGFR signaling in OS cells. Stimulation of murine and human OS cell lines with FGF2 showed an increase in both MAPK and pAkt/mTOR signaling and mTOR target genes that was inhibited by the FGFR inhibitor, PD173074. Colony growth in soft agar showed that inhibition of mTOR blocked FGF2-stimulated colony growth of OS cells and shRNA silencing of mTOR prevented FGF2-stimulated cell migration in wound/scratch assays. To confirm pathway cooperativity in vivo, we performed xenograft studies. Silencing of mTOR in FGFR1-expressing OS cells reduced tumor formation on a chick chorioallantoic membrane, with reduced pHistone-H3 expression. Orthotopic injection of OS cells demonstrated that small molecule inhibition of both FGFR1 and mTOR signaling (AZD4547 and AZD8055, respectively), showed greater inhibition of size and diameter of lung metastatic nodules than each inhibitor alone. This was associated with a decrease in the number of Ki67+ cells in lung metastases of FGFR/mTOR inhibitor-treated mice, whereas no changes in activated caspase-3 were detected. In a complementary in vivo model, tail vein injections of OS cells showed that combined FGFR/mTOR inhibition reduced cell seeding in the lungs, suggesting that FGFR/mTOR signaling are driving lung colonization independently of the primary tumor. Finally, preliminary studies indicate that long term growth of OS cells in the lung following tail vein injection may reveal a potential for OS cells to acquire chemoresistance to mTOR inhibition. The mechanisms are not yet known but are independent of the primary tumour. Taken together, our data suggest that combinatorial treatment significantly decreased lung metastasis of OS cells from primary xenografts. Ongoing analysis of activated FGFR and mTOR pathways in patient-derived tissue microarrays will enable patient stratification that will be useful in the clinical setting to exploit this as a potential anti-metastatic therapy in OS. Citation Format: Arshiya Banu, Carolina Zandueta, Fernando Lecanda, Agamemnon E. Grigoriadis. Regulation of osteosarcoma cell metastasis by FGFR and mTOR signaling [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 416.