Abstract 1636: A new invasive zebrafish model of Ewing sarcoma reveals EWSR1-FLI1-driven dysregulation of heparan sulfate proteoglycan metabolism in developing tumors

Abstract Ewing sarcoma (ES) is a malignant bone and soft-tissue tumor with an extremely poor prognosis for patients with metastatic or relapsed disease. ES is characterized by the appearance of a chimeric fusion oncogene, most frequently EWSR1-FLI1 (EF1). In the absence of a representative in vivo model the role of tumor cell/microenvironmental interactions in tumor initiation and progression remains a subject of constant debate. To address these concerns, we developed an innovative Cre-inducible model of ES in zebrafish which allows broad mosaic expression of human EF1 in zebrafish, which causes rapid onset of ES at high penetrance. This invasive model allows study of the behavior of GFP-labeled cancer cells during tumor initiation and progression, in a complex developmental context which is not currently possible in mammals. We found that observed tumors express canonical EF1 target genes and stain for known ES markers including CD99. Proteomic analysis revealed that EF1 expression affects heparan sulfate proteoglycan (HSPG) metabolism and activates HSPG-mediated ERK signaling in EF1 expressing cells, promoting cancer cell survival and proliferation. Proteoglycans are key regulators of signaling of cell surface receptors, playing an essential role in cell-to-cell communication. Targeting heparan sulfate proteoglycans with the specific heparan sulfate antagonist Surfen reduces ERK1/2 signaling and decreases tumorigenicity of ES cells in vitro and in vivo. These results highlight the important role of the extracellular matrix in ES tumor growth and the potential of agents targeting proteoglycan metabolism as novel therapies for this disease. Citation Format: Elena Vasileva, Mikako Warren, Timothy Triche, James Amatruda. A new invasive zebrafish model of Ewing sarcoma reveals EWSR1-FLI1-driven dysregulation of heparan sulfate proteoglycan metabolism in developing tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1636.