Abstract PR009: A new invasive zebrafish model of ewing sarcoma reveals EWSR1-FLI1-driven dysregulation of heparan sulfate proteoglycan metabolism and ERK signaling in developing tumors
Authors: Vasileva Elena , Warren Mikako , Triche Timothy J. , Amatrud James F. 
Published: September 2022

Abstract
Ewing sarcoma is a malignant tumor of bones or soft tissues with an extremely poor prognosis for patients with metastatic or relapsed disease. Ewing sarcoma is associated with the appearance of a chimeric fusion oncogene, most frequently EWSR1-FLI1 (EF1). The interaction of Ewing sarcoma cells with the tumor microenvironment is essential for tumor growth, angiogenesis, and metastasis. The tumor microenvironment includes surrounding blood vessels, immune cells, signaling molecules, and extracellular matrix. The dependence of a tumor cell on its microenvironment opens new possibilities to target not just cancer cells but also the tumor microenvironment itself. In the absence of a representative in vivo model, the role of tumor cell/microenvironmental interactions in Ewing sarcoma initiation and progression is not well-understood. To address these concerns, we developed a new in vivo genetic model of Ewing sarcoma by integrating the human EWSR1-FLI1 fusion oncogene into the zebrafish genome. Our system allows broad mosaic Cre-inducible expression of human EF1 in zebrafish, which causes rapid onset of Ewing sarcoma at high penetrance. This invasive model allows studying 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 Ewing sarcoma markers including CD99. Proteomic analysis revealed that EF1 expression affects the expression of enzymes involved in heparan sulfate proteoglycan (HSPG) metabolism. Such dysregulation of proteoglycan metabolism is associated with activation of ERK1/2 signaling pathway in tumor cells resulting in increased tumor cell proliferation and survival. 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 Ewing sarcoma cells in vitro and in vivo. Taken together, our new zebrafish model will open new possibilities to study EWSR1-FLI- driven tumorigenesis, as well as mechanisms of tumor development and progression. Our results highlight the important role of the extracellular matrix in Ewing sarcoma tumor growth and the potential of agents targeting proteoglycan metabolism as novel therapies for this disease.
Citation Format: Elena Vasileva, Mikako Warren, Timothy J. Triche, James F. Amatrud. A new invasive zebrafish model of ewing sarcoma reveals EWSR1-FLI1-driven dysregulation of heparan sulfate proteoglycan metabolism and ERK signaling in developing 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 PR009.