Abstract 4190: Expression of a human CIC-DUX4 fusion is sufficient to induce malignant small round blue cell tumors in zebrafish: a new model of CIC-DUX4 sarcoma for translational research

Abstract

Abstract CIC-DUX4 sarcomas are aggressive soft-tissue malignancies characterized by frequent metastases and uniformly poor survival. Histologically, CIC-DUX4 sarcomas resemble Ewing sarcomas but do not express EWS-FLI1 or other FET-ETS fusion genes typical of Ewing sarcoma. The molecular origins of these tumors began to be clarified with the discovery that they harbor characteristic t(4; 19) or t(10; 19) chromosomal translocations that fuse the transcriptional repressor CIC with the homeodomain-containing protein DUX4. The resulting CIC-DUX4 fusion protein acts as an aberrant transcription factor. However, the critical targets of CIC-DUX4 have been only partly described, the cell of origin and mechanism of transformation are unknown and animal models of the disease are lacking. Owing to this lack of biologic understanding, patients with CIC-DUX4 sarcomas are treated with the same regimens used for classical Ewing sarcoma, despite generally poor outcomes. To comprehensively address these problems we are taking a cross-species comparative oncology approach via analysis of human CIC-DUX4 sarcomas and genetically engineered in vivo zebrafish models. To study in vivo effects of CIC-DUX4, we used highly efficient Tol2 transposon-based transgenesis techniques to induce tumors in the zebrafish. In the absence of a known cell of origin for CIC-DUX4 sarcoma, we used a variety of ubiquitous promoters to induce mosaic expression of human CIC-DUX4 in zebrafish, along with GFP or mCherry fluorophores to mark transgenic cells. CIC-DUX4 exerted stong effects on zebrafish embryonic development. In particular, expression of CIC-DUX4 was prominent in the developing vasculature including hemogenic endothelium, indicating that the endothelial environment is favorable to the expression of CIC-DUX4. Beginning at 5 weeks of age, almost 40% of injected animals developed invasive, rapidly-growing tumors. Similar to human CIC-DUX4 sarcomas, tumors in the zebrafish occurred in soft tissues including the trunk musculature, the ventral abdominal tissue and the head and neck. The tumors exhibited histologic features of small round blue cells, identical to the appearance of human CIC-DUX4 sarcomas. Zebrafish CIC-DUX4 sarcomas were readily transplantable as allografts into recipient zebrafish. To further understand the molecular mechanisms of tumorigenesis, and to establish aspects of CIC-DUX4 function common to human and zebrafish tumors, we are carrying out detailed molecular analysis of the zebrafish tumors including RNASeq and whole-exome sequencing. Taken together these findings demonstrate that CIC-DUX4 expression is sufficient to promote the development of SRBCT, give insight into the cellular origins of CIC-DUX4 sarcomas and provide a valuable new animal model for translational research in this disease. Citation Format: Sarah Watson, Genevieve Kendall, Olivier Delattre, Franck Tirode, James F. Amatruda. Expression of a human CIC-DUX4 fusion is sufficient to induce malignant small round blue cell tumors in zebrafish: a new model of CIC-DUX4 sarcoma for translational research. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4190.