Abstract 2452: Exosomes as mediators of paracrine signalling that promote invasive behavior in rhabdomyosarcoma

Abstract

Abstract Exosomes are small membranous vesicles secreted into body fluids by multiple cell types, including tumor cells. Tumor exosomes contain intact and functional protein, mRNA and miRNA that may alter the cellular environment to favor tumor growth. Rhabdomyosarcoma (RMS) is an aggressive childhood soft tissue tumor, with two distinct subtypes, alveolar (ARMS) and embryonal (ERMS) histology. ARMS tumors are characterized in the majority of cases by a fusion oncoprotein PAX3-FOXO1, thought to be an initiating factor in tumorigenesis. To date, no studies have been performed to investigate the possible role or content of exosomes in paracrine signaling in RMS. In the present study, we isolated and characterized exosomes secreted from RMS cells, using 3 ERMS (fusion oncoprotein negative) and 2 ARMS (fusion oncoprotein positive) cell lines. RNA analysis showed that small RNA were enriched in RMS-derived exosomes, therefore we focused on evaluating the miRNA content. Array expression analysis showed that exosome miRNA clustered together well, and to a higher extent than cellular miRNA, in ARMS cell lines. Similarly, in the 2 ERMS cell lines that had mutant p53, exosome miRNA clustered together and the pattern of expression was very different from the corresponding cellular miRNA. ARMS and ERMS exosome-enriched miRNA were different, and only 2 miRNA were found to be common among both; putative targets are implicated in cancer and inflammation. Functionally, using in vitro assays, we found that both ERMS- and ARMS-derived exosomes significantly increased the cellular migration and invasion of normal human fibroblasts, and had a positive effect on viability and proliferation of both fibroblasts and RMS cells. In vivo, Matrigel plug assay showed that RMS-derived exosomes had a positive effect on the migration and invasion of stromal cells, suggesting a positive role on angiogenesis. We conclude that RMS-derived exosomes can exert specific paracrine effects on recipient cells, enhancing cell viability as well as invasive properties of fibroblasts and stromal cells, and therefore is likely to play a role in promoting RMS angiogenesis and metastasis. Ongoing studies are aimed at directly assessing the role of RMS-derived exosomes in clinical angiogenesis and metastasis, using in vivo murine models, in addition to dissecting the role of specific enriched miRNA on recipient cell biology. Citation Format: Sandra E. Ghayad, Ghina Rammal, Farah Ghamloush, Hussein Basma, Raya Saab. Exosomes as mediators of paracrine signalling that promote invasive behavior in rhabdomyosarcoma. [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 2452.