Abstract 3549: Exosome-mediated transfer of sh-CD99 is sufficient to modulate cell differentiation in Ewing sarcoma
Authors: Feo Alessandra De , Sciandra Marika , Felicetti Federica , Ferracin Manuela , Carè Alessandra , Scotlandi Katia 
Published: August 2018

Abstract
Background
Ewing sarcoma (EWS) is an aggressive childhood bone tumor with still highly unmet clinical needs. The tumor is characterized by the fusion oncoprotein EWS-FLI1 and the high expression of the membrane glycoprotein CD99. CD99 has been found to be released by EWS cells linked to exosomes (EXOs), small vesicles able to influence cellular behavior and surrounding microenvironment by transferring their contents into nearby or distant recipient cells. The delivery of EXOs devoid of CD99 was sufficient to induce neural differentiation in recipient EWS cells through miR- 34a-dependent inhibition of Notch-NF-kB signaling, thus indicating a possible therapeutic potential.
Aims
The study has the ambition to:
1. Evaluate the capabilities of EXOs released by Ewing's sarcoma, to influence cancer growth and/or metastasis through the horizontal transfer of their cargos.
2. Characterize EXOs secreted by CD99-silenced EWS cells in terms of miRNAs and protein and evaluate their general antimetastatic function, if any, taking advantage of their capabilities to be transferred into a broad panel of different Ewing's sarcoma cell lines, as recipients.
Results
In the present study we identified the role of Ewing sarcoma-derived EXOs as mediators of signals involved in cancer growth, metastases and differentiation. In particular, we analyzed the ability of EXOs, expressing or not CD99, to modulate the phenotype of EWS cells. Delivery of EXOs from CD99-silenced cells was sufficient to induce neural differentiation in recipient EWS cells by neurite outgrowth and increased expression of β-III tubulin marker of neural differentiation accompanied in vitro by a significant reduction of proliferation, invasion and chemotaxis convey the same phenotype obtained by stable CD99 silencing. Moreover, microarray analysis revealed a signature of 56 miRNAs differentially expressed in EXOs derived from CD99-silenced cells compared to EWS-derived EXOs. We focused our attention on miR-214 and miR-199. Those miRNAs are involved in the regulation of CD99 itself like, EWS-FLI1 or CD99-mediated pathways related to cytoskeleton and membrane organization. As a next step we searched for any tumorigenic effect possibly associated with miR-199 and mir-214. The restored expression of miR-199 and miR-214 in two Ewing Sarcoma cell lines was accompanied by a significant reduction of proliferation, invasion and chemotaxis in vitro. The outcomes deriving from miR-199 and miR-214 enforced expression were also evaluated on capability of forming foci in agar semisolid medium. Results showed a significant decrease of the number of foci in both cell lines.
Conclusions
Exosomes deprived of CD99 can alter the balance of important cellular components necessary for the metastatic process of EWS cells, thus representing a novel exciting therapeutic possibility for the design of novel therapy against metastatic EWS. AIRC IG18451 to KS; IG18815 to AC.
Citation Format: Alessandra De Feo, Marika Sciandra, Federica Felicetti, Manuela Ferracin, Alessandra Carè, Katia Scotlandi. Exosome-mediated transfer of sh-CD99 is sufficient to modulate cell differentiation in Ewing sarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3549.