(P 266) ROMIDEPSIN DECREASES DNA DAMAGE REPAIR AND INCREASES SENSITIVITY TO CHEMOTHERAPY IN EWING SARCOMA

Objective: Treatment options for Ewing sarcoma (EWS) patients have not improved in several decades; the poor survival rates, especially for those with metastatic and relapsed disease, highlight the need for improved therapeutic options. Through sequencing of patient tumors, we have identified HDAC2 as a potential therapeutic target for treating EWS. Our aims are to evaluate the efficacy and mechanism of Romidepsin monotherapy and in combination with standard of care chemotherapeutic agents in Ewing sarcoma cells in vitro and in vivo Ewing sarcoma xenograft mouse models.

Methods: EWS cells were treated with a range of clinically relevant concentrations of Romidepsin alone or in combination with standard of care chemotherapy agents and cell viability was measured by CellTiter-Glo. SynergyFinder 3.0 was used to determine if there is a synergistic response. To investigate the mechanism of Romidepsin, cells were treated with drug and western blotting was used to look at changes in proteins related to cell cycle, DNA damage response, and apoptosis.

Results: Romidepsin was cytotoxic to all Ewing sarcoma cell lines tested with clinically relevant IC50s ( < 10nM). Romidepsin synergizes with Doxorubicin and etoposide, and significantly decreases cell viability when added to standard chemotherapy combinations at clinically relevant doses. Romidepsin represses expression of Cyclin D1, CHEK1, and CHEK2, and increases cleavage of Caspase 3.

Conclusion: HDAC inhibition shows a decrease in cell viability in EWS cell line models alone and when combined with doxorubicin or etoposide. The addition of Romidepsin to chemotherapy combinations significantly decreases cell viability compared to that of chemotherapy alone, suggesting that the addition of Romidepsin to patient care may lead to improved outcomes. Mouse models are in development to further test in vivo and mice will be monitored for tumor growth and survival.