LAUSR

Purpose: The survival rate of those with Ewing sarcoma (ES) has seen very little improvement over the past several decades and remains dismal for those with recurrent or metastatic disease. Current treatment for Ewing sarcoma includes a combination of cytotoxic chemotherapeutic agents and local control with radiation and/or surgery. The purpose of this study is to identify currently available targeted agents which may be combined with chemotherapy for use in Ewing sarcoma to improve patient outcomes. Methods: Novel targeted approaches for the treatment of ES were identified using RNA sequencing performed on ES patient tumors with bioinformatic analysis of gene expression. HDAC inhibitors were tested on patient cell lines at escalating doses and cell viability was assessed with CellTiter-Glo 2.0 and analyzed with GraphPad Prism to determine the IC50. Cells were treated with Panobinostat for 12 and 24 hours and RNA sequencing was performed. Cell cycle analysis was performed using Incucyte® Cell Cycle Lentivirus Reagent and analyzed using an Incucyte® S3. At 24- and 48-hours western blot analysis was performed to evaluate the effect on cell cycle and apoptosis. Combination studies with standard chemotherapy were performed and viability was assessed with CellTiter-Glo 2.0. At 24 hours of treatment with a combination of doxorubicin and HDAC inhibition western blot analysis was performed to evaluate changes in DNA damage and repair. Results: RNA analysis identified HDAC2 as a potential therapeutic target. The pan-HDAC inhibitors, Panobinostat and Belinostat, and the HDAC1/2 inhibitor, Romidepsin, were cytotoxic to all Ewing sarcoma cell lines tested with clinically relevant IC50s. Mechanistically, pathways involved in cell cycle progression and DNA repair were repressed by Panobinostat as shown by RNA sequencing and western blotting (Cyclin D1, pRb, CHK1). Additionally, cell cycle analysis has shown a G1 arrest in response to HDAC inhibition. HDAC inhibitors significantly decrease cell viability when combined with standard chemotherapy (upfront and relapse therapy) compared to that of chemotherapy alone. When combined with doxorubicin, CHK1 and CHK2 were significantly decreased and pH2AX was significantly increased indicating an accumulation of DNA damage. Conclusion: This work highlights that combining HDAC inhibitors with standard of care chemotherapy may be an effective treatment and improve outcomes for Ewing sarcoma patients. Future studies of HDAC inhibitors combined with chemotherapy drugs will aim to determine efficacy in xenograft models. Citation Format: Kaitlyn H. Smith, Chloe Sholler, Divya Gandra, Kimberly McKinney, Karl Dykema, Abhinav Nagulapally, Erin Trovillion. HDAC inhibition increases Ewing sarcoma sensitivity to chemotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6252.