Abstract 4149: Inhibition of ribonucleotide reductase (RNR) in Ewing sarcoma cells results in suppression of protein synthesis

Abstract

Abstract Ewing sarcoma is a highly aggressive bone and soft tissue cancer that is caused by the EWS-FLI1 fusion protein. EWS-FLI1 is required for tumor growth and survival. However, directly targeting EWS-FLI1 with drugs has been challenging and an alternative therapeutic approach is to identify unique vulnerabilities incurred by the oncoprotein. In previous work, we identified that Ewing sarcoma cells are uniquely vulnerable to drugs that inhibit ribonucleotide reductase (RNR), which is the rate limiting enzyme in the synthesis of deoxyribonucleotides. Furthermore, we also showed that blocking the function of checkpoint kinase 1 (CHK1), a major regulator of the response to impaired DNA replication, using either a small molecule inhibitor or siRNA-mediated knockdown causes synergistic toxicity with gemcitabine, an irreversible inhibitor of the RRM1 subunit of RNR, in Ewing sarcoma cells. In the current work, we identifiy that inhibition of RNR in Ewing sarcoma cells in vitro and in vivo results in the suppression of protein synthesis. Moreover, we have found that the treatment of Ewing sarcoma cell lines with gemcitabine results in an increase in the active (unphosphorylated) form of 4E-BP1, which is a well-described inhibitor of protein translation. However, in contrast to the Ewing sarcoma cells, treatment of other cell types with gemcitabine did not alter 4E-BP1 phosphorylation or protein synthesis. Currently, ongoing work is focused on the in vivo testing of gemcitabine, alone and in combination with CHK1, ataxia telangiectasia and rad3-related protein (ATR), and protein synthesis inhibitors, as a novel therapeutic approach for the treatment of Ewing sarcoma. Citation Format: Stacia Koppenhafer, Kelli Goss, David Gordon. Inhibition of ribonucleotide reductase (RNR) in Ewing sarcoma cells results in suppression of protein synthesis [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 4149.