Abstract LB-197: YK-4-279 is effective in treating EWS-FLI1 induced myeloid/erythroid leukemia in a transgenic mouse model

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Ewing sarcoma is an aggressive neoplasm affecting bone and soft tissue occurring almost exclusively in children and young adults. It is characterized by a distinct chromosomal translocation involving EWS and FLI1 genes making targeted therapy feasible since the resulting oncoprotein, EWS-FLI1, is exclusively expressed in the cancerous cells. The fusion protein has been shown to confer its tumorigenic phenotype through aberrant transcriptional activity, splicing, and protein-protein interactions. Previous work from our lab has identified a small molecule inhibitor, YK-4-279 that directly binds to EWS-FLI1 and inhibits its oncogenic activity in Ewing Sarcoma cell lines. Uncertainty about the cell of origin for Ewing sarcoma contributes to the lack of in vivo models for the disease, which has hindered preclinical study efforts. Torchia et al. (Mol. and Cell. Bio. 2007. 27(22): 7918-7934) has generated a transgenic mouse model where expression of EWS-FLI1 was targeted to the bone marrow, spleen, and liver by crossing Rosa26-loxP-stop-loxP-EWS-FLI1 mice with mice that express cre recombinase under Mx1-promoter, which responds to pIpC. Expression of EWS-FLI1 in these tissues induce a rapid expansion of primitive myeloid progenitors leading to rapid leukemia development. We used this mouse model to assess the efficacy of YK-4-279 in disrupting oncogenic activity of EWS-FLI1 in vivo. The mice were injected with 1mg of pIpC at an age of one month to induce leukemia. Once an increase in white blood cell count is observed following pIpC injection, the mice were randomly assigned to a treatment or control groups. Treatment of the transgenic mice daily, five times a week, intraperitoneally with 75mg/kg YK-4-279 vs. vehicle led to improved overall survival. Median survival for control group was 10.5 days while for treatment group was 24 days (p=0.045). Mice treated with 75mg/kg YK-4-279 showed significant reduction of disease burden within two weeks as monitored by weekly White Blood Cell count (DMSO vs. 75mg/kg YK Week 1: p=0.023 and Week 2: p=0.004). Mice treated with 150mg/kg YK-4-279 showed even more reduction of disease burden where one week after treatment WBC for DMSO group increased on average by 6495 cells/ul of blood while for YK-4-279 group it decreased by 1278 cells/ul of blood. Two weeks after the treatment started, the WBC for DMSO group increased even more by an average of 17,500 cells/ul of blood while the disease was stabilized for 150mg/kg YK-4-279 treated group (DMSO vs. 150mg/kg YK-4-279 Week 1: p-value<0.0001 and Week 2: p-value<0.002). Additionally, we observed reduced proliferation of blast cells in the peripheral blood by differential counting in YK-4-279 treated group vs. those treated with vehicle alone. Furthermore, we show that following two weeks treatment, YK-4-279 inhibits genes that are up-regulated in response to EWS-FLI1 activation in EF/+ Mx1cre+ mice. In conclusion, findings from this in vivo study highlight the effect of YK-4-279 in treating EWS-FLI1 induced leukemia and suggest its potential for early clinical trials in humans. Citation Format: Tsion Z. Minas, Jenny Han, Sung-Hyeok Hong, Jeffrey Toretsky, Aykut Uren. YK-4-279 is effective in treating EWS-FLI1 induced myeloid/erythroid leukemia in a transgenic mouse model. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-197. doi:10.1158/1538-7445.AM2014-LB-197