Abstract 485: EWS-FLI1 targeted small molecule YK-4-279 synergizes with vinca alkaloids through double hit to mitotic machinery

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA A multi-chemotherapeutic regimen remains the benchmark of first- and second-line therapy for patients with Ewing Sarcoma (ES), yet almost one third of patients will relapse and die of their disease. The small molecule YK-4-279 specifically inhibits EWS-FLI1 function both in vivo and in vitro, and represents the first molecule to directly target EWS-FLI1, a specific oncogene to be considered a critical ES target. Given the likelihood of ultimate resistance to any single agent, even a targeted new agent, combinations of YK-4-279 with established anti-cancer agents were investigated. Our hypothesis is that currently used chemotherapy with YK-4-279 would be more potent and have significantly more durable anti-tumor effects while therapy-limiting adverse drug effects would be reduced. Methods: The Approved Oncology Drugs Set of 85 different anti-cancer drugs with a spectrum of cellular toxicity mechanisms was obtained from the Developmental Therapeutics Program at the NCI/NIH, and tested with YK-4-279 for synergistic activity in ES cell lines. Successful synergistic combinations were evaluated in xenograft models. Mechanistic studies were pursued using immunofluorescence and cell cycle investigations. Results: Combinatorial testing of YK-4-279 revealed synergy in four ES cell lines with vinca alkaloids. Vincristine (VCR) showed the greatest consistency across all cell lines with a combination index of 0.7-0.8 in all four cell lines, including COG-E-352, which is reported to be VCR resistant. This synergy translates as a 10-fold decrease in VCR required for the equivalent cytotoxicity when combined with YK-4-279. The combination of YK-4-279 (50 mg/kg) and VCR (1 mg/kg) exhibited synergistic effect upon xenograft tumor growth leading to significantly increased survival in the combination compared to VCR alone (p = 0.0019). YK-4-279 led to a G2/M-phase cell-cycle arrest as confirmed by H3 phosphorylation at Thr-11. Treatment with VCR and YK-4-279 led to an increase in both spindle and chromatin perturbation in a time and dose-dependent manner. Combination therapy also showed enhanced reduction of MCL-1 protein. Conclusion: YK-4-279, a promising, EWS-FLI1 specific small molecule, exhibits synergistic activity with vinca alkaloids. The mechanism appears to be at the cell cycle level of mitotic progression with a subsequent decrease in survival protein MCL-1. These data support future clinical combinatorial studies as YK-4-279 completes preclinical development towards a planned Phase 1 clinical trial in 2015. Citation Format: Stefan K. Zollner, Ryan Commins, Sung H. Hong, Hayriye V. Erkizan, Jeffrey A. Toretsky. EWS-FLI1 targeted small molecule YK-4-279 synergizes with vinca alkaloids through double hit to mitotic machinery. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 485. doi:10.1158/1538-7445.AM2015-485