Abstract A155: Small molecule metabolic inhibitors, compound A and the derivatives specifically inhibit the cell growth of Ewing's sarcoma cells harbor EWS-FLI1 in vitro and in vivo

Background: Ewing9s sarcoma family of tumors (ESFTs) are characterized by chromosomal translocations that fuses EWSR1 gene and other types of ETS family genes. Among them, EWS-FLI1 is the most common transcriptional factor which regulates many genes of biological pathways leading to cell cycle, metabolic and DNA repair. EWS-FLI1 oncoprotein is an ideal therapeutic target for ESFTs whereas it turned out to be difficult to obtain direct small-molecule inhibitor of EWS-FLI1 due to lack of intrinsic enzymatic activity. Therefore, we postulate indirect inhibitors of EWS-FLI1 function that can suppress the transcriptional activity of EWS-FLI1, resulting in selectively inhibition of growth of ESFTs. Results: To discover small molecular compounds which inhibit the cell growth in Ewing9s sarcoma cells, a cell proliferation assay using Ewing9s sarcoma A-673 cells harboring EWS-FLI1 fusion protein was performed. We identified compound A which inhibited the cell proliferation in A-673 and Ewing9s sarcoma TC-71 cells with GI50 values of 27 nM and 25 nM, respectively. Compound A also inhibited colony formation of all some Ewing9s sarcoma cells. In contrast, growth inhibition by compound A in pancreatic AsPC-1 cells which express no EWS-FLI1 was not observed at the concentration up to 10000 nM. A derivative of compound A as well as EWS-FLI1 siRNA decreased the expression of NKX2.2 and CCND1, and increased the expressions of IGFBP3, PHLDA1 and DKK1. These genes are under the downstream control of EWS-FLI1 so that compound A might down-modulate EWS-FLI1 function. We found that a series of derivatives inhibited the enzymatic activity of nucleotide biosynthesis. IC50 values of the enzyme inhibitory activities among derivatives were correlated well with GI50 values of anti-proliferative activities in A-673 cells (r = 0.86). Moreover, overexpression of the enzyme gene in A-673 cells could attenuate the anti-proliferative activities of the derivatives, suggesting that inhibition of the enzyme by compound A is involved in the down-modulation of EWS-FLI1 driven growth. Finally, using a Ewing9s sarcoma xenograft mouse model, oral daily administration of the derivative at 100 mg/kg considerably inhibited the tumor growth with a minimum T/C ratio of 0.13 without body weight loss. Conclusions: Compound A and its derivatives may be a therapeutic agent with potent antitumor activity for Ewing9s sarcoma patients. Citation Format: Hiromichi Kosaka, Yasuo Watanabe, Michihiro Maemoto, Masamori Sugawara, Miwa Watanabe, Yoko Ono, Yoshisuke Nakasato, Masahiro Matsubara, Ryuichiro Nakai. Small molecule metabolic inhibitors, compound A and the derivatives specifically inhibit the cell growth of Ewing9s sarcoma cells harbor EWS-FLI1 in vitro and in vivo. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A155.