Abstract B61: Transcriptomic landscape of the immune suppressant FTY720 in antitumor

Purpose: Sphingosine-1-phosphate (S1P) is a bioactive lipid that promotes cell survival and proliferation, and modulation of lymphocyte egress. It plays important roles in the pathogenesis of inflammation and cancer. FTY720 is a “functional antagonist” of S1P by binding and induces the internalization and degradation of S1P receptors. FTY720 showed antitumor activity in several tumor models, but the mechanism has not been fully illustrated. In this study, we used microarray to explore the signaling pathways and genes regulated by FTY720, which may help to illustrate the mechanism of action. Experimental Procedures: We tested the inhibitory activity of FTY720 in various human cancer cell lines. Human colon cancer cells SW620, which are sensitive to FTY720, were selected and used for further study. SW620 was subcutaneously inoculated into Balb/c nude mice, then treated intraperitoneally with low dose (0.5 mg/kg/d) and high dose (5 mg/kg/d) of FTY720. Meanwhile, microarray analysis was used to explore the modulated genes by FTY720. Moreover, we tested the anti-neovascularization effect of FTY720 on endothelial cells (HMEC), which was shown to have this activity in vivo, and we also profiled the differentially expressed genes regulated by FTY720 on HMEC cells. Summary: FTY720 showed potent inhibitory activity on various cancer cell lines. The colon cancer cell SW620 was one of the most sensitive cells in response to FTY720 with an IC50 of 3.71 μM. FTY720 also inhibited new vessel formation at cellular level. In animal study, both low-dose and high-dose FTY720 dramatically inhibited the tumor growth in SW620 xenograft model. Since the serum concentration of FTY720 was much lower than its cellular cytotoxicity at low dose, we propose the antitumor activity may not only be due to a direct effect on tumor growth, but also on neovascularization and lowering of circulating lymphocytes. In transcriptomic study, we found cell cycle and DNA repair pathways were downregulated by FTY720 both in SW620 and HMEC cells. In HMEC cells, mTORC1, MYC, P53, FOXO1, and immune response pathways were downregulated while steroid metabolism and terpenoid backbone biosynthesis pathways were upregulated by FTY720. In SW620 cells, fatty acid metabolism, FOXO1, inflammatory and immune response pathways were downregulated while steroid metabolism and terpenoid backbone biosynthesis pathways were upregulated by FTY720. Thus, there are many overlaps of regulated pathways and genes by FTY720