The Mechanistic Action Of FTY720 On Tumor Immune Microeviroment

Background FTY720 represents a putatively potent immunosuppressant, which displays therapeutic efficacy in inflammation-related diseases including autoimmune disotders. and has been approved by FDA to treat multiple sclerosis in clinic. Acucmulating evidence has demontrated that ligation of FTY720 to S1 P receptor leads to the internalization of S1 P receptor(particularly S1PR1), thereby blocks or down-regulates S1 P signals. As a consequence, effector lymphocytes are sequestered in lymphoid tissues so that the infiltration of these cells in lesions is impaired, which ultimately blocks the development and progression of autoimmune diseases. Recently, FTY720 has been shown to repress tumor growth by inducing apoptosis of cancer cells. However, a large body of evidence has shown that tumor microenvironment, particularly immune microenvironment, plays an essential role in tumor development. Cancer cells secret a set of growth factor and/or chemokines, and trigger aberrant myelopoiesis in bone marrow and outsides, which leads to massive accumulation of immature myeloid cells with immunosuppressive function.These cells blunts host immunosuveillance, which is recognized as a key step for shaping tumor microenvironment.Thus, we raise the issue to be addressed: does FTY720 modulates tumor environment, particularly MDSC accumulation, to regulate tumor growth? To this end, we establish several tumor models and evaluate the efficacy of FTY720. Furthermore, we will investigate the mechanisms by FTY720 involving MDSC.Objective To address the efficacy of FTY720 on tumor growth and underlying mechanisms.Methods colitis-associated colorectal cancer(CAC) model is established by combined administration of AOM and DSS. CT26 and B16-transplantion models are established by subcutaneously injection of syngeneic tumor cells in Balb/c or C57BL/6 mice. FTY720 is gavaged daily at the dose of 1 mg/kg/day and tumor growth is monitored. After sacrificed, extramedullary hematopoiesis is examined. MDSC frequencies in lymphoid organs are detected by flow cytometry. Thereafter, MDSC are isolated by FACS or magnetic beads and S1 PR expression is detected by flow cytometry or quantitative RT-PCR.GM-CSF levels are determined by ELISA and the regulation of GM-CSF by FTY720 or S1 P is assayed ex vivo.Results Long-term or end-stage administration of FTY720 promotes tumor growth in CAC model and tumor-engrafted models. FTY720 significantly enhances extramedullary myelopoiesis, as reflected by increased number of C-kit+ progenitors in the spleen of FTY720-treated mice compared to vehicle-treated littermates. Accordingly, FTY720 increases the frequences and number of MDSC in peripheral blood and spleen, but not in bone marrow. Similar results are obtained in tumor transplantation models. Furthermore, GM-CSF levels are elevated dramatically in FTY720-treated mice. Of importance, neutralization of GM-CSF activity using specific monoclonal antibody abrogates FTY720-driven effects.S1 P or S1P3 agonist trigger MDSC to release GM-CSF, rather than S1PR1 agonist. Finally, similar phenotyes are observed in S1PR3 agonist-treated tumor-bearing mice.Conclusions our findings demonstrate a pro-tumor effect of FTY720. Mechanistic investigations reveal that FTY720 augments extramedullary hematopoiesis and MDSC accumulation. GM-CSF is verified as a key factor in this porcess. FTY720 trigger GM-CSF production in MDSC via S1PR3.