OP22 Topical Sphingosine-1-Phosphate (S1P) Receptor 1 Modulation Regulates Gut Angiogenesis in Inflammatory Bowel Diseases

Abstract Background S1P receptor (S1PR)1/5 modulators have been tested successfully in clinical development programs in ulcerative colitis (UC), leading to their FDA approval. They are believed to act through lymphocyte redistribution in peripheral lymphoid tissue and reduced numbers of circulating lymphocytes, but evidence from other organs suggests potential additional mechanisms of action. Methods A post-hoc analysis of the phase 3 trial of the S1PR1/5 modulator Ozanimod in patients with moderately to severely active UC was performed assessing an association of absolute lymphocyte count (ALC) with efficacy. Expression levels of S1PRs were analyzed in human intestinal tissues and primary cells using qPCR and/or immunohistochemistry (IHC). Effects of S1P, S1PR1/5 modulators and S1P1 knockdown on migration, proliferation, cytokine production, downstream signaling (immunoblot), tube formation of human intestinal microvascular endothelial cells (HIMEC) was evaluated. S1P and S1PR1/5 modulators were examined in a murine matrix plug angiogenesis model and with topical and systemic S1PR1/5 modulator therapy in dextrane sodium sulfate (DSS) colitis in vivo. Results Baseline ALC and relative or absolute ALC reductions were neither correlated with nor predictive of clinical or endoscopic outcomes. In murine DSS colitis topical therapy with a S1PR1/5 modulator ameliorated colitis but did not alter peripheral lymphocyte numbers. S1PR1 gene and protein expression was increased in UC and Crohn’s disease (CD) patients and predominantly expressed on HIMEC. S1P promoted HIMEC migration, proliferation, tube formation, IL-8 secretion, indicative of pro-angiogenic responses in vitro. Modulation of S1PR1/5 and knockdown of S1PR1 markedly inhibited these pro-angiogenic functions in the presence of high concentrations of S1P, but enhanced angiogenesis when low S1P concentrations were present. S1PR5 had no effect on angiogenesis. In the murine plug assay, S1PR1 induced angiogenesis. In acute DSS colitis, treatment of S1PR modulator by enema reduced blood vessels, but left lymphatics unaffected. Conclusion We present a novel mechanism of action of S1PR1 modulators in IBD intestinal tissue, potentially explaining a disconnect between ALC and efficacy observed in a post-hoc analysis of the phase 3 Ozanimod UC trial. The data presented suggest that S1P induced angiogenesis is attenuated by S1PR1 modulation in HIMEC from IBD patients when S1P levels comparable to blood were present. In the presence of S1P at concentrations consistent with lymph fluid angiogenesis was increased. Together with reduced numbers of circulating lymphocytes, this may contribute to efficacy of S1PR1 modulators in IBD patients.