Targeting the Sphingosine-1-Phosphate Pathway: New Opportunities in Inflammatory Bowel Disease Management.

Inflammatory bowel diseases (IBD), including Crohn's disease (CD) and ulcerative colitis (UC) are chronic immune-mediated diseases which primarily target the intestines. In recent years, the development and regulatory approval of various immunotherapies, both biological agents and small molecules, that target specific pathways of the IBD-associated inflammatory cascade have revolutionized the treatment of IBD. Small molecules offer the advantages of oral administration and short wash-out times. Sphingosine-1-phosphate (S1P) is a bioactive metabolite of ceramide, which exerts its functions after binding to five G-protein-coupled receptors (S1PR1-S1PR5). Concerning IBD, S1P participates in the egress of lymphocytes from the secondary lymphoid tissue and their re-circulation to sites of inflammation, mainly through S1PR1 binding. In addition, this system facilitates the differentiation of T-helper cells towards proinflammatory immunophenotypes. Recently, S1P modulators have offered a valuable addition to the IBD treatment armamentarium. They exert their anti-inflammatory function via sequestration of T cell subsets in the lymphoid tissues and prevention of gut homing. In this review, we revisit the role of the S1P/S1PR axis in the pathogenesis of IBD and discuss efficacy and safety data from clinical trials and real-world reports on the two S1PR modulators, ozanimod and etrasimod, that are currently approved for IBD treatment, and comment on their potential positioning in the IBD day-to-day management. We also present recent data on emerging S1P modulators. Finally, based on the successes and failures of S1PR modulators in IBD, we discuss future avenues of IBD treatments targeting the S1P/S1PR axis.