Recent progress in the development of selective S1P1 receptor agonists for the treatment of inflammatory and autoimmune disorders

Abstract

Background: The sphingosine-1-phosphate receptor 1 (S1P1) belongs to the endothelial differentiation gene family of G-protein-coupled receptors involved in embryonic development, cellular differentiation and survival, adherence and tight junction assembly, and leukocyte trafficking. In vivo S1P1 is required for egress of thymocytes into the blood and of naive lymphocytes from secondary lymphoid organs back into the lymph. Downregulation of S1P1 disrupts lymphocyte migration, tissue homing and recirculation. To explore the immunomodulatory potential of S1P1, pharma is developing S1P1-selective agonists for treating autoimmune and inflammatory disorders. FTY720 (fingolimod, Novartis AG), a nonselective S1P1 agonist that induces sustained lymphopenia, is a promising pseudo-lipid aminodiol prodrug that has been shown in preclinical and early clinical trials to be effective in suppressing various autoimmune conditions and to aid in acute organ transplant, and is currently in pivotal Phase III clinical trials for relapsing-remitting multiple sclerosis. Objective: In this review article, we outline recent advances made in the discovery and patenting of new small-molecule S1P1 selective agonists and summarize a rapidly growing body of intellectual property. Conclusion: Fingolimod-like S1P1 agonists with a novel mechanism of action have emerged as promising immunosuppressants. S1P1 agonists induce T-cell sequestration in lymph nodes and Peyer's patches, diminishing their ability to reach distant sites and cause pathology. Preclinical studies have already provided preliminary evidence that low-dose treatment with fingolimod in conjunction with subtherapeutic doses of ciclosporin A and tacrolimus enable potent immunosuppression in the absence of immediately serious side effects. Future efforts will determine whether S1P1 agonists do indeed synergize with existing DMAs to create new mutidrug paradigms with superior efficacy and safety for the treatment of autoimmune diseases and the prevention of organ transplant rejection.