The lyso-phospholipid sphingosine 1-phosphate modulates lymphocyte trafficking, endothelial development and integrity, heart rate, and vascular tone and maturation by activating G-protein-coupled sphingosine 1-phosphate receptors. Here we present the crystal structure of the sphingosine 1-phosphate receptor 1 fused to T4-lysozyme (S1P1-T4L) in complex with an antagonist sphingolipid mimic. Access to the binding pocket is completely occluded by the N-terminus and extracellular loops of the receptor. Access is gained by ligands entering laterally between helices I and VII within the transmembrane region of the receptor. This structure, along with mutagenesis, agonist structure-activity relationship data and modeling, provides a detailed view of the molecular recognition and hydrophobic volume triggering that activates S1P1 resulting in the modulation of immune and stromal cell responses.

BACKGROUND AND PURPOSESphingosine1-phosphate (S1P) receptors mediate multiple events including lymphocyte trafficking, cardiac function, and endothelial barrier integrity. Stimulation of S1P 1 receptors sequesters lymphocyte subsets in peripheral lymphoid organs, preventing their trafficking to inflamed tissue sites, modulating immunity. Targeting S1P receptors for treating autoimmune disease has been established in clinical studies with the non-selective S1P modulator, FTY720 (fingolimod, Gilenya ™ ). The purpose of this study was to assess RPC1063 for its therapeutic utility in autoimmune diseases. EXPERIMENTAL APPROACHThe specificity and potency of RPC1063 (ozanimod) was evaluated for all five S1P receptors, and its effect on cell surface S1P 1 receptor expression, was characterized in vitro. The oral pharmacokinetic (PK) parameters and pharmacodynamic effects were established in rodents, and its activity in three models of autoimmune disease (experimental autoimmune encephalitis, 2,4,6-trinitrobenzenesulfonic acid colitis and CD4 + CD45RB hi T cell adoptive transfer colitis) was assessed. KEY RESULTSRPC1063 was specific for S1P 1 and S1P 5 receptors, induced S1P 1 receptor internalization and induced a reversible reduction in circulating B and CCR7 + T lymphocytes in vivo. RPC1063 showed high oral bioavailability and volume of distribution, and a circulatory half-life that supports once daily dosing. Oral RPC1063 reduced inflammation and disease parameters in all three autoimmune disease models. CONCLUSIONS AND IMPLICATIONSS1P receptor selectivity, favourable PK properties and efficacy in three distinct disease models supports the clinical development of RPC1063 for the treatment of relapsing multiple sclerosis and inflammatory bowel disease, differentiates RPC1063 from other S1P receptor agonists, and could result in improved safety outcomes in the clinic.

Sphingosine 1-Phosphate Receptor 1 (S1P1) plays a critical role in lymphocyte recirculation and is a clinical target for treatment of multiple sclerosis. By generating a short-duration S1P1 agonist and mice where fluorescently tagged S1P1 replaces wild-type receptor, we elucidate physiological and agonist-perturbed changes in expression of S1P1 at a subcellular level in vivo. We demonstrate differential downregulation of S1P1 on lymphocytes and endothelia following agonist treatment.

We report the first small-molecule protease-activated receptor (PAR) 2 agonists, AC-55541

BackgroundSignalling through platelet-derived growth factor receptor (PDGFR), colony-stimulating factor 1 receptor (CSF1R) and mast/stem cell growth factor receptor kit (c-KIT) plays a critical role in pulmonary arterial hypertension (PAH). We examined the preclinical efficacy of inhaled seralutinib, a unique small-molecule PDGFR/CSF1R/c-KIT kinase inhibitor in clinical development for PAH, in comparison to a proof-of-concept kinase inhibitor, imatinib.MethodsSeralutinib and imatinib potency and selectivity were compared. Inhaled seralutinib pharmacokinetics/pharmacodynamics were studied in healthy rats. Efficacy was evaluated in two rat models of PAH: SU5416/Hypoxia (SU5416/H) and monocrotaline pneumonectomy (MCTPN). Effects on inflammatory/cytokine signalling were examined. PDGFR, CSF1R and c-KIT immunohistochemistry in rat and human PAH lung samples and microRNA (miRNA) analysis in the SU5416/H model were performed.ResultsSeralutinib potently inhibited PDGFRα/β, CSF1R and c-KIT. Inhaled seralutinib demonstrated dose-dependent inhibition of lung PDGFR and c-KIT signalling and increased bone morphogenetic protein receptor type 2 (BMPR2). Seralutinib improved cardiopulmonary haemodynamic parameters and reduced small pulmonary artery muscularisation and right ventricle hypertrophy in both models. In the SU5416/H model, seralutinib improved cardiopulmonary haemodynamic parameters, restored lung BMPR2 protein levels and decreased N-terminal pro-brain natriuretic peptide (NT-proBNP), more than imatinib. Quantitative immunohistochemistry in human lung PAH samples demonstrated increased PDGFR, CSF1R and c-KIT. miRNA analysis revealed candidates that could mediate seralutinib effects on BMPR2.ConclusionsInhaled seralutinib was an effective treatment of severe PAH in two animal models, with improved cardiopulmonary haemodynamic parameters, a reduction in NT-proBNP, reverse remodelling of pulmonary vascular pathology and improvement in inflammatory biomarkers. Seralutinib showed greater efficacy compared to imatinib in a preclinical study.