Highly selective and potent agonists of sphingosine-1-phosphate 1 (S1P1) receptor

Novel series of sphingosine-1-phosphate (S1P) receptor agonists were developed through a systematic SAR aimed to achieve high selectivity for a single member of the S1P family of receptors, S1P1. The optimized structure represents a highly S1P1-selective and efficacious agonist: S1P1/S1P2, S1P1/S1P3, S1P1/S1P4>10,000-fold, S1P1/S1P5>600-fold, while EC50 (S1P1) <0.2 nM. In vivo experiments are consistent with S1P1 receptor agonism alone being sufficient for achieving desired lymphocyte-lowering effect.     

Design and synthesis of conformationally constrained 3-(N-alkylamino)propylphosphonic acids as potent agonists of sphingosine-1-phosphate (S1P) receptors

A series of conformationally constrained 3-(N-alkylamino)propylphosphonic acids were systematically synthesized and their activities as S1P receptor agonists were evaluated. Several pyrrolidine and cyclohexane analogs had S1P receptor profiles comparable to the acyclic lead compound, 3-(N-tetradecylamino)propylphosphonic acid (3), lowered circulating lymphocytes in mice after iv administration and were thus identified as being suitable for further investigations.     

2,5-Disubstituted pyrrolidine carboxylates as potent, orally active sphingosine-1-phosphate (S1P) receptor agonists

A series of 2,5-cis-disubstituted pyrrolidines were synthesized and evaluated as S1P receptor agonists. Compounds 15-21 were identified with good selectivity over S1P3 which lowered circulating lymphocytes after oral administration in mice.     

Indole-propionic acid derivatives as potent, S1P3-sparing and EAE efficacious sphingosine-1-phosphate 1 (S1P1) receptor agonists

Novel indole-propionic acid derivatives were developed as sphingosine-1-phosphate (S1P) receptor agonists through a systematic SAR study. The optimized and S1P(3) selective S1P(1) agonist 9f induced peripheral blood lymphocyte reduction in vivo and has an excellent efficacy in mouse experimental autoimmune encephalomyelitis (EAE).     

Synthesis of 4(5)-phenylimidazole-based analogues of sphingosine-1-phosphate and FTY720: discovery of potent S1P1 receptor agonists

The novel immunosuppressant FTY720 has been demonstrated to elicit immunomodulating effects via interaction with the G-protein coupled receptor S1P(1). FTY720 induced agonism at the S1P(3) receptor, however, has been shown to result in mild bradycardia, a minor side-effect of initial FTY720 therapy. This report describes the synthesis of several potent 4(5)-phenylimidazole-based S1P(1) receptor agonists that are accompanied by poor agonist activity at S1P(3). For instance, compound 20 displayed an EC(50)=4.7+/-1.3 nM at the S1P(1) receptor and EC(50)=780+/-1.3 nM at the S1P(3) receptor using a [gamma-(35)S]GTP-binding assay as compared to phospho-FTY720 (S1P(1): EC(50)=1.3+/-1.3nM, S1P(3): EC(50)=2.0+/-2.4 nM).     

SAR studies of 3-arylpropionic acids as potent and selective agonists of sphingosine-1-phosphate receptor-1 (S1P1) with enhanced pharmacokinetic properties

Structure-activity relationship (SAR) studies of 3-arylpropionic acids-a class of novel S1P(1) selective agonists-by introducing substitution to the propionic acid chain and replacing the adjacent phenyl ring with pyridine led to a series of modified 3-arylpropionic acids with enhanced half-life in rat. These analogs (e.g., cyclopropanecarboxylic acids) exhibited longer half-life in rat than did unmodified 3-arylpropionic acids. This result suggests that metabolic oxidation at the propionic acid chain, particularly at the C3 benzylic position of 3-arylpropionic acids, is probably responsible for their short half-life in rodent.     

Discovery of 3-arylpropionic acids as potent agonists of sphingosine-1-phosphate receptor-1 (S1P1) with high selectivity against all other known S1P receptor subtypes

A series of 3-arylpropionic acids were synthesized as S1P1 receptor agonists. Structure-activity relationship studies on the pendant phenyl ring revealed several structural features offering selectivity of S1P1 binding against S1P2-5. These highly selective S1P1 agonists induced peripheral blood lymphocyte lowering in mice and one of them was found to be efficacious in a rat skin transplantation model, supporting that S1P1 agonism is primarily responsible for the immunosuppressive efficacy observed in preclinical animal models.     

Synthesis of benzimidazole based analogues of sphingosine-1-phosphate: discovery of potent, subtype-selective S1P4 receptor agonists

Sphingosine-1-phosphate (S1P) is a biologically active lysophospholipid with the capacity to induce a broad range of cellular responses via its interaction with the S1P family of G-protein coupled receptors. A member of this receptor family, S1P(4), is highly and almost exclusively expressed in the lymphoid system and has been implicated in regulation of cell shape and motility. This report describes the synthesis of several potent benzimidazole based S1P(4) receptor selective agonists. For instance, compound 9b displayed an EC(50)=36 nM at the S1P(4) receptor using a [gamma-(35)S]GTP binding assay as compared to an EC(50)=37 nM for the endogenous ligand. We also report the effects of altering stereochemistry at the C2 position, methylation at the C1 and C2 position, and activity differences between the alcohol and phosphate head groups of the analogues.     

Synthesis of para-alkyl aryl amide analogues of sphingosine-1-phosphate: discovery of potent S1P receptor agonists

Sphingosine-1-phosphate (S1P) is a biologically active lysophospholipid with the capacity to induce a broad range of cellular responses via its interaction with the S1P family of G-protein coupled receptors. This report describes the synthesis of several potent S1P receptor agonists. For instance, compound 9c displayed an EC(50)=8.6 nM at the S1P(1) receptor using a [gamma-35S]GTP binding assay as compared to an EC(50)=4.5 nM for the endogenous ligand. We also report the effects associated with introduction of a phenyl ring between the 'linker' and 'lipophilic tail' regions of the analogues, for example total loss of activity at S1P(2) and increased agonism at S1P(5).     

Lentiviral siRNA silencing of sphingosine-1-phosphate receptors S1P1 and S1P2 in smooth muscle

Sphingosine-1-phosphate regulates diverse biological processes through five receptor types, S1P(1-5). Two or more S1P receptors are usually co-expressed on target cells. We have previously shown that smooth muscle cells of the gut co-express S1P(1) and S1P(2) receptors that could mediate distinct functions. In the absence of selective agonists and antagonists, we developed siRNA constructs to silence each receptor separately. The constructs were based on identical sequences in several mammalian species. A lentiviral vector-based system was used to deliver siRNA into HEK293T cells and smooth muscle cells. One S1P(1) and two S1P(2) siRNA constructs specifically inhibited ectopic expression of S1P(1) and S1P(2) receptors, respectively, as determined by immunocytochemistry and Western blot, and endogenous expression of S1P(1) and S1P(2) receptors in smooth muscle cells, as determined by RT-PCR. Measurement of PLC-beta and Rho kinase activities, which mediate initial and sustained muscle contraction, confirmed receptor silencing and showed that contraction is mediated exclusively by S1P(2) receptors.     

Synthesis of trans-L/D-2-(tert-butoxycarbonyl-aminomethyl)-4-(thymin-1-yl) pyrrolidin-1-yl acetic acid

To delineate the binding preferences of stereochemically divergent pyrrolidine PNAs, synthesis of all four diastreomeric monomers of I and the systematic complexation studies of the resultant PNAs with complementary DNA/RNA is essential. We herein report the synthesis of trans-L/D-2-(tert-butoxycarbonyl-aminomethyl)-4-(thymin-1-yl) pyrrolidin-1-yl acetic acids I, their incorporation in PNA oligomers and DNA binding studies will be presented.     

Homodimerization and heterodimerization of S1P/EDG sphingosine-1-phosphate receptors

Sphingosine-1-phosphate (S1P) binds to and signals through several members of a group of G protein-coupled receptors (GPCRs) known as the S1P/EDG family. Several of these receptors are coexpressed in various cell types and recent reports have shown that biological effects of S1P often require more than one S1P receptor subtype. Recent evidence indicates that many GPCRs exist as dimers. We show that S1P receptors form both homodimers as well as heterodimers with other members of the S1P subfamily of receptors. We also discuss the role that GPCR dimers play in receptor function and what this may mean for S1P signaling.     

Discovery, design and synthesis of the first reported potent and selective sphingosine-1-phosphate 4 (S1P4) receptor antagonists

Selective S1P₄ receptor antagonists could be novel therapeutic agents for the treatment of influenza infection in addition to serving as a useful tool for understanding S1P₄ receptor biological functions. 5-(2,5-Dichlorophenyl)-N-(2,6-dimethylphenyl)furan-2-carboxamide was identified from screening the Molecular Libraries-Small Molecule Repository (MLSMR) collection and selected as a promising S1P₄ antagonist hit with moderate in vitro potency and high selectivity against the other family receptor subtypes (S1P_1-3,5). Rational chemical modifications of the hit allowed the disclosure of the first reported highly selective S1P₄ antagonists with low nanomolar activity and adequate physicochemical properties suitable for further lead-optimization studies.     

Pyrazole derived from (+)-3-carene; a novel potent,selective scaffold for sphingosine-1-phosphate (S1P1) receptor agonists

High throughput screening and hit to lead optimization led to the identification of ‘carene’ as a promising scaffold showing selective S1P₁ receptor agonism. In parallel to this work we have established a pharmacophore model for the S1P₁ receptor highlighting the minimal structural requirement necessary for potent receptor agonism.     

The sphingosine-1-phosphate receptors S1P1, S1P2, and S1P3 function coordinately during embryonic angiogenesis

Sphingosine-1-phosphate (S1P) elicits diverse cellular responses through a family of G-protein-coupled receptors. We have shown previously that genetic disruption of the S1P(1) receptor, the most widely expressed of the family, results in embryonic lethality because of its key role within endothelial cells in regulating the coverage of blood vessels by vascular smooth muscle cells. To understand the physiologic functions of the two other widely expressed S1P receptors, we generated S1P(2) and S1P(3) null mice. Neither the S1P(2) null mice nor the S1P(3) null mice exhibited significant embryonic lethality or obvious phenotypic abnormalities. To unmask possible overlapping or collaborative functions between the S1P(1), S1P(2), and S1P(3) receptors, we examined embryos with multiple S1P receptor mutations. We found that S1P(1) S1P(2) double null and S1P(1) S1P(2) S1P(3) triple null embryos displayed a substantially more severe vascular phenotype than did embryos with only S1P(1) deleted. We also found partial embryonic lethality and vascular abnormalities in S1P(2) S1P(3) double null embryos. Our results indicate that the S1P(1), S1P(2) and S1P(3) receptors have redundant or cooperative functions for the development of a stable and mature vascular system during embryonic development.     

2-(1H-Pyrazol-4-yl)acetic acids as CRTh2 antagonists

High throughput screening identified the pyrazole-4-acetic acid substructure as CRTh2 receptor antagonists. Optimisation of the compounds uncovered a tight SAR but also identified some low nanomolar inhibitors.     

Exploring amino acids derivatives as potent,selective, and direct agonists of sphingosine-1-phosphate receptor subtype-1

In the quest to discover a potent and selective class of direct agonists to the sphingosine-1-phosphate receptor, we explored the carboxylate functional group as a replacement to previously reported lead phosphates. This has led to the discovery of potent and selective direct agonists with moderate to substantial in vivo lymphopenia. The previously reported selectivity enhancing moiety (SEM) and selectivity enhancing orientation (SEO) in the phenylamide and phenylimidazole scaffolds were crucial to obtaining selectivity for S1P receptor subtype 1 over 3.     

Signaling of sphingosine-1-phosphate via the S1P/EDG-family of G-protein-coupled receptors

The sphingosine-1-phosphate/Endothelial Differentiation Gene (S1P/EDG) family of G-protein-coupled receptors (GPCR) currently includes five different isoforms, which differentially regulate fundamental cellular processes such as migration, proliferation, cytoskeletal organization, adherens junction assembly and morphogenesis. Additionally, specific S1P/EDG isoforms can regulate important physiological processes such as blood vessel maturation, cardiac development and angiogenesis in vivo. Herein, we review the current state of knowledge of the expression patterns, signaling pathways and functional characteristics of the different S1P receptors. Further investigation in this field will likely improve our understanding of cardiovascular development as well as vascular diseases and may lead to novel therapeutic approaches.     

Roles of sphingosine-1-phosphate (S1P) receptors in malignant behavior of glioma cells. Differential effects of S1P2 on cell migration and invasiveness

Sphingosine-1-phosphate (S1P) is a bioactive lipid that signals through a family of five G-protein-coupled receptors, termed S1P(1-5). S1P stimulates growth and invasiveness of glioma cells, and high expression levels of the enzyme that forms S1P, sphingosine kinase-1, correlate with short survival of glioma patients. In this study we examined the mechanism of S1P stimulation of glioma cell proliferation and invasion by either overexpressing or knocking down, by RNA interference, S1P receptor expression in glioma cell lines. S1P(1), S1P(2) and S1P(3) all contribute positively to S1P-stimulated glioma cell proliferation, with S1P(1) being the major contributor. Stimulation of glioma cell proliferation by these receptors correlated with activation of ERK MAP kinase. S1P(5) blocks glioma cell proliferation, and inhibits ERK activation. S1P(1) and S1P(3) enhance glioma cell migration and invasion. S1P(2) inhibits migration through Rho activation, Rho kinase signaling and stress fiber formation, but unexpectedly, enhances glioma cell invasiveness by stimulating cell adhesion. S1P(2) also potently enhances expression of the matricellular protein CCN1/Cyr61, which has been implicated in tumor cell adhesion, and invasion as well as tumor angiogenesis. A neutralizing antibody to CCN1 blocked S1P(2)-stimulated glioma invasion. Thus, while S1P(2) decreases glioma cell motility, it may enhance invasion through induction of proteins that modulate glioma cell interaction with the extracellular matrix.     

Syntheses of sphingosine-1-phosphate analogues and their interaction with EDG/S1P receptors

Sphingosine-1-phosphate (S1P) is an important regulator of a wide variety of biological processes acting as an endogenous ligand to EDG/S1P receptors. In an effort to establish structure-activity relationship between EDG/S1P and ligands, we report herein homology modeling study of EDG-1/S1P(1), syntheses of S1P analogues, and cell based binding affinity study for EDG/S1P receptors.