5-Alkyl-2-urea-Substituted Pyridines: Identification of Efficacious Glucokinase Activators with Improved Properties.

Two 1-(4-aryl-5-alkyl-pyridin-2-yl)-3-methylurea glucokinase activators were identified with robust in vivo efficacy. These two compounds possessed higher solubilities than the previously identified triaryl compounds (i.e., AM-2394). Structure-activity relationship studies are presented along with relevant pharmacokinetic and in vivo data.

Novel Series of Potent Glucokinase Activators Leading to the Discovery of AM-2394.

Glucokinase (GK) catalyzes the phosphorylation of glucose to glucose-6-phosphate. We present the structure-activity relationships leading to the discovery of AM-2394, a structurally distinct GKA. AM-2394 activates GK with an EC50 of 60 nM, increases the affinity of GK for glucose by approximately 10-fold, exhibits moderate clearance and good oral bioavailability in multiple animal models, and lowers glucose excursion following an oral glucose tolerance test in an ob/ob mouse model of diabetes.

C5-Alkyl-2-methylurea-Substituted Pyridines as a New Class of Glucokinase Activators.

Glucokinase (GK) activators represent a class of type 2 diabetes therapeutics actively pursued due to the central role that GK plays in regulating glucose homeostasis. Herein we report a novel C5-alkyl-2-methylurea-substituted pyridine series of GK activators derived from our previously reported thiazolylamino pyridine series. Our efforts in optimizing potency, enzyme kinetic properties, and metabolic stability led to the identification of compound 26 (AM-9514). This analogue showed a favorable combination of in vitro potency, enzyme kinetic properties, acceptable pharmacokinetic profiles in preclinical species, and robust efficacy in a rodent PD model.

Structure-assisted discovery of the first non-retinoid ligands for Retinol-Binding Protein 4.

Retinol-Binding Protein 4 (RBP4) is a plasma protein that transports retinol (vitamin A) from the liver to peripheral tissues. This Letter highlights our efforts in discovering the first, to our knowledge, non-retinoid small molecules that bind to RBP4 at the retinol site and reduce serum RBP4 levels in mice, by disrupting the interaction between RBP4 and transthyretin (TTR), a plasma protein that binds RBP4 and protects it from renal excretion. Potent compounds were discovered and optimized quickly from high-throughput screen (HTS) hits utilizing a structure-based approach. Inhibitor co-crystal X-ray structures revealed unique disruptions of RBP4-TTR interactions by our compounds through induced loop conformational changes instead of steric hindrance exemplified by fenretinide. When administered to mice, A1120, a representative compound in the series, showed concentration-dependent retinol and RBP4 lowering.

Characterization of a novel glucokinase activator in rat and mouse models.

Glucokinase (GK) is a hexokinase isozyme that catalyzes the phosphorylation of glucose to glucose-6-phosphate. Glucokinase activators are being investigated as potential diabetes therapies because of their effects on hepatic glucose output and/or insulin secretion. Here, we have examined the efficacy and mechanisms of action of a novel glucokinase activator, GKA23. In vitro, GKA23 increased the affinity of rat and mouse glucokinase for glucose, and increased glucose uptake in primary rat hepatocytes. In vivo, GKA23 treatment improved glucose homeostasis in rats by enhancing beta cell insulin secretion and suppressing hepatic glucose production. Sub-chronic GKA23 treatment of mice fed a high-fat diet resulted in improved glucose homeostasis and lipid profile.

Discovery and optimization of 5-(2-((1-(phenylsulfonyl)-1,2,3,4-tetrahydroquinolin-7-yl)oxy)pyridin-4-yl)-1,2,4-oxadiazoles as novel gpr119 agonists.

We describe the discovery and optimization of 5-(2-((1-(phenylsulfonyl)-1,2,3,4-tetrahydroquinolin-7-yl)oxy)pyridin-4-yl)-1,2,4-oxadiazoles as novel agonists of GPR119. Previously described aniline 2 had suboptimal efficacy in signaling assays using cynomolgus monkey (cyno) GPR119 making evaluation of the target in preclinical models difficult. Replacement of the aniline ring with a tetrahydroquinoline ring constrained the rotation of the aniline C-N bond and gave compounds with increased efficacy on human and cyno receptors. Additional optimization led to the discovery of 10, which possesses higher free fraction in plasma and improved pharmacokinetic properties in rat and cyno compared to 2.

Discovery and optimization of N-(3-(1,3-dioxo-2,3-dihydro-1H-pyrrolo[3,4-c]pyridin-4-yloxy)phenyl)benzenesulfonamides as novel GPR119 agonists.

The discovery and optimization of novel N-(3-(1,3-dioxo-2,3-dihydro-1H-pyrrolo[3,4-c]pyridin-4-yloxy)phenyl)benzenesulfonamide GPR119 agonists is described. Modification of the pyridylphthalimide motif of the molecule with R(1)=-Me and R(2)=-(i)Pr substituents, incorporated with a 6-fluoro substitution on the central phenyl ring offered a potent and metabolically stable tool compound 22.

Discovery and optimization of arylsulfonyl 3-(pyridin-2-yloxy)anilines as novel GPR119 agonists.

We describe the discovery of a series of arylsulfonyl 3-(pyridin-2-yloxy)anilines as GPR119 agonists derived from compound 1. Replacement of the three methyl groups in 1 with metabolically stable moieties led to the identification of compound 34, a potent and efficacious GPR119 agonist with improved pharmacokinetic (PK) properties.

Identification and characterization of a non-retinoid ligand for retinol-binding protein 4 which lowers serum retinol-binding protein 4 levels in vivo.

Retinol-binding protein 4 (RBP4) transports retinol from the liver to extrahepatic tissues, and RBP4 lowering is reported to improve insulin sensitivity in mice. We have identified A1120, a high affinity (K(i) = 8.3 nm) non-retinoid ligand for RBP4, which disrupts the interaction between RBP4 and its binding partner transthyretin. Analysis of the RBP4-A1120 co-crystal structure reveals that A1120 induces critical conformational changes at the RBP4-transthyretin interface. Administration of A1120 to mice lowers serum RBP4 and retinol levels but, unexpectedly, does not improve insulin sensitivity. In addition, we show that Rpb4(-/-) mice display normal insulin sensitivity and are not protected from high fat diet-induced insulin resistance. We conclude that lowering RBP4 levels does not improve insulin sensitivity in mice. Therefore, RBP4 lowering may not be an effective strategy for treating diabetes.

Application of an allosteric model to describe the interactions among retinol binding protein 4, transthyretin, and small molecule retinol binding protein 4 ligands.

Retinol binding protein 4 (RBP4) is a serum protein that serves as the major transport protein for retinol (vitamin A). Recent reports suggest that elevated levels of RBP4 are associated with insulin resistance and that insulin sensitivity may be improved by reducing serum RBP4 levels. This can be accomplished by administration of small molecules, such as fenretinide, that compete with retinol for binding to RBP4 and disrupt the protein-protein interaction between RBP4 and transthyretin (TTR), another serum protein that protects RBP4 from renal clearance. We developed a fluorescence resonance energy transfer (FRET) assay that measures the interaction between RBP4 and TTR and can be used to determine the binding affinities of RBP4 ligands. We present an allosteric model that describes the pharmacology of interaction among RBP4, TTR, retinol, and fenretinide, and we show data that support the model. We show that retinol increases the affinity of RBP4 for TTR by a factor of 4 and determine the affinity constants of fenretinide and retinyl acetate. The assay may be useful for characterizing small molecule ligands that bind to RBP4 and disrupt its interaction with TTR. In addition, such a model could be used to describe other protein-protein interactions that are modulated by small molecules.

Identification of substrates of human protein-tyrosine phosphatase PTPN22.

Stimulation of mature T cells activates a downstream signaling cascade involving temporally and spatially regulated phosphorylation and dephosphorylation events mediated by protein-tyrosine kinases and phosphatases, respectively. PTPN22 (Lyp), a non-receptor protein-tyrosine phosphatase, is expressed exclusively in cells of hematopoietic origin, notably in T cells where it represses signaling through the T cell receptor. We used substrate trapping coupled with mass spectrometry-based peptide identification in an unbiased approach to identify physiological substrates of PTPN22. Several potential substrates were identified in lysates from pervanadate-stimulated Jurkat cells using PTPN22-D195A/C227S, an optimized substrate trap mutant of PTPN22. These included three novel PTPN22 substrates (Vav, CD3epsilon, and valosin containing protein) and two known substrates of PEP, the mouse homolog of PTPN22 (Lck and Zap70). T cell antigen receptor (TCR) zeta was also identified as a potential substrate in Jurkat lysates by direct immunoblotting. In vitro experiments with purified recombinant proteins demonstrated that PTPN22-D195A/C227S interacted directly with activated Lck, Zap70, and TCRzeta, confirming the initial substrate trap results. Native PTPN22 dephosphorylated Lck and Zap70 at their activating tyrosine residues Tyr-394 and Tyr-493, respectively, but not at the regulatory tyrosines Tyr-505 (Lck) or Tyr-319 (Zap70). Native PTPN22 also dephosphorylated TCRzeta in vitro and in cells, and its substrate trap variant co-immunoprecipitated with TCRzeta when both were coexpressed in 293T cells, establishing TCRzeta as a direct substrate of PTPN22.

Kinetics and comparative reactivity of human class I and class IIb histone deacetylases.

Histone deacetylase (HDAC) enzymes modulate gene expression through the deacetylation of acetylated lysine residues on histone proteins. They operate in biological systems as part of multiprotein corepressor complexes. To understand the reactivity of isolated HDACs and the contribution of cofactor binding to reactivity, the reaction kinetics of isolated, recombinant human HDACs 1, 2, 3, 6, 8, and 10 were measured using a novel, continuous protease-coupled enzyme assay. Values of k(cat) and k(cat)/K(m) and the pH dependence of these values were determined for the reactions of each isozyme with acetyl-Gly-Ala-(N(epsilon)-acetyl-Lys)-AMC. Values of k(cat) spanned the range of 0.006-2.8 s(-1), and k(cat)/K(m) values ranged from 60 to 110000 M(-1) s(-1). The pH profiles for both k(cat) and k(cat)/K(m) were bell-shaped for all of the HDAC isozymes, with pH optima at approximately pH 8. Values of K(i) for the inhibitor trichostatin A were determined for each isozyme. The inhibition constants were generally similar for all HDAC isozymes, except that the value for HDAC8 was significantly higher than that for the other isozymes. The reaction of HDAC8 with an alternative substrate was performed to assess the steric requirements of the HDAC8 active site, and the effect of phosphorylation on HDAC1 activity was examined. The results are discussed in terms of the biological roles of the HDAC enzymes and the proposed reaction mechanism of acetyllysine hydrolysis by these enzymes.

A missense single-nucleotide polymorphism in a gene encoding a protein tyrosine phosphatase (PTPN22) is associated with rheumatoid arthritis.

Rheumatoid arthritis (RA) is the most common systemic autoimmune disease, affecting approximately 1% of the adult population worldwide, with an estimated heritability of 60%. To identify genes involved in RA susceptibility, we investigated the association between putative functional single-nucleotide polymorphisms (SNPs) and RA among white individuals by use of a case-control study design; a second sample was tested for replication. Here we report the association of RA susceptibility with the minor allele of a missense SNP in PTPN22 (discovery-study allelic P=6.6 x 10(-4); replication-study allelic P=5.6 x 10(-8)), which encodes a hematopoietic-specific protein tyrosine phosphatase also known as "Lyp." We show that the risk allele, which is present in approximately 17% of white individuals from the general population and in approximately 28% of white individuals with RA, disrupts the P1 proline-rich motif that is important for interaction with Csk, potentially altering these proteins' normal function as negative regulators of T-cell activation. The minor allele of this SNP recently was implicated in type 1 diabetes, suggesting that the variant phosphatase may increase overall reactivity of the immune system and may heighten an individual carrier's risk for autoimmune disease.