Gino Salituro

Selective Small-Molecule Agonists of G Protein–Coupled Receptor 40 Promote Glucose-Dependent Insulin Secretion and Reduce Blood Glucose in Mice

OBJECTIVE— Acute activation of G protein–coupled receptor 40 (GPR40) by free fatty acids (FFAs) or synthetic GPR40 agonists enhances insulin secretion. However, it is still a matter of debate whether activation of GPR40 would be beneficial for the treatment of type 2 diabetes, since chronic exposure to FFAs impairs islet function. We sought to evaluate the specific role of GPR40 in islets and its potential as a therapeutic target using compounds that specifically activate GPR40. RESEARCH DESIGN AND METHODS— We developed a series of GPR40-selective small-molecule agonists and studied their acute and chronic effects on glucose-dependent insulin secretion (GDIS) in isolated islets, as well as effects on blood glucose levels during intraperitoneal glucose tolerance tests in wild-type and GPR40 knockout mice (GPR40−/−). RESULTS— Small-molecule GPR40 agonists significantly enhanced GDIS in isolated islets and improved glucose tolerance in wild-type mice but not in GPR40−/− mice. While a 72-h exposure to FFAs in tissue culture significantly impaired GDIS in islets from both wild-type and GPR40−/− mice, similar exposure to the GPR40 agonist did not impair GDIS in islets from wild-type mice. Furthermore, the GPR40 agonist enhanced insulin secretion in perfused pancreata from neonatal streptozotocin-induced diabetic rats and improved glucose levels in mice with high-fat diet–induced obesity acutely and chronically. CONCLUSIONS— GPR40 does not mediate the chronic toxic effects of FFAs on islet function. Pharmacological activation of GPR40 may potentiate GDIS in humans and be beneficial for overall glucose control in patients with type 2 diabetes.

Small molecule insulin mimetics reduce food intake and body weight and prevent development of obesity

Obesity and insulin resistance are major risk factors for a number of metabolic disorders, such as type 2 diabetes mellitus. Insulin has been suggested to function as one of the adiposity signals to the brain for modulation of energy balance. Administration of insulin into the brain reduces food intake and body weight, and mice with a genetic deletion of neuronal insulin receptors are hyperphagic and obese. However, insulin is also an anabolic factor; when administered systemically, pharmacological levels of insulin are associated with body weight gain in patients. In this study, we investigated the efficacy and feasibility of small molecule insulin mimetic compounds to regulate key parameters of energy homeostasis. Central intracerebroventricular (i.c.v.) administration of an insulin mimetic resulted in a dose-dependent reduction of food intake and body weight in rats, and altered the expression of hypothalamic genes known to regulate food intake and body weight. Oral administration of a mimetic in a mouse model of high-fat diet-induced obesity reduced body weight gain, adiposity and insulin resistance. Thus, insulin mimetics have a unique advantage over insulin in the control of body weight and hold potential as a novel anti-obesity treatment.

Omarigliptin (MK-3102): A Novel Long-Acting DPP-4 Inhibitor for Once-Weekly Treatment of Type 2 Diabetes.

In our effort to discover DPP-4 inhibitors with added benefits over currently commercially available DPP-4 inhibitors, MK-3102 (omarigliptin), was identified as a potent and selective dipeptidyl peptidase 4 (DPP-4) inhibitor with an excellent pharmacokinetic profile amenable for once-weekly human dosing and selected as a clinical development candidate. This manuscript summarizes the mechanism of action, scientific rationale, medicinal chemistry, pharmacokinetic properties, and human efficacy data for omarigliptin, which is currently in phase 3 clinical development.

Antidiabetic and antisteatotic effects of the selective fatty acid synthase (FAS) inhibitor platensimycin in mouse models of diabetes

Platensimycin (PTM) is a recently discovered broad-spectrum antibiotic produced by Streptomyces platensis. It acts by selectively inhibiting the elongation-condensing enzyme FabF of the fatty acid biosynthesis pathway in bacteria. We report here that PTM is also a potent and highly selective inhibitor of mammalian fatty acid synthase. In contrast to two agents, C75 and cerulenin, that are widely used as inhibitors of mammalian fatty acid synthase, platensimycin specifically inhibits fatty acid synthesis but not sterol synthesis in rat primary hepatocytes. PTM preferentially concentrates in liver when administered orally to mice and potently inhibits hepatic de novo lipogenesis, reduces fatty acid oxidation, and increases glucose oxidation. Chronic administration of platensimycin led to a net reduction in liver triglyceride levels and improved insulin sensitivity in db/+ mice fed a high-fructose diet. PTM also reduced ambient glucose levels in db/db mice. These results provide pharmacological proof of concept of inhibiting fatty acid synthase for the treatment of diabetes and related metabolic disorders in animal models.

Activation of Insulin Signal Transduction Pathway and Anti-diabetic Activity of Small Molecule Insulin Receptor Activators

We recently described the identification of a non-peptidyl fungal metabolite (l-783,281, compound 1), which induced activation of human insulin receptor (IR) tyrosine kinase and mediated insulin-like effects in cells, as well as decreased blood glucose levels in murine models of Type 2 diabetes (Zhang, B., Salituro, G., Szalkowski, D., Li, Z., Zhang, Y., Royo, I., Vilella, D., Diez, M. T., Pelaez, F., Ruby, C., Kendall, R. L., Mao, X., Griffin, P., Calaycay, J., Zierath, J. R., Heck, J. V., Smith, R. G. & Moller, D. E. (1999) Science 284, 974–977). Here we report the characterization of an active analog (compound 2) with enhanced IR kinase activation potency and selectivity over related receptors (insulin-like growth factor I receptor, epidermal growth factor receptor, and platelet-derived growth factor receptor). The IR activators stimulated tyrosine kinase activity of partially purified native IR and recombinant IR tyrosine kinase domain. Administration of the IR activators to mice was associated with increased IR tyrosine kinase activity in liver.In vivo oral treatment with compound 2 resulted in significant glucose lowering in several rodent models of diabetes. In db/db mice, oral administration of compound 2 elicited significant correction of hyperglycemia. In a streptozotocin-induced diabetic mouse model, compound 2 potentiated the glucose-lowering effect of insulin. In normal rats, compound 2 improved oral glucose tolerance with significant reduction in insulin release following glucose challenge. A structurally related inactive analog (compound 3) was not effective on insulin receptor activation or glucose lowering in db/db mice. Thus, small molecule IR activators exert insulin mimetic and sensitizing effects in cells and in animal models of diabetes. These results have implications for the future development of new therapies for diabetes mellitus.

Discovery of 5-aryloxy-2,4-thiazolidinediones as potent GPR40 agonists.

Systematic structure-activity relationship (SAR) studies of a screening lead led to the discovery of a series of thiazolidinediones (TZDs) as potent GPR40 agonists. Among them, compound C demonstrated an acute mechanism-based glucose-lowering in an intraperitoneal glucose tolerance test (IPGTT) in lean mice, while no effects were observed in GPR40 knock-out mice.

Evaluation of Cynomolgus Monkeys for the Identification of Endogenous Biomarkers for Hepatic Transporter Inhibition and as a Translatable Model to Predict Pharmacokinetic Interactions with Statins in Humans

Inhibition of hepatic transporters such as organic anion transporting polypeptides (OATPs) 1B can cause drug-drug interactions (DDIs). Determining the impact of perpetrator drugs on the plasma exposure of endogenous substrates for OATP1B could be valuable to assess the risk for DDIs early in drug development. As OATP1B orthologs are well conserved between human and monkey, we assessed in cynomolgus monkeys the endogenous OATP1B substrates that are potentially suitable to assess DDI risk in humans. The effect of rifampin (RIF), a potent inhibitor for OATP1B, on plasma exposure of endogenous substrates of hepatic transporters was measured. From the 18 biomarkers tested, RIF (18 mg/kg, oral) caused significant elevation of plasma unconjugated and conjugated bilirubin, which may be attributed to inhibition of cOATP1B1 and cOATP1B3 based on in vitro to in vivo extrapolation analysis. To further evaluate whether cynomolgus monkeys are a suitable translational model to study OATP1B-mediated DDIs, we determined the inhibitory effect of RIF on in vitro transport and pharmacokinetics of rosuvastatin (RSV) and atorvastatin (ATV). RIF strongly inhibited the uptake of RSV and ATV by cOATP1B1 and cOATP1B3 in vitro. In agreement with clinical observations, RIF (18 mg/kg, oral) significantly decreased plasma clearance and increased the area under the plasma concentration curve (AUC) of intravenously administered RSV by 2.8- and 2.7-fold, and increased the AUC and maximum plasma concentration of orally administered RSV by 6- and 10.3-fold, respectively. In contrast to clinical findings, RIF did not significantly increase plasma exposure of either intravenous or orally administered ATV, indicating species differences in the rate-limiting elimination pathways.

Meridamycin: a novel nonimmunosuppressive FKBP12 ligand from Streptomyces hygroscopicus

Abstract A novel, 27-membered macrolide, meridamycin, was isolated from a strain of Streptomyces hygroscopicus and found to inhibit the binding of FK-506 to FKBP 12 and to antagonize the immunosuppressive activity of both FK-506 and rapamycin. The isolation, structure elucidation, and biological activity of this compound are described in this paper.

Utility of unbound plasma drug levels and P-glycoprotein transport data in prediction of central nervous system exposure

Drug concentrations in cerebrospinal fluid have been assumed to be a natural surrogate for total drug exposures in the central nervous system. The present communication reports a data set from a study of 30 compounds in mice. An attempt was made to correlate cerebrospinal fluid and unbound plasma drug concentrations via incorporation of in vitro P-glycoprotein (Pgp)-mediated transport data. Pgp-deficient (Pgp –/–) and wild-type mice were dosed with compounds of interest by oral gavage (orally) at 5 mg kg−1. Plasma and cerebrospinal fluid samples were collected at 1 h post-dosing, and analysed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) for drug concentrations. Mouse and human Pgp-mediated transport were evaluated in vitro by a bi-directional (B to A and A to B) transport assay using LLC-PK1 cells expressing mouse (mdr1a) and human (MDR1) forms of Pgp, respectively. Compounds with B to A/A to B transport ratios < 2 were defined as non-substrates of Pgp, whereas those exhibiting B to A/A to B transport ratios ≥2 were considered Pgp substrates. Plasma protein binding was also determined in vitro via equilibrium dialysis. Of the 30 compounds, 13 were identified to be mouse Pgp substrates, all of which were also human Pgp substrates, demonstrating a good agreement between mouse and human data. In Pgp wild-type mice, the unbound plasma and cerebrospinal fluid concentrations of the non-Pgp substrates correlated well, with a regression slope of approximately 1.0. A similar relationship existed for Pgp substrates in Pgp –/– mice. On the other hand, an improved correlation of cerebrospinal fluid and systemic exposures of the Pgp substrates in Pgp wild-type mice was observed when the unbound plasma concentrations were normalized to the corresponding B to A/A to B transport ratios. These results reinforce the premise that a combined use of unbound plasma drug concentrations and in vitro Pgp transport data may be of value for the estimation of central nervous system exposures.

Novel tetrahydropyran analogs as dipeptidyl peptidase IV inhibitors: Profile of clinical candidate (2R,3S,5R)-2-(2,5-difluorophenyl)-5-[2-(methylsulfonyl)-2,6-dihydropyrrolo[3,4-c]pyrazol-5(4H)-yl]tetrahydro-2H-pyran-3-amine (23)

A series of novel tri-2,3,5-substituted tetrahydropyran analogs were synthesized and evaluated as inhibitors of dipeptidyl peptidase IV (DPP-4) for the treatment of type 2 diabetes. Optimization of the series provided inhibitors with good DPP-4 potency and selectivity over other peptidases (QPP, DPP8, and FAP). Compound 23, which is very potent, selective, efficacious in the diabetes PD model, and has an excellent pharmacokinetic profile, is selected as a clinical candidate.