Tomoharu Iino

Structure-activity relationships of 3,5-disubstituted benzamides as glucokinase activators with potent in vivo efficacy

The optimization of our lead GK activator 2a to 3-[(1S)-2-hydroxy-1-methylethoxy]-5-[4-(methylsulfonyl)phenoxy]-N-1,3-thiazol-2-ylbenzamide (6g), a potent GK activator with good oral availability, is described, including to uncouple the relationship between potency and hydrophobicity. Following oral administration, this compound exhibited robust glucose lowering in diabetic model rodents.

Identification of novel and potent 2-amino benzamide derivatives as allosteric glucokinase activators

The identification and structure-activity-relationships (SARs) of novel 2-amino benzamide glucokinase activators are described. Compounds in this series were developed to be potent GK activators, and their binding mode to the GK protein was determined by crystal structure analysis. In vivo pharmacokinetic and acute in vivo efficacy studies of compound 18 are also described.

Discovery of potent and orally active 3-alkoxy-5-phenoxy-N-thiazolyl benzamides as novel allosteric glucokinase activators

Identification and synthesis of novel 3-alkoxy-5-phenoxy-N-thiazolyl benzamides as glucokinase activators are described. Removal of an aniline structure of the prototype lead (2a) and incorporation of an alkoxy or phenoxy substituent led to the identification of 3-Isopropoxy-5-[4-(methylsulfonyl)phenoxy]-N-(4-methyl-1,3-thiazol-2-yl)benzamide (27e) as a novel, potent, and orally bioavailable GK activator. Rat oral glucose tolerance test indicated that 27e exhibited a glucose-lowering effect after 10 mg/kg oral administration.

Pharmacokinetic and Pharmacodynamic Properties of the Glucokinase Activator MK-0941 in Rodent Models of Type 2 Diabetes and Healthy Dogs

Glucokinase activators (GKAs) are small-molecule agents that enhance glucose sensing by pancreatic β cells and glucose metabolism by hepatocytes. There is strong interest in these agents as potential therapies for type 2 diabetes. Here, we report key pharmacokinetic and pharmacodynamic findings from preclinical studies of the GKA 3-[[6-(ethylsulfonyl)-3-pyridinyl]oxy]-5-[(1S)-2-hydroxy-1-methylethoxy]-N-(1-methyl-1H-pyrazol-3-yl)benzamide (MK-0941). Incubated in vitro with recombinant human glucokinase, 1 μM MK-0941 lowered the S0.5 of this enzyme for glucose from 6.9 to 1.4 mM and increased the maximum velocity of glucose phosphorylation by 1.5-fold. In 2.5 and 10 mM glucose, the EC50 values for activation of GK by MK-0941 were 0.240 and 0.065 μM, respectively. Treatment of isolated rat islets of Langerhans and hepatocytes with 10 μM MK-0941 increased insulin secretion by 17-fold and glucose uptake up to 18-fold, respectively. MK-0941 exhibited strong glucose-lowering activity in C57BL/6J mice maintained on a high-fat diet (HFD), db/db mice, HFD plus low-dose streptozotocin-treated mice, and nondiabetic dogs. In both mice and dogs, oral doses of MK-0941 were rapidly absorbed and rapidly cleared from the blood; plasma levels reached maximum within 1 h and fell thereafter with a half-life of ∼2 h. During oral glucose tolerance testing in dogs, MK-0941 reduced total area-under-the-curve postchallenge (0–2 h) plasma glucose levels by up to 48% compared with vehicle-treated controls. When administered twice daily to mice for 16 days, and once daily to the dog for 4 days, MK-0941 remained efficacious on successive days. These findings support further investigation of MK-0941 as a potential therapeutic agent for treatment of type 2 diabetes.

Discovery and structure-activity relationships of a novel class of quinazoline glucokinase activators.

We describe design, syntheses and structure-activity relationships of a novel class of 4,6-disubstituted quinazoline glucokinase activators. Prototype quinazoline leads (4 and 5) were designed based on the X-ray analyses of the previous 2-aminobenzamide lead classes. Modifications of the quinazoline leads led to the identification of a potent GK activator (21d).

A small-molecule glucokinase activator lowers blood glucose in the sulfonylurea-desensitized rat.

Glucokinase activators increase insulin release from pancreatic beta-cells and hepatic glucose utilization by modifying the activity of glucokinase, a key enzyme in glucose-sensing and glycemic regulation. Sulfonylureas are antihyperglycemic agents that stimulate insulin secretion via a glucose-independent mechanism that is vulnerable to secondary failure through beta-cell desensitization. The present study determined whether glucokinase activator treatment retains its glucose-lowering efficacy in male, adult, non-diabetic Sprague-Dawley rats desensitized to sulfonylurea treatment and whether glucose-lowering during chronic glucokinase activator treatment is subject to secondary failure. Animals were given food containing either glimepiride (a sulfonylurea), Compound B (3-[(1S)-2-hydroxy-1-methylethoxy]-5-[4-(methylsulfonyl)phenoxy]-N-1,3-thiazol-2-ylbenzamide, an experimental glucokinase activator), or no drug for up to 5 weeks. Food containing 0.04% of either drug produced acute (within 4-8 h) and significant (P<0.05) reductions in blood glucose to approximately 50% of control levels. Chronic treatment with either 0.01% or 0.04% glimepiride resulted in complete failure of glucose-lowering efficacy within 3 days whereas the efficacy of Compound B was sustained throughout the entire study. Glipizide, also a sulfonylurea, had no glucose-lowering effect when given by gavage (3mg/kg) to glimepiride-desensitized animals whereas Compound B retained full glucose-lowering efficacy in glimepiride-desensitized animals. Oral glucose tolerance was significantly impaired, compared with controls, in animals treated with glimepiride for two weeks but was enhanced to a small extent in animals treated with Compound B. Compound B also significantly increased pancreatic insulin content, compared with controls. These findings suggest that Compound B has sustained glucose-lowering effects in a rat model of sulfonylurea failure.

A selective small molecule glucagon-like peptide-1 secretagogue acting via depolarization-coupled Ca2+ influx

Glucagon-like peptide-1 (GLP-1) is an incretin hormone that potentiates insulin secretion in a glucose-dependent manner. Selective GLP-1 secretagogue would be one of the potential therapeutic targets for type 2 diabetes. Here, we describe a newly identified small molecule compound (compound A) that stimulates secretion of GLP-1 in murine enteroendocrine cell lines, STC-1 and GLUTag cells, and in primary cultured fetal rat intestinal cells (FRIC). The underlying mechanism by which compound A stimulated GLP-1 secretion was also examined. Compound A stimulated GLP-1 secretion from STC-1 cells in a concentration-dependent manner, and also from GLUTag cells and FRIC. The action of compound A was selective against other tested endocrine functions such as secretion of insulin from rat islets, growth hormone from rat pituitary gland cells, and norepinephrine from rat PC-12 cells. In STC-1 cells, the compound A-stimulated GLP-1 secretion was neither due to cyclic AMP production nor to Ca(2+) release from intracellular stores, but to extracellular Ca(2+) influx. The response was inhibited by the presence of either L-type Ca(2+) channel blockers or K(+) ionophore. Perforated-patch clamp study revealed that compound A induces membrane depolarization. These results suggest that neither Galphas- nor Galphaq-coupled signaling account for the mechanism of action, but depolarization-coupled Ca(2+) influx from extracellular space is the primary cause for the GLP-1 secretion stimulated by compound A. Identifying a specific target molecule for compound A will reveal a selective regulatory pathway that leads to depolarization-mediated GLP-1 secretion.

Metabolic activation of N-thiazol-2-yl benzamide as glucokinase activators: Impacts of glutathione trapping on covalent binding

Glucokinase activators (GKAs) are currently under investigation as potential antidiabetic agents by many pharmaceutical companies. Most of GKAs reported previously possess N-aminothiazol-2-yl amide moiety in their structures because the aminothiazole moiety interacts with glucokinase (GK) and shows strong GK activation. During the development of N-aminothiazol-2-yl amide derivatives, we identified a bioactivation and metabolic liability of 2-aminothizole substructure of GKA 3 by assessing covalent binding, metabolites in liver microsomes and glutathione (GSH) trap assay.