Glucokinase: old enzyme, new target

The use of docking-based comparative intermolecular contacts analysis to identify optimal docking conditions within glucokinase and to discover of new GK activators

Glucokinase (GK) is involved in normal glucose homeostasis and therefore it is a valid target for drug design and discovery efforts. GK activators (GKAs) have excellent potential as treatments of hyperglycemia and diabetes. The combined recent interest in GKAs, together with docking limitations and shortages of docking validation methods prompted us to use our new 3D-QSAR analysis, namely, docking-based comparative intermolecular contacts analysis (dbCICA), to validate docking configurations performed on a group of GKAs within GK binding site. dbCICA assesses the consistency of docking by assessing the correlation between ligands' affinities and their contacts with binding site spots. Optimal dbCICA models were validated by receiver operating characteristic curve analysis and comparative molecular field analysis. dbCICA models were also converted into valid pharmacophores that were used as search queries to mine 3D structural databases for new GKAs. The search yielded several potent bioactivators that experimentally increased GK bioactivity up to 7.5-folds at 10 μM.

Anti-diabetic effects of lemon balm (Melissa officinalis) essential oil on glucose- and lipid-regulating enzymes in type 2 diabetic mice

The antioxidant activity of lemon balm (Melissa officinalis) essential oil (LBEO) on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals and its hypoglycaemic effect in db/db mice were investigated. LBEO scavenged 97 % of DPPH radicals at a 270-fold dilution. Mice administered LBEO (0·015 mg/d) for 6 weeks showed significantly reduced blood glucose (65 %; P < 0·05) and TAG concentrations, improved glucose tolerance, as assessed by an oral glucose tolerance test, and significantly higher serum insulin levels, compared with the control group. The hypoglycaemic mechanism of LBEO was further explored via gene and protein expression analyses using RT-PCR and Western blotting, respectively. Among all glucose metabolism-related genes studied, hepatic glucokinase and GLUT4, as well as adipocyte GLUT4, PPAR-γ, PPAR-α and SREBP-1c expression, were significantly up-regulated, whereas glucose-6-phosphatase and phosphoenolpyruvate carboxykinase expression was down-regulated in the livers of the LBEO group. The results further suggest that LBEO administered at low concentrations is an efficient hypoglycaemic agent, probably due to enhanced glucose uptake and metabolism in the liver and adipose tissue and the inhibition of gluconeogenesis in the liver.

Glucokinase activator PSN-GK1 displays enhanced antihyperglycaemic and insulinotropic actions

AIMS/HYPOTHESIS

We evaluated the insulinotropic and antihyperglycaemic actions of glucokinase activators (GKAs), especially through acute and subchronic studies in rodent diabetes models with (2R)-2-(4-cyclopropanesulphonylphenyl)-N-(5-fluorothiazol-2-yl)-3-(tetrahydropyran-4-yl)propionamide (PSN-GK1), a novel and potent GKA.

MATERIALS AND METHODS

The action of PSN-GK1 on or in the following were investigated: (1) on human liver glucokinase, insulin secretion from MIN6 cells and 2-deoxy-D: -[(3)H]glucose (2-DG) uptake into rat hepatocytes; and (2) in Zucker diabetic fatty rats and in non-diabetic C57Bl/6, diabetic db/db and ob/ob mice.

RESULTS

At 5 mmol/l glucose, PSN-GK1 activated glucokinase (4.3-fold, median effective concentration [EC(50)] 130 nmol/l), increased MIN6 insulin secretion (26-fold, EC(50) 267 nmol/l) and 2-DG hepatocytic uptake (threefold, EC(50) 1 micromol/l); at higher glucose concentrations, EC(50)s and fold-effectiveness were both lower. In C57Bl/6 mice, PSN-GK1 reduced blood glucose at 1 and 10 mg/kg (by mouth), but insulin was increased significantly at only the higher dose. In hyperinsulinaemic 10-mmol/l glucose clamps, PSN-GK1 increased 2-DG incorporation into liver glycogen sixfold, directly demonstrating liver effects. PSN-GK1 improved glycaemic profiles in db/db mice and Zucker diabetic fatty rats, diabetic animal models in which GKA efficacy has not previously been described, without causing hypoglycaemia. In ob/ob mice, it dose-dependently reduced excursions in OGTTs. Moreover, after subchronic administration, no tachyphylaxis was evident and glycaemia was improved without alterations to lipid levels, liver weight, glycogen content or body weight.

CONCLUSIONS/INTERPRETATION

PSN-GK1 was potently antihyperglycaemic through its effects on insulin release and hepatic glucose metabolism. It is one of the most potent GKAs described in the literature and is active in diabetic animal models where GKAs have not been reported to show efficacy to date. Ongoing human trials are investigating the potential of this novel therapeutic approach.

Applying science to drug discovery

Scientists and science in the pharmaceutical industry rely heavily on the more academically orientated basic research carried out at Universities, for first of all training, but also as a source of new ideas and approaches to drug discovery. Progress in the discovery and development of novel therapeutics benefits from a healthy alliance with, and the output from, more basic research institutions, and the reverse is also true, with many advances in understanding of physiological and pathological processes being as the result of the application of novel targeted molecules. To illustrate this, some examples related to the themes of this meeting from my experiences in three different companies will be described. The first involves a metabolic angle in the unravelling of the mechanism of the novel anti-anginal agent ranolazine. The second describes the application of detailed knowledge of insulin structure and action to then use recombinant approaches to design novel molecules to be able to offer the Type I (insulin-dependent) diabetic patient therapies allowing a more physiological treatment regime, and also the further application of learned technology to then discover a means of harnessing the potential of GLP-1 (glucagon-like polypeptide 1) for treating Type II (non-insulin-dependent) diabetes. The last illustrates how findings of novel binding sites on glycogen phosphorylase and glucokinase as the result of drug discovery programmes have led to increased understanding of these key metabolic enzymes and also potential new therapies for Type II diabetes.