sb-415286 and Diabetes-Mellitus--Type-2

Three closely related forms of glycogen synthase kinase 3 (GSK-3alpha, GSK-3beta and GSK-3beta2) have a major role in Wnt and Hedgehog signaling pathways and regulate the cell-division cycle, stem-cell renewal and differentiation, apoptosis, circadian rhythm, transcription and insulin action. A large body of evidence supports speculation that pharmacological inhibitors of GSK-3 could be used to treat several diseases, including Alzheimer's disease and other neurodegenerative diseases, bipolar affective disorder, diabetes, and diseases caused by unicellular parasites that express GSK-3 homologues. The toxicity, associated side-effects and concerns regarding the absorption, distribution, metabolism and excretion of these inhibitors affect their clinical potential. More than 30 inhibitors of GSK-3 have been identified. Seven of these have been co-crystallized with GSK-3beta and all localize within the ATP-binding pocket of the enzyme. GSK-3, as part of a multi-protein complex that contains proteins such as axin, presenilin and beta-catenin, contains many additional target sites for specific modulation of its activity.

Topics: Animals; Cell Differentiation; Diabetes Mellitus, Type 2; Enzyme Inhibitors; Glycogen Synthase Kinase 3; Humans; Neoplasms; Nervous System Diseases; Parasitic Diseases; Signal Transduction; Stem Cells; Structure-Activity Relationship

A major action of insulin is to regulate the transcription rate of specific genes. The expression of these genes is dramatically altered in type 2 diabetes. For example, the expression of two hepatic genes, glucose-6-phosphatase and PEPCK, is normally inhibited by insulin, but in type 2 diabetes, their expression is insensitive to insulin. An agent that mimics the effect of insulin on the expression of these genes would reduce gluconeogenesis and hepatic glucose output, even in the presence of insulin resistance. The repressive actions of insulin on these genes are dependent on phosphatidylinositol (PI) 3-kinase. However, the molecules that lie between this lipid kinase and the two gene promoters are unknown. Glycogen synthase kinase-3 (GSK-3) is inhibited following activation of PI 3-kinase and protein kinase B. In hepatoma cells, we find that selectively reducing GSK-3 activity strongly reduces the expression of both gluconeogenic genes. The effect is at the level of transcription and is observed with induced or basal gene expression. In addition, GSK-3 inhibition does not result in the subsequent activation of protein kinase B or inhibition of the transcription factor FKHR, which are candidate regulatory molecules for these promoters. Thus, GSK-3 activity is required for basal activity of each promoter. Inhibitors of GSK-3 should therefore reduce hepatic glucose output, as well as increase the synthesis of glycogen from L-glucose. These findings indicate that GSK-3 inhibitors may have greater therapeutic potential for lowering blood glucose levels and treating type 2 diabetes than previously realized.

Topics: Aminophenols; Animals; Blood Glucose; Calcium-Calmodulin-Dependent Protein Kinases; Choline O-Acetyltransferase; Culture Media, Serum-Free; Dexamethasone; Diabetes Mellitus, Type 2; DNA-Binding Proteins; Enzyme Inhibitors; Forkhead Box Protein O1; Forkhead Transcription Factors; Gene Expression Regulation, Enzymologic; Glucose-6-Phosphatase; Glycogen Synthase Kinase 3; Glycogen Synthase Kinases; Humans; Insulin; Lithium Chloride; Liver Neoplasms, Experimental; Maleimides; Nerve Tissue Proteins; Phosphatidylinositol 3-Kinases; Phosphoenolpyruvate Carboxykinase (GTP); Potassium Chloride; Promoter Regions, Genetic; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Rats; Recombinant Proteins; Transcription Factors; Transfection; Tumor Cells, Cultured

Glycogen synthase kinase-3 (GSK-3) is a serine/threonine protein kinase, the activity of which is inhibited by a variety of extracellular stimuli including insulin, growth factors, cell specification factors and cell adhesion. Consequently, inhibition of GSK-3 activity has been proposed to play a role in the regulation of numerous signalling pathways that elicit pleiotropic cellular responses. This report describes the identification and characterisation of potent and selective small molecule inhibitors of GSK-3.. SB-216763 and SB-415286 are structurally distinct maleimides that inhibit GSK-3alpha in vitro, with K(i)s of 9 nM and 31 nM respectively, in an ATP competitive manner. These compounds inhibited GSK-3beta with similar potency. However, neither compound significantly inhibited any member of a panel of 24 other protein kinases. Furthermore, treatment of cells with either compound stimulated responses characteristic of extracellular stimuli that are known to inhibit GSK-3 activity. Thus, SB-216763 and SB-415286 stimulated glycogen synthesis in human liver cells and induced expression of a beta-catenin-LEF/TCF regulated reporter gene in HEK293 cells. In both cases, compound treatment was demonstrated to inhibit cellular GSK-3 activity as assessed by activation of glycogen synthase, which is a direct target of this kinase.. SB-216763 and SB-415286 are novel, potent and selective cell permeable inhibitors of GSK-3. Therefore, these compounds represent valuable pharmacological tools with which the role of GSK-3 in cellular signalling can be further elucidated. Furthermore, development of similar compounds may be of use therapeutically in disease states associated with elevated GSK-3 activity such as non-insulin dependent diabetes mellitus and neurodegenerative disease.

Topics: Adenosine Triphosphate; Aminophenols; beta Catenin; Binding, Competitive; Calcium-Calmodulin-Dependent Protein Kinases; Cell Line; Cytoskeletal Proteins; Diabetes Mellitus, Type 2; Enzyme Activation; Gene Expression Regulation; Genes, Reporter; Glycogen; Glycogen Synthase; Glycogen Synthase Kinase 3; Glycogen Synthase Kinases; Humans; Indoles; Kinetics; Liver; Maleimides; Molecular Structure; Neurodegenerative Diseases; Protein Kinases; Recombinant Proteins; Signal Transduction; Trans-Activators; Transcription, Genetic