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

Abstract

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.Insulin elicits a diverse array of biological responses by binding to its specific receptor (1). The insulin receptor (IR) 1 is a heterotetrameric protein consisting of two extracellular ␣ subunits and two transmembrane ␤ subunits. The binding of the ligand to the ␣ subunit of IR not only concentrates insulin at its site of action, but also induces conformational changes in the receptor, which in turn stimulates the tyrosine kinase activity intrinsic to the ␤ subunit of the IR. Extensive studies have indicated that the ability of the receptor to autophosphorylate and phosphorylate intracellular substrates is essential for its mediation of the complex cellular responses of insulin (2-5).Insulin receptors trans-phosphorylate several immediate substrates (on Tyr residues), including insulin receptor substrate (IRS) proteins 1-4, Shc, and Gab 1, each of which provide specific docking sites for other signaling proteins containing Src homology 2 domains (6). These events lead to the activation of downstream signaling molecules, including phosphatidylinositol 3-kinase (PI 3-kinase). Numerous studies have adduced that PI 3-kinase is required for the metabolic effec...

Therapeutic Actions of an Insulin Receptor Activator and a Novel Peroxisome Proliferator-Activated Receptor γ Agonist in the Spontaneously Hypertensive Obese Rat Model of Metabolic Syndrome X

“…DMAQ-B1 itself has been shown to have a direct effect on phosphorylation of the insulin receptor and IRS-1 (Ding et al, 2002). In vitro studies suggest that this compound may interact with the inactive receptor kinase domain of the insulin receptor, thereby changing its confirmation and partially relieving the autoinhibition, allowing ATP to access the active site of the receptor and mimicking insulin (Qureshi et al, 2000). This agent also potentiated insulin receptor tyrosine kinase activity by 30% in liver extracts from normal .…”

“…A small molecule that mimics many of the actions of insulin has been described Qureshi et al, 2000;Li et al, 2001;Salituro et al, 2001;Air et al, 2002;Ding et al, 2002;Roper et al, 2002). This benzoquinone, DMAQ-B1, directly activates the intrinsic tyrosine kinase activity of the insulin receptor Qureshi et al, 2000;Li et al, 2001;Salituro et al, 2001).…”

“…This benzoquinone, DMAQ-B1, directly activates the intrinsic tyrosine kinase activity of the insulin receptor Qureshi et al, 2000;Li et al, 2001;Salituro et al, 2001). This orally active compound has the potential to augment insulin action in murine models of type 2 diabetes.…”

Structural and Biochemical Evidence for an Autoinhibitory Role for Tyrosine 984 in the Juxtamembrane Region of the Insulin Receptor

“…One of the compounds (L-783,281) modestly elevates insulin receptor autophosphorylation in the absence of insulin, whereas the other compound (TLK16998) potentiates receptor autophosphorylation in the presence of insulin, suggesting two different mechanisms of action (40). Interestingly, L-783,281 and a derivative (41) are of an appropriate size to bind in the ␤ sheet-␣C cleft, and L-783,281 was shown to alter the trypsin susceptibility at Lys-1030 (38), not far spatially from Tyr-984 (Fig. 5A).…”

Functional Genomics and Cardiovascular Drug Discovery

“…Screening a library of 50 000 mixtures of synthetic and natural compounds led to the identification of a nonpeptide, orally absorbable molecule from a fungus found in the Congo; this molecule activates the insulin receptor selectively, and analogs of this compound reduce glucose when given orally to rodents with diabetes. 20,21 This demonstrates the potential value of natural product chemical diversity.…”