Identification of a Molecular Activator for Insulin Receptor with Potent Anti-diabetic Effects

Abstract

Insulin exerts its actions through the insulin receptor (IR) and plays an essential role in diabetes. The inconvenient daily injection and undesirable side-effects associated with insulin injection demand novel drugs for the diseases. To search for bioactive insulin mimetics, we developed an in vitro screening assay using phospho-IR ELISA. After screening the small molecule chemical libraries, we have obtained a compound (5,8-diacetyloxy-2,3-dichloro-1,4-naphthoquinone) that provokes IR activation by directly binding to the receptor kinase domain to trigger its kinase activity at micromolar concentrations. This compound selectively activates IR but not other receptors and sensitizes insulin's action. Moreover, it elevates glucose uptake in adipocytes and has oral hypoglycemic effect in wild-type C57BL/6J mice and db/db and ob/ob mice without demonstrable toxicity. Hence, this promising compound mimics the biological functions of insulin and is useful for further drug development for diabetes treatment.Type 2 diabetes mellitus is a heterogeneous disease that results from defective insulin actions and secretions. Various pharmacological agents are used to improve glucose homeostasis via different modes of action: sulfonylureas stimulate insulin secretion, biguanides (e.g. metformin) promote glucose utilization and reduce hepatic-glucose production, ␣-glucosidase inhibitors (e.g. acarbose) slow down carbohydrate absorption from the gut, and thiazolidinediones enhance cellular insulin action on glucose metabolism (1). Insulin replacement therapy is also needed when insulin production declines in the patients with poor glycemic control (2). In recent years, treatment strategies have focused on the development of novel therapeutic options to substitute insulin therapy. Several small compounds like demethylasterriquinone-B1 and TLK19780 have been identified as the functional insulin mimetics; however, they have poor bioavailability or low receptor specificity (3-5).Therefore, the search for new orally active insulin mimetics with stringent receptor selectivity is highly warranted.In this report, we demonstrate that the naphthoquinone derivative 5,8-diacetyloxy-2,3-dichloro-1,4-naphthoquinone (DDN) 3 is a highly selective IR activator that interacts directly with the IR tyrosine kinase domain to induce Akt and ERK phosphorylations. It is also an insulin sensitizer that enhances insulin's action to stimulate glucose uptake. Oral administration of this compound robustly decreases blood glucose in wildtype and diabetic ob/ob and db/db mice. Therefore, DDN is a bioactive insulin mimetic with hypoglycemic activity. EXPERIMENTAL PROCEDURESAnimals-Male C57BL/6J mice, male C57BL/KsJ db/db mice, and female C57BL/KsJ ob/ob mice were obtained from the Jackson Laboratory. Adult animals aged 10 -12 weeks were used. Mice were housed in environmentally controlled conditions with a 12-h light/dark cycle and had free access to standard rodent pellet food and water. The animal protocols were approved by the Institutional Animal Care and ...

Overview of food products and dietary constituents with antidiabetic properties and their putative mechanisms of action: A natural approach to complement pharmacotherapy in the management of diabetes

“…Insulin replacement therapy is required in patients with type 1 diabetes and is often also needed in type 2 diabetic patients when insulin production declines. The search for alternative options to insulin therapy that would circumvent the inconvenience of insulin administration and its side effects have led to the discovery of several small molecules, such as demethylasterriquinone‐B1 (also known as L‐783281) from a fungal extract and the synthetic hydroxyfuroic acid compound D‐410639 , that mimic the in vivo function of insulin . These compounds trigger insulin signaling by selectively activating the insulin receptor without displacing insulin and were found to reduce blood glucose levels in rodent models .…”

Biasing Receptor Tyrosine Kinase Signaling Pathways

“…Reportedly, compounds with replacements of DMAQ-B1's quinone moiety have been prepared but little information is available on their signaling properties. 80 A series of apparently unbiased 1,4 napthoquinone derivatives have been described that stimulate phosphorylation of both Akt and ERK in transfected cells, 81 suggesting that determinants of DMAQ-B1 signaling bias might be located in its indoyl substituents.…”

Novel therapies in type 2 diabetes: insulin resistance

“…In addition, D‐410639 inhibited epidermal growth factor receptor (EGF‐R/ErbB1) which is involved in vascular dysfunction in patients with diabetes; which suggests that this compound might have vascular benefits . Another promising compound is compound 5,8‐diacetyloxy‐2,3‐dichloro‐1,4‐naphthoquinone which also binds to the kinase domain of the insulin receptor to trigger insulin action . This oral compound improved glucose levels in wild‐type C57BL/6 J mice and db/db and ob/ob mice without evidence of toxicity …”

“…Another promising compound is compound 5,8‐diacetyloxy‐2,3‐dichloro‐1,4‐naphthoquinone which also binds to the kinase domain of the insulin receptor to trigger insulin action . This oral compound improved glucose levels in wild‐type C57BL/6 J mice and db/db and ob/ob mice without evidence of toxicity …”