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Small molecule insulin receptor activators potentiate insulin action in insulin-resistant cells
M Li1, J F Youngren, V P Manchem
1University of California at San Francisco, Mount Zion Medical Center, San Francisco, California 94143-1616, USA.
Abstract:
In type 2 diabetes, impaired insulin signaling leads to hyperglycemia and other metabolic abnormalities. To study a new class of antidiabetic agents, we compared two small, nonpeptide molecules that activate insulin receptor (IR) beta-subunit tyrosine kinase activity: Merck L7, a direct IR agonist, and Telik's TLK16998, an IR sensitizer. In rat hepatoma cells (HTCs) that overexpress the IR (HTC-IR), IR autophosphorylation was directly activated by L7 in the absence of insulin. TLK16998 did not directly activate IR autophosphorylation, but it enhanced IR autophosphorylation in the presence of insulin. Tyrosine phosphorylation of an endogenous 185-kDa IR substrate was also significantly enhanced by both Merck L7 alone and TLK16998 plus insulin. Adding TLK16998 to L7 produced synergistic effects, further indicating that these two compounds act on the IR through separate mechanisms. We next studied HTC-IR(Delta485-599) cells, which overexpress a mutant IR with a deletion in the alpha-subunit connecting domain that does not undergo autophosphorylation in response to insulin binding. L7 was able to directly activate autophosphorylation of the deletion mutant IR in these cells, whereas TLK16998 had no effect. Compounds were then tested in three other cell models of impaired IR function. Both TLK16998 and Merck L7 improved IR autophosphorylation in cells with diminished IR signaling due to either treatment with tumor necrosis factor-alpha or overexpression of membrane glycoprotein PC-1. However, in TPA (tetradecanoylphorbol acetate)-treated cells, TLK16998 but not Merck L7 was able to significantly reverse the impaired insulin-stimulated IR autophosphorylation. In summary, these two classes of IR activators selectively increased IR function in a variety of insulin-resistant cell lines.
Insights
Two novel compounds, Merck L7 and TLK16998, activate insulin receptor (IR) signaling differently. Both show potential in improving IR function in various insulin-resistant cell models, offering new avenues for type 2 diabetes treatment.
Area of Science:
- Biochemistry
- Pharmacology
- Cell Biology
Background:
- Type 2 diabetes is characterized by impaired insulin signaling, leading to hyperglycemia.
- Insulin receptor (IR) beta-subunit tyrosine kinase activity is crucial for insulin signal transduction.
- Developing novel antidiabetic agents that modulate IR function is a key therapeutic goal.
Purpose of the Study:
- To compare the mechanisms of two nonpeptide molecules, Merck L7 (direct IR agonist) and TLK16998 (IR sensitizer), in activating IR beta-subunit tyrosine kinase activity.
- To evaluate the efficacy of these compounds in various cell models of insulin resistance.
Main Methods:
- Utilized rat hepatoma cells (HTCs) overexpressing wild-type and mutant IR (HTC-IR and HTC-IR(Delta485-599)).
- Assessed IR autophosphorylation and tyrosine phosphorylation of an endogenous IR substrate in response to insulin, Merck L7, and TLK16998.
- Tested compound effects in cell models with impaired IR signaling induced by tumor necrosis factor-alpha, PC-1 overexpression, and TPA treatment.
Main Results:
- Merck L7 directly activated IR autophosphorylation independently of insulin, while TLK16998 enhanced insulin-stimulated IR autophosphorylation.
- Both compounds significantly enhanced tyrosine phosphorylation of an 185-kDa IR substrate.
- Synergistic effects were observed when TLK16998 was combined with L7, suggesting distinct mechanisms of action.
- Merck L7 activated a mutant IR (HTC-IR(Delta485-599)) that L7 could not activate.
- Both compounds improved IR function in TNF-alpha-treated and PC-1-overexpressing cells.
- TLK16998, but not Merck L7, reversed impaired insulin-stimulated IR autophosphorylation in TPA-treated cells.
Conclusions:
- Merck L7 and TLK16998 represent distinct classes of IR activators.
- These compounds selectively enhance IR function in different insulin-resistant cellular contexts.
- Their distinct mechanisms and selective actions suggest potential for targeted therapeutic strategies in type 2 diabetes.
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