CP-91149

CP-91149 is a selective inhibitor of glycogen phosphorylase (GP) with an IC50 value of 0.13 μM.

Glycogen phosphorylase is a phosphorylase enzymes that can catalize phosphorolytic cleavage of the glycosidic linkages of glycogen by releasing glucose-1-phosphate from the terminal alpha-1, 4-glycosidic bond. It controls the rate-limiting step in glycogenolysis in the cells.

In vitro, CP-91149 treatment suppressed glycogenolysis stimulated by glucagon in in primary human hepatocytes and isolated rat hepatocytes with IC50 value of 2.1 μM and 10–100 μM, respectively 1. Inhibition of phosphorylase a by CP-91149 resulted in activation of glycogen synthase and translocation of the protein from a soluble to a particulate fraction, which mimicked the insulin- stimulated glycogen synthesis 2.

In vivo, treatment of CP-91149 on diabetic ob/ob mice at a dosage of 25–50 mg/kg was shown to lead to a rapid glucose lowering but did not change glucose levels in normoglycemic, nondiabetic mice 1.

References:
1.  Martin WH, Hoover DJ, Armento SJ, et al. Discovery of a human liver glycogen phosphorylase inhibitor that lowers blood glucose in vivo. Proceedings of the National Academy of Sciences of the United States of America. 1998;95(4):1776-1781.
2.  Aiston S, Coghlan MP, Agius L. Inactivation of phosphorylase is a major component of the mechanism by which insulin stimulates hepatic glycogen synthesis. European journal of biochemistry / FEBS. 2003;270(13):2773-2781.

Regulation of glycogen metabolism in cultured human muscles by the glycogen phosphorylase inhibitor CP-91149.[Pubmed:14651477]

Biochem J. 2004 Mar 15;378(Pt 3):1073-7.

Pharmacological inhibition of liver GP (glycogen phosphorylase), which is currently being studied as a treatment for Type II (non-insulin-dependent) diabetes, may affect muscle glycogen metabolism. In the present study, we analysed the effects of the GP inhibitor CP-91149 on non-engineered or GP-overexpressing cultured human muscle cells. We found that CP-91149 treatment decreased muscle GP activity by (1) converting the phosphorylated AMP-independent a form into the dephosphorylated AMP-dependent b form and (2) inhibiting GP a activity and AMP-mediated GP b activation. Dephosphorylation of GP was exerted, irrespective of incubation of the cells with glucose, whereas inhibition of its activity was synergic with glucose. As expected, CP-91149 impaired the glycogenolysis induced by glucose deprivation. CP-91149 also promoted the dephosphorylation and activation of GS (glycogen synthase) in non-engineered or GP-overexpressing cultured human muscle cells, but exclusively in glucose-deprived cells. However, this inhibitor did not activate GS in glucose-deprived but glycogen-replete cells overexpressing PTG (protein targeting to glycogen), thus suggesting that glycogen inhibits the CP-91149-mediated activation of GS. Consistently, CP-91149 promoted glycogen resynthesis, but not its overaccumulation. Hence, treatment with CP-91149 impairs muscle glycogen breakdown, but enhances its recovery, which may be useful for the treatment of Type II (insulin-dependent) diabetes.

CP-91149 is a selective glycogen phosphorylase (GP) inhibitor with IC50 of 0.13 μM in the presence of glucose, 5- to 10-fold less potent in the absence of glucose.

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