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.