Agonists and Antagonists of GIP and GLP-1 Receptors: Recombinant Species-Specific Variants and Mutual Neutralization of Activity

The development of recombinant modified derivatives of human glucose-dependent insulinotropic polypeptide (rmGIP) and glucagon-like peptide 1 (rmGLP-1) has been carried out as part of the project to create a prototype of a two-component drug. The aims were to increase the activity of GIP derivatives and obtain antagonists of GIP and GLP-1 receptors for selective neutralization of the activity of the corresponding components of a promising drug. For this purpose, well-known mutations were introduced into the structure of the basic human rmGIP(1‒42)h variant: a deletion of residues 32–42 and a H18R substitution, which is species specific for the mouse/rat hormones. The hypoglycemic activity of the drugs was measured using a glucose tolerance test on healthy mice. In most cases, the engineered mutations turned out to be unexpectedly ineffective or did not affect the hypoglycemic activity of GIP derivatives at all. The maximum two-fold increase in activity was recorded only in the modified rmGIP(1‒31) rat variant, which contained both mutations simultaneously. Inactivated rmGIP(3‒31)rat and rmGLP-1(3‒31) derivatives, containing the deletion of two N-terminal residues, specific for natural antagonists of the GIP and GLP-1 receptors (GIPR and GLP-1R, respectively) individually exhibited the expected dose-dependent antagonistic activity. At the same time, their equimolar mixture, instead of the expected additive effect, showed a complete loss of sugar-increasing activity. Based on the obtained results, we formulated the hypothesis about the ability of metabolites of the derivatives of incretin hormones GIP and GLP-1 to interact with each other in the process of glycemic regulation. This fact should be taken into account when studying the mechanisms of glycemic control and developing drugs based on agonists and antagonists of GIP and GLP-1 receptors.