Discovery and mechanism of action of pegvisomant.

Using a structure-function approach to the understanding of the molecular topology of the GH molecule, we discovered that glycine in the third alpha-helix of GH (G119 of bovine GH and G120 of human GH) was an important amino acid required for GH action. Substitution of this glycine residue with a variety of amino acids results in molecules that lack growth-promoting activity. More importantly, these molecules inhibit the actions of GH both in vitro and in vivo. These results, obtained more than a decade ago, were the basis for the discovery of GH antagonists. Since that time, efforts have been focused on establishing the mechanism by which these antagonists inhibit GH action. In this regard, in vivo expression of GH-antagonist genes in transgenic mice results in dwarf animals. The animals are fertile and possess no abnormal 'phenotypes'. Dwarf mice have also been created by disrupting or 'knocking out' the GH receptor gene. Together, these results have laid the foundation for the clinical use of GH antagonists when endogenous GH levels are increased or when GH is known to be a factor in the progression of the disorder.