Nonpeptide ligands for peptidergic G protein-coupled receptors

Neuropeptides play essential roles in many physiological systems in vertebrates and invertebrates. Peptides per se are difficult to use as therapeutic agents, as they are generally very unstable in biological fluid environments and cross biological membranes poorly. Recognition that nonpeptide ligands for peptide receptors have clinical utility came from the discovery that opiates (such as morphine) act by binding to G protein-coupled receptors (GPCRs) for which the endogenous ligands are a family of neuropeptides (enkephalins and endorphins). Basic research has revealed a very large number of distinct neuropeptides that influence virtually every aspect of mammalian physiology and considerable effort has been expended in the pursuit of new drugs that act through peptidergic signaling systems. Although useful drugs have been found to affect various aspects ofneuropeptide biology, most work has been devoted to the discovery of nonpeptide ligands that act as agonists or antagonists at peptidergic GPCRs. Similar opportunities are apparent for the discovery of nonpeptide ligands that act on invertebrate GPCRs. A consideration of the knowledge gained from the process as conducted for mammalian peptidergic systems can inform and illuminate promising strategies for the discovery of new drugs for the treatment and control of pests and parasites.