Characterization of the Mechanism of Action for Novel Dopamine D2 Receptor Allosteric Modulators

Abstract

<p>Allosteric modulators are a newly emerging concept in the field of drug discovery which have shown remarkable success in their ability to alter G-protein coupled receptor (GPCR) activity in a precise and subtle manner. A GPCR of particular interest for allosteric targeting is the dopamine D2 receptor. This receptor has repeatedly been implicated in the etiology of complex neurological and neuropsychiatric disorders including Parkinson’s disease and schizophrenia. Previous studies from our lab have effectively developed allosteric modulators targeting the D2 receptor based on the pharmacophore of the endogenous tripeptide L-prolyl-L-leucyl-glycinamide (PLG). PLG and its potent peptidomimetics, particularly 3(R)-[(2(S)-pyrrolidinylcarbonyl)amino]-2-oxo-1-pyrrolidineacetamide (PAOPA) (PCT/CA2011/000968), have shown robust preclinical efficacy in treating models of Parkinson’s disease, depression, tardive dyskinesia and schizophrenia. These ligands modulate agonist binding to the D2 receptor in a biphasic manner, although further information on their mechanisms of action are currently unknown. Therefore, the overarching objective of this thesis was to enhance our knowledge on the mechanisms of action of the promising D2 allosteric ligands PLG and PAOPA. Results of the studies presented here show PAOPA to cause significant upregulation of D2 regulatory proteins and downstream signaling kinases, as well as cause an increase in D2 internalization. Additionally, the PLG allosteric binding site was narrowed down to be localized between transmembrane domains 5 and 6 on the D2 receptor. The collection of work presented here enhance our understanding of the mechanisms of action of the potentially therapeutic D2 allosteric ligands PLG and PAOPA, progressing them closer to helping clinically affected populations. The findings of these studies prove globally significant as they highlight the diverse cellular pathways which could be affected by allosteric modulators, and bring to light the importance of studying these candidate ligands for eventual improvements in the treatment of human health.</p>