Development of a human vasopressin V1a-receptor antagonist from an evolutionary-related insect neuropeptide.

Characterisation of G protein-coupled receptors (GPCR) relies on the availability of a toolbox of ligands that selectively modulate different functional states of the receptors. To uncover such molecules, we explored a unique strategy for ligand discovery that takes advantage of the evolutionary conservation of the 600-million-year-old oxytocin/vasopressin signalling system. We isolated the insect oxytocin/vasopressin orthologue inotocin from the black garden ant (Lasius niger), identified and cloned its cognate receptor and determined its pharmacological properties on the insect and human oxytocin/vasopressin receptors. Subsequently, we identified a functional dichotomy: inotocin activated the insect inotocin and the human vasopressin V1b receptors, but inhibited the human V1aR. Replacement of Arg8 of inotocin by D-Arg8 led to a potent, stable and competitive V1aR-antagonist ([D-Arg8]-inotocin) with a 3,000-fold binding selectivity for the human V1aR over the other three subtypes, OTR, V1bR and V2R. The Arg8/D-Arg8 ligand-pair was further investigated to gain novel insights into the oxytocin/vasopressin peptide-receptor interaction, which led to the identification of key residues of the receptors that are important for ligand functionality and selectivity. These observations could play an important role for development of oxytocin/vasopressin receptor modulators that would enable clear distinction of the physiological and pathological responses of the individual receptor subtypes.

Identification of Potential Pharmacoperones Capable of Rescuing the Functionality of Misfolded Vasopressin 2 Receptor Involved in Nephrogenic Diabetes Insipidus.

Pharmacoperones correct the folding of otherwise misfolded protein mutants, restoring function (i.e., providing "rescue") by correcting their trafficking. Currently, most pharmacoperones possess intrinsic antagonist activity because they were identified using methods initially aimed at discovering such functions. Here, we describe an ultra-high-throughput homogeneous cell-based assay with a cAMP detection system, a method specifically designed to identify pharmacoperones of the vasopressin type 2 receptor (V2R), a GPCR that, when mutated, is associated with nephrogenic diabetes insipidus. Previously developed methods to identify compounds capable of altering cellular trafficking of V2R were modified and used to screen a 645,000 compound collection by measuring the ability of library compounds to rescue a mutant hV2R [L83Q], using a cell-based luminescent detection system. The campaign initially identified 3734 positive modulators of cAMP. The confirmation and counterscreen identified only 147 of the active compounds with an EC50 of ≤5 µM. Of these, 83 were reconfirmed as active through independently obtained pure samples and were also inactive in a relevant counterscreen. Active and tractable compounds within this set can be categorized into three predominant structural clusters, described here, in the first report detailing the results of a large-scale pharmacoperone high-throughput screening campaign.