AUTHOR=Sturaro Chiara , Malfacini Davide , Argentieri Michela , Djeujo Francine M. , Marzola Erika , Albanese Valentina , Ruzza Chiara , Guerrini Remo , Calo’ Girolamo , Molinari Paola 

TITLE=Pharmacology of Kappa Opioid Receptors: Novel Assays and Ligands

JOURNAL=Frontiers in Pharmacology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/pharmacology/articles/10.3389/fphar.2022.873082

DOI=10.3389/fphar.2022.873082

ISSN=1663-9812

ABSTRACT=<p>The present study investigated the <italic>in vitro</italic> pharmacology of the human kappa opioid receptor using multiple assays, including calcium mobilization in cells expressing chimeric G proteins, the dynamic mass redistribution (DMR) label-free assay, and a bioluminescence resonance energy transfer (BRET) assay that allows measurement of receptor interaction with G protein and β-arrestin 2. In all assays, dynorphin A, U-69,593, and [D-Pro<sup>10</sup>]dyn(1-11)-NH<sub>2</sub> behaved as full agonists with the following rank order of potency [D-Pro<sup>10</sup>]dyn(1-11)-NH<sub>2</sub> &gt; dynorphin A ≥ U-69,593. [Dmt<sup>1</sup>,Tic<sup>2</sup>]dyn(1-11)-NH<sub>2</sub> behaved as a moderate potency pure antagonist in the kappa-β-arrestin 2 interaction assay and as low efficacy partial agonist in the other assays. Norbinaltorphimine acted as a highly potent and pure antagonist in all assays except kappa-G protein interaction, where it displayed efficacy as an inverse agonist. The pharmacological actions of novel kappa ligands, namely the dynorphin A tetrameric derivative PWT2-Dyn A and the palmitoylated derivative Dyn A-palmitic, were also investigated. PWT2-Dyn A and Dyn A-palmitic mimicked dynorphin A effects in all assays showing similar maximal effects but 3–10 fold lower potency. In conclusion, in the present study, multiple <italic>in vitro</italic> assays for the kappa receptor have been set up and pharmacologically validated. In addition, PWT2-Dyn A and Dyn A-palmitic were characterized as potent full agonists; these compounds are worthy of further investigation <italic>in vivo</italic> for those conditions in which the activation of the kappa opioid receptor elicits beneficial effects e.g. pain and pruritus.</p>