In vitro functional characterization of novel nociceptin/orphanin FQ receptor agonists in recombinant and native preparations

Nociceptin/Orphanin FQ (N/OFQ) regulates several biological functions via selective activation of the N/OFQ receptor (NOP). In this study novel nonpeptide NOP ligands were characterized in vitro in receptor binding and [(35)S]GTPγS stimulated binding in membranes of cells expressing human NOP and classical opioid receptors, calcium mobilization assay in cells coexpressing the receptors and chimeric G proteins, bioluminescence resonance energy transfer (BRET) based assay for studying NOP receptor interaction with G protein and arrestin, the electrically stimulated mouse vas deferens and the mouse colon bioassays. The action of the AT compounds were compared with standard NOP agonists (N/OFQ and Ro 65-6570) and the NOP selective antagonist SB-612111. AT compounds displayed high NOP affinity and behaved as NOP agonists in all the functional assays consistently showing the following rank order of potency AT-127≥AT-090≥AT-035>AT-004= AT-001. AT compounds behaved as NOP full agonists in the calcium mobilization and mouse colon assays and as partial agonists in the [(35)S]GTPγS and BRET assays. Interestingly AT-090 and AT-127, contrary to standard nonpeptide agonists that display G protein biased agonism, behaved as an unbiased agonists. AT-090 and AT-127 displayed higher NOP selectivity than Ro 65-6570 at native mouse receptors. AT-090 and AT-127 might be useful pharmacological tools for investigating the therapeutic potential of NOP partial agonists.