Abstract

The compound SB-612111 [(–)-cis-1-methyl-7-[[4-(2,6-dichlorophenyl)piperidin-1-yl]methyl]-6,7,8,9-tetrahydro-5H-benzocyclohepten-5-ol] was recently identified as a selective antagonist for the nociceptin/orphanin FQ (N/OFQ) peptide receptor (NOP). In the present study, the in vitro pharmacological profile of SB-612111 at human recombinant NOP receptors expressed in Chinese hamster ovary (CHO) cells [receptor binding, guanosine 5′-O-(3-[³⁵S]thio)triphosphate (GTPγ[³⁵S]) binding, and cAMP level experiments] as well as at native NOP receptors expressed in peripheral (mouse and rat vas deferens, guinea pig ileum) and central (mouse cerebral cortex synaptosomes releasing [³H]5-HT) preparations was evaluated and compared with that of the standard nonpeptide antagonist (±)J-113397 [(±)-trans-1-[1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one]. SB-612111 produced a concentration-dependent displacement of [³H]N/OFQ binding to CHO_hNOP cell membranes, showing higher affinity and NOP selectivity over classical opioid receptors than (±)J-113397. SB-612111 and (±)J-113397 competitively antagonized the effects of N/OFQ on GTPγ[³⁵S] binding in CHO_hNOP cell membranes (pK_B, 9.70 and 8.71, respectively) and on cAMP accumulation in CHO_hNOP cells (pK_B, 8.63 and 7.95, respectively), being per se inactive. In isolated peripheral tissues of mice, rats, and guinea pigs and in mouse cerebral cortex synaptosomes preloaded with [³H]5-HT, SB-612111 competitively antagonized the inhibitory effects of N/OFQ, with pA₂ values in the range of 8.20 to 8.50. In parallel experiments, (±)J-113397 was found to be 2- to 9-fold less potent than SB-612111. In the electrically stimulated tissues, 1 μM SB-612111 did not modify the effects of classical opioid receptor agonists. In conclusion, the results of the present study demonstrated that SB-612111 is among the most potent and NOP-selective nonpeptide antagonists identified to date.