Assessment of the activity of a novel nociceptin/orphanin FQ analogue at recombinant human nociceptin/orphanin FQ receptors expressed in Chinese hamster ovary cells

Abstract

The neuropeptide nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand for the nociceptin receptor (NOP). In an attempt to identify high potency NOP agonists for use in the brain we have compared the activity of a novel N/OFQ analogue [Phe1Ψ(CH2-O)Gly2]N/OFQ(1-13)NH 2 ([F/G-O]) with the existing [Phe1Ψ(CH2-NH)Gly2]N/OFQ(1-13)NH 2 ([F/G]). Both peptides are modified between the first two N-terminal amino acids and are further compared with the agonist template N/OFQ(1-13)NH2 in [3H]N/OFQ binding, GTPγ[35S] binding and cAMP inhibition studies using Chinese hamster ovary cells expressing the recombinant human NOP. All peptides displaced [3H]N/OFQ, stimulated GTPγ[35S] binding and inhibited cAMP formation. In [3H]N/OFQ binding and GTPγ[35S] binding the rank order affinity and potency was N/OFQ(1-13)NH2>[F/G-O]>[F/G]. In GTPγ[35S] binding [F/G] was a clear partial agonist with intrinsic activity (Emax stimulation factor, mean±SEM, n=4) of 7.75±1.02 compared with N/OFQ(1-13)NH2 of 11.13±1.76. The efficacy of [F/G-O] (10.17±1.88) approached that of the full agonist N/OFQ(1-13)NH2. Downstream, at the level of cAMP formation, all peptides were full agonists with the following rank order potency: N/OFQ(1-13)NH2>[F/G-O]=[F/G]. The enhanced potency and intrinsic activity of the novel [F/G-O] modification makes this an interesting peptide for further in vivo analysis. © 2003 Elsevier Science Ireland Ltd. All rights reserved.