title: Nociceptin antagonism: probing the receptor by N-acetyl oligopeptides.
abstract: In search for effective antagonist structures for the nociceptin (NOP) receptor, a number of N-acylated oligopeptides, including N-acyl tetra- and pentapeptides selective for the kappa-opioid receptor, as well as N-acyl hexapeptides bearing the Ac-Arg-Tyr-Tyr-Arg-Ile-Lys (Ac-RYYRIK) core sequence originally isolated from combinatorial chemical libraries, were synthesized and studied in radioreceptor binding assays, [(35)S]GTPgammaS functional tests and in mouse vas deferens (MVD) bioassays. The properties of the novel antagonist candidates were compared to known antagonists. A new antagonist structure with a reduced, primer alcohol C-terminus, Ac-Arg-Tyr-Tyr-Arg-Ile-lysinol (Ac-RYYRIK-ol) was described in the mouse vas deferens tests, showing an equilibrium inhibitory constant value (K(e)) of 2.44 nM, and no agonist effect at 10 microM ligand concentration. Schild-analysis indicated a clearly competitive interaction at the NOP receptor, whereas the peptide did not affect the action of the delta-opioid receptor agonist [D-Ala(2),D-Leu(5)]enkephalin. Ac-RYYRIK-ol also exhibited a high affinity in [(3)H]nociceptin-NH(2) binding competition assays using rat brain membranes. Agonist-induced G-protein activation via NOP receptors was studied in [(35)S]GTPgammaS binding stimulation assays by the use of both native brain tissue preparations and membranes from cultured CHO cells expressing recombinant nociceptin receptors. Ac-RYYRIK-ol displayed only weak intrinsic agonist activity, whereas it effectively inhibited the stimulation generated by nociceptin. The results support the high potency and antagonist nature of Ac-RYYRIK-ol and reveal important roles for both the N- and the C-terminal region of the molecule.
authors.affiliation: Research Group for Peptide Chemistry, Hungarian Academy of Sciences and Department of Organic Chemistry, Eötvös University, P.O. Box 32, Budapest H-1518, Hungary.
authors.forename: László
authors.initials: L
authors.lastname: Kocsis
authors.forename: György
authors.initials: G
authors.lastname: Orosz
authors.forename: Anna
authors.initials: A
authors.lastname: Magyar
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Al-Khrasani
authors.forename: Erzsébet
authors.initials: E
authors.lastname: Kató
authors.forename: Andás Z
authors.initials: AZ
authors.lastname: Rónai
authors.forename: Brice
authors.initials: B
authors.lastname: Bes
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Meunier
authors.forename: Ozge
authors.initials: O
authors.lastname: Gündüz
authors.forename: Géza
authors.initials: G
authors.lastname: Tóth
authors.forename: Anna
authors.initials: A
authors.lastname: Borsodi
authors.forename: Sándor
authors.initials: S
authors.lastname: Benyhe
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D051379:Mice; D009292:Narcotic Antagonists; D009842:Oligopeptides / Q000737:chemistry / Q000494:pharmacology*; D011869:Radioligand Assay; D051381:Rats; D011957:Receptors, Opioid; D015398:Signal Transduction / Q000187:drug effects; D000094942:Nociceptin Receptor
chemical_list: D009292:Narcotic Antagonists; D009842:Oligopeptides; D011957:Receptors, Opioid; D000094942:Nociceptin Receptor