Nociceptin antagonism: probing the receptor by N-acetyl oligopeptides.
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.
Kocsis
László
L
Research Group for Peptide Chemistry, Hungarian Academy of Sciences and Department of Organic Chemistry, Eötvös University, P.O. Box 32, Budapest H-1518, Hungary.
Orosz
György
G
Magyar
Anna
A
Al-Khrasani
Mahmoud
M
Kató
Erzsébet
E
Rónai
Andás Z
AZ
Bes
Brice
B
Meunier
Jean-Claude
JC
Gündüz
Ozge
O
Tóth
Géza
G
Borsodi
Anna
A
Benyhe
Sándor
S
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
D009292:Narcotic Antagonists; D009842:Oligopeptides; D011957:Receptors, Opioid; D000094942:Nociceptin Receptor