UFP-101, a high affinity antagonist for the nociceptin/orphanin FQ receptor: radioligand and GTPgamma(35)S binding studies.
Studies of the pharmacology of nociceptin/orphanin FQ (N/OFQ) and its receptor (NOP) have been hampered by the lack of a range of high potency antagonists. In this study we have examined the effects of a novel N/OFQ analogue [Nphe(1),Arg(14),Lys(15)]N/OFQ NH(2) hereafter referred to as UFP-101. [(3)H]N/OFQ competition binding and GTPgamma(35)S binding assays were performed using CHO cells expressing the human NOP receptor (CHO(hNOP)). UFP-101 (pK(i) of 10.14+/-0.09) and a range of NOP selective agonists displaced [(3)H]N/OFQ binding with the following rank order of affinity: [Arg(14),Lys(15)]N/OFQ>[( pF)Phe(4)]N/OFQ(1-13)NH(2)>N/OFQ(1-13)NH(2)>UFP-101>N/OFQ>Ro64-6198>[Nphe(1)]N/OFQ(1-13)NH(2). N/OFQ, N/OFQ(1-13)NH(2), [( pF)Phe(4)]N/OFQ(1-13)NH(2), [Arg(14),Lys(15)]N/OFQ and Ro64-6198 also produced a concentration dependent (pEC(50) values of 8.75+/-0.11, 9.28+/-0.15, 9.69+/-0.04, 9.12+/-0.11 and 8.09+/-0.07 respectively) and saturable stimulation of GTPgamma(35)S binding and all were full agonists. UFP-101 did not stimulate GTPgamma(35)S binding per se, but produced a concentration dependent and parallel rightward shift in the concentration response curves to all agonists. UFP-101 yielded pA(2) values in the range 8.4-9.0. For comparison a pA(2) for [Nphe(1)]N/OFQ(1-13)NH(2) (the template for UFP-101) against N/OFQ of 7.33+/-0.08 was obtained. Slope factors for the Schild regression lines were approximately 1 indicating competitivity. When UFP-101 is compared with its template molecule [Nphe(1)]N/OFQ(1-13)NH(2), Arg(14),Lys(15) substitution produced approximately 1 log greater potency. We suggest that due to its high potency UFP-101 should prove a further useful tool in the evaluation of the N/OFQ-NOP receptor system.
McDonald
J
J
University Department of Anaesthesia, Critical Care and Pain Management, Leicester Royal Infirmary, LE1 5WW, Leicester, UK.
Calo
G
G
Guerrini
R
R
Lambert
D G
DG
D000818:Animals; D001667:Binding, Competitive; D016466:CHO Cells; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism*; D006801:Humans; D009292:Narcotic Antagonists; D018847:Opioid Peptides / Q000008:administration & dosage / Q000494:pharmacology*; D011869:Radioligand Assay; D011957:Receptors, Opioid / Q000819:agonists; D011994:Recombinant Proteins / Q000819:agonists / Q000037:antagonists & inhibitors; D013329:Structure-Activity Relationship; D000094942:Nociceptin Receptor
C479838:(Nphe(1),Arg(14),Lys(15))N-OFQ NH(2); D009292:Narcotic Antagonists; D018847:Opioid Peptides; D011957:Receptors, Opioid; D011994:Recombinant Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000094942:Nociceptin Receptor