Pharmacodynamic Characterization of ZP120 (Ac-RYYRWKKKKKKK-NH 2 ), a Novel, Functionally Selective Nociceptin/Orphanin FQ Peptide Receptor Partial Agonist with Sodium-Potassium-Sparing Aquaretic Activity Daniel R. Kapusta, Christian Thorkildsen, Velga A. Kenigs, Eddi Meier, Mette M. Vinge, Charlotte Quist, and Jørgen Søberg Petersen Department of Pharmacology and Experimental Therapeutics, Louisiana State University Health Sciences Center, New Orleans, Louisiana (D.R.K., V.A.K.); and Zealand Pharma A/S, Glostrup, Denmark (C.T., E.M., M.M.V., C.Q., J.S.P.) Received January 10, 2005; accepted April 18, 2005 ABSTRACT In conscious rats, intravenous (i.v.) administration of the hexapeptide Ac-RYYRWK-NH 2 , a partial agonist of the noci- ceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor, produces a selective water diuresis without marked cardiovascular or behavioral effects. The present study examined the in vitro and in vivo pharmacodynamic profile of the novel and potentially metabolically stable NOP receptor ligand ZP120 (Ac-RYYR- WKKKKKKK-NH 2 ), which was created by conjugation of a structure-inducing probe (SIP) (i.e., K 6 sequence) to Ac- RYYRWK-NH 2 . In cells transfected with human NOP receptors, both Ac-RYYRWK-NH 2 and ZP120 displaced [ 3 H]N/OFQ (both peptides, pK i = 9.6), and similar to N/OFQ inhibited forskolin- induced cAMP formation (Ac-RYYRWK-NH 2 , pEC 50 = 9.2; ZP120, 9.3; N/OFQ, 9.7). In the mouse vas deferens assay (MVD), Ac-RYYRWK-NH 2 and ZP120 behaved as partial ago- nists, inhibiting electrically induced contractions with similar pEC 50 values (9.0 and 8.6, respectively) but with submaximal efficacy compared with N/OFQ. In MVD, both peptides blocked the responses to N/OFQ, with ZP120 being approximately 50-fold more potent than Ac-RYYRWK-NH 2 . In vivo, dose- response studies in rats showed that at doses (i.v. bolus or i.v. infusion) that produced a sodium-potassium-sparing aquare- sis, ZP120 and Ac-RYYRWK-NH 2 elicited a mild vasodilatory response without reflex tachycardia. However, the renal re- sponses to ZP120 were of greater magnitude and duration. Finally, each peptide blocked the bradycardia and hypotension to N/OFQ in conscious rats, but the effect of ZP120 was of much greater duration. Together, these findings demonstrate that ZP120 is a novel, functionally selective SIP-modified NOP receptor partial agonist with increased biological activity and sodium-potassium-sparing aquaretic activity, the actions of which may be useful in the management of hyponatremia/ hypokalemia in water-retaining states. Nociceptin/orphanin FQ (N/OFQ) is an endogenous opioid- like peptide that was first identified in porcine and rat cen- tral nervous system tissue (Meunier et al., 1995; Reinscheid et al., 1995). N/OFQ binds selectively to and is the endoge- nous ligand for the N/OFQ peptide (NOP) receptor (previ- ously known as opioid receptor-like 1) (Mollereau et al., 1994; Lachowicz et al., 1995; Meunier et al., 1995; Reinscheid et al., 1995; Cox et al., 2000). Although many studies have focused on the effects of N/OFQ in the CNS, this peptide also pro- duces important physiological responses when administered into the periphery. In particular, N/OFQ exerts prominent effects on the neural and humoral mechanisms that control arterial blood pressure and fluid and electrolyte balance. Thus, N/OFQ relaxes vascular smooth muscle (Gumusel et al., 1997; Armstead, 1999; Champion et al., 1999) and when administered as an intravenous (i.v.) bolus to anesthetized (Champion and Kadowitz, 1997; Bigoni et al., 1999) or con- scious (Giuliani et al., 1997; Madeddu et al., 1999; Kapusta, This work was supported by funds provided by Zealand Pharma A/S; Na- tional Institutes of Health Grants DK43337, DK02605, and HL71212; and American Heart Association, Southeastern Affiliate Grant 0255314B (to D.R.K.). We note that funds made available to D.R.K. from the American Heart Association Grant 0255314B were entirely provided to the American Heart Association by a gracious donation from Herbert H. McElveen (DeRidder, LA). Article, publication date, and citation information can be found at http://jpet.aspetjournals.org. doi:10.1124/jpet.105.083436. ABBREVIATIONS: N/OFQ, nociceptin/orphanin FQ; NOP, nociceptin/orphanin FQ peptide; CNS, central nervous system; SIP, structure-inducing probe; ZP120, Ac-RYYRWKKKKKKK-NH 2 ; hNOP, human nociceptin/orphanin FQ peptide receptor; MVD, mouse vas deferens; HEK, human embryonic kidney; ANOVA, analysis of variance; CompB, 1-[()-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-ben- zimidazol-2-one; Ro64-6198, (1S,3aS)-8-(2,3,3a,4,5,6-hexahydro-1H-phenalen-1-yl)-1-phenyl-1,3,8-triazaspiro[4.5]decan-4-one. 0022-3565/05/3142-652–660$20.00 THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Vol. 314, No. 2 Copyright © 2005 by The American Society for Pharmacology and Experimental Therapeutics 83436/3039840 JPET 314:652–660, 2005 Printed in U.S.A. 652 at ASPET Journals on March 6, 2016 jpet.aspetjournals.org Downloaded from