DiPOA ([8-(3,3-Diphenyl-propyl)-4-oxo-1-phenyl-1,3,8-triaza- spiro[4.5]dec-3-yl]-acetic Acid), a Novel, Systemically Available, and Peripherally Restricted Mu Opioid Agonist with Antihyperalgesic Activity: I. In Vitro Pharmacological Characterization and Pharmacokinetic Properties Kenneth J. Valenzano, Wendy Miller, Zhengming Chen, Shen Shan, Gregg Crumley, Sam F. Victory, Ellen Davies, Jin-Cheng Huang, Nezima Allie, Scott J. Nolan, Yakov Rotshteyn, Donald J. Kyle, and Kevin Brogle ´ Departments of Molecular Pharmacology (K.J.V., W.M., S.S., G.C.) and Computational, Combinatorial, and Medicinal Chemistry (Z.C., S.F.V., E.D., J.-C.H., D.J.K., K.B.), Purdue Pharma Discovery Research, Cranbury, New Jersey; and Discovery Support, Purdue Pharma, Ardsley, New York (N.A., S.J.N., Y.R.) Received December 15, 2003; accepted March 29, 2004 ABSTRACT Mu opioid receptors are present throughout the central and peripheral nervous systems. Peripheral inflammation causes an increase in mu receptor levels on peripheral terminals of pri- mary afferent neurons. Recent studies indicate that activation of peripheral mu receptors produces antihyperalgesic effects in animals and humans. Here, we describe the in vitro pharmaco- logical and in vivo pharmacokinetic properties of a novel, highly potent, and peripherally restricted mu opioid agonist, [8-(3,3- diphenyl-propyl)-4-oxo-1-phenyl-1,3,8-triaza-spiro[4.5]dec-3- yl]-acetic acid (DiPOA). In a radioligand binding assay, DiPOA inhibited [ 3 H]-diprenorphine binding to recombinant human mu receptors with a K i value of 0.8 nM. The rank order of affinity for DiPOA binding to recombinant human opioid receptors was mu  kappa  ORL-1  delta. DiPOA showed potent agonist effects in a human mu receptor guanosine 5'-O-(3-[ 35 S]thio)- triphosphate functional assay, with an EC 50 value of 33 nM and efficacy of 85% {normalized to the mu agonist, [D-Ala2,MePhe4,Gly(ol)5]enkephalin}. Low potency agonist ac- tivity was also seen at ORL-1 and kappa receptors. DiPOA bound competitively to the opioid binding site of human mu receptors as demonstrated by a parallel rightward shift in its concentration-response curve in the presence of increasing concentrations of naltrexone. High and sustained (5 h) plasma levels for DiPOA were achieved following intraperito- neal administration at 3 and 10 mg/kg; central nervous system penetration, however, was 4% of the plasma concentration, even at levels exceeding 1500 ng/ml. As such, DiPOA repre- sents a systemically available, peripherally restricted small mol- ecule mu opioid agonist that will aid in understanding the role played by mu opioid receptors in the periphery. Opioid receptors belong to the superfamily of G-protein- coupled receptors. To date, four members have been cloned and characterized: the mu, kappa, delta, and opioid receptor- like 1 (ORL-1) receptors (for review, see Pleuvry, 2003). All signal through activation of pertussis toxin-sensitive G pro- teins to mediate inhibition of adenylate cyclase (Herz, 1993). In addition, receptor activation results in suppression of volt- age-gated calcium currents and the opening of receptor-op- erated potassium channels (Duggan and North, 1983). En- dogenous peptidic ligands have been identified for the opioid receptors and divided into four major classes: the enkepha- lins, dynorphins, endorphins, and nociceptin (for review, see Terenius, 2000). Both the opioid receptors and ligands are widely distributed in the central nervous system (CNS) and peripheral nervous system as well as in peripheral tissues. It is well established that the centrally mediated analgesic effects of opioids are due to inhibition of ascending excitatory transmission of nociceptive information from the spinal cord dorsal horn and activation of descending inhibitory pain con- trol circuits from the midbrain to the spinal cord (Fields and Article, publication date, and citation information can be found at http://jpet.aspetjournals.org. DOI: 10.1124/jpet.103.063313. ABBREVIATIONS: ORL-1, opioid receptor-like 1; CNS, central nervous system; DiPOA, [8-(3,3-diphenyl-propyl)-4-oxo-1-phenyl-1,3,8-triaza- spiro[4.5]dec-3-yl]-acetic acid; DAMGO, [D-Ala 2 ,MePhe 4 ,Gly(ol) 5 ]enkephalin; GTP[ 35 S], guanosine 5'-O-(3-[ 35 S]thio)triphosphate; HEK-293, human embryonic kidney-293; DMSO, dimethylsulfoxide; P-gp, P-glycoprotein. 0022-3565/04/3102-783–792$20.00 THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Vol. 310, No. 2 Copyright © 2004 by The American Society for Pharmacology and Experimental Therapeutics 63313/1157695 JPET 310:783–792, 2004 Printed in U.S.A. 783 at ASPET Journals on October 27, 2016 jpet.aspetjournals.org Downloaded from