title: N-cyclobutylmethyl analog of normorphinone, N-CBM-TAMO: a short-term opioid agonist and long-term Mu-selective irreversible opioid antagonist.
abstract: The antinociceptive and opioid binding properties of the N-cyclobutylmethyl analog of normorphinone, 14 alpha, 14' beta-[dithiobis[(2-oxo-2, 1-ethanediyl)imino]]bis[7,8-dihydro-N-(cyclobutylmethyl)-normor phinone] (N-CBM-TAMO) were investigated. This compound is a dimer, containing a disulfide capable of binding to thiol groups on the opioid receptor. Competition radioligand binding assays with bovine striatal membranes demonstrated that N-CBM-TAMO displayed a higher affinity for mu opioid receptors than for kappa and delta receptors. Incubation of membranes with N-CBM-TAMO resulted in wash-resistant inhibition of the binding of the mu-selective peptide [3H][D-Ala2,(Me)Phe4, Gly(ol)5]-enkephalin, the kappa-selective opioid [3H]U69,593 ((trans)-3, 4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]benzenacetamide+ ++ methanesulfonate hydrate)) and, to a lesser extent, the delta-selective peptide [D-Pen2, p-Cl-phenylalanine4, D-Pen5]enkephalin. Scatchard analysis of saturation binding data showed that N-CBM-TAMO decreased the Bmax value without affecting the Kd value for [3H][D-Ala2,(Me)Phe4, Gly(ol)5]enkephalin binding, whereas, N-CBM-TAMO increased the Kd value without altering the Bmax value for [3H]U69,593, which suggests that N-CBM-TAMO interacted covalently with the mu but not the kappa receptor. In the mouse 55 degrees C warm-water tail-flick test, N-CBM-TAMO given supraspinally acted as an agonist with low efficacy because only submaximal antinociception was observed at doses up to 100 nmol. The antinociception induced by N-CBM-TAMO in the tail-flick test was partially blocked by both the mu-selective antagonist beta-funaltrexamine and the kappa-selective antagonist nor-binaltorphimine. In the mouse acetic acid writhing test, N-CBM-TAMO acted as a full agonist with a D50 value of 0.08 (0.04-0.14) nmol, and the antinociception was blocked by coadministration of the kappa-selective antagonist nor-binaltorphimine. Pretreatment of mice with an i.c.v. dose of N-CBM-TAMO of 10 nmol, a dose that exhibited modest short-term antinociception in the tail-flick test, produced a time- and dose-dependent long-term antagonism of morphine-induced antinociception in an irreversible manner in this assay. Pretreatment of mice with i.c.v. N-CBM-TAMO at doses of 3 nmol and higher, which produced supermaximal short-term antinociception in the writhing test, produced a time- and dose-dependent long-term antagonism of U50,488 (trans)-3, 4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]benzeneacetamide methanesulfonate hydrate)-induced antinociception in a reversible manner, probably because of the development of tolerance. These in vivo data, together with the in vitro binding data, demonstrate that N-CBM-TAMO is a potent kappa agonist and at higher doses produces antinociception mediated by mu receptors. N-CBM-TAMO also produces long-term noncompetitive antagonism of antinociception mediated by mu opioid receptors.
authors.affiliation: Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, New York, USA.
authors.forename: J Y
authors.initials: JY
authors.lastname: Xu
authors.forename: A
authors.initials: A
authors.lastname: Seyed-Mozaffari
authors.forename: S
authors.initials: S
authors.lastname: Archer
authors.forename: J M
authors.initials: JM
authors.lastname: Bidlack
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D044482:Benzeneacetamides; D002417:Cattle; D004305:Dose-Response Relationship, Drug; D004091:Hydromorphone / Q000031:analogs & derivatives* / Q000494:pharmacology; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009020:Morphine / Q000037:antagonists & inhibitors; D009292:Narcotic Antagonists / Q000494:pharmacology*; D009293:Opioid-Related Disorders / Q000188:drug therapy; D011759:Pyrrolidines / Q000494:pharmacology; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors*
chemical_list: C102303:14,14'-(dithio-bis((2-oxo-2,1-ethanediyl)imino))bis(7,8-dihydro-N-(cyclobutylmethyl)normophinone); D000701:Analgesics, Opioid; D044482:Benzeneacetamides; D009292:Narcotic Antagonists; D011759:Pyrrolidines; D017450:Receptors, Opioid, mu; D009020:Morphine; C045444:U 69593; D004091:Hydromorphone