Synthesis and pharmacological characterization of a novel, highly potent, peptidomimetic delta-opioid radioantagonist, [3H]Tyr-Tic-(2S,3R)-beta-MePhe-Phe-OH.
[(3)H]Tyr-Tic-(2S,3R)-beta-MePhe-Phe-OH (where Tic: 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid) with a specific radioactivity of 53.7 Ci/mmol was synthesized and characterized in receptor binding assays at 25 degrees C in rat brain membranes. The specific binding was saturable and displayed high affinity, with a K(D) of 0.16+/-0.005 nM and B(max) of 85.9+/-6.3 fmol/mg protein. NaCl increased its affinity by about 4-fold in membranes of rat brain and Chinese Hamster Ovary Cells stably transfected with the human delta-opioid receptors (hDOR-CHO) showing that the new ligand is an antagonist. The prototypic delta-opioid ligands were much more potent than mu- or kappa-specific ligands in competition assays. The autoradiographic distribution of the binding sites of the new ligand agreed with the known locations of the delta-opioid receptors in rat brain. The unlabeled new ligand was about 7-fold more potent than the parent peptide in competing for the binding sites of [(3)H]Tyr-Tic-(2S,3R)-beta-MePhe-Phe-OH in rat brain membranes. Likewise, the threo-beta-methyl analog was 3.8-fold more potent than the parent compound in antagonizing the effect of DPDPE in the [(35)S]GTPgammaS functional assay in hDOR-CHO membranes. The new, highly potent, conformationally constrained antagonist may be a valuable pharmacological tool in understanding the structural and topographical requirements of peptide ligand binding to the delta-opioid receptors.
Birkas
Erika
E
Institute of Biochemistry, Biological Research Center, Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged, Hungary.
Kertesz
Istvan
I
Toth
Geza
G
Bakota
Lidia
L
Gulya
Karoly
K
Szucs
Maria
M
D000701:Analgesics, Opioid / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000818:Animals; D001345:Autoradiography; D001665:Binding Sites; D001923:Brain Chemistry / Q000187:drug effects; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000037:antagonists & inhibitors / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006801:Humans; D008297:Male; D009842:Oligopeptides / Q000138:chemical synthesis* / Q000494:pharmacology*; D011869:Radioligand Assay; D019275:Radiopharmaceuticals / Q000138:chemical synthesis* / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D017465:Receptors, Opioid, delta / Q000037:antagonists & inhibitors*
C528325:(3H)Tyr-Tic-(2S,3R)-beta-MePhe-Phe-OH; D000701:Analgesics, Opioid; D009842:Oligopeptides; D019275:Radiopharmaceuticals; D017465:Receptors, Opioid, delta; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D020881:Enkephalin, D-Penicillamine (2,5)-