Synthesis and binding characteristics of [3H] H-Tyr-Ticpsi[CH2-NH] Cha-Phe-OH, a highly specific and stable delta-opioid antagonist.
Substitution of the Phe3 aromatic ring in H-Tyr-Ticpsi[CH2-NH]Phe-Phe-OH with cyclohexylalanine (Cha) has been reported to result in a compound, H-Tyr-Ticpsi[CH2-NH]Cha-Phe-OH (TICP[psi]), showing substantially increased delta-opioid antagonist potency and high delta selectivity. TICP[psi] was radiolabeled by catalytic tritiation of its precursor Tyr(3',5'-I2)1TICP[psi]. Binding characteristics of the new tritiated pseudopeptide were determined using the radioligand binding assay in rat brain membranes. On the basis of the results of saturation binding studies performed at 25 degrees C, an equilibrium dissociation constant (Kd) of 0.35 nM and a receptor density (Bmax) of 112 fmol/mg protein were calculated. This new tritiated ligand exhibits high affinity for delta-opioid receptors, whereas its binding to mu and kappa receptors is weak. A study of [H3]TICP[psi] binding displacement by various receptor-selective opioids showed the following rank order of potency: delta > kappa = mu. These receptor binding characteristics of the ligand, together with its high specific radioactivity (41.3 Ci/mmol) and stability, makes it a useful tool for labeling delta-opioid receptors, both in vitro and in vivo.
Szatmári
I
I
Institute of Biochemistry, Biological Research Center, Hungarian Academy of Sciences, Szeged.
Tóth
G
G
Kertész
I
I
Schiller
P W
PW
Borsodi
A
A
D000818:Animals; D001921:Brain / Q000378:metabolism; D007700:Kinetics; D009842:Oligopeptides / Q000138:chemical synthesis* / Q000378:metabolism* / Q000494:pharmacology; D011869:Radioligand Assay; D051381:Rats; D017465:Receptors, Opioid, delta / Q000037:antagonists & inhibitors* / Q000378:metabolism; D044005:Tetrahydroisoquinolines; D014316:Tritium
D009842:Oligopeptides; D017465:Receptors, Opioid, delta; D044005:Tetrahydroisoquinolines; C400216:tyrosyl-1,2,3,4-tetrahydro--3--isoquinolinecarbonyl-psi(CH2-NH)-cyclohexylalanyl-phenylalanine; D014316:Tritium