Receptor binding profiles of KB-5492, a novel anti-ulcer agent, at σ receptors in guinea-pig brain

Abstract

We studied the receptor binding profile of 4-methoxyphenyl 4-(3,4,5-trimethoxybenzyl)-1-piperazine acetate monofumarate monohydrate (KB-5492), a novel anti-ulcer agent, for the σ receptor in guinea-pig brain membranes. KB-5492 selectively inhibited specific [ 3H]1,3-di(2-tolyl)guanidine (DTG) binding to the σ receptor ( IC 50 = 3.15 μ M ) with a pseudo-Hill coefficient of 0.3. Computer-assisted analysis revealed that KB-5492 bound to high- and low-affinity sites. Although KB-5492 had weak affinity for α 2- adrenoceptors at 10 μM, it was almost inactive at a concentration of 10 μM in 33 other binding assays for receptors, second messenger system and ion channels. σ Receptor ligands such as haloperidol, DTG, (+)-3-(3-hydroxyphenol)- N-(1-propyl)piperidine (3-PPP), rimcazole and (−)-3-PPP inhibited specific [ 3H]DTG binding and their IC 50 values were 0.003, 0.044, 0.33, 0.67 and 1.03 μM, respectively. On the other hand, various anti-ulcer agents such as cetraxate, cimetidine, omeprazole, sofalcone, sucralfate, teprenone and troxipide could hardly displace specific [ 3H]DTG binding at 100 μM. Scatchard-Rosenthal analysis indicated that [ 3H]DTG bound to a single site, and K D and B max values for [ 3H]DTG were 87 .3 nM and 679.3 fmol/mg protein, respectively. KB-5492 significantly decreased the B max value, but did not affect the K D value . In contrast, haloperidol and DTG significantly increased the K D values, but did not affect the B max values. These findings indicate that KB-5492 selectively bound to the [ 3H]DTG-labeled σ receptor and that other anti-ulcer agents had little affinity for the σ receptor. Furthermore, KB-5492 inhibited specific [ 3H]DTG binding in a non-competitive manner.