Tomonobu Koizumi, Yuji Saita, Akira Miyake, Akito Nishida, Hidenori Yazawa and Kazuo Honda
Institute for Drug Discovery Research, Yamanouchi Pharmaceutical Co., Ltd., 21 Miyukigaoka, Tsukuba, Ibaraki 305, Japan
Abstract: We recently isolated a cDNA clone for the human cholecystokinin (CCK)B/gastrin receptor and permanently expressed this receptor cDNA in NIH-3T3 cells. [125I]CCK-8 specifically bound to the membrane of the transfectant, and this binding was displaced by unlabeled CCK-8 with an IC50 of 0.32 nM. Treatment of these cells with CCK-8 increased the intracellular Ca2+ concentration with an EC50 of 0.30 nM. Using these cells expressing functional human CCKB/gastrin receptors, we investigated the pharmacological properties of (R)-1-[2,3-dihydro-1-(2'-methylphenacyl)-2-oxo-5-phenyl-1H-1,4-benzodiazepin- 3-yl]-3-(3-methylphenyl) urea (YM022), a potent and selective CCKB/gastrin receptor antagonist in rats. YM022 potently inhibited [125I]CCK-8 binding to the membrane with an IC50 of 55 pM and CCK-8-induced Ca2+ mobilization with that of 7.4 nM. On the other hand, its racemate and enantiomer more weakly inhibited this binding (IC50 of 110 pM and 11 nM, respectively) and Ca2+ mobilization (IC50 of 18 nM and 94 nM, respectively). These results indicate that YM022 stereoselectively recognizes the human CCKB/gastrin receptor as a potent antagonist and that the established transfectant is useful for characterization of human CCKB/gastrin-receptor ligands.
YM022, Cholecystokinin (CCK)-8, CCKB/gastrin receptor, Calcium mobilization,
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