SR146131: A new potent, orally active, and selective nonpeptide cholecystokinin subtype 1 receptor agonist. I: In vitro studies

SR146131 inhibited the binding of [I-125]-Bolton Hunter (BH)sulfated cholec ystokinin octapeptide (CCK-8S) for the human recombinant cholecystokinin su btype 1 (CCK1) receptor (IC50 = 0.56 nM) with high (300-fold) selectivity t o the CCK2 receptor. The biological activity of SR146131 was characterized in vitro in a NIH-3T3 cell line expressing the human recombinant CCK1 recep tor (3T3-hCCK(1)). Measuring intracellular calcium release, SR146131 behave d as a full agonist with an efficacy comparable with that of CCK-8S (EC50 = 1.38 +/- 0.06 nM). On individual cells, SR146131 induced, like CCK-8S, Ca2 + oscillations at subnanomolar concentrations and sustained responses at hi gher concentrations. Like CCK-8S, SR146131 also fully stimulated inositol m onophosphate formation (EC50 = 18 +/- 4 nM). SR146131 partially activated m itogen-activated protein kinase and enhanced the expression of the immediat e early gene krox 24. In the human CHP212 and IMR32 neuroblastoma cell line s, which constitutively express the CCK, receptor, SR146131 behaved as a pa rtial agonist on intracellular calcium release and inositol monophosphate f ormation. All of these effects of SR146131 were inhibited by the CCK, recep tor antagonists SR27897B and devazepide, suggesting that the effects of SR1 46131 were entirely mediated by the CCK, receptor. In contrast, high concen trations (>1 mu M) of SR146131 had only minimal effects on CCK-8S-stimulate d and unstimulated Chinese hamster ovary (CHO) cells expressing the human C CK2 receptor, indicating that SR146131 is functionally inactive on the CCK2 receptor. In conclusion, these in vitro experiments show that SR146131 is a highly potent and selective agonist of the CCK1 receptor.