SR146131: a new potent, orally active, and selective nonpeptide cholecystokinin subtype 1 receptor agonist. II. In vivo pharmacological characterization.

SR146131 is a potent and selective agonist at cholecystokinin subtype 1 (CCK1) receptors in vitro. The present study evaluates the activity of the compound in vivo. SR146131 completely inhibited gastric and gallbladder emptying in mice (ED50 of 66 and 2.7 micrograms/kg p.o., respectively). SR146131 dose dependently reduced food intake in fasted rats (from 0.1 mg/kg p.o.), in nonfasted rats in which food intake had been highly stimulated by the administration of neuropeptide Y (1-36) (from 0.3 mg/kg p.o.), in fasted gerbils (from 0.1 mg/kg p.o.), and in marmosets maintained on a restricted diet (from 3 mg/kg p.o.). SR146131 (10 mg/kg p.o.) also increased the number of Fos-positive cells in the hypothalamic paraventricular nucleus of rats. Locomotor activity of mice was reduced by orally administered SR146131 (from 0.3 mg/kg p.o.). When administered intrastriatally, SR146131 elicited contralateral turning behavior in mice. Furthermore, orally administered SR146131 (0.3-10 mg/kg), also reduced the levels of cerebellar cyclic GMP. Finally, SR146131 (0.1 microgram/kg to 1 mg/kg, p.o.) significantly and dose dependently antagonized fluphenazine-induced mouth movements in rats. The CCK1 antagonist SR27897B prevented all the effects of SR146131. Conversely, SR146131 was unable to elicit any agonist or antagonist effects in a model of CCK2 receptor stimulation in vivo. SR146131 is a very potent and selective nonpeptide CCK1 agonist in vivo. SR146131 is more potent than any other CCK1 agonists reported to date. Because pharmacodynamic studies suggest that SR146131 should have a high absolute bioavailability, it may be a promising drug for the treatment of eating and motor disorders in humans.

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

SR146131 inhibited the binding of [125I]-Bolton Hunter (BH)-sulfated cholecystokinin octapeptide (CCK-8S) for the human recombinant cholecystokinin subtype 1 (CCK1) receptor (IC50 = 0.56 nM) with high (300-fold) selectivity to the CCK2 receptor. The biological activity of SR146131 was characterized in vitro in a NIH-3T3 cell line expressing the human recombinant CCK1 receptor (3T3-hCCK1). Measuring intracellular calcium release, SR146131 behaved 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 higher concentrations. Like CCK-8S, SR146131 also fully stimulated inositol monophosphate formation (EC50 = 18 +/- 4 nM). SR146131 partially activated mitogen-activated protein kinase and enhanced the expression of the immediate early gene krox 24. In the human CHP212 and IMR32 neuroblastoma cell lines, which constitutively express the CCK1 receptor, SR146131 behaved as a partial agonist on intracellular calcium release and inositol monophosphate formation. All of these effects of SR146131 were inhibited by the CCK1 receptor antagonists SR27897B and devazepide, suggesting that the effects of SR146131 were entirely mediated by the CCK1 receptor. In contrast, high concentrations (>1 microM) of SR146131 had only minimal effects on CCK-8S-stimulated and unstimulated Chinese hamster ovary (CHO) cells expressing the human CCK2 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.