Vol. 289, Issue 2, 742-751, May 1999

SR146131: A New Potent, Orally Active, and Selective Nonpeptide Cholecystokinin Subtype 1 Receptor Agonist. I: In Vitro Studies

Eric Bignon, André Bachy, Robert Boigegrain¹, Roger Brodin¹, Michèle Cottineau, Danielle Gully, Jean-Marc Herbert, Peter Keane, Christophe Labie, Jean-Charles Molimard¹, Dominique Olliero¹, Florence Oury-Donat¹, Christophe Petereau, Valérie Prabonnaud, Marie-Pierre Rockstroh, Paul Schaeffer, Orlane Servant, Olivier Thurneyssen¹, Philippe Soubrié¹, Marc Pascal, Jean-Pierre Maffrand and Gérard Le Fur¹

Sanofi Recherche, Toulouse Cedex, France

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 µM) 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.