title: Characterization of the binding of [3H]L-365,260: a new potent and selective brain cholecystokinin (CCK-B) and gastrin receptor antagonist radioligand.
abstract: [3H]L-365,260, [(3R-(+)-2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4- benzodiazepin-3-yl)-N'-(3-methylphenyl)urea], a new potent and selective nonpeptide brain cholecystokinin (CCK-B) and gastrin receptor antagonist, bound saturably and reversibly to guinea pig brain membranes. Scatchard analysis indicated a single class of high affinity (Kd = 2.3 nM) binding sites. The binding of [3H]L-365,260 was stereospecific, because unlabeled L-365,260 (an R-enantiomer) was approximately 100 times more potent than its S-enantiomer in displacing binding. The relative potencies of various CCK/gastrin-related peptides and nonpeptide peripheral CCK-A antagonists in displacing [3H]L-365,260 brain binding correlated with their potencies in displacing the binding of 125I-CCK to brain receptors but not their potencies in displacing the peripherally selective CCK-A ligand [3H]L-364,718 from pancreatic receptors. The regional distribution of [3H]L-365,260 binding in various brain areas correlated with 125I-CCK binding. Specific [3H]L-365,260 binding to guinea pig brain membranes was reduced by omission of NaCl but was not affected by omission of MgCl2 or addition of guanosine 5'-(beta-gamma-imido)triphosphate or various pharmacological agents known to interact with other common peptide and nonpeptide receptor systems. [3H]L-365,260 also bound in a specific manner to guinea pig gastric glands but only negligibly to guinea pig or rat pancreas. The binding of [3H]L-365,260 to gastric glands was inhibited by CCK/gastrin antagonists with potencies similar to those for inhibition of 125I-gastrin binding in this tissue. Collectively, the data indicates that [3H]L-365,260 represents a new potent nonpeptide antagonist radioligand suitable for the study of brain CCK-B and gastrin receptors.
authors.affiliation: Department of New Lead Pharmacology, Merck Sharp and Dohme Research Laboratories, West Point, Pennsylvania 19486.
authors.forename: R S
authors.initials: RS
authors.lastname: Chang
authors.forename: T B
authors.initials: TB
authors.lastname: Chen
authors.forename: M G
authors.initials: MG
authors.lastname: Bock
authors.forename: R M
authors.initials: RM
authors.lastname: Freidinger
authors.forename: R
authors.initials: R
authors.lastname: Chen
authors.forename: A
authors.initials: A
authors.lastname: Rosegay
authors.forename: V J
authors.initials: VJ
authors.lastname: Lotti
mesh_terms: D000818:Animals; D001570:Benzodiazepinones / Q000378:metabolism*; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D002766:Cholecystokinin / Q000037:antagonists & inhibitors*; D006168:Guinea Pigs; D007700:Kinetics; D008297:Male; D009928:Organ Specificity; D010179:Pancreas / Q000378:metabolism; D010295:Parietal Cells, Gastric / Q000378:metabolism; D051381:Rats; D011949:Receptors, Cholecystokinin / Q000378:metabolism*
chemical_list: D001570:Benzodiazepinones; D011949:Receptors, Cholecystokinin; C053649:L 365031; D002766:Cholecystokinin