Molecular Basis for Binding and Subtype Selectivity of 1,4-Benzodiazepine Antagonist Ligands of the Cholecystokinin Receptor

Abstract

Background: Allosteric ligands targeting cholecystokinin receptors are needed. Results: Stereochemically distinct iodinated 1,4-benzodiazepine antagonists of type 1 and 2 cholecystokinin receptors dock to analogous intramembranous pockets that have distinct shape and molecular determinants. Conclusion: The geometry of the binding pockets and specific residue interactions are unique for each receptor. Significance: The predictive power of these insights should be useful in the discovery of lead compounds and in their refinement.

Cholecystokinin-induced satiety, a key gut servomechanism that is affected by the membrane microenvironment of this receptor

“…40 It was also confirmed using fluorescence quenching of ligand binding 41 and the impact of receptor mutagenesis on ligand binding. 42,43 The allosteric nature of this small-molecule-binding site was further confirmed using pharmacologic analyses, including the kinetics of ligand dissociation and the impact of orthosteric and possible allosteric ligands on the functions of each other. [42][43][44] Radioiodinated small-molecule CCK1R ligands have been developed 45,46 that provide a means for direct displacement from this allosteric pocket to establish the molecular basis for the binding of small-molecule ligands.…”

“…This effort included not only the docking of a single benzodiazepine antagonist ligand, but also a ligand-guided computational approach using many molecules that have been reported and that reside in public databases to gain more general understanding of this pocket. 42,43 This molecular model has substantial predictive power, with the model being able to distinguish ligands of this receptor from those of other receptors, and it was even able to very effectively distinguish ligands binding to the CCK1R from those binding to the very closely related type 2 CCK receptor (CCK2R).…”

Development of a Highly Selective Allosteric Antagonist Radioligand for the Type 1 Cholecystokinin Receptor and Elucidation of Its Molecular Basis of Binding

“…An understanding of the varied residues lining the small molecule-binding pocket high in the helical bundle of these receptors has provided a useful starting point for understanding the size and chemical characteristics of potential ligands. It has also become possible to extend these insights computationally, particularly when a series of ligands can be used to guide such refinement (Cawston et al, 2012;Harikumar et al, 2013).…”

“…It is reported to distinguish the CCK1R from the type 2 CCK receptor (CCK2R) with 23,000-fold selectivity, while the classic benzodiazepine antagonist 3S(2)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepine-3-yl)-1H-indole-2-carboxamide (L-364,718) exhibits 1500-fold selectivity (Taniguchi et al, 1996a). The molecular basis of the selectivity of benzodiazepine antagonists like L-364,718 and (S)-1-(3-iodophenyl)-3-(1-methyl-2-oxo-5-phenyl-2,3-dihydro-1H-benzo[e] [1,4]diazepin-3-yl)urea (BDZ-1) has recently been carefully evaluated, with specific, nonconserved residues within the intramembranous interhelical pocket identified as key determinants (Cawston et al, 2012). The selectivity for these benzodiazepine ligands can be reversed by substituting these key residues into the other subtype of CCK receptor (Cawston et al, 2012).…”

“…The molecular basis of the selectivity of benzodiazepine antagonists like L-364,718 and (S)-1-(3-iodophenyl)-3-(1-methyl-2-oxo-5-phenyl-2,3-dihydro-1H-benzo[e] [1,4]diazepin-3-yl)urea (BDZ-1) has recently been carefully evaluated, with specific, nonconserved residues within the intramembranous interhelical pocket identified as key determinants (Cawston et al, 2012). The selectivity for these benzodiazepine ligands can be reversed by substituting these key residues into the other subtype of CCK receptor (Cawston et al, 2012).…”