Nonpeptide Cholecystokinin-2 Receptor Agonists

Abstract

In the course of structural explorations around a series of potent CCK2 receptor antagonists, it was noted that simple N-methylation of the indolic N-H in the parent molecule gave rise to behavior in vivo that was consistent with the compound acting as an agonist. Exploration in vitro confirmed this property, and it was shown that the agonist action could be blocked by the reference CCK2 receptor antagonist, L-365,260. Further examples of this type of modification were explored, and a common theme with regard to agonist behavior was uncovered. Some molecular modeling is also presented in an attempt to throw light on the nature of the ligand receptor interactions that may be giving rise to the differing properties of these, apparently, structurally similar molecules.

Linking Non-peptide Ligand Binding Mode to Activity at the Human Cholecystokinin-2 Receptor

“…This last stacking aromatic interaction maintains the CCK2R in the CCK2R°conformation by preventing rotation of helix VI, a motion that is required for CCK2R°to CCK2R* conversion (14). Methyl substitution in the partial agonist JB93,242 not only introduced a steric repulsion, as previously proposed (15), but also eliminated the hydrogen bonding capability of the indole nitrogen with Thr-2.61, causing displacement of the ligand in the CCK2R°binding pocket. Interestingly, JB93,242 finally adopted a location in the CCK2R°similar to that found in the active conformation (CCK2R*).…”

“…In an attempt to examine whether the hydrogen attached to the indole nitrogen was crucial for ligand activity, this hydrogen was substituted by a methyl. Surprisingly, the resultant compound, JB93,242, behaved as a partial agonist (15).…”

“…In the present work we wanted to answer the important question previously raised in the course of CCK2R antagonist design, why two high affinity high selectivity very similar non-peptide ligands of the CCK2R display differential pharmacological activity, namely antagonism and partial agonism at the CCK2R (15). The two ligands have the same chemical core, but they differ by the absence (JB93,182) or presence (JB93,242) of a methyl group on the indole nitrogen ( Fig.…”

Identification of a series of CCK-2 receptor nonpeptide agonists: Sensitivity to stereochemistry and a receptor point mutation

“…There is an increasing number of studies reporting that slight modifications in ligand structure may translate into loss or gain of agonist function (25)(26)(27)(28)(29)(30). At the wild-type CCK-2R, the addition of two methyl groups to the S enantiomer of compound 3 markedly enhances ligand function (compare 2S and 3S in Table 1 and Fig.…”

Cholecystokinin and Gastrin Receptors

“…Mutation of nonconserved amino acids from transmembrane helices led to the identification of a single amino acid in the canine sequence (Leu355, TM VI) that is responsible for this reversal of specificity (38). In general, studies with so-called nonpeptide antagonists of CCK2R revealed that although the amino acid sequence homology of CCK2R in the different species is near 90%, the efficacy of the nonpeptide molecules to stimulate phospholipase C varied from 0 to 60% of the CCK-induced maximal response according to the species and the compound tested (L365,260, L740,093, YM022, PD135158, PD136,450, PD134,308) (39, 47, 48, 227,232,255,256). Incorporation of nonconservative amino acids in the human CCK2R sequence enabled identification of amino acids in transmembrane helices that account for these variations (47, 48).…”