YM022 [(R)-1-[2,3-dihydro-1-(2'-methylphenacyl)-2-oxo-5-phenyl-1H-1,4- benzodiazepin-3-yl]-3-(3-methylphenyl)urea]: an irreversible cholecystokinin type-B receptor antagonist

Natural compounds: leads or ideas? Bioinspired molecules for drug discovery

In this article, we compare drugs of natural origin to synthetic compounds and analyze the reasons why natural compounds occupy a place of choice in the current pharmacopoeia. The observations reported here support the design of synthetic compounds inspired from plant alkaloids and their biosynthetic pathway. Our reasoning leads to very efficient syntheses of compounds which complexity matches that of indolomonoterpenic alkaloids.

Thermodynamic analysis of ligands at cholecystokinin CCK2 receptors in rat cerebral cortex

BACKGROUND AND PURPOSE

Several studies using radioligand binding assays, have shown that measurement of thermodynamic parameters can allow discrimination of agonists and antagonists (Weiland et al., 1979; Borea et al., 1996a). Here we investigate whether agonists and antagonists can be thermodynamically discriminated at CCK(2) receptors in rat cerebral cortex.

EXPERIMENTAL APPROACH

The pK(L) of [(3)H]-JB93182 in rat cerebral cortex membranes was determined at 4, 12, 21 and 37 degrees C in 50 mM Tris-HCl buffer (buffer B pH 6.96; containing 0.089 mM bacitracin). pK(I) values of ligands of diverse chemical structure and with differing intrinsic activity (alpha), as defined by the lumen-perfused rat and mouse stomach bioassays, were determined in buffer B at 4, 12, 21 and 37 degrees C.

KEY RESULTS

[(3)H]-JB93182 labelled a homogeneous population of receptors in rat cerebral cortex at 4, 12, 21 and 37 degrees C and the pK(L) and B(max) were not altered by incubation temperature. [(3)H]-JB93182 binding reached equilibrium after 10, 50, 90 and 220 min at 37, 21, 12 and 4 degrees C, respectively. pK(I) values for R-L-365,260, R-L-740,093, YM220, PD134,308 and JB95008 were higher at 4 degrees C than at 37 degrees C. There was no effect of temperature on pK(I) values for pentagastrin, CCK-8S, S-L-365,260, YM022, PD140,376 and JB93242.

CONCLUSIONS AND IMPLICATIONS

CCK(2) receptor agonists and antagonists at rat CCK(2) receptors cannot be discriminated by thermodynamic analysis using [(3)H]-JB93182 as the radioligand.

New insights in insurmountable antagonism

Antagonists that produce parallel rightward shifts of agonist dose-response curves with no alteration of the maximal response are traditionally classified as surmountable, while insurmountable antagonists also depress the maximal response. Although the longevity of the antagonist-receptor complex is quoted in many studies to explain insurmountable antagonism, slowly interconverting receptor conformations, allosteric binding sites, and receptor internalization have been evoked as alternative explanations. To complicate matters even further, insurmountable antagonism is not only drug-related; it may also depend on the tissue, species and experimental design. For the sake of drug development, it is important to elucidate the molecular mechanisms of insurmountable antagonism. New experimental approaches, such as intact cell studies and the use of computer-assisted simulations based on dynamic receptor models, herald the advent of better insight in the future.

Pharmacological analysis of CCK(2) receptor ligands using COS-7 and SK-N-MC cells, expressing the human CCK(2) receptor

A series of CCK(2) receptor ligands were analysed with respect to their interaction with binding sites in the membranes of COS-7 cells and SK-N-MC cells transiently expressing the human CCK(2) receptor (short isoform). The ligands were YF476, YM022, AG041R, L-740,093, JB93182, PD134308, and PD136450. Their binding was analysed by radioligand competition using [3H]L-365,260 as the labelled ligand. Saturation binding analysis indicated that [3H]L-365,260 interacted with a single class of binding sites. In competition binding experiments using COS-7-cell membranes, all seven ligands were incubated together with 2 nM [3H]L-365,260. The data for four of the compounds fitted a one-site model (pK(i) values: YM022: 9.2+/-0.02; YF476: 9.6+/-0.04; L-740,093: 9.2+/-0.01; and AG041R: 8.3+/-0.06), while the data for the three others fitted a two-site model (pK(i) values: JB93182: 8.8+/-0.04 and 6.0+/-0.15; PD134308: 9.0+/-0.04 and 6.1+/-0.15; and PD136450: 9.0+/-0.02 and 5.4+/-0.41). SK-N-MC cell membranes and 2 nM [3H]L-365,260 were incubated together with YM022, YF476, JB93182, and PD134308. The data for YM022 and YF476 fitted a one-site model (pK(i) values: YM022: 9.3+/-0.06; YF476: 9.4+/-0.02), while the data for JB93182 and PD134308 fitted a two-site model (pK(i) values: JB93182: 8.7+/-0.06 and 6.2+/-0.06; PD134308: 9.1+/-0.06 and 7.0+/-0.17). Competition binding experiments in the presence of the GTP-analogue guanylylimidodiphosphate, using either of the two cell types, produced similar binding data for PD134308 and JB93182 as in the absence of GTP-analogue. The human receptor seems to exist in a low and/or high affinity state. The shift from low to high affinity does not seem to reflect the degree of G protein coupling.

Pharmacological and molecular characterization of muscular cholecystokinin receptors in the human lower oesophageal sphincter

In vitro cholecystokinin (CCK) contracts the human lower oesophageal sphincter by stimulating muscular receptors. The aim of this study was to characterize the muscular CCK receptor subtypes in the human lower oesophageal sphincter. Twenty-five circular strips from six patients were studied. RNA was extracted, reverse transcribed, and cDNAs were amplified with primers for human CCK-A and B receptors. The potency of the contraction induced by CCK-8, desulphated CCK-8, and gastrin-I, and the effect of the CCK-A (loxiglumide and SR 27897) and the CCK-B (YM022 and L-365 260) specific receptor antagonists were compared. Both CCK-A and CCK-B receptor mRNAs were found in functional lower oesophageal sphincter strips. The potency of the CCK-8 concentration-dependent contraction was two and three orders of magnitude higher than that of desulphated CCK-8 and gastrin-I, respectively. The CCK-8-induced contraction was blocked by the CCK-A receptor antagonists loxiglumide (IC50 11 micromol L-1) and SR 27897 (IC50 74 nmol L-1) but not by CCK-B receptor antagonists (1 micromol L-1). Our data suggest that, although the human lower oesophageal sphincter expresses both CCK-A and CCK-B receptors, the contractile effect of CCK-8 on the circular muscle is mainly due to the activation of CCK-A receptors.

Human formyl peptide receptor function role of conserved and nonconserved charged residues

In this study, we investigated the role of charged residues in ligand binding interactions of f-Met-Leu-Phe receptors (FPR). Charged residues of FPR, both conserved and nonconserved, which are located close to the membrane interface were mutated to alanine to determine their role in ligand binding. The mutated residues belonged to specific domains of FPR which have previously been implicated in FPR ligand binding interactions. We demonstrate that nonconserved charged residues such as Arg84, Lys85, Arg205 and Asp284 and conserved charge residue Arg163 seem to play a role in ligand binding. However, alteration of nonconserved charged residue Asp106 did not have any effect. In conclusion, specific charged residues of FPR, both conserved nonconserved, may contribute to FPR function either directly or indirectly.

Pharmacological analysis of CCK2 receptor antagonists using isolated rat stomach ECL cells

1. Gastrin stimulates rat stomach ECL cells to secrete histamine and pacreastatin, a chromogranin A (CGA)-derived peptide. The present report describes the effect of nine cholecystokinin2 (CCK2) receptor antagonists and one CCK1 receptor antagonist on the gastrin-evoked secretion of pancreastatin from isolated ECL cells. 2. The CCK2 receptor antagonists comprised three benzodiazepine derivatives L-740,093, YM022 and YF476, one ureidoacetamide compound RP73870, one benzimidazole compound JB 93182, one ureidoindoline compound AG041R and three tryptophan dipeptoids PD 134308 (CI988), PD135158 and PD 136450. The CCK1 receptor antagonist was devazepide. 3. A preparation of well-functioning ECL cells (approximately 80% purity) was prepared from rat oxyntic mucosa using counter-flow elutriation. The cells were cultured for 48 h in the presence of 0.1 nM gastrin; they were then washed and incubated with antagonist alone or with various concentrations of antagonist plus 10 nM gastrin (a maximally effective concentration) for 30 min. Gastrin dose-response curves were constructed in the absence or presence of increasing concentrations of antagonist. The amount of pancreastatin secreted was determined by radioimmunoassay. 4. The gastrin-evoked secretion of pancreastatin was inhibited in a dose-dependent manner. YM022, AG041R and YF476 had IC50 values of 0.5, 2.2 and 2.7 nM respectively. L-740,093, JB93182 and RP73870 had IC50 values of 7.8, 9.3 and 9.8 nM, while PD135158, PD136450 and PD134308 had IC50 values of 76, 135 and 145 nM. The CCK1 receptor antagonist devazepide was a poor CCK2 receptor antagonist with an IC50 of about 800 nM. 5. YM022, YF476 and AG041R were chosen for further analysis. YM022 and YF476 shifted the gastrin dose-response curve to the right in a manner suggesting competitive antagonism, while the effects of AG041R could not be explained by simple competitive antagonism. pK(B) values were 11.3 for YM022, 10.8 for YF476 and the apparent pK(B) for AG041R was 10.4.

CCK receptor antagonists

1. The peptide hormone and neurotransmitter, cholecystokinin, is widely distributed throughout the gastrointestinal tract and central nervous system and mediates a diverse number of biological functions. 2. Two receptor subtypes, CCK-A and CCK-B, have been identified by both pharmacological characterization and molecular cloning. The CCK-A receptor is the predominant peripheral CCK receptor subtype and the CCK-B receptor is the predominant central CCK receptor. In addition, there are discrete populations of CCK-A receptors in the brain and CCK-B receptors are present in gastric mucosa. 3. Subtype selective antagonists have been developed which discriminate between the two receptor subtypes. One of the major chemical classes has exploited a benzodiazepine template present in asperlicin which was initially discovered in a natural product screen for CCK receptor antagonists. 4. The structurally related benzodiazepines L-365,260, L-740,093, and YM022 are selective antagonists of the CCK-B receptor subtype. Their in vitro pharmacological profiles have been characterized using the human CCK-B receptor expressed in CHO cells. 5. L-365,260 behaves in a manner consistent with that of a competitive antagonist and both L-740,093 and YM022 behave as insurmountable CCK-B receptor antagonists in vitro.