Negative versus positive allosteric modulation of metabotropic glutamate receptors (mGluR5): indices for potential pro-cognitive drug properties based on EEG network oscillations and sleep-wake organization in rats.

RATIONALE: Evidence is emerging that positive and negative modulation of the metabotropic glutamate (mGluR5) receptors has the potential for treating cognitive deficits and neuroprotection associated with psychiatric and neurodegenerative diseases, respectively. Sleep and synchronisation of disparate neuronal networks are critically involved in neuronal plasticity, and disturbance in vigilance states and cortical network connectivity contribute significantly to cognitive deficits described in schizophrenia and Alzheimer's disease. Here, we examined the circadian changes of mGluR5 density and the functional response to modulation of mGluR5 signaling. METHODS: The current study carried out in Sprague-Dawley rats quantified the density of mGluR5 across the light-dark cycle with autoradiography. The central activity of mGluR5 negative allosteric modulators (2-methyl-6-(phenylethynyl)pyridine (MPEP) and [(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) and positive allosteric modulators (S-(4-fluoro-phenyl)-{3-[3-(4-fluoro-phenyl)-[1,2,4]oxadiazol-5-yl]-piperidin-1-yl}-methanone (ADX47273) and (7S)-3-tert-butyl-7-[3-(4-fluoro-phenyl)-1,2,4-oxadiazol-5-yl]-5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-a]pyridine (LSN2814617) was examined on sleep-wake architecture. The functional effect of mGluR5 modulation on cortical networks communication was described in freely moving animals. RESULTS: The density of mGluR5 in the striatal, cortical, hippocampal and thalamic structures was unchanged across the light-dark cycle. Allosteric blockade of mGluR5 consistently consolidated deep sleep, enhanced sleep efficiency and elicited prominent functional coherent network activity in slow theta and gamma oscillations. However, allosteric activation of mGluR5 increased waking, decreased deep sleep and reduced functional network connectivity following the activation of slow alpha oscillatory activity. CONCLUSION: This functional study differentiates the pharmacology of allosteric blockade of mGluR5 from that of allosteric activation and suggests that mGluR5 blockade enhances sleep and facilitates oscillatory network connectivity, both processes being known to have relevance in cognition processes.

Pharmacological study of IQM-97,423, a potent and selective CCK1 receptor antagonist with protective effect in experimental acute pancreatitis.

The pharmacological profile of the new CCK1 receptor antagonist IQM-97,423, (4aS,5R)-2-benzyl-5-(tert-butylaminocarbonyl-tryptophyl)amino-1,3-dioxoperhydropyrido-[1,2-c]pyrimidine, was examined in in vitro and in vivo studies and compared with typical CCK1 antagonists such as devazepide and lorglumide. IQM-97,423 showed a high affinity at [3H]-pCCK8-labeled rat pancreatic CCK1 receptors, and was virtually devoid of affinity at brain CCK2 receptors. IQM-97,423 antagonized CCK8S-stimulated alpha-amylase release from rat pancreatic acini with a potency similar to devazepide and much higher than lorglumide. In the guinea pig isolated longitudinal muscle-myenteric plexus preparation, IQM-97,423 produced a full antagonism of the contractile response elicited by CCK8S and a weaker effect on the contraction elicited by CCK4, suggesting a selective antagonism at CCK1 receptors. The protective effect of IQM-97,423 and devazepide was tested in two models of acute pancreatitis in rats, induced by injection of cerulein or by combined bile and pancreatic duct obstruction. The new compound fully prevented the cerulein-induced increase in plasma pancreatic enzymes and in pancreas weight with a potency similar to devazepide. In common bile-pancreatic duct ligature-induced acute pancreatitis, IQM-97,423 partially prevented, like devazepide, the increase in plasma pancreatic enzyme activity and in pancreas weight. Consequently, the pyridopyrimidine derivative IQM-97,423 is a potent and highly selective CCK1 receptor antagonist with preventive effects in two experimental models of acute pancreatitis and a potential therapeutic interest.

5-(Tryptophyl)amino-1,3-dioxoperhydropyrido[1,2-c]pyrimidine-based potent and selective CCK(1) receptor antagonists: structure-activity relationship studies on the central 1,3-dioxoperhydropyrido[1,2-c]pyrimidine scaffold.

To further define the pharmacophore of the potent and selective 5-(tryptophyl)amino-1,3-dioxoperhydropyrido[1,2-c]pyrimidine-based CCK(1) receptor antagonists the electronic and topographic properties of the central 1,3-dioxoperhydro-pyrido[1,2-c]pyrimidine scaffold have been modified. With this aim, the 1- and 3-oxo groups have been replaced by the thioxo- and deoxi-analogues, and the fused piperidine ring has been contracted to the corresponding pyrrolidine moiety. The results of the evaluation of the new analogues as CCK receptor ligands, in rat pancreas and cerebral cortex preparations, showed that, whereas replacement of oxygen with sulfur is allowed, reduction of the 1- or 3-oxo groups or the contraction of the fused piperidine ring lead to the complete loss of binding affinity at CCK(1) receptors. The thioxo-analogues 5a, 8a, 12a, and 12b showed functional CCK(1) antagonist activity, inhibiting the CCK-8-stimulated amylase release from pancreatic acinar cells. The 1-thioxo analogue 5a, with subnanomolar affinity (IC(50) = 0.09 x 10(-9) M), was found to be the most potent and selective compound within the family of 5-(tryptophyl)amino-1,3-dioxoperhydropyrido[1,2-c]pyrimidine-based CCK(1) antagonists.

5-(Tryptophyl)amino-1,3-dioxoperhydropyrido[1,2-c]pyrimidine-based potent and selective CCK(1)receptor antagonists: structure-activity relationship studies on the substituent at N2-position.

To establish structure-activity relationships a new series of analogues of the highly potent and selective CCK(1) receptor antagonist (4aS,5R)-2-benzyl-5-(N-Boc-tryptophyl)amino-1,3-dioxoperhydropyrido[1,2-c]-pyrimidine (1a) modified at N2-position of the central scaffold has been prepared and evaluated as CCK receptor ligands. With this aim the N2-benzyl group has been replaced by methyl, cyclohexyl, aromatic groups, 1-phenylethyl, and 1-carboxy-2-phenylethyl group. Then, substituents with different electronic and steric properties were introduced into different positions of the phenyl group of analogues 19a and 19b. The results of the CCK receptor binding and in vitro functional activity evaluation suggest the importance of the lipophilic character and an appropriate spatial orientation of the moiety linked at the N2-position of the 1,3-dioxoperhydropyrido[1,2-c]pyrimidine template for potent and selective binding and antagonist activity at CCK(1) receptor subtype. The 2-cyclohexyl and (2S)-1-naphthyl derivatives 18a and (2S)-20a have emerged as more potent and selective CCK(1) receptor antagonists than the lead compound 1a. Additionally, the results confirm the (4aS,5R)-stereochemistry at the central bicyclic skeleton as an essential structural requirement for potent binding to this receptor subtype.

5-(Tryptophyl)amino-1,3-dioxoperhydropyrido[1,2-c]pyrimidine-based potent and selective CCK(1) receptor antagonists: structural modifications at the tryptophan domain.

Analogues of the previously reported potent and highly selective CCK(1) receptor antagonist (4aS, 5R)-2-benzyl-5-(N-Boc-tryptophyl)amino-1,3-dioxoperhydropyrido-[1, 2-c]pyrimidine (2a) were prepared to explore the structural requirements at the Boc-tryptophan domain for CCK(1) receptor affinity. Structural modifications of 2a involved the Trp side chain, its conformational freedom, the Boc group, and the carboxamide bond. Results of the CCK binding and in vitro functional activity evaluation showed three highly strict structural requirements: the type and orientation of the Trp side chain, the H-bonding acceptor carbonyl group of the carboxamide bond, and the presence of the Trp amino protection Boc. Replacement of this acid-labile group with 3, 3-dimethylbutyryl or tert-butylaminocarbonyl conferred acid stability to analogues 14a and 15a, which retained a high potency and selectivity in binding to CCK(1) receptors, as well as an in vivo antagonist activity against the acute pancreatitis induced by caerulein in rats. Oral administration of compounds 14a and 15a also produced a lasting antagonism to the hypomotility induced by CCK-8 in mice, suggesting a good bioavailability and metabolic stability.

Synthesis and stereochemical structure-activity relationships of 1,3-dioxoperhydropyrido[1,2-c]pyrimidine derivatives: potent and selective cholecystokinin-A receptor antagonists.

The synthesis and stereochemical structure--activity relationships of a new class of potent and selective non-peptide cholecystokinin-A (CCK-A) receptor antagonists based on the 1,3-dioxoperhydropyrido[1,2-c]pyrimidine skeleton are described. The most potent member of this series of eight diastereoisomers, (4aS,5R)-2-benzyl-5-[N-[(tert-butoxycarbonyl)-L-tryptophyl]-amino] - 1,3-dioxoperhydropyrido[1,2-c]pyrimidine, displays nanomolar CCK-A receptor affinity and higher than 8000-fold potency at the CCK-A than at the CCK-B receptor. As CCK-A antagonist, this compound inhibits the CCK-8-evoked amylase release from pancreatic acinar cells at a low concentration, similar to that of the typical antagonist Devazepide. Highly strict stereochemical requirements for CCK-A receptor binding and selectivity have been found. The L-Trp and the 4a,5-trans disposition of the bicyclic perhydropyrido[1,2-c]pyrimidine are essential for binding potency and selectivity.