prucalopride and Alzheimer-Disease

Alzheimer's disease (AD) is a neurodegenerative disease which has a higher prevalence and incidence in older people. The need for improved AD therapies is unmet. The 5-hydroxytryptamine4 receptor (5-HT4R) partial agonists may be of benefit for both the symptomatic and disease-modifying treatment of cognitive disorders associated with AD. Herein, we report the design, synthesis and SAR of imidazo[1,5-a] pyridine derivatives as 5-HT4R partial agonists. The focused SAR, optimization of ADME properties resulted the discovery of compound 5a as potent, selective, brain penetrant 5-HT4 partial agonist as a lead compound with good ADME properties and efficacy in both symptomatic and disease modifying animal models of cognition.

Topics: Alzheimer Disease; Animals; Cognition Disorders; Dogs; Dose-Response Relationship, Drug; Drug Design; Drug Partial Agonism; Humans; Molecular Structure; Pyridines; Rats; Receptors, Serotonin, 5-HT4; Structure-Activity Relationship

In addition to the amyloidogenic pathway, amyloid precursor protein (APP) can be cleaved by α-secretases, producing soluble and neuroprotective APP alpha (sAPPα) (nonamyloidogenic pathway) and thus preventing the generation of pathogenic amyloid-β. However, the mechanisms regulating APP cleavage by α-secretases remain poorly understood. Here, we showed that expression of serotonin type 4 receptors (5-HT(4)Rs) constitutively (without agonist stimulation) induced APP cleavage by the α-secretase ADAM10 and the release of neuroprotective sAPPα in HEK-293 cells and cortical neurons. This effect was independent of cAMP production. Interestingly, we demonstrated that 5-HT(4) receptors physically interacted with the mature form of ADAM10. Stimulation of 5-HT(4) receptors by an agonist further increased sAPPα secretion, and this effect was mediated by cAMP/Epac signaling. These findings describe a new mechanism whereby a GPCR constitutively stimulates the cleavage of APP by α-secretase and promotes the nonamyloidogenic pathway of APP processing.

Topics: ADAM Proteins; ADAM10 Protein; Alzheimer Disease; Amyloid beta-Protein Precursor; Amyloid Precursor Protein Secretases; Benzofurans; Cerebral Cortex; Cyclic AMP; HEK293 Cells; Humans; Membrane Proteins; Neuroprotective Agents; Receptors, G-Protein-Coupled; Receptors, Serotonin, 5-HT4; Serotonin 5-HT4 Receptor Agonists

The cognitive impairments observed in Alzheimer's disease (AD) are in part a consequence of reduced acetylcholine (ACh) levels resulting from a loss of cholinergic neurons. Preclinically, serotonin 4 receptor (5-HT(4)) agonists are reported to modulate cholinergic function and therefore may provide a new mechanistic approach for treating cognitive deficits associated with AD. Herein we communicate the design and synthesis of potent, selective, and brain penetrant 5-HT(4) agonists. The overall goal of the medicinal chemistry strategy was identification of structurally diverse clinical candidates with varying intrinsic activities. The exposure-response relationships between binding affinity, intrinsic activity, receptor occupancy, drug exposure, and pharmacodynamic activity in relevant preclinical models of AD were utilized as key selection criteria for advancing compounds. On the basis of their excellent balance of pharmacokinetic attributes and safety, two lead 5-HT(4) partial agonist candidates 2d and 3 were chosen for clinical development.

Topics: Alzheimer Disease; Animals; ATP Binding Cassette Transporter, Subfamily B, Member 1; CHO Cells; Cognition Disorders; Cricetinae; Cricetulus; Cyclic AMP; Dogs; Drug Partial Agonism; Haplorhini; HEK293 Cells; Humans; In Vitro Techniques; Indoles; Madin Darby Canine Kidney Cells; Male; Microsomes, Liver; Permeability; Piperidines; Protein Isoforms; Pyrans; Rats; Rats, Sprague-Dawley; Receptors, Serotonin, 5-HT4; Serotonin 5-HT4 Receptor Agonists; Stereoisomerism; Structure-Activity Relationship

5-HT(4) receptors are widely distributed in both peripheral and central nervous systems where they couple, via a G-protein, to the activation of adenylate cyclase. In the brain, the highest 5-HT(4) receptor densities are found in the limbic system, including the hippocampus and frontal cortex. It has been suggested that activation of these receptors may be of therapeutic benefit in diseases that produce cognitive deficits such as Alzheimer's disease (AD). Previous electrophysiological studies have shown that the 5-HT(4) agonist, Zacopride, can increase population spike amplitude recorded in region CA1 of rat hippocampal slices in a cyclic AMP (cAMP)/cAMP-dependent protein kinase A-dependent manner. We report here that the 5-HT(4) agonist, Prucalopride, and the 5-HT(4) partial agonist, SL65.0155, produce a similar effect in rat hippocampal slices and that the specific 5-HT(4) antagonist, GR113808, blocks these effects. To investigate the potential use of 5-HT(4) agonists in the treatment of AD, Prucalopride was applied to hippocampal slices from a transgenic mouse line that overexpresses the Abeta peptide. Despite the deficit in synaptic transmission present in these mice, the percentage increase of the CA1 population spike induced by Prucalopride was the same as that observed in wild-type mice. These data support 5-HT(4) receptors as a target for cognitive enhancement and suggest that a partial agonist would be sufficient to produce benefits, while reducing potential peripheral side effects. In addition, we show that 5-HT(4) receptors remain functional in the presence of excess Abeta peptide and may therefore be a useful target in AD.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Animals, Genetically Modified; Benzofurans; Dioxanes; Disease Models, Animal; Excitatory Postsynaptic Potentials; Hippocampus; Humans; Indoles; Male; Neurons; Organ Culture Techniques; Oxadiazoles; Patch-Clamp Techniques; Rats; Receptors, Serotonin, 5-HT4; Serotonin Antagonists; Serotonin Receptor Agonists; Sulfonamides

The serotonin 5-HT(4) receptor has recently gained a lot of attention for its functional roles in central processes such as memory and cognition. In this study, we show that activation of the human 5-HT(4) (h5-HT(4)) receptor stimulates the secretion of the non-amyloidogenic soluble form of the amyloid precursor protein (sAPPalpha). 5-HT enhanced the level of secreted sAPPalpha in a time- and dose-dependent manner in Chinese hamster ovary cells stably expressing the h5-HT(4(e)) receptor isoform. The increase was inhibited by the selective 5-HT(4) receptor antagonist, GR113808. The 5-HT(4) selective agonists, prucalopride and renzapride, also increased secreted sAPPalpha in IMR32 human neuroblastoma cells. The stimulatory effect of 5-HT was mimicked by forskolin, a direct activator of adenylyl cyclase, and 8-bromo-cAMP, a membrane-permeant cAMP analogue. On the contrary, inhibition of protein kinase A (PKA) by H89 potentiated the 5-HT-induced increase in both secreted and cellular sAPPalpha. This phenomenon involves a novel PKA-independent stimulatory process that overcomes a PKA-dependent inhibitory one. Finally, activation of the h5-HT(4(e)) receptor did not modify extracellular amyloid beta-protein in Chinese hamster ovary cells transfected with the human APP695. Given the neuroprotective and enhancing memory effects of sAPPalpha, our results may open a new avenue for the treatment of Alzheimer's disease.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Adenylyl Cyclases; Alzheimer Disease; Amyloid beta-Protein Precursor; Animals; Benzamides; Benzofurans; Blotting, Western; Bridged Bicyclo Compounds, Heterocyclic; CHO Cells; Colforsin; Cricetinae; Cyclic AMP-Dependent Protein Kinases; Dose-Response Relationship, Drug; Humans; Indoles; Ligands; Memory; Polymerase Chain Reaction; Protein Binding; Protein Isoforms; Radioimmunoassay; Receptors, Serotonin; Receptors, Serotonin, 5-HT4; Serotonin; Sulfonamides; Time Factors; Transfection; Tumor Cells, Cultured