Emerging chemical therapies targeting 5-hydroxytryptamine in the treatment of Alzheimer's disease

Development and crystallography-aided SAR studies of multifunctional BuChE inhibitors and 5-HT6R antagonists with β-amyloid anti-aggregation properties

The lack of an effective treatment makes Alzheimer's disease a serious healthcare problem and a challenge for medicinal chemists. Herein we report interdisciplinary research on novel multifunctional ligands targeting proteins and processes involved in the development of the disease: BuChE, 5-HT₆ receptors and β-amyloid aggregation. Structure-activity relationship analyses supported by crystallography and docking studies led to the identification of a fused-type multifunctional ligand 50, with remarkable and balanced potencies against BuChE (IC₅₀ = 90 nM) and 5-HT₆R (K_i = 4.8 nM), and inhibitory activity against Aβ aggregation (53% at 10 μM). In in vitro ADME-Tox and in vivo pharmacokinetic studies compound 50 showed good stability in the mouse liver microsomes, favourable safety profile and brain permeability with the brain to plasma ratio of 6.79 after p.o. administration in mice, thus being a promising candidate for in vivo pharmacology studies and a solid foundation for further research on effective anti-AD therapies.

Discovery of 1-(phenylsulfonyl)-1H-indole-based multifunctional ligands targeting cholinesterases and 5-HT6 receptor with anti-aggregation properties against amyloid-beta and tau

Multifunctional ligands as an essential variant of polypharmacology are promising candidates for the treatment of multi-factorial diseases like Alzheimer's disease. Based on clinical evidence and following the paradigm of multifunctional ligands we have rationally designed and synthesized a series of compounds targeting processes involved in the development of the disease. The biological evaluation led to the discovery of two compounds with favorable pharmacological characteristics and ADMET profile. Compounds 17 and 35 are 5-HT₆R antagonists (K_i = 13 nM and K_i = 15 nM respectively) and cholinesterase inhibitors with distinct mechanisms of enzyme inhibition. Compound 17, a tacrine derivative is a reversible inhibitor of acetyl- and butyrylcholinesterase (IC₅₀ = 8 nM and IC₅₀ = 24 nM respectively), while compound 35 with rivastigmine-derived phenyl N-ethyl-N-methylcarbamate fragment is a selective, pseudo-irreversible inhibitor of butyrylcholinesterase (IC₅₀ = 455 nM). Both compounds inhibit aggregation of amyloid β in vitro (75% for compound 17 and 68% for 35 at 10 μM) moreover, compound 35 is a potent tau aggregation inhibitor in cellulo (79%). In ADMET in vitro studies both compounds showed acceptable metabolic stability on mouse liver microsomes (28% and 60% for compound 17 and 35 respectively), no or little effect on CYP3A4 and 2D6 up to a concentration of 10 μM and lack of toxicity on HepG2 cell line (IC₅₀ values of 80 and 21 μM, for 17 and 35 respectively). Based on the pharmacological characteristics and favorable pharmacokinetic properties, we propose compounds 17 and 35 as an excellent starting point for further optimization and in-depth biological studies.

Therapy for Alzheimer's disease: Missing targets and functional markers?

The development of the next generation therapy for Alzheimer's disease (AD) presents a huge challenge given the number of promising treatment candidates that failed in trials, despite recent advancements in understanding of genetic, pathophysiologic and clinical characteristics of the disease. This review reflects some of the most current concepts and controversies in developing disease-modifying and new symptomatic treatments. It elaborates on recent changes in the AD research strategy for broadening drug targets, and potentials of emerging non-pharmacological treatment interventions. Established and novel biomarkers are discussed, including emerging cerebrospinal fluid and plasma biomarkers reflecting tau pathology, neuroinflammation and neurodegeneration. These fluid biomarkers together with neuroimaging findings can provide innovative objective assessments of subtle changes in brain reflecting disease progression. A particular emphasis is given to neurophysiological biomarkers which are well-suited for evaluating the brain overall neural network integrity and function. Combination of multiple biomarkers, including target engagement and outcome biomarkers will empower translational studies and facilitate successful development of effective therapies.

Management of Dementia-Related Psychosis, Agitation and Aggression: A Review of the Pharmacology and Clinical Effects of Potential Drug Candidates

Along with cognitive decline, 90% of patients with dementia experience behavioral and psychological symptoms of dementia, such as psychosis, aggression, agitation, and depression. Atypical antipsychotics are commonly prescribed off-label to manage certain symptoms, despite warnings from the regulatory agencies regarding the increased risk of mortality associated with their use in elderly patients. Moreover, these compounds display a limited clinical efficacy, mostly owing to the fact that they were developed to treat schizophrenia, a disease characterized by neurobiological deficits. Thus, to improve clinical efficacy, it has been suggested that patients with dementia should be treated with exclusively designed and developed drugs that interact with pharmacologically relevant targets. Within this context, numerous studies have suggested druggable targets that might achieve therapeutically acceptable pharmacological profiles. Based on this, several different drug candidates have been proposed that are being investigated in clinical trials for behavioral and psychological symptoms of dementia. We highlight the recent advances toward the development of therapeutic agents for dementia-related psychosis and agitation/aggression and discuss the relationship between the relevant biological targets and their etiology. In addition, we review the compounds that are in the early stage of development (discovery or preclinical phase) and those that are currently being investigated in clinical trials for dementia-related psychosis and agitation/aggression. We also discuss the mechanism of action of these compounds and their pharmacological utility in patients with dementia.

Novel Treatment Opportunities Against Cognitive Impairment in Parkinson's Disease with an Emphasis on Diabetes-Related Pathways

Cognitive impairment is highly prevalent in patients with Parkinson's disease (PD) and causes adverse health outcomes. Novel procognitive therapies are needed to address this unmet need. It is now established that there is an increased risk of dementia in patients with type 2 diabetes mellitus (T2DM) and, moreover, T2DM and PD may have common underlying biological mechanisms. As such, T2DM medications are emerging as potential therapies in the context of PD dementia (PDD). In this review, we provide an update on pathophysiological mechanisms underlying cognitive impairments and PDD, focusing on diabetes-related pathways. Finally, we have conducted a review of ongoing clinical trials in PD patients with dementia, highlighting the multiple pharmacological mechanisms that are targeted to achieve cognitive enhancement.

The role of 5 HT6-receptor antagonists in Alzheimer's disease: an update

INTRODUCTION

Despite recent advances in Alzheimer's disease (AD) research, no breakthrough treatments have been discovered. Cholinesterase inhibitors and the NMDA-receptor antagonist memantine are currently the two approved symptomatic treatments for AD. 5-HT6 receptor antagonism has recently emerged as a promising treatment strategy to improve cognition in AD, with a modest side-effect profile.

AREAS COVERED

5-HT6 receptors, exclusively found in the central nervous system, modulate primarily GABA and glutamate levels, facilitating the secondary release of other neurotransmitters including dopamine, noradrenaline, and acetylcholine, all of which are compromised in AD. This review discusses findings of preclinical and phase I-III clinical trials conducted with three major 5-HT6 receptor antagonists: idalopirdine, intepirdine, and SUVN-502, in the field of AD.

EXPERT OPINION

Despite early positive findings, larger phase-III trials have failed to demonstrate any statistically significant impact on cognition for both idalopirdine and intepirdine, as adjunct to cholinesterase inhibitors. Paradoxically, 5-HT6 receptor agonists have also been shown to have cognitive enhancing properties. Thus, a better understanding of the mechanism of action of the 5-HT6 receptor and its ligands is warranted. Investigating 5-HT6 receptor partial or inverse agonists may be promising in future AD trials.

Novel Multitarget-Directed Ligands Aiming at Symptoms and Causes of Alzheimer's Disease

Alzheimer's disease (AD) is a major public health problem, which is due to its increasing prevalence and lack of effective therapy or diagnostics. The complexity of the AD pathomechanism requires complex treatment, e.g. multifunctional ligands targeting both the causes and symptoms of the disease. Here, we present new multitarget-directed ligands combining pharmacophore fragments that provide a blockade of serotonin 5-HT₆ receptors, acetyl/butyrylcholinesterase inhibition, and amyloid β antiaggregation activity. Compound 12 has displayed balanced activity as an antagonist of 5-HT₆ receptors ( K_i = 18 nM) and noncompetitive inhibitor of cholinesterases (IC_{50 hAChE} = 14 nM, IC_{50 eqBuChE} = 22 nM). In further in vitro studies, compound 12 has shown amyloid β antiaggregation activity (IC₅₀ = 1.27 μM) and ability to permeate through the blood-brain barrier. The presented findings may provide an excellent starting point for further studies and facilitate efforts to develop new effective anti-AD therapy.

Pharmacotherapy for the treatment of depression in patients with alzheimer's disease: a treatment-resistant depressive disorder

INTRODUCTION

Pharmacotherapy for the treatment of depressive disorders in Alzheimer's Disease (AD) represents a clinical challenge. pharmacological options are often attempted after a period of watchful waiting (8-12 weeks). monoaminergic antidepressant drugs have shown only modest or null clinical benefits, maybe because the etiology of depressive symptoms in ad patients is fundamentally different from that of nondemented subjects.

AREAS COVERED

The following article looks at the selective serotonin reuptake inhibitor sertraline, which is one of the most frequently studied antidepressant medications in randomized controlled trials (RCTs). It also discusses many other pharmacological approaches that have proven to be inadequate (antipsychotics, acetylcholinesterase inhibitors, anticonvulsants, hormone replacement therapy) and new drug classes (mainly affecting glutamate transmission) that are being studied for treating depression in AD. It also gives discussion to the phase II RCT on the alternative drug S47445 and the potential effect on cognition of the multimodal antidepressant vortioxetine in older depressed patients. Finally, it discusses the N-methyl-D-aspartate antagonist ketamine.

EXPERT OPINION

The present RCT methodologies are too disparate to draw firm conclusions. Future studies are required to identify effective and multimodal pharmacological treatments that efficiently treat depression in AD. Genotyping may boost antidepressant treatment success.

Recent Progress in the Pharmacotherapy of Alzheimer's Disease

Alzheimer's disease is the most common major neurocognitive disorder with substantial social and economic impacts. This article is an update on current pharmacotherapy, advancements in biomarker use, and drugs in the pipeline for this disease. To date, no new drug has qualified to be added to the current therapeutic arsenal comprising cholinesterase inhibitors and the NMDA receptor antagonist memantine. Drugs in the pipeline include symptomatic therapies that are neurotransmitter-based, but mostly disease-modifying therapies. The latter have yielded disappointing results by focusing mainly on the two pathophysiological hallmarks of Alzheimer's disease: Aβ amyloid deposits and tau protein aggregates forming neurofibrillary tangles. These unsuccessful trials may have resulted from studying these drugs 'too late' relative to Alzheimer's disease onset, in addition to focusing only on the amyloid cascade. In fact, Alzheimer's disease is a complex multifactorial disease. Combining different biomarkers might enhance our ability to identify those patients most at risk of developing the disease, and better predict their conversion rates. Furthermore, adopting an integrative treatment approach by targeting additional pathophysiological pathways in Alzheimer's disease such as inflammation and oxidative stress could be the key to better outcomes in Alzheimer's disease pharmacotherapy research.

Reciprocal Interactions of Mitochondria and the Neuroimmunoendocrine System in Neurodegenerative Disorders: An Important Role for Melatonin Regulation

Structural and functional alterations of mitochondria are intimately linked to a wide array of medical conditions. Many factors are involved in the regulation of mitochondrial function, including cytokines, chaperones, chemokines, neurosteroids, and ubiquitins. The role of diffusely located cells of the neuroendocrine system, including biogenic amines and peptide hormones, in the management of mitochondrial function, as well as the role of altered mitochondrial function in the regulation of these cells and system, is an area of intense investigation. The current article looks at the interactions among the cells of the neuronal-glia, immune and endocrine systems, namely the diffuse neuroimmunoendocrine system (DNIES), and how DNIES interacts with mitochondrial function. Whilst changes in DNIES can impact on mitochondrial function, local, and systemic alterations in mitochondrial function can alter the component systems of DNIES and their interactions. This has etiological, course, and treatment implications for a wide range of medical conditions, including neurodegenerative disorders. Available data on the role of melatonin in these interactions, at cellular and system levels, are reviewed, with directions for future research indicated.

Citalopram restores short-term memory deficit and non-cognitive behaviors in APP/PS1 mice while halting the advance of Alzheimer's disease-like pathology

Alzheimer's disease (AD) is the most common cause of dementia. In addition to cognitive impairments, deficits in non-cognitive behaviors are also common neurological sequelae in AD. Here, we show that complex behavioral deficits in 7-month-old APPswe/PSEN1dE9 (APP/PS1) mice include impairments in object recognition, deficient social interaction, increased depression and buried marbles. Citalopram, one of the selective serotonin reuptake inhibitors (SSRIs), ameliorated the amyloid deposition in AD patients and transgenic animal models. After treatment for 4 weeks, citalopram rescued the deficits in short-term memory, sociability and depression in these mice. Further immunohistochemical analysis showed chronic citalopram treatment significantly attenuated β-amyloid deposition and microglial activation in the brains of APP/PS1 mice as demonstrated previously. Parvalbumin (PV) interneurons, which are the primary cellular subtype of GABAergic neurons and considered indispensable for short-term memory and social interaction, also contributed to the progress of depression. Additionally, we found the citalopram could significantly increase the PV-positive neurons in the cortex of APP/PS1 mice without alteration in the hippocampus, which might contribute to the improvement of behavioral performance. Our findings suggest that citalopram might be a potential candidate for the early treatment of AD.

Novel 3-(1,2,3,6-Tetrahydropyridin-4-yl)-1H-indole-Based Multifunctional Ligands with Antipsychotic-Like, Mood-Modulating, and Procognitive Activity

The most troublesome aspects of behavioral and psychological symptoms of dementia (BPSD) are nowadays addressed by antidepressant, anxiolytic, and antipsychotic drugs, often administered off-label. Considering their modest effectiveness in dementia patients, the increased risk of adverse events and cognitive decline, there is an unmet need for well-tolerated and effective therapy of BPSD. We designed and synthesized multifunctional ligands characterized in vitro as high-affinity partial agonists of D₂R, antagonists of 5-HT₆R, and blockers of SERT. Moreover, the molecules activated 5-HT_1AR and blocked 5-HT₇R while having no relevant affinity for off-target M₁R and hERG channel. Compound 16 (N-{2-[4-(5-chloro-1H-indol-3-yl)-1,2,3,6-tetrahydropyridin-1-yl]ethyl}-3-methylbenzene-1-sulfonamide) exhibited a broad antipsychotic-, antidepressant-, and anxiolytic-like activity, not eliciting motor impairments in mice. Most importantly, 16 showed memory-enhancing properties and it ameliorated memory deficits induced by scopolamine. The molecule outperformed most important comparators in selected tests, indicating its potential in the treatment of both cognitive and noncognitive (behavioral and psychological) symptoms of dementia.

The Serotonin Receptor 6 Antagonist Idalopirdine and Acetylcholinesterase Inhibitor Donepezil Have Synergistic Effects on Brain Activity-A Functional MRI Study in the Awake Rat

The 5-HT₆ receptor is a promising target for cognitive disorders, in particular for Alzheimer's disease (AD) and other CNS disorders. The high-affinity and selective 5-HT₆ receptor antagonist idalopirdine (Lu AE58054) is currently in development for mild-moderate AD as adjunct therapy to acetylcholinesterase inhibitors (AChEIs). We studied the effects of idalopirdine alone and in combination with the AChEI donepezil on brain activity using BOLD (Blood Oxygen Level Dependent) functional magnetic resonance imaging (fMRI) in the awake rat. Idalopirdine (2 mg/kg, i.v.) alone had a modest effect on brain activity, resulting in activation of eight brain regions at the peak response. Of these, the cholinergic diagonal band of Broca, the infralimbic cortex, the ventral pallidum, the nucleus accumbens shell, and the magnocellular preoptic area were shared with the effects of donepezil (0.3 mg/kg, i.v.). Donepezil alone activated 19 brain regions at the peak response, including several cortical regions, areas of the septo-hippocampal system and the serotonergic raphe nucleus. When idalopirdine and donepezil were combined, there was a robust stimulation pattern with activation of 36 brain regions spread across the extended-amygdala-, striato-pallidal, and septo-hippocampal networks as well as the cholinergic system. These findings indicate that, whilst idalopirdine and donepezil recruit a number of overlapping regions including one of the forebrain cholinergic nuclei, the synergistic effect of both compounds extends beyond the cholinergic system and the effects of donepezil alone toward recruitment of multiple neural circuits and neurotransmitter systems. These data provide new insight into the mechanisms via which idalopirdine might improve cognition in donepezil-treated AD patients.

Development and validation of sensitive LC-MS/MS method for the quantification of SUVN-502 and its metabolite and its application for first in human pharmacokinetic study

A sensitive and rapid LC-MS/MS method was developed and validated for the quantification of SUVN-502 and M1 of SUVN-502, a 5-HT₆ receptor antagonist for the treatment of dementia associated with Alzheimer's disease. Following solid-phase extraction, SUVN-502 and M1 of SUVN-502 and IS were eluted with 10mM ammonium acetate (pH 4.0) and acetonitrile using a rapid gradient program on reverse phase column. Multiple reaction monitoring mode was used to monitor the respective transitions of m/z 478.2→377.7 for SUVN-502 and m/z 464.1→377.7 for M1 of SUVN-502. The assay exhibited a linear dynamic range of 10-10000pg/mL for SUVN-502 and 20-20000pg/mL for M1 of SUVN-502 in human plasma. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. The within batch accuracy and precision were within acceptable limits. All the other validation parameters were within the acceptable limits. The validated method was applied to analyze human plasma samples obtained from a human pharmacokinetic study consisting single and multiple ascending doses.