Predicting biological activity and design of 5-HT6 antagonists through assessment of ANN-QSAR models in the context of Alzheimer's disease.

CONTEXT: Alzheimer's disease (AD) is the leading cause of dementia around the world, totaling about 55 million cases, with an estimated growth to 74.7 million cases in 2030, which makes its treatment widely desired. Several studies and strategies are being developed considering the main theories regarding its origin since it is not yet fully understood. Among these strategies, the 5-HT6 receptor antagonism emerges as an auspicious and viable symptomatic treatment approach for AD. The 5-HT6 receptor belongs to the G protein-coupled receptor (GPCR) family and is closely implicated in memory loss processes. As a serotonin receptor, it plays an important role in cognitive function. Consequently, targeting this receptor presents a compelling therapeutic opportunity. By employing antagonists to block its activity, the 5-HT6 receptor's functions can be effectively modulated, leading to potential improvements in cognition and memory. METHODS: Addressing this challenge, our research explored a promising avenue in drug discovery for AD, employing Artificial Neural Networks-Quantitative Structure-Activity Relationship (ANN-QSAR) models. These models have demonstrated great potential in predicting the biological activity of compounds based on their molecular structures. By harnessing the capabilities of machine learning and computational chemistry, we aimed to create a systematic approach for analyzing and forecasting the activity of potential drug candidates, thus streamlining the drug discovery process. We assembled a diverse set of compounds targeting this receptor and utilized density functional theory (DFT) calculations to extract essential molecular descriptors, effectively representing the structural features of the compounds. Subsequently, these molecular descriptors served as input for training the ANN-QSAR models alongside corresponding biological activity data, enabling us to predict the potential efficacy of novel compounds as 5-hydroxytryptamine receptor 6 (5-HT6) antagonists. Through extensive analysis and validation of ANN-QSAR models, we identified eight new promising compounds with therapeutic potential against AD.

Activation of 5-HT6 Receptors in the Ventrolateral Orbital Cortex Produces Anti-Anxiodepressive Effects in a Rat Model of Neuropathic Pain.

The comorbidity of anxiety and depression frequently occurs in patients with neuropathic pain. The ventrolateral orbital cortex (VLO) plays a critical role in mediating neuropathic pain and anxiodepression in rodents. Previous studies suggested that 5-HT6 receptors in the VLO are involved in neuropathic pain. Strong evidence supports a close link between 5-HT6 receptors and affective disorders such as depression and anxiety disorders. However, it remains unclear whether the 5-HT6 receptors in the VLO are involved in neuropathic pain-induced anxiodepression. Using a rat neuropathic pain model of spared nerve injury (SNI), we demonstrated that rats exhibited significant anxiodepression-like behaviors and the expression of VLO 5-HT6 receptors obviously decreased four weeks after SNI surgery. Microinjection of the 5-HT6 receptor agonist EMD-386088 into the VLO or overexpression of VLO 5-HT6 receptors alleviated anxiodepression-like behaviors. These effects were blocked by pre-microinjection of a selective 5-HT6 receptor antagonist (SB-258585) or inhibitors of AC (SQ-22536), PKA (H89), and MEK1/2 (U0126) respectively. Meanwhile, the expression of p-ERK, p-CREB, and BDNF in the VLO decreased four weeks after SNI surgery. Furthermore, administration of EMD-386088 upregulated the expression of BDNF, p-ERK, and p-CREB in the VLO of SNI rats, which were reversed by pre-injection of SB-258585. These findings suggest that activating 5-HT6 receptors in the VLO has anti-anxiodepressive effects in rats with neuropathic pain via activating AC-cAMP-PKA-MERK-CREB-BDNF signaling pathway. Accordingly, 5-HT6 receptor in the VLO could be a potential target for the treatment of the comorbidity of neuropathic pain and anxiodepression.

5-HT6 receptor neutral antagonists protect astrocytes: A lesson from 2-phenylpyrrole derivatives.

The serotonin type 6 receptor (5-HT6R) displays a strong constitutive activity, suggesting it participates largely in the physiological and pathological processes controlled by the receptor. The active states of 5-HT6R engage particular signal transduction pathways that lead to different biological responses. In this study, we present the development of 5-HT6R neutral antagonists at Gs signaling built upon the 2-phenylpyrrole scaffold. Using molecular dynamics simulations, we outline the relationship between the exposure of the basic center of the molecules and their ability to target the agonist-activated state of the receptor. Our study identifies compound 30 as a potent and selective neutral antagonist at 5-HT6R-operated Gs signaling. Furthermore, we demonstrate the cytoprotective effects of 30 and structurally diverse 5-HT6R neutral antagonists at Gs signaling in C8-D1A cells and human astrocytes exposed to rotenone. This effect is not observed for 5-HT6R agonists or inverse agonists. In light of these findings, we propose compound 30 as a valuable molecular probe to study the biological effects associated with the agonist-activated state of 5-HT6R and provide insight into the glioprotective properties of 5-HT6R neutral antagonists at Gs signaling.

Non-hallucinogenic compounds derived from iboga alkaloids alleviate neuropathic and visceral pain in mice through a mechanism involving 5-HT2A receptor activation.

The aim of this study was to determine the anti-hypersensitivity activity of novel non-hallucinogenic compounds derived from iboga alkaloids (i.e., ibogalogs), including tabernanthalog (TBG), ibogainalog (IBG), and ibogaminalog (DM506), using mouse models of neuropathic (Chronic Constriction Injury; CCI) and visceral pain (dextrane sulfate sodium; DSS). Ibogalogs decreased mechanical hyperalgesia and allodynia induced by CCI in a dose- and timeframe-dependent manner, where IBG showed the longest anti-hyperalgesic activity at a comparatively lower dose, whereas DM506 displayed the quickest response. These compounds also decreased hypersensitivity induced by colitis, where DM506 showed the longest activity. To understand the mechanisms involved in these effects, two approaches were utilized: ibogalogs were challenged with the 5-HT2A receptor antagonist ketanserin and the pharmacological activity of these compounds was assessed at the respective 5-HT2A, 5-HT6, and 5-HT7 receptor subtypes. The behavioral results clearly demonstrated that ketanserin abolishes the pain-relieving activity of ibogalogs without inducing any effect per se, supporting the concept that 5-HT2A receptor activation, but not inhibition, is involved in this process. The functional results showed that ibogalogs potently activate the 5-HT2A and 5-HT6 receptor subtypes, whereas they behave as inverse agonists (except TBG) at the 5-HT7 receptor. Considering previous studies showing that 5-HT6 receptor inhibition, but not activation, and 5-HT7 receptor activation, but not inhibition, relieved chronic pain, we can discard these two receptor subtypes as participating in the pain-relieving activity of ibogalogs. The potential involvement of 5-HT2B/2 C receptor subtypes was also ruled out. In conclusion, the anti-hypersensitivity activity of ibogalogs in mice is mediated by a mechanism involving 5-HT2A receptor activation.

SB-258585 reduces food motivation while blocking 5-HT6 receptors in the non-human primate striatum.

The interest in new 5-HT6 agents stems from their ability to modulate cognition processing, food motivation and anxiety-like behaviors. While these findings come primarily from rodent studies, no studies on primates have been published. Furthermore, our understanding of where and how they act in the brain remains limited. Although the striatum is involved in all of these processes and expresses the highest levels of 5-HT6 receptors, few studies have focused on it. We thus hypothesized that 5-HT6 receptor blockade would influence food motivation and modulate behavioral expression in non-human primates through striatal 5-HT6 receptors. This study thus aimed to determine the effects of acute administration of the SB-258585 selective 5-HT6 receptor antagonist on the feeding motivation and behaviors of six male macaques. Additionally, we investigated potential 5-HT6 targets using PET imaging to measure 5-HT6 receptor occupancy throughout the brain and striatal subregions. We used a food-choice task paired with spontaneous behavioral observations, checking 5-HT6 receptor occupancy with the specific PET imaging [18F]2FNQ1P radioligand. We demonstrated, for the first time in non-human primates, that modulation of 5-HT6 transmission, most likely through the striatum (the putamen and caudate nucleus), significantly reduces food motivation while exhibiting variable, weaker effects on behavior. While these results are consistent with the literature showing a decrease in food intake in rodents and proposing that 5-HT6 receptor antagonists can be used in obesity treatment, they question the antagonists' anxiolytic potential.

Stress induced exacerbation of Alzheimer's disease brain pathology is thwarted by co-administration of nanowired cerebrolysin and monoclonal amyloid beta peptide antibodies with serotonin 5-HT6 receptor antagonist SB-399885.

Alzheimer's disease is one of the devastating neurodegenerative diseases affecting mankind worldwide with advancing age mainly above 65 years and above causing great misery of life. About more than 7 millions are affected with Alzheimer's disease in America in 2023 resulting in huge burden on health care system and care givers and support for the family. However, no suitable therapeutic measures are available at the moment to enhance quality of life to these patients. Development of Alzheimer's disease may reflect the stress burden of whole life inculcating the disease processes of these neurodegenerative disorders of the central nervous system. Thus, new strategies using nanodelivery of suitable drug therapy including antibodies are needed in exploring neuroprotection in Alzheimer's disease brain pathology. In this chapter role of stress in exacerbating Alzheimer's disease brain pathology is explored and treatment strategies are examined using nanotechnology based on our own investigation. Our observations clearly show that restraint stress significantly exacerbate Alzheimer's disease brain pathology and nanodelivery of a multimodal drug cerebrolysin together with monoclonal antibodies (mAb) to amyloid beta peptide (AßP) together with a serotonin 5-HT6 receptor antagonist SB399885 significantly thwarted Alzheimer's disease brain pathology exacerbated by restraint stress, not reported earlier. The possible mechanisms and future clinical significance is discussed.

5-HT6 receptor antagonists. Design, synthesis, and structure-activity relationship of substituted 2-(1-methyl-4-piperazinyl)pyridines.

In this study, we present the discovery and pharmacological characterization of a new series of 6-piperazinyl-7-azaindoles. These compounds demonstrate potent antagonism and selectivity against the 5-HT6 receptor. Our research primarily focuses on optimizing the lead structure and investigating the structure-activity relationship (SAR) of these compounds. Our main objective is to improve their activity and selectivity against off-target receptors. Overall, our findings contribute to the advancement of novel compounds targeting the 5-HT6 receptor. Compound 29 exhibits significant promise in terms of pharmacological, physicochemical, and ADME (Absorption, Distribution, Metabolism, and Excretion) properties. Consequently, it merits thorough exploration as a potential drug candidate due to its favorable activity profile and successful outcomes in a range of in vivo experiments.

Imidazoles as Serotonin Receptor Modulators for Treatment of Depression: Structural Insights and Structure-Activity Relationship Studies.

Serotoninergic signaling is identified as a crucial player in psychiatric disorders (notably depression), presenting it as a significant therapeutic target for treating such conditions. Inhibitors of serotoninergic signaling (especially selective serotonin reuptake inhibitors (SSRI) or serotonin and norepinephrine reuptake inhibitors (SNRI)) are prominently selected as first-line therapy for the treatment of depression, which benefits via increasing low serotonin levels and norepinephrine by blocking serotonin/norepinephrine reuptake and thereby increasing activity. While developing newer heterocyclic scaffolds to target/modulate the serotonergic systems, imidazole-bearing pharmacophores have emerged. The imidazole-derived pharmacophore already demonstrated unique structural characteristics and an electron-rich environment, ultimately resulting in a diverse range of bioactivities. Therefore, the current manuscript discloses such a specific modification and structural activity relationship (SAR) of attempted derivatization in terms of the serotonergic efficacy of the resultant inhibitor. We also featured a landscape of imidazole-based development, focusing on SAR studies against the serotoninergic system to target depression. This study covers the recent advancements in synthetic methodologies for imidazole derivatives and the development of new molecules having antidepressant activity via modulating serotonergic systems, along with their SAR studies. The focus of the study is to provide structural insights into imidazole-based derivatives as serotonergic system modulators for the treatment of depression.

5-HT6 Receptors Control GABAergic Transmission and CA1 Pyramidal Cell Output of Dorsal Hippocampus.

The blockade of 5-HT6 receptors represents an experimental approach that might ameliorate the memory deficits associated with brain disorders, including Alzheimer's disease and schizophrenia. However, the synaptic mechanism by which 5-HT6 receptors control the GABAergic and glutamatergic synaptic transmission is barely understood. In this study, we demonstrate that pharmacological manipulation of 5-HT6 receptors with the specific agonist EMD 386088 (7.4 nM) or the antagonist SB-399885 (300 nM) modulates the field inhibitory postsynaptic potentials of the dorsal hippocampus and controls the strength of the population spike of pyramidal cells. Likewise, pharmacological modulation of 5-HT6 controls the magnitude of paired-pulse inhibition, a phenomenon mediated by GABAergic interneurons acting via GABAA receptors of pyramidal cells. The effects of pharmacological manipulation of the 5-HT6 receptor were limited to GABAergic transmission and did not affect the strength of field excitatory postsynaptic potentials mediated by the Schaffer collaterals axons. Lastly, in a modified version of the Pavlovian autoshaping task that requires the activation of the hippocampal formation, we demonstrated that the anti-amnesic effect induced by the blockade of the 5-HT6 receptor is prevented when the GAT1 transporter is blocked, suggesting that modulation of GABAergic transmission is required for the anti-amnesic properties of 5-HT6 receptor antagonists.

Hydrophobicity modulation via the substituents at positions 2 and 4 of 1,3,5-triazine to enhance therapeutic ability against Alzheimer's disease for potent serotonin 5-HT6R agents.

Alzheimer's disease (AD), a neurodegenerative disorder with a complex aetiology, is the most common memory dysfunction particularly affecting the elderly. Various protein targets have been classified to be involved in the AD treatment, including 5-HT6 receptor (5-HT6R). So far, the 5-HT6R ligands obtained by our research group have become a good basis for hydrophobicity modulation to give a chance for more effective action toward AD by additional influence on target enzymes, e.g. cyclin-dependent kinase 5 (CDK5). In the search for 5-HT6R agents with additional inhibitory action on the enzyme, a series of 25 new 1,3,5-triazines (7-31) as modifications of lead, 4-[1-(2,5-dichlorophenoxy)propyl]-6-(4-methylpiperazin-1-yl)-1,3,5-triazine-2-amine (6), was rationally designed. Molecular modelling, synthesis, crystallographic studies, in vitro biological assays and behavioral studies in vivo were performed. The new triazines showed high affinity (Ki < 100 nM) and selectivity for 5-HT6R. The most effective one, 4-[1-(2,5-difluorophenoxy)propyl]-6-(4-methylpiperazin-1-yl)-1,3,5-triazine-2-amine (8), exhibited the strong antagonistic action towards 5-HT6R (Ki = 5 nM, pKb = 8.16), had an impact on the memory processes in the Novel Object Recognition test and displayed anxiolytic-like activity in the Elevated Plus Maze test in rats. Moreover, it had the antiplatelet effect as well as very good permeability (PAMPA model), high metabolic stability (RLMs) and satisfactory safety in vitro. Although the CDK5 inhibitory effects in vitro for the tested compounds (8, 10, 14, 18, 26-31) missed the potency expected from in silico simulations, the novel antagonist (8) with a very satisfying pharmacological and ADMET profile can serve as a new lead structure in further searches for innovative therapy against AD with accompanying symptoms.

Differential Contribution of 5-HT4, 5-HT5, and 5-HT6 Receptors to Acute Pruriceptive Processing Induced by Chloroquine and Histamine in Mice.

The involvement of serotonin (5-HT) and/or noradrenaline in acute pruriceptive processing in the central nervous system (CNS) has been reported using antidepressants, such as milnacipran, a serotonin and noradrenaline reuptake inhibitor, and mirtazapine, a noradrenergic and specific serotonergic antidepressant; however, the roles of 5-HT receptor family in acute pruriceptive processing have not been fully elucidated in the CNS. In the present study, scratching behavior induced by chloroquine (CQ) was ameliorated by milnacipran or mirtazapine, and these effects were reversed by SB207266, a 5-HT4 antagonist, or SB258585, a 5-HT6 antagonist, but not by SB258585, a 5-HT5 antagonist. Moreover, CQ-induced scratches were mitigated by intrathecal injection of 5-HT4 agonists, such as BIMU8 and ML10302, and the 5-HT6 agonist, WAY208466. Conversely, histamine-induced scratches were not affected by the 5-HT4 agonists or a 5-HT6 agonist. Similarly, the amelioration of histamine-induced scratches by these antidepressants was not reversed by the 5-HT4, 5-HT5, or 5-HT6 receptor antagonist. Therefore, 5-HT is involved in the amelioration of CQ-induced scratches by milnacipran and mirtazapine, and 5-HT4, 5-HT5, and 5-HT6 receptors play differential roles in acute pruriceptive processing after administration of CQ or histamine.

Synthesis, computational and experimental pharmacological studies for (thio)ether-triazine 5-HT6R ligands with noticeable action on AChE/BChE and chalcogen-dependent intrinsic activity in search for new class of drugs against Alzheimer's disease.

Alzheimer's disease is becoming a growing problem increasing at a tremendous rate. Serotonin 5-HT6 receptors appear to be a particularly attractive target from a therapeutic perspective, due to their involvement not only in cognitive processes, but also in depression and psychosis. In this work, we present the synthesis and broad biological characterization of a new series of 18 compounds with a unique 1,3,5-triazine backbone, as potent 5-HT6 receptor ligands. The main aim of this research is to compare the biological activity of the newly synthesized sulfur derivatives with their oxygen analogues and their N-demethylated O- and S-metabolites obtained for the first time. Most of the new triazines displayed high affinity (Ki < 200 nM) and selectivity towards 5-HT6R, with respect to 5-HT2AR, 5-HT7R, and D2R, in the radioligand binding assays. For selected, active compounds crystallographic studies, functional bioassays, and ADME-Tox profile in vitro were performed. The exciting novelty is that the sulfur derivatives exhibit an agonistic mode of action contrary to all other compounds obtained to date in this chemical class herein and previously reported. Advanced computational studies indicated that this intriguing functional shift might be caused by presence of chalcogen bonds formed only by the sulfur atom. In addition, the N-demethylated derivatives have emerged highly potent antioxidants and, moreover, show a significant improvement in metabolic stability compared to the parent structures. The cholinesterase study present micromolar inhibitory AChE and BChE activity for both 5-HT6 agonist 19 and potent antagonist 5. Finally, the behavioral experiments of compound 19 demonstrated its antidepressant-like properties and slight ability to improve cognitive deficits, without inducing memory impairments by itself. Described pharmacological properties of both compounds (5 and 19) allow to give a design clue for the development of multitarget compounds with 5-HT6 (both agonist and antagonist)/AChE and/or BChE mechanism in the group of 1,3,5-triazine derivatives.

Safety, tolerability, and preliminary efficacy of SYN120, a dual 5-HT6/5-HT2A antagonist, for the treatment of Parkinson disease dementia: A randomized, controlled, proof-of-concept trial.

BACKGROUND: SYN120 is a dual serotonin receptor (5-HT6/5-HT2A) antagonist hypothesized to improve cognition and psychiatric symptoms. OBJECTIVES: We evaluated the safety, tolerability, and efficacy of SYN120 in patients with Parkinson disease dementia (PDD). METHODS: In a multicenter, double-blind, parallel-group, 16-week phase 2a proof-of-concept trial in PDD with concomitant cholinesterase inhibitor use, eligible patients were randomized to oral SYN120 (100 mg/day) or placebo. Adverse events (AEs), Unified Parkinson's Disease Rating Scale (UPDRS) scores, and discontinuations assessed safety and tolerability. The primary and key secondary efficacy measures were the Cognitive Drug Research (CDR) computerized assessment system Continuity of Attention and Quality of Episodic Memory scores. Other efficacy measures were: Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog), Alzheimer's Disease Cooperative Study-Clinician's Global Impression of Change (ADCS-CGIC), Brief Penn Parkinson's Daily Activity Questionnaire-15 (PDAQ-15), Scales for Outcomes in Parkinson's Disease-Sleep Scale (SCOPA-Sleep), and Neuropsychiatric Inventory (NPI). RESULTS: Eighty-two patients were randomized to SYN120 (N = 38) or placebo (N = 44), AEs occurred in 74% and 77% of patients, and treatment discontinuation in both groups was 16%. Nausea and vomiting were more frequent, and motor symptoms (UPDRS) worsened in the SYN120 group. At week 16, the SYN120 and placebo groups did not differ significantly for any cognitive assessment. Cognitive activities of daily living (PDAQ-15) and the NPI-Apathy/Indifference scores improved nominally in the SYN120 group compared with placebo (unadjusted p = 0.029 and 0.028). CONCLUSIONS: SYN120 was adequately tolerated, mild worsening of motor symptoms was noted and it did not improve cognition in PDD patients. Its potential benefits for cognitive activities of daily living and apathy warrant further study. REGISTRATION: Clinicaltrials.gov as NCT02258152.

Selective 5-HT6 Receptor Ligands (Agonist and Antagonist) Show Different Effects on Antipsychotic Drug-Induced Metabolic Dysfunctions in Rats.

It is estimated that in patients taking antipsychotic drugs (APDs), metabolic syndrome occurs 2-3 times more often than in the general population. It manifests itself in abdominal obesity, elevated glucose concentration, and dyslipidemia. Despite the high prevalence of this disorder, only a small percentage of patients receive appropriate and effective treatment, and none of the available methods for preventing or treating APD-induced metabolic side effects is satisfactory. A promising supplement to antipsychotic therapy appears to be ligands of the serotonin 6 (5-HT6) receptor. The present study aimed to examine the chronic effects of the selected APDs (haloperidol, risperidone, olanzapine), administered alone and in combination with a selective 5-HT6 agonist (WAY-181187) or antagonist (SB-742457), on weight gain, food intake, serum lipid profile, glucose level, and a spectrum of hormones derived from adipose (leptin, adiponectin) and gastrointestinal (insulin, ghrelin) tissue in rats. SB-742457 inhibited increased weight gain and alleviated hyperglycemia induced by APDs more strongly than did WAY-181187, but also intensified dyslipidemia. WAY-181187 tended to improve the lipid profile, but increased the glucose level. The greatest benefits were obtained when WAY-181187 or SB-742457 were co-administered with haloperidol. It is difficult to assess whether the modification of the serum levels of insulin, leptin, ghrelin, and adiponectin depended on the treatment applied or other drug-independent factors; therefore, further research is needed.

Dual Molecules Targeting 5-HT6 and GABA-A Receptors as a New Approach to Combat Depression Associated with Neuroinflammation.

While monoaminergic deficits are evident in all depressed patients, nonresponders are characterized by impaired GABA-ergic signaling and the simultaneous presence of the inflammatory component. Pharmacological agents able to curb pathological immune responses and modulate ineffective GABA-ergic neurotransmission are thought to improve therapeutic outcomes in the treatment-resistant subgroup of depressed patients. Here, we report on a set of dually acting molecules designed to simultaneously modulate GABA-A and 5-HT6 receptor activity. The serotonin 5-HT6 receptor was chosen as a complementary molecular target, due to its promising antidepressant-like activities reported in animal studies. Within the study we identified that lead molecule 16 showed a desirable receptor profile and physicochemical properties. In pharmacological studies, 16 was able to reduce the secretion of proinflammatory cytokines and decrease oxidative stress markers. In animal studies, 16 exerted antidepressant-like activity deriving from a synergic interplay between 5-HT6 and GABA-A receptors. Altogether, the presented findings point to hybrid 16 as an interesting tool that interacts with pharmacologically relevant targets, matching the pathological dysfunction of depression associated with neuroinflammation.

The gut-brain axis: Effect of electroacupuncture pretreatment on learning, memory, and JNK signaling in D-galactose-induced AD-like rats.

Objectives: To examine the effect and potential mechanism of electroacupuncture (EA) pretreatment in spatial learning, memory, gut microbiota, and JNK signaling in D-galactose-induced AD-like rats. Materials and Methods: The AD-like rat model was generated by intraperitoneal injection of D-galactose. Morris water maze was used to determine spatial learning and memory ability, Real-time PCR to determine intestinal flora levels, ELISA to determine tryptophan (Trp) and 5-HT levels in the colon and hippocampal tissues, immunofluorescence to determine 5-HT levels in enterochromaffin cells (ECs), and immunoblotting to determine JNK signaling protein levels in hippocampal tissues. Results: Electroacupuncture pretreatment significantly reduced escape latency and prolonged exploration time in the target quadrant, and significantly increased the relative DNA abundance of Lactobacillus and Bifidobacterium. Meanwhile, electroacupuncture pretreatment also reduced colonic 5-HT levels and increased hippocampal 5-HT levels. Moreover, electroacupuncture pretreatment significantly inhibited hippocampal JNK pathway-related protein expression, including 5-HT6R, JNK, p-JUNK, c-JUN, and p-c-Jun. And the combination of GV20 and ST36 was more effective than single acupoints. Conclusion: Electroacupuncture pretreatment improved the learning and memory ability of D-galactose-induced AD-like model rats, changed the gut microbiota composition, and the mechanism may be related to the gut-brain axis and the JNK signaling pathway. In addition, the combination of GV20 and ST36 could further enhance the efficacy.

Novel thienocycloalkylpyridazinones as useful scaffolds for acetylcholinesterase inhibition and serotonin 5-HT6 receptor interaction.

A library of eighteen thienocycloalkylpyridazinones was synthesized for human acetylcholinesterase (hAChE) and butyrylcholinesterase (hBChE) inhibition and serotonin 5-HT6 receptor subtype interaction by following a multitarget-directed ligand approach (MTDL), as a suitable strategy for treatment of Alzheimer's disease (AD). The novel compounds featured a tricyclic scaffold, namely thieno[3,2-h]cinnolinone, thienocyclopentapyridazinone and thienocycloheptapyridazinone, connected through alkyl chains of variable length to proper amine moieties, most often represented by N-benzylpiperazine or 1-(phenylsulfonyl)-4-(piperazin-1-ylmethyl)-1H-indole as structural elements addressing AChE and 5-HT6 interaction, respectively. Our study highlighted the versatility of thienocycloalkylpyridazinones as useful architectures for AChE interaction, with several N-benzylpiperazine-based analogues emerging as potent and selective hAChE inhibitors with IC50 in the 0.17-1.23 µM range, exhibiting low to poor activity for hBChE (IC50 = 4.13-9.70 µM). The introduction of 5-HT6 structural moiety phenylsulfonylindole in place of N-benzylpiperazine, in tandem with a pentamethylene linker, gave potent 5-HT6 thieno[3,2-h]cinnolinone and thienocyclopentapyridazinone-based ligands both displaying hAChE inhibition in the low micromolar range and unappreciable activity towards hBChE. While docking studies provided a rational structural explanation for AChE/BChE enzyme and 5-HT6 receptor interaction, in silico prediction of ADME properties of tested compounds suggested further optimization for development of such compounds in the field of MTDL for AD.

Structural insights into constitutive activity of 5-HT6 receptor.

While most therapeutic research on G-protein-coupled receptors (GPCRs) focuses on receptor activation by (endogenous) agonists, significant therapeutic potential exists through agonist-independent intrinsic constitutive activity that can occur in various physiological and pathophysiological settings. For example, inhibiting the constitutive activity of 5-HT6R-a receptor that is found almost exclusively in the brain and mediates excitatory neurotransmission-has demonstrated a therapeutic effect on cognitive/memory impairment associated with several neuropsychiatric disorders. However, the structural basis of such constitutive activity remains unclear. Here, we present a cryo-EM structure of serotonin-bound human 5-HT6R-Gs heterotrimer at 3.0-Å resolution. Detailed analyses of the structure complemented by comprehensive interrogation of signaling illuminate key structural determinants essential for constitutive 5-HT6R activity. Additional structure-guided mutagenesis leads to a nanobody mimic Gαs for 5-HT6R that can reduce its constitutive activity. Given the importance of 5-HT6R for a large number of neuropsychiatric disorders, insights derived from these studies will accelerate the design of more effective medications, and shed light on the molecular basis of constitutive activity.

Progress in Investigational Agents Targeting Serotonin-6 Receptors for the Treatment of Brain Disorders.

Serotonin (5-HT) plays an important role in the regulation of several basic functions of the central and peripheral nervous system. Among the 5-HT receptors, serotonin-6 (5-HT6) receptor has been an area of substantial research. 5-HT6 receptor is a G-protein-coupled receptor mediating its effects through diverse signaling pathways. Exceptional features of the receptors fueling drug discovery efforts include unique localization and specific distribution in the brain regions having a role in learning, memory, mood, and behavior, and the affinity of several clinically used psychotropic agents. Although non-clinical data suggest that both agonist and antagonist may have similar behavioral effects, most of the agents that entered clinical evaluation were antagonists. Schizophrenia was the initial target; more recently, cognitive deficits associated with Alzheimer's disease (AD) or other neurological disorders has been the target for clinically evaluated 5-HT6 receptor antagonists. Several 5-HT6 receptor antagonists (idalopirdine, intepirdine and latrepirdine) showed efficacy in alleviating cognitive deficits associated with AD in the proof-of-concept clinical studies; however, the outcomes of the subsequent phase 3 studies were largely disappointing. The observations from both non-clinical and clinical studies suggest that 5-HT6 receptor antagonists may have a role in the management of neuropsychiatric symptoms in dementia. Masupirdine, a selective 5-HT6 receptor antagonist, reduced agitation/aggression-like behaviors in animal models, and a post hoc analysis of a phase 2 trial suggested potential beneficial effects on agitation/aggression and psychosis in AD. This agent will be assessed in additional trials, and the outcome of the trials will inform the use of 5-HT6 receptor antagonists in the treatment of agitation in dementia of the Alzheimer's type.

The Constitutive Activity of Spinal 5-HT6 Receptors Contributes to Diabetic Neuropathic Pain in Rats.

Diabetic neuropathy is often associated with chronic pain. Serotonin type 6 (5-HT6) receptor ligands, particularly inverse agonists, have strong analgesic potential and may be new candidates for treating diabetic neuropathic pain and associated co-morbid cognitive deficits. The current study addressed the involvement of 5-HT6 receptor constitutive activity and mTOR signaling in an experimental model of diabetic neuropathic pain induced by streptozocin (STZ) injection in the rat. Here, we show that mechanical hyperalgesia and associated cognitive deficits are suppressed by the administration of 5-HT6 receptor inverse agonists or rapamycin. The 5-HT6 receptor ligands also reduced tactile allodynia in traumatic and toxic neuropathic pain induced by spinal nerve ligation and oxaliplatin injection. Furthermore, both painful and co-morbid cognitive symptoms in diabetic rats are reduced by intrathecal delivery of a cell-penetrating peptide that disrupts 5-HT6 receptor-mTOR physical interaction. These findings demonstrate the deleterious influence of the constitutive activity of spinal 5-HT6 receptors upon painful and cognitive symptoms in diabetic neuropathic pains of different etiologies. They suggest that targeting the constitutive activity of 5-HT6 receptors with inverse agonists or disrupting the 5-HT6 receptor-mTOR interaction might be valuable strategies for the alleviation of diabetic neuropathic pain and cognitive co-morbidities.