Potent 5-HT3 Research Articles

Design of an innovative nanovehicle to enhance brain permeability of a novel 5-HT6 receptor antagonist

An innovative nanovehicle based on lipid nanocapsules (LNC) was designed to facilitate the passage of a new 5-HT6 receptor antagonist, namely PUC-10, through the blood-brain barrier. PUC-10 is a new synthetic N-arylsulfonylindole that has demonstrated potent 5-HT6 receptor antagonist activity, but it exhibits poor solubility in water, which indicates limited absorption. The lipid nanocapsules designed had a nanometric size (53 nm), a monomodal distribution (PI<0.2), a negative Z potential (−17 ± 7 mV) and allowed efficient PUC-10 encapsulation (74 %). Furthermore, the LNC demonstrated to be stable for at least 4 weeks at 4 °C (storage conditions), for at least 4 h in DMEM at pH 7.4, and for 18 h in water with 5 % DMSO, with both latter conditions maintained at 37 °C. They also demonstrated that cell viability was not affected at the different concentrations studied. Finally, in vitro studies that simulate the blood brain barrier (PAMPA-BBB) demonstrated that the nanoencapsulation of PUC-10 promoted their penetration through the blood-brain barrier, with a calculated permeability of 1.3 × 10−8 cm/s, compared to the null permeability exhibited by non-nanoencapsulated PUC-10.

Synthesis and Structure-Activity Relationships of 2,5-Dimethoxy-4-Substituted Phenethylamines and the Discovery of CYB210010: A Potent, Orally Bioavailable and Long-Acting Serotonin 5-HT2 Receptor Agonist.

Structure-activity studies of 4-substituted-2,5-dimethoxyphenethylamines led to the discovery of 2,5-dimethoxy-4-thiotrifluoromethylphenethylamines, including CYB210010, a potent and long-acting serotonin 5-HT2 receptor agonist. CYB210010 exhibited high agonist potency at 5-HT2A and 5-HT2C receptors, modest selectivity over 5-HT2B, 5-HT1A, 5-HT6, and adrenergic α2A receptors, and lacked activity at monoamine transporters and over 70 other proteins. CYB210010 (0.1-3 mg/kg) elicited a head-twitch response (HTR) and could be administered subchronically at threshold doses without behavioral tolerance. CYB210010 was orally bioavailable in three species, readily and preferentially crossed into the CNS, engaged frontal cortex 5-HT2A receptors, and increased the expression of genes involved in neuroplasticity in the frontal cortex. CYB210010 represents a new tool molecule for investigating the therapeutic potential of 5-HT2 receptor activation. In addition, several other compounds with high 5-HT2A receptor potency, yet with little or no HTR activity, were discovered, providing the groundwork for the development of nonpsychedelic 5-HT2A receptor ligands.

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.

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.

Investigating CNS distribution of PF-05212377, a P-glycoprotein substrate, by translation of 5-HT6 receptor occupancy from non-human primates to humans.

PF-05212377 (SAM760) is a potent and selective 5-HT6 antagonist, previously under development for the treatment of Alzheimer's disease. In vitro, PF-05212377 was determined to be a P-gp/non-BCRP human transporter substrate. Species differences were observed in the in vivo brain penetration of PF-05212377 with a ratio of the unbound concentration in brain/unbound concentration in plasma (Cbu /Cpu ) of 0.05 in rat and 0.64 in non-human primates (NHP). Based on pre-clinical evidence, brain penetration and target engagement of PF-05212377 was confirmed in NHP using positron emission tomography (PET) measured 5-HT6 receptor occupancy (%RO). The NHP Cpu EC50 of PF-05212377 was 0.31nM (consistent with the in vitro human 5HT6 Ki : 0.32nM). P-gp has been reported to be expressed in higher abundance at the rat BBB and in similar abundance at the BBB of non-human primates and human; brain penetration of PF-05212377 in humans was postulated to be similar to that in non-human primates. In humans, PF-05212377 demonstrated dose and concentration dependent increases in 5-HT6 RO; maximal 5-HT6 RO of ∼80% was measured in humans at doses of ≥15mg with an estimated unbound plasma EC50 of 0.37nM (which was similar to the in vitro human 5HT6 binding Ki 0.32nM). In conclusion, cumulative evidence from NHP and human PET RO assessments confirmed that NHP is more appropriate than the rat for the prediction of human brain penetration of PF-05212377, a P-gp/non-BCRP substrate. Clinical trial number: NCT01258751.

Quetiapine Fumarate: A Review of Analytical Methods.

Atypical antipsychotics are newer second-generation antipsychotics with weak dopamine type 2 blocking but potent 5-HT2 antagonistic activity. They are considered first-line treatments for schizophrenia and gradually replace typical antipsychotics. Extrapyramidal side effects are minimal, and they tend to improve impaired cognitive function in psychotics. Quetiapine fumarate is an atypical antipsychotic drug used to treat schizophrenia, mania and depression in people with bipolar disorder combined with other drugs or alone. Quetiapine was developed in 1985 and approved for medical use in the USA in 1997. Thorough computer-aided literature, surveys revealed that numerous analytical methods were reported over the years. The present study reviews analytical methods with their validation parameters published during the last 22years (1999-2021) either as a single entity or combination in dosage form, and determination from biological samples. Novel strategies for increasing separation quality, such as QbD analysis and green spectroscopy, were discovered during the evaluation, and this review can be utilized for further research reference.

Serotonin 5-HT6 Receptor Ligands and Butyrylcholinesterase Inhibitors Displaying Antioxidant Activity-Design, Synthesis and Biological Evaluation of Multifunctional Agents against Alzheimer's Disease.

Neurodegeneration leading to Alzheimer’s disease results from a complex interplay of a variety of processes including misfolding and aggregation of amyloid beta and tau proteins, neuroinflammation or oxidative stress. Therefore, to address more than one of these, drug discovery programmes focus on the development of multifunctional ligands, preferably with disease-modifying and symptoms-reducing potential. Following this idea, herein we present the design and synthesis of multifunctional ligands and biological evaluation of their 5-HT6 receptor affinity (radioligand binding assay), cholinesterase inhibitory activity (spectroscopic Ellman’s assay), antioxidant activity (ABTS assay) and metal-chelating properties, as well as a preliminary ADMET properties evaluation. Based on the results we selected compound 14 as a well-balanced and potent 5-HT6 receptor ligand (Ki = 22 nM) and human BuChE inhibitor (IC50 = 16 nM) with antioxidant potential expressed as a reduction of ABTS radicals by 35% (150 μM). The study also revealed additional metal-chelating properties of compounds 15 and 18. The presented compounds modulating Alzheimer’s disease-related processes might be further developed as multifunctional ligands against the disease.

Effect of Concurrent Use of Memantine on the Efficacy of Masupirdine (SUVN-502): A Post Hoc Analysis of a Phase2 Randomized Placebo-Controlled Study.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive deterioration in cognition, memory and activities of daily living. Selective blockade of serotonin-6 (5-HT6) receptors, which are exclusively localized to the central nervous system, is reported to play an important role in learning and memory. Masupirdine is a potent and selective 5-HT6 receptor antagonist with pro-cognitive properties in animal models of cognition. The efficacy and safety of masupirdine were evaluated in patients with moderate AD concurrently treated with donepezil and memantine. A total of 564 patients were randomized in a 1:1:1 ratio. The study consisted of a 26-week double-blind treatment period. The primary efficacy outcome was the 11-item cognitive subscale of the Alzheimer's Disease Assessment Scale (ADAS-Cog 11). Changes from baseline were analyzed using a mixed effects model for repeated measures (MMRM). In exploratory post hoc analyses, patients were subdivided based on the use of memantine dosage forms and memantine plasma concentrations, to evaluate the impact of memantine on the efficacy of masupirdine. In an exploratory post hoc analysis, less worsening in cognition (ADAS-Cog 11 scores) was observed with masupirdine treatment as compared with placebo in patients whose trough memantine plasma concentrations were ≤ 100ng/mL. Although prespecified study endpoints of the phase2 study were not met, these exploratory post hoc subgroup observations are hypothesis-generating and suggest that the efficacy of masupirdine was adversely affected by concurrent therapy with memantine. Further assessment of masupirdine to determine its potential role as a treatment option for cognitive deficits associated with AD is warranted. The study was registered at ClinicalTrials.gov (NCT02580305).

Novel difluoromethylated 1-(phenylsulfonyl)-4-(piperazin-1-yl)-1H-indole derivatives as potent 5-HT6 receptor antagonist with AMDE-improving properties: Design, synthesis, and biological evaluation

Serotonin type 6 receptor (5-HT6R) has been considered as a particularly promising target for treating cognitive deficits due to the positive effects of its antagonists in a wide range of memory impairment paradigms. In this study, we designed, synthesized, and evaluated a series of 3-(difluoromethyl)-1-(phenylsulfonyl)-4-(piperazin-1-yl)-1H-indole derivatives as potent 5-HT6R antagonists. Structure-activity relationship study led to the discovery of five compounds (6a, 6m, 6n, 6p and 6q) with potent binding affinity at 5-HT6R. In in vivo pharmacokinetic studies in rats, 6p showed 30-folds higher AUC (267 ng·h/mL) and better bioavailability (34.39 %) than those of 6a (9.37 ng·h/mL and 5.95 %, respectively) by using difluoromethyl group replacing a methyl group. Besides, 6p showed good brain penetration with Cb/Cp ratio ∼6. Based on the pharmacological characteristics and favorable pharmacokinetic properties, 6p was further chosen to evaluate cognition-enhancing property in the preliminary in vivo models. It is identified that 6p not only prevented scopolamine-induced learning deficits in the novel object recognition test but also rescued the recognition barrier caused by scopolamine. Finally, the combination of 6p and donepezil produces synergistic effects on increasing the acetylcholine levels in the intracerebral hippocampus. In light of these findings, we propose 6p as a potential 5-HT6R antagonist for treatment of AD.

An exit beyond the pharmacophore model for 5-HT6R agents - a new strategy to gain dual 5-HT6/5-HT2A action for triazine derivatives with procognitive potential

This research allowed us to find the first highly potent 5-HT6/5-HT2A receptor (5-HT6/5-HT2AR) dual antagonists in a group of 1,3,5-triazine compounds as a result of an exit beyond the hydrophobic feature of the pharmacophore model for 5-HT6R antagonists. Design and synthesis of the series (2–16) of new O- and S-containing ether derivatives of 1,3,5-triazines with the double-ring aromatic region have been performed. The new compounds were examined within the comprehensive pharmacological screening, including: radioligand binding assays, functional and ADMET studies in vitro as well as behavioral tests in rats. Crystallographic aspects and computer-aided structure–activity relationship were analyzed, as well. The comprehensive approach led to selection of compound 12 (4-(4-methylpiperazin-1-yl)-6-(2-(naphthalen-2-ylthio)propan-2-yl)-1,3,5-triazin-2-amine) with the most significant dual 5-HT6/5-HT2AR antagonistic action (5-HT6R Ki = 11 nM, 5-HT2AR Ki = 39 nM). Moreover, the compound 12 has satisfactory ADMETox properties in vitro, i.e.: the high permeability through biological membranes, high metabolic stability, neither mutagenic nor hepatotoxic effects, and moderate ability to inhibit CYP3A4. Above all, 12 showed ability to reverse the pharmacologically-induced (MK-801) memory impairment at low doses (1–3 mg/kg) in Novel Object Recognition (NOR) test in rats. Our results indicate a promising potency of dual 5-HT6/5-HT2AR antagonism in the search for novel strategy to fight Alzheimer’s disease, which remains an unmet clinical need.

Clinical and Nonclinical Disposition and In Vitro Drug-Drug Interaction Potential of Felcisetrag, a Highly Selective and Potent 5-HT4 Receptor Agonist.

Background and ObjectiveFelcisetrag (previously TAK-954 or TD-8954) is a highly selective and potent 5-HT4 receptor agonist in clinical development for prophylaxis and treatment of postoperative gastrointestinal dysfunction (POGD). The rat, dog, and human absorption, distribution, metabolism, and excretion (ADME) properties of felcisetrag were investigated.MethodsThe metabolism and victim and perpetrator drug interaction potentials towards cytochrome P450s (CYP) and transporters were determined using in vitro models. The excretion, metabolite profile, and pharmacokinetics were determined during unlabeled and radiolabeled ADME studies in rat and dog for comparison with human. Due to a low clinical dose (0.5 mg) and radioactivity (~ 1.5 μCi), a combination of liquid scintillation counting and accelerator mass spectrometry was used for analysis of samples in this study.ResultsThe ADME properties, including metabolite profile, for felcisetrag are generally conserved across species. Felcisetrag is primarily cleared through renal excretion (0.443) and metabolism in humans (0.420), with intact parent as the predominant species in circulation. There are multiple metabolites, each representing < 10% of the circulating radioactivity, confirming no metabolites in safety testing (MIST) liabilities. Metabolites were also detected in animals. The potential for major CYP- and transporter-based drug–drug interaction (DDI) of felcisetrag as a victim or perpetrator is considered to be low.ConclusionsFelcisetrag is primarily cleared in humans through renal excretion. Although the metabolism of felcisetrag is primarily through CYP3A, the potential for clinically relevant DDI as a victim is significantly reduced as metabolism plays a minor role in the overall clearance.Graphical Supplementary InformationThe online version contains supplementary material available at 10.1007/s13318-021-00751-8.

Effect of ramosetron, a 5-HT3 receptor antagonist on the severity of seizures and memory impairment in electrical amygdala kindled rats

The entorhinal cortex (EC) plays a pivotal role in epileptogenesis and seizures. EC expresses high density of serotonergic receptors, especially 5-HT3 receptors. Cognitive impairment is common among people with epilepsy. The present study investigated the role of 5-HT3 receptor on the severity of seizures and learning and memory impairment by electrical kindling of amygdala in rats. The amygdala kindling was conducted in a chronic kindling manner in male Wistar rats. In fully kindled animals, ramosetron (as a potent and selective 5-HT3 receptor antagonist) was microinjected unilaterally (ad doses of 1, 10 or 100 µg/0.5 µl) into the EC 5 min before the novel object recognition (NOR) and Y-maze tests or kindling stimulations. Applying ramosetron at the concentration of 100 μg/0.5 µl (but not at 1 and 10 µg/0.5 µl) reduced afterdischarge (AD) duration and increased stage 4 latency in the kindled rats. Moreover, the obtained data from the NOR test showed that treatment by ramosetron (10 and 100 µg/0.5 µl) increased the discrimination index in the fully kindled animals. Microinjection of ramosetron (10 and 100 µg/0.5 µl) in fully kindled animals reversed the kindling induced changes in the percentage of spontaneous alternation in Y-maze task. The findings demonstrated an anticonvulsant role for a selective 5-HT3 receptor antagonist microinjected into the EC, therefore, suggesting an excitatory role for the EC 5-HT3 receptors in the amygdala kindling model of epilepsy. This anticonvulsive effect was accompanied with a restoring effect on cognitive behavior in NOR and Y-maze tests.

SUVN-D4010: A serotonin-4 receptor partial agonist for the treatment of cognitive disorders.

Memory impairments are clinical symptoms of a wide range of neurodegenerative diseases, and natural physiological process such as ageing. SUVN-D4010 is an investigational clinical candidate which acts by modulating 5-HT4 receptors. Experimental evidences from animals and humans suggest that 5-HT4 receptor activation holds promise for the treatment of cognitive impairment. Additionally, activation of 5-HT4 receptor also modulates mood. The present investigation is to characterize SUVN-D4010 and evaluate its drug-like properties. SUVN-D4010 has been studied for its affinity and functional activity at 5-HT4 receptor using in vitro methods. ADME properties were evaluated using in vitro and in vivo methods. SUVN-D4010 was studied for its effects on learning and memory using social and object recognition tasks. The effects on the neurotransmitters were monitored using the brain microdialysis technique in rats. The effects on the beta amyloid processing were studied using in vitro and in vivo systems. The safety and tolerability was evaluated in both animals and humans. SUVN-D4010 showed potent affinity towards 5-HT4 receptor when tested using radioligand binding and cell based reporter gene assay. SUVN-D4010 has minimal binding over 70 target sites (at 1 µM, Caliper) including GPCRs, transporters, ion channels, peptides, steroids, second messengers, growth factors and prostaglandins. SUVN-D4010 is orally bioavailable with good brain penetration and CSF concentrations. The likelihood of drug-drug interaction of SUVN-D4010 as an inhibitor/ inducer is remote. No unique metabolites were identified in non-clinical and clinical samples. SUVN-D4010 showed procognitve effects at doses ranging from 0.3 to 3 mg/kg, p.o. SUVN-D4010 significantly increased extracellular acetylcholine levels as a standalone, or treatment adjunct to donepezil. SUVN-D4010 promoted non-amyloidogenic APPα processing and reduced toxic Aβ load. SUVN-D4010 was found to be safe and well tolerated in healthy human volunteers. SUVN-D4010 is a potent, selective, orally bioavailable and brain penetrant 5-HT4 receptor partial agonist with potential utility in treatment of cognitive disorders.

Design and synthesis of new potent 5-HT7 receptor ligands as a candidate for the treatment of central nervous system diseases

Owing to their multifunctional pharmacological profiles (including dual 5-HT1A/5-HT7 action), arylpiperazine derivatives are widely used for treating central nervous system diseases including the depression or neuropathic pain. Herein we describe the design, synthesis and evaluation of biological activity of novel 5-HT7 ligands derived of 2,4,6-triamino-1,3,5-triazine. The studied compounds showed affinity and high selectively towards 5-HT7 receptor with the two most active compounds 34 (Ki = 61 nM), 22 (Ki = 109 nM) showing good metabolic stability and moderate affinity to CYP3A4 isoenzyme. Compound 22 had high hepatotoxicity at a concentration below 50 μM, while compound 34 showed low hepatotoxicity even at a concentration above 50 μM.

The Phenoxyalkyltriazine Antagonists for 5-HT6 Receptor with Promising Procognitive and Pharmacokinetic Properties In Vivo in Search for a Novel Therapeutic Approach to Dementia Diseases.

Among the serotonin receptors, one of the most recently discovered 5-HT6 subtype is an important protein target and its ligands may play a key role in the innovative treatment of cognitive disorders. However, none of its selective ligands have reached the pharmaceutical market yet. Recently, a new chemical class of potent 5-HT6 receptor agents, the 1,3,5-triazine-piperazine derivatives, has been synthesized. Three members, the ortho and meta dichloro- (1,2) and the unsubstituted phenyl (3) derivatives, proved to be of special interest due to their high affinities (1,2) and selectivity (3) toward 5-HT6 receptor. Thus, a broader pharmacological profile for 1–3, including comprehensive screening of the receptor selectivity and drug-like parameters in vitro as well as both, pharmacokinetic and pharmacodynamic properties in vivo, have been investigated within this study. A comprehensive analysis of the obtained results indicated significant procognitive-like activity together with beneficial drug-likeness in vitro and pharmacokinetics in vivo profiles for both, (RS)-4-[1-(2,3-dichlorophenoxy)propyl]-6-(4-methylpiperazin-1-yl)-1,3,5-triazin-2-amine (2) and (RS)-4-(4-methylpiperazin-1-yl)-6-(1-phenoxypropyl)-1,3,5-triazin-2-amine (3), but insensibly predominant for compound 2. Nevertheless, both compounds (2 and 3) seem to be good Central Nervous System drug candidates in search for novel therapeutic approach to dementia diseases, based on the 5-HT6 receptor target.

New Drugs on the Horizon for Functional and Motility Gastrointestinal Disorders

New Drugs on the Horizon for Functional and Motility Gastrointestinal Disorders

Pleiotropic prodrugs: Design of a dual butyrylcholinesterase inhibitor and 5-HT6 receptor antagonist with therapeutic interest in Alzheimer's disease.

Beside acetylcholinesterase, butyrylcholinesterase could be considered as a putative target of interest for the symptomatic treatment of Alzheimer's disease (AD). As a result of complexity of AD, no molecule has been approved since 2002. Idalopirdine, a 5-HT6 receptors antagonist, did not show its effectiveness in clinical trial despite its evaluation as adjunct to cholinesterase inhibitors. Pleiotropic molecules, known as multitarget directed ligands (MTDLs) are currently developed to tackle the multifactorial origin of AD. In this context, we have developed a pleiotropic carbamate 7, that behaves as a covalent inhibitor of BuChE (IC50=0.97μM). The latter will deliver after hydrolysis, compound 6, a potent 5-HT6 receptors antagonist (Ki=11.4nM) related to idalopirdine. In silico and invitro evaluation proving our concept were performed completed with first invivo results that demonstrate great promise in restoring working memory.

The Opioid Interactions of the Antipsychotic Medications Risperidone and Amisulpride in Mice and Their Potential Use in the Treatment of Other Non-Psychotic Medical Conditions.

Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage. The opioid epidemic in the USA has highlighted the need for alternative treatments for pain. Following reports on the opioid interactions of various antipsychotic medications, we speculated that the involvement of the opioid system in some of the antipsychotics' mechanism of action may suggest their potential use in the treatment of pain. Risperidone is a neuroleptic with a potent dopamine D2 and serotonin 5-HT2 receptor-blocking activity as well as a high affinity for adrenergic and histamine H1 receptors. Amisulpride is a neuroleptic which selectively blocks dopamine D2 and D3 receptors. Both had a potent antinociceptive effect on ICR mice tested with a tail flick assay. That effect on both medications was antagonized by naloxone, indicating that at least some of the antinociceptive effects were mediated by an opioid mechanism of action. Further investigation found that β-Funaltrexamine hydrochloride (β-FNA), naloxonazine, and nor-Binaltorphimine dihydrochloride (nor-BNI) reversed the antinociceptive effect of both risperidone and amisulpride. Naltrindole at a dose that blocked [D-Pen2,D-Pen5]enkephalin (DPDPE, δ analgesia) blocked notably amisplride effect and only partially reversed that of risperidone. Risperidone induced an antinociceptive effect, implying involvement of μ and κ-opioid and δ-opioid mechanisms. Amisulpride-induced antinociception was mediated through selective involvement of all three opioid receptor subtypes. These findings emphasize the need for clinical trials to assess the possibility of extending the spectrum of medications available for the treatment of pain.

SUVN-502: A PURE 5-HT6 RECEPTOR ANTAGONIST ATTENUATES MEMORY DEFICITS INDUCED BY DIVERSE CHALLENGES

Alzheimer's disease (AD) is a neurodegenerative disorder that destroys the higher anatomical structures of the brain leading to dementia. The 5-HT6 receptor is an attractive target for the development of cognitive enhancers due to its unique localization and pharmacology. 5-HT6 receptor antagonists have been shown to modulate multiple neurotransmitter systems and thereby enhance cognition in preclinical studies. The effect of SUVN-502, a pure 5-HT6 receptor antagonist was evaluated in various rodent models of cognition. The procognitive effects of SUVN-502 were evaluated in object recognition task, the inter trial intervals being 24 or 48 h. SUVN-502 was administered during either acquisition or consolidation or retention phase of memory. The procognitive effects of SUVN-502 on scopolamine induced memory deficits were evaluated using the Morris water maze, radial arm maze and fear conditioning apparatus. SUVN-502 reversed both 24 and 48 h time induced memory deficits in the object recognition task. The memory enhancing effects were also observed when SUVN-502 was administered in any of the three phases of cognition. SUVN-502 reversed scopolamine induced memory deficits in the Morris water maze, radial maze and enhanced freezing time in the fear conditioning task. SUVN-502 reversed a combined scopolamine and MK-801 induced memory deficits in the object recognition task. SUVN-502 is a potent, selective, orally bioavailable and efficacious 5-HT6 receptor antagonist that holds promise in the treatment of dementia associated with hypocholinergic disease conditions such as Alzheimer's disease.

SUVN-502: IN-VITRO PHARMACOLOGICAL PROFILE OF A PURE 5-HT6 RECEPTOR ANTAGONIST

Alzheimer's disease (AD), the most common cause of dementia among older people, is characterized by behavioral disorders and a progressive decline in memory function. Senile plaques, neurofibrillary tangles, and cholinergic dysfunction are major hallmarks of the disease. 5-HT6 receptors appear to be localized in brain areas involved in learning and memory processes. 5-HT6 mediates its effect by modulating multiple cellular signaling pathways and neurotransmitter systems, thereby enhance cognition. During the past 20 years, the 5-HT6 receptor has received increasing attention and become a promising target for improving cognition. The in-vitro pharmacological characteristic of SUVN-502 that selectively binds to 5-HT6 receptor was profiled. Binding of SUVN-502 to 5-HT6 and 5-HT2A receptor was evaluated by in-vitro radioligand binding assay. The functional nature of SUVN-502 was evaluated using 5-HT6 cell based functional assay. Selectivity of SUVN-502 was assessed in a panel of targets inclusive of GPCRs, ion channels, transporters, second messengers, prostaglandins, growth factors/ hormones, enzymes and peptides. SUVN-502 binds to human 5-HT6 receptor with an affinity (Ki) of 2.04 nM when tested in in-vitro radioligand binding assay. SUVN-502 has shown high selectivity (>1000 fold) over 5-HT2A receptor with respect to its affinity at 5-HT6 receptor. SUVN-502 exhibited competitive and reversible antagonist nature when tested in cell based functional assay at human 5-HT6 receptor. SUVN-502 has selectivity of more than 250 fold against over hundred target sites including neurotransmitter related receptors, enzymes, peptides, growth factors/ hormones, ion channels, transporters, steroids, immunological factors, second messengers, and prostaglandins. SUVN-502 is a potent, selective and pure 5-HT6 receptor antagonist that holds promise for the treatment of cognitive deficits associated with Alzheimer's disease.