Serotonin 5-HT3 Receptor Research Articles

Physical interaction between neurofibromin and serotonin 5-HT6 receptor promotes receptor constitutive activity

Active G protein-coupled receptor (GPCR) conformations not only are promoted by agonists but also occur in their absence, leading to constitutive activity. Association of GPCRs with intracellular protein partners might be one of the mechanisms underlying GPCR constitutive activity. Here, we show that serotonin 5 hydroxytryptamine 6 (5-HT6) receptor constitutively activates the Gs/adenylyl cyclase pathway in various cell types, including neurons. Constitutive activity is strongly reduced by silencing expression of the Ras-GTPase activating protein (Ras-GAP) neurofibromin, a 5-HT6 receptor partner. Neurofibromin is a multidomain protein encoded by the NF1 gene, the mutation of which causes Neurofibromatosis type 1 (NF1), a genetic disorder characterized by multiple benign and malignant nervous system tumors and cognitive deficits. Disrupting association of 5-HT6 receptor with neurofibromin Pleckstrin Homology (PH) domain also inhibits receptor constitutive activity, and PH domain expression rescues 5-HT6 receptor-operated cAMP signaling in neurofibromin-deficient cells. Furthermore, PH domains carrying mutations identified in NF1 patients that prevent interaction with the 5-HT6 receptor fail to rescue receptor constitutive activity in neurofibromin-depleted cells. Further supporting a role of neurofibromin in agonist-independent Gs signaling elicited by native receptors, the phosphorylation of cAMP-responsive element-binding protein (CREB) is strongly decreased in prefrontal cortex of Nf1+/- mice compared with WT mice. Moreover, systemic administration of a 5-HT6 receptor inverse agonist reduces CREB phosphorylation in prefrontal cortex of WT mice but not Nf1+/- mice. Collectively, these findings suggest that disrupting 5-HT6 receptor-neurofibromin interaction prevents agonist-independent 5-HT6 receptor-operated cAMP signaling in prefrontal cortex, an effect that might underlie neuronal abnormalities in NF1 patients.

Peripheral Serotonin 1B Receptor Transcription Predicts the Effect of Acute Tryptophan Depletion on Risky Decision-Making.

BackgroundThe effects of acute tryptophan depletion on human decision-making suggest that serotonin modulates the processing of rewards and punishments. However, few studies have assessed which of the many types of serotonin receptors are responsible.MethodsUsing a within-subject, double-blind, sham-controlled design in 26 subjects, we examined whether individual differences in serotonin system gene transcription, measured in peripheral blood, predicted the effect of acute tryptophan depletion on decision-making. Participants performed a task in which they chose between successive pairs of fixed, lower-stakes (control) and variable, higher-stakes (experimental) gambles, each involving wins or losses. In 21 participants, mRNA from 9 serotonin system genes was measured in whole blood prior to acute tryptophan depletion: 5-HT1B, 5-HT1F, 5-HT2A, 5-HT2B, 5-HT3A, 5-HT3E, 5-HT7 (serotonin receptors), 5-HTT (the serotonin transporter), and tryptophan hydroxylase 1.ResultsAcute tryptophan depletion did not significantly influence participants’ sensitivity to probability, wins, or losses, although there was a trend for a lower tendency to choose experimental gambles overall following depletion. Significant positive correlations, which survived correction for multiple comparisons, were detected between baseline 5-HT1B mRNA levels and acute tryptophan depletion-induced increases in both the overall tendency to choose the experimental gamble and sensitivity to wins. No significant relationship was observed with any other peripheral serotonin system markers. Computational analyses of decision-making data provided results consistent with these findings.ConclusionsThese results suggest that the 5-HT1B receptor may modulate the effects of acute tryptophan depletion on risky decision-making. Peripheral levels of serotonin markers may predict response to treatments that act upon the serotonin system, such as selective serotonin reuptake inhibitors.

Structure-5-HT/D2 Receptor Affinity Relationship in a New Group of 1-Arylpiperazynylalkyl Derivatives of 8-Dialkylamino-3,7-dimethyl-1H-purine-2,6(3H,7H)-dione.

In our previous papers, we have reported that some 8-amino-1,3-dimethyl-1H-purine-2,6(3H,7H)-dione derivatives possessed high affinity and displayed agonistic, partial agonistic, or antagonistic activity for serotonin 5-HT1A and dopamine D2 receptors. In order to examine further the influence of the substituent in the position 8 of the purine moiety and the influence of the xanthine core on the affinity for serotonin 5-HT1A , 5-HT2A , 5-HT6 , 5-HT7 , and dopamine D2 receptors, two series of 1-arylpiperazynylalkyl derivatives of 8-amino-3,7-dimethyl-1H-purine-2,6(3H,7H)-dione were synthesized. All the final compounds were investigated in in vitro competition binding experiments for the serotonin 5-HT1A , 5-HT2A , 5-HT6 , 5-HT7 , and dopamine D2 receptors. The structure-affinity relationships for this group of compounds were discussed. For selected compounds, the functional assays for the 5-HT1A and D2 receptors were carried out. The results of the assays indicated that these groups of derivatives possessed antagonistic activity for 5-HT1A receptors and agonistic, partial agonistic, or antagonistic activity for D2 receptors. In total, 26 new compounds were synthesized, 20 of which were tested in in vitro binding experiments and 5 were tested in in vitro functional assays.

Fosaprepitant Dimeglumine: A Review in the Prevention of Nausea and Vomiting Associated with Chemotherapy.

Intravenous fosaprepitant dimeglumine (Emend(®) for injection, IVEmend(®); henceforth referred to as fosaprepitant) is a prodrug of and is rapidly converted to the antiemetic aprepitant, and is approved in several countries worldwide (as part of an antiemetic regimen) for the prevention of nausea and vomiting associated with highly and moderately emetogenic chemotherapy (HEC and MEC). This narrative review discusses the pharmacological properties of intravenous fosaprepitant and its clinical efficacy and tolerability in the prevention of nausea and vomiting associated with HEC and MEC. In large, randomized phase III clinical trials, a single intravenous dose of fosaprepitant 150mg was an effective and generally well tolerated addition to an antiemetic regimen that included dexamethasone and a serotonin 5-HT3 receptor antagonist in adult cancer patients undergoing treatment with HEC or MEC. It was also noninferior to an oral aprepitant-based regimen in adult cancer patients undergoing HEC treatment. The tolerability profile of a fosaprepitant-based regimen was typical of that in patients receiving emetogenic chemotherapy, and adverse events were generally consistent with those observed with an aprepitant-based regimen. Fosaprepitant provides a useful addition to antiemetic therapy regimens.

Discriminative stimulus properties of 1.25 mg/kg clozapine in rats: Mediation by serotonin 5-HT2 and dopamine D4 receptors

The atypical antipsychotic drug clozapine remains one of most effective treatments for schizophrenia, given a lack of extrapyramidal side effects, improvements in negative symptoms, cognitive impairment, and in symptoms in treatment-resistant schizophrenia. The adverse effects of clozapine, including agranulocytosis, make finding a safe clozapine-like a drug a goal for drug developers. The drug discrimination paradigm is a model of interoceptive stimulus that has been used in an effort to screen experimental drugs for clozapine-like atypical antipsychotic effects. The present study was conducted to elucidate the receptor-mediated stimulus properties that form this clozapine discriminative cue by testing selective receptor ligands in rats trained to discriminate a 1.25mg/kg dose of clozapine from vehicle in a two choice drug discrimination task. Full substitution occurred with the 5-HT2A inverse agonist M100907 and the two preferential D4/5-HT2/α1 receptor antagonists Lu 37-114 ((S)-1-(3-(2-(4-(1H-indol-5-yl)piperazin-1-yl)ethyl)indolin-1-yl)ethan-1-one) and Lu 37-254 (1-(3-(4-(1H-indol-5-yl)piperazin-1-yl)propyl)-3,4-dihydroquinolin-2(1H)-one). Partial substitution occurred with the D4 receptor antagonist Lu 38-012 and the α1 adrenoceptor antagonist prazosin. Drugs selective for 5-HT2C, 5-HT6 muscarinic, histamine H1, and benzodiazepine receptors did not substitute for clozapine. The present findings suggest that 5-HT2A inverse agonism and D4 receptor antagonism mediate the discriminative stimulus properties of 1.25mg/kg clozapine in rats, and further confirm that clozapine produces a complex compound discriminative stimulus.

Ca2+ signaling and emesis: Recent progress and new perspectives.

Cisplatin-like chemotherapeutics cause vomiting via calcium (Ca2+)-dependent release of multiple neurotransmitters (dopamine, serotonin, substance P, etc.) from the gastrointestinal enterochromaffin cells and/or the brainstem. Intracellular Ca2+ signaling is triggered by activation of diverse emetic receptors (including tachykininergic NK1, serotonergic 5-HT3, dopaminergic D2, cholinergic M1, or histaminergic H1), whose activation in vomit-competent species can evoke emesis. Other emetogens such as cisplatin, rotavirus NSP4 protein and bacterial toxins can also induce intracellular Ca2+ elevation. Netupitant is a highly selective neurokinin NK1 receptor (NK1R) antagonist and palonosetron is a selective second-generation serotonin 5-HT3 receptor (5-HT3R) antagonist with a distinct pharmacological profile. An oral fixed combination of netupitant/palonosetron (NEPA; Akynzeo(®)) with >85% antiemetic efficacy is available for use in the prevention of acute and delayed chemotherapy-induced nausea and vomiting (CINV). Cannabinoid CB1 receptor agonists possess broad-spectrum antiemetic activity since they prevent vomiting caused by a variety of emetic stimuli including the chemotherapeutic agent cisplatin, 5-HT3R agonists, and D2R agonists. Our findings demonstrate that application of the L-type Ca2+ channel (LTCC) agonist FPL 64176 and the intracellular Ca2+ mobilizing agent thapsigargin (a sarco/endoplasmic reticulum Ca2+-ATPase inhibitor) cause vomiting in the least shrew. On the other hand, blockade of LTCCs by corresponding antagonists (nifedipine or amlodipine) not only provide broad-spectrum antiemetic efficacy against diverse agents that specifically activate emetogenic receptors such as 5-HT3, NK1, D2, and M1 receptors, but can also potentiate the antiemetic efficacy of palonosetron against the non-specific emetogen, cisplatin. In this review, we will provide an overview of Ca2+ involvement in the emetic process; discuss the relationship between Ca2+ signaling and the prevailing therapeutics in control of vomiting; highlight the evidence for Ca2+-signaling blockers/inhibitors in suppressing emetic behavior in the least shrew model of emesis as well as in the clinical setting; and also draw attention to the clinical benefits of Ca2+-signaling blockers/inhibitors in the treatment of nausea and vomiting.

Genotype frequencies for polymorphisms related to chemotherapy-induced nausea and vomiting in a Japanese population.

BackgroundGenotype frequencies for chemotherapy-induced nausea and vomiting (CINV)-related polymorphisms have not yet been reported for Japanese subjects.MethodsWe analyzed 10 genotype frequencies for following polymorphisms associated with the development of CINV: serotonin 5-HT3 receptors (HTR3); neurokinin-1 receptors (Tachykinin-1 receptors, TACR1); dopamine D2 receptors (DRD2); and catechol-O-methyltransferase (COMT).ResultsAll polymorphisms were successfully genotyped in 200 Japanese subjects and were in Hardy-Weinberg equilibrium. Almost all genotype frequencies were similar to those in the HapMap database or in the previous reports, while frequencies for the Y192H polymorphism in TACR1 were different in Japanese subjects from those in a previous report.ConclusionsThe present study revealed genotype frequencies for polymorphisms, which were related to the appearance of CINV in Japanese subjects. Individual therapy based on genotype variations for each race is needed to allow cancer patients to undergo chemotherapy more safely and to understand etiology of CINV.

Antidépresseurs et tolérance : déterminants et prise en charge des principaux effets indésirables

Antidepressant therapy aims to reach remission of depressive symptoms while reducing the complications and risks of relapse. Even though they have proven their efficacy, it takes several weeks for antidepressants to demonstrate full effectiveness, and adverse effects occur more quickly or (quicker) which can be a source of poor compliance. This latest aspect often leads to dose reduction and/or change of molecule that have the effect of delaying remission. This review attempts to present, from the pharmacological properties of the major classes of antidepressants (monoamine oxidase inhibitor [MAOI], tricyclic antidepressants [TCA], selective serotonin reuptake inhibitor [SSRI] and serotonin and noradrenaline reuptake inhibitor [SNRI]), to the pharmacological mechanisms involved in adverse effects by focusing on sexual dysfunction, nausea/vomiting, and weight changes and sleep disruption. If the activation of dopamine D1/2 or norepinephrine receptors through the autonomic nervous system controls and facilitates sexual desire, increasing serotoninergic transmission through 5-HT1B/2A/2C receptors activation inhibits this process. The pharmacological properties of drugs inducing nausea/vomiting activate opiate receptors μ, increase dopaminergic and serotoninergic transmission activating the dopamine D2 and serotonin 5-HT3 receptors, respectively. Among the causes responsible for weight gain under antidepressant therapy, monoamine neurotransmission still plays an important role. The blockade of serotonin 5-HT2C or histamine H1 receptors is directly responsible for weight gain. Finally, the activation of 5-HT1A/1B/3/7 serotoninergique receptors modulates wakefulness, raid eyes movement or sleep duration. In conclusion, if antidepressant activity of SERT or MAO inhibitors is an indirect consequence of postsynaptic 5-HT, DA, NA receptor activation, it is also responsible for side effects, causes of poor compliance and hence therapeutic failures. Finally, we need to take into account the key role of the nocebo effect in the occurrence of adverse effects. The next generation of antidepressant would aim to have a rapid efficacy in patients unresponsive or resistant to drugs currently available while improving certain effects of tolerance through an optimization of their psychopharmacological properties leading to a reduction of their side effects.

Modulation of cannabinoid signaling by hippocampal 5-HT4 serotonergic system in fear conditioning.

Behavioral studies have suggested a key role for the cannabinoid system in the modulation of conditioned fear memory. Likewise, much of the literature has revealed that the serotonergic system affects Pavlovian fear conditioning and extinction. A high level of functional overlap between the serotonin and cannabinoid systems has also been reported. To clarify the interaction between the hippocampal serotonin (5-HT4) receptor and the cannabinoid CB1 receptor in the acquisition of fear memory, the effects of 5-HT4 agents, arachidonylcyclopropylamide (ACPA; CB1 receptor agonist), and the combined use of these drugs on fear learning were studied in a fear conditioning task in adult male NMRI mice. Pre-training intraperitoneal administration of ACPA (0.1 mg/kg) decreased the percentage of freezing time in both context- and tone-dependent fear conditions, suggesting impairment of the acquisition of fear memory. Pre-training, intra-hippocampal (CA1) microinjection of RS67333, a 5-HT4 receptor agonist, at doses of 0.1 and 0.2 or 0.2 µg/mouse impaired contextual and tone fear memory, respectively. A subthreshold dose of RS67333 (0.005 µg/mouse) did not alter the ACPA response in either condition. Moreover, intra-CA1 microinjection of RS23597 as a 5-HT4 receptor antagonist did not alter context-dependent fear memory acquisition, but it did impair tone-dependent fear memory acquisition. However, a subthreshold dose of the RS23597 (0.01 µg/mouse) potentiated ACPA-induced fear memory impairment in both conditions. Therefore, we suggest that the blockade of hippocampal 5-HT4 serotonergic system modulates cannabinoid signaling induced by the activation of CB1 receptors in conditioned fear.

IN VIVO ALTERATIONS IN BRAIN GLUCOSE UTILIZATION WITH RVT-101, A 5HT6 INHIBITOR FOR THE TREATMENT OF ALZHEIMER’S DISEASE

RVT-101 is a potent antagonist of the 5-hydroxytryptamine 6 (5-HT6) serotonin receptor. Reduced glucose utilization is an early sign of decreasing brain function in AD. Altered neuronal glucose uptake assessed by flurodeoxyglucose-positron emission tomography (FDG-PET) may be useful as a diagnostic foundation for identifying patients with AD. This study evaluates RVT-101 at clinically relevant doses on healthy rat brain glucose utilization using FDG-PET/CT. Healthy, young CD rats were pre-dosed with placebo or RVT-101 (10 mg/kg or 20 mg/kg) 3 h prior to FDG (18.1 ± 3.5 MBq, i.v.). Brain FDG standard uptake values (SUV) were quantified using scanning in single 20 min list mode (BioPET/CT, Sedecal) starting 30 min post FDG dosing. PET/CT scans were analyzed as a single time frame summarizing counts over 20 min. All experiments were completed in an accredited facility according to NIH guidelines. PET/CT imaging data were analyzed using Student’s t-test, cluster analysis, and multivariate analysis of variance (MANOVA) using a subset of SUV from 5 cluster-identified regions. RVT-101 increased glucose uptake in healthy young CD rats in a dose dependent manner in almost all brain regions, but pairwise comparisons did not reach statistical significance. SUV from 5 regions that clustered separately were identified: acumbens, cerebellum (white), orbitofrontal cortex, insular cortex and pituitary. Analyzing the composite SUV profile from 5 brain regions in a linear regression model showed a statistically significant overall dose effect (p=0.0006) Further, cluster analysis revealed a placebo outlier, which when removed, provide additional support of a drug effect on glucose uptake in sub-regions. Glucose uptake after pre-treatment with RVT-101 compared to placebo showed a trend of increased glucose uptake in the majority of brain regions analyzed, especially in the 20 mg/kg group. Selection of a subset of regions for regression analysis revealed a statistically significant dose effect related to glucose uptake. These data suggest that RVT-101 may increase brain glucose utilization, an important biologic marker for drugs being developed for AD.

Time-dependent impact of glutamatergic modulators on the promnesiant effect of 5-HT6R blockade on mice recognition memory

Selective antagonists at serotonin 5-HT6 receptors (5-HT6R) improve memory performance in rodents and are currently under clinical investigations. If blockade of 5-HT6R is known to increase glutamate release, only two studies have so far demonstrated an interaction between 5-HT6R and glutamate transmission, but both, using the non-competitive NMDA antagonist MK-801, insensitive to variations of glutamate concentrations. In a place recognition task, we investigated here in mice the role of glutamate transmission in the beneficial effects of 5-HT6R blockade (SB-271046). Through the use of increasing intervals (2, 4 and 6h) between acquisition and retrieval, we investigated the time-dependent impact of two different glutamatergic modulators. NMDAR-dependant glutamate transmission (NMDA Receptors) was either blocked by the competitive antagonist at NMDAR, CGS 19755, or potentiated by the glycine transporter type 1 (GlyT1) inhibitor, NFPS. Results showed that neither SB-271046, nor CGS 19755, nor NFPS, alter behavioural performances after short intervals, i.e. when control mice displayed significant memory performances (2h and 4h) (respectively 10, 3, and 0.625mg.kg−1). Conversely, with the 6h-interval, a situation in which spontaneous forgetting is observed in control mice, SB-271046 improved recognition memory performances. This beneficial effect was prevented when co-administered with either CGS 19755 or NFPS, which themselves had no effect. Interestingly, a dose-dependent effect was observed with NFPS, with promnesic effect observed at lower dose (0.156mg.kg−1) when administrated alone, whereas it did no modify promnesic effect of SB-271046. These results demonstrate that promnesiant effect induced by 5-HT6R blockade is sensitive to the competitive blockade of NMDAR and underline the need of a fine adjustment of the inhibition of GlyT1. Overall, our findings support the idea of a complex crosstalk between serotonergic and glutamatergic systems in the promnesic properties of 5-HT6R antagonists.

Design and synthesis of new homo and hetero bis-piperazinyl-1-propanone derivatives as 5-HT7R selective ligands over 5-HT1AR

In this work we report the discovery of new homo and hetero bis-piperazinyl-1-propanone derivatives as selective ligands for 5-HT7 over 5-HT1A receptor. These newly synthesized compounds possess a 4-arylpiperazine linked through an acyl spacer to another substituted piperazine system and were tested for their binding properties on human cloned 5-HT1A and 5-HT7 serotonin receptors. Among these, phenyl, 4- and 2-chlorophenyl, 2-methoxyphenyl, 2-pyridyl, and 2-pyrimidyl derivatives 15, 24, 25, and 27–29 displayed nanomolar affinity values for the 5-HT7 receptor (Ki 23.5–52.0nM) and no affinity for the 5-HT1A receptor.

Ixaltis gets funds to repurpose drug

Ixaltis, a start-up company focused on urogenital disorders, has raised $9 million in its first funding round. The French firm’s pipeline consists of three compounds licensed from Sanofi. The most advanced is litoxetine, a serotonin reuptake inhibitor and 5-HT3 receptor antagonist that Sanofi had studied as an antidepressant. Ixaltis will soon begin testing the compound in a Phase II trial for treating urinary incontinence. The company also received a $3.2 million loan under an academic-industrial research project dedicated to urogenital diseases.

Pharmacologic Evaluation of Antidepressant Activity and Synthesis of 2-Morpholino-5-phenyl-6H-1,3,4-thiadiazine Hydrobromide.

Substituted thiadiazines exert a reliable therapeutic effect in treating stress, and a schematic description of their ability to influence all aspects of a stress response has been depicted. This study was conducted to pharmacologically evaluate compound L-17, a substituted thiadiazine, (2-morpholino-5-phenyl-6H-1,3,4-thiadiazine, hydrobromide) for possible anti-psychotic/antidepressant activity. Compound L-17 was synthesized by cyclocondensation of α-bromoacetophenone with the original morpholine-4-carbothionic acid hydrazide. Pharmacologic evaluations were conducted using methods described by E.F. Lavretskaya (1985), and in accordance with published guidelines for studying drugs for neuroleptic activity. Compound L-17 was evaluated for various possible mechanisms of action, including its effects on cholinergic system agonists/antagonists, dopaminergic neurotransmission, the adrenergic system, and 5-HT3 serotonin receptors. One or more of these mechanisms may be responsible for the beneficial effects shown by thiadiazine compounds in experiments conducted to evaluate their activity in models of acute stress and acute myocardial infarction.

Structural modifications of the serotonin 5-HT7 receptor agonist N-(4-cyanophenylmethyl)-4-(2-biphenyl)-1-piperazinehexanamide (LP-211) to improve in vitro microsomal stability: A case study

The 5-HT7 serotonin receptor is revealing a promising target for innovative therapeutic strategies of neurodevelopmental and neuropsychiatric disorders. Here, we report the synthesis of thirty long-chain arylpiperazine analogs of the selective and brain penetrant 5-HT7 receptor agonist LP-211 (1) designed to enhance stability towards microsomal oxidative metabolism. Commonly used medicinal chemistry strategies were used (i.e., reduction of overall lipophilicity, introduction of electron-withdrawing groups, blocking of potential vulnerable sites of metabolism), and in vitro microsomal stability was tested. The data showed that the adopted design strategy does not directly translate into improvements in stability. Instead, the metabolic stability of the compounds was related to the presence of specific substituents in well-defined regions of the molecule. The collected data allowed for the construction of a machine learning model that, in a given chemical space, is able to describe and quantitatively predict the metabolic stability of the compounds. The majority of the synthesized compounds maintained high affinity for 5-HT7 receptors and showed selectivity towards 5-HT6 and dopamine D2 receptors and different selectivity for 5-HT1A and α1 adrenergic receptors. Compound 50 showed 3-fold higher in vitro stability towards oxidative metabolism than 1 and was able to stimulate neurite outgrowth in neuronal primary cultures through the 5-HT7 receptor in a shorter time and at a lower concentration than the agonist 1. A preliminary disposition study in mice revealed that compound 50 was metabolically stable and was able to pass the blood–brain barrier, thus representing a new tool for studying the pharmacotherapeutic potential of 5-HT7 receptor in vivo.

DREADD Modulation of Transplanted DA Neurons Reveals a Novel Parkinsonian Dyskinesia Mechanism Mediated by the Serotonin 5-HT6 Receptor

SummaryTransplantation of DA neurons is actively pursued as a restorative therapy in Parkinson’s disease (PD). Pioneering clinical trials using transplants of fetal DA neuroblasts have given promising results, although a number of patients have developed graft-induced dyskinesias (GIDs), and the mechanism underlying this troublesome side effect is still unknown. Here we have used a new model where the activity of the transplanted DA neurons can be selectively modulated using a bimodal chemogenetic (DREADD) approach, allowing either enhancement or reduction of the therapeutic effect. We show that exclusive activation of a cAMP-linked (Gs-coupled) DREADD or serotonin 5-HT6 receptor, located on the grafted DA neurons, is sufficient to induce GIDs. These findings establish a mechanistic link between the 5-HT6 receptor, intracellular cAMP, and GIDs in transplanted PD patients. This effect is thought to be mediated through counteraction of the D2 autoreceptor feedback inhibition, resulting in a dysplastic DA release from the transplant.

Novel 1H-Pyrrolo[3,2-c]quinoline Based 5-HT6 Receptor Antagonists with Potential Application for the Treatment of Cognitive Disorders Associated with Alzheimer's Disease.

Modulators of the serotonin 5-HT6 receptor (5-HT6R) offer a promising strategy for the treatment of the cognitive deficits that are associated with dementia and Alzheimer's disease. Herein, we report the design, synthesis, and characterization of a novel class of 5-HT6R antagonists that is based on the 1H-pyrrolo[3,2-c]quinoline core. The most active compounds exhibited comparable binding affinity to the reference compound, SB-742457, and markedly improved selectivity. Lead optimization led to the identification of (S)-1-[(3-chlorophenyl)sulfonyl]-4-(pyrrolidine-3-yl-amino)-1H-pyrrolo[3,2-c]quinoline (14) (Ki = 3 nM and Kb = 0.41 nM). Pharmacological characterization of the 5-HT6R's constitutive activity at Gs signaling revealed that 14 behaved as a neutral antagonist, while SB-742457 was classified as an inverse agonist. Both compounds 14 and SB-742457 reversed phencyclidine-induced memory deficits and displayed distinct procognitive properties in cognitively unimpaired animals (3 mg/kg) in NOR tasks. Compounds 14 and SB-742457 were also active in the Vogel test, yet the anxiolytic effect of 14 was 2-fold higher (MED = 3 mg/kg). Moreover, 14 produced, in a 3-fold higher dose (MED = 10 mg/kg), antidepressant-like effects that were similar to those produced by SB-742457 (MED = 3 mg/kg). Together, these data suggest that the 4-(pyrrolidine-3-yl-amino)-1H-pyrrolo[3,2-c]quinoline scaffold is an attractive molecular framework for the development of procognitive agents. The results are promising enough to warrant further detailed mechanistic studies on the therapeutic potential of 5-HT6R antagonists and inverse agonists for the treatment of cognitive decline and depression/anxiety symptoms that are comorbidities of Alzheimer's disease.

Knockout of p11 attenuates the acquisition and reinstatement of cocaine conditioned place preference in male but not in female mice.

Cocaine's enhancement of dopamine signaling is crucial for its rewarding effects but its serotonergic effects are also relevant. Here we examined the role of the protein p11, which recruits serotonin 5HT1B and 5HT4 receptors to the cell surface, in cocaine reward. For this purpose we tested wild-type (WT) and p11 knockout (KO) male and female mice for cocaine conditioned place preference (CPP) and its cocaine-induced reinstatement at different abstinence times, after 8 days of extinction and 28 days of being home-caged. All mice showed significant cocaine CPP. Among males, p11KO showed lower CPP than WT; this difference was also evident after 28 days of home-cage abstinence. In contrast, in females there were no CPP differences between p11KO and WT mice at any time point tested. Cocaine priming after the 28-day home-cage abstinence period also resulted in lower cocaine conditioned motor activity in both male and female p11KO mice. These results suggest that cocaine CPP and its persistence during extinction and reinstatement are modulated in a sex-differentiated manner by p11. The lack of protein p11 confers protection from CPP on male, but not female mice, immediately after cocaine conditioning as well as after prolonged abstinence, but not after short-term withdrawal. Synapse 70:293-301, 2016. © 2016 Wiley Periodicals, Inc.

A Gating Mechanism of the Serotonin 5-HT3 Receptor

Our recently solved high-resolution structure of the serotonin 5-HT3 receptor (5-HT3R) delivered the first detailed structural insights for a mammalian pentameric ligand-gated ion channel. Based on this structure, we here performed a total of 2.8-μs all-atom molecular dynamics simulations to unravel at atomic detail how neurotransmitter binding on the extracellular domain induces sequential conformational transitions in the receptor, opening an ion channel and translating a chemical signal into electrical impulses across the membrane. We found that serotonin binding first induces distinct conformational fluctuations at the side chain of W156 in the highly conserved ligand-binding cage, followed by tilting-twisting movements of the extracellular domain which couple to the transmembrane TM2 helices, opening the hydrophobic gate at L260 and forming a continuous transmembrane water pathway. The structural transitions in the receptor's transmembrane part finally couple to the intracellular MA helix bundle, opening lateral ports for ion passage.

Synthesis and evaluation of (S)-[18F]fesetron in the rat brain as a potential PET imaging agent for serotonin 5-HT3 receptors

Serotonin 5-HT3 receptors are involved in various brain functions including as an emesis target during cancer chemotherapy. We report here the development of (S)-2,3-dimethoxy-5-(3′-[18F]fluoropropyl)-N-(1-azabicyclo[2.2.2]oct-3-yl)benzamide ([18F]fesetron) as a potential PET imaging agent for serotonin 5-HT3 receptors. By radiolabeling((S)-2,3-dimethoxy-5-(3′-tosyloxypropyl)-N-(1-azabicyclo[2.2.2]oct-3-yl)benzamide) with fluorine-18, (S)-[18F]fesetron was obtained in 5 to 10% decay-corrected yields and with specific activities >74GBq/μmol at the end of radiosynthesis. PET imaging in rats showed low uptake of [18F]fesetron in the brain with retention of binding in the striatal and cerebellar regions. Using colliculi as a reference region, ratios were 3.4 for striata and 2.5 for cerebellum. Ex vivo brain PET analysis displayed binding of [18F]fesetron in the hippocampus, striatum and cerebellar regions. Cerebellar regions corresponded to area postrema and nucleus tract solitaris known to contain 5-HT3 receptors. Dorsal hippocampus showed the highest uptake with ratio of >17 with respect to colliculi, while area postrema and striata had ratios of >10. Thus, [18F]fesetron exhibited a unique binding profile to rat brain regions known to contain significant amounts of serotonin 5-HT3 receptors. However, the very low brain uptake limits its usefulness as a PET radiotracer in this animal model.