A 6-week randomized, double-blind, placebo-controlled, comparator referenced trial of vabicaserin in acute schizophrenia

The effect of differences in trial design on estimates of efficacy of olanzapine in randomized studies

BACKGROUND

Differences in trial design may affect estimates of efficacy of psychotropic drugs. The purpose of this meta-analysis is to evaluate whether the use of Olanzapine (OLZ) as either investigational or control drug affects the observed efficacy of OLZ.

METHODS

We performed a search for Randomized-Controlled Trials (RCTs) in which the efficacy of OLZ is assessed in patients with schizophrenia or schizoaffective disorder. We assessed overall efficacy of OLZ and performed subgroup analyses of studies with OLZ as intervention or comparator. Mixed-effect meta-regression analyses were performed.

RESULTS

Of the 25 RCTs included, OLZ was considered as investigational drug or active control in 13 and 12 studies, respectively. The reduction of PANSS score was greater in trials in which OLZ was used as investigational drug. Multivariate meta-regression models showed that a higher PANSS score at baseline and trial duration were the main predictors of greater PANSS score reduction.

CONCLUSIONS

Trials with OLZ used as investigational drug differ from those of trials with OLZ as comparator for baseline PANSS scores and study duration; these differences may produce differences in estimates of efficacy. As a consequence, the severity of illness at enrollment and trial duration should be carefully considered to ensure the reliability of indirect comparisons among antipsychotics.

Advancements in Non-Dopaminergic Treatments for Schizophrenia: A Systematic Review of Pipeline Developments

INTRODUCTION

Conventional antipsychotic drugs that attenuate dopaminergic neural transmission are ineffective in approximately one-third of patients with schizophrenia. This necessitates the development of non-dopaminergic agents.

METHODS

A systematic search was conducted for completed phase II and III trials of compounds for schizophrenia treatment using the US Clinical Trials Registry and the EU Clinical Trials Register. Compounds demonstrating significant superiority over placebo in the primary outcome measure in the latest phase II and III trials were identified. Collateral information on the included compounds was gathered through manual searches in PubMed and press releases.

RESULTS

Sixteen compounds were identified; four compounds (ulotaront, xanomeline/trospium chloride, vabicaserin, and roluperidone) were investigated as monotherapy and the remaining 12 (pimavanserin, bitopertin, BI 425809, encenicline, tropisetron, pregnenolone, D-serine, estradiol, tolcapone, valacyclovir, cannabidiol, and rimonabant) were examined as add-on therapy. Compared to the placebo, ulotaront, xanomeline/trospium chloride, vabicaserin, bitopertin, estradiol, cannabidiol, rimonabant, and D-serine showed efficacy for positive symptoms; roluperidone and pimavanserin were effective for negative symptoms; and encenicline, tropisetron, pregnenolone, tolcapone, BI 425809, and valacyclovir improved cognitive function.

DISCUSSION

Compounds that function differently from existing antipsychotics may offer novel symptom-specific therapeutic strategies for patients with schizophrenia.

NU-1223, a simplified analog of alstonine, with 5-HT2cR agonist-like activity, rescues memory deficit and positive and negative symptoms in subchronic phencyclidine mouse model of schizophrenia

The serotonin (5-HT)2 C receptor(R) is a widely distributed G-protein-coupled receptor, expressed abundantly in the central nervous system. Alstonine is a natural product that has significant properties of atypical antipsychotic drugs (AAPDs), in part attributed to 5-HT2 CR agonism. Based on alstonine, we developed NU-1223, a simplified β carboline analog of alstonine, which shows efficacies comparable to alstonine and to other 5-HT2 CR agonists, Ro-60-0175 and lorcaserin. The 5-HT2 CR antagonism of some APDs, including olanzapine, contributes to weight gain, a major side effect which limits its tolerability, while the 5-HT2 CR agonists and/or modulators, may minimize weight gain. We used the well-established rodent subchronic phencyclidine (PCP) model to test the efficacy of NU-1223 on episodic memory, using novel object recognition (NOR) task, positive (locomotor activity), and negative symptoms (social interaction) of schizophrenia (SCH). We found that NU-1223 produced both transient and prolonged rescue of the subchronic PCP-induced deficits in NOR and SI. Further, NU-1223, but not Ro-60-0175, blocked PCP and amphetamine (AMPH)-induced increase in LMA in subchronic PCP mice. These transient efficacies in LMA were blocked by the 5-HT2 CR antagonist, SB242084. Sub-chronic NU-1223 treatment rescued NOR and SI deficits in subchronic PCP mice for at least 39 days after 3 days injection. Chronic treatment with NU-1223, ip, twice a day for 21 days, did not increase average body weight vs olanzapine. These findings clearly indicate NU-1223 as a class of small molecules with a possible 5-HT2 CR-agonist-like mechanism of action, attributing to its efficacy. Additional in-depth receptor mechanistic studies are warranted, as this small molecule, both transiently and chronically rescued PCP-induced deficits. Furthermore, NU-1223 did not induce weight gain post long-term administrations vs AAPDs such as olanzapine, making NU-1223 a putative therapeutic compound for SCH.

Adverse effects of antipsychotics on sleep in patients with schizophrenia. Systematic review and meta-analysis

Introduction

Our objective was to conduct a systematic review and meta-analysis of adverse effects on sleep in patients with schizophrenia receiving antipsychotic treatment.

Methods

A systematic search was performed in PubMed, Cochrane Central, Embase, Toxline, Ebsco, Virtual Health Library, Web of Science, SpringerLink, and in Database of abstracts of Reviews of Effects of Randomized Clinical Trials to identify eligible studies published from January 1990 to October 2021. The methodological quality of the studies was evaluated using the CONSORT list, and the Cochrane bias tool. Network meta-analysis was performed using the Bayesian random-effects model, with multivariate meta-regression to assess the association of interest.

Results

87 randomized clinical trials were identified that met the inclusion criteria, and 70 articles were included in the network meta-analysis. Regarding the methodological quality of the studies, 47 had a low or moderate bias risk. The most common adverse effects on sleep reported in the studies were insomnia, somnolence, and sedation. The results of the network meta-analysis showed that ziprasidone was associated with an increased risk of insomnia (OR, 1.56; 95% credible interval CrI, 1.18-2.06). Several of the included antipsychotics were associated with a significantly increased risk of somnolence; haloperidol (OR, 1.90; 95% CrI, 1.12-3.22), lurasidone (OR, 2.25; 95% CrI, 1.28-3.97) and ziprasidone (OR, 1.79; 95% CrI, 1.06-3.02) had the narrowest confidence intervals. In addition, perphenazine (OR, 5.33; 95% CrI, 1.92-14.83), haloperidol (OR, 2.61; 95% CrI, 1.14-5.99), and risperidone (OR, 2.41; 95% CrI, 1.21-4.80) were associated with an increased risk of sedation compared with placebo, and other antipsychotics did not differ. According to the SUCRAs for insomnia, chlorpromazine was ranked as the lowest risk of insomnia (57%), followed by clozapine (20%), while flupentixol (26 %) and perospirone (22.5%) were associated with a lower risk of somnolence. On the other hand, amisulpride (89.9%) was the safest option to reduce the risk of sedation.

Discussion

Insomnia, sedation, and somnolence were the most frequent adverse effects on sleep among the different antipsychotics administered. The evidence shows that chlorpromazine, clozapine, flupentixol, perospirone, and amisulpride had favorable safety profiles. In contrast, ziprasidone, perphenazine, haloperidol, and risperidone were the least safe for sleep.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42017078052, identifier: PROSPERO 2017 CRD42017078052.

Onset of Action of Selected Second-Generation Antipsychotics (Pines)-A Systematic Review and Meta-Analyses

Recommendations for duration of treatment with antipsychotics before considering a switch vary from 2 to 8 weeks, although several studies suggest a rapid onset of action. The objective of this review was to estimate time to onset of action and time to maximum antipsychotic effect of asenapine, olanzapine, quetiapine, and zotepine (pines). We searched bibliographic databases for randomized, placebo-controlled trials in adults with schizophrenia estimating the antipsychotic effect of pines over time. Thirty-five studies including 6331 patients diagnosed with chronic schizophrenia were included. We estimated the standardized mean differences (SMD) of changes in symptom score from baseline to follow-up between intervention and placebo groups across studies using meta-analysis techniques. The summarized effect across all included pines administered as immediate-release formulations showed a statistically significant effect at week 1 (SMD, -0.20 [CI95% -0.28, -0.13]), which increased until week 3 (SMD, -0.42 [CI95% -0.50, -0.34]), after which the effect leveled off (week 6: SMD, -0.53 [CI95% -0.62, -0.44]). The sensitivity analyses of the individual pines confirm this finding, although data sparsity increases variability and limits conclusiveness of these analyses.

Samidorphan/olanzapine combination therapy for schizophrenia: Efficacy, tolerance and adverse outcomes of regimen, evidence-based review of clinical trials

Introduction

Objectives

Methods

Results

Conclusion

•

FDA approved a combination dose of olanzapine and samidorphan (OLZ/SAM) for treatment of schizophrenia and bipolar I disorder.

•

Overall, OLZ/SAM showed a significant reduction in symptoms for long-term treatment.

•

Major adverse events included nervous system disorders, blood, metabolic or nutritional changes.

Discovery of Highly Potent Serotonin 5-HT2 Receptor Agonists Inspired by Heteroyohimbine Natural Products

The serotonin 5-HT₂ receptors are important pharmaceutical targets involved in signaling pathways underlying various neurological, psychiatric, and cardiac functions and dysfunctions. As such, numerous ligands for the investigation of these receptors' activity and downstream effects have been developed synthetically or discovered in nature. For example, the heteroyohimbine natural product alstonine exhibits antispychotic activity mediated by 5-HT_2A/2C agonism. In this work, we identified a heteroyohimbine metabolite containing a serotonin pharmacophore and truncated the scaffold, leading to the discovery of potent agonist activity of substituted tetrahydro-β-carbolines across the 5-HT₂ receptor family. Extensive SAR development resulted in compound 106 with EC₅₀ values of 1.7, 0.58, and 0.50 nM at 5-HT_2A, 5-HT_2B, and 5-HT_2C, respectively. Docking studies suggest a π-stacking interaction between the tetrahydro-β-carboline core and conserved residue Trp^6.48 as the structural basis for this activity. This work lays a foundation for future investigation of these compounds in neurological and psychiatric disorders.

MK212, a 5-hydroxytryptamine 2C receptor agonist, reverses prepulse inhibition deficits in the medial prefrontal cortex and ventral hippocampus

Prepulse inhibition (PPI) is disrupted in many neuropsychiatric diseases. Molecules such as 5-HT_2C receptor agonists alleviate PPI deficits in rodents; however, the precise mechanisms and critical regions of the brain responsible for the reversal effect of these agonists remain inconclusive. The present study aimed to investigate the areas of the brain critical for the reversal effect of 5-HT_2C receptor agonists on PPI deficits in mice. The results showed that systemic administration of the 5-HT_2C receptor agonist MK212 did not affect normal PPI behavior, but reversed the PPI deficits induced by the N-methyl d-aspartate receptor antagonist MK801 in mice. In addition, the 5-HT_2C receptor antagonist SB242084 had no effect on PPI behavior despite MK801 treatment. Moreover, local infusion of MK212 into the medial prefrontal cortex and ventral hippocampus, excluding the nucleus accumbens or ventral tegmental area, rescued the PPI deficits induced by MK801. These data suggest that the medial prefrontal cortex and ventral hippocampus are critical brain areas responsible for the reversal of 5-HT_2C agonists on PPI deficits. The results will contribute to our current knowledge on the molecular and neural mechanisms underlying the antipsychotic effects of 5-HT_2C receptor agonists, especially the neural circuits modulated by 5-HT_2C receptor activity.

Antipsychotic-Induced Weight Gain: Dose-Response Meta-Analysis of Randomized Controlled Trials

BACKGROUND

Weight gain is among the most important side-effects of antipsychotics. It is, however, unclear whether it is associated with antipsychotic doses. We aimed to fill this gap with a dose-response meta-analysis.

METHODS

We searched multiple electronic databases (last update search June 2021) for all fixed-dose studies that investigated 16 second-generation antipsychotics and haloperidol in adults with acute exacerbation of schizophrenia or with negative symptoms. We estimated the dose-response curves by conducting random-effects dose-response meta-analyses. We used the restricted cubic spline to model the dose-response relationship. The primary outcome was mean weight gain in kg from baseline to endpoint, the secondary outcome was the number of patients with clinically important weight gain.

FINDINGS

Ninety-seven studies with 333 dose arms (36 326 participants) provided data for meta-analyses. Most studies were short-term with median duration of 6 weeks (range 4 to 26 weeks). In patients with acute exacerbation, amisulpride, aripiprazole, brexpiprazole, cariprazine, haloperidol, lumateperone, and lurasidone produced mild weight gain in comparison to placebo (mean difference at any dose≤1 kg), while more significant weight gain was observed by all other drugs. For most drugs, dose-response curves showed an initial dose-related increase in weight which plateaued at higher doses, while for others there was no plateau and some even had bell-shaped curves, meaning less weight gain to be associated with higher doses.

INTERPRETATION

Second-generation antipsychotics do not only differ in their propensity to produce weight gain, but also in the shapes of their dose-response curves. This information is important for dosing decisions in clinical practice.

Response efficacy and heterogeneity of antipsychotic drugs in schizophrenia: Systemic review and meta-analysis

BACKGROUNDS

This meta-analysis aimed to assess antipsychotic and placebo effects in patients with schizophrenia at the level of symptom factors.

METHODS

A systematic literature search up to June 2020 was undertaken and 62 studies were included, with 23,478 patients with schizophrenia at the study baseline point. We calculated mean differences with 95% confidence intervals. The comparison was made according to the study content using a continuous method with a random-effects model.

RESULTS

Patients with schizophrenia treated by antipsychotic drugs had a significantly lower psychiatric rating scale total score; lower clinical global impression of severity; lower positive and negative syndrome scale; and lower assessment of negative symptoms total score, when compared to placebo treated patients.

CONCLUSIONS

Patients with schizophrenia treated with an antipsychotic drug show a much greater improvement and lower inconsistency in the level of symptom factors when compared to the effects of placebo. Our findings evidence for a comparatively homogeneous outcome of the antipsychotic-treatment in improving schizophrenia symptoms. This opposes the notion of the presence of patient sub-groups with treatment non-responsive schizophrenia.

Examining Side Effect Variability of Antipsychotic Treatment in Schizophrenia Spectrum Disorders: A Meta-analysis of Variance

Side effects of antipsychotic drugs play a key role in nonadherence of treatment in schizophrenia spectrum disorders (SSD). While clinical observations suggest that side effect variability between patients may be considerable, statistical evidence is required to confirm this. Here, we hypothesized to find larger side effect variability under treatment compared with control. We included double-blind, placebo-controlled, randomized controlled trials (RCTs) of adults with a diagnosis of SSD treated with 1 out of 14 antipsychotics. Standard deviations of the pre-post treatment differences of weight gain, prolactin levels, and corrected QT (QTc) times were extracted. The outcome measure was the variability ratio of treatment to control for individual antipsychotic drugs and the overall variability ratio of treatment to control across RCTs. Individual variability ratios were weighted by the inverse-variance method and entered into a random-effects model. We included N = 16 578 patients for weight gain, N = 16 633 patients for prolactin levels, and N = 10 384 patients for QTc time. Variability ratios (VR) were significantly increased for weight gain (VR = 1.08; 95% CI: 1.02-1.14; P = .004) and prolactin levels (VR = 1.38; 95% CI: 1.17-1.62; P < .001) but did not reach significance for QTc time (VR = 1.05; 95% CI: 0.98-1.12; P = 0.135). We found marked differences between individual antipsychotics and increased variability in side effects in patients under treatment with antipsychotics suggesting that subgroups of patients or individual patients may benefit from treatment allocation through stratified or personalized medicine.

Serotonin/dopamine interaction: Electrophysiological and neurochemical evidence

The interaction between serotonin (5-HT) and dopamine (DA) in the central nervous system (CNS) plays an important role in the adaptive properties of living animals to their environment. These are two modulatory, divergent systems shaping and regulating in a widespread manner the activity of neurobiological networks and their interaction. The concept of one interaction linking these two systems is rather elusive when looking at the mechanisms triggered by these two systems across the CNS. The great variety of their interacting mechanisms is in part due to the diversity of their neuronal origin, the density of their fibers in a given CNS region, the distinct expression of their numerous receptors in the CNS, the heterogeneity of their intracellular signaling pathway that depend on the cellular type expressing their receptors, and the state of activity of neurobiological networks, conditioning the outcome of their mutual influences. Thus, originally conceptualized as inhibition of 5-HT on DA neuron activity and DA neurotransmission, this interaction is nowadays considered as a multifaceted, mutual influence of these two systems in the regulation of CNS functions. These new ways of understanding this interaction are of utmost importance to envision the consequences of their dysfunctions underlined in several CNS diseases. It is also essential to conceive the mechanism of action of psychotropic drugs directly acting on their function including antipsychotic, antidepressant, antiparkinsonian, and drug of abuse together with the development of therapeutic strategies of Alzheimer's diseases, epilepsy, obsessional compulsive disorders. The 5-HT/DA interaction has a long history from the serendipitous discovery of antidepressants and antipsychotics to the future, rationalized treatments of CNS disorders.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Remote Monitoring in Clinical Trials During the COVID-19 Pandemic

The coronavirus disease 2019 (COVID‐19) pandemic has rapidly challenged the pharmaceutical industry to implement remote clinical trials. The industry’s lack of extensive experience with remote measurements initiates multiple questions about how to select candidates for remote collection, their validity, and regulatory implications of moving certain assessments to a remote mode. We propose a decision tree for migration of clinic to remote assessments and highlight activities required to ensure that these measurements are valid, safe, and usable.

Risperidone stimulates food intake and induces body weight gain via the hypothalamic arcuate nucleus 5-HT2c receptor-NPY pathway

Aims

Many patients taking risperidone for the treatment of psychiatric disorders experience substantial body weight gain. Researchers have speculated that risperidone induces obesity by modulating central signals; however, the precise central mechanisms involved remain to be fully elucidated.

Methods

Twenty‐four C57BL/6J mice were divided into four groups: a control group; a risperidone‐treated group; a lorcaserin‐treated group; and a combined risperidone + lorcaserin‐treated group. The mice were received the corresponding treatments for 4 weeks, and their brains were collected for in situ hybridization analysis. A subset of C57BL/6J mice was administrated with risperidone or placebo, and brains were collected 60 minutes post‐treatment for determination of c‐fos activity. In addition, brains of NPY‐GFP mice treated with or without risperidone were collected to perform colocalization of NPY and c‐fos, as well as NPY and 5‐HT2c receptor using immunohistochemistry.

Results

There was significantly elevated c‐fos expression in the hypothalamic arcuate nucleus (Arc) of risperidone‐treated mice. More than 68% c‐fos‐positive neurons were NPY‐expressing neurons. Furthermore, in situ hybridization revealed that Arc NPY mRNA expression was significantly increased in the risperidone‐treated group compared with control group. Moreover, we identified that 95% 5‐HT2c receptors were colocalized with NPY positive neurons, and increased Arc NPY mRNA expression induced by risperidone was markedly reduced by cotreatment with lorcaserin, a specific 5‐HT2c receptor agonist.

Conclusion

Our findings provide critical insight into the mechanisms underlying antipsychotic‐induced obesity, which may assist the development of therapeutic strategies to address metabolic side effects of risperidone.

Evaluation of Differences in Individual Treatment Response in Schizophrenia Spectrum Disorders: A Meta-analysis

IMPORTANCE

An assumption among clinicians and researchers is that patients with schizophrenia vary considerably in their response to antipsychotic drugs in randomized clinical trials (RCTs).

OBJECTIVE

To evaluate the overall variation in individual treatment response from random variation by comparing the variability between treatment and control groups.

DATA SOURCES

Cochrane Schizophrenia, MEDLINE/PubMed, Embase, PsycINFO, Cochrane CENTRAL, BIOSIS Previews, ClinicalTrials.gov, and World Health Organization International Clinical Trials Registry Platform from January 1, 1955, to December 31, 2016.

STUDY SELECTION

Double-blind, placebo-controlled, RCTs of adults with a diagnosis of schizophrenia spectrum disorders and prescription for licensed antipsychotic drugs.

DATA EXTRACTION AND SYNTHESIS

Means and SDs of the Positive and Negative Syndrome Scale pretreatment and posttreatment outcome difference scores were extracted. Data quality and validity were ensured by following the PRISMA guidelines.

MAIN OUTCOMES AND MEASURES

The outcome measure was the overall variability ratio of treatment to control in a meta-analysis across RCTs. Individual variability ratios were weighted by the inverse-variance method and entered into a random-effects model. A personal element of response was hypothesized to be reflected by a substantial overall increase in variability in the treatment group compared with the control group.

RESULTS

An RCT was simulated, comprising 30 patients with schizophrenia randomized to either the treatment or the control group. The different components of variation in RCTs were illustrated with simulated data. In addition, we assessed the variability ratio in 52 RCTs involving 15 360 patients with a schizophrenia or schizoaffective diagnosis. The variability was slightly lower in the treatment compared with the control group (variability ratio = 0.97; 95% CI, 0.95-0.99; P = .01).

CONCLUSIONS AND RELEVANCE

In this study, no evidence was found in RCTs that antipsychotic drugs increased the outcome variance, suggesting no personal element of response to treatment but instead indicating that the variance was slightly lower in the treatment group than in the control group; although the study cannot rule out that subsets of patients respond differently to treatment, it suggests that the average treatment effect is a reasonable assumption for the individual patient.

New virtual reality tool (Nesplora Aquarium) for assessing attention and working memory in adults: A normative study

Attentional and working memory (WM) processes undergo significant changes during different stages of development. However, currently there are not many continuous performance tools based on virtual reality (VR) for measuring attentional capacity in adults. The present study aimed to obtain normative data for the Nesplora Aquarium VR test in a Spanish population, looking at sex and age variables. In addition, this study also aimed to analyze the psychometric properties of the tool such as scale, internal consistency, and item difficulty and discrimination indices. A total of 1,469 participants from different regions of Spain (57.6% female) with ages ranging from 16 to 90 years old took part in this normative study. Nesplora Aquarium was developed in order to support clinicians in the assessment of attentional processes and WM in adults over 16 years old. It is an 18-minute individual test performed through a VR system. The system provides better visual and auditory immersion in the task than computerized CPTs. This study revealed that the new VR tool, designed to measure adult attention and working memory levels, exhibited good psychometric properties related to reliability and internal consistency. In addition, item difficulty and discrimination values were also acceptable.

Meta-analysis of Dropout Rates in Placebo-Controlled Randomized Clinical Trials of Atypical Antipsychotics Assessed by PANSS

BACKGROUND AND OBJECTIVES

Subject dropout rates in placebo-controlled randomized clinical trials (RCTs) of antipsychotics are high. The missing values due to dropout represent a potential source of bias in clinical trials. We aimed to identify the potential factors affecting subject dropout in atypical antipsychotics RCTs by conducting a meta-analysis.

METHODS

Placebo-controlled RCTs for atypical antipsychotics using positive and negative syndrome scale (PANSS) as a psychiatric assessment scale were selected by database search. The potential factors affecting subject dropout, such as publication year, study design, and operational factors, were analyzed by meta-regression.

RESULTS

Forty-seven placebo controlled RCTs of atypical antipsychotics of which results were published between 1993 and 2018 were identified through the database search. In the multivariate meta-regression analysis, earlier publication year, older age of subjects, and longer study duration were significantly associated with high subject dropout rates in placebo-controlled clinical trials of atypical antipsychotics.

CONCLUSION

Subject dropout rates in clinical trials of atypical antipsychotics published between 1993 and 2018 year decreased over time. Study duration should be taken into consideration when designing future studies, where short study periods yet appropriate for evaluating the efficacy of new atypical antipsychotics are preferable. Additionally, previous medications and the degree of subject satisfaction with antipsychotics might affect subject dropout rate.

MK212, a 5-hydroxytryptamine 2C receptor agonist, inhibits conditioned avoidance responses independent of blocking endogenous dopamine release in rats

Although it is widely accepted that 5-hydroxytryptamine (5-HT) 2C receptor agonists produce antipsychotic effects by reducing endogenous dopamine release from presynaptic neurons, no direct evidence supports this. The aim of the present study was to investigate whether the antipsychotic effects induced by 5-HT_2C receptor agonists are dependent on the inhibition of endogenous dopamine release. We developed a novel conditioned avoidance response paradigm to test this hypothesis. In this assay, rats in which dopamine was depleted by reserpine failed to show conditioned avoidance responses, and the acute administration of quinpirole reversed the disruption of avoidance responses induced by reserpine. This suggests that animals successfully showed conditioned avoidance responses independent of endogenous dopamine release under these experimental conditions. Our results revealed that MK212 (0.5 mg/kg) reduced avoidance responses triggered by quinpirole in dopamine-depleted rats. Therefore, 5-HT_2C receptor agonists can inhibit conditioned avoidance responses independent of blocking endogenous dopamine release. Furthermore, the 5-HT_2C receptor agonist, MK212, decreased the extracellular concentration of glutamate in the nucleus accumbens, indicating that this mechanism may be critical for the antipsychotic effects of 5-HT_2C receptor agonists.

The past and future of novel, non-dopamine-2 receptor therapeutics for schizophrenia: A critical and comprehensive review

Since the discovery of chlorpromazine in the 1950's, antipsychotic drugs have been the cornerstone of treatment of schizophrenia, and all attenuate dopamine transmission at the dopamine-2 receptor. Drug development for schizophrenia since that time has led to improvements in side effects and tolerability, and limited improvements in efficacy, with the exception of clozapine. However, the reasons for clozapine's greater efficacy remain unclear, despite the great efforts and resources invested therewith. We performed a comprehensive review of the literature to determine the fate of previously tested, non-dopamine-2 receptor experimental treatments. Overall we included 250 studies in the review from the period 1970 to 2017 including treatments with glutamatergic, serotonergic, cholinergic, neuropeptidergic, hormone-based, dopaminergic, metabolic, vitamin/naturopathic, histaminergic, infection/inflammation-based, and miscellaneous mechanisms. Despite there being several promising targets, such as allosteric modulation of the NMDA and α7 nicotinic receptors, we cannot confidently state that any of the mechanistically novel experimental treatments covered in this review are definitely effective for the treatment of schizophrenia and ready for clinical use. We discuss potential reasons for the relative lack of progress in developing non-dopamine-2 receptor treatments for schizophrenia and provide recommendations for future efforts pursuing novel drug development for schizophrenia.

Association of Serotonin2c Receptor Polymorphisms With Antipsychotic Drug Response in Schizophrenia

There is conflicting evidence for the association between genetic polymorphisms in the serotonin (5-HT)_2C receptor (HTR2C) and response to antipsychotic drugs (APD) in schizophrenic patients. We tested the association between the HTR2C polymorphisms, Cys23Ser, -759C/T, and -697G/C, and response to APDs (mainly clozapine) in a 6 month prospective study in 171 patients with schizophrenia. Ser23 was significantly associated with treatment response (positive symptoms, X ² = 7.540, p = 0.01; negative symptoms, X ² = 4.796, p = 0.03) in male patients only. A -759C-Ser23 haplotype was similar associated with positive (X ² = 6.648, p = 0.01) and negative (X ² = 6.702, p = 0.01) symptom improvement. Logistic regression, after controlling for covariates, also showed significant haplotypic associations. A meta-analysis of six studies for Ser23 and treatment response showed an overall odds ratio of 2.00 (95%CI, 1.38-2.91, p = 0.0003) or 1.94 (95%CI, 1.27-2.99, p = 0.0024) under fixed or random effect models. These results provide additional evidence that HTR2C polymorphisms are associated with treatment response to APD with HTR2C antagonism or inverse agonism, in male schizophrenic patients.

Meta-analysis of Placebo Response in Randomized Clinical Trials of Antipsychotic Drugs Using PANSS Focusing on Different Approaches to the Handling of Missing Data

BACKGROUND AND OBJECTIVE

Schizophrenia treatment has been shifting to resocialization by efficacious antipsychotic drugs. However, even some of the pivotal studies of approved new antipsychotic drugs with proven efficacy had failed due to high placebo response. The aim of this study was to identify the potential factors affecting placebo response by meta-analysis for randomized clinical trials for antipsychotic drugs using Positive and Negative Syndrome Scale (PANSS) focusing on the current methodological change in the handling of missing data [from last observation carried forward (LOCF) to mixed-effect models for repeated measures (MMRM)] for successful future clinical trials.

METHODS

Recent trends in the degree of placebo response were investigated between publication year (1993 to 2016) and the mean change of PANSS total score in the placebo arm. The potential factors affecting the degree of placebo response, such as study design and operational factors, were analyzed separately by meta-regression for LOCF- and MMRM-based data.

RESULTS

There was no correlation between publication year and the mean change of PANSS score in the placebo arm in schizophrenia studies of 10 years applying MMRM. The number of countries and treatment setting in MMRM-based data and study duration in LOCF-based data were significantly associated with placebo response.

CONCLUSION

Placebo response in schizophrenia clinical trials published between 2007 and 2016 has not increased over time. Differences in the healthcare environment among countries were suggested to affect the evaluation of antipsychotic drugs. Further analyses on the potential factors of placebo response for MMRM-based data are required.

The potentially beneficial central nervous system activity profile of ivacaftor and its metabolites

Ivacaftor-lumacaftor and ivacaftor are two new breakthrough cystic fibrosis transmembrane conductance modulators. The interactions of ivacaftor and its two metabolites hydroxymethylivacaftor (iva-M1) and ivacaftorcarboxylate (iva-M6) with neurotransmitter receptors were investigated in radioligand binding assays. Ivacaftor displayed significant affinity to the 5-hydroxytryptamine (5-HT; serotonin) 5-HT2C receptor (pKi=6.06±0.03), β3-adrenergic receptor (pKi=5.71±0.07), δ-opioid receptor (pKi=5.59±0.06) and the dopamine transporter (pKi=5.50±0.20); iva-M1 displayed significant affinity to the 5-HT2C receptor (pKi=5.81±0.04) and the muscarinic M3 receptor (pKi=5.70±0.10); iva-M6 displayed significant affinity to the 5-HT2A receptor (pKi=7.33±0.05). The in vivo central nervous system activity of ivacaftor (40 mg·kg-1 intraperitoneally for 21 days) was assessed in a chronic mouse model of depression. In the forced swim test, the ivacaftor-treated group displayed decreased immobility (52.8±7.6 s), similarly to fluoxetine (33.8±11.0 s), and increased climbing/swimming activity (181.5±9.2 s). In the open field test, ivacaftor produced higher locomotor activity than the fluoxetine group, measured both as mean number of paw touches (ivacaftor 81.1±9.6 versus fluoxetine 57.9±9.5) and total distance travelled (ivacaftor 120.6±16.8 cm versus fluoxetine 84.5±16.0 cm) in 600 s. Treatment of 23 cystic fibrosis patients with ivacaftor-lumacaftor resulted in significant improvements in quality of life (including anxiety) in all five domains of the AweScoreCF questionnaire (p=0.092-0.096). Our findings suggest ivacaftor displays potential clinical anxiolytic and stimulating properties, and may have beneficial effects on mood.

The activity of the serotonin receptor 2C is regulated by alternative splicing

The central nervous system-specific serotonin receptor 2C (5HT2C) controls key physiological functions, such as food intake, anxiety, and motoneuron activity. Its deregulation is involved in depression, suicidal behavior, and spasticity, making it the target for antipsychotic drugs, appetite controlling substances, and possibly anti-spasm agents. Through alternative pre-mRNA splicing and RNA editing, the 5HT2C gene generates at least 33 mRNA isoforms encoding 25 proteins. The 5HT2C is a G-protein coupled receptor that signals through phospholipase C, influencing the expression of immediate/early genes like c-fos. Most 5HT2C isoforms show constitutive activity, i.e., signal without ligand binding. The constitutive activity of 5HT2C is decreased by pre-mRNA editing as well as alternative pre-mRNA splicing, which generates a truncated isoform that switches off 5HT2C receptor activity through heterodimerization; showing that RNA processing regulates the constitutive activity of the 5HT2C system. RNA processing events influencing the constitutive activity target exon Vb that forms a stable double stranded RNA structure with its downstream intron. This structure can be targeted by small molecules and oligonucleotides that change exon Vb alternative splicing and influence 5HT2C signaling in mouse models, leading to a reduction in food intake. Thus, the 5HT2C system is a candidate for RNA therapy in multiple models of CNS disorders.

Identification of Optically Active Pyrimidine Derivatives as Selective 5-HT2C Modulators

A series of pyrimidine derivatives 4a-i were synthesized and evaluated for their binding affinities towards 5-HT_2C receptors. With regard to designed molecules 4a-i, the influence of the size of alkyl ether and the absolute configuration of a stereogenic center on the 5-HT_2C binding affinity and selectivity was studied. The most promising diasteromeric mixtures 4d and 4e were selected in the initial radioligand binding assay and they were further synthesized as optically active forms starting from optically active alcohols 5d and 5e, prepared by an enzymatic kinetic resolution. Pyrimidine analogue (R,R)-4e displayed an excellent 5-HT_2C binding affinity with good selectivity values against a broad range of other 5-HT receptor subtypes.

The impact of genetics on future drug discovery in schizophrenia

INTRODUCTION

Failures of investigational new drugs (INDs) for schizophrenia have left huge unmet medical needs for patients. Given the recent lackluster results, it is imperative that new drug discovery approaches (and resultant drug candidates) target pathophysiological alterations that are shared in specific, stratified patient populations that are selected based on pre-identified biological signatures. One path to implementing this paradigm is achievable by leveraging recent advances in genetic information and technologies. Genome-wide exome sequencing and meta-analysis of single nucleotide polymorphism (SNP)-based association studies have already revealed rare deleterious variants and SNPs in patient populations. Areas covered: Herein, the authors review the impact that genetics have on the future of schizophrenia drug discovery. The high polygenicity of schizophrenia strongly indicates that this disease is biologically heterogeneous so the identification of unique subgroups (by patient stratification) is becoming increasingly necessary for future investigational new drugs. Expert opinion: The authors propose a pathophysiology-based stratification of genetically-defined subgroups that share deficits in particular biological pathways. Existing tools, including lower-cost genomic sequencing and advanced gene-editing technology render this strategy ever more feasible. Genetically complex psychiatric disorders such as schizophrenia may also benefit from synergistic research with simpler monogenic disorders that share perturbations in similar biological pathways.

Purposeless oral activity induced by meta-chlorophenylpiperazine (m-CPP): Undefined tic-like behaviors?

BACKGROUND

The pathophysiological hypothesis underlying tic disorders in Tourette syndrome (TS) is that basal ganglia are not capable of properly filtering cortical information, leading patients with difficulties in inhibiting unwanted behaviors or impulses. One of the main challenges for furthering such a hypothesis is to find appropriate animal models summarizing some aspects of the disease.

METHODS

It has been established for more than 25 years in rodents that the prototypical serotonin (5-HT) agonist meta-chlorophenylpiperazine (m-CPP) elicits purposeless oral movements including chewing behavior. These bouts of oral movements, originally thought to mimic human oral dyskinesia consequent to long-term administration of antipsychotic drugs or parkinsonian tremor, could correspond to an undefined form of tics. Here, we describe the nature of the purposeless oral movements triggered by m-CPP and other agonists which could be associated with obsessive compulsive disorders. We report the pharmacology of this response with a focus on the 5-HT_2C receptor subtype and the degree to which the dopaminergic and cholinergic systems are involved. The orofacial dyskinetic effects are related to the action of these compounds in associative/limbic territories of the basal ganglia, rather than sensorimotor ones, as expected from the human disease.

CONCLUSION

In spite of the low translational value of these oral movements, the neurobiological analysis of these oral movements could help to a better understanding of the pathophysiology of tics and compulsive disorders often cormorbid with TS.

A short history of the 5-HT2C receptor: from the choroid plexus to depression, obesity and addiction treatment

This paper is a personal account on the discovery and characterization of the 5-HT_2C receptor (first known as the 5-HT_1C receptor) over 30 years ago and how it translated into a number of unsuspected features for a G protein-coupled receptor (GPCR) and a diversity of clinical applications. The 5-HT_2C receptor is one of the most intriguing members of the GPCR superfamily. Initially referred to as 5-HT_1CR, the 5-HT_2CR was discovered while studying the pharmacological features and the distribution of [³H]mesulergine-labelled sites, primarily in the brain using radioligand binding and slice autoradiography. Mesulergine (SDZ CU-085), was, at the time, best defined as a ligand with serotonergic and dopaminergic properties. Autoradiographic studies showed remarkably strong [³H]mesulergine-labelling to the rat choroid plexus. [³H]mesulergine-labelled sites had pharmacological properties different from, at the time, known or purported 5-HT receptors. In spite of similarities with 5-HT₂ binding, the new binding site was called 5-HT_1C because of its very high affinity for 5-HT itself. Within the following 10 years, the 5-HT_1CR (later named 5-HT_2C) was extensively characterised pharmacologically, anatomically and functionally: it was one of the first 5-HT receptors to be sequenced and cloned. The 5-HT_2CR is a GPCR, with a very complex gene structure. It constitutes a rarity in the GPCR family: many 5-HT_2CR variants exist, especially in humans, due to RNA editing, in addition to a few 5-HT_2CR splice variants. Intense research led to therapeutically active 5-HT_2C receptor ligands, both antagonists (or inverse agonists) and agonists: keeping in mind that a number of antidepressants and antipsychotics are 5-HT_2CR antagonists/inverse agonists. Agomelatine, a 5-HT_2CR antagonist is registered for the treatment of major depression. The agonist Lorcaserin is registered for the treatment of aspects of obesity and has further potential in addiction, especially nicotine/ smoking. There is good evidence that the 5-HT_2CR is involved in spinal cord injury-induced spasms of the lower limbs, which can be treated with 5-HT_2CR antagonists/inverse agonists such as cyproheptadine or SB206553. The 5-HT_2CR may play a role in schizophrenia and epilepsy. Vabicaserin, a 5-HT_2CR agonist has been in development for the treatment of schizophrenia and obesity, but was stopped. As is common, there is potential for further indications for 5-HT_2CR ligands, as suggested by a number of preclinical and/or genome-wide association studies (GWAS) on depression, suicide, sexual dysfunction, addictions and obesity. The 5-HT_2CR is clearly affected by a number of established antidepressants/antipsychotics and may be one of the culprits in antipsychotic-induced weight gain.

Monoaminergic and Histaminergic Strategies and Treatments in Brain Diseases

The monoaminergic systems are the target of several drugs for the treatment of mood, motor and cognitive disorders as well as neurological conditions. In most cases, advances have occurred through serendipity, except for Parkinson's disease where the pathophysiology led almost immediately to the introduction of dopamine restoring agents. Extensive neuropharmacological studies first showed that the primary target of antipsychotics, antidepressants, and anxiolytic drugs were specific components of the monoaminergic systems. Later, some dramatic side effects associated with older medicines were shown to disappear with new chemical compounds targeting the origin of the therapeutic benefit more specifically. The increased knowledge regarding the function and interaction of the monoaminergic systems in the brain resulting from in vivo neurochemical and neurophysiological studies indicated new monoaminergic targets that could achieve the efficacy of the older medicines with fewer side-effects. Yet, this accumulated knowledge regarding monoamines did not produce valuable strategies for diseases where no monoaminergic drug has been shown to be effective. Here, we emphasize the new therapeutic and monoaminergic-based strategies for the treatment of psychiatric diseases. We will consider three main groups of diseases, based on the evidence of monoamines involvement (schizophrenia, depression, obesity), the identification of monoamines in the diseases processes (Parkinson's disease, addiction) and the prospect of the involvement of monoaminergic mechanisms (epilepsy, Alzheimer's disease, stroke). In most cases, the clinically available monoaminergic drugs induce widespread modifications of amine tone or excitability through neurobiological networks and exemplify the overlap between therapeutic approaches to psychiatric and neurological conditions. More recent developments that have resulted in improved drug specificity and responses will be discussed in this review.

Repeated administration of 5-hydroxytryptamine 2C agonist MK212 produces a sensitization effect of antipsychotic activity

5-Hydroxytryptamine 2C (5-HT_2C ) receptor agonists have been suggested to possess an antipsychotic activity in several acute preclinical tests of antipsychotic drugs with low extra-pyramidal side effect liability. However, little is known about the long-term effect associated with chronic use of 5-HT_2C receptor agonists. The present study examined whether repeated activation of 5-HT_2C receptor with a highly selective 5-HT_2C receptor agonist MK212 would induce a long-term change in its antipsychotic-like activity (either a sensitization or tolerance) in the conditioned avoidance response and MK801-induced hyperlocomotion tests. Sprague-Dawley rats were first tested under the intraperitoneal (i.p.) treatment of MK212 (0.25, 0.5, 1.0 mg/kg) for 5 consecutive days. Three days later, when all rats were injected with a low dose of MK 212 (0.25 mg/kg) and tested for avoidance responding, rats that had been pretreated with 1.0 and 0.5 mg/kg MK212 made significantly fewer avoidance responses than those that had been treated with vehicle (0.9% saline). However, this past drug exposure-induced group difference was not significant in the MK801-induced hyperlocomotion test. Overall, results from this study suggest that repeated treatment of MK212 is capable of inducing a dose-dependent sensitization of antipsychotic activity in conditioned avoidance response. The discrepancy in sensitization of MK212 in CAR and MK801-induce hyperlocomotion may be related to the different mechanism underlying the effect of MK212 in these two tests. © 2016 IUBMB Life, 68(12):985-993, 2016.

Antipsychotic Drug-Induced Somnolence: Incidence, Mechanisms, and Management

Somnolence is a common side effect of antipsychotics. To assess the incidence of this side effect, we performed a MEDLINE search for randomized, double-blinded, placebo- or active-controlled studies of adult patients treated with antipsychotics for schizophrenia, mania, bipolar depression, or bipolar disorder. We extracted rates of somnolence from original publications and pooled them based on the dose of each antipsychotic in the same psychiatric condition, then estimated the absolute risk increase (ARI) and the number needed to harm (NNH) of an antipsychotic relative to placebo or an active comparator in the same psychiatric condition. According to the ARI in acute schizophrenia, bipolar mania, and bipolar depression, antipsychotics can be classified as high somnolence (clozapine), moderate somnolence (olanzapine, perphenazine, quetiapine, risperidone, ziprasidone), and low somnolence (aripiprazole, asenapine, haloperidol, lurasidone, paliperidone, cariprazine). The risk of somnolence with blonanserin, brexpiprazole, chlorpromazine, iloperidone, sertindole, and zotepine needs further investigation. The rates of somnolence were positively correlated to dose and duration for some antipsychotics, but not for others. Many factors, including antipsychotic per se, the method used to measure somnolence, patient population, study design, and dosing schedule, might affect the incidence of antipsychotic-induced somnolence. The mechanisms of antipsychotic-induced somnolence are likely multifactorial, although the blockade of histamine 1 receptors and α1 receptors may play a major role. The management of antipsychotic-induced somnolence should include sleep hygiene education, choosing an antipsychotic with a lower risk for somnolence, starting at a lower dose with a slower titration based on psychiatric diagnoses, adjusting doses when necessary, and minimizing concurrent somnolence-prone agents. Since most cases of somnolence were mild to moderate, allowing tolerance to develop over at least 4 weeks is reasonable before discontinuing an antipsychotic.

Atypical antipsychotics and inverse agonism at 5-HT2 receptors

It is now well accepted that receptors can regulate cellular signaling pathways in the absence of a stimulating ligand, and inverse agonists can reduce this ligand-independent or "constitutive" receptor activity. Both the serotonin 5-HT2A and 5-HT2C receptors have demonstrated constitutive receptor activity in vitro and in vivo. Each has been identified as a target for treatment of schizophrenia. Further, most, if not all, atypical antipsychotic drugs have inverse agonist properties at both 5-HT2A and 5-HT2C receptors. This paper describes our current knowledge of inverse agonism of atypical antipsychotics at 5-HT2A/2C receptor subtypes in vitro and in vivo. Exploiting inverse agonist properties of APDs may provide new avenues for drug development.

Serotonergic modulation of the activity of mesencephalic dopaminergic systems: Therapeutic implications

Since their discovery in the mammalian brain, it has been apparent that serotonin (5-HT) and dopamine (DA) interactions play a key role in normal and abnormal behavior. Therefore, disclosure of this interaction could reveal important insights into the pathogenesis of various neuropsychiatric diseases including schizophrenia, depression and drug addiction or neurological conditions such as Parkinson's disease and Tourette's syndrome. Unfortunately, this interaction remains difficult to study for many reasons, including the rich and widespread innervations of 5-HT and DA in the brain, the plethora of 5-HT receptors and the release of co-transmitters by 5-HT and DA neurons. The purpose of this review is to present electrophysiological and biochemical data showing that endogenous 5-HT and pharmacological 5-HT ligands modify the mesencephalic DA systems' activity. 5-HT receptors may control DA neuron activity in a state-dependent and region-dependent manner. 5-HT controls the activity of DA neurons in a phasic and excitatory manner, except for the control exerted by 5-HT_2C receptors which appears to also be tonically and/or constitutively inhibitory. The functional interaction between the two monoamines will also be discussed in view of the mechanism of action of antidepressants, antipsychotics, anti-Parkinsonians and drugs of abuse.

Further Advances in Optimizing (2-Phenylcyclopropyl)methylamines as Novel Serotonin 2C Agonists: Effects on Hyperlocomotion, Prepulse Inhibition, and Cognition Models

A series of novel compounds with two halogen substituents have been designed and synthesized to further optimize the 2-phenylcyclopropylmethylamine scaffold in the quest for drug-like 5-HT2C agonists. Compound (+)-22a was identified as a potent 5-HT2C receptor agonist, with good selectivity against the 5-HT2B and the 5-HT2A receptors. ADMET assays showed that compound (+)-22a possessed desirable properties in terms of its microsomal stability, and CYP and hERG inhibition, along with an excellent brain penetration profile. Evaluation of (+)-22a in animal models of schizophrenia-related behaviors revealed that it had a desirable activity profile, as it reduced d-amphetamine-stimulated hyperlocomotion in the open field test, it restored d-amphetamine-disrupted prepulse inhibition, it induced cognitive improvements in the novel object recognition memory test in NR1-KD animals, and it produced very little catalepsy relative to haloperidol. These data support the further development of (+)-22a as a drug candidate for the treatment of schizophrenia.

We Need 2C but Not 2B: Developing Serotonin 2C (5-HT2C) Receptor Agonists for the Treatment of CNS Disorders

The serotonin 2C (5-HT2C ) receptor has been identified as a potential drug target for the treatment of a variety of central nervous system (CNS) disorders, such as obesity, substance abuse, and schizophrenia. In this Viewpoint article, recent progress in developing selective 5-HT2C agonists for use in treating these disorders is summarized, including the work of our group. Challenges in this field and the possible future directions are described. Homology modeling as a method to predict the binding modes of 5-HT2C ligands to the receptor is also discussed. Compared to known ligands, the improved pharmacological profiles of the 2-phenylcyclopropylmethylamine-based 5-HT2C agonists make them preferred candidates for further studies.

New therapeutic opportunities for 5-HT2C receptor ligands in neuropsychiatric disorders

The 5-HT2C receptor (R) displays a widespread distribution in the CNS and is involved in the action of 5-HT in all brain areas. Knowledge of its functional role in the CNS pathophysiology has been impaired for many years due to the lack of drugs capable of discriminating among 5-HT2R subtypes, and to a lesser extent to the 5-HT1B, 5-HT5, 5-HT6 and 5-HT7Rs. The situation has changed since the mid-90s due to the increased availability of new and selective synthesized compounds, the creation of 5-HT2C knock out mice, and the progress made in molecular biology. Many pharmacological classes of drugs including antipsychotics, antidepressants and anxiolytics display affinities toward 5-HT2CRs and new 5-HT2C ligands have been developed for various neuropsychiatric disorders. The 5-HT2CR is presumed to mediate tonic/constitutive and phasic controls on the activity of different central neurobiological networks. Preclinical data illustrate this complexity to a point that pharmaceutical companies developed either agonists or antagonists for the same disease. In order to better comprehend this complexity, this review will briefly describe the molecular pharmacology of 5-HT2CRs, as well as their cellular impacts in general, before addressing its central distribution in the mammalian brain. Thereafter, we review the preclinical efficacy of 5-HT2C ligands in numerous behavioral tests modeling human diseases, highlighting the multiple and competing actions of the 5-HT2CRs in neurobiological networks and monoaminergic systems. Notably, we will focus this evidence in the context of the physiopathology of psychiatric and neurological disorders including Parkinson's disease, levodopa-induced dyskinesia, and epilepsy.

Therapeutic Potential of 5-HT2C Receptor Agonists for Addictive Disorders

The neurotransmitter 5-hydroxytryptamine (5-HT; serotonin) has long been associated with the control of a variety of motivated behaviors, including feeding. Much of the evidence linking 5-HT and feeding behavior was obtained from studies of the effects of the 5-HT releaser (dex)fenfluramine in laboratory animals and humans. Recently, the selective 5-HT2C receptor agonist lorcaserin received FDA approval for the treatment of obesity. This review examines evidence to support the use of selective 5-HT2C receptor agonists as treatments for conditions beyond obesity, including substance abuse (particularly nicotine, psychostimulant, and alcohol dependence), obsessive compulsive, and excessive gambling disorder. Following a brief survey of the early literature supporting a role for 5-HT in modulating food and drug reinforcement, we propose that intrinsic differences between SSRI and serotonin releasers may have underestimated the value of serotonin-based pharmacotherapeutics to treat clinical forms of addictive behavior beyond obesity. We then highlight the critical involvement of the 5-HT2C receptor in mediating the effect of (dex)fenfluramine on feeding and body weight gain and the evidence that 5-HT2C receptor agonists reduce measures of drug reward and impulsivity. A recent report of lorcaserin efficacy in a smoking cessation trial further strengthens the idea that 5-HT2C receptor agonists may have potential as a treatment for addiction. This review was prepared as a contribution to the proceedings of the 11th International Society for Serotonin Research Meeting held in Hermanus, South Africa, July 9-12, 2014.

Negative symptoms of schizophrenia: clinical characteristics, pathophysiological substrates, experimental models and prospects for improved treatment

Schizophrenia is a complex and multifactorial disorder generally diagnosed in young adults at the time of the first psychotic episode of delusions and hallucinations. These positive symptoms can be controlled in most patients by currently-available antipsychotics. Conversely, they are poorly effective against concomitant neurocognitive dysfunction, deficits in social cognition and negative symptoms (NS), which strongly contribute to poor functional outcome. The precise notion of NS has evolved over the past century, with recent studies - underpinned by novel rating methods - suggesting two major sub-domains: "decreased emotional expression", incorporating blunted affect and poverty of speech, and "avolition", which embraces amotivation, asociality and "anhedonia" (inability to anticipate pleasure). Recent studies implicate a dysfunction of frontocortico-temporal networks in the aetiology of NS, together with a disruption of cortico-striatal circuits, though other structures are also involved, like the insular and parietal cortices, amygdala and thalamus. At the cellular level, a disruption of GABAergic-glutamatergic balance, dopaminergic signalling and, possibly, oxytocinergic and cannibinoidergic transmission may be involved. Several agents are currently under clinical investigation for the potentially improved control of NS, including oxytocin itself, N-Methyl-d-Aspartate receptor modulators and minocycline. Further, magnetic-electrical "stimulation" strategies to recruit cortical circuits and "cognitive-behavioural-psychosocial" therapies likewise hold promise. To acquire novel insights into the causes and treatment of NS, experimental study is crucial, and opportunities are emerging for improved genetic, pharmacological and developmental modelling, together with more refined readouts related to deficits in reward, sociality and "expression". The present article comprises an integrative overview of the above issues as a platform for this Special Issue of European Neuropsychopharmacology in which five clinical and five preclinical articles treat individual themes in greater detail. This Volume provides, then, a framework for progress in the understanding - and ultimately control - of the debilitating NS of schizophrenia.

A novel aminotetralin-type serotonin (5-HT) 2C receptor-specific agonist and 5-HT2A competitive antagonist/5-HT2B inverse agonist with preclinical efficacy for psychoses

Development of 5-HT2C agonists for treatment of neuropsychiatric disorders, including psychoses, substance abuse, and obesity, has been fraught with difficulties, because the vast majority of reported 5-HT2C selective agonists also activate 5-HT2A and/or 5-HT2B receptors, potentially causing hallucinations and/or cardiac valvulopathy. Herein is described a novel, potent, and efficacious human 5-HT2C receptor agonist, (-)-trans-(2S,4R)-4-(3'[meta]-bromophenyl)-N,N-dimethyl-1,2,3,4-tetrahydronaphthalen-2-amine (-)-MBP), that is a competitive antagonist and inverse agonist at human 5-HT2A and 5-HT2B receptors, respectively. (-)-MBP has efficacy comparable to the prototypical second-generation antipsychotic drug clozapine in three C57Bl/6 mouse models of drug-induced psychoses: the head-twitch response elicited by [2,5]-dimethoxy-4-iodoamphetamine; hyperlocomotion induced by MK-801 [(5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (dizocilpine maleate)]; and hyperlocomotion induced by amphetamine. (-)-MBP, however, does not alter locomotion when administered alone, distinguishing it from clozapine, which suppresses locomotion. Finally, consumption of highly palatable food by mice was not increased by (-)-MBP at a dose that produced at least 50% maximal efficacy in the psychoses models. Compared with (-)-MBP, the enantiomer (+)-MBP was much less active across in vitro affinity and functional assays using mouse and human receptors and also translated in vivo with comparably lower potency and efficacy. Results indicate a 5-HT2C receptor-specific agonist, such as (-)-MBP, may be pharmacotherapeutic for psychoses, without liability for obesity, hallucinations, heart disease, sedation, or motoric disorders.