Differential regional and dose-related effects of asenapine on dopamine receptor subtypes

Estimation of target occupancy in repeated dosing design studies using positron emission tomography: Biases due to target upregulation

Positron emission tomography (PET) has become indispensable in the quantification of target engagement by brain targeting medications. The relationship between the drug plasma concentration (or drug dose administered) and target occupancy determined during a PET occupancy study has provided valuable information for the assessment of novel pharmaceuticals in the early phases of drug development. Such information is also critical for the understanding of the mechanisms of action and side-effect profile of approved medication commonly used in the clinic. Occupancy studies conducted following repeated drug dosing (RD) can produce systematic differences from those conducted following single drug dose (SD), differences that have not been adequately explored. We have hypothesised that when differences are observed between RD and SD studies, they are related to changes in target density induced by repeated drug accumulation. We have developed a modified occupancy model to account for potential changes in target density and tested it on a sample dataset. We found that target upregulation can parsimoniously explain the differences in drug affinity estimated in SD and RD studies. Our findings have implications for the interpretation of RD occupancy data in the literature and the relationship between specific target occupancy levels and drug efficacy and tolerability.

Structural and expression analysis of the dopamine receptors reveals their crucial roles in regulating the insulin signaling pathway in oysters

Dopamine performs its critical role upon binding to receptors. Since dopamine receptors are numerous and versatile, understanding their protein structures and evolution status, and identifying the key receptors involved in the modulation of insulin signaling will provide essential clues to investigate the molecular mechanism of neuroendocrine regulating the growth in invertebrates. In this study, seven dopamine receptors were identified in the Pacific oysters (Crassostrea gigas) and were classified into four subtypes according to their protein secondary and tertiary structures, and ligand-binding activities. Of which, DR2 (dopamine receptor 2) and D(2)RA-like (D(2) dopamine receptor A-like) were considered the invertebrate-specific type 1 and type 2 dopamine receptors, respectively. Expression analysis indicated that the DR2 and D(2)RA-like were highly expressed in the fast-growing oyster "Haida No.1". After in vitro incubation of ganglia and adductor muscle with exogenous dopamine and dopamine receptor antagonists, the expression of these two dopamine receptors and ILPs (insulin-like peptides) was also significantly affected. Dual-fluorescence in situ hybridization results showed that D(2)RA-like and DR2 were co-localized with MIRP3 (molluscan insulin-related peptide 3) and MIRP3-like (molluscan insulin-related peptide 3-like) in the visceral ganglia, and were co-localized with ILP (insulin-like peptide) in the adductor muscle. Furthermore, the downstream components of dopamine signaling, including PKA, ERK, CREB, CaMKK1, AKT, and GSK3β were also significantly affected by the exogenous dopamine and dopamine receptor antagonists. These findings confirmed that dopamine might affect the secretion of ILPs through the invertebrate-specific dopamine receptors D(2)RA-like and DR2, and thus played crucial roles in the growth regulation of the Pacific oysters. Our study establishes the potential regulatory relationship between the dopaminergic system and insulin-like signaling pathway in marine invertebrates.

The Effects of Antipsychotics on the Synaptic Plasticity Gene Homer1a Depend on a Combination of Their Receptor Profile, Dose, Duration of Treatment, and Brain Regions Targeted

Background: Antipsychotic agents modulate key molecules of the postsynaptic density (PSD), including the Homer1a gene, implicated in dendritic spine architecture. How the antipsychotic receptor profile, dose, and duration of administration may influence synaptic plasticity and the Homer1a pattern of expression is yet to be determined. Methods: In situ hybridization for Homer1a was performed on rat tissue sections from cortical and striatal regions of interest (ROI) after acute or chronic administration of three antipsychotics with divergent receptor profile: Haloperidol, asenapine, and olanzapine. Univariate and multivariate analyses of the effects of topography, treatment, dose, and duration of antipsychotic administration were performed. Results: All acute treatment regimens were found to induce a consistently higher expression of Homer1a compared to chronic ones. Haloperidol increased Homer1a expression compared to olanzapine in striatum at the acute time-point. A dose effect was also observed for acute administration of haloperidol. Conclusions: Biological effects of antipsychotics on Homer1a varied strongly depending on the combination of their receptor profile, dose, duration of administration, and throughout the different brain regions. These molecular data may have translational valence and may reflect behavioral sensitization/tolerance phenomena observed with prolonged antipsychotics.

The role of dopamine D3 receptors in the mechanism of action of cariprazine

Cariprazine is a new atypical antipsychotic drug (APD) with a unique pharmacodynamic profile, different from both typical and atypical APDs. Specifically, cariprazine acts as a partial agonist at the dopamine (DA) D2 and D3 receptors and serotonin 5-HT1A receptors, and as an antagonist at the 5-HT2B receptors. Moreover, it shows moderate affinities for adrenergic, histaminergic, and cholinergic receptors that are involved in mediating the side effects characteristic of typical APDs. In this review, we discuss the contribution of DA D3 receptors (D3Rs) in the etiology and pathophysiology of schizophrenia and the potential benefits that may be associated with a more selective targeting of D3R by APDs, as compared to other dopaminergic and non-dopaminergic receptor subtypes. Cariprazine, by acting on D3Rs, ameliorates anhedonia and cognitive deficits in animal models based on environmental or pharmacological manipulation. The reviewed results support the potential benefits of cariprazine in treating negative symptoms and cognitive deficits of schizophrenia, and therefore representing a promising approach in addressing the unmet clinical needs for the improved treatment of this serious neuropsychiatric disorder.

Long-term effects of iloperidone on cerebral dopamine receptor subtypes

The atypical antipsychotic drug iloperidone has high affinity for a wide range of neurotransmitter receptors, including dopaminergic (DA), serotonergic, and adrenergic receptors. We examined the long-term effects of multiple doses of iloperidone on DA D1 , D2 , D3 , and D4 receptor subtypes. Sprague-Dawley adult rats (n = 8/group) received daily intraperitoneal injections of iloperiodone (0.5, 1, or 5 mg/kg) or vehicle for 4 weeks. Receptor autoradiography quantified the levels of DA receptors in medial prefrontal cortex (MPC), dorsolateral frontal cortex (DFC), caudate putamen (CPu), nucleus accumbens (NAc), and hippocampus (HIP). Four weeks of iloperidone treatment at 5 mg/kg significantly increased D1 receptors in NAc (36%) and CPu (38%). Iloperidone (1.5 and 5 mg/kg) dose-dependently increased D2 receptors in MPC (37 and 47%) and HIP (32 and 40%). Only the high dose of iloperidone (5 mg/kg) increased D2 receptors in NAc (39%) and CPu (38%). Repeated treatment with iloperidone (1.5 and 5 mg/kg) increased D4 receptors in the NAc (39 and 78%), CPu (42 and 83%) and HIP (54 and 72%). The three doses of iloperidone failed to alter D3 receptors in the brain regions examined in this study. These results suggest that iloperidone exerts region- and dose-specific effects on forebrain DA receptor subtypes, which may contribute to its therapeutic benefits in improving the positive and negative symptoms of schizophrenia with minimal extrapyramidal side effects.

The preclinical discovery and development of cariprazine for the treatment of schizophrenia

INTRODUCTION

Cariprazine is approved in the United States and Europe for the treatment of manic or mixed episodes associated with bipolar I disorder and for the treatment of schizophrenia in adult patients. It is typically administered orally once a day (a dose range 1.5 - 6 mg/day), does require titration, and may be given with or without food. It has a half-life of 2 - 4 days with an active metabolite that has a terminal half-life of 2 - 3 weeks. Areas covered: This review article focuses on the preclinical discovery of cariprazine providing details regarding its pharmacological, behavioral, and neurochemical mechanisms and its contribution to clinical therapeutic benefits. This article is based on the available literature with respect to the preclinical and clinical findings and product labels of cariprazine. Expert opinion: Cariprazine shows highest affinity toward D₃ receptors, followed by D₂, 5-HT_2B, and 5-HT_1A receptors. It also shows moderate affinity toward σ₁, 5-HT_2A, and histamine H₁ receptors. Long-term administration of cariprazine altered the abundance of dopamine, serotonin, and glutamate receptor subtypes in different brain regions. All these mechanisms of cariprazine may contribute toward its unique preclinical profile and its clinically observed benefits in the treatment of schizophrenia, bipolar mania, and possibly other psychiatric disorders.

Dopamine and μ-opioid receptor dysregulation in the brains of binge-eating female rats - possible relevance in the psychopathology and treatment of binge-eating disorder

Adult, female rats given irregular, limited access to chocolate develop binge-eating behaviour with normal bodyweight and compulsive/perseverative and impulsive behaviours similar to those in binge-eating disorder. We investigated whether (a) dysregulated central nervous system dopaminergic and opioidergic systems are part of the psychopathology of binge-eating and (b) these neurotransmitter systems may mediate the actions of drugs ameliorating binge-eating disorder psychopathology. Binge-eating produced a 39% reduction of striatal D₁ receptors with 22% and 23% reductions in medial and lateral caudate putamen and a 22% increase of striatal μ-opioid receptors. There was no change in D₁ receptor density in nucleus accumbens, medial prefrontal cortex or dorsolateral frontal cortex, striatal D₂ receptors and dopamine reuptake transporter sites, or μ-opioid receptors in frontal cortex. There were no changes in ligand affinities. The concentrations of monoamines, metabolites and estimates of dopamine (dopamine/dihydroxyphenylacetic acid ratio) and serotonin/5-hydroxyindolacetic acid ratio turnover rates were unchanged in striatum and frontal cortex. However, turnover of dopamine and serotonin in the hypothalamus was increased ~20% and ~15%, respectively. Striatal transmission via D₁ receptors is decreased in binge-eating rats while μ-opioid receptor signalling may be increased. These changes are consistent with the attenuation of binge-eating by lisdexamfetamine, which increases catecholaminergic neurotransmission, and nalmefene, a μ-opioid antagonist.

Repeated asenapine treatment does not participate in the mild stress induced FosB/ΔFosB expression in the rat hypothalamic paraventricular nucleus neurons

Effect of repeated asenapine (ASE) treatment on FosB/ΔFosB expression was studied in the hypothalamic paraventricular nucleus (PVN) of male rats exposed to chronic mild stress (CMS) for 21days. Our intention was to find out whether repeated ASE treatment for 14days may: 1) induce FosB/ΔFosB expression in the PVN; 2) activate selected PVN neuronal phenotypes, synthesizing oxytocin (OXY), vasopressin (AVP), corticoliberin (CRH) or tyrosine hydroxylase (TH); and 3) interfere with the impact of CMS. Control, ASE, CMS, and CMS+ASE treated groups were used. CMS included restraint, social isolation, crowding, swimming, and cold. From the 7th day of CMS, rats received ASE (0.3mg/kg) or saline (300μl/rat) subcutaneously, twice a day for 14days. They were sacrificed on the day 22nd (16-18h after last treatments). FosB/ΔFosB was visualized with avidin biotin peroxidase complex and OXY, AVP, CRH or TH antibodies by fluorescent dyes. Saline and ASE did not promote FosB/ΔFosB expression in the PVN. CMS and CMS+ASE elicited FosB/ΔFosB-expression in the PVN, whereas, ASE did not augment or attenuate FosB/ΔFosB induction elicited by CMS. FosB/ΔFosB-CRH occurred after CMS and CMS+ASE treatments in the PVN middle sector, while FosB/ΔFosB-AVP and FosB/ΔFosB-OXY after CMS and CMS+ASE treatments in the PVN posterior sector. FosB/ΔFosB-TH colocalization was rare. Larger FosB/ΔFosB profiles, running above the PVN, did not show any colocalizations. The study provides an anatomical/functional knowledge about an unaccented nature of prolonged ASE treatment at the level of PVN and excludes its positive or negative interplay with CMS effect. Data indicate that long-lasting ASE treatment might not act as a stressor acting at the PVN level.

Impact of repeated asenapine treatment on FosB/ΔFosB expression in the forebrain structures under normal conditions and mild stress preconditioning in the rat

Long-term effect of asenapine (ASE), an atypical antipsychotic drug, on FosB/ΔFosB quantitative variations in the striatum, septum, nucleus accumbens, and prefrontal cortex, was light microscopically evaluated in normal rats and rats preconditioned with chronic unpredictable mild stress (CMS). CMS included restraint, social isolation, crowding, swimming, and cold. The rats were exposed to CMS for 21 days. From the 7th day of CMS, the rats were injected subcutaneously with saline (300μl/rat) or ASE (0.3mg/kg b.w.), twice a day for 14 days. On the 22nd day, i.e. 16-18h after the last treatment, the animals were perfused with fixative and the brains cut into 30μm thick coronal sections. FosB/ΔFosB protein was immunohistochemically visualized by avidin-biotin peroxidase complex (ABC). Four groups of animals were investigated: control+vehicle, control+ASE, CMS+vehicle, and CMS+ASE. Repeated ASE treatment significantly increased the amount of FosB/ΔFosB immunostained cell nuclei in the dorsolateral and dorsomedial striatum and the shell of the nucleus accumbens, followed by strVM and coACC, as assessed by numerical analysis in both total (different size for each structure) and unified (equal size for each structure) brain sectors. The effect of ASE was significantly lowered by CMS preconditioning only in the dorsolateral striatum, dorsomedial striatum, and the shell of the nucleus accumbens, indicated by both total and unified calculations. Although, highest FosB/ΔFosB expression was seen in the prefrontal cortex and lowest in the dorsolateral and ventrolateral septum, no differences between the groups occurred. CMS itself did not affect FosB/ΔFosB expression level. These findings demonstrate for the first time that repeated administration of ASE may result in eliciting of long-lasting FosB/ΔFosB-like transcription factors that could mediate some of the persistent and region-specific changes in brain function, interconnected with chronic drug exposure. However, it cannot be excluded that the impact of repeated ASE exposure might be influenced by an ambient stressogen leverage.

The Incidence of Akathisia in the Treatment of Schizophrenia with Aripiprazole, Asenapine and Lurasidone: A Meta-Analysis

Akathisia is a troubling side effect that leads to non-adherence with antipsychotic regimens. Second generation antipsychotics (SGAs) tend to cause less akathisia than older agents but the risk still exists and rates vary between agents. Little is known about the incidence of akathisia among the newer SGAs. The purpose of this study was to conduct a meta-analysis of akathisia incidence rates for three of the newer SGAs: aripiprazole, asenapine, and lurasidone. Data were drawn from published and unpublished clinical trials comparing the drug of interest to either placebo or another SGA in adults with schizophrenia. Twenty-four studies (11 aripiprazole, 5 asenapine, and 8 lurasidone) provided incidence rates for akathisia and related nervous system events. Data showed that the relative risk (RR) of akathisia was double that of controls, with lurasidone having the highest individual RR at 2.7 [CI: 2-3.6]. Sensitivity analysis changed the RR of akathisia to less than 10%. The RR of akathisia was still elevated (1.75 [1.4-2.1]) when these drugs were compared only to actives (older SGAs). Agitation and anxiety RRs were also higher with the newer SGAs as compared to the older SGAs. Previous theory suggests antagonism of serotonin (5-HT)2A receptors may decrease akathisia risk. Expectations were that aripiprazole, asenapine and lurasidone would have a low incidence of akathisia, as all display strong antagonism at 5-HT2A. However, in this study all three had a significantly higher risk of akathisia compared to placebo or other SGAs. This suggests the pathophysiology of akathisia involves other receptors and is multifactorial.

Asenapine in the Treatment of Acute Mania: A Real-World Observational Study With 6 Months Follow-Up

Asenapine is a second-generation antipsychotic with a unique pharmacological profile that was recently approved for the treatment of moderate/severe manic episodes. Real-world data on rapidity of action in inpatient settings are lacking.The aims of the current real-world observational study were to evaluate: (i) short-term efficacy of asenapine after 7 days (T0-T1) in patients hospitalized for a manic episode in the course of bipolar I disorder or schizoaffective disorder (group A), (ii) differences in length of stay (LoS), and (iii) rehospitalization compared to a control population (group B) with a 6-month follow-up.Twenty patients were included in each group. The mean total Young Mania Rating Scale score decreased by 12.6 (SD ±10.3; t(17) = 5.2, P < 0.005), implying a mean 37.8% improvement. A statistically significant reduction was observed for all Young Mania Rating Scale items, except for "sexual interest." The mean total BPRS score decreased by 17.2 (SD ±14.9; t(17) = 4.9, P < 0.005). A statistically significant reduction was observed for several items, including "conceptual disorganization," "grandiosity," "unusual thought content," and "excitement". Length of stay was 17.9 (SD ±9.0) days for group A and 14.7 (SD ±12.7) days for group B; the result of the Kruskal-Wallis test showed no significant differences (χ = 2.199, P = 0.138). Despite a high discontinuation rate, only 17.7% of patients in group A were rehospitalized in the following 6 months compared to 41.2% of those in group B (relative risk = 0.43, 95% confidence interval, 0.13-1.39).Findings from this small, preliminary study at least partially support the results of previous trials, confirming effectiveness and tolerability in the context of comorbidity and polypsychopharmacology.

Progressive recruitment of cortical and striatal regions by inducible postsynaptic density transcripts after increasing doses of antipsychotics with different receptor profiles: insights for psychosis treatment

Antipsychotics may modulate the transcription of multiple gene programs, including those belonging to postsynaptic density (PSD) network, within cortical and subcortical brain regions. Understanding which brain region is activated progressively by increasing doses of antipsychotics and how their different receptor profiles may impact such an activation could be relevant to better correlate the mechanism of action of antipsychotics both with their efficacy and side effects. We analyzed the differential topography of PSD transcripts by incremental doses of two antipsychotics: haloperidol, the prototypical first generation antipsychotic with prevalent dopamine D2 receptors antagonism, and asenapine, a second generation antipsychotic characterized by multiple receptors occupancy. We investigated the expression of PSD genes involved in synaptic plasticity and previously demonstrated to be modulated by antipsychotics: Homer1a, and its related interacting constitutive genes Homer1b/c and PSD95, as well as Arc, C-fos and Zif-268, also known to be induced by antipsychotics administration. We found that increasing acute doses of haloperidol induced immediate-early genes (IEGs) expression in different striatal areas, which were progressively recruited by incremental doses with a dorsal-to-ventral gradient of expression. Conversely, increasing acute asenapine doses progressively de-recruited IEGs expression in cortical areas and increased striatal genes signal intensity. These effects were mirrored by a progressive reduction in locomotor animal activity by haloperidol, and an opposite increase by asenapine. Thus, we demonstrated for the first time that antipsychotics may progressively recruit PSD-related IEGs expression in cortical and subcortical areas when administered at incremental doses and these effects may reflect a fine-tuned dose-dependent modulation of the PSD.

Asenapine sensitization from adolescence to adulthood and its potential molecular basis

Asenapine is a new antipsychotic drug that induces a long-lasting behavioral sensitization in adult rats. The present study investigated the developmental impacts of adolescent asenapine treatment on drug sensitivity and on 3 proteins implicated in the action of antipsychotic drugs (i.e. brain-derived neurotrophic factor (BDNF), dopamine D2 receptor, and ΔFosB) in adulthood. Male adolescent Sprague-Dawley rats (postnatal days, P 43-48) were first treated with asenapine (0.05, 0.10 or 0.20mg/kg, sc) and tested in the conditioned avoidance or PCP (2.0mg/kg, sc)-induced hyperlocomotion tasks for 5 days. After they became adults (∼P 76), asenapine sensitization was assessed in a single avoidance or PCP-induced hyperlocomotion challenge test with all rats being injected with asenapine (0.10mg/kg, sc). Rats were then sacrificed 1 day later and BDNF, D2 and ΔFosB in the prefrontal cortex, striatum and hippocampus were examined using Western blotting. In adolescence, repeated asenapine treatment produced a persistent and dose-dependent inhibition of avoidance response, spontaneous motor activity and PCP-induced hyperlocomotion. In the asenapine challenge test, adult rats treated with asenapine (0.10 and 0.20mg/kg) in adolescence made significantly fewer avoidance responses and showed a stronger inhibition of spontaneous motor activity than those previously treated with saline. However, no group difference in the levels of BDNF, D2 and ΔFosB expression was found. These findings suggest that although adolescent asenapine treatment for a short period of time induces a robust behavioral sensitization that persists into adulthood, such a long-term effect is not likely to be mediated by BDNF, D2 and ΔFosB.

Long-term effects of cariprazine exposure on dopamine receptor subtypes

INTRODUCTION

All clinically effective antipsychotics are known to act on the dopaminergic system, and previous studies have demonstrated that repeated treatment with antipsychotics produced region-specific changes in dopamine receptor levels. Cariprazine is a dopamine D₃ and D₂ receptor partial agonist with preferential binding to D₃ receptors. We examined the effects of chronic cariprazine administration on dopamine receptor levels.

METHODS

Rats were administered either vehicle or cariprazine (0.06, 0.2, or 0.6 mg/kg) for 28 days. Dopamine receptor levels were quantitated using autoradiographic assays on brain tissue sections from the medial prefrontal cortex (mPFC), nucleus accumbens (NAc), caudate putamen (CPu), hippocampus (HIPP), olfactory tubercle (OT), and islands of Calleja (ICj).

RESULTS

Chronic treatment with cariprazine did not alter D₁ receptor levels in any brain region tested. Cariprazine increased D₂ receptor levels in mPFC (27%-43%), NAc (40%-45%), medial (41%-53%) and lateral (52%-63%) CPu, and HIPP (38%). Cariprazine dose-dependently upregulated D₃ receptor levels in ICj (32%-57%), OT (27%-67%), and NAc shell (31%-48%). Repeated cariprazine treatment increased D₄ receptor in NAc (53%-82%), medial (54%-98%) and lateral (58%-74%) CPu, and HIPP (38%-98%).

CONCLUSION

Similar to other antipsychotics, cariprazine upregulated D₂ and D₄ receptor levels in various brain regions. Cariprazine was unique among antipsychotics in increasing D₃ receptor levels, which may support its unique psychopharmacologic properties.

Time-dependence of risperidone and asenapine sensitization and associated D2 receptor mechanism

When an antipsychotic drug is given repeatedly and intermittently, there is often a long-term increase in its behavioral efficacy, termed antipsychotic sensitization. With the passage of time, the magnitude of antipsychotic sensitization may increase or decrease based on the principle of time-dependent sensitization (TDS) or memory decay, respectively. In the present study, we examined the time-dependent feature and possible dopamine D2 receptor mechanism of sensitization induced by risperidone and asenapine in the conditioned avoidance response test. Well-trained male adult Sprague-Dawley rats were first repeatedly treated with risperidone (1.0mg/kg) or asenapine (0.2mg/kg) and tested for avoidance response daily for 5 consecutive days. Eight, 18 or 38 days after the 5th drug treatment, all rats were retested drug-free to assess the long-term impact of prior risperidone or asenapine treatment. Drug-pretreated rats had significantly lower avoidance than vehicle-pretreated ones on this test, and the group differences increased with the passage of time. In the subsequent drug challenge test at 10, 20 or 40 days after the 5th drug treatment, all rats were injected with a low dose of risperidone (0.3mg/kg) or asenapine (0.1mg/kg). Drug-pretreated rats again made significantly fewer avoidances than controls, confirming the antipsychotic sensitization effect. Finally, in the quinpirole (a D2/3 receptor agonist, 1.0mg/kg, sc)-induced hyperlocomotion test, risperidone-pretreated rats exhibited a significantly higher level of motor activity than the vehicle-pretreated ones. These findings suggest that risperidone and asenapine sensitization is long-lasting, follows the TDS principle, and is likely mediated by D2 receptor supersensitivity.

Repeated asenapine treatment produces a sensitization effect in two preclinical tests of antipsychotic activity

Among several commonly used atypical antipsychotic drugs, olanzapine and risperidone cause a sensitization effect in the conditioned avoidance response (CAR) and phencyclidine (PCP)-induced hyperlocomotion paradigms--two well established animal tests of antipsychotic drugs, whereas clozapine causes a tolerance effect. Asenapine is a novel antipsychotic drug recently approved for the treatment of schizophrenia and manic disorders. It shares several receptor binding sites and behavioral features with other atypical antipsychotic drugs. However, it is not clear what type of repeated effect (sensitization or tolerance) asenapine would induce, and whether such an effect is transferrable to other atypicals. In this study, male adult Sprague-Dawley rats were first repeatedly tested with asenapine (0.05, 0.10 or 0.20 mg/kg, sc) for avoidance response or PCP (3.20 mg/kg, sc)-induced hyperlocomotion daily for 5 consecutive days. After 2-3 days of retraining/drug-free recovery, they were then challenged with asenapine (0.10 mg/kg, sc), followed by olanzapine (0.50 mg/kg, sc) and clozapine (2.50 mg/kg, sc). During the 5-day drug test period (the induction phase), repeated asenapine treatment progressively increased its inhibition of avoidance response and PCP-induced hyperlocomotion in a dose-dependent fashion. On the asenapine and olanzapine challenge tests (the expression phase), rats previously treated with asenapine still showed significantly lower avoidance response and lower PCP-induced hyperlocomotion than those previously treated with vehicle. An increased reactivity to clozapine challenge in prior asenapine-treated rats was also found in the PCP-induced hyperlocomotion test. These findings suggest that asenapine is capable of inducing a sensitization effect and a cross-sensitization to olanzapine and clozapine (to a lesser extent). Because the behavioral profile of asenapine in both tests is similar to that of olanzapine, but different from that of clozapine, we suggest that asenapine resembles olanzapine to a greater extent than clozapine in its therapeutic and side effect profiles.

Asenapine for the treatment of manic and mixed episodes associated with bipolar I disorder: from clinical research to clinical practice

INTRODUCTION

Asenapine is a sublingually administered second-generation antipsychotic with proven efficacy for the treatment of moderate to severe manic episodes associated with bipolar I disorder in adults. Its relatively favorable weight and metabolic profile, as well as the lack of appreciable activity at muscarinic cholinergic receptors and the sublingual administration are of clinical interest.

AREAS COVERED

This paper comprises a review and commentary regarding the use of sublingual asenapine in the treatment of acute manic and mixed episodes of bipolar disorder. Basic principles in dosing, switching, management of side effects and co-administration with other medications are provided.

EXPERT OPINION

Asenapine displays quick and reliable effects on manic symptoms, very low risk of depressive switches, efficacy on depressive symptoms during manic and mixed episodes, usually good tolerability and continued longer-term efficacy on residual and subthreshold symptoms. The fast-dissolving sublingual route of administration may favor those who have difficulties in swallowing medications. Also, the sublingual administration reduces the risk of overdose when more than the prescribed tablets are swallowed. The relatively low metabolic risk and the lack of anticholinergic side effects contribute to making this medication a useful tool for the treatment of patients with bipolar disorder.

Iloperidone, asenapine and lurasidone: a primer on their current status

INTRODUCTION

Three newer atypical antipsychotic drugs were FDA-approved in 2009 and 2010 in the following order: iloperidone, asenapine and lurasidone. The three drugs are indicated for the treatment of acute schizophrenia. Asenapine is also approved for treatment of manic or mixed episodes associated with bipolar I disorder, for the maintenance treatment of schizophrenia and as an adjunctive therapy with lithium or valproate for the acute treatment of manic or mixed episodes associated with bipolar I disorder in adults.

AREAS COVERED

This review compares and contrasts the current preclinical, clinical, safety and tolerability profiles of the three newer drugs, as reported in published preclinical and clinical studies, product labels, poster presentations and press releases.

EXPERT OPINION

Preclinical studies have reported that the three drugs have variable affinities for a wide range of neurotransmitter receptors, and are active in animal models predictive of antipsychotic activity. Asenapine is the first antipsychotic to be administered sublingually, whereas iloperidone requires titration to minimize orthostatic hypotension. Asenapine and lurasidone are associated with dose-related akathisia, whereas iloperidone is not. The three drugs appear to have relatively benign metabolic profiles. The availability of the three novel antipsychotics should provide additional options for improved treatment of schizophrenia and other psychotic disorders.

Asenapine: a clinical review of a second-generation antipsychotic

BACKGROUND

Schizophrenia and bipolar disorder are both prevalent types of psychiatric illness in the United States. As second-generation antipsychotics have become a more viable first-line treatment option, their use has been associated with a new era of adverse events (AEs), most notably metabolic and cardiovascular concerns. Although treatment options for schizophrenia and bipolar disorder have arguably improved, there continues to be a need for medications that achieve and maintain desired efficacy with minimal AEs.

OBJECTIVES

This article serves as a comprehensive review of the pharmacologic profile of the second-generation antipsychotic asenapine, as well as a review of its efficacy and safety profiles based on the findings from clinical trials in schizophrenia and bipolar disorder.

METHODS

Searches of Ovid MEDLINE, EMBASE, and IDIS were conducted (January 1996 to November 2011) to identify clinical studies and other primary literature sources with the following search terms: asenapine, bipolar disorder, antipsychotic, psychosis, dopamine, and schizophrenia. Only studies of asenapine and placebo and/or active-comparator arms were included.

RESULTS

The literature search yielded 67 unique articles, including review articles, which were excluded. The efficacy of asenapine was reported in 3 clinical studies in patients with schizophrenia, 1 each in acute and long-term settings, measured as significant changes in Positive and Negative Syndrome Scale scores over 6 and 52 weeks. Asenapine also had reported efficacy in the prevention of relapse in schizophrenia during a 26-week extension study. In addition, efficacy of asenapine was reported in 2 studies in acute mania as well as extension phases of both 9 and 40 weeks, as determined by significant changes in Young Mania Rating Scale scores. The most commonly reported AEs in these studies were somnolence (13%-24%), extrapyramidal symptoms (EPS) (7%-12%), and dizziness (11%).

CONCLUSIONS

The findings from multiple studies have suggested that asenapine is efficacious in the acute treatment of schizophrenia. Asenapine has reported long-term efficacy for this indication and the potential to reduce the incidence of relapse. Asenapine efficacy was also reported in the treatment of acute manic or mixed states associated with bipolar I disorder. Asenapine had an acceptable safety profile across the different disease states studied, although it was not devoid of metabolic and EPS-related AEs.

Asenapine: a synthesis of efficacy data in bipolar mania and schizophrenia

INTRODUCTION

This article briefly reviews the efficacy, as well as safety and tolerability, data pertaining to asenapine in bipolar mania and schizophrenia. Postulated mechanism of action is also reviewed.

METHODS

A PubMed search was conducted using the search term asenapine. All displayed articles were reviewed; we selected for review studies that were part of the regulatory registration package to the FDA as part of the bipolar disorder and schizophrenia indication. We also included a review of articles reporting on asenapine's preclinical profile.

RESULTS

Asenapine is a recently introduced atypical antipsychotic approved by the FDA for bipolar mania and mixed states with or without psychotic features, as well as for the treatment and prevention of psychotic relapses in schizophrenia. Preliminary evidence suggests that asenapine mitigates depressive symptoms in bipolar mania and offers superior efficacy to olanzapine or risperidone in the negative symptoms of schizophrenia. The pharmacodynamic profile of asenapine provides a rationale for hypothesizing efficacy in the treatment of cognitive deficits in mood and psychotic disorders. Asenapine is associated with sedation and/or somnolence; it has a lower propensity to weight gain and metabolic disruption than olanzapine. Extrapyramidal side effects (EPS) are associated with asenapine and may be dose-dependent. Asenapine is not associated with sustained hyperprolactinemia or cardiovascular toxicity. Dysgeusia and oral hypoesthesia/paresthesia is associated with asenapine, but is rarely a cause for treatment discontinuation.

CONCLUSIONS

Asenapine is the only atypical antipsychotic available exclusively as a sublingual, fast-dissolved formulation. Electrophysiological, behavioral, pharmacological, and radioligand studies are predictive of antidepressant, mood-stabilizing, as well as antipsychotic, effects.

Attenuation of chronic mild stress-induced 'anhedonia' by asenapine is not associated with a 'hedonic' profile in intracranial self-stimulation

Chronic mild stress (CMS)-induced 'anhedonia' is a predictive model of antidepressant activity. We assessed the reversal of CMS-induced behavioral changes by asenapine, the antidepressant imipramine, and the atypical antipsychotics olanzapine and risperidone. Secondarily, the ability of these agents to facilitate intracranial self-stimulation (ICSS) was assessed to ensure that any attenuation of CMS-induced anhedonia was not associated with an overt hedonic profile. After 2 weeks of CMS, male Wistar rats were administered asenapine (0.06-0.6 mg/kg), olanzapine (2 mg/kg), risperidone (0.5 mg/kg), or imipramine (10 mg/kg) by intraperitoneal injection over 5 weeks to examine their ability to reverse CMS-induced reductions in the intake of a sucrose solution. For the ICSS study, rats were trained to deliver an electrical stimulus to the ventral tegmental area. The effects of acute doses of subcutaneous asenapine (0.01-0.3 mg/kg), olanzapine (0.3 and 1 mg/kg), risperidone (0.1 and 0.3 mg/kg), and intraperitoneal imipramine (3-30 mg/kg), cocaine (5.0 mg/kg), or amphetamine (1.0 mg/kg) on ICSS were then examined. CMS significantly reduced sucrose intake (P < 0.001). All active agents (0.6 mg/kg asenapine, 2 mg/kg olanzapine, 0.5 mg/kg risperidone, and 10 mg/kg imipramine) reversed the effect of CMS (all P < 0.001). In the ICSS protocol, asenapine (0.01 and 0.03 mg/kg), olanzapine (1 mg/kg), and risperidone (0.3 mg/kg) impaired ICSS performance, whereas positive controls (5 mg/kg cocaine, 1 mg/kg amphetamine) facilitated ICSS. Asenapine reversed CMS-induced anhedonia without facilitating ICSS, providing support for a role of asenapine in treating bipolar disorder and aspects of negative and/or affective symptoms in schizophrenia.

Pharmacology and efficacy of asenapine for manic and mixed states in adults with bipolar disorder

Asenapine sublingual is a novel atypical antipsychotic approved in August 2009 for the acute treatment of schizophrenia, as well as for manic or mixed episodes as part of adult bipolar I disorder. Asenapine's in vitro profile is similar to other atypical antipsychotic agents insofar as there is higher affinity for serotonin 5-HT(2A) versus dopamine D(2) receptors. Asenapine exhibits a unique effect on monoamine, histamine and muscarinic receptor affinities, as well as effects on NMDA and AMPA receptors. This pharmacodynamic signature may mediate its symptom relief in positive, negative and mood symptoms, as well as conferring upon this agent an improved tolerability and safety profile when compared with some atypical agents. Asenapine has a relatively low propensity for changes in metabolic parameters, body composition, sedation/somnolence and extrapyramidal side effects, and is not associated with prolactin elevation or clinically significant electrocardiographic changes. Asenapine is available only in sublingual formulation, which has advantages (e.g., patient acceptance, compliance, difficulty swallowing) as well as disadvantages (i.e., patients are encouraged not to eat or drink within 10 min of administration). Its efficacy in mania is unequivocally established as is the sustaining of its acute antimanic effect. Its antidepressant and recurrence prevention effects in bipolar disorder are under investigation, as is its possible role in major depressive disorder.

Repeated effects of asenapine on adrenergic and cholinergic muscarinic receptors

Adrenergic (alpha1 and alpha2) and cholinergic muscarinic (M1-M5) receptor binding in rat forebrain was quantified after 4 wk of twice-daily subcutaneous administration of asenapine or vehicle. Asenapine (0.03, 0.1, and 0.3 mg/kg) produced increases in [3H]prazosin binding to alpha1-adrenergic receptors in the medial prefrontal cortex (mPFC: 30%, 39%, 57%) and dorsolateral frontal cortex (DFC: 27%, 37%, 53%) and increased [3H]RX821002 binding to alpha2-adrenergic receptors in mPFC (36%, 43%, 50%) and DFC (41%, 44%, 52%). Despite showing no appreciable affinity for muscarinic receptors, asenapine produced regionally selective increases in binding of [3H]QNB to M1-M5 receptors in mPFC (26%, 31%, 43%), DFC (27%, 34%, 41%), and hippocampal CA1 (40%, 44%, 42%) and CA3 (25%, 52%, 48%) regions. These regionally selective effects of asenapine on adrenergic and cholinergic muscarinic receptor subtypes may contribute to its beneficial clinical effects in the treatment of schizophrenia and bipolar disorder.

A functional fast scan cyclic voltammetry assay to characterize dopamine D2 and D3 autoreceptors in the mouse striatum

Dopamine D2 and D3 autoreceptors are located on pre-synaptic terminals and are known to control the release and synthesis of dopamine. Dopamine D3 receptors have a fairly restricted pattern of expression in the mammalian brain. Their localization in the nucleus accumbens core and shell is of particular interest because of their association with the rewarding properties of drugs of abuse. Using background subtracted fast scan cyclic voltammetry, we investigated the effects of dopamine D2 and D3 agonists on electrically stimulated dopamine release and uptake rates in the mouse caudate-putamen and nucleus accumbens core and shell. The dopamine D2 agonists (-)-quinpirole hydrochloride and 5,6,7,8-Tetrahydro-6-(2-propen-1-yl)-4H-thiazolo[4,5-d]azepin-2-amine dihydrochloride (B-HT 920) had the same dopamine release inhibition effects on caudate-putamen and nucleus accumbens (core and shell) based on their EC(50) and efficacies. This suggests that the dopamine D2 autoreceptor functionality is comparable in all three striatal regions investigated. The dopamine D3 agonists (4aR,10bR)-3,4a,4,10b-Tetrahydro-4-propyl-2H,5H-[1]benzopyrano-[4,3-b]-1,4-oxazin-9-ol hydrochloride ((+)-PD 128907) and (+/-)-7-Hydroxy-2-dipropylaminotetralin hydrobromide (7-OH-DPAT) had a significantly greater effect on dopamine release inhibition in the nucleus accumbens shell than in caudate-putamen. This study confirms that, the dopamine D3 autoreceptor functionality is greater in the nucleus accumbens shell followed by the nucleus accumbens core, with the caudate-putamen having the least. Neither dopamine D2 nor D3 agonists affected the uptake rates in nucleus accumbens but concentrations greater than 0.3 muM lowered the uptake rate in caudate-putamen. To validate our method of evaluating dopamine D2 and D3 autoreceptors, sulpiride (D2 antagonist) and nafadotride (D3 antagonist) were used to reverse the effects of the dopamine agonists to approximately 100% of the pre-agonist dopamine release concentration. Finally, these results demonstrate a functional voltammetric assay that characterizes dopamine D2-like agonist as either D2- or D3-preferring agonists by taking advantage of the unique receptor density within the striatum.

Asenapine effects in animal models of psychosis and cognitive function

RATIONALE

Asenapine, a novel psychopharmacologic agent in the development for schizophrenia and bipolar disorder, has high affinity for serotonergic, alpha-adrenergic, and dopaminergic receptors, suggesting potential for antipsychotic and cognitive-enhancing properties.

OBJECTIVES

The effects of asenapine in rat models of antipsychotic efficacy and cognition were examined and compared with those of olanzapine and risperidone.

MATERIALS AND METHODS

Amphetamine-stimulated locomotor activity (Amp-LMA; 1.0 or 3.0 mg/kg s.c.) and apomorphine-disrupted prepulse inhibition (Apo-PPI; 0.5 mg/kg s.c.) were used as tests for antipsychotic activity. Delayed non-match to place (DNMTP) and five-choice serial reaction (5-CSR) tasks were used to assess short-term spatial memory and attention, respectively. Asenapine doses varied across tasks: Amp-LMA (0.01-0.3 mg/kg s.c.), Apo-PPI (0.001-0.3 mg/kg s.c.), DNMTP (0.01-0.1 mg/kg s.c.), and 5-CSR (0.003-0.3 mg/kg s.c.).

RESULTS

Asenapine was highly potent (active at 0.03 mg/kg) in the Amp-LMA and Apo-PPI assays. DNMTP or 5-CSR performance was not improved by asenapine, olanzapine, or risperidone. All agents (P < 0.01) reduced DNMTP accuracy at short delays; post hoc analyses revealed that only 0.1 mg/kg asenapine and 0.3 mg/kg risperidone differed from vehicle. All active agents (asenapine, 0.3 mg/kg; olanzapine, 0.03-0.3 mg/kg; and risperidone, 0.01-0.1 mg/kg) significantly impaired 5-CSR accuracy (P < 0.05).

CONCLUSIONS

Asenapine has potent antidopaminergic properties that are predictive of antipsychotic efficacy. Asenapine, like risperidone and olanzapine, did not improve cognition in normal rats. Rather, at doses greater than those required for antipsychotic activity, asenapine impaired cognitive performance due to disturbance of motor function, an effect also observed with olanzapine and risperidone.

Asenapine

Asenapine is a novel psychopharmacological agent that binds with high affinity and specificity to numerous dopamine, serotonin, noradrenaline (norepinephrine) and histamine receptor subtypes. It is being developed for the treatment of schizophrenia and bipolar mania. In two randomized, controlled trials of asenapine monotherapy and in one randomized, controlled trial of adjunctive asenapine therapy in adult patients with bipolar I disorder, sublingual asenapine produced significantly greater reductions from baseline than placebo in clinician-assessed Young Mania Rating Scale (YMRS) total score at 3 weeks. In two randomized, controlled trials in adult patients with acute schizophrenia, treatment with asenapine reduced from baseline the clinician-assessed Positive and Negative Syndrome Scale (PANSS) total score to a significantly greater extent than placebo at 6 weeks. In schizophrenic patients with predominant, persistent, negative symptoms, asenapine at 26 weeks reduced the Negative Symptom Assessment (NSA-16) total score from baseline to an extent similar to that observed with olanzapine. Sublingual asenapine was generally well tolerated in clinical trials, with most treatment-emergent adverse events being of mild to moderate severity. Incidence rates of clinically significant weight gain, extrapyramidal symptoms, hyperprolactinaemia and alterations in glucose or lipid metabolism were generally low.

Asenapine monotherapy in the acute treatment of both schizophrenia and bipolar I disorder

Asenapine is a new atypical antipsychotic agent currently under development for the treatment of schizophrenia and bipolar disorder. It has high affinity for various receptors including antagonism at 5HT(2A), 5HT(2B), 5HT(2C), 5HT(6) and 5HT(7) serotonergic receptor subtypes, alpha(1A), alpha(2A), alpha(2B) and alpha(2C) adrenergic and D(3) and D(4) dopaminergic receptors. As with other atypicals, asenapine exhibits a high 5HT(2A):D(2) affinity ratio. Although similar to clozapine in its multi-target profile, it shows no appreciable affinity for muscarinic receptors. Asenapine has shown efficacy in alleviating both positive and negative symptoms of schizophrenia compared with placebo. Although promising, further studies are required in order to determine whether it has advantages over placebo and other antipsychotics in alleviating cognitive impairment associated with schizophrenia. It has also shown long-term efficacy comparable with olanzapine in bipolar I disorder. Asenapine is generally well tolerated and appears to be metabolically neutral. It has low propensity to cause weight gain and prolactin elevation. There were no concerns in the studies about its effects on the cardiovascular system and QTc prolongation. The incidence of extrapyramidal symptoms with asenapine however has been found to be higher than that with olanzapine. It may be a useful alternative to aripiprazole in schizophrenia and bipolar disorder in patients who are at high risk of metabolic abnormalities.