Antipsychotic occupancy of dopamine receptors in schizophrenia

Association between dopamine receptor D2 Taq IA gene polymorphism (rs1800497) and personality traits

Objective

This study aimed to find a potential association between the DRD2 Taq1A gene polymorphism (rs1800497 C32806T) and personality traits.

Methods

In all, 249 youths were recruited for this study. The Short-form Revised Eysenck Personality Questionnaire was administered to assess personality traits. The participants were genotyped for the DRD2 Taq1A polymorphism using the polymerase chain reaction-restriction fragment length polymorphism method. Statistical analysis was carried out to find a possible association between the genotypes and aspects of personality traits assessed.

Results

The frequencies of the A1 and A2 alleles in our sampled population were 215 (43.2%) and 283 (56.8%), while the frequencies of A1A1, A1A2, and A2A2 were 67 (26.9%), 81 (32.5%), and 101 (40.6%), respectively. The study population was not in Hardy-Weinberg equilibrium (χ2 = 17.64, p < 0.001). The A2 allele was significantly associated with extraversion. Although this allele was also associated with neuroticism, psychoticism, and lie, the association was not significant.

Conclusion

The A2 allele of the DRD2 Taq1A polymorphism was found to be more associated with extraversion, as measured by the Short-form Revised Eysenck Personality Questionnaire.

A proposal for reducing maximum target doses of drugs for psychosis: Reviewing dose-response literature

BACKGROUND

Presently, there is limited guidance on the maximal dosing of psychosis drugs that is based on effectiveness rather than safety or toxicity. Current maximum dosing recommendations may far exceed the necessary degree of dopamine D2 receptor blockade required to treat psychosis. This may lead to excess harm through cognitive impairment and side effects.

AIMS

This analysis aimed to establish guidance for prescribers by optimally dosing drugs for psychosis based on efficacy and benefit.

METHODS

We used data from two dose-response meta-analyses and reviewed seven of the most prescribed drugs for psychosis in the UK. Where data were not available, we used appropriate comparison techniques based on D2 receptor occupancy to extrapolate our recommendations.

RESULTS

We found that the likely threshold dose for achieving remission of psychotic symptoms was often significantly below the currently licensed dose for these drugs. We therefore recommend that clinicians are cautious about exceeding our recommended doses. Individual factors, however, should be accounted for. We outline potentially relevant factors including age, ethnicity, sex, smoking status and pharmacogenetics. Additionally, we recommend therapeutic drug monitoring as a tool to determine individual pharmacokinetic variation.

CONCLUSIONS

In summary, we propose a new set of maximum target doses for psychosis drugs based on efficacy. Further research through randomised controlled trials should be undertaken to evaluate the effect of reducing doses from current licensing maximums or from doses that are above our recommendations. However, dose reductions should be implemented in a manner that accounts for and reduces the effects of drug withdrawal.

Activation of prefrontal parvalbumin interneurons ameliorates working memory deficit even under clinically comparable antipsychotic treatment in a mouse model of schizophrenia

One of the critical unmet medical needs in schizophrenia is the treatment for cognitive deficits. However, the neural circuit mechanisms of them remain unresolved. Previous studies utilizing animal models of schizophrenia did not consider the fact that patients with schizophrenia generally cannot discontinue antipsychotic medication due to the high risk of relapse. Here, we used multi-dimensional approaches, including histological analysis of the prelimbic cortex (PL), LC-MS/MS-based in vivo dopamine D2 receptor occupancy analysis for antipsychotics, in vivo calcium imaging, and behavioral analyses of mice using chemogenetics to investigate neural mechanisms and potential therapeutic strategies for working memory deficit in a chronic phencyclidine (PCP) mouse model of schizophrenia. Chronic PCP administration led to alterations in excitatory and inhibitory synapses, specifically in dendritic spines of pyramidal neurons, vesicular glutamate transporter 1 (VGLUT1) positive terminals, and parvalbumin (PV) positive GABAergic interneurons located in layer 2-3 of the PL. Continuous administration of olanzapine, which achieved a sustained therapeutic window of dopamine D2 receptor occupancy (60-80%) in the striatum, did not ameliorate these synaptic abnormalities and working memory deficit in the chronic PCP-treated mice. We demonstrated that chemogenetic activation of PV neurons in the PL, as confirmed by in vivo calcium imaging, ameliorated working memory deficit in this model even under clinically comparable olanzapine treatment which by itself inhibited only PCP-induced psychomotor hyperactivity. Our study suggests that targeting prefrontal PV neurons could be a promising therapeutic intervention for cognitive deficits in schizophrenia in combination with antipsychotic medication.

Recent applications of positron emission tomographic (PET) imaging in psychiatric drug discovery

INTRODUCTION

Psychiatry is one of the medical disciplines that suffers most from a lack of innovation in its therapeutic arsenal. Many failures in drug candidate trials can be explained by pharmacological properties that have been poorly assessed upstream, in terms of brain passage, brain target binding and clinical outcomes. Positron emission tomography can provide pharmacokinetic and pharmacodynamic data to help select candidate-molecules for further clinical trials.

AREAS COVERED

This review aims to explain and discuss the various methods using positron-emitting radiolabeled molecules to trace the cerebral distribution of the drug-candidate or indirectly measure binding to its therapeutic target. More than an exhaustive review of PET studies in psychopharmacology, this article highlights the contributions this technology can make in drug discovery applied to psychiatry.

EXPERT OPINION

PET neuroimaging is the only technological approach that can, in vivo in humans, measure cerebral delivery of a drug candidate, percentage and duration of target binding, and even the pharmacological effects. PET studies in a small number of subjects in the early stages of the development of a psychotropic drug can therefore provide the pharmacokinetic/pharmacodynamic data required for subsequent clinical evaluation. While PET technology is demanding in terms of radiochemical, radiopharmacological and nuclear medicine expertise, its integration into the development process of new drugs for psychiatry has great added value.

Design and Synthesis of D3R Bitopic Ligands with Flexible Secondary Binding Fragments: Radioligand Binding and Computational Chemistry Studies

A series of bitopic ligands based on Fallypride with a flexible secondary binding fragment (SBF) were prepared with the goal of preparing a D3R-selective compound. The effect of the flexible linker ((R,S)-trans-2a-d), SBFs ((R,S)-trans-2h-j), and the chirality of orthosteric binding fragments (OBFs) ((S,R)-trans-d, (S,R)-trans-i, (S,S)-trans-d, (S,S)-trans-i, (R,R)-trans-d, and (R,R)-trans-i) were evaluated in in vitro binding assays. Computational chemistry studies revealed that the interaction of the fragment binding to the SBF increased the distance between the pyrrolidine nitrogen and ASP1103.32 of the D3R, thereby reducing the D3R affinity to a suboptimal level.

Development of Atypical Neuroleptic Malignant Syndrome After Treatment of Cocaine Intoxication: A Case Report and Literature Review

Neuroleptic malignant syndrome (NMS) is a life-threatening condition classically associated with the use of antipsychotic medications. NMS commonly presents with initial mental status changes, followed by muscle rigidity, fever, and eventual dysautonomia. Cocaine intoxication can present with symptoms that are very similar to those found in NMS, making differentiating the two disorders challenging. We present the case of a 28-year-old female with a history of cocaine use disorder who presented with acute cocaine intoxication. She had severe agitation associated with her intoxication, requiring the use of antipsychotic medications. Subsequently, she developed atypical NMS from abrupt dopamine withdrawal after receiving the antipsychotics. Although overlapping dopamine pathways between cocaine use and NMS could deter one from this practice and guidelines recommend against it, antipsychotics are routinely used in the emergency setting for cocaine-associated agitation. This case highlights the need for a more standardized treatment protocol, provides an explanation of why treating cocaine intoxication with antipsychotics is inappropriate, and suggests that chronic cocaine users may be more prone to NMS in this scenario. Furthermore, this is a unique case because it describes atypical NMS in the context of cocaine intoxication, chronic cocaine use, and administration of antipsychotics to an antipsychotic-naïve patient.

Positron Emission Tomography for the Discovery of New Drugs in Psychiatry

The arsenal of drugs for psychiatry has been difficult to renew for several decades. Many failures in therapeutic trials can be explained by poorly evaluated pharmacological properties, in terms of brain passage, target binding, and functional modulation. Positron emission tomography can provide pharmacokinetic and pharmacodynamic data that will help to better select candidate molecules for larger-scale clinical trials.

Beyond monoamines: I. Novel targets and radiotracers for Positron emission tomography imaging in psychiatric disorders

With the emergence of positron emission tomography (PET) in the late 1970s, psychiatry had access to a tool capable of non-invasive assessment of human brain function. Early applications in psychiatry focused on identifying characteristic brain blood flow and metabolic derangements using radiotracers such as [¹⁵ O]H₂ O and [¹⁸ F]FDG. Despite the success of these techniques, it became apparent that more specific probes were needed to understand the neurochemical bases of psychiatric disorders. The first neurochemical PET imaging probes targeted sites of action of neuroleptic (dopamine D₂ receptors) and psychoactive (serotonin receptors) drugs. Based on the centrality of monoamine dysfunction in psychiatric disorders and the measured success of monoamine-enhancing drugs in treating them, the next 30 years witnessed the development of an armamentarium of PET radiopharmaceuticals and imaging methodologies for studying monoamines. Continued development of monoamine-enhancing drugs over this time however was less successful, realizing only modest gains in efficacy and tolerability. As patent protection for many widely prescribed and profitable psychiatric drugs lapsed, drug development pipelines shifted away from monoamines in search of novel targets with the promises of improved efficacy, or abandoned altogether. Over this period, PET radiopharmaceutical development activities closely paralleled drug development priorities resulting in the development of new PET imaging agents for non-monoamine targets. Part one of this review will briefly survey novel PET imaging targets with relevance to the field of psychiatry, which include the metabotropic glutamate receptor type 5 (mGluR5), purinergic P₂ X₇ receptor, type 1 cannabinoid receptor (CB₁ ), phosphodiesterase 10A (PDE10A), and describe radiotracers developed for these and other targets that have matured to human subject investigations. Current limitations of the targets and techniques will also be discussed.

D1 receptor-expressing neurons in ventral tegmental area alleviate mouse anxiety-like behaviors via glutamatergic projection to lateral septum

Dopamine (DA) acts as a key regulator in controlling emotion, and dysfunction of DA signal has been implicated in the pathophysiology of some psychiatric disorders, including anxiety. Ventral tegmental area (VTA) is one of main regions with DA-producing neurons. VTA DAergic projections in mesolimbic brain regions play a crucial role in regulating anxiety-like behaviors, however, the function of DA signal within VTA in regulating emotion remains unclear. Here, we observe that pharmacological activation/inhibition of VTA D1 receptors will alleviate/aggravate mouse anxiety-like behaviors, and knockdown of VTA D1 receptor expression also exerts anxiogenic effect. With fluorescence in situ hybridization and electrophysiological recording, we find that D1 receptors are functionally expressed in VTA neurons. Silencing/activating VTA D1 neurons bidirectionally modulate mouse anxiety-like behaviors. Furthermore, knocking down D1 receptors in VTA DA and glutamate neurons elevates anxiety-like state, but in GABA neurons has the opposite effect. In addition, we identify the glutamatergic projection from VTA D1 neurons to lateral septum is mainly responsible for the anxiolytic effect induced by activating VTA D1 neurons. Thus, our study not only characterizes the functional expression of D1 receptors in VTA neurons, but also uncovers the pivotal role of DA signal within VTA in mediating anxiety-like behaviors.

The Effect of Menopause on Antipsychotic Response

Background: It has been hypothesized that, whenever estrogen levels decline, psychosis symptoms in women increase. At menopause, this can happen in two main ways: (a) the loss of estrogen (mainly estradiol) can directly affect central neurotransmission, leading to increase in schizophrenia-related symptoms, and (b) the loss of estrogen can decrease the synthesis of enzymes that metabolize antipsychotic drugs, thus weakening their efficacy. Aims and Methods: The aim of this narrative review was to investigate the second possibility by searching PubMed and ClinicalTrials.gov for studies over the last two decades that investigated the metabolism of antipsychotics and their efficacy before and after menopause in women or that studied systemic and local estrogen level effects on the pharmacokinetics and pharmacodynamics of individual antipsychotic drugs. Results: The evidence suggests that symptom level in women with schizophrenia rises after menopause for many reasons beyond hormones but, importantly, there is an estrogen-dependent loss of efficacy related to antipsychotic treatment. Conclusion: Effective clinical intervention is challenging; nevertheless, several promising routes forward are suggested.

Striatal D1 and D2 receptor availability are selectively associated with eye-blink rates after methylphenidate treatment

Eye-blink rate has been proposed as a biomarker of the brain dopamine system, however, findings have not been consistent. This study assessed the relationship between blink rates, measured after oral placebo) (PL) and after a challenge with oral methylphenidate (MP; 60 mg) and striatal D1 receptor (D1R) (measured at baseline) and D2 receptor (D2R) availability (measured after PL and after MP) in healthy participants. PET measures of baseline D1R ([¹¹C]NNC112) (BL-D1R) and D2R availability ([¹¹C]raclopride) after PL (PL-D2R) and after MP (MP-D2R) were quantified in the striatum as non-displaceable binding potential. MP reduced the number of blinks and increased the time participants kept their eyes open. Correlations with dopamine receptors were only significant for the eye blink measures obtained after MP; being positive for BL-D1R in putamen and MP-D2R in caudate (PL-D2R were not significant). MP-induced changes in blink rates (PL minus MP) were negatively correlated with BL-D1R in caudate and putamen. Our findings suggest that eye blink measures obtained while stressing the dopamine system might provide a more sensitive behavioral biomarker of striatal D1R or D2R in healthy volunteers than that obtained at baseline or after placebo.

PET imaging in human participants revealed that D1 and D2 dopamine receptor availability was associated with eye-blink rates following treatment with oral methylphenidate, but not a placebo.

The metabolic adverse effects of antipsychotic use in individuals with intellectual and/or developmental disability: A systematic review and meta-analysis

OBJECTIVE

Individuals with intellectual and/or developmental disability (IDD) are often prescribed antipsychotics (APs). However, despite their known propensity to cause metabolic adverse effects, including weight gain, diabetes, and increased risk of cardiovascular events, there is currently a limited body of literature describing the metabolic consequences of AP use in this population.

METHODS

We searched MEDLINE, EMBASE, PsychINFO, CENTRAL, and CINAHL databases to identify all randomized trials that reported on the metabolic effects of APs in individuals with IDD. Random effects meta-analyses were used to examine weight gain as both a continuous and dichotomous outcome.

RESULTS

Eighteen randomized trials met our inclusion criteria with a total of 1376 patients across a variety of IDDs. AP use was associated with significantly greater weight gain compared with placebo (Continuous: mean difference = 1.10 kg, [0.79, 1.40], p < 0.00001, I²  = 54%; Dichotomous: odds ratio = 3.94, [2.15, 7.23], p < 0.00001, I²  = 0). Sub-group analysis revealed no significant effect of AP type. Data regarding the effects of APs on other metabolic outcomes were limited.

CONCLUSION

This review (PROSPERO # CRD42021255558) demonstrates that AP use is associated with significant weight gain among patients with IDD. Concerningly, most reported studies were in children and adolescents, which sets up an already vulnerable population for adverse medical sequalae at an early age. There was also a lack of long-term studies in adults with IDD. Further studies are required to better understand how AP use affects metabolic parameters in this group of individuals.

Toward recovery in schizophrenia: Current concepts, findings, and future research directions

Schizophrenia was initially defined as "dementia praecox" by E. Kraepelin, which implies progressive deterioration. However, recent studies have revealed that early effective intervention may lead to social and functional recovery in schizophrenia. In this review, we provide an overview of current concepts in schizophrenia and pathophysiological hypotheses. In addition, we present recent findings from clinical and basic research on schizophrenia. Recent neuroimaging and neurophysiological studies have consistently revealed specific biological differences in the structure and function of the brain in those with schizophrenia. From a basic research perspective, to determine the essential pathophysiology underlying schizophrenia, it is crucial that findings from all lines of inquiry-induced pluripotent stem cell (iPSC)-derived neural cells from patients, murine models expressing genetic mutations identified in patients, and patient clinical data-be integrated to contextualize the analysis results. However, the findings remain insufficient to serve as a diagnostic tool or a biomarker for predicting schizophrenia-related outcomes. Collaborations to conduct clinical research based on the patients' and their families' values are just beginning, and further development is expected.

SNMMI Clinical Trials Network Research Series for Technologists: Clinical Research Primer- Use of Imaging Agents in Therapeutic Drug Development and Approval

The process of bringing a new drug to market is complex and has recently necessitated a new drug discovery paradigm for the pharmaceutical industry that is both more efficient and more economical. Key to this has been the increasing use of nuclear medicine and molecular imaging to support drug discovery efforts by answering critical questions on the pathway for development and approval of a new therapeutic drug. Some of these questions include: (i) Does the new drug reach its intended target in the body at sufficient levels to effectively treat or diagnose disease without unacceptable toxicity? (ii) How is the drug absorbed, metabolized, and excreted? (iii) What is the effective dose in humans? To conduct the appropriate imaging studies to answer such questions, pharmaceutical companies are increasingly partnering with molecular imaging departments. Nuclear medicine technologists are critical to this process as they perform scans to collect the qualitative and quantitative imaging data used to measure study endpoints. This article describes preclinical and clinical research trials and provides an overview of the different ways that radiopharmaceuticals are used to answer critical questions during therapeutic drug development.

PET as a Translational Tool in Drug Development for Neuroscience Compounds

In central nervous system drug discovery programs, early development of new chemical entities (NCEs) requires a multidisciplinary strategy and a translational approach to obtain proof of distribution, proof of occupancy, and proof of function in specific brain circuits. Positron emission tomography (PET) provides a way to assess in vivo the brain distribution of NCEs and their binding to the target of interest, provided that radiolabeling of the NCE is possible or that a suitable radioligand is available. PET is therefore a key tool for early phases of drug discovery programs. This review will summarize the main applications of PET in early drug development and discuss the usefulness of PET microdosing studies performed with direct labelling of the NCE and PET occupancy studies. The purpose of this review is also to propose an alignment of the nomenclatures used by drug metabolism and pharmacokinetic scientists and PET imaging scientists to indicate key pharmacokinetic parameters and to provide guidance in the performance and interpretation of PET studies.

Role of Brain Imaging in Drug Development for Psychiatry

Background:

Over the last decades, many brain imaging studies have contributed to new insights in the pathogenesis of psychiatric disease. However, in spite of these developments, progress in the development of novel therapeutic drugs for prevalent psychiatric health conditions has been limited.

Objective:

In this review, we discuss translational, diagnostic and methodological issues that have hampered drug development in CNS disorders with a particular focus on psychiatry. The role of preclinical models is critically reviewed and opportunities for brain imaging in early stages of drug development using PET and fMRI are discussed. The role of PET and fMRI in drug development is reviewed emphasizing the need to engage in collaborations between industry, academia and phase I units.

Conclusion:

Brain imaging technology has revolutionized the study of psychiatric illnesses, and during the last decade, neuroimaging has provided valuable insights at different levels of analysis and brain organization, such as effective connectivity (anatomical), functional connectivity patterns and neurochemical information that may support both preclinical and clinical drug development. Since there is no unifying pathophysiological theory of individual psychiatric syndromes and since many symptoms cut across diagnostic boundaries, a new theoretical framework has been proposed that may help in defining new targets for treatment and thus enhance drug development in CNS diseases. In addition, it is argued that new proposals for data-mining and mathematical modelling as well as freely available databanks for neural network and neurochemical models of rodents combined with revised psychiatric classification will lead to new validated targets for drug development.

Enhancing the Antipsychotic Effect of Risperidone by Increasing Its Binding Affinity to Serotonin Receptor via Picric Acid: A Molecular Dynamics Simulation

The aim of this study was to assess the utility of inexpensive techniques in evaluating the interactions of risperidone (Ris) with different traditional -acceptors, with subsequent application of the findings into a Ris pharmaceutical formulation with improved therapeutic properties. Molecular docking calculations were performed using Ris and its different charge-transfer complexes (CT) with picric acid (PA), 2,3-dichloro-5,6-dicyanop-benzoquinon (DDQ), tetracyanoquinodimethane (TCNQ), tetracyano ethylene (TCNE), tetrabromo-pquinon (BL), and tetrachloro-p-quinon (CL), as donors, and three receptors (serotonin, dopamine, and adrenergic) as acceptors to study the comparative interactions among them. To refine the docking results and further investigate the molecular processes of receptor–ligand interactions, a molecular dynamics simulation was run with output obtained from AutoDock Vina. Among all investigated complexes, the [(Ris) (PA)]-serotonin (CTcS) complex showed the highest binding energy. Molecular dynamics simulation of the 100 ns run revealed that both the Ris-serotonin (RisS) and CTcS complexes had a stable conformation; however, the CTcS complex was more stable.

W. Emerging technologies and their impact on regulatory science

There is an evolution and increasing need for the utilization of emerging cellular, molecular and in silico technologies and novel approaches for safety assessment of food, drugs, and personal care products. Convergence of these emerging technologies is also enabling rapid advances and approaches that may impact regulatory decisions and approvals. Although the development of emerging technologies may allow rapid advances in regulatory decision making, there is concern that these new technologies have not been thoroughly evaluated to determine if they are ready for regulatory application, singularly or in combinations. The magnitude of these combined technical advances may outpace the ability to assess fit for purpose and to allow routine application of these new methods for regulatory purposes. There is a need to develop strategies to evaluate the new technologies to determine which ones are ready for regulatory use. The opportunity to apply these potentially faster, more accurate, and cost-effective approaches remains an important goal to facilitate their incorporation into regulatory use. However, without a clear strategy to evaluate emerging technologies rapidly and appropriately, the value of these efforts may go unrecognized or may take longer. It is important for the regulatory science field to keep up with the research in these technically advanced areas and to understand the science behind these new approaches. The regulatory field must understand the critical quality attributes of these novel approaches and learn from each other's experience so that workforces can be trained to prepare for emerging global regulatory challenges. Moreover, it is essential that the regulatory community must work with the technology developers to harness collective capabilities towards developing a strategy for evaluation of these new and novel assessment tools.

Thalamic dopamine D2-receptor availability in schizophrenia: a study on antipsychotic-naive patients with first-episode psychosis and a meta-analysis

Pharmacological and genetic evidence support a role for an involvement of the dopamine D2-receptor (D2-R) in the pathophysiology of schizophrenia. Previous molecular imaging studies have suggested lower levels of D2-R in thalamus, but results are inconclusive. The objective of the present study was to use improved methodology to compare D2-R density in whole thalamus and thalamic subregions between first-episode psychosis patients and healthy controls. Differences in thalamocortical connectivity was explored based on the D2-R results. 19 antipsychotic-naive first-episode psychosis patients and 19 age- and sex-matched healthy controls were examined using high-resolution Positron Emission Tomography (PET) and the high-affinity D2-R radioligand [¹¹C]FLB457. The main outcome was D2-R binding potential (BP_ND) in thalamus, and it was predicted that patients would have lower binding. Diffusion tensor imaging (DTI) was performed in a subgroup of 11 patients and 15 controls. D2-R binding in whole thalamus was lower in patients compared with controls (Cohen's dz = -0.479, p = 0.026, Bayes Factor (BF) > 4). Among subregions, lower BP_ND was observed in the ROI representing thalamic connectivity to the frontal cortex (Cohen's dz = -0.527, p = 0.017, BF > 6). A meta-analysis, including the sample of this study, confirmed significantly lower thalamic D2-R availability in patients. Exploratory analyses suggested that patients had lower fractional anisotropy values compared with controls (Cohen's d = -0.692, p = 0.036) in the inferior thalamic radiation. The findings support the hypothesis of a dysregulation of thalamic dopaminergic neurotransmission in schizophrenia, and it is hypothesized that this could underlie a disturbance of thalamocortical connectivity.

Potential Mechanisms for Why Not All Antipsychotics Are Able to Occupy Dopamine D3 Receptors in the Brain in vivo

Dysfunctions of the dopaminergic system are believed to play a major role in the core symptoms of schizophrenia such as positive, negative, and cognitive symptoms. The first line of treatment of schizophrenia are antipsychotics, a class of medications that targets several neurotransmitter receptors in the brain, including dopaminergic, serotonergic, adrenergic and/or muscarinic receptors, depending on the given agent. Although the currently used antipsychotics display in vitro activity at several receptors, majority of them share the common property of having high/moderate in vitro affinity for dopamine D₂ receptors (D₂Rs) and D₃ receptors (D₃Rs). In terms of mode of action, these antipsychotics are either antagonist or partial agonist at the above-mentioned receptors. Although D₂Rs and D₃Rs possess high degree of homology in their molecular structure, have common signaling pathways and similar in vitro pharmacology, they have different in vivo pharmacology and therefore behavioral roles. The aim of this review, with summarizing preclinical and clinical evidence is to demonstrate that while currently used antipsychotics display substantial in vitro affinity for both D₃Rs and D₂Rs, only very few can significantly occupy D₃Rs in vivo. The relative importance of the level of endogenous extracellular dopamine in the brain and the degree of in vitro D₃Rs receptor affinity and selectivity as determinant factors for in vivo D₃Rs occupancy by antipsychotics, are also discussed.

Trends in big data analyses by multicenter collaborative translational research in psychiatry

The underlying pathologies of psychiatric disorders, which cause substantial personal and social losses, remain unknown, and their elucidation is an urgent issue. To clarify the core pathological mechanisms underlying psychiatric disorders, in addition to laboratory-based research that incorporates the latest findings, it is necessary to conduct large-sample-size research and verify reproducibility. For this purpose, it is critical to conduct multicenter collaborative research across various fields, such as psychiatry, neuroscience, molecular biology, genomics, neuroimaging, cognitive science, neurophysiology, psychology, and pharmacology. Moreover, collaborative research plays an important role in the development of young researchers. In this respect, the Enhancing Neuroimaging Genetics through Meta-Analysis (ENIGMA) consortium and Cognitive Genetics Collaborative Research Organization (COCORO) have played important roles. In this review, we first overview the importance of multicenter collaborative research and our target psychiatric disorders. Then, we introduce research findings on the pathophysiology of psychiatric disorders from neurocognitive, neurophysiological, neuroimaging, genetic, and basic neuroscience perspectives, focusing mainly on the findings obtained by COCORO. It is our hope that multicenter collaborative research will contribute to the elucidation of the pathological basis of psychiatric disorders.

The Role of Dopaminergic Genes in Probabilistic Reinforcement Learning in Schizophrenia Spectrum Disorders

Schizophrenia spectrum disorders (SZ) are characterized by impairments in probabilistic reinforcement learning (RL), which is associated with dopaminergic circuitry encompassing the prefrontal cortex and basal ganglia. However, there are no studies examining dopaminergic genes with respect to probabilistic RL in SZ. Thus, the aim of our study was to examine the impact of dopaminergic genes on performance assessed by the Probabilistic Selection Task (PST) in patients with SZ in comparison to healthy control (HC) subjects. In our study, we included 138 SZ patients and 188 HC participants. Genetic analysis was performed with respect to the following genetic polymorphisms: rs4680 in COMT, rs907094 in DARP-32, rs2734839, rs936461, rs1800497, and rs6277 in DRD2, rs747302 and rs1800955 in DRD4 and rs28363170 and rs2975226 in DAT1 genes. The probabilistic RL task was completed by 59 SZ patients and 95 HC subjects. SZ patients performed significantly worse in acquiring reinforcement contingencies during the task in comparison to HCs. We found no significant association between genetic polymorphisms and RL among SZ patients; however, among HC participants with respect to the DAT1 rs28363170 polymorphism, individuals with 10-allele repeat genotypes performed better in comparison to 9-allele repeat carriers. The present study indicates the relevance of the DAT1 rs28363170 polymorphism in RL in HC participants.

MicroRNAs in the Onset of Schizophrenia

Mounting evidence implicates microRNAs (miRNAs) in the pathology of schizophrenia. These small noncoding RNAs bind to mRNAs containing complementary sequences and promote their degradation and/or inhibit protein synthesis. A single miRNA may have hundreds of targets, and miRNA targets are overrepresented among schizophrenia-risk genes. Although schizophrenia is a neurodevelopmental disorder, symptoms usually do not appear until adolescence, and most patients do not receive a schizophrenia diagnosis until late adolescence or early adulthood. However, few studies have examined miRNAs during this critical period. First, we examine evidence that the miRNA pathway is dynamic throughout adolescence and adulthood and that miRNAs regulate processes critical to late neurodevelopment that are aberrant in patients with schizophrenia. Next, we examine evidence implicating miRNAs in the conversion to psychosis, including a schizophrenia-associated single nucleotide polymorphism in MIR137HG that is among the strongest known predictors of age of onset in patients with schizophrenia. Finally, we examine how hemizygosity for DGCR8, which encodes an obligate component of the complex that synthesizes miRNA precursors, may contribute to the onset of psychosis in patients with 22q11.2 microdeletions and how animal models of this disorder can help us understand the many roles of miRNAs in the onset of schizophrenia.

The Relation between the Plasma Concentrations of Long-Acting Atypical Antipsychotics and Clinical Effectiveness in Patients Affected by Schizophrenia or Schizoaffective Disorder: A Comprehensive Overview

Atypical antipsychotic depot medications are currently recommended for patients with schizophrenia (SCZ) to prevent relapse and ameliorate the long-term prognosis of these patients. This review critically summarizes the available data about the association between the plasma concentrations of long-acting Second- Generation Antipsychotics (SGAs) and the clinical effectiveness of these compounds in patients affected by SCZ or schizoaffective disorder. Our question is if the measurement of these concentrations can be helpful for clinicians in predicting treatment response and clinical stabilization of patients. Bibliographic research on the main databases was performed, and 13 studies were finally included in this review. Contrasting results were found between plasma concentrations of long-acting injectable (LAI) risperidone and clinical amelioration according to rating scale scores. Data are too scanty to draw conclusions for olanzapine and paliperidone. In contrast, despite small sample sizes, data are quite concordant in showing a relation between long-acting SGA plasma concentrations and D2 receptor occupancy. Despite the preliminary encouraging results, particularly for D2 receptor occupancy, future research with larger samples will have to confirm the clinical usefulness of measuring LAI SGA plasma concentrations to predict the clinical response of patients affected by severe mental conditions such as SCZ.

Dosing antipsychotics in special populations of patients with schizophrenia: severe psychotic agitation, first psychotic episode and elderly patients

Antipsychotic (AP) dosing is well established in nonelderly patients with acute exacerbations of schizophrenia, but not in special populations.This review describes the AP dosing procedures that have been used in clinical studies for acute psychotic agitation, a first episode of psychosis (FEP), and elderly patients. AP dosing data was extracted from the databases of drug regulatory authorities, and from clinical studies available in the medical literature. In acute psychotic agitation, intramuscular and oral APs are frequently prescribed in higher doses than those that saturate D2 receptors. Supersaturating doses of APs should be avoided due to an increased risk of adverse effects. In FEP, many studies showed efficacy of low doses of APs. Studies with risperidone and haloperidol suggested a dose reduction of approximately one third. Titration with a lower starting dose is recommended in elderly patients, due to possible decreases in pharmacokinetic clearance, and due to the risk of concomitant diseases and drug interactions. Exposure to some APs has been associated with QTc prolongation and arrhythmias, and a small but significant increase in the risk of stroke and mortality with APs has been seen, particularly in older people with dementia-related psychosis.

Worldwide antipsychotic drug search intensities: pharmacoepidemological estimations based on Google Trends data

Prescription patterns of antipsychotic drugs (APDs) are typically sourced from country-specific data. In this study, a digital pharmacoepidemiological approach was used to investigate APD preferences globally. Publicly available data on worldwide web search intensities in Google for 19 typical and 22 atypical APDs were temporally and spatially normalized and correlated with reported prescription data. The results demonstrated an increasing global preference for atypical over typical APDs since 2007, with quetiapine, olanzapine, risperidone, and aripiprazole showing the largest search intensities in 2020. Cross-sectional analysis of 122 countries in 2020 showed pronounced differences in atypical/typical APD preferences that correlated with gross domestic product per capita. In conclusion, the investigation provides temporal and spatial assessments of global APD preferences and shows a trend towards atypical APDs, although with a relative preference for typical APDs in low-income countries. Similar data-sourcing methodologies allow for prospective studies of other prescription drugs.

Clozapine Withdrawal-Induced Malignant Catatonia or Neuroleptic Malignant Syndrome: A Case Report and a Brief Review of the Literature

ABSTRACT

In our brief literature review, we discuss the changes in the concept of catatonia as well as its various types and symptoms. We also succinctly review the possible symptoms of clozapine withdrawal. In addition, we analyze the main features of the very few published cases of clozapine withdrawal-induced catatonia and the relationship between neuroleptic malignant syndrome and the malignant subtype of catatonia. Furthermore, we present the case of a 29-year-old male patient with schizophrenia in whom a malignant catatonic episode/neuroleptic malignant syndrome (with negativism, stupor, mutism, autonomic signs [eg, fever, hyperhidrosis], and elevated creatine kinase levels) began 5 days after the patient decided arbitrarily to cease his clozapine treatment. His catatonic symptoms quickly (ie, within a few days) resolved after the reinstitution of clozapine. Finally, we attempt to provide a theoretical explanation for the surprising finding in the literature that the withdrawal of clozapine, unlike the withdrawal of any other antipsychotics, may be associated with catatonia (frequently its malignant subtype). The take-home message of our case is that clinicians should bear in mind the risk of catatonia (especially the malignant subtype of it) after the prompt withdrawal of clozapine therapy.

Safety and Tolerability of Cariprazine in Patients with Schizophrenia: A Pooled Analysis of Eight Phase II/III Studies

BACKGROUND

Long-term treatment with antipsychotic agents is indicated for patients with schizophrenia, but treatment is associated with adverse events (AEs) that contribute to medication discontinuation and nonadherence. Understanding drug safety profiles is critical to avoid unwanted side effects. Cariprazine is a potent dopamine D3/D2 receptor partial agonist that is approved for the treatment of adults with schizophrenia (EU, US) and acute manic/mixed and depressive episodes associated with bipolar I disorder (US).

METHODS

Post hoc analyses were conducted to characterize the safety profile of cariprazine within the recommended 1.5-6 mg/d dose range for schizophrenia; data from 8 short- or long-term clinical trials were analyzed.

RESULTS

In the pooled cariprazine-treated safety population (n=2048), the rate of study completion was 52.8%, with withdrawal of consent, insufficient response, and AEs the most common reasons for premature discontinuation. The most commonly reported AEs (>10%) in the overall cariprazine-treatment group were akathisia (14.6%), insomnia (14.0%), and headache (12.1%); most AEs were considered mild (71.0%) or moderate (26.5%). Most akathisia was mild/moderate (97.5%) and >93% of patients remained on treatment; akathisia events were managed by rescue medications (56.3%) or dose reduction (18.3%). The metabolic profile of cariprazine was neutral in patients with short- and long-term exposure; mean weight gain was 1 kg for overall cariprazine, with an AE of weight increased reported for 5.1%. Other AEs of special interest that occurred at >3% for overall cariprazine were extrapyramidal disorder (7.0%), sedation (3.7%), and somnolence (3.1%); prolactin elevation, cognition impairment, sexual dysfunction, suicidality, and QT prolongation occurred at ≤1%.

CONCLUSION

Akathisia, the most common cariprazine-related AE, was mild/moderate and resulted in few study discontinuations; symptoms were well managed and most patients remained on treatment. Results of this analysis indicated that cariprazine in the recommended dose range was safe and generally well tolerated in patients with schizophrenia.

TRIAL REGISTRATION

Studies registered with ClinicalTrials.gov (NCT00404573, NCT01104779, NCT00694707, NCT01104766, NCT01104792, NCT00839852, and NCT01412060) and EudraCT (2012-005485-36).

Modulation of glutamatergic functional connectivity by a prototypical antipsychotic: Translational inference from a postsynaptic density immediate-early gene-based network analysis

BACKGROUND

Although extensively studied, the effect of antipsychotics is not completely understood at a network level. We tested the hypothesis that acute administration of haloperidol would modulate functional connectivity of brain regions relevant to schizophrenia pathophysiology. To assess putative changes in brain network properties and regional interactivity, we studied the expression of Homer1a, an Immediate Early Gene (IEG) demonstrated to be induced by antipsychotic administration and coding for a protein involved in glutamatergic synapses remodeling.

METHODS

Sprague-Dawley rats (n = 26) assigned to vehicle (VEH; NaCl 0.9%) or haloperidol (HAL; 0.8 mg/kg) were included in the network analysis. Homer1a mRNA induction was evaluated by in situ hybridization. Signal intensity analysis was performed in 33 Regions of Interest (ROIs) in the cortex, the caudate putamen, and the nucleus accumbens. A signal correlation analysis was performed, computing all possible pairwise Pearson correlations among ROIs in the two groups. Two networks were generated for HAL and VEH groups, and their properties and topography were explored.

RESULTS

VEH and HAL networks showed qualitative differences in global efficiency and clustering coefficient. The HAL network showed enhanced interactivity between cortical and striatal regions, and within caudate putamen subdivisions. On the other hand, it exhibited reduced inter-correlations between cingulate cortex and anterior insula and caudate putamen and nucleus accumbens. Moreover, haloperidol was able to modulate centrality of crucial functional hubs. These preclinical results corroborate and expand the clinical evidence that antipsychotics may modulate specific brain network properties and disease-related circuits' interactivity.

Cariprazine as a therapeutic option for schizophrenia: a drug evaluation

Introduction: Schizophrenia is a very disabling condition that may result in a significant impairment of individual, professional, and social adjustments. Antipsychotics (APs), the first-line treatment for schizophrenia, in many cases modify the course of the disease, by reducing the institutionalization risk, at the price of severe and invalidating side effects. Cariprazine is one of the latest second-generation APs (SGAs) acting as a partial agonist of type 2 and 3 dopamine receptors, which was recently approved for the treatment of adult schizophrenia.Areas covered: The authors provide a critical review and commentary on the currently available data on the effectiveness and tolerability of cariprazine in schizophrenic patients, with a particular focus on its specific target symptoms.Expert opinion: Cariprazine appears significantly effective on both acute and maintenance treatment of schizophrenia, and in improving positive, negative, and cognitive symptoms, slightly more than other SGAs. It shows a good safety and tolerability profile, with akathisia being its most common side effect. Although further independent studies are needed to clarify its precise advantages over other SGAs, cariprazine seems a promising compound not only in schizophrenia, but also in a broad range of psychiatric conditions, including perhaps bipolar and addictive disorders.

Low convergent validity of [11C]raclopride binding in extrastriatal brain regions: A PET study of within-subject correlations with [11C]FLB 457

Dopamine D2 receptors (D2-R) in extrastriatal brain regions are of high interest for research in a wide range of psychiatric and neurologic disorders. Pharmacological competition studies and test-retest experiments have shown high validity and reliability of the positron emission tomography (PET) radioligand [¹¹C]FLB 457 for D2-R quantification in extrastriatal brain regions. However, this radioligand is not available at most research centers. Instead, the medium affinity radioligand [¹¹C]raclopride, which has been extensively validated for quantification of D2-R in the high-density region striatum, has been applied also in studies on extrastriatal D2-R. Recently, the validity of this approach has been questioned by observations of low occupancy of [¹¹C]raclopride in extrastriatal regions in a pharmacological competition study with quetiapine. Here, we utilise a data set of 16 healthy control subjects examined with both [¹¹C]raclopride and [¹¹C]FLB 457 to assess the correlation in binding potential (BP_ND) in extrastriatal brain regions. BP_ND was quantified using the simplified reference tissue model with cerebellum as reference region. The rank order of mean regional BP_ND values were similar for both radioligands, and corresponded to previously reported data, both post-mortem and using PET. Nevertheless, weak to moderate within-subject correlations were observed between [¹¹C]raclopride and [¹¹C]FLB 457 BP_ND extrastriatally (Pearson's R: 0.30-0.56), in contrast to very strong correlations between repeated [¹¹C]FLB 457 measurements (Pearson's R: 0.82-0.98). In comparison, correlations between repeated [¹¹C]raclopride measurements were low to moderate (Pearson's R: 0.28-0.75). These results are likely related to low signal to noise ratio of [¹¹C]raclopride in extrastriatal brain regions, and further strengthen the recommendation that extrastriatal D2-R measures obtained with [¹¹C]raclopride should be interpreted with caution.

Ligand with Two Modes of Interaction with the Dopamine D2 Receptor-An Induced-Fit Mechanism of Insurmountable Antagonism

A solid understanding of the mechanisms governing ligand binding is crucial for rational design of therapeutics targeting the dopamine D₂ receptor (D₂R). Here, we use G protein-coupled inward rectifier potassium (GIRK) channel activation in Xenopus oocytes to measure the kinetics of D₂R antagonism by a series of aripiprazole analogues, as well as the recovery of dopamine (DA) responsivity upon washout. The aripiprazole analogues comprise an orthosteric and a secondary pharmacophore and differ by the length of the saturated carbon linker joining these two pharmacophores. Two compounds containing 3- and 5-carbon linkers allowed for a similar extent of recovery from antagonism in the presence of 1 or 100 μM DA (>25 and >90% of control, respectively), whereas recovery was less prominent (∼20%) upon washout of the 4-carbon linker compound, SV-III-130, both with 1 and 100 μM DA. Prolonging the coincubation time with SV-III-130 further diminished recovery. Curve-shift experiments were consistent with competition between SV-III-130 and DA. Two mutations in the secondary binding pocket (V91A and E95A) of D₂R decreased antagonistic potency and increased recovery from SV-III-130 antagonism, whereas a third mutation (L94A) only increased recovery. Our results suggest that the secondary binding pocket influences recovery from inhibition by the studied aripiprazole analogues. We propose a mechanism, supported by in silico modeling, whereby SV-III-130 initially binds reversibly to the D₂R, after which the drug-receptor complex undergoes a slow transition to a second ligand-bound state, which is dependent on secondary binding pocket integrity and irreversible during the time frame of our experiments.

Glycine Signaling in the Framework of Dopamine-Glutamate Interaction and Postsynaptic Density. Implications for Treatment-Resistant Schizophrenia

Treatment-resistant schizophrenia (TRS) or suboptimal response to antipsychotics affects almost 30% of schizophrenia (SCZ) patients, and it is a relevant clinical issue with significant impact on the functional outcome and on the global burden of disease. Among putative novel treatments, glycine-centered therapeutics (i.e. sarcosine, glycine itself, D-Serine, and bitopertin) have been proposed, based on a strong preclinical rationale with, however, mixed clinical results. Therefore, a better appraisal of glycine interaction with the other major players of SCZ pathophysiology and specifically in the framework of dopamine - glutamate interactions is warranted. New methodological approaches at cutting edge of technology and drug discovery have been applied to study the role of glycine in glutamate signaling, both at presynaptic and post-synaptic level and have been instrumental for unveiling the role of glycine in dopamine-glutamate interaction. Glycine is a non-essential amino acid that plays a critical role in both inhibitory and excitatory neurotransmission. In caudal areas of central nervous system (CNS), such as spinal cord and brainstem, glycine acts as a powerful inhibitory neurotransmitter through binding to its receptor, i.e. the Glycine Receptor (GlyR). However, glycine also works as a co-agonist of the N-Methyl-D-Aspartate receptor (NMDAR) in excitatory glutamatergic neurotransmission. Glycine concentration in the synaptic cleft is finely tuned by glycine transporters, i.e. GlyT1 and GlyT2, that regulate the neurotransmitter's reuptake, with the first considered a highly potential target for psychosis therapy. Reciprocal regulation of dopamine and glycine in forebrain, glycine modulation of glutamate, glycine signaling interaction with postsynaptic density proteins at glutamatergic synapse, and human genetics of glycinergic pathways in SCZ are tackled in order to highlight the exploitation of this neurotransmitters and related molecules in SCZ and TRS.

Atypical but not typical antipsychotic drugs ameliorate phencyclidine-induced emotional memory impairments in mice

Schizophrenia is associated with cognitive impairments related to hypofunction in glutamatergic N-methyl-D-aspartate receptor (NMDAR) transmission. Phencyclidine (PCP), a non-competitive NMDAR antagonist, models schizophrenia-like behavioral symptoms including cognitive deficits in rodents. This study examined the effects of PCP on emotional memory function examined in the passive avoidance (PA) task in mice and the ability of typical and atypical antipsychotic drugs (APDs) to rectify the PCP-mediated impairment. Pre-training administration of PCP (0.5, 1, 2 or 3 mg/kg) dose-dependently interfered with memory consolidation in the PA task. In contrast, PCP was ineffective when administered after training, and immediately before the retention test indicating that NMDAR blockade interferes with memory encoding mechanisms. The typical APD haloperidol and the dopamine D_2/3 receptor antagonist raclopride failed to block the PCP-induced PA impairment suggesting a negligible role of D₂ receptors in the PCP impairment. In contrast, the memory impairment was blocked by the atypical APDs clozapine and olanzapine in a dose-dependent manner while risperidone was effective only at the highest dose tested (1 mg/kg). The PCP-induced impairment involves 5-HT_1A receptor mechanisms since the antagonist NAD-299 blocked the memory impairment caused by PCP and the ability of clozapine to attenuate the impairment by PCP. These results indicate that atypical but not typical APDs can ameliorate NMDAR-mediated memory impairments and support the view that atypical APDs such as clozapine can modulate glutamatergic memory dysfunctions through 5-HT_1A receptor mechanisms. These findings suggest that atypical APDs may improve cognitive impairments related to glutamatergic dysfunction relevant for emotional memories in schizophrenia.

Hypofunctional Dopamine Uptake and Antipsychotic Treatment-Resistant Schizophrenia

Antipsychotic treatment resistance in schizophrenia remains a major issue in psychiatry. Nearly 30% of patients with schizophrenia do not respond to antipsychotic treatment, yet the underlying neurobiological causes are unknown. All effective antipsychotic medications are thought to achieve their efficacy by targeting the dopaminergic system. Here we review early literature describing the fundamental mechanisms of antipsychotic drug efficacy, highlighting mechanistic concepts that have persisted over time. We then reconsider the original framework for understanding antipsychotic efficacy in light of recent advances in our scientific understanding of the dopaminergic effects of antipsychotics. Based on these new insights, we describe a role for the dopamine transporter in the genesis of both antipsychotic therapeutic response and primary resistance. We believe that this discussion will help delineate the dopaminergic nature of antipsychotic treatment-resistant schizophrenia.

Efficacy of cariprazine across symptom domains in patients with acute exacerbation of schizophrenia: Pooled analyses from 3 phase II/III studies

Schizophrenia affects various symptom domains, including positive and negative symptoms, mood, and cognition. Cariprazine, a dopamine D₃/D₂ receptor partial agonist and serotonin 5-HT_1A receptor partial agonist, with preferential binding to D₃ receptors, is approved for the treatment of adult patients with schizophrenia (US, Europe) and mania associated with bipolar I disorder (US). For these investigations, data were pooled from 3 positive, 6-week, double-blind, placebo-controlled, phase II/III trials of cariprazine in patients with acute exacerbation of schizophrenia (NCT00694707, NCT01104766, NCT01104779); 2 trials were fixed-dose and 1 trial was flexible-dose. Post hoc analyses evaluated mean change from baseline to week 6 in Positive and Negative Syndrome Scale (PANSS) -derived symptom factors (positive symptoms, negative symptoms, disorganized thought, uncontrolled hostility/excitement, anxiety/depression) and PANSS single items for cariprazine (1.5-9.0 mg/d) versus placebo. P values were not adjusted for multiple comparisons. At week 6, statistically significant differences versus placebo were seen for cariprazine on all 5 PANSS factors (P < 0.01 all). Effects sizes ranged from 0.21 (anxiety/depression) to 0.47 (disorganized thought). Dose-response analysis from the fixed-dose studies found significant differences for all cariprazine doses (1.5, 3.0, 4.5, and 6.0 mg/d) versus placebo in PANSS total score, and in negative symptom and disorganized thought factor scores (P < 0.001). Differences between cariprazine and placebo were also statistically significant on 26 of 30 PANSS single items (P < 0.05). In these post hoc analyses, cariprazine was effective versus placebo in improving all 5 PANSS factor domains, suggesting that it may have broad-spectrum efficacy in patients with acute schizophrenia.

Analogues of Arylamide Phenylpiperazine Ligands To Investigate the Factors Influencing D3 Dopamine Receptor Bitropic Binding and Receptor Subtype Selectivity

We have previously reported on the ability of arylamide phenylpiperazines to bind selectively to the D3 versus the D2 dopamine receptor subtype. For these studies, we used LS-3-134 as the prototypic arylamide phenylpiperazine ligand because it binds with high affinity at D3 dopamine receptor (0.17 nM) and exhibits >150-fold D3 vs D2 receptor binding selectivity. Our goal was to investigate how the composition and size of the nonaromatic ring structure at the piperazine position of substituted phenylpiperazine analogues might influence binding affinity at the human D2 and D3 dopamine receptors. Two factors were identified as being important for determining the binding affinity of bitropic arylamide phenylpiperazines at the dopamine D3 receptor subtype. One factor was the strength of the salt bridge between the highly conserved residue Asp^3.32 with the protonated nitrogen of the nonaromatic ring at the piperazine position. The second factor was the configuration of the unbound ligand in an aqueous solution. These two factors were found to be related to the logarithm of the affinities using a simple correlation model, which could be useful when designing high affinity subtype selective bitropic ligands. While this model is based upon the interaction of arylamide phenylpiperazines with the D2 and D3 D2-like dopamine receptor subtypes, it provides insights into the complexity of the factors that define a bitropic mode of the binding at GPCRs.

Review of withdrawal catatonia: what does this reveal about clozapine?

Withdrawal symptoms are common upon discontinuation of psychiatric medications. Catatonia, a neuropsychiatric condition proposed to be associated with gamma-aminobutyric acid (GABA) hypoactivity due to its robust response to benzodiazepines, has been described as a withdrawal syndrome in case reports but is not a well-recognized phenomenon. The authors undertook a review of withdrawal catatonia with an aim to understand its presentation as well as the medications and psychoactive substances it is associated with. The review identified 55 cases of withdrawal catatonia, the majority of which occurred upon discontinuation of benzodiazepines (24 cases) and discontinuation of clozapine (20 cases). No other antipsychotic medications were identified as having been associated with the onset of a catatonic episode within 2 weeks following their discontinuation. Increasing GABA activity and resultant GABA receptor adaptations with prolonged use is postulated as a shared pharmacological mechanism between clozapine and benzodiazepines that underlie their association with withdrawal catatonia. The existing evidence for clozapine's activity on the GABA system is reviewed. The clinical presentations of benzodiazepine withdrawal catatonia and clozapine withdrawal catatonia appear to differ and reasons for this are explored. One reason is that benzodiazepines act directly on GABAA receptors as allosteric agonists, while clozapine has more complex and indirect interactions, primarily through effects on receptors located on GABA interneurons. Another possible reason for the difference in clinical presentation is that clozapine withdrawal catatonia may also involve receptor adaptations in non-GABA receptors such as dopamine and acetylcholine. The findings from our review have implications for the treatment of withdrawal catatonia, and treatment recommendations are provided. Further research understanding the uniqueness of clozapine withdrawal catatonia among antipsychotic medication may give some insight as to clozapine's differential mechanism of action.

Functionally Biased D2R Antagonists: Targeting the β-Arrestin Pathway to Improve Antipsychotic Treatment

Schizophrenia is a severe neuropsychiatric disease that lacks completely effective and safe therapies. As a polygenic disorder, genetic studies have only started to shed light on its complex etiology. To date, the positive symptoms of schizophrenia are well-managed by antipsychotic drugs, which primarily target the dopamine D2 receptor (D2R). However, these antipsychotics are often accompanied by severe side effects, including motoric symptoms. At D2R, antipsychotic drugs antagonize both G-protein dependent (Gα_i/o) signaling and G-protein independent (β-arrestin) signaling. However, the relevant contributions of the distinct D2R signaling pathways to antipsychotic efficacy and on-target side effects (motoric) are still incompletely understood. Recent evidence from mouse genetic and pharmacological studies point to β-arrestin signaling as the major driver of antipsychotic efficacy and suggest that a β-arrestin biased D2R antagonist could achieve an additional level of selectivity at D2R, increasing the therapeutic index of next generation antipsychotics. Here, we characterize BRD5814, a highly brain penetrant β-arrestin biased D2R antagonist. BRD5814 demonstrated good target engagement via PET imaging, achieving efficacy in an amphetamine-induced hyperlocomotion mouse model with strongly reduced motoric side effects in a rotarod performance test. This proof of concept study opens the possibility for the development of a new generation of pathway selective antipsychotics at D2R with reduced side effect profiles for the treatment of schizophrenia.

Affinity States of Striatal Dopamine D2 Receptors in Antipsychotic-Free Patients with Schizophrenia

BACKGROUND

Dopamine D2 receptors are reported to have high-affinity (D2High) and low-affinity (D2Low) states. Although an increased proportion of D2High has been demonstrated in animal models of schizophrenia, few clinical studies have investigated this alteration of D2High in schizophrenia in vivo.

METHODS

Eleven patients with schizophrenia, including 10 antipsychotic-naive and 1 antipsychotic-free individuals, and 17 healthy controls were investigated. Psychopathology was assessed by Positive and Negative Syndrome Scale, and a 5-factor model was used. Two radioligands, [11C]raclopride and [11C]MNPA, were employed to quantify total dopamine D2 receptor and D2High, respectively, in the striatum by measuring their binding potentials. Binding potential values of [11C]raclopride and [11C]MNPA and the binding potential ratio of [11C]MNPA to [11C]raclopride in the striatal subregions were statistically compared between the 2 diagnostic groups using multivariate analysis of covariance controlling for age, gender, and smoking. Correlations between binding potential and Positive and Negative Syndrome Scale scores were also examined.

RESULTS

Multivariate analysis of covariance demonstrated a significant effect of diagnosis (schizophrenia and control) on the binding potential ratio (P=.018), although the effects of diagnosis on binding potential values obtained with either [11C]raclopride or [11C]MNPA were nonsignificant. Posthoc test showed that the binding potential ratio was significantly higher in the putamen of patients (P=.017). The Positive and Negative Syndrome Scale "depressed" factor in patients was positively correlated with binding potential values of both ligands in the caudate.

CONCLUSIONS

The present study indicates the possibilities of: (1) a higher proportion of D2High in the putamen despite unaltered amounts of total dopamine D2 receptors; and (2) associations between depressive symptoms and amounts of caudate dopamine D2 receptors in patients with schizophrenia.

The Use of Microdosing in the Development of Small Organic and Protein Therapeutics

Microdosing as a regulatory concept was introduced to facilitate exploratory studies in humans. The concept involves the use of very low doses of a radionuclide-labeled compound for imaging studies or for assessing plasma pharmacokinetics using equipment that has a highly sensitive readout. The supporting principle is that use of these low doses for a limited time in well-controlled, small populations will limit exposure and have a low risk of adverse effects. Microdosing regulations specify a reduced preclinical toxicology-assessment package in order to shorten the route to human studies and reduce its cost. However, for extrapolation to therapeutically relevant doses and plasma concentrations, there are specific aspects of the use of these low doses and low plasma concentrations that require special attention. These specific aspects are reviewed in this article, with separate attention being paid to small organic molecules and protein therapeutics. The indications for microdosing in drug development are discussed in terms of the 3 pillars of survival in drug development, the first of which is characterization of tissue distribution and access to the site of action; the second, engagement of the target; and the third, induction of tissue responses relevant to a therapeutic response.

Chemistry-based molecular signature underlying the atypia of clozapine

The central nervous system is functionally organized as a dynamic network of interacting neural circuits that underlies observable behaviors. At higher resolution, these behaviors, or phenotypes, are defined by the activity of a specific set of biomolecules within those circuits. Identification of molecules that govern psychiatric phenotypes is a major challenge. The only organic molecular entities objectively associated with psychiatric phenotypes in humans are drugs that induce psychiatric phenotypes and drugs used for treatment of specific psychiatric conditions. Here, we identified candidate biomolecules contributing to the organic basis for psychosis by deriving an in vivo biomolecule-tissue signature for the atypical pharmacologic action of the antipsychotic drug clozapine. Our novel in silico approach identifies the ensemble of potential drug targets based on the drug's chemical structure and the region-specific gene expression profile of each target in the central nervous system. We subtracted the signature of the action of clozapine from that of a typical antipsychotic, chlorpromazine. Our results implicate dopamine D4 receptors in the pineal gland and muscarinic acetylcholine M1 (CHRM1) and M3 (CHRM3) receptors in the prefrontal cortex (PFC) as significant and unique to clozapine, whereas serotonin receptors 5-HT_2A in the PFC and 5-HT_2C in the caudate nucleus were common significant sites of action for both drugs. Our results suggest that D4 and CHRM1 receptor activity in specific tissues may represent underappreciated drug targets to advance the pharmacologic treatment of schizophrenia. These findings may enhance our understanding of the organic basis of psychiatric disorders and help developing effective therapies.

Safety and tolerability of cariprazine in the long-term treatment of schizophrenia: results from a 48-week, single-arm, open-label extension study

RATIONALE

Cariprazine, a dopamine D3/D2 receptor partial agonist antipsychotic, demonstrated efficacy and tolerability in 6-week, randomized, placebo-controlled schizophrenia trials. Schizophrenia is a chronic disorder that requires continuous treatment; therefore, the long-term safety and tolerability profile of antipsychotic agents is an important factor in guiding clinician decisions.

OBJECTIVE

This single-arm, open-label extension study evaluated the long-term safety and tolerability of cariprazine in patients with schizophrenia.

METHODS

Patients enrolled in this study completed a 6-week, randomized, placebo- and active-controlled study and had responded (Clinical Global Impressions-Severity [CGI-S] ≤3; ≥20 % reduction in Positive and Negative Syndrome Scale [PANSS] total score) to treatment at the end of the lead-in study. Patients (N = 93) received flexibly dosed, open-label cariprazine (1.5-4.5 mg/day) for up to 48 weeks.

RESULTS

Approximately 50 % (46/93) of patients completed the 48 weeks of open-label treatment. The most common adverse events (AEs) were akathisia (14 %), insomnia (14 %), and weight increased (12 %). Serious AEs (SAEs) occurred in 13 % of patients; 11 % discontinued due to AEs. Mean changes in metabolic parameters were generally small and not clinically relevant. Mean body weight increased by 1.9 kg from the start of the lead-in study to the end of the extension study. There were no discontinuations associated with change in metabolic parameters or body weight. Long-term cariprazine treatment was not associated with prolactin elevation or clinically significant changes in cardiovascular parameters.

CONCLUSIONS

In this 48-week, single-arm trial, open-label cariprazine (1.5-4.5 mg/day) treatment was generally safe and well tolerated with no new safety concerns associated with long-term treatment.

The Harms of Antipsychotic Drugs: Evidence from Key Studies

This safety assessment provides a detailed analysis of key studies and focuses on the six most widely used antipsychotic drugs. Lines of evidence include mechanisms of action, short-term treatment of psychosis, relapse prevention, early intervention in schizophrenia, long-term comparisons between first- and second-generation agents, and flexible treatment algorithms. Despite the diversity of study settings, several common features were seen. All the agents obstruct normal signaling through widely dispersed dopamine D₂ receptors. Treatment failure or psychosis relapse was the most frequent outcome in most key studies, ranging from 38 to 93%. High discontinuation rates caused most trials to fail to demonstrate a substantial treatment benefit, or difference from an active comparator. Assessment of harm to the extrapyramidal motor system was confounded because of extensive neurological impairment from previous antipsychotic drug treatment measured at baseline, abrupt discontinuation effects, and high rates of concomitant medications to manage drug adverse effects. Claims that second-generation antipsychotic drugs have safety advantages over classical neuroleptic drugs and prevent relapse were not supported in these key studies. The extent of injury to and impairment of multiple body systems caused by antipsychotic drugs shows the need for a scientific, clinical, and regulatory reappraisal of the appropriate use of these agents.

Tolerability and Safety Profile of Cariprazine in Treating Psychotic Disorders, Bipolar Disorder and Major Depressive Disorder: A Systematic Review with Meta-Analysis of Randomized Controlled Trials

BACKGROUND

Cariprazine is a novel antipsychotic agent recently approved for treating schizophrenia and bipolar mania in the USA. The sample sizes of published randomized controlled trials (RCTs) of the drug are small; previous meta-analyses included few RCTs and did not specifically investigate the tolerability/safety profile of cariprazine.

OBJECTIVE

Our objective was to conduct a meta-analysis of published RCTs to systematically review the tolerability and safety of cariprazine versus placebo.

METHODS

We searched the clinical trial registers (the metaRegister of controlled trials, ClinicalTrials.gov and the World Health Organization International Clinical Trials Registry Platform) and electronic databases (PubMed, Embase, PsycINFO and Cochrane library) up to June 2016 to identify phase II/III RCTs of cariprazine in patients with schizophrenia, bipolar disorder or major depressive disorder. We conducted a meta-analysis to investigate outcomes, including risks of discontinuation due to adverse events (AEs), extrapyramidal side effects (EPS) or related events, metabolic syndrome and cardiovascular-related events.

RESULTS

We included nine RCTs, with a total of 4324 subjects. The risk of discontinuation due to AEs for cariprazine was similar to that for placebo (risk ratio [RR] 1.13, 95 % confidence interval [CI] 0.77-1.66). Cariprazine was associated with higher risks of EPS-related events than was placebo, including risk of akathisia (RR 3.92, 95 % CI 2.83-5.43), tremor (RR 2.41, 95 % CI 1.53-3.79) and restlessness (RR 2.17, 95 % CI 1.38-3.40). The cariprazine treatment group was more likely to have clinically significant weight gain (RR 1.68, 95 % CI 1.12-2.52). No statistically significant differences in results were found in other metabolic parameters or cardiovascular-related events.

CONCLUSION

There was a statistically significant higher risk of EPS-related AEs and a slight increase in mean body weight with cariprazine. There were no statistically significant effects on prolactin level or cardiovascular parameters. EPSs were the main short-term adverse reactions reported in the limited number of patients studied. Further clinical and post-marketing pharmacovigilance studies are needed to investigate the long-term safety of cariprazine.

Association between olfactory identification and parkinsonism in patients with non-affective psychosis

AIM

Olfactory identification deficits (OIDs) are seen in schizophrenia patients and individuals at increased risk for psychosis but its pathophysiology remains unclear. Although dopaminergic imbalance is known to lie at the core of schizophrenia symptomatology, its role in the development of OIDs has not been elucidated yet. This study investigated the association between OIDs and symptoms of parkinsonism as a derivative of dopaminergic functioning.

METHODS

In 320 patients diagnosed with non-affective psychosis, olfactory identification performance was assessed by means of the Sniffin' Sticks task. Level of parkinsonian symptoms was assessed by means of the Unified Parkinson's Disease Rating Scale (UPDRS-III). By means of multiple linear regression with bootstrapping, the association between UPDRS and Sniffin' Sticks score was investigated while correcting for potential confounders. A Bonferroni corrected P-value of 0.007 was used.

RESULTS

Higher UPDRS scores significantly predicted worse olfactory identification in patients with non-affective psychosis with an unadjusted b = -0.07 (95% CI -0.10 to -0.04) and an adjusted b = -0.04 (95% CI -0.07 to -0.01).

CONCLUSION

Results provide preliminary evidence that the same vulnerability may underlie the development of parkinsonism and OIDs in patients with non-affective psychosis. Further investigation should evaluate the clinical value of OIDs as a marker of dopaminergic vulnerability that may predict psychosis.

Derisking Psychiatric Drug Development: The NIMH's Fast Fail Program, A Novel Precompetitive Model

The lack of success of psychiatric drug research and development has increased attention on the use of precompetitive models of early stage clinical drug development, whereby foundations, companies and academic researchers led by NIH, work together to advance a pipeline of potential novel therapeutics. This commentary presents an example of such an approach through which the National Institute of Mental Health contracted a network of academic researchers to work with other stakeholders to investigate AZD7325, a drug targeting the GABA-A α2/α3 receptor subtype, in young adult subjects with autism spectrum disorder using an experimental medicine approach. Instead of relying on traditional clinical measures, electroencephalography was used to evaluate pharmacodynamic responses and was established as the primary outcome measure, in order to objectively identify dose ranges that can modulate central nervous system activity in the absence of significant side effects. Many trial considerations and “lessons learned” were identified through the process of setting up and performing the trial. These considerations are important to present to the research community more broadly, to emphasize what processes and resources are needed to integrate pharmacodynamics measures into multisite trials in research areas which have traditionally relied on clinical rating scales alone. The goal is to design and implement studies that will provide sufficient objective data of brain effects to make go/no-go decisions to clinical efficacy studies in which one is confident that the underlying mechanistic hypothesis of drug action is being tested. We here provide a real life example of what is required to execute this strategy.

Preclinical Effects of Antipsychotic Drugs

Antipsychotic drugs have been the drugs of choice for the treatment of schizophrenia ever since the introduction of chlorpromazine in the early 1950s of the last century. Since then, about 60 different antipsychotics have been introduced. Although pharmacologically these drugs show large differences, in terms of potency, duration of action and selectivity, all antipsychotics appear to reduce the positive symptoms of schizophrenia, while having little or no effect on the negative symptoms or the cognitive deficits. The only apparent exception is clozapine, which is also effective in therapy-resistant patients. On the other hand, antipsychotics induce significant side effects as well, including neurological, behavioural and metabolic side effects. In the present paper, we will discuss the preclinical pharmacology of the current antipsychotic drugs focussing both on the therapeutic and on side effects of these drugs.