Cariprazine: A Review in Schizophrenia

Lack of Clinically Meaningful Effect of Cariprazine on the Pharmacokinetics of a Combined Oral Contraceptive

INTRODUCTION

Cariprazine (CAR) is a potent dopamine receptor partial agonist antipsychotic approved by the EMA and the FDA. To address the uncertainty regarding the effectiveness of hormonal contraceptives during CAR co-administration and whether a second barrier method is necessary, a drug-drug interaction study with an oral contraceptive was conducted post-approval.

METHODS

The phase I, fixed-sequence multicenter study involved two periods with 24 patients with schizophrenia, aiming to evaluate the effect of CAR on the pharmacokinetics (PK) of a combined oral contraceptive (COC) containing 30 μg ethinylestradiol (EE) and 150 μg levonorgestrel (LNG). In period A, a single dose of COC alone was administered on day 1. In period B, the highest therapeutic dose of 6 mg CAR was administered once daily from day 4, and a second dose of COC was given concomitantly on day 31.

RESULTS

Overall, CAR had no clinically meaningful effect on the PK of the COC. The terminal half-life and the time of maximum plasma concentration of EE and LNG were not altered by CAR co-administration. The highest difference observed was a decrease of 14% in the maximum plasma concentration of EE, with only slight deviation of the 90% confidence interval (CI) of the test/reference ratio (77.09-96.81) from the generally accepted bioequivalence range of 80-125%, which is not considered clinically relevant. Confidence intervals of all other exposure measures were within the 80-125% range for both EE and LNG.

CONCLUSIONS

According to these results, hormonal contraceptives can be considered effective during CAR treatment.

TRIAL REGISTRATION

Trial registration number (EudraCT) 2018-003722-80.

Recent Advances in representative small-molecule DRD2 inhibitors: Synthetic Routes and clinical applications

The dopamine D2 receptor (DRD2) represents a pivotal target for therapeutic intervention in the treatment of neuropsychiatric disorders, including schizophrenia, bipolar disorder, and Parkinson's disease. The successful discovery of numerous effective DRD2 inhibitors has led to their clinical application and ongoing evaluation in various clinical trials. This review explores the synthetic approaches and clinical applications of prototypical small-molecule DRD2 inhibitors that have received approval or are currently undergoing clinical trials, highlighting their therapeutic potential and challenges. The synthesis of these inhibitors employs various chemical strategies, including modifications of phenothiazine and butyrophenone structures, which have yielded significant antipsychotic agents like chlorpromazine and haloperidol. Additionally, newer classes of inhibitors, such as aripiprazole, exhibit partial agonist activity at DRD2, offering a unique therapeutic profile. Clinically, DRD2 inhibitors demonstrate efficacy in managing positive symptoms of schizophrenia, manic episodes in bipolar disorder, and dopaminergic imbalance in Parkinson's disease. However, the emergence of adverse effects, including tardive dyskinesia, extrapyramidal symptoms and metabolic syndrome, presents substantial challenges. Advances in the development of second-generation antipsychotics aim to balance efficacy with a better side effect profile by targeting additional neurotransmitter receptors. This review aims to deliver an overview of the synthesis and clinical applications of representative small-molecule DRD2 inhibitors across various clinical phases, thereby offering strategic insights for the advancement of DRD2 inhibitor development.

Pd-Catalyzed Enantioselective Three-Component Carboamination of 1,3-Cyclohexadiene

Asymmetric Pd-catalyzed three-component carboamination reactions of dienes to construct chiral cyclohexenylamines, which are of great importance in many fields of chemistry, have remained largely unexplored. Here, we demonstrate a highly enantio- and regioselective Pd/Ming-Phos-catalyzed carboamination reactions of 1,3-cyclohexadiene with readily available aryl iodides and anilines for facile access to diverse valuable chiral cyclohexenylamines. The process shows excellent functional group tolerance, easy scalability, and mild conditions. Moreover, mechanistic studies suggest that this reaction has a first-order dependence on the concentration of the palladium catalyst and aniline.

Characteristics of eye disorders induced by atypical antipsychotics: a real-world study from 2016 to 2022 based on Food and Drug Administration Adverse Event Reporting System

Background

Common atypical antipsychotics include risperidone, paliperidone, olanzapine, lurasidone, quetiapine, clozapine, aripiprazole, ziprasidone, asenapine, brexpiprazole, and cariprazine. Previous studies on ocular adverse reactions of antipsychotics were mainly focused on typical antipsychotics. Systematic research on atypical antipsychotics remains limited.

Objective

This study aimed to evaluate the potential risks of different atypical antipsychotics causing ocular side effects by mining the Food and Drug Administration Adverse Event Reporting System (FAERS) database.

Methods

Extract reports from the FAERS from the first quarter of 2016 to the fourth quarter of 2022 were obtained. Data mining of eye disorders associated with atypical antipsychotics was carried out using The Reporting Odds Ratio (ROR) method and The Medicines and Healthcare Products Regulatory Agency (MHRA) method to determine positive signals.

Results

FAERS reports for 9913783 cases were included in these 28 quarters. 64 defined ocular adverse events were classified into 10 categories according to High-Level Group Terms (HLGT).

Conclusions

There were differences in the types and severity of ocular-related adverse events associated with atypical antipsychotics. Ocular neuromuscular-related adverse events were found among all 11 atypical antipsychotics. Olanzapine had the highest signal intensity in oculogyric crisis. Aripiprazole had the highest signal strength in blepharospasm. Cariprazine was associated with cataract-related ocular adverse reactions. In terms of the types of adverse events, our study found that aripiprazole was associated with 28 types of ocular adverse events, followed by quetiapine. Clozapine was only associated with two types of ocular adverse events.

Aromatic linker variations in novel dopamine D2 and D3 receptor ligands

Dopamine D2-like receptors, especially D2 and D3 receptor subtypes, are important targets of antipsychotic agents. Many of these antipsychotics share an aliphatic linker element between a protonable amine group and an acyl-like moiety. Here, we have modified this aliphatic linker into phenylmethyl and phenylethyl linkers substituted in different positions. The design, synthesis, and in vitro evaluation of 18 dopamine D2 and D3 receptor ligands were performed in this study. Using a radioligand displacement assay, all ligands were found to have modest nanomolar affinity to D2R and D3R. N-(4-{2-[4-(2-Methoxyphenyl)piperazin-1-yl]ethyl}phenyl)acetamide (6c) demonstrates the highest D3R and D2R affinity values (pKi values of 7.83 [D2R] and 8.04 [D3R]), featuring a slight preference to D3R. This derivative can be taken as a reference structure for the development of a new class of D2R and D3R ligands.

Challenges in the Treatment of Psychotic Bipolar Depression

BACKGROUND

Psychotic bipolar depression (PBD) is a prevalent yet understudied psychiatric illness, and there are no specific guidelines or Food and Drug Administration-approved medications for its treatment. Recent studies suggest that some antipsychotics and mood stabilizers may be effective in managing bipolar depression; however, their effectiveness for PBD remains unclear. Given the urgent need for more focused research for managing PBD, we conducted a literature review to summarize the existing literature on PBD.

METHODS

We conducted an electronic literature search from the 1960s to 2023, utilizing PubMed, MEDLINE, EMBASE, and Google, and selected studies based on their relevance to PBD.

FINDINGS

PBD is a complex disorder, with 50%-75% of patients with bipolar disorder exhibiting psychotic features. This likelihood increases among those with a history of psychotic mania. Treatment guidelines often recommend a combination of mood stabilizers, antipsychotics, or electroconvulsive therapy, but they do not specify a first-line treatment. PBD symptoms can be masked by mixed high mood and energy feelings, potentially delaying diagnosis and treatment while increasing suicide risk. Limited research has evaluated outcomes of various treatments for PBD, and despite the lack of evidence for superior efficacy, in clinical practice, antipsychotics are frequently prescribed. Notably, combining an antipsychotic with selective noradrenaline reuptake inhibitors or tricyclic antidepressants may be effective, but including a mood stabilizer is necessary.

CONCLUSION

PBD poses a significant challenge in mental health due to its severity and the lack of consensus on optimal treatment approaches. There is a critical need for more dedicated clinical trials and research to answer key questions about the effective treatment of acute PBD, ideal follow-up care, traits of responders to different therapies, and decision models for subsequent treatments.

A 12-month longitudinal naturalistic follow-up of cariprazine in schizophrenia

Background

Cariprazine, a third-generation antipsychotic (TGAs), has demonstrated efficacy in the treatment of schizophrenia with good tolerability profile. Actual real-world literature data are lacking, particularly when exploring its efficacy in the long term. The present study examined the effects of cariprazine treatment on specific psychopathological domains with a particular focus on outcomes and side effects in real-life experience, after a long-term treatment.

Methods

The present 12-month longitudinal naturalistic study included a sample of subjects with a DSM-5-TR diagnosis of schizophrenia, recruited in the outpatients' psychiatric services of university and community hospitals in Italy, naturally treated with cariprazine. The assessments included: a sociodemographic data sheet, the Structured Clinical Interview for the DSM-5 (SCID-5), the Positive and Negative Symptom Scale (PANSS) and the St. Hans Rating Scale (SHRS). The PANSS was also administered after 6 (T1) and 12 (T2) months of treatment with cariprazine while the SHRS at T1.

Results

The total sample consisted of 31 patients, 15 males and 16 females. A significant decrease of the PANSS' subscales, Marder factors and total mean scores emerged at both T1 and T2 with respect to T0. Extrapyramidal symptoms occurred in a minority of patients and in mild or mild/moderate forms: no patient showed moderate forms of psychic/motor akathisia or dystonia, three subjects showed moderate parkinsonism.

Conclusions

This study confirms a good efficacy profile of cariprazine in both positive and negative symptoms in patients with Schizophrenia, combined with a good tolerability profile in extrapyramidal symptoms.

Effects of Icariin and Its Metabolites on GPCR Regulation and MK-801-Induced Schizophrenia-Like Behaviors in Mice

Icariin, a major bioactive compound found in the Epimedium genus, has been reported to exert protective effects against neurodegenerative disorders. In the current study, we aimed to investigate the regulatory effect of icariin and its active metabolites (icariside II and icaritin) against prime G-protein-coupled receptor targets, considering their association with neuronal disorders. Icariside II exhibited selective agonist activity towards the dopamine D3 receptor (D3R), with half-maximal effective concentrations of 13.29 μM. Additionally, they effectively inhibited the specific binding of radioligands to D3R. Molecular docking analysis revealed that icariside II potentially exerts its agonistic effect through hydrogen-bonding interaction with Asp110 of the D3R, accompanied by negative binding energy. Conversely, icaritin demonstrated selective antagonist effects on the muscarinic acetylcholine M2 receptor (M2R). Radioligand binding assay and molecular docking analysis identified icaritin as an orthosteric ligand for M2R. Furthermore, all three compounds, icariin and its two metabolites, successfully mitigated MK-801-induced schizophrenia-like symptoms, including deficits in prepulse inhibition and social interaction, in mice. In summary, these findings highlight the potential of icariin and its metabolites as promising lead structures for the discovery of new drugs targeting cognitive and neurodegenerative disorders.

Effects of the atypical antipsychotic and D3/D2 dopamine partial agonist cariprazine on effort-based choice behavior: implications for modeling avolition

RATIONALE

Cariprazine is an atypical antipsychotic that acts as a D3/D2 receptor partial agonist. In addition to treating positive symptoms of schizophrenia, cariprazine may have utility for treating negative symptoms. Rodent studies have focused on the effects of cariprazine on cognitive functions and behaviors thought to be related to anhedonia. Avolition, which is characterized by reduced initiation and persistence of goal-directed behavior, is another important negative symptom.

OBJECTIVES

Effort-related choice tasks have been used as animal models of avolition. In these studies, cariprazine was assessed for its effects on effort-based choice in both rats and mice. Previous work has shown that D2 antagonists such as haloperidol and eticlopride produce a low-effort bias in rodents tested on effort-based choice tasks.

RESULTS

Low doses of cariprazine produced a low-effort bias in rats tested on the fixed ratio 5/chow feeding choice task, decreasing lever pressing for high carbohydrate pellets but increasing chow intake. Cariprazine did not alter preference or intake of these foods in free-feeding tests. The effort-related effects of cariprazine were reversed by co-administration of the adenosine A2A antagonist istradefylline, and cariprazine failed to reverse the effort-related effects of the dopamine-depleting agent tetrabenazine. In mouse touchscreen choice tests, low doses of cariprazine also produced a low-effort bias, shifting behavior away from panel pressing.

CONCLUSIONS

These results demonstrate that with these rodent models of avolition, cariprazine appears to act like a D2-family antagonist even at very low doses. Furthermore, the pharmacological regulation of avolition may differ from that of other negative symptoms.

Cariprazine for Treating Schizophrenia, Mania, Bipolar Depression, and Unipolar Depression: A Review of Its Efficacy

This drug review presents a comprehensive review of Cariprazine, a medication that received FDA approval in 2015 for treating schizophrenia and bipolar disorder. The paper begins by exploring Cariprazine's mechanism of action, which involves modulating dopamine and serotonin receptors. Additionally, the review assesses Cariprazine's metabolic profile and notes its low potential for weight gain and metabolic side effects. The study examines Cariprazine's efficacy and safety in treating various psychiatric disorders, such as schizophrenia, bipolar maintenance, mania, and bipolar depression. A meticulous analysis of clinical trials is included, demonstrating Cariprazine's potential advantages over existing medications used for these disorders. Additionally, the review covers Cariprazine's recent approval as an adjuvant treatment for unipolar depression. Furthermore, the paper examines the limitations of Cariprazine, such as the absence of head-to-head trials comparing it to other commonly used medications for these disorders. The paper concludes by emphasizing the need for more research to establish Cariprazine's position in treating schizophrenia and bipolar disorder and determine its comparative effectiveness with other available treatments.

Cariprazine - an Alternative Treatment for Clozapine-resistant Schizophrenia?

Treatment-resistant schizophrenia (TRS) poses a significant therapeutic challenge in psychiatric practice. Clozapine is recognized as a treatment of choice in TRS but is not always effective in alleviating patients' symptoms. Additionally, clozapine therapy is associated with multiple side effects and monitoring requirements that often limit its use and negatively affect patients' compliance with the treatment. Although clozapine augmentation options are available, there is currently no alternative monotherapy proven to be effective in TRS. We present a case of a young man with TRS who failed to respond to appropriate trials of risperidone, aripiprazole and also clozapine, and who experienced impairing adverse effects of clozapine that made further clozapine treatment not only futile but also detrimental to his health. He was successfully treated with cariprazine monotherapy, which culminated in the remission of his both positive and negative symptoms of psychosis as well as in the marked improvement in social functioning. Cariprazine, a newer atypical antipsychotic endowed with a D3-preferring mode of action, may offer a better tolerated and more acceptable treatment option for patients with difficult-to-treat psychotic symptoms.

Identifying Dopamine D3 Receptor Ligands through Virtual Screening and Exploring the Binding Modes of Hit Compounds

The dopamine D3 receptor (D3R) is an important central nervous system target for treating various neurological diseases. D3R antagonists modulate the improvement of psychostimulant addiction and relapse, while D3R agonists can enhance the response to dopaminergic stimulation and have potential applications in treating Parkinson’s disease, which highlights the importance of identifying novel D3R ligands. Therefore, we performed auto dock Vina-based virtual screening and D3R-binding-affinity assays to identify human D3R ligands with diverse structures. All molecules in the ChemDiv library (>1,500,000) were narrowed down to a final set of 37 molecules for the binding assays. Twenty-seven compounds exhibited over 50% inhibition of D3R at a concentration of 10 μM, and 23 compounds exhibited over 70% D3R inhibition at a concentration of 10 μM. Thirteen compounds exhibited over 80% inhibition of D3R at a concentration of 10 μM and the IC50 values were measured. The IC50 values of the five compounds with the highest D3R-inhibition rates ranged from 0.97 μM to 1.49 μM. These hit compounds exhibited good structural diversity, which prompted us to investigate their D3R-binding modes. After trial and error, we combined unbiased molecular dynamics simulation (MD) and molecular mechanics generalized Born surface area (MM/GBSA) binding free-energy calculations with the reported protein−ligand-binding pose prediction method using induced-fit docking (IFD) and binding pose metadynamics (BPMD) simulations into a self-consistent and computationally efficient method for predicting and verifying the binding poses of the hit ligands to D3R. Using this IFD-BPMD-MD-MM/GBSA method, we obtained more accurate and reliable D3R−ligand-binding poses than were obtained using the reported IFD-BPMD method. This IFD-BPMD-MD-MM/GBSA method provides a novel paradigm and reference for predicting and validating other protein−ligand binding poses.

Seventy Years of Antipsychotic Development: A Critical Review

Since the mid-1950s discovery of the first effective antipsychotic medications (APM), we have only been able to improve the tolerability but not the overall efficacy of currently available APMs, as reflected by effectiveness trials in Europe and the United States. This inability to develop more effective APMs is attributable to multiple factors, including failure to create and use assessment tools to assess core symptom domains in schizophrenia, move beyond the dopaminergic hypothesis and to develop "me too" drugs, imposing ill-defined research domain criteria, and lacking federal funding for clinical trials. The classification of APMs is also confusing, including second-generation, partial agonists, and multimodal APMs in the same class of APMs, despite significant differences in their mechanisms of action. Other factors stagnating drug development include inadequate sample sizes to address heterogeneity, lack of statistical measures correlating with clinical significance, using the atheoretical basis of psychiatric diagnoses, failure to control placebo response, and high cost of newer and perhaps more tolerable APMs. Furthermore, there has been a failure to develop early predictors of antipsychotic response and various tools to optimize an APM response. Finally, some mental health providers are also responsible for the suboptimal use of APMs, by using excessive maintenance doses, often with irrational polypharmacy, further compromising effectiveness and medication adherence. However, some bright spots in antipsychotic development include improved tolerability of APMs and long-acting injectables to address the high prevalence of medication nonadherence. This review critically reviews 70 years of antipsychotic development, the reasons behind the failure to develop more effective APMs, and suggestions for future direction.

Cariprazine for treating coprophagia and organic psychosis in a young woman with acquired brain injury

Coprophagia or the ingestion of faeces has been associated with medical conditions (seizure disorders, cerebral atrophy and tumours) and psychiatric disorders (mental retardation, alcoholism, depression, obsessive compulsive disorder, schizophrenia, fetishes, delirium and dementia). The case of a woman in her 30s presenting with coprophagia and psychotic symptoms following hypoxic brain injury is reported. The case is discussed and literature is reviewed. We investigate cariprazine, a relatively new atypical antipsychotic for treating coprophagia, associated with psychotic symptoms. Psychiatric evaluation revealed cognitive dysfunction and psychotic symptoms. Physical examination and laboratory evaluation were unremarkable. She was treated with haloperidol resulting in resolution of coprophagia. Attempts at switching to alternative antipsychotics, due to side effects, resulted in recurrence of coprophagia. Subsequent relapses required higher doses of haloperidol for remission of coprophagia and psychotic symptoms. She finally responded to cariprazine. While firm conclusions are not possible from the experience of a single case, we suggest cariprazine may also be a treatment option for coprophagia, particularly in patients with psychotic symptoms.

Case series: Cariprazine in early-onset schizophrenia

Introduction

Negative symptoms are part of the clinical manifestations of schizophrenia and their presence is associated with a poorer prognosis, significantly limited vocational opportunities, impaired quality of life and social functioning. In the clinical practice, treatment of negative symptoms in patients with schizophrenia, is a challenge. Cariprazine is a novel partial agonist of D3 and D2 receptors, and shows a high affinity for D3, with good tolerability, good response to schizophrenic symptoms and limited side effects. We present two cases of young patients with predominantly negative symptoms during treatment with an atypical antipsychotic, administered in a stable dose and therapeutic range, and for at least 4 weeks prior to the Cariprazine switch.

Methods

Two patients (men aged 21 and 22) with schizophrenia, exhibiting predominantly negative symptoms, are presented. Their diagnosis was based on, DSM-5 criteria (295.10).Patients were treated with Cariprazine at a daily dose of 4.5 mg. They were followed for a period of 18 months and assessed with Positive and Negative Syndrome Scale (PANSS), Global Assessment of Functioning (GAF) and Clinical Global Impression-Severity (CGI-S), at the fourth week of initiation of treatment with Cariprazine, at 6 months, at 12 months and at 18 months. Their mean initial value was 75.5 on PANSS, 4.0 on CGI-S, and 52.5 on GAF. Both patients were treated with stable doses of atypical antipsychotic-Risperidone at a daily dose of 4,5 mg. Cross-titration to Cariprazine was initiated, from 1.5 mg daily dose up to 4,5 mg daily dose, during a period of 2 weeks.

Results

After 18 months of treatment with Cariprazine at a daily dose of 4.5 mg, the following results were reported: mean value was 57.5 on PANSS, 3.0 on CGI-S, and 74.5 on GAF. The overall PANSS mean score decreased by 23.8%, the CGI-S mean score improved by 25% and the mean GAF score increased by 29.5%. The positive PANSS subscale score decreased minimally, from 20 to 16, while for the negative subscale the improvement was 29.8%.Cariprazine was well tolerated by patients and no side effects were observed from it during therapy.

Discussion

After 18 months Cariprazine succeeded in improving negative symptoms, global functioning, and global clinical impression. In young schizophrenic patients with a predominance of negative symptoms, the cariprazine may be a successful alternative.

Scalability of the Positive and Negative Syndrome Scale in first-episode schizophrenia assessed by Rasch models

OBJECTIVE

Historically, assessment of the psychometric properties of the Positive and Negative Syndrome Scale (PANSS) has had several foci: (1) calculation of reliability indexes, (2) extraction of subdimensions from the scale, and (3) assessment of the validity of the total score. In this study, we aimed to examine the scalability and to assess the clinical performance of the 30-item PANSS total score as well as the scalability of a shorter version (PANSS-6) of the scale.

METHODS

A composite data set of 1073 patients with first-episode schizophrenia or schizophrenia spectrum disorder was subjected to Rasch analysis of PANSS data from baseline and 4-6 weeks follow-up.

RESULTS

The central tests of fit of the Rasch model failed to satisfy the statistical requirements behind item homogeneity for the PANSS-30 as well as the PANSS-6 total score. For the PANSS-30, Differential Item Functioning was pronounced both for the 7-point Likert scale rating categories and when dichotomizing the rating categories. Subsequently, the Rasch structure analysis in the context of dichotomized items was used to isolate and estimate a systematic error because of item inhomogeneity, as well as a random error. The size of the combined sources of error for the PANSS-30 total score approximated 20% which is often regarded as clinical cut-off between response versus no-response.

CONCLUSION

The results demonstrate the operational consequences of a lack of statistical fit of the Rasch model and suggest that the calculated measure of uncertainty needs to be considered when using the PANSS-30 total score.

Cariprazine on Psychosis: Beyond Schizophrenia - A Case Series

Cariprazine is an atypical antipsychotic that has D2 and D3 partial agonism properties in addition to the usual 5-HT2A receptor antagonist action of second-generation antipsychotics. It has a distinctly higher affinity for D3 receptors, which is 10-fold higher than for D2 receptors. Cariprazine is also a 5-HT1A partial agonist, with a potential antidepressant effect. Cariprazine has been approved for treatment of both positive and negative symptoms of schizophrenia and for treatment of bipolar disorder. It could potentially be used in depression as an add-on treatment. There are few data reporting effectiveness of cariprazine in the broader spectrum of psychosis. In this paper, the authors report three cases where cariprazine was used in the treatment of psychotic conditions other than schizophrenia, namely a first episode psychosis, a case of delusional disorder, and a case of a patient with borderline personality disorder and psychotic symptoms. The authors suggest that cariprazine may be effective in the treatment of psychosis in a broader sense and should be considered a first-line treatment option.

Switching Clozapine to Cariprazine in Three Patients with Persistent Symptoms of Schizophrenia: A Case Series

Despite many available treatments for schizophrenia, several unmet needs persist in treating individuals with this disorder, and the response rate to first-line antipsychotics remains relatively low. Clozapine has shown efficacy in treating schizophrenia patients who failed to respond to previous antipsychotics. However, side effects and the need for routine blood tests have limited its use as a first-line treatment. Cariprazine is a D₂/D₃ partial agonist antipsychotic with a mechanism of action that differs from other antipsychotics due to its higher affinity for D₃ receptors. Several trials have demonstrated the efficacy of cariprazine on positive and negative symptoms of schizophrenia and have shown that it is a well-tolerated treatment. In this series, we present 3 cases of patients diagnosed with schizophrenia who were initially under treatment with clozapine. Despite some initial improvement, the patients showed persisting positive and negative symptoms or developed limiting side effects while in treatment with clozapine. Cariprazine treatment was titrated concurrently with clozapine tapering until its discontinuation. Significant improvement in both positive and negative symptoms was observed up to 14 months after starting cariprazine, and resolution of side effects was reported in all cases. Our case series supports cariprazine as an effective treatment for positive and negative symptoms in patients who failed to adequately respond or poorly tolerated treatment with clozapine, as well as a potential treatment in dual disorders, specifically psychotic disorders and cocaine use disorder.

New and emerging treatments for schizophrenia: a narrative review of their pharmacology, efficacy and side effect profile relative to established antipsychotics

Schizophrenia is associated with substantial unmet needs, highlighting the necessity for new treatments. This narrative review compares the pharmacology, clinical trial data and tolerability of novel medications to representative antipsychotics. Cariprazine, brexpiprazole and brilaroxazine are partial dopamine agonists effective in acute relapse. Lumateperone (serotonin and dopamine receptor antagonist) additionally benefits asocial and depressive symptoms. F17464 (D3 antagonist and 5-HT1A partial agonist) has one positive phase II study. Lu AF35700 (dopamine and serotonin receptor antagonist) was tested in treatment-resistance with no positive results. Pimavanserin, roluperidone, ulotaront and xanomeline do not act directly on the D2 receptor at clinical doses. Initial studies indicate pimavanserin and roluperidone improve negative symptoms. Ulotaront and xanomeline showed efficacy for positive and negative symptoms of schizophrenia in phase II trials. BI 409306, BI 425809 and MK-8189 target glutamatergic dysfunction in schizophrenia, though of these only BI 425809 showed efficacy. These medications largely have favourable cardiometabolic side-effect profiles. Overall, the novel pharmacology, clinical trial and tolerability data indicate these compounds are promising new additions to the therapeutic arsenal.

Using Cariprazine to Ameliorate Negative Symptoms and Metabolic Side Effects of Clozapine and Paliperidone - Clinical Cases

INTRODUCTION

Cariprazine is a third-generation antipsychotic approved in Europe in 2017 for the treatment of schizophrenia. It presents distinct pharmacodynamic properties, such as D3/D2 partial agonism, preferential binding to D3 receptors, antagonism at the serotonin 5-HT2A and 5-HT2B receptors, partial agonism at 5-HT1A receptors, and low affinity to other receptors (including noradrenergic, histaminergic, and cholinergic). It has demonstrated efficacy in the treatment of positive and negative symptoms of schizophrenia with a safe side effect and metabolic profile.

METHODS

Here, we describe one clinical case of a patient that benefited from an add-on of cariprazine to a regimen of clozapine; and two clinical cases of patients that benefited from the switch from clozapine and paliperidone long-acting injectable to cariprazine.

RESULTS AND DISCUSSION

Those cases illustrate how cariprazine can be used in patients with schizophrenia in the treatment of both positive and negative symptoms, and when aiming to ameliorate the metabolic burden associated with other treatments. However, further studies are needed to consubstantiate those findings.

2-Phenylcyclopropylmethylamine Derivatives as Dopamine D2 Receptor Partial Agonists: Design, Synthesis, and Biological Evaluation

Partial agonist activity at the dopamine D₂ receptor (D₂R) is the primary pharmacological feature of the third-generation antipsychotics─aripiprazole, brexpiprazole, and cariprazine. However, all these drugs share a common phenyl-piperazine moiety as the primary pharmacophore. In this study, we designed and synthesized a series of novel compounds based on the 2-phenylcyclopropylmethylamine (PCPMA) scaffold and studied their pharmacological activity at the D₂R. A number of potent D₂R partial agonists were identified through binding affinity screening and functional activity profiling in both G protein and β-arrestin assays. The structure-functional activity relationship results showed that the spacer group is crucial for fine-tuning the intrinsic activity of these compounds. Compounds (+)-14j and (+)-14l showed good pharmacokinetic properties and an unexpected selectivity against the serotonin 2A (5-HT_2A) receptor. Preliminary suppressive effects in a mouse hyperlocomotion model proved that these PCPMA-derived D₂R partial agonists are effective as potential novel antipsychotics.

New drugs in psychiatry - cariprazine, lurasidone, esketamine

Introduction: Invariably, the search for an “ideal drug” in psychiatry has been going for years, one that is safe and effective, prevents relapse and shows the least possible side effects.

Material and methods: The aim of this study authors is to draw attention to new drugs used in psychiatry- cariprazine, lurazidone and esketamine, their mechanism of action, dosage, the most common side effects and metabolism.

The article reviews the research and works on these drugs available in Google Scholar and PubMed databases and the characteristics of medical products on years 2010-2021.

Results: Cariprazine is a drug registered in Poland for the treatment of schizophrenia in adults since July,13 2017. In the world, it is additionally used in the treatment of manic and mixed episodes in the course of bipolar disorder, depression in the course of bipolar disorder and unipolar depression. Lurasidone in Poland is indicated for the treatment of schizophrenia in adult patients and adolescents from 13 years of age. In the world it is also used to treat depression in bipolar disorder, in some cases off-label in the treatment of mania in bipolar disorder and irritability and anger in autism spectrum disorders. Esketamine in nasal spray in combination with an oral antidepressant has been approved in the US for the treatment of depression in adults for whom other antidepressants have not benefited, in Poland, it is also used in such an indication.

Conclusions: The action profile of these drugs, the research to date and the results of treatment with these drugs are very promising. The drugs are safe and well tolerated. However, it is clinical practice that will verify the usefulness and effectiveness of treatment with them and show the effects of long-term therapies with their use.

The dual hit hypothesis of schizophrenia: Evidence from animal models

Schizophrenia is a heterogeneous psychiatric disorder, which can severely impact social and professional functioning. Epidemiological and clinical studies show that schizophrenia has a multifactorial aetiology comprising genetic and environmental risk factors. Although several risk factors have been identified, it is still not clear how they result in schizophrenia. This knowledge gap, however, can be investigated in animal studies. In this review, we summarise animal studies regarding molecular and cellular mechanisms through which genetic and environmental factors may affect brain development, ultimately causing schizophrenia. Preclinical studies suggest that early environmental risk factors can affect the immune, GABAergic, glutamatergic, or dopaminergic system and thus increase the susceptibility to another risk factor later in life. A second insult, like social isolation, stress, or drug abuse, can further disrupt these systems and the interactions between them, leading to behavioural abnormalities. Surprisingly, first insults like maternal infection and early maternal separation can also have protective effects. Single gene mutations associated with schizophrenia did not have a major impact on the susceptibility to subsequent environmental hits.

Contrasting Typical and Atypical Antipsychotic Drugs

The beliefs that antipsychotic drugs (APDs) are 1) effective only to treat delusions and hallucinations (positive symptoms), 2) that typical and atypical APDs differ only in ability to cause extrapyramidal side effects, and 3) that their efficacy as antipsychotics is due solely to their dopamine D₂ receptor blockade are outmoded concepts that prevent clinicians from achieving optimal clinical results when prescribing an APD. Atypical APDs are often more effective than typical APDs in treating negative symptoms, cognitive impairment, and mood symptoms as well as reducing the risk for suicide and decreasing aggression. This applies not only to those diagnosed with schizophrenia or schizoaffective disorder but also to bipolar disorder, major depression, and other psychiatric diagnoses. The greater advantage of an atypical APD is not evident in all patients for every atypical APD due, in part, to individual differences in genetic and epigenetic endowment and differences in the pharmacology of the atypical APDs, their mode of action being far more complex than that of the typical APDs. A common misconception is that among the atypical APDs, only clozapine is effective for reducing psychosis in treatment-resistant schizophrenia. Aripiprazole, lurasidone, olanzapine, and risperidone also can be more effective than typical APDs for treatment-resistant schizophrenia; clozapine is uniquely indicated for reducing the risk for suicide. The ability of the atypical APDs to improve cognition and negative symptoms in some patients together with lower propensity to cause tardive dyskinesia (an underappreciated advantage) leads to better overall outcomes. These advantages of the atypical APDs in efficacy and safety are due, in part, to initiation of synaptic plasticity via direct and indirect effects of the atypical APDs on a variety of proteins, especially G proteins, and release of neurotrophins (e.g., brain-derived neurotrophic factor). The typical APDs beneficial effects on psychosis are mainly the result of D₂ receptor blockade, which can be associated with serious side effects and lack of tolerability.

Synthesis, in silico, and in vitro studies of novel dopamine D2 and D3 receptor ligands

Dopamine is an important neurotransmitter in the human brain and its altered concentrations can lead to various neurological diseases. We studied the binding of novel compounds at the dopamine D₂ (D₂ R) and D₃ (D₃ R) receptor subtypes, which belong to the D₂ -like receptor family. The synthesis, in silico, and in vitro characterization of 10 dopamine receptor ligands were performed. Novel ligands were docked into the D₂ R and D₃ R crystal structures to examine the precise binding mode. A quantum mechanics/molecular mechanics study was performed to gain insights into the nature of the intermolecular interactions between the newly introduced pentafluorosulfanyl (SF₅ ) moiety and D₂ R and D₃ R. A radioligand displacement assay determined that all of the ligands showed moderate-to-low nanomolar affinities at D₂ R and D₃ R, with a slight preference for D₃ R, which was confirmed in the in silico studies. N-{4-[4-(2-Methoxyphenyl)piperazin-1-yl]butyl}-4-(pentafluoro-λ6-sulfanyl)benzamide (7i) showed the highest D₃ R affinity and selectivity (pK_i values of 7.14 [D₂ R] and 8.42 [D₃ R]).

[Cariprazine in schizophrenia with predominantly negative symptoms: early effects of therapy (observational study)]

BACKGROUND

Currently available antipsychotics have limited efficacy in the treatment of negative symptoms in schizophrenia and new drugs with wider spectrums of clinical efficacy are very desirable. Cariprazine is a newer antipsychotic acting as dopamine D3- and in lesser extent D2-receptor partial agonist found to be effective in the treatment of negative symptoms in schizophrenia.

OBJECTIVES

To evaluate cariprazine early effects at the first stage of therapy of schizophrenia patients with predominantly negative symptoms.

DESIGN AND PATIENTS

Open-lable observational assessment of 60 adult schizophrenia patients (F20 on ICD-10, 49% males) with predominantly negative symptoms (PANSS-FSNS ≥15, PANSS-FSPS <19) treated by cariprazine (starting daily dose 1.5 mg followed by upward titration by 1.5 mg weekly up to 6 mg if needed) were assessed with PANSS, CAINS, CDSS and SAS scales at baseline and on week 1, 2, and 4. Efficacy criteria were.

RESULTS

Most patients (75%) improved during 28 days of cariprazine treatment. Negative symptoms mean total scores on PANSS-NS and CAINS significantly (p<0.05) reduced by 4.3 and 4.9 respectively at the end of assessment (day 28). Cariprazine tolerability was good, only 4 patients discontinued because of TEAEs (akathisia, insomnia).

CONCLUSIONS

The study results preliminary suggest initial effect of cariprazine on negative symptoms at least in some schizophrenia patients with predominantly negative symptoms starting from 1-2 weeks of treatment and available for observation and assessment and could be useful for determination of early clinical predictors for efficacy. Considering limitations of observational open-lable design with no control groups these data need to be confirmed.

Early Clinical Effects of Novel Partial D3/D2 Agonist Cariprazine in Schizophrenia Patients With Predominantly Negative Symptoms (Open-Label, Non-controlled Study)

BACKGROUND

Because of limited efficacy of antipsychotics against negative symptoms in schizophrenia new drugs with wider spectrums of clinical efficacy are very desirable. The newer 3rd generation antipsychotic cariprazine presents the unique mode of action acting as partial agonist predominantly for dopamine D3- and in lesser extent D2-receptors. Cariprazine is found to be effective in the treatment of negative symptoms in schizophrenia comparing to second generation antipsychotic risperidone.

OBJECTIVES

To evaluate initial effects of cariprazine in schizophrenia patients with predominantly negative symptoms.

DESIGN AND PATIENTS

Open-label, non-controlled study included 60 adult schizophrenia patients (F20 on ICD-10, 49% males) with predominantly negative symptoms (Positive and Negative Syndrome Scale, S factor score for negative and positive symptoms, PANSS-FSNS ≥ 15 and PANSS-FSPS <19) treated with cariprazine (starting daily dose 1.5 mg followed by upward titration by 1.5 mg weekly up to 6 mg if needed) were assessed with PANSS, CAINS (The Clinical Assessment Interview for Negative Symptoms), CDSS (Calgary Depression Scale for Schizophrenia), and SAS (Simpson-Angus Scale for Extrapyramidal Symptoms) scales at baseline and on week 1, 2, and 4.

RESULTS

Most patients (75%) improved during 28 days of cariprazine treatment. At the end of assessment (day 28) mean starting total scores for negative symptoms on PANSS-NS and CAINS scales significantly (p < 0.05) reduced by 4.3 and 4.9, respectively, with no significant changes in depression symptoms (CDSS). Cariprazine tolerability was very good, only four patients discontinued because of TEAEs (akathisia, insomnia).

CONCLUSIONS

The results of this study suggest early effect of cariprazine on negative symptoms at least in some schizophrenia patients with predominantly negative symptoms starting from 1 to 2 weeks of treatment and could be useful for determination of early clinical predictors for efficacy. Considering limitations of open-label design with no control groups these data need to be confirmed.

Case Report: Cariprazine Efficacy in Young Patients Diagnosed With Schizophrenia With Predominantly Negative Symptoms

Negative symptoms of schizophrenia are among the most invalidating clinical manifestations of this disorder, and they are correlated with poorer prognosis, lower quality of life, and fewer chances for successful social reintegration and professional rehabilitation. Although atypical antipsychotics have been associated with higher efficacy on negative symptoms than typical agents, not all of them are equally effective. Cariprazine is a new D3 and D2 receptor partial agonist, and its high D3 affinity may be useful for decreasing several adverse events (e.g., extrapyramidal symptoms or hyperprolactinemia), and also for increasing this drug's efficacy over negative symptoms. This case series presents three young adults with predominantly negative symptoms during treatment with an atypical antipsychotic, administered in stable dose within the therapeutic range, and for at least 4 weeks prior to the cariprazine switch. These patients (two male and one female, mean age 35.7 years) were diagnosed with schizophrenia, according to the DSM-5 criteria. They were evaluated using Positive and Negative Syndrome Scale (PANSS), Clinical Global Impression-Severity (CGI-S), and Global Assessment of Functioning (GAF). Their mean initial values were 80.3 on PANSS, 4.3 on CGI-S, and 48 on GAF. All these patients were already on a treatment with stable doses of atypical antipsychotics (olanzapine 10 mg/day, n = 1, risperidone 6 mg/day, n = 1, and quetiapine 600 mg/day, n = 1). Cross-titration to cariprazine was initiated, from 1.5 mg qd up to 6 mg qd, during a mean period of 2.7 weeks. After 12 weeks of cariprazine 6 mg/day, the positive scale of PANSS was relatively stable compared to baseline, while the negative mean score decreased by 22%. Also, the mean CGI-S improvement was 15.4% and the GAF mean score increased by 17%. The overall tolerability was good, without severe adverse events being reported. Conclusions: Cariprazine is well tolerated and efficient for patients diagnosed with schizophrenia who have significant negative symptoms that impair daily functioning. After 12 weeks cariprazine succeeded in improving negative symptoms, global functioning, and clinical global impression.

Preclinical Pharmacology of [2-(3-Fluoro-5-Methanesulfonyl-phenoxy)Ethyl](Propyl)amine (IRL790), a Novel Dopamine Transmission Modulator for the Treatment of Motor and Psychiatric Complications in Parkinson Disease

IRL790 ([2-(3-fluoro-5-methanesulfonylphenoxy)ethyl](propyl)amine, mesdopetam) is a novel compound in development for the clinical management of motor and psychiatric disabilities in Parkinson disease. The discovery of IRL790 was made applying a systems pharmacology approach based on in vivo response profiling. The chemical design idea was to develop a new type of DA D3/D2 receptor type antagonist built on agonist rather than antagonist structural motifs. We hypothesized that such a dopamine antagonist with physicochemical properties similar to agonists would exert antidyskinetic and antipsychotic effects in states of dysregulated dopaminergic signaling while having little negative impact on physiologic dopamine transmission and, hence, minimal liability for side effects related to dopamine-dependent functions. At the level of in vivo pharmacology, IRL790 displays balancing effects on aberrant motor phenotypes, reducing l-DOPA-induced dyskinesias in the rodent 6-hydroxydopamine lesion model and reducing psychostimulant-induced locomotor hyperactivity elicited by pretreatment with either d-amphetamine or dizocilpine, without negatively impacting normal motor performance. Thus, IRL790 has the ability to normalize the behavioral phenotype in hyperdopaminergic as well as hypoglutamatergic states. Neurochemical and immediate early gene (IEG) response profiles suggest modulation of DA neurotransmission, with some features, such as increased DA metabolites and extracellular DA, shared by atypical antipsychotics and others, such as increased frontal cortex IEGs, unique to IRL790. IRL790 also increases extracellular levels of acetylcholine in the prefrontal cortex and ventral hippocampus. At the receptor level, IRL790 appears to act as a preferential DA D3 receptor antagonist. Computational docking studies support preferential affinity at D3 receptors with an agonist-like binding mode. SIGNIFICANCE STATEMENT: This paper reports preclinical pharmacology along with molecular modeling results on IRL790, a novel compound in clinical development for the treatment of motor and psychiatric complications in advanced Parkinson disease. IRL790 is active in models of perturbed dopaminergic and glutamatergic signaling, including rodent 6-hydroxydopamine l-DOPA-induced dyskinesias and psychostimulant-induced hyperactivity, in a dose range that does not impair normal behavior. This effect profile is attributed to interactions at dopamine D2/D3 receptors, with a 6- to 8-fold preference for the D3 subtype.

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.

BCL9 provides multi-cellular communication properties in colorectal cancer by interacting with paraspeckle proteins

Colorectal cancer (CRC) is the third most commonly diagnosed cancer, which despite recent advances in treatment, remains incurable due to molecular heterogeneity of tumor cells. The B-cell lymphoma 9 (BCL9) oncogene functions as a transcriptional co-activator of the Wnt/β-catenin pathway, which plays critical roles in CRC pathogenesis. Here we have identified a β-catenin-independent function of BCL9 in a poor-prognosis subtype of CRC tumors characterized by expression of stromal and neural associated genes. In response to spontaneous calcium transients or cellular stress, BCL9 is recruited adjacent to the interchromosomal regions, where it stabilizes the mRNA of calcium signaling and neural associated genes by interacting with paraspeckle proteins. BCL9 subsequently promotes tumor progression and remodeling of the tumor microenvironment (TME) by sustaining the calcium transients and neurotransmitter-dependent communication among CRC cells. These data provide additional insights into the role of BCL9 in tumor pathogenesis and point towards additional avenues for therapeutic intervention.

The Role of Dopamine D3 Receptor Partial Agonism in Cariprazine-Induced Neurotransmitter Efflux in Rat Hippocampus and Nucleus Accumbens

Cariprazine is an approved antipsychotic and antidepressant which is a dopamine (DA) D3-preferring D3/D2 receptor partial agonist, serotonin (5-HT) 5-HT1A receptor partial agonist, and 5-HT2B and 5-HT2A receptor antagonist, a profile unique for atypical antipsychotic drugs. The purpose of this study was to clarify the effects of cariprazine and selective D3 receptor ligands on neurotransmitter efflux in the rat nucleus accumbens (NAC) and ventral hippocampus (HIP), brain regions important for reality testing, rewarded behavior, and cognition. In vivo microdialysis was performed in awake, freely moving rats after administration of cariprazine; (+)-PD-128907 [(4aR,10bR)-3,4a,4,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano-[4,3-b]-1,4-oxazin-9-ol hydrochloride], a D3 receptor-preferring agonist; and SB-277011A [trans-N-[4-[2-(6-cyano-1,2,3,4-tetrahydroisoquinolin-2-yl)ethyl]cyclohexyl]-4-quinolininecarboxamide hydrochloride], a selective D3 receptor antagonist, alone or combined, and extracellular levels of multiple neurotransmitters and metabolites were measured in the NAC and HIP by ultraperformance liquid chromatography with tandem mass spectrometry. Cariprazine increased DA, norepinephrine (NE), and 5-HT efflux in both regions, whereas it increased glycine (Gly) and glutamate efflux only in the NAC and efflux of DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) only in the HIP. Similarly, SB-277011A increased DA, NE, DOPAC, and HVA, but not 5-HT, efflux in the NAC and HIP, and acetylcholine efflux in the HIP. Most of these effects of cariprazine and SB-277011A were fully or partially attenuated by the D3 receptor agonist (+)-PD-128907, suggesting these effects of cariprazine are related to its D3 receptor partial agonism, and that this mechanism, leading to diminished stimulation of D3 receptors, may contribute to its efficacy in both schizophrenia and bipolar disorder. The possible role of Gly in the action of cariprazine is discussed. SIGNIFICANCE STATEMENT: The novel atypical antipsychotic drug cariprazine increased nucleus accumbens and hippocampal neurotransmitter efflux, similar to the actions of the D3 receptor antagonist SB-277011A [trans-N-[4-[2-(6-cyano-1,2,3,4-tetrahydroisoquinolin-2-yl)ethyl]cyclohexyl]-4-quinolininecarboxamide hydrochloride]. The D3 receptor-preferring agonist (+)-PD-128907 [(4aR, 10bR)-3,4a,4,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano-[4,3-b]-1,4-oxazin-9-ol hydrochloride], diminished the effects of both compounds on neurotransmitter efflux in both regions. These results suggested D3 receptor partial agonist activity of cariprazine, producing functional antagonism, may contribute to its efficacy in schizophrenia and bipolar disorder.

Brexpiprazole: A Review in Schizophrenia

Brexpiprazole (Rxulti^®, Rexulti^®) is an oral atypical antipsychotic agent approved for the treatment of schizophrenia in the EU (in adult patients) and the USA, as well as in some other countries, including Japan. Like aripiprazole, it is a partial agonist at dopamine D₂ and serotonin 5-HT_1A receptors and an antagonist at serotonin 5-HT_2A receptors. However, brexpiprazole displays less intrinsic activity at D₂ receptors and, coupled with actions at 5HT_1A, 5HT_2A and noradrenaline α_1B receptors that are at least as potent as its action at D₂ receptors, is predicted to demonstrate a lower propensity for activating adverse events and extrapyramidal symptoms than aripiprazole. Brexpiprazole 2-4 mg/day produced statistically significant and clinically meaningful improvements in overall symptomatology and psychosocial functioning compared with placebo in adults with acute exacerbation of schizophrenia. As maintenance treatment, brexpiprazole 1-4 mg/day significantly delayed the time to relapse compared with placebo in patients who were already stabilized on the drug and was associated with stabilization or continued improvement in patients' symptoms and functioning. Brexpiprazole was generally well tolerated, exhibiting an adverse event profile characterized by a relatively low incidence of activating and sedating adverse effects, small changes in QT interval and metabolic parameters that were not clinically significant, and moderate weight gain. Clinical evidence to date suggests it usefully extends the range of therapeutic options for schizophrenia.

Current Concepts and Treatments of Schizophrenia

Schizophrenia is a debilitating mental illness which involves three groups of symptoms, i.e., positive, negative and cognitive, and has major public health implications. According to various sources, it affects up to 1% of the population. The pathomechanism of schizophrenia is not fully understood and current antipsychotics are characterized by severe limitations. Firstly, these treatments are efficient for about half of patients only. Secondly, they ameliorate mainly positive symptoms (e.g., hallucinations and thought disorders which are the core of the disease) but negative (e.g., flat affect and social withdrawal) and cognitive (e.g., learning and attention disorders) symptoms remain untreated. Thirdly, they involve severe neurological and metabolic side effects and may lead to sexual dysfunction or agranulocytosis (clozapine). It is generally agreed that the interactions of antipsychotics with various neurotransmitter receptors are responsible for their effects to treat schizophrenia symptoms. In particular, several G protein-coupled receptors (GPCRs), mainly dopamine, serotonin and adrenaline receptors, are traditional molecular targets for antipsychotics. Comprehensive research on GPCRs resulted in the exploration of novel important signaling mechanisms of GPCRs which are crucial for drug discovery: intentionally non-selective multi-target compounds, allosteric modulators, functionally selective compounds and receptor oligomerization. In this review, we cover current hypotheses of schizophrenia, involving different neurotransmitter systems, discuss available treatments and present novel concepts in schizophrenia and its treatment, involving mainly novel mechanisms of GPCRs signaling.

Molecular targets of atypical antipsychotics: From mechanism of action to clinical differences

The introduction of atypical antipsychotics (AAPs) since the discovery of its prototypical drug clozapine has been a revolutionary pharmacological step for treating psychotic patients as these allow a significant recovery not only in terms of hospitalization and reduction in symptoms severity, but also in terms of safety, socialization and better rehabilitation in the society. Regarding the mechanism of action, AAPs are weak D₂ receptor antagonists and they act beyond D₂ antagonism, involving other receptor targets which regulate dopamine and other neurotransmitters. Consequently, AAPs present a significant reduction of deleterious side effects like parkinsonism, hyperprolactinemia, apathy and anhedonia, which are all linked to the strong blockade of D₂ receptors. This review revisits previous and current findings within the class of AAPs and highlights the differences in terms of receptor properties and clinical activities among them. Furthermore, we propose a continuum spectrum of "atypia" that begins with risperidone (the least atypical) to clozapine (the most atypical), while all the other AAPs fall within the extremes of this spectrum. Clozapine is still considered the gold standard in refractory schizophrenia and in psychoses present in Parkinson's disease, though it has been associated with adverse effects like agranulocytosis (0.7%) and weight gain, pushing the scientific community to find new drugs as effective as clozapine, but devoid of its side effects. To achieve this, it is therefore imperative to characterize and compare in depth the very complex molecular profile of AAPs. We also introduce relatively new concepts like biased agonism, receptor dimerization and neurogenesis to identify better the old and new hallmarks of "atypia". Finally, a detailed confrontation of clinical differences among the AAPs is presented, especially in relation to their molecular targets, and new means like therapeutic drug monitoring are also proposed to improve the effectiveness of AAPs in clinical practice.