Brain uptake and distribution of the dopamine D3 /D2 receptor partial agonist [11 C]cariprazine: an in vivo positron emission tomography study in nonhuman primates

The role of the D3 dopamine receptor and its partial agonist cariprazine in patients with schizophrenia and substance use disorder

INTRODUCTION

Comorbidity of substance use disorder (SUD) with schizophrenia, referred to as dual disorder (DD), significantly increases morbidity and mortality compared to schizophrenia alone. A dopaminergic dysregulation seems to be a common pathophysiological basis of the comorbidity.

AREAS COVERED

This article reports the current evidence on the role of dopamine dysregulations in DD, the pharmacological profile of cariprazine, a partial agonist of D3 and D2 dopamine receptors, and first clinical observations that may support its usefulness in the therapy of DD. PubMed/MEDLINE was searched for the keywords 'cariprazine,' 'schizophrenia,' 'dual disorder,' 'dopamine,' and 'dopamine receptor.' Preclinical and clinical studies, and reviews published in English were retrieved.

EXPERT OPINION

Although the management of DD remains challenging, and the evidence for pharmacologic treatments is still unsatisfactory, cariprazine may be a candidate medication in DD due to its unique mechanism of action. Preliminary clinical experiences suggest that cariprazine has both antipsychotic and anticraving properties and should be considered early in patients with DD.

Antidepressant efficacy of cariprazine in bipolar disorder and the role of its pharmacodynamic properties: A hypothesis based on data

The treatment of bipolar depression is one of the most challenging needs in contemporary psychiatry. Currently, only quetiapine, olanzapine-fluoxetine combination, lurasidone, cariprazine, and recently lumateperone have been FDA-approved to treat this condition. The neurobiology of bipolar depression and the possible targets of bipolar antidepressant therapy remain elusive. The current study investigated whether the pharmacodynamic properties of cariprazine fit into a previously developed model which was the first to be derived based on the strict combination of clinical and preclinical data. The authors performed a systematic review of the literature to identify the pharmacodynamic properties of cariprazine. The original model suggests that a constellation of effects on different receptors is necessary and that serotonin reuptake inhibition does not appear to play a significant role in acute bipolar depression. On the contrary, norepinephrine activity seems to be necessary. Probably the early antidepressant effect can be achieved through an agonistic activity at 5HT-1A and antagonism at alpha1 noradrenergic and 5-HT2A receptors, but the presence of a norepinephrine reuptake inhibition appears essential to sustain it. Overall, the properties of cariprazine fit well the proposed model and add to its validity. A point that needs further clarification is norepinephrine reuptake inhibition which is not yet fully studied for cariprazine.

Mini Review on Cariprazine: A Promising Antipsychotic Agent

Cariprazine is a piperazine derivative approved by the USFDA in 2015 as a novel atypical antipsychotic drug (APD) to treat adults with schizophrenia and bipolar manic or mixed episodes in adults. However, due to the partial agonist action on dopamine D₂, D₃ receptors, and serotonin 5-HT_1A receptors as well as the antagonist effect on 5-HT_2A, 5-HT_2B, and H₁ receptors, cariprazine differs pharmacologically from other APDs, both typical and atypical. Moreover, cariprazine also has a unique pharmacokinetic profile due to the formation of two clinically significant metabolites: desmethyl-cariprazine (DCAR) and desmethyl-cariprazine (DDCAR). They are eliminated by CYP3A4 and also, to a lesser extent, by CYP2D6. Here, we also review the effectiveness, safety, as well as current clinical update of cariprazine in bipolar I disorder associated with/without mania and schizophrenia through randomized and post-hoc analysis. The potential benefits of cariprazine as a promising therapeutic alternative in addressing major clinical requirements for better therapy of such severe neuropsychiatric conditions were demonstrated in this summarized review study.

Metoprolol Inhibits Developmental Brain Sterol Biosynthesis in Mice

De novo sterol synthesis is a critical homeostatic mechanism in the brain that begins during early embryonic development and continues throughout life. Multiple medications have sterol-biosynthesis-inhibiting side effects, with potentially detrimental effects on brain health. Using LC-MS/MS, we investigated the effects of six commonly used beta-blockers on brain sterol biosynthesis in vitro using cell lines. Two beta-blockers, metoprolol (MTP) and nebivolol, showed extreme elevations of the highly oxidizable cholesterol precursor 7-dehydrocholesterol (7-DHC) in vitro across multiple cell lines. We followed up on the MTP findings using a maternal exposure model in mice. We found that 7-DHC was significantly elevated in all maternal brain regions analyzed as well as in the heart, liver and brain of the maternally exposed offspring. Since DHCR7-inhibiting/7-DHC elevating compounds can be considered teratogens, these findings suggest that MTP utilization during pregnancy might be detrimental for the development of offspring, and alternative beta-blockers should be considered.

Add-on Cariprazine in Patients with Long-term Clozapine Treatment and Treatment Resistant Schizophrenia: Two Cases of Psychotic Deterioration and Pisa Syndrome

An increasing number of studies deal with medical options for treatment resistant schizophrenia. If no remission can be achieved with clozapine, a combination of antipsychotics can be considered. The combination of clozapine and cariprazine is rarely studied. Cariprazine is a partial agonist on dopamine D₂ and D₃ receptors and a pharmaceutically rational add-on to clozapine. Stimulating D₃ receptors has been linked to improved cognition and mood, with negligible extrapyramidal side effects. We present two patients with long-term treatment resistant schizophrenia receiving cariprazine and clozapine. Whereas psychotic symptoms worsened, the patients developed extrapyramidal side effects with a Pisa syndrome. The syndrome remitted after discontinuation of cariprazine. Possible explanations by pharmacodynamic interactions and drug specific receptor profiles are discussed.

Present and future antipsychotic drugs: a systematic review of the putative mechanisms of action for efficacy and a critical appraisal under a translational perspective

Antipsychotics represent the mainstay of schizophrenia pharmacological therapy, and their role has been expanded in the last years to mood disorders treatment. Although introduced in 1952, many years of research were required before an accurate picture of how antipsychotics work began to emerge. Despite the well-recognized characterization of antipsychotics in typical and atypical based on their liability to induce motor adverse events, their main action at dopamine D2R to elicit the "anti-psychotic" effect, as well as the multimodal action at other classes of receptors, their effects on intracellular mechanisms starting with receptor occupancy is still not completely understood. Significant lines of evidence converge on the impact of these compounds on multiple molecular signaling pathways implicated in the regulation of early genes and growth factors, dendritic spine shape, brain inflammation, and immune response, tuning overall the function and architecture of the synapse. Here we present, based on PRISMA approach, a comprehensive and systematic review of the above mechanisms under a translational perspective to disentangle those intracellular actions and signaling that may underline clinically relevant effects and represent potential targets for further innovative strategies in antipsychotic therapy.

New Antipsychotic Medications in the Last Decade

PURPOSE OF REVIEW

Over the last ten years, the treatment of psychosis has seen a near explosion of creative development in both novel agents and new delivery modalities. The current review summarizes these developments over the past decade (2011-2020). We performed a systematic review utilizing PubMed and PsychInfo with the aim of identifying all the RCT and related analyses in adults with psychosis (schizophrenia and mania).

RECENT FINDINGS

We identified 11 significant developments: the introduction of new antipsychotics cariprazine, brexpiprazole, lumateperone, and pimavanserin; introduction of new delivery methods: subcutaneous long-acting risperidone, aripiprazole lauroxil, transdermal asenapine, and inhaled loxapine; and the introduction of new approaches such as olanzapine/samidorphan for olanzapine-associated weight gain, examination of the TAAR1 agonist SEP 363,856 as a test of concept, and the combination of Xanomeline/Trospium, an M₁ and M₄ muscarinic receptor agonist in conjunction with a peripheral anticholinergic. Last decade has seen a tremendous development in second-generation antipsychotics which provides unprecedented treatment options for clinicians in treating psychosis.

Cariprazine Add-on in Inadequate Clozapine Response: A Report on Two Cases

Cariprazine is a novel antipsychotic drug that exerts partial agonism of dopamine D₂/D₃ receptors with preferential binding to the D₃ receptor, antagonism of 5HT_2B receptors, and partial agonism of 5HT_1A. Currently, cariprazine has shown clinical efficacy in patients with schizophrenia and with bipolar disorder, as well as adjunctive treatment in patients with Major Depressive Disorder (MDD) and drug-resistant MDD. In the present case series, we report on two patients with treatment-resistant schizophrenia and partial response to clozapine who benefit from combination with cariprazine. The effects of cariprazine combination were remarkable also concerning the adverse metabolic effects of clozapine.

Hunting for the high-affinity state of G-protein-coupled receptors with agonist tracers: Theoretical and practical considerations for positron emission tomography imaging

The concept of the high‐affinity state postulates that a certain subset of G‐protein‐coupled receptors is primarily responsible for receptor signaling in the living brain. Assessing the abundance of this subset is thus potentially highly relevant for studies concerning the responses of neurotransmission to pharmacological or physiological stimuli and the dysregulation of neurotransmission in neurological or psychiatric disorders. The high‐affinity state is preferentially recognized by agonists in vitro. For this reason, agonist tracers have been developed as tools for the noninvasive imaging of the high‐affinity state with positron emission tomography (PET). This review provides an overview of agonist tracers that have been developed for PET imaging of the brain, and the experimental paradigms that have been developed for the estimation of the relative abundance of receptors configured in the high‐affinity state. Agonist tracers appear to be more sensitive to endogenous neurotransmitter challenge than antagonists, as was originally expected. However, other expectations regarding agonist tracers have not been fulfilled. Potential reasons for difficulties in detecting the high‐affinity state in vivo are discussed.

Cariprazine for acute and maintenance treatment of adults with schizophrenia: an evidence-based review and place in therapy

Cariprazine is an oral antipsychotic approved in the US and EU for the treatment of schizophrenia. Cariprazine differs from other antipsychotics in that it is a dopamine D3- and D2-receptor partial agonist, with tenfold higher affinity for D3 receptors than for D2 receptors. Cariprazine is metabolized in two steps by CYP3A4 to didesmethyl-cariprazine (DDCAR). DDCAR has a long half-life of 1-3 weeks and is the predominant circulating active moiety. Efficacy and safety in persons with acute schizophrenia were assessed in four similarly designed, short-term, randomized, placebo-controlled clinical trials in nonelderly adults, with three studies considered positive and yielding a number needed to treat vs placebo for response (change from baseline ≥30% in Positive and Negative Syndrome Scale total score) of ten for the approved dose range of cariprazine 1.5-6 mg/day. The most common adverse reactions were extrapyramidal symptoms (15% and 19% for 1.5-3 and 4.5-6 mg/day, respectively, vs 8% for placebo) and akathisia (9% and 12.5% for 1.5-3 and 4.5-6 mg/day, respectively, vs 4% for placebo). For the approved dose range, rates of discontinuation because of an adverse event were lower overall for patients receiving cariprazine vs placebo (9% vs 12%). Weight and metabolic profile appear favorable. Cariprazine does not increase prolactin levels or prolong the electrocardiographic QT interval. Cariprazine has also been found to be effective for the maintenance treatment of schizophrenia by delaying time to relapse when compared with placebo (HR 0.45). A 26-week randomized clinical trial evidenced superiority of cariprazine over risperidone for the treatment of predominantly negative symptoms in patients with schizophrenia. Cariprazine is also approved in the US for the acute treatment of manic or mixed episodes associated with bipolar I disorder in adults and is being studied for the treatment of bipolar I depression and major depressive disorder.

Preferential binding to dopamine D3 over D2 receptors by cariprazine in patients with schizophrenia using PET with the D3/D2 receptor ligand [(11)C]-(+)-PHNO

RATIONALE

Second-generation antipsychotics occupy dopamine D2 receptors and act as antagonists or partial agonists at these receptors. While these drugs alleviate positive symptoms in patients with schizophrenia, they are less effective for treating cognitive deficits and negative symptoms. Dopamine D3 receptors are highly expressed in areas of the brain thought to play a role in the regulation of motivation and reward-related behavior. Consequently, the dopamine D3 receptor has become a target for treating negative symptoms in combination with D2 antagonism to treat positive symptoms in patients with schizophrenia.

OBJECTIVE

The purpose of this study was to determine the cariprazine receptor occupancies in brain for D2 and D3 receptors in patients with schizophrenia.

METHODS

Using [(11)C]-(+)-PHNO as a radioligand, positron emission tomography (PET) scans were performed in eight patients at baseline and postdose on days 1, 4, and 15. Plasma and cerebrospinal fluid (CSF) samples were analyzed for cariprazine concentrations.

RESULTS

A monotonic dose-occupancy relationship was observed for both receptor types. After 2 weeks of treatment, near complete (∼100 %) occupancies were observed for both receptors at a dose of 12 mg/day. At the lowest cariprazine dose (1 mg/day), mean D3 and D2 receptor occupancies were 76 and 45 %, respectively, suggesting selectivity for D3 over D2 receptors at low doses. An exposure-response analysis found a ∼3-fold difference in EC50 (D3 = 3.84 nM and D2 = 13.03 nM) in plasma after 2 weeks of dosing.

CONCLUSION

This PET imaging study in patients with schizophrenia demonstrated that cariprazine is a D3-preferring dual D3/D2 receptor partial agonist.

A new generation of antipsychotics: pharmacology and clinical utility of cariprazine in schizophrenia

Cariprazine is a potential antipsychotic awaiting approval from the US Food and Drug Administration. It is a dopamine D2- and D3-receptor partial agonist, with higher affinity for D3 receptors, as opposed to the D2 antagonism of most older antipsychotic agents. Like most lipophilic antipsychotics, it undergoes extensive hepatic metabolism by cytochrome P450 (CYP), mainly the highly variable 3A4, with the formation of active metabolites. However, the parent compound - particularly its active didesmethyl derivative - is cleared very slowly, with elimination half-lives in schizophrenic patients ranging from 2-5 days for cariprazine to 2-3 weeks for didesmethyl-cariprazine. Exposure to the latter was several times that for cariprazine, although didesmethyl-cariprazine did not reach steady state within the 3 weeks of 12.5 mg/day dosing. Preliminary information on its therapeutic role comes from press releases and a few abstracts presented at scientific meetings. In short-term controlled trials, it was more effective than placebo in reducing positive and negative symptoms of schizophrenia, with an effective dose range of 1.5-12 mg/day. Although cariprazine was associated with a higher incidence of akathisia and extrapyramidal side effects than placebo, it did not cause weight gain, metabolic abnormalities, prolactin increase, or corrected QT prolongation. Similarly, cariprazine's efficacy and tolerability for the treatment of bipolar disorder (manic/mixed and depressive episodes) was established in the dose range of 3-12 mg/day, although again no long-term data are available. Well-designed clinical trials, mainly direct "head-to-head" comparisons with other second-generation antipsychotic agents, are needed to define the therapeutic role and safety profile of cariprazine in schizophrenia and bipolar mania.