Low striatal and extra-striatal D2 receptor occupancy during treatment with the atypical antipsychotic sertindole

Optimisation of pharmacotherapy in psychiatry through therapeutic drug monitoring, molecular brain imaging and pharmacogenetic tests: Focus on antipsychotics

BACKGROUND

For psychotic disorders (i.e. schizophrenia), pharmacotherapy plays a key role in controlling acute and long-term symptoms. To find the optimal individual dose and dosage strategy, specialised tools are used. Three tools have been proven useful to personalise drug treatments: therapeutic drug monitoring (TDM) of drug levels, pharmacogenetic testing (PG), and molecular neuroimaging.

METHODS

In these Guidelines, we provide an in-depth review of pharmacokinetics, pharmacodynamics, and pharmacogenetics for 45 antipsychotics. Over 30 international experts in psychiatry selected studies that have measured drug concentrations in the blood (TDM), gene polymorphisms of enzymes involved in drug metabolism, or receptor/transporter occupancies in the brain (positron emission tomography (PET)).

RESULTS

Study results strongly support the use of TDM and the cytochrome P450 (CYP) genotyping and/or phenotyping to guide drug therapies. Evidence-based target ranges are available for titrating drug doses that are often supported by PET findings.

CONCLUSION

All three tools discussed in these Guidelines are essential for drug treatment. TDM goes well beyond typical indications such as unclear compliance and polypharmacy. Despite its enormous potential to optimise treatment effects, minimise side effects and ultimately reduce the global burden of diseases, personalised drug treatment has not yet become the standard of care in psychiatry.

Inhibition of voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells by the atypical antipsychotic agent sertindole

The regulation of membrane potential and the contractility of vascular smooth muscle cells (VSMCs) by voltage-dependent K+ (Kv) potassium channels are well-established. In this study, native VSMCs from rabbit coronary arteries were used to investigate the inhibitory effect of sertindole, an atypical antipsychotic agent, on Kv channels. Sertindole induced dose-dependent inhibition of Kv channels, with an IC50 of 3.13 ± 0.72 μM. Although sertindole did not cause a change in the steady-state activation curve, it did lead to a negative shift in the steady-state inactivation curve. The application of 1- or 2-Hz train pulses failed to alter the sertindole-induced inhibition of Kv channels, suggesting use-independent effects of the drug. The inhibitory response to sertindole was significantly diminished by pretreatment with a Kv1.5 inhibitor but not by Kv2.1 and Kv7 subtype inhibitors. These findings demonstrate the sertindole dose-dependent and use-independent inhibition of vascular Kv channels (mainly the Kv1.5 subtype) through a mechanism that involves altering steady-state inactivation curves. Therefore, the use of sertindole as an antipsychotic drug may have adverse effects on the cardiovascular system.

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.

Pharmacotherapy of schizophrenia: Mechanisms of antipsychotic accumulation, therapeutic action and failure

Schizophrenia is a multi-dimensional disorder with a complex and mostly unknown etiology, leading to a severe decline in life quality. Antipsychotic drugs (APDs) remain beneficial interventions in the treatment of the disorder, but vary significantly in binding profile, clinical effects and adverse reactions. The present review summarizes the main principles of APD mechanisms of action with a particular focus on recent findings in APD accumulation and its role in the therapeutic efficacy and treatment failure. High and low doses of APDs were shown to be effective in different dimensions of antipsychotic-like behaviour in rodent models. Efficacy of the APDs correlates with high dopamine D2 receptor occupancy, which occurs quickly after drug administration. However, onset and peak of action are delayed up to several days or weeks. APD accumulation via acidic trapping in synaptic vesicles is considered to underlie the time course of APD action. Use-dependent exocytosis, co-release with dopamine and serotonin and inhibition of ion channels impact on the neuronal transmission and determine effects of APDs. Disruption in accumulating properties leads to diminished APD effects. In addition, long-term APD administration at therapeutic doses leads to treatment failure both in animal models and in humans. APD failure was associated with treatment induced neuroadaptations, including a decline in extracellular dopamine levels, dopamine transporter upregulation, and altered neuronal firing. However, enhanced synaptic vesicle release has also been reported. APD loss of efficacy may be reversed through inhibition of the dopamine transporter or switching the administration regimen from continuous to intermittent. Thus, manipulating the accumulation properties of APDs, changes in the administration regimen and doses, or co-administration with dopamine transporter inhibitors may be considered to yield benefits in the development of new effective strategies in the treatment of schizophrenia.

PET Radiotracers for CNS-Adrenergic Receptors: Developments and Perspectives

Epinephrine (E) and norepinephrine (NE) play diverse roles in our body’s physiology. In addition to their role in the peripheral nervous system (PNS), E/NE systems including their receptors are critical to the central nervous system (CNS) and to mental health. Various antipsychotics, antidepressants, and psychostimulants exert their influence partially through different subtypes of adrenergic receptors (ARs). Despite the potential of pharmacological applications and long history of research related to E/NE systems, research efforts to identify the roles of ARs in the human brain taking advantage of imaging have been limited by the lack of subtype specific ligands for ARs and brain penetrability issues. This review provides an overview of the development of positron emission tomography (PET) radiotracers for in vivo imaging of AR system in the brain.

Imaging drug action in schizophrenia: research update

Functional neuroimaging using techniques such as positron emission tomography (PET) and single photon emission computerised tomography (SPECT) provide a direct in vivo assessment of the expression and function of neuroreceptors, transporters and enzymes. This article examines the technical aspects of molecular imaging and the application of those techniques in drug development.

Classics in Chemical Neuroscience: Aripiprazole

Aripiprazole was the first antipsychotic developed to possess agonist properties at dopamine D₂ autoreceptors, a groundbreaking strategy that presented a new vista for schizophrenia drug discovery. The dopamine D₂ receptor is the crucial target of all extant antipsychotics, and all developed prior to aripiprazole were D₂ receptor antagonists. Extensive blockade of these receptors, however, typically produces extrapyramidal (movement) side effects, which plagued first-generation antipsychotics, such as haloperidol. Second-generation antipsychotics, such as clozapine, with unique polypharmacology and D₂ receptor binding kinetics, have significantly lower risk of movement side effects but can cause myriad additional ones, such as severe weight gain and metabolic dysfunction. Aripiprazole's polypharmacology, characterized by its unique agonist activity at dopamine D₂ and D₃ and serotonin 5-HT_1A receptors, as well as antagonist activity at serotonin 5-HT_2A receptors, translates to successful reduction of positive, negative, and cognitive symptoms of schizophrenia, while also mitigating risk of weight gain and movement side effects. New observations, however, link aripiprazole to compulsive behaviors in a small group of patients, an unusual side effect for antipsychotics. In this review, we discuss the chemical synthesis, pharmacology, pharmacogenomics, drug metabolism, and adverse events of aripiprazole, and we present a current understanding of aripiprazole's neurotherapeutic mechanisms, as well as the history and importance of aripiprazole to neuroscience.

Efficacy and safety of sertindole in schizophrenia: a clinical review

Sertindole is an atypical antipsychotic reintroduced into the European market in 2005 after a reevaluation of its risks and benefits, under the agreement that close electrocardiographic screening would be conducted. It has a high affinity for dopamine D2, serotonin 5-HT2A and 5-HT2C, and α1 adrenergic receptors. Moreover, sertindole shows modest affinity for H1-histaminergic and muscarinic receptors. The pharmacological properties, clinical efficacy, safety, and tolerability of sertindole are covered in this article based on a literature review from 1990 to 2014. Given current available findings, sertindole is at least effective as haloperidol, risperidone, and olanzapine on schizophrenia symptoms. Regarding its efficacy on cognitive symptoms, sertindole effect is supported by both preclinical and clinical studies versus haloperidol and olanzapine; however, its role on cognition needs further clarification. Concerning safety and tolerability issues, sertindole is characterized by a low potential to cause sedation and extrapyramidal symptoms, and by an acceptable metabolic profile; nevertheless, cardiac safety remains a major concern, and the electrocardiographic monitoring should be carried out during treatment to substantially reduce cardiovascular risk. In conclusion, although it has an equivalent profile compared to other antipsychotic drugs, sertindole actually remains a second-line choice for schizophrenic patients intolerant to at least one other antipsychotic agent.

Biodistribution and radiation dosimetry in humans of [¹¹C]FLB 457, a positron emission tomography ligand for the extrastriatal dopamine D₂ receptor

PURPOSE

[(11)C]FLB 457, a radioligand with very high affinity and selectivity for dopamine D2/3 receptors, is used to measure receptor binding in extrastriatal regions showing low density of the receptors. The purpose of this study was to estimate the whole-body biodistribution of radioactivity and the radiation absorbed doses to organs after intravenous injection of [(11)C]FLB 457 in healthy human subjects.

METHODS

Whole-body images were acquired for 2 h after an injection of [(11)C]FLB 457 in six healthy humans. Radiation absorbed doses were estimated by the MIRD scheme implemented in OLINDA/EXM 1.1 software.

RESULTS

Organs with the longest residence time were the liver, lungs, and brain. The organs with the highest radiation doses were the kidneys, liver, and pancreas. The effective dose delivered by [(11)C]FLB 457 is 5.9 μSv/MBq, similar to those of other (11)C-labeled tracers.

CONCLUSIONS

This effective dose would allow multiple scans in the same individual based on prevailing maximum recommended-dose guidelines in the USA and Europe.

The relationship between antipsychotic D2 occupancy and change in frontal metabolism and working memory : A dual [(11)C]raclopride and [(18) F]FDG imaging study with aripiprazole

RATIONALE

The effects of aripiprazole on cognitive function are obscure, possibly due to the difficulty in disentangling the specific effects on cognitive function from effects secondary to the improvement of other schizophrenic symptoms. This prompts the necessity of using an intermediate biomarker relating the drug effect on the brain to change in cognitive function.

OBJECTIVES

To explore the effect of aripiprazole on cognitive function, we measured changes in frontal metabolism as an intermediate biomarker and sought to determine its relationship with D2 receptor occupancy and changes in working memory.

METHODS

Fifteen healthy male volunteers participated in the study. Serial positron emission tomography (PET) scans with [(11)C]raclopride and [(18) F]FDG were conducted 1 day before and 2 days after the administration of aripiprazole. The subjects performed the N-back task just after finishing the [(18) F]FDG scan.

RESULTS

The mean (±SD) D2 receptor occupancies were 22.2 ± 16.0 % in the 2 mg group, 35.5 ± 3.6 % in the 5 mg group, 63.2 ± 9.9 % in the 10 mg group and 72.8 ± 2.1 % in the 30 mg group. The frontal metabolism was significantly decreased after the administration of aripiprazole (t = 2.705, df = 14, p = 0.017). Greater striatal D2 receptor occupancy was related to greater decrease in frontal metabolism (r = -0.659, p = 0.010), and greater reduction in frontal metabolism was associated with longer reaction times (r = -0.597, p = 0.019) under the greatest task load.

CONCLUSIONS

Aripiprazole can affect cognitive function and alter frontal metabolic function. The changes in these functions are linked to greater D2 receptor occupancy. This suggests that it may be important to find the lowest effective dose of aripiprazole in order to prevent adverse cognitive effects.

Drug safety and efficacy evaluation of sertindole for schizophrenia

INTRODUCTION

Despite the progress in antipsychotic treatment, modern antipsychotic medication is still associated with side effects, reduced compliance, drug discontinuation and insufficient effects on negative and cognitive symptoms. Sertindole is an antipsychotic compound, with high affinity for dopamine D(2), serotonin 5-HT(2A), 5-HT(2C) and α(1)-adrenergic receptors, which has been reintroduced in the market after extended re-evaluation of its safety and risk-benefit profile.

AREAS COVERED

Sertindole's pharmacological profile, pharmacokinetics, neuophysiological properties, efficacy on positive, negative and cognitive symptoms and safety issues are covered in this article, based on a literature review from 1990 to 2012.

EXPERT OPINION

Based on five double-blind, randomized, placebo-, haloperidol- or risperidone-controlled studies in patients with schizophrenia, sertindole shows a comparable efficacy with haloperidol and risperidone on positive symptoms, while the effect on negative symptoms seems to be superior. Sertindole is generally well tolerated, but is associated with a dose-related QTc interval prolongation (+22 ms). Risk factors for drug-induced arrhythmia, such as cardiac diseases, congenital long QT syndrome, prolongated QTc at baseline, etc. and drug interactions should be considered before prescribing sertindole. To minimize cardiovascular risk, regular ECG recording is required. Sertindole can be an important second-line option for the treatment of schizophrenia for patients intolerant to at least one other antipsychotic. Further comparison with other SGAs and investigations on subgroups (e.g., children, elderly, first-episode, treatment-refractory patients, etc.) are still needed for a precise understanding of the therapeutic benefits and its role in schizophrenia therapy.

Role of dopamine D(2) receptors for antipsychotic activity

This review summarizes the current state of knowledge regarding the proposed mechanisms by which antipsychotic agents reduce the symptoms of schizophrenia while giving rise to adverse side effects. The first part summarizes the contribution of neuroimaging studies to our understanding of the neurochemical substrates of schizophrenia, putting emphasis on direct evidence suggestive of a presynaptic rather than a postsynaptic dysregulation of dopaminergic neurotransmission in this disorder. The second part addresses the role of D(2) and non-D(2) receptor blockade in the treatment of schizophrenia and highlights a preponderant role of D(2) receptors in the mechanism of antipsychotic action. Neuroimaging studies have defined a narrow, but optimal, therapeutic window of 65-78 % D(2) receptor blockade within which most antipsychotics achieve optimal clinical efficacy with minimal side effects. Some antipsychotics though do not conform to that therapeutic window, notably clozapine. The reasons for its unexcelled clinical efficacy despite subthreshold levels of D(2) blockade are unclear and current theories on clozapine's mechanisms of action are discussed, including transiency of its D(2) receptor blocking effects or preferential blockade of limbic D(2) receptors. Evidence is also highlighted to consider the use of extended antipsychotic dosing to achieve transiency of D(2) blockade as a way to optimize functional outcomes in patients. We also present some critical clinical considerations regarding the mechanisms linking dopamine disturbance to the expression of psychosis and its blockade to the progressive resolution of psychosis, keeping in perspective the speed and onset of antipsychotic action. Finally, we discuss potential novel therapeutic strategies for schizophrenia.

Suicide attempts in a prospective cohort of patients with schizophrenia treated with sertindole or risperidone

The incidence of suicide attempts (fatal and non-fatal) was analysed in a prospective cohort of patients with schizophrenia randomly assigned to sertindole (4905 patients) or risperidone (4904 patients) in a parallel-group open-label study with blinded classification of outcomes (the sertindole cohort prospective study--SCoP). The total exposure was 6978 and 7975 patient-years in the sertindole and risperidone groups, respectively. Suicide mortality in the study was low (0.21 and 0.28 per 100 patients per year with sertindole and risperidone, respectively). The majority (84%) of suicide attempts occurred within the first year of treatment. Cox's proportional hazards model analysis of the time to the first suicide attempt, reported by treating psychiatrists and blindly reviewed by an independent expert group according to the Columbia Classification Algorithm of Suicide Assessment (both defining suicide attempts by association of suicidal act and intent to die), showed a lower risk of suicide attempt for sertindole-treated patients than for risperidone-treated patients. The effect was statistically significant with both evaluation methods during the first year of randomized treatment (hazard ratios [95% CI]: 0.5 [0.31-0.82], p=0.006; and 0.57 [0.35-0.92], p=0.02, respectively). With classification by an independent safety committee using a broader definition including all incidences of intentional self-harm, also those without clear suicidal intent, the results were not significant. A history of previous suicide attempts was significantly associated with attempted suicides in both treatment groups.

Emerging treatments in the management of schizophrenia - focus on sertindole

The antipsychotic treatment of schizophrenia is still marked by poor compliance, and drug discontinuation; the development of more effective and safer drugs still remains a challenge. Sertindole is a second-generation antipsychotic with high affinity for dopamine D₂, serotonin 5-HT_2A, 5-HT_2C, and α₁-adrenergic receptors, and low affinity for other receptors. Sertindole undergoes extensive hepatic metabolism by the cytochrome P450 isoenzymes CYP2D6 and CYP3A4 and has an elimination half-life of approximately three days. In controlled clinical trials sertindole was more effective than placebo in reducing positive and negative symptoms, whereas it was as effective as haloperidol and risperidone against the positive symptoms of schizophrenia. The effective dose-range of sertindole is 12–20 mg, administered orally once daily. The most common adverse events are headhache, insomnia, rhinitis/nasal congestion, male sexual dysfunction, and moderate weight gain, with few extrapyramidal symptoms and metabolic changes. Sertindole is associated with corrected QT interval prolongation, with subsequent risk of serious arrythmias. Due to cardiovascular safety concerns, sertindole is available as a second-line choice for patients intolerant to at least one other antipsychotic agent. Further clinical studies, mainly direct “head-to-head” comparisons with other second-generation antipsychotic agents, are needed to define the role of sertindole in the treatment of schizophrenia.

Sertindole improves sub-chronic PCP-induced reversal learning and episodic memory deficits in rodents: involvement of 5-HT(6) and 5-HT (2A) receptor mechanisms

AIM

This study examined the efficacy of sertindole in comparison with a selective 5-HT(6) and a 5-HT(2A) receptor antagonist to reverse sub-chronic phencyclidine (PCP)-induced cognitive deficits in female rats.

METHODS

In the first test, adult female hooded Lister rats were trained to perform an operant reversal learning task to 90% criterion. After training, rats were treated with PCP at 2 mg/kg (i.p.) or vehicle twice daily for 7 days, followed by 7 days washout. For the second test, novel object recognition (NOR), a separate batch of rats, had the same sub-chronic PCP dosing regime and washout period. In reversal learning, rats were treated acutely with sertindole, the selective 5-HT(2A) receptor antagonist M100.907 or the selective 5-HT(6) receptor antagonist SB-742457.

RESULTS

The PCP-induced selective reversal learning deficit was significantly improved by sertindole, M100.907 and SB-742457. Sertindole also significantly improved the sub-chronic PCP-induced deficit in NOR, a test of episodic memory following a 1 min and 1 h inter-trial interval. In vivo binding studies showed that the dose-response relationship for sertindole in this study most closely correlates with affinity for 5-HT(6) receptor in vivo binding in striatum, although contribution from binding to 5-HT(2A) receptors in vivo in cortex may also provide an important mechanism.

CONCLUSION

The efficacies of selective 5-HT(2A) and 5-HT(6) receptor antagonists suggest potential mechanisms mediating the effects of sertindole, which has high affinity for these 5-HT receptor subtypes. The sertindole-induced improvement in cognitive function in this animal model suggests relevance for the management of cognitive deficit symptoms in schizophrenia.

FDG-PET and MRI imaging of the effects of sertindole and haloperidol in the prefrontal lobe in schizophrenia

Sertindole, a 2nd generation antipsychotic with low movement disorder side effects, was compared with haloperidol in a 6-week crossover study. Fifteen patients with schizophrenia (mean age=42.6, range=22-59, 11 men and 4 women) received sertindole (12-24 mg) or haloperidol (4-16 mg) for 6 weeks and then received a FDG-PET scan and an anatomical MRI. Patients were then crossed to the other treatment and received a second set of scans at week 12. Dose was adjusted by a physician blind to the medication type. Brodmann areas were identified stereotaxically using individual MRI templates applied to the coregistered FDG-PET image. Sertindole administration was associated with higher dorsolateral prefrontal cortex metabolic rates than haloperidol and lower orbitofrontal metabolic rates than haloperidol. This effect was greatest for gray matter of the dorsolateral Brodmann areas 8, 9, 10, 44, 45, and 46. Patients were further contrasted with an approximately age and sex-matched group of 33 unmedicated patients with schizophrenia and with a group of 55 normal volunteers. Sertindole administration was associated with greater change toward normal values and away from the values found in the unmedicated comparison group for dorsolateral prefrontal cortex gray matter and white matter underlying medial prefrontal and cingulate cortex. These results are consistent with the low motor side-effect profile of sertindole, greater improvement on prefrontal cognitive tasks with sertindole than haloperidol, and with the tendency of 2nd generation antipsychotic drugs to have greater frontal activation than haloperidol.

Cortical dopamine D2/D3 receptors are a common site of action for antipsychotic drugs--an original patient data meta-analysis of the SPECT and PET in vivo receptor imaging literature

Subject numbers in neuroreceptor imaging studies of antipsychotic treatment in schizophrenia are generally insufficient to directly test the relationship of regional D(2)/D(3) and 5HT(2A) receptor binding to clinical efficacy. We selected positron emission tomography (PET) and single photon emission computed tomography (SPECT) studies of antipsychotic dose vs occupancy at both temporal cortex and striatal D(2)/D(3) receptors. We selected corresponding SPECT and PET studies of 5HT(2A) receptor occupancy. We also selected randomized double-blind clinical trials of antipsychotics, where patients were treated with randomly assigned fixed doses. For each antipsychotic drug, we compared the optimum effective antipsychotic dose with the dose inducing maximal occupancy of D(2)/D(3) receptors in striatum and in temporal cortex as well as at 5HT(2A) receptors. Both first- and second-generation antipsychotic (FGA, SGA) drugs produced high temporal cortex D(2)/D(3) occupancy. Only FGA produced high striatal D(2)/D(3) receptor occupancy. The clinically effective dose showed correlation with doses inducing maximal dopamine D(2)/D(3) receptor occupancy both in striatum and in temporal cortex, the strongest correlation being with temporal cortex binding. Extrapyramidal side effects (EPSE) were primarily related to striatal D(2)/D(3) receptor occupancy. There was no correlation between 5HT(2A) occupancy and clinically effective dose. We conclude that cortical dopamine D(2)/D(3) receptor occupancy is involved in antipsychotic efficacy, with striatal D(2)/D(3) occupancy having a likely therapeutic role while also inducing EPSE. We found no evidence for 5HT(2A) blockade involvement in antipsychotic action, although we cannot exclude this possibility.

Using pharmacokinetic-pharmacodynamic modelling as a tool for prediction of therapeutic effective plasma levels of antipsychotics

In the rat, selective suppression of conditioned avoidance response has been widely reported as a test with high predictive validity for antipsychotic efficacy. Recent studies have shown that the relationship between dopamine D2 receptor occupancy and the suppression of conditioned avoidance response behaviour correlates well with the relationship between human dopamine D2 receptor occupancy and clinical effect. The aim of the present study was to evaluate how pharmacokinetic/pharmacodynamic (PK/PD) predictions of therapeutic effective steady-state plasma levels by means of conditioned avoidance response behaviour in rodents, correlate with clinically relevant plasma exposure for the classical antipsychotic drug haloperidol and four second generation antipsychotics: sertindole, clozapine, risperidone and olanzapine, including selected metabolites. In order to confirm the validity of the present conditioned avoidance response procedure, in vivo striatal dopamine D2 receptor occupancy was determined in parallel using 3H-raclopride as the radioligand. The PK/PD relationship was established by modelling the time-response and time-plasma concentration data. We found the order of dopamine D2 receptor occupancy required to suppress conditioned avoidance response behaviour according to EC50 measurements to be sertindole (+dehydrosertindole)=dehydrosertindole=paliperidone (the metabolite of risperidone)=haloperidol=olanzapine>risperidone>>clozapine. Overall, a good agreement was observed between the rat dopamine D2 receptor occupancy levels providing 50% response in the conditioned avoidance response test and the dopamine D2 receptor occupancy levels reported from responding schizophrenic patients treated with antipsychotics. Predictions of therapeutically effective steady-state levels for sertindole (+dehydrosertindole) and olanzapine were 3-4-fold too high whereas for haloperidol, clozapine and risperidone the predicted steady-state EC50 in conditioned avoidance responding rats correlated well with the therapeutically effective plasma levels observed in patients. Accordingly, the proposed PK/PD model may act as a guide for determining effective plasma concentrations of potential antipsychotics in the clinical setting and thereby accelerating the overall drug development process.

Striatal vs extrastriatal dopamine D2 receptors in antipsychotic response--a double-blind PET study in schizophrenia

Blockade of dopamine D2 receptors remains a common feature of all antipsychotics. It has been hypothesized that the extrastriatal (cortical, thalamic) dopamine D2 receptors may be more critical to antipsychotic response than the striatal dopamine D2 receptors. This is the first double-blind controlled study to examine the relationship between striatal and extrastriatal D2 occupancy and clinical effects. Fourteen patients with recent onset psychosis were assigned to low or high doses of risperidone (1 mg vs 4 mg/day) or olanzapine (2.5 mg vs 15 mg/day) in order to achieve a broad range of D2 occupancy levels across subjects. Clinical response, side effects, striatal ([11C]-raclopride-positron emission tomography (PET)), and extrastriatal ([11C]-FLB 457-PET) D2 receptors were evaluated after treatment. The measured D2 occupancies ranged from 50 to 92% in striatal and 4 to 95% in the different extrastriatal (frontal, temporal, thalamic) regions. Striatal and extrastriatal occupancies were correlated with dose, drug plasma levels, and with each other. Striatal D2 occupancy predicted response in positive psychotic symptoms (r=0.62, p=0.01), but not for negative symptoms (r=0.2, p=0.5). Extrastriatal D2 occupancy did not predict response in positive or negative symptoms. The two subjects who experienced motor side effects had the highest striatal occupancies in the cohort. Striatal D2 blockade predicted antipsychotic response better than frontal, temporal, and thalamic occupancy. These results, when combined with the preclinical data implicating the mesolimbic striatum in antipsychotic response, suggest that dopamine D2 blockade within specific regions of the striatum may be most critical for ameliorating psychosis in schizophrenia.

The physiological and pathophysiological roles of neuronal histamine: an insight from human positron emission tomography studies

Histamine neurons are exclusively located in the posterior hypothalamus, and project their fibers to almost all regions of the human brain. Although a significant amount of research has been done to clarify the functions of the histaminergic neuron system in animals, a few studies have been reported on the roles of this system in the human brain. In past studies, we have been able to clarify some of the functions of histamine neurons using different methods, such as histamine-related gene knockout mice or human positron emission tomography (PET). The histaminergic neuron system is known to modulate wakefulness, the sleep-wake cycle, appetite control, learning, memory and emotion. Accordingly we have proposed that histamine neurons have a dual effect on the CNS, with both stimulatory and suppressive actions. As a stimulator, neuronal histamine is one of the most important systems that stimulate and maintain wakefulness. Brain histamine also functions as a suppressor in bioprotection against various noxious and unfavorable stimuli of convulsion, drug sensitization, denervation supersensitivity, ischemic lesions and stress susceptibility. This review summarizes our works on the functions of histamine neurons using human PET studies, including the development of radiolabeled tracers for histamine H1 receptors (H1R: (11)C-doxepin and (11)C-pyrilamine), PET measurements of H1R in depression, schizophrenia, and Alzheimer's disease (AD), and studies on the sedative effects of antihistamines using H(2)(15)O and H1R occupancy in the human brain. These molecular and functional PET studies in humans are useful for drug development in this millennium.

Sertindole, in contrast to clozapine and olanzapine, does not disrupt water maze performance after acute or chronic treatment

Cognitive deficits in schizophrenia are associated with poor functional outcome, and may be further aggravated by treatment with antipsychotics. In the present study the acute and chronic (3 weeks of treatment) effects of clozapine, olanzapine, and sertindole on performance in the Morris water maze in rats was compared, using pharmacologically and/or clinically relevant dose regimens. An experimental design consisting of three trials/day over 3 days was used. Performance was expressed as the distance and latency to find a submerged platform, as well as the percentage of "non-finders", i.e. percentage of trials where the rat was unable to find the platform within the total trial time of 60 s. Clozapine (40 mg/kg, p.o.) and olanzapine (2.5 mg/kg, s.c.) impaired water maze performance when given acutely. However, tolerance developed to the deficit induced by clozapine, whereas the olanzapine-mediated impairment was enhanced after chronic treatment. Sertindole (2.5 mg/kg, p.o.) had no disruptive effect on performance after either acute or chronic treatment. Exposure measurements confirmed that all three compounds were present in the serum at least at clinically effective concentrations. Thus, the three antipsychotics tested differentially affected rodent cognition, whereby sertindole appeared to have a lower potential than either clozapine or olanzapine to induce cognitive impairment. The hypothesis that the low potency of sertindole in inducing dopamine D2 receptor blockade, combined with lack of antimuscarinic and histamine H1 antagonist activity in vivo is discussed. Clearly further studies are needed to assess the potential cognition-enhancing effects of sertindole vs. other antipsychotics in a relevant animal model of schizophrenia.

Sertindole : a review of its use in schizophrenia

Oral sertindole (Serdolect) is an atypical antipsychotic approved in the EU for once-daily use in patients with schizophrenia who are intolerant to at least one other antipsychotic agent. Extensive data from post-marketing studies do not indicate an excess of overall mortality with sertindole. Sertindole is at least as effective as haloperidol and risperidone in the treatment of neuroleptic-responsive schizophrenia. Sertindole improves negative symptoms, and is also effective for the treatment of neuroleptic-resistant schizophrenia. Sertindole is generally well tolerated and is associated with a low rate of extrapyramidal symptoms (EPS). Thus, sertindole is a useful option in the treatment of patients with schizophrenia.

Brain histamine H receptor occupancy of orally administered antihistamines measured by positron emission tomography with (11)C-doxepin in a placebo-controlled crossover study design in healthy subjects: a comparison of olopatadine and ketotifen

AIMS

The strength of sedation due to antihistamines can be evaluated by using positron emission tomography (PET). The purpose of the present study is to measure histamine H(1) receptor (H(1)R) occupancy due to olopatadine, a new second-generation antihistamine and to compare it with that of ketotifen.

METHODS

Eight healthy males (mean age 23.5 years-old) were studied following single oral administration of olopatadine 5 mg or ketotifen 1 mg using PET with (11)C-doxepin in a placebo-controlled crossover study design. Binding potential ratio and H(1)R occupancy were calculated and were compared between olopatadine and ketotifen in the medial prefrontal (MPFC), dorsolateral prefrontal (DLPFC), anterior cingulate (ACC), insular (IC), temporal (TC), parietal (PC), occipital cortices (OC). Plasma drug concentration was measured, and correlation of AUC to H(1)R occupancy was examined.

RESULTS

H(1)R occupancy after olopatadine treatment was significantly lower than that after ketotifen treatment in the all cortical regions (P < 0.001). Mean H(1)R occupancies for olopatadine and ketotifen were, respectively: MPFC, 16.7 vs. 77.7; DLPFC, 14.1 vs. 85.9; ACC, 14.7 vs. 76.1; IC, 12.8 vs. 69.7; TC, 12.5 vs. 66.5; PC, 13.9 vs. 65.8; and OC, 19.5 vs. 60.6. Overall cortical mean H(1)R occupancy of olopatadine and ketotifen were 15% and 72%, respectively. H(1)R occupancy of both drugs correlated well with their respective drug plasma concentrations (P < 0.001).

CONCLUSION

It is suggested that 5 mg oral olopatadine, with its low H(1)R occupancy and thus minimal sedation, could safely be used an antiallergic treatment for various allergic disorders. Abbreviations histamine H(1) receptor (H(1)R), histamine H(1) receptor occupancy (H(1)RO), dopamine D(2) receptor (D(2)R), positron emission tomography (PET), blood-brain barrier (BBB), binding potential ratio (BPR), distribution volume (DV).

New α1-adrenoceptor antagonists derived from the antipsychotic sertindole - carbon-11 labelling and pet examination of brain uptake in the cynomolgus monkey

Central alpha(1)-adrenergic receptors are potential targets for recently developed antipsychotic drugs. Two new 11C labeled potent and selective alpha(1)-adrenoceptor antagonists, 1- [2- [4-[1-(4-fluorophenyl)-5-(2-[(11)C]methyl-tetrazol-5-yl)-1H-indol-3-yl]-1-piperidinyl]ethyl]-imidazolidin-2-one ([(11)C]2) and 1- [2- [4-[1-(4-fluorophenyl)-5-(1-[(11)C]methyl-(1,2,3-triazol-4-yl)-1H-indol-3-yl]-1-piperidinyl]ethyl]-imidazolidin-2-one ([(11)C]3) were prepared and evaluated for imaging of central alpha(1)-adrenergic receptors in the cynomolgus monkey brain. For both compounds, the total brain radioactivity was only about 0.6% of the radioactivity injected i.v. There was no evident binding in regions known to contain alpha(1)-adrenoceptors. This observation suggests that the affinity of the radioligands in primates in vivo is not sufficient to provide a signal for specific binding that can be differentiated from the background. In addition, active efflux by P-glycoprotein may be responsible for the low total brain-uptake of the two radioligands. Both compounds showed a highly polarised and verapamile sensitive transport across monolayers of Caco-2 cells. The total brain-uptake of [(3)H]2 was 6 times higher in mdr1a(-/-) knock-out mice lacking the gene encoding P-glycoprotein compared to wild type mice. Pretreatment of one monkey with Cyclosporin A (15 mg/kg) resulted in 40% higher brain uptake for [(11)C]3 when compared with baseline. These observations support the view that efflux by P-glycoprotein can be of quantitative importance for the total brain-uptake of some PET radioligands.