GABAA receptor occupancy by subtype selective GABAAα2,3 modulators: PET studies in humans

RATIONALE

Sedation, dependence, and abuse liability limit the use of non-selective γ-aminobutyric acid (GABA_A) receptor positive modulators for the treatment of anxiety. AZD7325 and AZD6280 are novel, subtype-selective GABA_Aα2,3 receptor positive modulators with limited sedative effects.

OBJECTIVES

The current study aimed to confirm target engagement at GABA_A receptors by AZD7325 and AZD6280 in humans and to determine the relationship between exposure, GABA_A receptor occupancy, and tolerability.

METHOD

Two PET studies, using high-resolution research tomography (HRRT) and the radioligand [¹¹C]flumazenil, were performed in 12 subjects at baseline and after administration of single oral doses of AZD7325 (0.2 to 30 mg) and AZD6280 (5 to 40 mg). PET images were analyzed using a simplified reference tissue model, and regional binding potentials (BP_ND) were obtained. The relationship between plasma concentration of AZD7325 or AZD6280 and GABA_A receptor occupancy was described by hyperbolic function, and K _i,plasma (plasma concentration required for 50% receptor occupancy) was estimated. Assessments of safety and tolerability included recording of adverse events, vital signs, electrocardiogram, and laboratory tests.

RESULTS

The [¹¹C]flumazenil binding was reduced in a dose-dependent, saturable manner by both agents. Maximum receptor occupancy could be reached for both compounds without causing sedation or cognitive impairment. The K _i,plasma estimates for AZD7325 and AZD6280 were 15 and 440 nmol/l, respectively.

CONCLUSION

High GABA_A receptor occupancy by AZD7325 and AZD6280 could be reached without clear sedative effects.

From the Blood to the Central Nervous System: A Nanoparticle's Journey Through the Blood-Brain Barrier by Transcytosis

Designing nanoparticles that effectively enter the central nervous system (CNS) rapidly and without alteration is one of the major challenges in the use of nanotechnology for the brain. In this chapter, we explore the process of transcytosis, a receptor-mediated transport pathway that permits endogenous macromolecules to enter the CNS by crossing the blood-brain barrier. Transcytosis across the blood-brain barrier involves a number of distinct stages, including receptor binding, endocytosis into a transport vesicle, trafficking of the vesicle to the opposite side of the cell, and finally exocytosis and release of cargo. For each stage, we discuss the current knowledge on biological, physiological, and physical factors that influence nanoparticle transit through that stage of transcytosis, with implications for nanoparticle design. Finally, we look at the current progress in designing nanoparticles that exploit transcytosis for CNS delivery.

["Active health management" can provide support for vulnerable patients. New model for the prevention of unplanned healthcare]

A small group of frequent emergency department visitors account for a disproportionally large fraction of health care consumption, including unplanned hospitalizations and overall healthcare costs. In response, case and disease management programs aimed at reducing health care consumption in this group have been tested, however results vary widely. In this study, we aimed to investigate if a telephone-based, nurse led case management intervention can reduce health care consumption for frequent emergency department visitors in a large-scale set-up. A total of 12,181 frequent emergency department users in three counties in Sweden were randomized either using Zelen's design or a traditional randomized design to receive a nurse led case management intervention or no intervention. Patients were followed for health care consumption for up to 2 years. The results of the study with traditional design showed an overall 12% (95% confidence interval [CI], 4-19%) decreased rate of hospitalization, which was mostly driven by effects among patients included in the last year. Similar results were achieved in the Zelen studies, with significant reduction of hospitalization, again in the last year, but mixed results in the early development of the project. Our study provides evidence that a carefully designed telephone-based intervention with accurate and systematic patient selection and appropriate staff training in a centralized set-up can lead to significant decreases in health care consumption and costs. However, we also demonstrate that the effects are sensitive to the delivery model chosen.

Quetiapine and its metabolite norquetiapine: translation from in vitro pharmacology to in vivo efficacy in rodent models

BACKGROUND AND PURPOSE

Quetiapine has a range of clinical activity distinct from other atypical antipsychotic drugs, demonstrating efficacy as monotherapy in bipolar depression, major depressive disorder and generalized anxiety disorder. The neuropharmacological mechanisms underlying this clinical profile are not completely understood; however, the major active metabolite, norquetiapine, has been shown to have a distinct in vitro pharmacological profile consistent with a broad therapeutic range and may contribute to the clinical profile of quetiapine.

EXPERIMENTAL APPROACH

We evaluated quetiapine and norquetiapine, using in vitro binding and functional assays of targets known to be associated with antidepressant and anxiolytic drug actions and compared these activities with a representative range of established antipsychotics and antidepressants. To determine how the in vitro pharmacological properties translate into in vivo activity, we used preclinical animal models with translational relevance to established antidepressant-like and anxiolytic-like drug action.

KEY RESULTS

Norquetiapine had equivalent activity to established antidepressants at the noradrenaline transporter (NET), while quetiapine was inactive. Norquetiapine was active in the mouse forced swimming and rat learned helplessness tests. In in vivo receptor occupancy studies, norquetiapine had significant occupancy at NET at behaviourally relevant doses. Both quetiapine and norquetiapine were agonists at 5-HT1A receptors, and the anxiolytic-like activity of norquetiapine in rat punished responding was blocked by the 5-HT1A antagonist, WAY100635.

CONCLUSIONS AND IMPLICATIONS

Quetiapine and norquetiapine have multiple in vitro pharmacological actions, and results from preclinical studies suggest that activity at NET and 5-HT1A receptors contributes to the antidepressant and anxiolytic effects in patients treated with quetiapine.

Job strain and risk of obesity: systematic review and meta-analysis of cohort studies

Job strain, the most widely used indicator of work stress, is a risk factor for obesity-related disorders such as cardiovascular disease and type 2 diabetes. However, the extent to which job strain is related to the development of obesity itself has not been systematically evaluated. We carried out a systematic review (PubMed and Embase until May 2014) and meta-analysis of cohort studies to address this issue. Eight studies that fulfilled inclusion criteria showed no overall association between job strain and the risk of weight gain (pooled odds ratio for job strain compared with no job strain 1.04, 95% confidence interval (CI) 0.99–1.09, N_Total=18 240) or becoming obese (1.00, 95% CI 0.89–1.13, N_Total=42 222). In addition, a reduction in job strain over time was not associated with lower obesity risk (1.13, 95% CI 0.90–1.41, N_Total=6507). These longitudinal findings do not support the hypothesis that job strain is an important risk factor for obesity or a promising target for obesity prevention.

Pharmacokinetic profile of the extended-release formulation of quetiapine fumarate (quetiapine XR): clinical implications

OBJECTIVES

A series of studies were conducted to guide the development and characterise the pharmacokinetics of extended-release quetiapine fumarate (quetiapine XR), a once-daily formulation to control the release of the drug.

METHODS

Data from these studies are described and discussed herein.

RESULTS

Once-daily quetiapine XR produced a similar area under the plasma concentration-time curve (AUC), minimum plasma concentration (Cmin) and a slightly lower maximum plasma concentration (Cmax) than the equivalent dose of immediate-release quetiapine (quetiapine IR) given twice daily. In a crossover, head-to-head study, total daily exposure, measured by AUC at steady state, was less variable with quetiapine XR versus quetiapine IR (percent coefficient of variation 39.2% versus 51.2%, respectively). Compared with fasting, a high-fat meal increased the AUC and Cmax for quetiapine XR, whereas a light meal had no significant effect on these parameters. Quetiapine XR exhibits a less pronounced D2 receptor occupancy peak and receptor occupancy levels remain higher for longer compared with quetiapine IR. Quetiapine XR was generally well tolerated with a safety profile similar to quetiapine IR, although the intensity of sedation in the first hours of treatment was significantly lower (p < 0.01) with quetiapine XR versus IR.

CONCLUSION

At steady state, quetiapine XR provided a similar AUC and Cmin and a slightly lower Cmax relative to an equivalent dose of quetiapine IR administered twice daily. Quetiapine XR exhibited linear pharmacokinetics in the dose range tested and no food effect was observed with a light meal. Once-daily dosing and simpler dose titration makes using quetiapine XR convenient for clinicians and patients. Quetiapine XR has predictable pharmacokinetics and was generally well tolerated, with significantly lower intensity of sedation after the first hours of administration compared with quetiapine IR. With once-daily quetiapine XR, the impact of daytime sedation may be mitigated by evening dosing.

Role of concomitant inhibition of the norepinephrine transporter for the antipsychotic effect of quetiapine

Quetiapine alleviates both positive and negative symptoms as well as certain cognitive impairments in schizophrenia despite a low D2 receptor occupancy and may also be used as monotherapy in bipolar and major depressive disorder. The mechanisms underlying the broad clinical utility of quetiapine remain to be clarified, but may be related to the potent inhibition of the norepinephrine transporter (NET) by norquetiapine, the major metabolite of quetiapine in humans. Since norquetiapine is not formed in rodents we here investigated in rats whether NET-inhibition may, in principle, contribute to the clinical effectiveness of quetiapine and allow for its low D2 receptor occupancy, by combining quetiapine with the selective NET-inhibitor reboxetine. Antipsychotic-like activity was assessed using the conditioned avoidance response (CAR) test, dopamine output in the medial prefrontal cortex (mPFC) and the nucleus accumbens was measured using in vivo microdialysis, and NMDA receptor-mediated transmission was measured using intracellular electrophysiological recordings in pyramidal cells of the mPFC in vitro. Adjunct reboxetine potentiated the suppression of CAR by quetiapine. Moreover, concomitant administration of quetiapine and reboxetine resulted in a synergistic increase in cortical, but not accumbal, dopamine output. The combination of low, clinically relevant concentrations of quetiapine (60 nM) and reboxetine (20 nM) markedly facilitated cortical NMDA receptor-mediated transmission in contrast to either drug alone, an effect that could be inhibited by the D₁ receptor antagonist SCH23390. We conclude that concomitant NET-inhibition by norquetiapine may contribute to the overall antipsychotic effectiveness of quetiapine in spite of its relatively low level of D₂ occupancy.

A positron emission tomography study in healthy volunteers to estimate mGluR5 receptor occupancy of AZD2066 - estimating occupancy in the absence of a reference region

AZD2066 is a new chemical entity pharmacologically characterized as a selective, negative allosteric modulator of the metabotropic glutamate receptor subtype 5 (mGluR5). Antagonism of mGluR5 has been implicated in relation to various diseases such as anxiety, depression, and pain disorders. To support translation from preclinical results and previous experiences with this target in man, a positron emission tomography study was performed to estimate the relationship between AZD2066 plasma concentrations and receptor occupancy in the human brain, using the mGluR5 radioligand [(11)C]-ABP688. The study involved PET scans on 4 occasions in 6 healthy volunteers. The radioligand was given as a tracer dose alone and following oral treatment with different doses of AZD2066. The analysis was based on the total volume of distribution derived from each PET-assessment. A non-linear mixed effects model was developed where ten delineated brain regions of interest from all PET scans were included in one simultaneous fit. For comparison the analysis was also performed according to a method described previously by Lassen et al. (1995). The results of the analysis showed that the total volume of distribution decreased with increasing drug concentrations in all regions with an estimated Kipl of 1170 nM. Variability between individuals and occasions in non-displaceable volume of distribution could explain most of the variability in the total volume of distribution. The Lassen approach provided a similar estimate for Kipl, but the variability was exaggerated and difficult to interpret.

Smart Polymersomes: Formation, Characterisation and Applications

The term polymersome, which refers to a fully synthetic polymeric vesicle, became commonplace around the turn of the millennium. Since then these highly intriguing structures have been at the center of multi-disciplinary research, bridging the fields of nanotechnology, chemistry, physics, biology, medicine and imaging and, more recently, pioneering the field of synthetic biology. As structures they offer greater control into understanding the relationship between amphiphile properties and membrane curvature. Moreover, as delivery vectors for therapeutic and diagnostic compounds they enable greater efficiency of current therapies and targeted delivery. With the rising costs of both healthcare and drug development, polymersomes and nanomedicine are well placed to combat these modern-day problems. This chapter provides an overview of the approaches to prepare and to characterize polymersomes as well as their applications in biomedicine, highlighting recent achievements in the stimuli-responsive drug delivery field.

Paradoxical effects of GABA-A modulators may explain sex steroid induced negative mood symptoms in some persons

Some women have negative mood symptoms, caused by progestagens in hormonal contraceptives or sequential hormone therapy or by progesterone in the luteal phase of the menstrual cycle, which may be attributed to metabolites acting on the GABA-A receptor. The GABA system is the major inhibitory system in the adult CNS and most positive modulators of the GABA-A receptor (benzodiazepines, barbiturates, alcohol, GABA steroids), induce inhibitory (e.g. anesthetic, sedative, anticonvulsant, anxiolytic) effects. However, some individuals have adverse effects (seizures, increased pain, anxiety, irritability, aggression) upon exposure. Positive GABA-A receptor modulators induce strong paradoxical effects including negative mood in 3%-8% of those exposed, while up to 25% have moderate symptoms. The effect is biphasic: low concentrations induce an adverse anxiogenic effect while higher concentrations decrease this effect and show inhibitory, calming properties. The prevalence of premenstrual dysphoric disorder (PMDD) is also 3%-8% among women in fertile ages, and up to 25% have more moderate symptoms of premenstrual syndrome (PMS). Patients with PMDD have severe luteal phase-related symptoms and show changes in GABA-A receptor sensitivity and GABA concentrations. Findings suggest that negative mood symptoms in women with PMDD are caused by the paradoxical effect of allopregnanolone mediated via the GABA-A receptor, which may be explained by one or more of three hypotheses regarding the paradoxical effect of GABA steroids on behavior: (1) under certain conditions, such as puberty, the relative fraction of certain GABA-A receptor subtypes may be altered, and at those subtypes the GABA steroids may act as negative modulators in contrast to their usual role as positive modulators; (2) in certain brain areas of vulnerable women the transmembrane Cl(-) gradient may be altered by factors such as estrogens that favor excitability; (3) inhibition of inhibitory neurons may promote disinhibition, and hence excitability. This article is part of a Special Issue entitled: Neuroactive Steroids: Focus on Human Brain.

Adjunct quetiapine xr in patients with major depressive disorder: a pooled analysis of data from patients with anxious depression

Objective

This pooled analysis evaluated efficacy of adjunct quetiapine XR (QTP-XR) in subgroups of patients with anxious depression and lower levels of anxiety.

Methods

Pooled data from two 6-week, double-blind, randomised, placebo-controlled trials (D1448C00006/D1448C00007) in patients with inadequate response to antidepressants were analysed. Patients received adjunct QTP-XR (150 or 300 mg/day) or placebo+antidepressant (SSRI or SNRI). Using criteria defined in the STAR*D study, analyses conducted in patients with anxious depression or lower baseline anxiety levels (HAM-D anxiety/somatic factor score >/ = 7 and < 7, respectively) included LSM change at Week 6 in: MADRS total (primary endpoint), HAM-A and CGI-S total scores.

Results

For patients with anxious depression (n = 697; 76% patients), adjunct QTP-XR 150mg/day (-14.44, p < 0.01) and 300 mg/day (-15.09, p < 0.001) significantly improved MADRS total scores versus placebo+antidepressant (-11.78) at Week 6, with significant improvement demonstrated from Week 1 onwards. Significant improvements were seen in HAM-A (QTP-XR 150 mg/day: -9.05, p < 0.01; 300 mg/day -9.43, p < 0.01) and CGI-S total scores (QTP-XR 150 mg/day: -1.60, p< 0.001; 300 mg/day -1.63, p < 0.001) versus placebo+antidepressant (-7.40, -1.22, respectively) at Week 6.

A smaller subgroup (n = 222; 24% patients) had lower baseline anxiety levels. At Week 1, adjunct QTP-XR (150 mg/day -9.09; p < 0.01; 300 mg/day -8.60; p < 0.05) significantly improved MADRS total score versus placebo+antidepressant (-5.93). At Week 6 there were no significant changes (QTP-XR 150 mg/day -14.49; p = 0.243; 300 mg/day -14.01; p = 0.388) versus placebo+antidepressant (-12.78).

Conclusions

For patients with anxious depression, adjunct QTP-XR (150 and 300 mg/day) was effective at reducing symptoms of anxiety and depression, with symptom improvement observed from Week 1 onwards. AstraZeneca funded.

Efficacy and tolerability of quetiapine XR 400/600/800mg/day in acute schizophrenia: a post-hoc analysis of data from two pooled randomised studies

Introduction

Data from two, identically designed, placebo-controlled, randomised, double-blind clinical trials (D1444C00132+D1444C00133) for once-daily extended-release quetiapine fumarate (QTP-XR) were pooled and analysed.

Objective

Evaluate dose response, efficacy and safety for QTP-XR in schizophrenia.

Methods

Post-hoc analysis of data from patients receiving QTP-XR 400, 600, 800 mg/day or placebo. Endpoints: least squares means (LSM) change from baseline to Day 42 in PANSS total and positive and negative subscale scores. No corrections for multiplicity were performed. Adverse events (AEs) were recorded.

Results

914 patients were included; PANSS scores were assessed in the MITT population (n = 889). LSM change from baseline in PANSS total score diverged significantly from placebo at: Day 14 for QTP-XR 800 mg/day (-15.3 vs -12.1 for placebo; p = 0.018); Day 21 for 600 mg/day (-17.3 vs -14.2; p = 0.039); Day 42 for 400 mg/day (-19.2 vs -15.4; p = 0.033).

Jonckheere-Terpstra analysis of change in PANSS total score at Day 42 showed a significant QTP-XR dose response (p = 0.0196; p < 0.001 with placebo). PANSS positive scores diverged by Day 21 for both QTP-XR 800 (-5.7 vs -4.8; p = 0.049) and 600 mg/day (-5.8 vs -4.8; p = 0.046). PANSS negative scores diverged by Day 21 (-4.0 vs -3.2; p = 0.040) and 42 (-4.8 vs -3.6; p = 0.009) for QTP-XR 800 and 600 mg/day, respectively. AEs occurred in 59.4%, 66.5%, 62.1% and 56.2% of patients in the QTP-XR 800, 600, 400 mg/day and placebo groups, respectively. Most common AEs were somnolence, dry mouth, sedation, insomnia, dizziness, headache, constipation and nausea.

Conclusions

QTP-XR was generally well tolerated and demonstrated efficacy that increased with dose in schizophrenia.

Financial support: AstraZeneca.

Dose-dependent binding of AZD3783 to brain 5-HT1B receptors in non-human primates and human subjects: a positron emission tomography study with [11C]AZ10419369

RATIONALE

The serotonin 5-HT(1B) receptor is a potential target for the pharmacologic treatment of depression. Positron emission tomography (PET) determination of 5-HT(1B) receptor occupancy with drug candidates targeting this receptor in non-human primate and human subjects may facilitate translation of research from animal models and guide dose selection for clinical studies. AZD3783 is a recently developed, orally bioavailable 5-HT(1B) receptor antagonist with potential antidepressant properties.

OBJECTIVES

To determine the relationship between plasma concentration of AZD3783 and occupancy at primate brain 5-HT(1B) receptors using PET and the radioligand [(11)C]AZ10419369.

METHODS

PET studies with [(11)C]AZ10419369 were performed in three non-human primates at baseline and after intravenous injection of AZD3783. Subsequently, PET measurements were undertaken in six human subjects at baseline and after administration of different single oral doses of AZD3783 (1-40 mg).

RESULTS

After administration in non-human primates and human subjects, AZD3783 reduced regional [(11)C]AZ10419369 binding in a dose-dependent and saturable manner. The AZD3783 plasma concentration required for 50% receptor occupancy (K (i,plasma)) for monkeys was 25 and 27 nmol/L in occipital cortex and striatum, respectively. Corresponding estimates for human occipital cortex and ventral striatum were 24 and 18 nmol/L, respectively.

CONCLUSIONS

The potential antidepressant AZD3783 binds in a saturable manner to brain 5-HT(1B) receptors with a similar in vivo affinity for human and monkey receptors. [(11)C]AZ10419369 can be successfully used to determine occupancy at brain 5-HT(1B) receptors in vivo and constitutes a useful tool for dose selection in clinical studies with 5-HT(1B) receptor compounds.

Radiosynthesis of the candidate beta-amyloid radioligand [(11)C]AZD2184: Positron emission tomography examination and metabolite analysis in cynomolgus monkeys

Beta-amyloid accumulation is associated with the pathogenesis of Alzheimer's disease (AD). AZD2184, a new radioligand for high-contrast positron emission tomography (PET) imaging of Abeta-deposits, has recently been developed and characterized in vitro and in rodents ex vivo. The objective of this study was to label AZD2184 with carbon-11, to perform in vivo characterization of [(11)C]AZD2184 ([(11)C]5) in the cynomolgus monkey brain as well as whole-body dosimetry, and to examine the metabolism of the labeled radioligand. [(11)C]5 was prepared by a two-step radiosynthesis starting with the reaction of 5-(6-(tert-butyldimethylsilyloxy)benzo[d]thiazol-2-yl)pyridin-2-amine with [(11)C]methyl iodide followed by deprotection using water. Four brain PET measurements in two cynomolgus monkeys and one whole-body PET measurement were performed with [(11)C]5. There was a high and rapid brain uptake (2.2-3.4% of injected dose at 2 min). The distribution of brain radioactivity was fairly uniform, with early to late-brain concentration ratios (peak vs. 60 min) higher for [(11)C]5 than ratios previously reported for [(11)C]PIB (8.2 and 4.6, respectively). Based on the whole-body data, it was estimated that an effective dose in an adult male would be 6.2 muSv/MBq and thus would be safe from a radiation point of view for multiple scans within the same year. [(11)C]5 shows binding characteristics, suggesting low levels of white-matter retention, and may thus provide improved contrast when compared with currently used PET radioligands for visualization of Abeta-deposits. On the basis of the labeling chemistry and the results of the biological evaluation, we conclude that [(11)C]5 should be useful for routine clinical studies.

Detection of amyloid in Alzheimer's disease with positron emission tomography using [11C]AZD2184

Purpose

Current positron emission tomography (PET) radioligands for detection of Aβ amyloid in Alzheimer’s disease (AD) are not ideal for quantification. To improve the signal to noise ratio we have developed the radioligand [¹¹C]AZD2184 and report here the first clinical evaluation.

Methods

Eight AD patients and four younger control subjects underwent 93-min PET measurements with [¹¹C]AZD2184. A ratio approach using the cerebellum as reference region was applied to determine binding parameters.

Results

Brain uptake of [¹¹C]AZD2184 peaked within 1 min at 3–4% of injected radioactivity. AD patients had high radioactivity in cortical regions while controls had uniformly low radioactivity uptake. Specific binding peaked within 30 min at which time standardized uptake value ratios (SUVR) ranged between 1.19 and 2.57.

Conclusion

[¹¹C]AZD2184 is a promising radioligand for detailed mapping of Aβ amyloid depositions in Alzheimer’s disease, due to low non-specific binding, high signal to background ratio and reversible binding as evident from early peak equilibrium.

Pharmacokinetics of progesterone and its metabolites allopregnanolone and pregnanolone after oral administration of low-dose progesterone

OBJECTIVES

To investigate the pharmacokinetics of progesterone, allopregnanolone and pregnanolone after treatment with a low oral dose of progesterone.

METHODS

Eight postmenopausal women were given a single oral dose of 20 mg of micronised progesterone on Day 1 and 20 mg twice daily on Days 2-7. Blood samples for the analysis of progesterone, allopregnanolone and pregnanolone were collected, and pharmacokinetic parameters were calculated.

RESULTS

After ingestion of a single dose, areas under the plasma concentration-time curve (AUC) from 0 to 12 h for progesterone, allopregnanolone and pregnanolone were 127%, 196% and 119% higher than the corresponding AUCs estimated to be caused by endogenous production. The maximum plasma concentration (Cmax) and the AUC values were significantly lower for pregnanolone than for progesterone and allopregnanolone. The trough concentrations at steady state (Css) were significantly higher than the baseline values, and Css for pregnanolone was significantly lower than for allopregnanolone and progesterone. Css for allopregnanolone was in the range of what is normally seen in the menstrual cycle.

CONCLUSIONS

After ingestion of a low-dose of progesterone, the concentrations of allopregnanolone were in the same range as those of progesterone. Oral doses of 20 mg of progesterone twice daily to postmenopausal women produced allopregnanolone concentrations comparable to those achieved physiologically in premenopausal women. Low-dose oral progesterone may be used as a prodrug to allopregnanolone when the aim is to investigate low-dose allopregnanolone effects in humans.

Pharmacokinetics and D2 receptor occupancy of long-acting injectable risperidone (Risperdal Consta) in patients with schizophrenia

Thirteen patients with schizophrenia received injections of 25, 50, or 75 mg of long-acting risperidone every 2 wk. Brain D2 receptor occupancy was assessed with [11C]raclopride 2 wk after the last (fifth) injection (day 71) in seven subjects and 2 wk after the third injection (day 44) in one subject. Stable plasma concentrations were reached after the third injection and steady-state concentrations of the active moiety (risperidone + 9-hydroxyrisperidone) after the fourth injection. Steady-state plasma concentrations were maintained for 4-5 wk after the last injection and then declined rapidly. After injections of 25, 50 and 75 mg on day 44 or day 71, D2 receptor occupancy ranged from 25-48%, 59-83% and 62-72% respectively, while plasma active-moiety levels ranged from 4.4-8.8, 15.0-31.1 and 22.5-26.3 ng/ml respectively. The results indicate that brain D2 receptor occupancy at steady state after injections of long-acting risperidone was in the range found in patients effectively treated with 2-6 mg of oral risperidone.

Kidney transplantation without calcineurin inhibitors using sirolimus

INTRODUCTION

With the introduction of new immunosuppressive medicines, it has become possible to determine the extent to which nephrotoxic medicines contribute to CAN. The aim of this study is to compare the safety and efficacy of calcineurin inhibitor (CI) free immunosuppression in a prospective, randomized trial comparing sirolimus-mycophenolate mofetil (MMF)-prednisone to tacrolimus- MMF-prednisone.

METHODS

Patients are randomized at the time of transplant to receive either tacrolimus (target level 12 to 15 ng/mL in the first month) or sirolimus (target level 12 to 18 ng/mL in the first month). All patients also receive MMF (750 mg bid) and prednisone tapered to 10 mg/d by 3 months and thymoglobulin induction (1.5 mg/kg/d on days 0, 1, 2, 4 and 6).

RESULTS

At this point we have 4-month follow-up in 85 patients. The acute rejection rate is 7.5% (3/40) in the tacrolimus group and 6.7% (3/45) in the sirolimus group. We have discontinued sirolimus in eight patients so far, with wound complications being the most common indication. Renal function appears to be better in the sirolimus group at 1 month after transplantation, but the difference is not statistically significant.

CONCLUSIONS

While longer follow-up is needed, these results demonstrate that total avoidance of CI can be achieved with extremely low acute cellular rejection rates using sirolimus-based immunosuppression in combination with thymoglobulin, MMF, and prednisone.

Biochemical effects in brain of low doses of haloperidol are qualitatively similar to those of high doses

Typical and atypical antipsychotic drugs (APD) show differential effects in brain on both dopamine output and activation of Fos-like immunoreactivity (FLI) in dopamine nerve terminal regions. Typical APD increase dopamine output preferentially in the core and atypical APD increase dopamine output preferentially in the shell of the nucleus accumbens (NAC). Whereas both typical and atypical APD increase FLI in NAC, typicals cause FLI activation in the striatum and atypicals cause FLI activation in the prefrontal cortex. Clinically, low doses of haloperidol cause less side-effects than higher doses, and low-dose haloperidol has been suggested as a cost-effective alternative to atypical APD. Here, in vivo voltammetry in anaesthetised, pargyline-pretreated rats was used to measure dopamine output in the two subdivisions of the NAC and, in addition, immunohistochemistry was used to assess FLI activation in dopamine target areas, following acute haloperidol administration. Haloperidol, 0.001 and 0.01 mg/kg i.v., caused a significantly higher dopamine output in the core than in the shell of the NAC. Moreover, haloperidol 0.05 and 0.5, but not 0.005, mg/kg s.c. increased FLI in the NAC and the striatum, but not in the medial prefrontal cortex. Thus, even extremely low doses of haloperidol generate, in principle, the same biochemical effects in brain as higher doses, and these effects remain different from those of atypical APD. These biological data indicate that clinical differences between haloperidol and atypicals are qualitative rather than dose-dependent. Consequently, our results do not support the use of low-dose haloperidol as replacement for atypical APD in the treatment of schizophrenia.

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

RATIONALE

Sertindole is a new atypical antipsychotic drug. Preclinical pharmacology suggests that sertindole has a preferential effect on the activity of limbic and cortical dopaminergic neurons. Clinical trials have shown antipsychotic efficacy and very few extrapyramidal symptoms (EPS) with sertindole at 20 mg/day.

OBJECTIVES

This positron emission tomography (PET) study aimed to measure D(2) receptor occupancy in striatal and extra-striatal regions induced by clinically representative doses of sertindole in patients with schizophrenia.

METHOD

Four stabilized schizophrenic out-patients received sertindole 20 mg/day for 6-8 weeks. PET was performed using [(11)C]raclopride to measure D(2) receptor occupancy in the striatum and [(11)C]FLB457 to measure occupancy in the neocortex and thalamus, i.e. regions with very low D(2) receptor density.

RESULTS

Striatal D(2) receptor occupancy was 52-68%. Similar occupancies were found in the thalamus, and the temporal and frontal cortices.

CONCLUSIONS

Sertindole appears efficacious at a low D(2) receptor occupancy, comparable to that produced by clozapine. This finding could explain the low risk of EPS. The functional limbic selectivity of sertindole was not reflected in regional differences in receptor occupancy.

Saturation of striatal D(2) dopamine receptors by clozapine

Positron emission tomography (PET) studies have demonstrated low striatal D2 dopamine receptor occupancy in clozapine-treated schizophrenic patients. The aim of this pilot study was to explore if this low receptor occupancy indeed represents partial saturability of striatal D2 dopamine receptors by clozapine. Three anaesthetized Cynomolgus monkeys were examined during one day with PET and [11C]raclopride at baseline and after intravenous injections of clozapine 1.5 mg/kg followed by 18.5 mg/kg. The estimated corresponding human oral doses were approx. 210 mg/d and 2800 mg/d. D2 dopamine receptor occupancy was calculated using an equilibrium-ratio analysis and ranged from 54 to 58% after 1.5 mg/kg and 87 to 89% after the total dose 20 mg/kg. The calculated maximal occupancy was 93%. We conclude that PET-measured D2 dopamine receptor occupancy by clozapine can be described using a model based on the law of mass action, previously validated for conventional antipsychotics. Therefore, sufficiently high doses of clozapine are expected to produce complete striatal D2 dopamine receptor occupancy. The findings further support our previous findings of low D2 dopamine receptor occupancy in patients treated with standard doses of clozapine.

The impact of different doses of medroxyprogesterone acetate on mood symptoms in sequential hormonal therapy

The aim of this study was to compare adverse mood effects of two different doses of medroxyprogesterone acetate (MPA) during postmenopausal hormone replacement therapy (HRT) in women with and without a history of premenstrual syndrome (PMS). The study was designed as a randomized double-blind cross-over study and included 36 postmenopausal women at three health care areas in northern Sweden. The women received 2 mg estradiol continuously during five 28-day cycles and 10 mg or 20 mg MPA sequentially for 12 days during each cycle. The main outcome measures were mood and physical symptoms noted on a daily rating scale. We found that physical symptoms did not differ between 10 and 20 mg MPA. Both women with a history of PMS and women without responded with more negative mood symptoms with the lower dose of MPA. In women with previous PMS the higher dose of MPA enhanced positive mood symptoms. With respect to mood and physical symptoms, the aim to lower MPA doses in HRT is unwarranted.

Binding of [3H]paroxetine to serotonin uptake sites and of [3H]lysergic acid diethylamide to 5-HT2A receptors in platelets from women with premenstrual dysphoric disorder during gonadotropin releasing hormone treatment

Changes in serotonergic parameters have been reported in psychiatric conditions such as depression but also in the premenstrual dysphoric disorder (PMDD). In addition, hormonal effects on serotonergic activity have been established. In the present study, binding of [3H]paroxetine to platelet serotonin uptake sites and binding of [3H]lysergic acid diethylamide ([3H]LSD) to platelet serotonin (5-HT)2A receptors were studied in patients with PMDD treated with a low dose of a gonadotropin releasing hormone (GnRH) agonist (buserelin) or placebo and compared to controls. The PMDD patients were relieved of premenstrual symptoms like depression and irritability during buserelin treatment. The number of [3H]paroxetine binding sites (Bmax) were significantly higher in the follicular phase in untreated PMDD patients compared to controls. When treated with buserelin the difference disappeared. No differences in [3H]LSD binding between the three groups were shown. The present study demonstrated altered platelet [3H]paroxetine binding characteristics in women with PMDD compared to controls. Furthermore, [3H]paroxetine binding was affected by PMDD treatment with a low dose of buserelin. The results are consistent with the hypothesis that changes in serotonergic transmission could be a trait in the premenstrual dysphoric disorder.

Sensitivity to a neurosteroid is increased during addition of progestagen to postmenopausal hormone replacement therapy

The aim of this study was to compare the pharmacodynamic response to a neuroactive steroid, pregnanolone, before and during different hormonal settings of postmenopausal hormone replacement therapy (HRT). Twenty-seven postmenopausal women with climacteric symptoms were administered HRT in a randomized, double-blinded, placebo-controlled crossover study. The women received 2 mg estradiol (E2) continuously during four 28-day cycles and 10 mg medroxyprogesterone acetate (MPA), 1 mg norethisterone acetate (NETA) or placebo sequentially for the last 14 days in each cycle. The pharmacodynamic response to pregnanolone was assessed before treatment and during the last week of each treatment, by comparing the effects of intravenous pregnanolone (3alpha-hydroxy-5beta-pregnan-20-one) on saccadic eye velocity (SEV), saccade deceleration, saccade latency and self-rated sedation. Throughout the study daily symptom rating scales were kept. During the progesta gen phase of the treatment cycles, negative mood symptoms and physical symptoms were increased, whereas positive mood symptoms were decreased. Compared to pretretreatment conditions, E2 alone did not change the responsiveness to pregnanolone. During progestagen addition to E2, the responsiveness to pregnanolone was increased. The sedation response increased compared to pretreatment conditions during both E2 + MPA and E2 + NETA treatment. Compared to E2 treatment alone, addition of MPA increased the postpregnanolone effect on saccade deceleration, whereas the SEV response to pregnanolone was increased during E2 + NETA treatment. It is concluded that pregnanolone sensitivity increases together with deterioration in mood symptoms during addition of progestagen to HRT.

No support for regional selectivity in clozapine-treated patients: a PET study with [(11)C]raclopride and [(11)C]FLB 457

OBJECTIVE

The authors' goal was to test the hypothesis of extrastriatal D(2) receptor selectivity as the mechanism of action of clozapine.

METHOD

Positron emission tomography (PET) was used to examine extrastriatal as well as striatal dopamine D(2) receptor occupancy in four patients treated with clozapine and three patients treated with haloperidol. The reference radioligand [(11)C]raclopride was used for determination of D(2) receptor occupancy in the striatum. The radioligand [(11)C]FLB 457 was chosen for determination of D(2) receptor occupancy in the thalamus, the temporal cortex, and the frontal cortex.

RESULTS

In patients treated with haloperidol the D(2) receptor occupancy was high in all examined brain regions. In clozapine-treated patients the D(2) receptor occupancy was relatively low in both the striatum and the extrastriatal regions.

CONCLUSIONS

The results from the present study give no support for the hypothesis of regional selectivity as the mechanism of action for clozapine.

Negative mood changes during hormone replacement therapy: a comparison between two progestogens

OBJECTIVE

The aim of this study was to compare side effects of medroxyprogesterone acetate and norethindrone acetate during postmenopausal hormone replacement therapy in women with and without a history of premenstrual syndrome.

STUDY DESIGN

Fifty-one postmenopausal women were randomly selected in a double-blind crossover study. The women received 2 mg of estradiol continuously during five 28-day cycles and 10 mg of medroxyprogesterone or 1 mg of norethindrone sequentially for 12 days of each cycle. Daily symptom rating scales were kept.

RESULTS

The women showed cyclic changes, with negative mood and physical symptoms culminating during the late progestogen phase and positive mood during the estrogen-only phase. Symptoms declined with time but remained after 5 months. Women with a history of premenstrual syndrome responded strongly to both progestogens. Medroxyprogesterone acetate induced less negative and more positive mood symptoms than norethindrone in women with no history of premenstrual syndrome. In both groups medroxyprogesterone caused more physical symptoms than norethindrone.

CONCLUSION

The addition of medroxyprogesterone to estrogen is preferable to norethindrone with respect to mood symptoms in women without a history of premenstrual syndrome.

High 5HT2A receptor occupancy in M100907-treated schizophrenic patients

RATIONALE

Selective drugs are required to test the hypothesis whether antipsychotic effects may be induced or modulated by 5HT(2A) receptor antagonism. M100907 (previously known as MDL 100,907) is a highly selective 5HT(2A) antagonist in clinical development.

OBJECTIVE

To test if the suggested clinical dose of 20 mg M100907 daily induces high 5HT(2A) receptor occupancy in patients with schizophrenia.

METHODS

The 5HT(2A) receptor occupancy was determined in two patients with schizophrenia treated with M100907, 20 mg once a day. Positron emission tomography (PET) with (11)C-labeled M100907, was performed prestudy and under steady state conditions. Clinical ratings were performed weekly.

RESULTS

Clinical treatment with M100907, 20 mg daily induced a very high 5HT(2A) receptor occupancy in the frontal cortex of both patients (>90%). M100907 was well tolerated. One patient improved minimally and one patient became minimally worse during treatment.

CONCLUSIONS

The results confirm that an oral dose of 20 mg per day ensures adequate 5HT(2A) receptor occupancy for clinical proof of concept. The sample is too small to allow conclusions about the clinical effect.

Treatment of premenstrual syndrome with gonadotropin-releasing hormone agonist in a low dose regimen

BACKGROUND

GnRH agonists constitute a well-documented treatment for premenstrual syndrome (PMS). However, the hypo-estrogenic state induced by the treatment renders it less suitable for long-term clinical use. The aim of the current study was to investigate the efficacy of a low dose GnRH agonist with respect to its ability to relieve premenstrual symptoms and maintain regular ovulatory cycles.

METHODS

The effect of a low dose GnRH agonist (buserelin) on luteal phase symptomatology was evaluated in 27 women with severe premenstrual syndrome. The design was doubleblind, placebo-controlled and cross-over. Patients were randomized to either GnRH-agonist intranasally in a dosage of 100 microg once daily for two months or placebo for two months before the cross-over was made. The primary outcome measure consisted of daily symptom ratings for mood and physical symptoms made by the patients throughout the study. Adverse events and hormone concentrations were assessed at visits every second week.

RESULTS

Premenstrual irritability and depression were significantly relieved by low dose GnRH agonist. Positive symptoms such as friendliness and cheerfulness were also improved during the premenstrual week. Likewise physical symptoms of swelling and headache displayed a significant improvement during buserelin treatment, whereas breast tenderness scores were unaffected by the treatment. The low dose GnRH agonist treatment regimen induced anovulation in as much as 56% of patients, but these subjects were significantly older than those women who maintained ovulatory cycles throughout the study.

CONCLUSION

GnRH treatment significantly reduced premenstrual depression and irritability. However, low dose GnRH therapy is prone to induce anovulation, particularly with increasing age.

The role of positron emission tomography in the drug development of M100907, a putative antipsychotic with a novel mechanism of action

Antipsychotic drug development has been a slow process since the discovery of chlorpromazine more than 45 years ago. Researchers identify a large number of potential compounds; screen them for antipsychotic activity in in vitro and animal test models; devise appropriate formulations; perform preclinical pharmacology, pharmacokinetic, and toxicology studies; perform healthy volunteer and then patient clinical studies; and finally negotiate with regulatory agencies for drug approval. In the United States, this process takes an average of 10 to 12 years and costs more than $500 million per approved drug. More recently, the pharmaceutical industry is benefiting from a new wave of technologic innovations that have advanced our understanding of the biology of disease processes and increased the efficiency of the research and development process. However, while these new technologies may appear to be expensive, by providing the basis for early go/no-go decisions, technologies such as PET can actually be cost-effective. To ensure that innovative drug research continues, a practical strategy (rational drug design) to evaluate drugs more efficiently in terms of both time and cost (fewer studies with fewer patients) must be developed for each new drug candidate. One of the most important and difficult steps in the drug development process is defining the dose-response relationship. Using M100907 as an example, we demonstrated that mechanism-based research promotes cost-effective drug development. The therapeutic index of M100907 was defined in phase I single- and multiple-dose tolerability studies. Nuclear imaging using PET technology was then used to confirm the mechanism of action of M100907 in the target organ (living human brain) and to target an appropriate dose range and regimen. With these data, clear go/no-go decision points could be established early within the clinical drug development process, and the selection of M100907 doses to carry forward into large-scale clinical trials in patients with schizophrenia could be narrowed.

Suggested minimal effective dose of risperidone based on PET-measured D2 and 5-HT2A receptor occupancy in schizophrenic patients

OBJECTIVE

Multicenter trials with the novel antipsychotic risperidone have suggested a standard dose of 6 mg/day. However, a dose producing the highest response rate in fixed-dose studies is likely to exceed the minimal effective dose in most patients. The aim of this positron emission tomography (PET) study was to suggest a minimal effective dose of risperidone based on measurements of dopamine D2 and serotonin 5-HT2A receptor occupancy.

METHOD

Eight first-episode or drug-free schizophrenic patients were treated with risperidone, 6 mg/day, for 4 weeks and then 3 mg/day for 2 weeks. PET was performed after 4 and 6 weeks, with [11C]raclopride to measure D2 receptor occupancy and [11C]N-methylspiperone to measure 5-HT2A receptor occupancy.

RESULTS

Seven patients completed the study and responded to treatment with risperidone. No patient had extrapyramidal side effects at the time of inclusion in the study. At the 6-mg/day dose, mean D2 receptor occupancy was 82% (range = 79%-85%), 5-HT2A receptor occupancy was 95% (range = 86%-109%), and six patients had developed extrapyramidal side effects. After dose reduction to 3 mg/day, D2 receptor occupancy was 72% (range = 53%-78%), and 5-HT2A receptor occupancy was 83% (range = 65%-112%). Three patients had extrapyramidal side effects at this time.

CONCLUSIONS

Treatment with risperidone, 6 mg/day, is likely to induce unnecessarily high D2 receptor occupancy, with a consequent risk of extrapyramidal side effects. High 5-HT2A receptor occupancy did not prevent extrapyramidal side effects completely. The authors previously suggested an optimal interval for D2 receptor occupancy of 70%-80%. To achieve this, resperidone, 4 mg/day, should be a suitable initial dose for antipsychotic effect with a minimal risk of extrapyramidal side effects in most patients.

D(2)- and 5-HT(2) receptor occupancy in high-dose neuroleptic-treated patients

Individual schizophrenic patients are sometimes reported to benefit from unusually high doses of neuroleptics. Such patients may have poor drug penetration into the brain or ultra-rapid metabolism. Alternately, very high doses may be required to induce occupancy of 5-HT(2) receptors, which have been suggested as mediators of atypical effects. Five schizophrenic patients treated with high doses of fluphenazine decanoate (100-250 mg/wk) and adjunct medications were examined with positron emission tomography and [(11)C]raclopride to measure D(2) receptor occupancy and [(11)C]NMSP to measure 5-HT(2) receptor occupancy. All patients were rated globally as 'markedly' to 'severely' ill and had high scores on all subscales of the Positive and Negative Syndrome Scale for schizophrenia. However, according to retrospective clinical evaluation, there was improved social function and reduced distress following high-dose treatment, an effect that deteriorated after previous explorative dose reduction. Extrapyramidal symptoms were modest. D(2) receptor occupancy was very high (89-97%). 5-HT(2) receptor occupancy was also high (76-105%). Plasma concentrations of fluphenazine were 5-37 nm. No patient had a cytochrome P450 CYP2D6 genotype associated with ultra-rapid drug metabolism. The findings suggest almost complete saturation of D(2) receptors, and do not support poor drug availability in the brain as the basis of the apparent high-dose requirement. The high 5-HT(2) receptor occupancy may have contributed to the apparent clinical improvement and modest degree of EPS. However, it is likely that the treatment used also induced occupancy of other neuroreceptors.

Positron emission tomographic analysis of dose-dependent MDL 100,907 binding to 5-hydroxytryptamine-2A receptors in the human brain

Selective 5-hydroxytryptamine-2A (5-HT2A) antagonism has been proposed as a mechanism of atypical antipsychotic drug action. MDL 100,907, a new selective 5-HT2A receptor antagonist, has high affinity in vitro for 5-HT2A receptors and is being developed as a potential antipsychotic drug. In this study, neocortical 5-HT2A receptor occupancy was measured in six healthy male volunteers after placebo and escalating single doses (1-72 mg) of MDL 100,907 using positron emission tomography and the nonspecific radioligand [11C]N-methylspiperone ([11C]NMSP). Receptor occupancy was calculated using a ratio-equilibrium analysis, assuming that maximal radioligand binding inhibition represents 100% 5-HT2A receptor occupancy. Plasma concentrations of MDL 100,907 were measured with high-pressure liquid chromatography. The pharmacokinetic parameters area under the curve and peak plasma concentration increased linearly with dose, with rapid absorption and a 6- to 9-hour elimination half-life. The neocortical binding of [11C]NMSP was inhibited dose-dependently. After administration of 6 mg of MDL 100,907 the inhibition was 70%, corresponding to a 5-HT2A receptor occupancy of 90%. The calculated maximal inhibition was 77%. These observations indicate that MDL 100,907 passes the blood-brain barrier and binds to 5-HT2A receptors in a saturable manner in the living human brain. Repeated doses of MDL 100,907, 10 mg/day or more, should induce a sustained 5-HT2A receptor occupancy in most patients. Thus, MDL 100,907 provides a suitable tool to evaluate the potential of selective 5-HT2A receptor antagonism in the treatment of schizophrenia.

Implications of brain imaging for the management of schizophrenia

Positron emission tomography (PET) can be used to explore relationships between central neuroreceptor occupancy, psychotropic drug blood levels and clinical effects. Treatment with conventional neuroleptics induces high (70-90%) dopamine (D2)-receptor occupancy. The risk of extrapyramidal side effects increases at D2-receptor occupancies above 80%. Standard doses of clozapine induced a low (20-67%) D2-receptor occupancy, but very high (85-90%) 5-hydroxytryptamine (5-HT2A)-receptor occupancy. The novel antipsychotics risperidone and olanzapine induced high occupancy of both D2 and 5-HT2A receptors at suggested standard doses. The occurrence of extrapyramidal side effects in some patients in the higher dose ranges does not support the view that 5-HT2A-receptor occupancy completely prevents the development of extrapyramidal side effects. These results emphasize the need for further exploration of the low dose ranges of risperidone and olanzapine. A preliminary analysis of an ongoing PET study showed that a schizophrenic patient treated with sertindole at 20 mg/day had a D2-receptor occupancy of below 70%. Further studies are needed to show whether sertindole is the first new antipsychotic that induces low occupancy in the clinical dose range, suggesting a mechanism of action distinct from that of classical neuroleptics and analogous to that of clozapine.

Patients with premenstrual syndrome have a different sensitivity to a neuroactive steroid during the menstrual cycle compared to control subjects

We have evaluated the functional sensitivity to a neuroactive steroid in 12 women with and 12 women without premenstrual syndrome (PMS) at two stages of the menstrual cycle, by comparing the effects of three increasing doses of intravenous pregnanolone (3alpha-hydroxy-5beta-pregnan-20-one) on saccadic eye velocity (SEV) and self-rated sedation. Control subjects in the follicular and luteal phase showed a significant reduction in SEV after pregnanolone injections compared to vehicle. In PMS patients, pregnanolone injections induced a significant dose-related decrease in SEV compared to vehicle only in the follicular phase, not in the luteal phase. After pregnanolone injections, sedation scores increased significantly from vehicle among control subjects in the luteal phase but not among PMS patients in either cycle phase. High-severity PMS patients responded with less decrease in SEV and less increase in sedation scores following pregnanolone injections compared to low-severity patients. Control subjects increased their SEV response to pregnanolone in the luteal phase compared to the follicular phase, whereas PMS patients did not. These findings are compatible with a decreased GABAA-receptor sensitivity in brain areas controlling saccadic eye movements among PMS patients in the late luteal phase.

PET imaging of central 5-HT2A receptors with carbon-11-MDL 100,907

Serotonergic 5-HT2A receptors are of central interest in the complex pathophysiology of schizophrenia. These receptors have also been proposed as putative targets for atypical antipsychotic drugs. Suitable radioligands for 5-HT2A receptors are required to evaluate this hypothesis in vivo with PET. MDL 100,907 is a highly selective 5-HT2A receptor antagonist that is currently being developed as a potential antipsychotic drug. We have previously reported on the preparation of [11C]MDL 100,907 and initial characterization of [11C]MDL 100,907 binding in the monkey brain. In this preliminary PET study, the regional distribution and binding kinetics of [11C]MDL 100,907 were examined in healthy men.

METHODS

A PET examination was performed in each of three subjects after intravenous injection of [11C]MDL 100,907. The metabolite-corrected arterial input function was used in a kinetic analysis according to the standard three-compartment model.

RESULTS

The highest radioactivity concentration was observed in the neocortex, whereas radioactivity was lower in the cerebellum, pons, thalamus, striatum and white matter. The binding potential (BP) in the neocortical regions was 4-6 times higher, whereas BP in the striatum was slightly higher than that in the cerebellum, demonstrating a regional distribution in good agreement with 5-HT2A receptor densities measured in vitro. The BP in the cerebellum was small but not negligible.

CONCLUSION

This preliminary study suggests that [11C]MDL 100,907 is a suitable PET radioligand for studies on 5-HT2A receptors in man. The high selectivity of MDL 100,907 represents a major advantage as compared to presently available radioligands with poor selectivity. Thus, [11C]MDL 100,907 is recommended in the future for PET studies in healthy subjects and schizophrenic patients, including the determination of drug-induced 5-HT2A receptor occupancy.

Patients with premenstrual syndrome have reduced sensitivity to midazolam compared to control subjects

Premenstrual syndrome (PMS) depends on gonadal hormones produced by the corpus luteum. Given the facilitory actions on GABAergic inhibitory neurotransmission exerted by certain progesterone metabolites, further studies on the GABAA receptor system in premenstrual syndrome are warranted. This study evaluated the benzodiazepine sensitivity in PMS patients and control subjects, using saccadic eye velocity (SEV) and visual analogue ratings of sedation as dependent measures. PMS patients displayed a significantly reduced SEV responsiveness to benzodiazepines compared to control subjects in the follicular phase, whereas there was no difference between groups in the luteal phase. In the luteal phase, the sedation response to benzodiazepines was significantly reduced in PMS patients compared to control subjects. There was also an influence of PMS symptom severity on these measures, as high-severity PMS patients displayed blunted SEV and sedation responses to benzodiazepines compared to low-severity patients. These results indicate that PMS patients have a reduced functional sensitivity at the GABAA/benzodiazepine receptor complex throughout the menstrual cycle.

A PET-study of [11C]FLB 457 binding to extrastriatal D2-dopamine receptors in healthy subjects and antipsychotic drug-treated patients

We recently developed [11C]FLB 457 a substituted benzamide with the very high affinity of 20 pM for D2-dopamine receptors in vitro. The aim of the present exploratory study was to examine the anatomical distribution of [11C]FLB 457 binding in the human brain and to determine extrastriatal D2-receptor occupancy in antipsychotic drug-treated patients. [11C]raclopride was used to obtain reference values for D2-dopamine receptor occupancy in the putamen. After IV injection of [11C]FLB 457 there was a high concentration of radioactivity, not only in the caudate putamen but also in the thalamus and the temporal cortex. The concentration of radioactivity in the frontal cortex, the substantia nigra and the colliculi was slightly higher than in the cerebellum. Pretreatment with haloperidol and fluphenazine indicated that [11C]FLB 457 binding in extrastriatal regions to a high degree represent specific binding to D2-dopamine receptors. The D2-occupancy in antipsychotic drug-treated patients was on the same level in the thalamus and the temporal cortex as that determined with [11C]raclopride in the putamen. The study shows that [11C]FLB 457 has potential for quantitative PET-examination of D2-dopamine receptors in man.

Delayed normalization of central D2 dopamine receptor availability after discontinuation of haloperidol decanoate. Preliminary findings

BACKGROUND

Antipsychotic drugs in depot formulations may prevent psychotic relapses, even after complete withdrawal. To examine the duration of drug remaining in the brain, central D2 dopamine receptor occupancy was measured with positron emission tomography for a year after discontinuation of depot neuroleptic treatment.

METHODS

Four schizophrenic patients were withdrawn from low-dose treatment with haloperidol decanoate (30-50 mg every 4 weeks). They were examined repeatedly with positron emission tomography and the radioligand carbon 11-labeled raclopride during the following year. At end point, a Scatchard analysis was performed to determine the density and affinity of D2 dopamine receptors.

RESULTS

Occupancy of D2 dopamine receptors was highest 1 week after depot injection (66%, 77%, 82%, and 78% in 4 patients) and then decreased slowly. Six months after discontinuation of treatment, D2 dopamine receptor occupancy was 24%, 32%, and 34% in 3 patients. After 1 year, D2 dopamine receptor density and affinity in 2 patients were within the ranges of control subjects, suggesting no remaining haloperidol.

CONCLUSIONS

Our preliminary finding of persistence of D2 dopamine receptor occupancy indicates that commonly used doses of haloperidol decanoate (200 mg every 4 weeks) maintain antipsychotic levels of receptor occupancy even 16 weeks after discontinuation of treatment. This may explain the lower relapse rates in patients withdrawn from depot neuroleptic treatment compared with those withdrawn from oral treatment. In addition, the remaining occupancy may confound the clinical evaluation of subsequent treatments. For controlled clinical trials of new antipsychotic drugs, we suggest a minimum washout of 6 months after the last depot injection.

D2 occupancy, extrapyramidal side effects and antipsychotic drug treatment: a pilot study with sertindole in healthy subjects

Acute extrapyramidal syndromes (EPS) are frequently recorded during treatment with classical neuroleptic drugs. In patients with EPS a consistent finding is high central D2-receptor occupancy (> 80%) as demonstrated with positron emission tomography (PET). The exception is clozapine, an atypical antipsychotic which has low EPS liability and also induces a low D2 occupancy (20-67%). We have proposed that the PET demonstration of low D2 occupancy at antipsychotic dose levels can be viewed as a strategy to confirm atypicality. There have been strong incentives in recent years to discover new drugs which do not induce EPS, but so far no drug has been shown unequivocally to have the low D2 occupancy and EPS liability reported for clozapine. Sertindole is a new antipsychotic drug which has shown a low incidence of acute EPS in clinical studies. In the present study PET was used to measure central D2-dopamine receptor binding in the basal ganglia at baseline and 6 h after oral administration of 4 mg sertindole to two healthy males. D2-dopamine receptor occupancy was 15% in one subject and 6% in the other. The low occupancy level demonstrated at 4 mg indicates the need for a PET study in patients at the suggested clinical dose level of 12-24 mg a day. In particular, it is important to determine whether sertindole induces antipsychotic effects at a D2 occupancy level which is lower that found in patients treated with classical antipsychotics.

A PET study of 5-HT2 and D2 dopamine receptor occupancy induced by olanzapine in healthy subjects

Olanzapine is a new antipsychotic drug with affinity for 5-HT2, D2, D1, and muscarinic receptors. Positron emission tomography and the radioligands [11C]raclopride and [11C]NMSP were used to measure D2 and 5-HT2 receptor occupancy in three healthy subjects after 10 mg olanzapine orally. After seven hours D2 receptor occupancy was 63%, 62% and 59%, respectively. After 9.5 hours 5-HT2 receptor occupancy was 74%, 86% and 92%. D2 and 5-HT2 receptor occupancy was comparable to that found in patients continuously treated with clozapine. Clinical efficacy has been demonstrated for olanzapine in the dose range 5 to 15 mg per day. Extrapolation from our present observations after a 10 mg single-dose suggest, that at the lower end of the clinically examined dose range the D2 and 5-HT2 receptor occupancy should be similar to that induced by standard doses of clozapine. Detailed evaluation of the dose-response characteristics of olanzapine and direct clinical comparison to clozapine will thus provide valuable leads to the clarification of atypical antipsychotic action.

Test-retest reliability of central [11C]raclopride binding at high D2 receptor occupancy. A PET study in haloperidol-treated patients

Central D2 dopamine receptor occupancy may be a useful measure to establish clinical guidelines for optimal antipsychotic drug treatment. The use of positron emission tomography (PET) to explore quantitative relationships among D2 receptor occupancy and clinical effects depends on the reliability of such measurements. The calculation of D2 receptor occupancy using [11C]raclopride is routinely based on a ratio-equilibrium analysis, in which the ratio of radioactivity concentration in the striatum to that in the cerebellum is determined. To examine the reliability of such ratios, a test-retest analysis was performed in four schizophrenic patients treated with haloperidol decanoate. PET experiments with [11C]raclopride were repeated in each subject during the same day. The putamen to cerebellum ratio (P/C ratio) ranged from 1.44 to 1.07 among the four patients, corresponding to a D2 receptor occupancy of 62 to 71%. In each subject, the P/C ratios remained highly similar, with quotients 0.98, 1.01, 1.04 and 1.06 between the two experiments. The high test-retest reproducibility of the P/C ratios indicates that measurements of D2 receptor occupancy with the present methods are highly reliable, and support the further use of PET to optimize the drug treatment of schizophrenia.