Receptor Occupancy of the κ-Opioid Antagonist LY2456302 Measured with Positron Emission Tomography and the Novel Radiotracer 11C-LY2795050.

The κ-opioid receptor (KOR) is thought to play an important therapeutic role in a wide range of neuropsychiatric and substance abuse disorders, including alcohol dependence. LY2456302 is a recently developed KOR antagonist with high affinity and selectivity and showed efficacy in the suppression of ethanol consumption in rats. This study investigated brain penetration and KOR target engagement after single oral doses (0.5-25 mg) of LY2456302 in 13 healthy human subjects. Three positron emission tomography scans with the KOR antagonist radiotracer (11)C-LY2795050 were conducted at baseline, 2.5 hours postdose, and 24 hours postdose. LY2456302 was well tolerated in all subjects without serious adverse events. Distribution volume was estimated using the multilinear analysis 1 method for each scan. Receptor occupancy (RO) was derived from a graphical occupancy plot and related to LY2456302 plasma concentration to determine maximum occupancy (rmax) and IC50. LY2456302 dose dependently blocked the binding of (11)C-LY2795050 and nearly saturated the receptors at 10 mg, 2.5 hours postdose. Thus, a dose of 10 mg of LY2456302 appears well suited for further clinical testing. Based on the pharmacokinetic (PK)-RO model, the rmax and IC50 of LY2456302 were estimated as 93% and 0.58 ng/ml to 0.65 ng/ml, respectively. Assuming that rmax is 100%, IC50 was estimated as 0.83 ng/ml.

Occupancy of Nociceptin/Orphanin FQ Peptide Receptors by the Antagonist LY2940094 in Rats and Healthy Human Subjects.

Therapeutic benefits from nociceptin opioid peptide receptor (NOP) antagonism were proposed for obesity, eating disorders, and depression. LY2940094 ([2-[4-[(2-chloro-4,4-difluoro-spiro[5H-thieno[2,3-c]pyran-7,4'-piperidine]-1'-yl)methyl]-3-methyl-pyrazol-1-yl]-3-pyridyl]methanol) is a novel, orally bioavailable, potent, and selective NOP antagonist. We studied NOP receptor occupancy (RO) after single oral LY2940094 doses in rat hypothalamus and human brain by use of liquid chromatography with tandem mass spectrometry (LC-MS/MS) (LSN2810397) and positron emission tomography (PET) ([(11)C]NOP-1A) tracers, respectively. A bolus plus constant infusion tracer protocol with PET was employed in humans at 2.5 and 26.5 hours after administration of the LY2940094 dose. The RO was calculated from the change in regional distributional volume (VT) corrected for nondisplaceable volume using Lasson plots. The RO followed a simple Emax relationship to plasma LY2940094 concentration, reaching near complete occupancy in both species. For rat hypothalamus, the plasma concentration at half-maximum RO (EC50) was 5.8 ng/ml. In humans, LY2940094 was well tolerated and safe over the 4-40 mg dose range, and it peaked in plasma at 2 to 6 hours after a 1- to 2-hour lag, with approximate dose-proportional exposure. After 4-40 mg doses, NOP RO was similar across the prefrontal cortex, occipital cortex, putamen, and thalamus, with EC50 of 2.94 to 3.46 ng/ml, less than 2-fold lower than in rats. Over 4-40 mg doses, LY2940094 mean plasma levels at peak and 24 hours were 7.93-102 and 1.17-14.1 ng/ml, corresponding to the cross-region average NOP RO of 73%-97% and 28%-82%, respectively. The rat EC50 translates well to humans. LY2940094 readily penetrates the human brain, and a once-daily oral dose of 40 mg achieves sustainably high (>80%) NOP RO levels suitable for testing clinical efficacy.

Retest imaging of [11C]NOP-1A binding to nociceptin/orphanin FQ peptide (NOP) receptors in the brain of healthy humans.

[(11)C]NOP-1A is a novel high-affinity PET ligand for imaging nociceptin/orphanin FQ peptide (NOP) receptors. Here, we report reproducibility and reliability measures of binding parameter estimates for [(11)C]NOP-1A binding in the brain of healthy humans. After intravenous injection of [(11)C]NOP-1A, PET scans were conducted twice on eleven healthy volunteers on the same (10/11 subjects) or different (1/11 subjects) days. Subjects underwent serial sampling of radial arterial blood to measure parent radioligand concentrations. Distribution volume (VT; a measure of receptor density) was determined by compartmental (one- and two-tissue) modeling in large regions and by simpler regression methods (graphical Logan and bilinear MA1) in both large regions and voxel data. Retest variability and intraclass correlation coefficient (ICC) of VT were determined as measures of reproducibility and reliability respectively. Regional [(11)C]NOP-1A uptake in the brain was high, with a peak radioactivity concentration of 4-7 SUV (standardized uptake value) and a rank order of putamen>cingulate cortex>cerebellum. Brain time-activity curves fitted well in 10 of 11 subjects by unconstrained two-tissue compartmental model. The retest variability of VT was moderately good across brain regions except cerebellum, and was similar across different modeling methods, averaging 12% for large regions and 14% for voxel-based methods. The retest reliability of VT was also moderately good in most brain regions, except thalamus and cerebellum, and was similar across different modeling methods averaging 0.46 for large regions and 0.48 for voxels having gray matter probability >20%. The lowest retest variability and highest retest reliability of VT were achieved by compartmental modeling for large regions, and by the parametric Logan method for voxel-based methods. Moderately good reproducibility and reliability measures of VT for [(11)C]NOP-1A make it a useful PET ligand for comparing NOP receptor binding between different subject groups or under different conditions in the same subject.

Evaluation in vitro and in animals of a new 11C-labeled PET radioligand for metabotropic glutamate receptors 1 in brain.

PURPOSE: Two allosteric modulators of the group I metabotropic glutamate receptors (mGluR1 and mGluR5) were evaluated as positron emission tomography (PET) radioligands for mGluR1. METHODS: LY2428703, a full mGluR1 antagonist (IC(50) 8.9 nM) and partial mGluR5 antagonist (IC(50) 118 nM), and LSN2606428, a full mGluR1 and mGluR5 antagonist (IC(50) 35.3 nM and 10.2 nM, respectively) were successfully labeled with (11)C and evaluated as radioligands for mGluR1. The pharmacology of LY2428703 was comprehensively assessed in vitro and in vivo, and its biodistribution was investigated by liquid chromatography-mass spectrometry/mass spectrometry, and by PET imaging in the rat. In contrast, LSN2606428 was only evaluated in vitro; further evaluation was stopped due to its unfavorable pharmacological properties and binding affinity. RESULTS: (11)C-LY2428703 showed promising characteristics, including: (1) high potency for binding to human mGluR1 (IC(50) 8.9 nM) with no significant affinity for other human mGlu receptors (mGluR2 through mGluR8); (2) binding to brain displaceable by administration of an mGluR1 antagonist; (3) only one major radiometabolite in both plasma and brain, with a negligible brain concentration (with 3.5 % of the total radioactivity in cerebellum) and no receptor affinity; (4) a large specific and displaceable signal in the mGluR1-rich cerebellum with no significant in vivo affinity for mGluR5, as shown by PET studies in rats; and (5) lack of substrate behavior for efflux transporters at the blood-brain barrier, as shown by PET studies conducted in wild-type and knockout mice. CONCLUSION: (11)C-LY2428703, a new PET radioligand for mGluR1 quantification, displayed promising characteristics both in vitro and in vivo in rodents.

Clinical Characterization of [18F]T-008, a Cholesterol 24-Hydroxylase PET Ligand: Dosimetry, Kinetic Modeling, Variability, and Soticlestat Occupancy.

This series of studies characterized [18F]T-008, a PET radiotracer for imaging cholesterol 24-hydroxylase (CH24H), in healthy volunteers (ClinicalTrials.gov identifier NCT02497235). Assessments included radiation dosimetry, kinetic modeling, test-retest variability (TRT) evaluation, and a dose occupancy evaluation using soticlestat, a selective CH24H inhibitor. Soticlestat is currently in phase 3 development for the treatment of seizures in Dravet syndrome and Lennox-Gastaut syndrome. Methods: In the dosimetry study, 5 participants (3 men) underwent serial whole-body scans to estimate organ-absorbed doses and effective doses of [18F]T-008 using OLINDA/EXM 1.1. For the kinetic modeling and TRT study, 6 participants (all men) underwent two 210-min dynamic [18F]T-008 PET scans with arterial blood sampling. The regional total volume of distribution was estimated using a 1-tissue-compartment model, a 2-tissue-compartment model, and Logan graphic analysis. In the dose occupancy study, 11 participants (all men) underwent 120-min scans at baseline and 2 time points (peak and trough) after receiving single oral doses of soticlestat (50-600 mg). The relationship between effect-site soticlestat concentration and brain occupancy was evaluated with a specially developed pharmacokinetic model and a saturable maximal occupancy model. Results: The estimated mean whole-body effective dose was 0.0292 mSv/MBq (SD, 0.00147 mSv/MBq). [18F]T-008 entered the brain rapidly, with a distribution consistent with known CH24H distribution densities. The 2-tissue-compartment model and Logan graphic analysis best described the tracer kinetics. The mean TRT for estimating total volume of distribution was 7%-15%. Single doses of soticlestat in the range 50-600 mg resulted in occupancies of 64%-96% at 2 h and 11%-79% at 24 h. The estimated half-maximal effect-site concentration of soticlestat was 5.52 ng/mL. Conclusion: [18F]T-008 is a suitable PET radiotracer for quantitatively analyzing CH24H in the human brain. Using [18F]T-008 and PET, we demonstrated that soticlestat was brain-penetrant and established target engagement by displacing [18F]T-008 in a dose-dependent manner in the brain.

Phenotypic differences between female and male individuals with suspicion of autism spectrum disorder.

BACKGROUND: Although autism spectrum disorder (ASD) is a common developmental disorder, our knowledge about a behavioral and neurobiological female phenotype is still scarce. As the conceptualization and understanding of ASD are mainly based on the investigation of male individuals, females with ASD may not be adequately identified by routine clinical diagnostics. The present machine learning approach aimed to identify diagnostic information from the Autism Diagnostic Observation Schedule (ADOS) that discriminates best between ASD and non-ASD in females and males. METHODS: Random forests (RF) were used to discover patterns of symptoms in diagnostic data from the ADOS (modules 3 and 4) in 1057 participants with ASD (18.1% female) and 1230 participants with non-ASD (17.9% % female). Predictive performances of reduced feature models were explored and compared between females and males without intellectual disabilities. RESULTS: Reduced feature models relied on considerably fewer features from the ADOS in females compared to males, while still yielding similar classification performance (e.g., sensitivity, specificity). LIMITATIONS: As in previous studies, the current sample of females with ASD is smaller than the male sample and thus, females may still be underrepresented, limiting the statistical power to detect small to moderate effects. CONCLUSION: Our results do not suggest the need for new or altered diagnostic algorithms for females with ASD. Although we identified some phenotypic differences between females and males, the existing diagnostic tools seem to sufficiently capture the core autistic features in both groups.

Endogenous dopamine release in the human brain as a pharmacodynamic biomarker: evaluation of the new GPR139 agonist TAK-041 with [11C]PHNO PET.

The use of positron emission tomography (PET) in early-phase development of novel drugs targeting the central nervous system, is well established for the evaluation of brain penetration and target engagement. However, when novel targets are involved a suitable PET ligand is not always available. We demonstrate an alternative approach that evaluates the attenuation of amphetamine-induced synaptic dopamine release by a novel agonist of the orphan G-protein-coupled receptor GPR139 (TAK-041). GPR139 agonism is a novel candidate mechanism for the treatment of schizophrenia and other disorders associated with social and cognitive dysfunction. Ten healthy volunteers underwent [11C]PHNO PET at baseline, and twice after receiving an oral dose of d-amphetamine (0.5 mg/kg). One of the post-d-amphetamine scans for each subject was preceded by a single oral dose of TAK-041 (20 mg in five; 40 mg in the other five participants). D-amphetamine induced a significant decrease in [11C]PHNO binding potential relative to the non-displaceable component (BPND) in all regions examined (16-28%), consistent with increased synaptic dopamine release. Pre-treatment with TAK-041 significantly attenuated the d-amphetamine-induced reduction in BPND in the a priori defined regions (putamen and ventral striatum: 26% and 18%, respectively). The reduction in BPND was generally higher after the 40 mg than the 20 mg TAK-041 dose, with the difference between doses reaching statistical significance in the putamen. Our findings suggest that TAK-041 enters the human brain and interacts with GPR139 to affect endogenous dopamine release. [11C]PHNO PET is a practical method to detect the effects of novel drugs on the brain dopaminergic system in healthy volunteers, in the early stages of drug development.

Is the Combination of ADOS and ADI-R Necessary to Classify ASD? Rethinking the "Gold Standard" in Diagnosing ASD.

Diagnosing autism spectrum disorder (ASD) requires extensive clinical expertise and training as well as a focus on differential diagnoses. The diagnostic process is particularly complex given symptom overlap with other mental disorders and high rates of co-occurring physical and mental health concerns. The aim of this study was to conduct a data-driven selection of the most relevant diagnostic information collected from a behavior observation and an anamnestic interview in two clinical samples of children/younger adolescents and adolescents/adults with suspected ASD. Via random forests, the present study discovered patterns of symptoms in the diagnostic data of 2310 participants (46% ASD, 54% non-ASD, age range 4-72 years) using data from the combined Autism Diagnostic Observation Schedule (ADOS) and Autism Diagnostic Interview-Revised (ADI-R) and ADOS data alone. Classifiers built on reduced subsets of diagnostic features yield satisfactory sensitivity and specificity values. For adolescents/adults specificity values were lower compared to those for children/younger adolescents. The models including ADOS and ADI-R data were mainly built on ADOS items and in the adolescent/adult sample the classifier including only ADOS items performed even better than the classifier including information from both instruments. Results suggest that reduced subsets of ADOS and ADI-R items may suffice to effectively differentiate ASD from other mental disorders. The imbalance of ADOS and ADI-R items included in the models leads to the assumption that, particularly in adolescents and adults, the ADI-R may play a lesser role than current behavior observations.

Identification of the most indicative and discriminative features from diagnostic instruments for children with autism.

Background: Diagnosing autism spectrum disorder (ASD) is complex and time-consuming. The present work systematically examines the importance of items from the Autism Diagnostic Interview-Revised (ADI-R) and Autism Diagnostic Observation Schedule (ADOS) in discerning children with and without ASD. Knowledge of the most discriminative features and their underlying concepts may prove valuable for the future training tools that assist clinicians to substantiate or extenuate a suspicion of ASD in nonverbal and minimally verbal children. Methods: In two samples of nonverbal (N = 466) and minimally verbal (N = 566) children with ASD (N = 509) and other mental disorders or developmental delays (N = 523), we applied random forests (RFs) to (i) the combination of ADI-R and ADOS data versus (ii) ADOS data alone. We compared the predictive performance of reduced feature models against outcomes provided by models containing all features. Results: For nonverbal children, the RF classifier indicated social orientation to be most powerful in differentiating ASD from non-ASD cases. In minimally verbal children, we find language/speech peculiarities in combination with facial/nonverbal expressions and reciprocity to be most distinctive. Conclusion: Based on machine learning strategies, we carve out those symptoms of ASD that prove to be central for the differentiation of ASD cases from those with other developmental or mental disorders (high specificity in minimally verbal children). These core concepts ought to be considered in the future training tools for clinicians.

Biodistribution and dosimetry in humans of two inverse agonists to image cannabinoid CB1 receptors using positron emission tomography.

PURPOSE: Cannabinoid subtype 1 (CB(1)) receptors are found in nearly every organ in the body, may be involved in several neuropsychiatric and metabolic disorders, and are therefore an active target for pharmacotherapy and biomarker development. We recently reported brain imaging of CB(1) receptors with two PET radioligands: (11)C-MePPEP and (18)F-FMPEP-d (2). Here we describe the biodistribution and dosimetry estimates for these two radioligands. METHODS: Seven healthy subjects (four men and three women) underwent whole-body PET scans for 120 min after injection with (11)C-MePPEP. Another seven healthy subjects (two men and five women) underwent whole-body PET scans for 300 min after injection with (18)F-FMPEP-d (2). Residence times were acquired from regions of interest drawn on tomographic images of visually identifiable organs for both radioligands and from radioactivity excreted in urine for (18)F-FMPEP-d (2). RESULTS: The effective doses of (11)C-MePPEP and (18)F-FMPEP-d (2) are 4.6 and 19.7 microSv/MBq, respectively. Both radioligands demonstrated high uptake of radioactivity in liver, lung, and brain shortly after injection and accumulated radioactivity in bone marrow towards the end of the scan. After injection of (11)C-MePPEP, radioactivity apparently underwent hepatobiliary excretion only, while radioactivity from (18)F-FMPEP-d (2) showed both hepatobiliary and urinary excretion. CONCLUSION: (11)C-MePPEP and (18)F-FMPEP-d (2) yield an effective dose similar to other PET radioligands labeled with either (11)C or (18)F. The high uptake in brain confirms the utility of these two radioligands to image CB(1) receptors in brain, and both may also be useful to image CB(1) receptors in the periphery.

Quantitation of cannabinoid CB1 receptors in healthy human brain using positron emission tomography and an inverse agonist radioligand.

[11C]MePPEP is a high affinity, CB1 receptor-selective, inverse agonist that has been studied in rodents and monkeys. We examined the ability of [11C]MePPEP to quantify CB1 receptors in human brain as distribution volume calculated with the "gold standard" method of compartmental modeling and compared results with the simple measure of brain uptake. A total of 17 healthy subjects participated in 26 positron emission tomography (PET) scans, with 8 having two PET scans to assess retest variability. After injection of [11C]MePPEP, brain uptake of radioactivity was high (e.g., 3.6 SUV in putamen at approximately 60 min) and washed out very slowly. A two-tissue compartment model yielded values of distribution volume (which is proportional to receptor density) that were both well identified (SE 5%) and stable between 60 and 210 min. The simple measure of brain uptake (average concentration of radioactivity between 40 and 80 min) had good retest variability ( approximately 8%) and moderate intersubject variability (16%, coefficient of variation). In contrast, distribution volume had two-fold greater retest variability ( approximately 15%) and, thus, less precision. In addition, distribution volume had three-fold greater intersubject variability ( approximately 52%). The decreased precision of distribution volume compared to brain uptake was likely due to the slow washout of radioactivity from brain and to noise in measurements of the low concentrations of [11C]MePPEP in plasma. These results suggest that brain uptake can be used for within subject studies (e.g., to measure receptor occupancy by medications) but that distribution volume remains the gold standard for accurate measurements between groups.

Mapping of the norepinephrine transporter in the human brain using PET with (S,S)-[18F]FMeNER-D2.

We have evaluated the detailed mapping of the norepinephrine transporter (NET) in the human brain with (S,S)-[(18)F]FMeNER-D(2) using a template method and the generation of functional ROIs based on the PET information. Brain PET measurements were performed from 90 to 210 min after the injection of (S,S)-[(18)F]FMeNER-D(2) in 20 healthy male subjects. Binding potential (BP(ND)) was calculated as late time ratio of the target region to the reference region (caudate) minus one. BP(ND) template images were generated from mean parametric images obtained in a group of 10 subjects using SPM2. On the BP(ND)/MRI template images, functional ROIs based on several different BP(ND) thresholds for the thalamus and brainstem were generated automatically using PMOD 2.8 software in addition to anatomical ROIs. PET/MRI data of another group of 10 subjects were used to evaluate the validity of the template method and the functional ROIs. NET BP(ND) template images demonstrated higher binding in the medial thalamus whereas the anterior and the pulvinar divisions had lower binding. In the brainstem, high binding was detected around the cerebral aqueduct of the midbrain and within the dorsal pons, in a volume comprising locus coeruleus. Functional ROIs with higher BP(ND) thresholds naturally yielded higher BP(ND) and lower coefficients of variance than did anatomical ROIs. This study indicated that (S,S)-[(18)F]FMeNER-D(2) combined with a template method provides detailed information on the distribution of NET in vivo and that functional ROIs on the template would be useful in further clinical studies.

The PET radioligand [11C]MePPEP binds reversibly and with high specific signal to cannabinoid CB1 receptors in nonhuman primate brain.

The cannabinoid CB(1) receptor is one of the most abundant G protein-coupled receptors in the brain and is a promising target of therapeutic drug development. Success of drug development for neuropsychiatric indications is significantly enhanced with the ability to directly measure spatial and temporal binding of compounds to receptors in central compartments. We assessed the utility of a new positron emission tomography (PET) radioligand to image CB(1) receptors in monkey brain. [(11)C]MePPEP ((3R,5R)-5-(3-methoxy-phenyl)-3-((R)-1-phenyl-ethylamino)-1-(4-trifluoromethyl-phenyl)-pyrrolidin-2-one) has high CB(1) affinity (K(b)=0.574+/-0.207 nM) but also moderately high lipophilicity (measured LogD(7.4)=4.8). After intravenous injection of [(11)C]MePPEP, brain activity reached high levels of almost 600% standardized uptake value (SUV) within 10-20 min. The regional uptake was consistent with the distribution of CB(1) receptors, with high radioactivity in striatum and cerebellum and low in thalamus and pons. Injection of pharmacological doses of CB(1)-selective agents confirmed that the tracer doses of [(11)C]MePPEP reversibly labeled CB(1) receptors. Preblockade or displacement with two CB(1) selective agents (ISPB; (4-(3-cyclopentyl-indole-1-sulfonyl)-N-(tetrahydro-pyran-4-ylmethyl)-benzamide) and rimonabant) showed that the majority (>89%) of brain uptake in regions with high receptor densities was specific and reversibly bound to CB(1) receptors in the high binding regions. [(11)C]MePPEP was rapidly removed from arterial plasma. Regional brain uptake could be quantified as distribution volume relative to the concentration of parent radiotracer in plasma. The P-glycoprotein (P-gp) inhibitor DCPQ ((R)-4-[(1a,6,10b)-1,1-dichloro-1,1a,6,10b-tetrahydrodibenzo[a,e]cyclopropa[c]cyclohepten-6-yl]-[(5-quinolinyloxy)methyl]-1-piperazineethanol) did not significantly increase brain uptake of [(11)C]MePPEP, suggesting it is not a substrate for this efflux transporter at the blood-brain barrier. [(11)C]MePPEP is a radioligand with high brain uptake, high specific signal to CB(1) receptors, and adequately fast washout from brain that allows quantification with (11)C (half-life=20 min). These promising results in monkey justify studying this radioligand in human subjects.

Imaging the norepinephrine transporter with positron emission tomography: initial human studies with (S,S)-[18F]FMeNER-D2.

INTRODUCTION: (S,S)-[(18)F]FMeNER-D(2) is a recently developed positron emission tomography (PET) ligand for in vivo quantification of norepinephrine transporter. A monkey occupancy study with the radioligand indicated that (S,S)-[(18)F]FMeNER-D(2) can be useful for quantitative PET analysis. In this preliminary study, regional distributions in the living human brain were evaluated. MATERIALS AND METHODS: Brain PET measurements were performed for a total of 255 min after the injection of 188.3 +/- 5.7 MBq of (S,S)-[(18)F]FMeNER-D(2) in four healthy male subjects. Regions of interests were drawn on the thalamus and the caudate in the coregistered MRI/PET images. RESULTS: (S,S)-[(18)F]FMeNER-D(2) displayed good brain penetration and selective retention in regions rich in norepinephrine reuptake sites. The transient peak equilibrium was reached during the PET measurements. The ratios of radioactivity uptake in the thalamus to that in the caudate were 1.50 +/- 0.06 for the time period of 90-255 min. CONCLUSION: The present preliminary investigation indicates that (S,S)-[(18)F]FMeNER-D(2) has suitable characteristics for probing the norepinephrine reuptake system with PET in the human brain.

Reduced serotonin-1A receptor binding in social anxiety disorder.

BACKGROUND: Results from studies in serotonin-1A (5-HT1A) knockout mice and previous positron emission tomography (PET) studies in humans imply a role for 5-HT1A receptors in normal state anxiety as well as in certain anxiety disorders. The objective of this study was to investigate 5-HT1A receptor binding potential (BP) in social anxiety disorder (SAD). METHODS: Using PET and [carbonyl-11C]WAY-100635, we compared a homogeneous group of 12 unmedicated, male SAD patients with 18 healthy control subjects (HC). A multivariate ANOVA with all regional BP values as dependent variables, age and four radiochemical variables as covariates was performed. RESULTS: We found a significantly lower 5-HT1A BP in several limbic and paralimbic areas but not in the hippocampus (p = .234) of SAD patients. The difference in 5-HT1A binding was most significant in the amygdala (-21.4%; p = .003). There was also a more than 20% lower 5-HT(1A) BP of SAD patients in the anterior cingulate cortex (p = .004), insula (p = .003), and dorsal raphe nuclei (p = .030). CONCLUSIONS: The lower 5-HT1A binding in the amygdala and mesiofrontal areas of SAD patients is consistent with 1) preclinical findings of elevated anxiety in 5-HT1A knockout mice, 2) a previous PET study in healthy volunteers showing an inverse correlation between 5-HT1A BP and state anxiety, and 3) another human PET study in patients with panic disorder showing reduced 5-HT1A binding, thus corroborating the potential validity of 5-HT1A receptors as targets in the treatment of human anxiety disorders.

Higher serotonin transporter occupancy after multiple dose administration of escitalopram compared to citalopram: an [123I]ADAM SPECT study.

OBJECTIVES: Previous studies have investigated the occupancy of the serotonin reuptake transporter (SERT) after clinical doses of citalopram and other selective serotonin reuptake inhibitors. In the present study, the occupancies of SERT after multiple doses of escitalopram and citalopram were compared using the radioligand [(123)I]ADAM and single photon emission computed tomography (SPECT). METHODS: Fifteen healthy subjects received escitalopram 10 mg/day (n = 6) or citalopram 20 mg/day (n = 9) for a total of 10 days. SERT occupancies in midbrain were determined with SPECT and [(123)I]ADAM at three different time points: at baseline (no medication) and at 6 and 54 h after last drug intake. RESULTS: At 6 h after the last dose, mean SERT occupancies were 81.5 +/- 5.4% (mean+/-SD) for escitalopram and 64.0 +/- 12.7% for citalopram (p < 0.01). At 54 h after the last dose, mean SERT occupancies were 63.3 +/- 12.1% for escitalopram and 49.0 +/- 11.7% for citalopram (p < 0.05). The plasma concentrations of the S-enantiomer were of the same magnitude in both substances. For both drugs, the elimination rate of the S-enantiomer in plasma was markedly higher than the occupancy decline rate in the midbrain. CONCLUSION: The significantly higher occupancy of SERT after multiple doses of escitalopram compared to citalopram indicates an increased inhibition of SERT by escitalopram. The results can also be explained by an attenuating effect of R-citalopram on the occupancy of S-citalopram at the SERT.

Striatal D(2) receptor occupancy in bipolar patients treated with olanzapine.

We explored the relationship between striatal dopamine-2 (D(2)) receptor occupancy and extra-pyramidal symptoms (EPS) in bipolar patients receiving olanzapine. Seventeen patients with a DSM-IV diagnosis of bipolar disorder were treated with 5-45 mg/day olanzapine for at least 14 days. After that period, D(2) receptor occupancy was determined using Iodobenzamide (IBZM) and SPECT. EPS were assessed by the Simpson-Angus Scale (SAS) and Barnes-Akathisia Scale (BAS). We found a dose-dependent increase in occupancy: 5 mg led to 28-50%, 10 mg to 40-68%, 15 mg to 69%, 20 mg to 57-66%, 30 mg to 66% and 45 mg to 80% D(2) receptor occupancy; and a significant correlation between plasma levels and occupancy (R(2)=.55, P=.001). Similar to schizophrenic patients, bipolar patients did not exhibit EPS at D(2) occupancy levels of 28 to 80%. Although we did not find an increased vulnerability for acute EPS in bipolar patients receiving olanzapine at clinical relevant doses, this needs to be replicated with larger sample sizes.

Atomoxetine occupies the norepinephrine transporter in a dose-dependent fashion: a PET study in nonhuman primate brain using (S,S)-[18F]FMeNER-D2.

RATIONALE: Atomoxetine is a potent and selective norepinephrine transporter (NET) reuptake inhibitor acting as a nonstimulant for the treatment of attention-deficit/hyperactivity disorder (ADHD). Previous positron emission tomography (PET) studies had failed to demonstrate the feasibility of measuring a dose-dependent and saturable NET occupancy in human brain using [11C]MeNER. OBJECTIVES: To determine if atomoxetine occupies NET in a dose-dependent fashion using (S,S)-[18F]FMeNER-D2 in nonhuman primate brain. METHODS: A total of eight PET measurements were performed in two cynomolgus monkeys. Each monkey was examined four times with PET: under baseline conditions and after steady-state infusion with 0.03, 0.06, or 0.12 mg/kg/h of atomoxetine. A prolonged intravenous (i.v.) infusion design was developed rather than an i.v. bolus to better mimic an oral absorption profile and to reach plasma steady state. RESULTS: During baseline conditions, (S,S)-[18F]FMeNER-D2 uptake was highest in the locus coeruleus, thalamus, mesencephalon, and the cingulate gyrus, whereas the radioactivity in the caudate was low. Peak equilibrium measurements were achieved using (S,S)-[18F]FMeNER-D2 in contrast to the previously reported data for [11C]MeNER. After administration of atomoxetine, a dose-dependent occupancy from 38 to 82% was observed for various brain regions known to contain high densities of NET. CONCLUSIONS: This is the first in vivo PET study to successfully demonstrate the ability to measure a dose-dependent change in NET occupancy in brain using (S,S)-[18F]FMeNER-D2. Furthermore, an asymptotic relationship between N-desmethylatomoxetine plasma concentration and NET occupancy was established. In total, these data encourage further PET studies using (S,S)-[18F]FMeNER-D2 in humans.

Volumetric MRI measurement of caudate nuclei in antipsychotic-naive patients suffering from a first episode of psychosis.

Magnetic resonance imaging (MRI) studies measuring basal ganglia volumes in first episode patients suggest that treatment with typical neuroleptics leads to alteration in these brain structures. However, caudate nuclei volumes (CNV) of untreated first-episode patients may even be smaller than in healthy controls. We investigated whether CNV of newly diagnosed neuroleptic-naive psychotic patients differ as compared to an age- and sex-matched healthy control group to detect possible treatment effects early in the course of this illness. Magnetic resonance images were acquired in 37 un-medicated psychotic patients and 37 healthy controls. Ten of the patients were re-examined after 12 weeks of treatment with the second generation antipsychotic quetiapine. Regions of interest (ROI) delineating the caudate nuclei bilaterally were drawn manually using Brain Image software. The neuroleptic-naive patients showed a mean CNV of 8.40 cc (SD=1.01) and the controls of 8.55 cc (SD=1.16). There was no significant difference between groups (F=.600; P=.441). In contrast to previous studies in patients treated with typical neuroleptics, this cross-sectional MRI study did not find significant differences in CNV of neuroleptic-naive first-episode patients compared to healthy controls.

Brain serotonin 5-HT(1A) receptor binding in schizophrenia measured by positron emission tomography and [11C]WAY-100635.

BACKGROUND: Results of postmortem studies show an elevation in serotonin-1A (5-hydroxytryptamine-1A [5-HT(1A)]) receptor density in the prefrontal and temporal cortices of patients with schizophrenia. This study examined 5-HT(1A) receptors in vivo in patients with schizophrenia using positron emission tomography and [carbonyl-(11)C]-N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexane carboxamide ([(11)C]WAY-100635). METHODS: The 5-HT(1A) binding potential of 14 antipsychotic drug-naïve patients with a DSM-IV diagnosis of schizophrenia was compared with that of 14 age-matched healthy controls. Positron emission tomography data were analyzed using 9 cortical regions of interest, which were delineated on a coregistered magnetic resonance image and transferred to the positron emission tomographic image, with the cerebellum as the reference region for a simplified reference tissue model. We also performed a voxel-wise comparison using statistical parametric mapping. RESULTS: The region of interest-based analysis revealed a significant mean +/- SD cortical 5-HT(1A) receptor binding potential increase of 7.1% +/- 6.4% in patients with schizophrenia (F = 2.975; P =.02); local differences were +20% in the left medial temporal cortex (F = 9.339;P =.005) and +13% in the right medio temporal cortex (F = 4.453; P =.045). There were no significant differences in regional tracer delivery or cerebellar [(11)C]WAY-100635 uptake. The voxel-based analysis also confirmed a group difference in the left medial temporal cortex. CONCLUSIONS: The biological significance of elevated 5-HT(1A) receptor density in schizophrenia remains unclear. Given the location of 5-HT(1A) receptors on pyramidal cells, this elevation may reflect an abnormal glutamatergic network. Our finding needs to be viewed in light of preclinical evidence supporting a role for 5-HT(1A) receptors in mediating antipsychotic action and extrapyramidal adverse effects of drugs.