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This phase 1 trial (NCT01938846) determined the maximum tolerated dose (MTD) of the mTOR serine/threonine kinase inhibitor, BI 860585, as monotherapy and with exemestane or paclitaxel in patients with advanced solid tumors. This 3+3 dose-escalation study assessed BI 860585 monotherapy (5-300 mg/day; Arm A), BI 860585 (40-220 mg/day; Arm B) with 25 mg/day exemestane, and BI 860585 (80-220 mg/day; Arm C) with 60-80 mg/m 2 /week paclitaxel, in 28-day cycles. Primary endpoints were the number of patients with dose-limiting toxicities (DLTs) in cycle 1 and the MTD. Forty-one, 25, and 24 patients were treated (Arms A, B, and C). DLTs were observed in four (rash ( n = 2), elevated alanine aminotransferase/aspartate aminotransferase, diarrhea), four (rash ( n = 3), stomatitis, and increased gamma-glutamyl transferase), and two (diarrhea, increased blood creatine phosphokinase) patients in cycle 1. The BI 860585 MTD was 220 mg/day (Arm A) and 160 mg/day (Arms B and C). Nine patients achieved an objective response (Arm B: Four partial responses (PRs); Arm C: Four PRs; one complete response). The disease control rate was 20%, 28%, and 58% (Arms A, B, and C). The most frequent treatment-related adverse events (AEs) were hyperglycemia (54%) and diarrhea (39%) (Arm A); diarrhea (40%) and stomatitis (40%) (Arm B); fatigue (58%) and diarrhea (58%) (Arm C). The MTD was determined in all arms. Antitumor activity was observed with BI 860585 monotherapy and in combination with exemestane or paclitaxel.

Recent genetic, molecular and post-mortem studies suggest impaired dopamine (DA)-D2 receptor (D2R) trafficking in patients with schizophrenia (SZ). Imaging and preclinical studies have shown agonist-induced D2R internalization can be imaged with positron emission tomography (PET) using D2R radiotracers combined with psychostimulant challenge. This is feasible if radiotracer binding is measured when postchallenge DA levels have returned to baseline, following the initial competition phase between DA and radiotracer for binding to D2R. Here we used 'late-phase' imaging after challenge to test the hypothesis that impaired D2R internalization in SZ leads to blunted late-phase displacement, or a faster return to baseline, in patients compared with healthy controls (HCs). We imaged 10 patients with SZ and 9 HCs with PET and [ 11 C]raclopride at baseline and two times (3-5 and 6-10 h) following 0.5 mg kg -1 dextroamphetamine. We measured binding potential relative to non-displaceable compartment (BP ND ) and derived percent reduction from baseline (ΔBP ND ) for each postamphetamine scan. To test the hypothesis that time course of return of striatal BP ND to baseline differed between SZ and HCs, we implemented a linear model with ΔBP ND as dependent variable, time after amphetamine as repeated measure and time after amphetamine and diagnostic group as fixed effects. Neither diagnostic group nor interaction of diagnostic group-by-time after amphetamine significantly affected striatal ΔBP ND (F=1.38, P=0.26; F=0.51, P=0.61). These results show similar pattern of return of BP ND to baseline as a function of time in patients with SZ and HC, suggesting that striatal D2R internalization as measured by our imaging paradigm is normal in patients with SZ.

Posterior reversible encephalopathy syndrome (PRES) is a clinical and radiological syndrome characterized by acute hypertension, headache, decreased level of consciousness, visual disturbances and seizures associated with characteristic neuroimaging changes indicative of vasogenic edema of the posterior cerebral white matter. Several medical conditions have been associated with PRES including hypertensive encephalopathy and eclampsia. The use of cytotoxic and immunosuppressant drugs, such as those which target vascular endothelial growth factor (VEGF), have also been implicated. We report here the case of a 71-year-old woman with metastatic clear cell renal carcinoma who developed PRES 3 months after commencing sorafenib. Elevated blood pressure (BP) was recorded, and MRI of the brain) of the brain showed asymmetric areas of increased signal intensity within the supratentorial white matter suggestive of PRES. Clinical and radiological features rapidly improved with BP control and discontinuation of sorafenib. Sorafenib was resumed with no sign of PRES recurrence. The present case report supports the hypothesis that, in selected patients, the re-introduction of anti-VEGF therapies after PRES is feasible., (© 2016 S. Karger AG, Basel.)

Unlabelled: The synaptic vesicle glycoprotein 2A (SV2A) is found in secretory vesicles in neurons and endocrine cells. PET with a selective SV2A radiotracer will allow characterization of drugs that modulate SV2A (e.g., antiepileptic drugs) and potentially could be a biomarker of synaptic density (e.g., in neurodegenerative disorders). Here we describe the synthesis and characterization of the SV2A PET radiotracer (11)C-UCB-J ((R)-1-((3-((11)C-methyl-(11)C)pyridin-4-yl)methyl)-4-(3,4,5-trifluorophenyl)pyrrolidin-2-one) in nonhuman primates, including whole-body biodistribution., Methods: (11)C-UCB-J was prepared by C-(11)C-methylation of the 3-pyridyl trifluoroborate precursor with (11)C-methyl iodide via the Suzuki-Miyaura cross-coupling method. Rhesus macaques underwent multiple scans including coinjection with unlabeled UCB-J (17, 50, and 150 μg/kg) or preblocking with the antiepileptic drug levetiracetam at 10 and 30 mg/kg. Scans were acquired for 2 h with arterial sampling and metabolite analysis to measure the input function. Regional volume of distribution (VT) was estimated using the 1-tissue-compartment model. Target occupancy was assessed using the occupancy plot; the dissociation constant (Kd) was determined by fitting self-blocking occupancies to a 1-site model, and the maximum number of receptor binding sites (Bmax) values were derived from baseline VT and from the estimated Kd and the nondisplaceable distribution volume (VND)., Results: (11)C-UCB-J was synthesized with greater than 98% purity. (11)C-UCB-J exhibited high free fraction (0.46 ± 0.02) and metabolized at a moderate rate (39% ± 5% and 24% ± 3% parent remaining at 30 and 90 min) in plasma. In the monkey brain, (11)C-UCB-J displayed high uptake and fast kinetics. VT was high (∼25-55 mL/cm(3)) in all gray matter regions, consistent with the ubiquitous expression of SV2A. Preblocking with 10 and 30 mg/kg of levetiracetam resulted in approximately 60% and 90% occupancy, respectively. Analysis of the self-blocking scans yielded a Kd estimate of 3.4 nM and Bmax of 125-350 nM, in good agreement with the in vitro inhibition constant (Ki) of 6.3 nM and regional Bmax in humans. Whole-body biodistribution revealed that the liver and the brain are the dose-limiting organs for males and females, respectively., Conclusion: (11)C-UCB-J exhibited excellent characteristics as an SV2A PET radiotracer in nonhuman primates. The radiotracer is currently undergoing first-in-human evaluation., (© 2016 by the Society of Nuclear Medicine and Molecular Imaging, Inc.)

Unlabelled: Antagonism of 5-hydroxytrypamine-6 (5HT6) receptors is associated with procognitive effects in preclinical species, suggesting a therapeutic potential for this mechanism in Alzheimer disease (AD) and other cognitive diseases. In a phase 2 dose study, SB742457, a novel 5HT6 antagonist, showed increasing procognitive effects in patients with AD as the dose increased, with a procognitive signal in AD patients at a dose of 35 mg/d superior to the other doses tested (5 and 15 mg/d)., Methods: In this article, we describe the quantification and pharmacologic selectivity of a new 5HT6 PET ligand ((11)C-GSK215083) in healthy volunteers and its use to measure occupancies achieved at various doses of SB742457., Results: Kinetic analysis of (11)C-GSK215083 uptake in the human brain demonstrated the multilinear model, MA2, to represent the method of choice when a blood input was available and the full tissue reference method when no input was available. Pharmacologic dissection of the in vivo (11)C-GSK215083-specific binding showed the ligand bound mostly the 5HT6 in the striatum (blocked by SB742457 but not by the selective 5-hydroxytryptamine-2A (5HT2A) antagonist ketanserin) and the 5HT2A in the frontal cortex (blocked by both ketanserin and SB742457). Repeated administration of SB742457 (3, 15, and 35 mg/d) saturated the 5HT6 receptors at all doses. In the cortex, 5HT2A receptor occupancy was 24% ± 6% (3 mg/d), 35% ± 4% (15 mg/d), and 58% ± 19% (35 mg/d; mean ± SD), suggesting a progressive engagement of 5HT2A as the dose increased., Conclusion: Collectively, these data support the use of (11)C-GSK215083 as a 5HT6 clinical imaging tool and suggest that blocking both the 5HT6 and the 5HT2A receptors may be required for the optimal therapeutic action of SB742457 in AD., (© 2015 by the Society of Nuclear Medicine and Molecular Imaging, Inc.)

Unlabelled: PET with selective adenosine 2A receptor (A2A) radiotracers can be used to study a variety of neurodegenerative and neuropsychiatric disorders in vivo and to support drug-discovery studies targeting A2A. The aim of this study was to describe the first in vivo evaluation of (18)F-MNI-444, a novel PET radiotracer for imaging A2A, in healthy human subjects., Methods: Ten healthy human volunteers were enrolled in this study; 6 completed the brain PET studies and 4 participated in the whole-body PET studies. Arterial blood was collected for invasive kinetic modeling of the brain PET data. Noninvasive methods of data quantification were also explored. Test-retest reproducibility was evaluated in 5 subjects. Radiotracer distribution and dosimetry was determined using serial whole-body PET images acquired over 6 h post-radiotracer injection. Urine samples were collected to calculate urinary excretion., Results: After intravenous bolus injection, (18)F-MNI-444 rapidly entered the brain and displayed a distribution consistent with known A2A densities in the brain. Binding potentials ranging from 2.6 to 4.9 were measured in A2A-rich regions, with an average test-retest variability of less than 10%. The estimated whole-body radiation effective dose was approximately 0.023 mSv/MBq., Conclusion: (18)F-MNI-444 is a useful PET radiotracer for imaging A2A in the human brain. The superior in vivo brain kinetic properties of (18)F-MNI-444, compared with previously developed A2A radiotracers, provide the opportunity to foster global use of in vivo A2A PET imaging in neuroscience research., (© 2015 by the Society of Nuclear Medicine and Molecular Imaging, Inc.)

Background: The ability to quantify the capacity of a central nervous system (CNS) drug to cross the human blood-brain barrier (BBB) provides valuable information for de-risking drug development of new molecules. Here, we present a study, where a suitable positron emission tomography (PET) ligand was not available for the evaluation of a potent muscarinic acetylcholine receptor type-1 (M1) allosteric agonist (GSK1034702) in the primate and human brain. Hence, direct radiolabelling of the novel molecule was performed and PET measurements were obtained and combined with in vitro equilibrium dialysis assays to enable assessment of BBB transport and estimation of the free brain concentration of GSK1034702 in vivo., Methods: GSK1034702 was radiolabelled with (11)C, and the brain distribution of [(11)C]GSK1034702 was investigated in two anaesthetised baboons and four healthy male humans. In humans, PET scans were performed (following intravenous injection of [(11)C]GSK1034702) at baseline and after a single oral 5-mg dose of GSK1034702. The in vitro brain and plasma protein binding of GSK1034702 was determined across a range of species using equilibrium dialysis., Results: The distribution of [(11)C]GSK1034702 in the primate brain was homogenous and the whole brain partition coefficient (V T) was 3.97. In contrast, there was mild regional heterogeneity for GSK1034702 in the human brain. Human whole brain V T estimates (4.9) were in broad agreement with primate V T and the f P/f ND ratio (3.97 and 2.63, respectively), consistent with transport by passive diffusion across the BBB., Conclusion: In primate and human PET studies designed to evaluate the transport of a novel M1 allosteric agonist (GSK1034702) across the BBB, we have demonstrated good brain uptake and BBB passage consistent with passive diffusion or active influx. These studies discharged some of the perceived development risks for GSK1034702 and provided information to progress the molecule into the next stage of clinical development., Trial Registration: Clinical trial details: 'Brain Uptake of GSK1034702: a Positron Emission Tomography (PET) Scan Study.'; clinicaltrial.gov identifier: NCT00937846 .

Several lines of evidence suggest that schizophrenia is associated with deficits in glutamatergic transmission at the N-methyl-d-aspartate (NMDA) receptors. Glycine is a NMDA receptor co-agonist, and extracellular levels of glycine are regulated in the forebrain by the glycine type-1 transporters (GlyT-1). GlyT-1 inhibitors elevate extracellular glycine and thus potentiate NMDA transmission. This mechanism represents a promising new avenue for the treatment of schizophrenia. Here, the recently introduced positron emission tomography radiotracer [11C]GSK931145 was used to quantify the relationship between occupancy of GlyT-1 by a GlyT-1 inhibitor, Org 25935, and its impact on spatial working memory performances in rhesus monkeys. The effect of Org 25935 on working memory was assessed both in control conditions and during a state of relative NMDA hypofunction induced by ketamine administration, at a dose selected for each animal to reduce task performance by about 50%. Under control conditions, Org 25935 had no effect on working memory at GlyT-1 occupancies lower than 75% and significantly impaired working memory at occupancies higher than 75%. Under ketamine conditions, Org 25935 reversed the deficit in working memory induced by ketamine and did so optimally in the 40-70% GlyT-1 occupancy range. The results confirm the efficacy of this mechanism to correct working memory deficits associated with NMDA hypofunction. These data also suggest the existence of an inverted-U dose-response curve in the potential therapeutic effect of this class of compounds.

Unlabelled: Motor symptoms in Parkinson disease (PD) are caused by a loss of dopamine input from the substantia nigra to the striatum. Blockade of adenosine 2A (A(2A)) receptors facilitates dopamine D(2) receptor function. In phase 2 clinical trials, A(2A) antagonists (istradefylline, preladenant, and tozadenant) improved motor function in PD. We developed a new A(2A) PET radiotracer, (18)F-MNI-444, and used it to investigate the relationship between plasma levels and A(2A) occupancy by preladenant and tozadenant in nonhuman primates (NHP)., Methods: A series of 20 PET experiments was conducted in 5 adult rhesus macaques. PET data were analyzed with both plasma-input (Logan graphical analysis) and reference-region-based (simplified reference tissue model and noninvasive Logan graphical analysis) methods. Whole-body PET images were acquired for radiation dosimetry estimates. Human pharmacokinetic parameters for tozadenant and preladenant were used to predict A(2A) occupancy in humans, based on median effective concentration (EC(50)) values estimated from the NHP PET measurements., Results: (18)F-MNI-444 regional uptake was consistent with A(2A) receptor distribution in the brain. Selectivity was demonstrated by dose-dependent blocking by tozadenant and preladenant. The specific-to-nonspecific ratio was superior to that of other A(2A) PET radiotracers. Pharmacokinetic modeling predicted that tozadenant and preladenant may have different profiles of A(2A) receptor occupancy in humans., Conclusion: (18)F-MNI-444 appears to be a better PET radiotracer for A(2A) imaging than currently available radiotracers. Assuming that EC(50) in humans is similar to that in NHP, it appears that tozadenant will provide a more sustained A(2A) receptor occupancy than preladenant in humans at clinically tested doses., (© 2014 by the Society of Nuclear Medicine and Molecular Imaging, Inc.)

Background and Purpose: This study aimed to investigate the relationship between the plasma concentration (PK) of the novel histamine H3 receptor antagonist, GSK239512, and the brain occupancy of H(3) receptors (RO) in healthy human volunteers., Experimental Approach: PET scans were obtained after i.v. administration of the H(3) -specific radioligand [(11) C]GSK189254. Each subject was scanned before and after single oral doses of GSK239512, at 4 and 24 h after dose. PET data were analysed by compartmental analysis, and regional RO estimates were obtained by graphical analysis of changes in the total volumes of distribution of the radioligand, followed by a correction for occupancy by the high affinity radioligand. The PK/RO relationship was analysed by a population-modelling approach, using the average PK of GSK239512 during each scan., Key Results: Following administration of GSK239512, there was a reduction in the brain uptake of [(11) C]GSK189254 in all regions, including cerebellum. RO at 4 h was higher than at 24 h, and the PK/RO model estimated a PK associated with 50% of RO of 0.0068 ng·mL(-1) . This corresponds to a free concentration of 4.50 × 10(-12 ) M (pK = 11.3)., Conclusions and Implications: The affinity of GSK239512 for brain H3 receptors in humans in vivo is much higher than that expected from studies in vitro, and higher than that observed in PET studies in pigs. The study illustrates the utility of carrying out PET studies in humans early in drug development, providing accurate quantification of GSK239512 RO in vivo as a function of time and dose., (© 2013 The British Pharmacological Society.)

Schizophrenia might be considered a neurodevelopmental disease. However, the fundamental process(es) associated with this disease remain(s) uncertain. Many lines of evidence suggest that schizophrenia is associated with excessive stimulation of dopamine D2 receptors in the associative striatum, with a lack of stimulation of dopamine D1 receptors in prefrontal cortex, and with modifications in prefrontal neuronal connectivity involving glutamate transmission at N-methyl aspartate (NMDA) receptors. This article, whilst briefly discussing the current knowledge of the disease, mainly concentrates on the NMDA hypofunction hypothesis. However, there are also potential consequences for a Dopamine imbalance on NMDA function. Thus, it is proposed that schizophrenia has a complex aetiology associated with strongly interconnected aberrations of dopamine and glutamate transmission., (Copyright © 2014. Published by Elsevier Ltd.)

Background: Atomoxetine (ATX), a drug for treatment of depression and ADHD, has a high affinity for the norepinephrine transporter (NET); however, our previous study showed it had a blocking effect similar to fluoxetine on binding of [(11)C]DASB, a selective serotonin transporter (SERT) ligand. Whether the therapeutic effects of ATX are due to inhibition of either or both transporters is not known. Here we report our comparative PET imaging studies with [(11)C]MRB (a NET ligand) and [(11)C]AFM (a SERT ligand) to evaluate in vivo IC50 values of ATX in monkeys., Methods: Rhesus monkeys were scanned up to four times with each tracer with up to four doses of ATX. ATX or saline (placebo) infusion began 2h before each PET scan, lasting until the end of the 2-h scan. The final infusion rates were 0.01-0.12mg/kg/h and 0.045-1.054mg/kg/h for the NET and SERT studies, respectively. ATX plasma levels and metabolite-corrected arterial input functions were measured. Distribution volumes (VT) and IC50 values were estimated., Results: ATX displayed dose-dependent occupancy on both NET and SERT, with a higher occupancy on NET: IC50 of 31±10 and 99±21ng/mL plasma for NET and SERT, respectively. At a clinically relevant dose (1.0-1.8mg/kg, approx. 300-600ng/mL plasma), ATX would occupy >90% of NET and >85% of SERT. This extrapolation assumes comparable free fraction of ATX in humans and non-human primates., Conclusion: Our data suggests that ATX at clinically relevant doses greatly occupies both NET and SERT. Thus, therapeutic modes of ATX action for treatment of depression and ADHD may be more complex than selective blockade of NET., (© 2013.)

The selection of a therapeutically meaningful dose of a novel pharmaceutical is a crucial step in drug development. Positron emission tomography (PET) allows the in vivo estimation of the relationship between the plasma concentration of a drug and its target occupancy, optimizing dose selection and reducing the time and cost of early development. Triple reuptake inhibitors (TRIs), also referred to as serotonin-norepinephrine-dopamine reuptake inhibitors, enhance monoaminergic neurotransmission by blocking the action of the monoamine transporters, raising extracellular concentrations of those neurotransmitters. GSK1360707 [(1R,6S)-1-(3,4-dichlorophenyl)-6-(methoxymethyl)-4-azabicyclo[4.1.0]heptane] is a novel TRI that until recently was under development for the treatment of major depressive disorder; its development was put on hold for strategic reasons. We present the results of an in vivo assessment of the relationship between plasma exposure and transporter blockade (occupancy). Studies were performed in baboons (Papio anubis) to determine the relationship between plasma concentration and occupancy of brain serotonin reuptake transporter (SERT), dopamine reuptake transporter (DAT), and norepinephrine uptake transporter (NET) using the radioligands [(11)C]DASB [(N,N-dimethyl-2-(2-amino-4-cyanophenylthio) benzylamine], [(11)C]PE2I [N-(3-iodoprop-2E-enyl)-2β-carbomethoxy-3β-(4-methylphenyl)nortropane], and [(11)C]2-[(2-methoxyphenoxy)phenylmethyl]morpholine (also known as [(11)C]MRB) and in humans using [(11)C]DASB and [(11)C]PE2I. In P. anubis, plasma concentrations resulting in half-maximal occupancy at SERT, DAT, and NET were 15.16, 15.56, and 0.97 ng/ml, respectively. In humans, the corresponding values for SERT and DAT were 6.80 and 18.00 ng/ml. GSK1360707 dose-dependently blocked the signal of SERT-, DAT-, and NET-selective PET ligands, confirming its penetration across the blood-brain barrier and blockade of all three monoamine transporters in vivo.

Introduction: A D-dimer (DD) test improves the diagnosis of PE (PE) when combined with clinical scores. However, as DD levels increase physiologically with age, this testing has less specificity in older patients. Douma et al. (1). proposed the use of an age adjusted DD cut-off to increase the specificity of this test., Methods: We performed chart reviews of patients, older than 75 years, hospitalized for suspicion of PE in 2010-2011 (n = 165). PE was assessed with either pulmonary scintigraphy (PS, n = 64) and/or pulmonary computed tomography (PC, n = 101). We compared the specificity, sensitivity and false negatives rates of an age adjusted DD cut-off level ("ADC" = (patient's age x 0.01) microg/ml) with those of the conventional cut off level ("CDC" = 0.5 microg/ml)., Results: PE was confirmed in 45 cases. In the 120 patients with no PE (negative PS or PC), 7 cases had CDC below cut-off levels, while 28 cases had an ADC below cutoff level. The use of the ADC thus increased the specificity (ADC: 23% vs CDC: 6%, p = 0.0001), and this was obtained without significant loss of sensitivity (ADC: 96% vs CDC: 98%, ns). Patients were clinically assessed with the revised Geneva scores. In the negative PE group, the number of patients classified with low, moderate or high clinical probability of PE were 31, 81 and 8, respectively. The percentage of patients with DD values below cut-off values was 4%, 0.8% and 0.8%, respectively using the CDC and 9%, 12% and 2.5% using the ADC., Conclusions: In this age group, the specificity of ADC was found superior to that of the CDC. The clinical use of the ADC might be associated with less useless diagnosis procedures, without significant increase in rate of diagnosis failure.

Episodic memory deficits are a core feature of neurodegenerative disorders. Muscarinic M(1) receptors play a critical role in modulating learning and memory and are highly expressed in the hippocampus. We examined the effect of GSK1034702, a potent M(1) receptor allosteric agonist, on cognitive function, and in particular episodic memory, in healthy smokers using the nicotine abstinence model of cognitive dysfunction. The study utilized a randomized, double-blind, placebo-controlled, cross-over design in which 20 male nicotine abstained smokers were tested following single doses of placebo, 4 and 8 mg GSK1034702. Compared to the baseline (nicotine on-state), nicotine abstinence showed statistical significance in reducing immediate (p=0.019) and delayed (p=0.02) recall. GSK1034702 (8 mg) significantly attenuated (i.e. improved) immediate recall (p=0.014) but not delayed recall. None of the other cognitive domains was modulated by either nicotine abstinence or GSK1034702. These findings suggest that stimulating M(1) receptor mediated neurotransmission in humans with GSK1034702 improves memory encoding potentially by modulating hippocampal function. Hence, selective M(1) receptor allosteric agonists may have therapeutic benefits in disorders of impaired learning including Alzheimer's disease.

The D(2)/D(3) agonist radioligand [(11)C]-(+)-PHNO is currently the most suitable D(3) imaging agent available, despite its limited selectivity for the D(3) over the D(2). Given the collocation of D(2) and D(3) receptors, and generally higher densities of D(2), the separation of D(2) and D(3) information from [(11)C]-(+)-PHNO PET data are somewhat complex. This complexity is compounded by recent data suggesting that [(11)C]-(+)-PHNO PET scans might be routinely performed in non-tracer conditions (with respect to D(3) receptors), and that the cerebellum (used as a reference region) might manifest some displaceable binding signal. Here we present the modelling and analysis of data from two human studies which employed an adequate dose range of selective D(3) antagonists (GSK598809 and GSK618334) to interrogate the [(11)C]-(+)-PHNO PET signal. Models describing the changes observed in the PET volume of distribution (V(T)) and binding potential (BP(ND)) were used to identify and quantify a [(11)C]-(+)-PHNO mass dose effect at the D(3), and displaceable signal in the cerebellum, as well as providing refined estimates of regional D(3) fractions of [(11)C]-(+)-PHNO BP(ND). The dose of (+)-PHNO required to occupy half of the available D(3) receptors (ED(50)(PHNO,D3)) was estimated as 40ng/kg, and the cerebellum BP(ND) was estimated as 0.40. These findings confirm that [(11)C]-(+)-PHNO human PET studies are in fact routinely performed under non-tracer conditions. This suggests that (+)-PHNO injection masses should be minimised and tightly controlled in order to mitigate the mass dose effect. The specific binding detected in the cerebellum was modest but could have a significant effect, for example on estimates of D(3) potency in drug occupancy studies. A range of methods for the analysis of future [(11)C]-(+)-PHNO data, incorporating models for the effects quantified here, were developed and evaluated. The comparisons and conclusions drawn from these can inform the design and analysis of future PET studies with [(11)C]-(+)-PHNO., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Unlabelled: In vivo estimation of β(2)-nicotinic acetylcholine receptor availability with molecular neuroimaging is complicated by competition between the endogenous neurotransmitter acetylcholine and the radioligand (123)I-3-[2(S)-2-azetidinylmethoxy]pyridine ((123)I-5-IA). We examined whether binding of (123)I-5-IA is sensitive to increases in extracellular levels of acetylcholine in humans, as suggested in nonhuman primates., Methods: Six healthy subjects (31 ± 4 y) participated in a (123)I-5-IA SPECT study. After baseline scans, physostigmine (1-1.5 mg) was administered intravenously over 60 min, and 9 additional scans were obtained., Results: We observed a significant reduction in the total volume of distribution after physostigmine administration (29% ± 17% in the cortex, 19% ± 15% in the thalamus, 19% ± 15% in the striatum, and 36% ± 30% in the cerebellum; P < 0.05). This reduction reflected a combination of a region-specific 7%-16% decrease in tissue concentration of tracer and a 9% increase in plasma parent concentration., Conclusion: These data suggest that increases in acetylcholine compete with (123)I-5-IA for binding to β(2)-nicotinic acetylcholine receptor. Additional validation of this paradigm is warranted, but it may be used to interrogate changes in extracellular acetylcholine.

The metabotropic glutamate 1 receptor (mGlu1) is an important protein in the regulation of glutamate transmission in the brain, and believed to be involved in disorders such as ischemia, epilepsy, neuropathic pain, anxiety, and schizophrenia. The goal of this study was to evaluate two selective mGlu1 antagonists [(11) C]3 and [(18) F]4 as potential PET radioligands for the in vivo imaging of the mGlu1 receptor. Biodistribution studies in rats indicated high uptake of [(11) C]3 and [(18) F]4 in the brain. The highest activity level was found in the cerebellum, followed by striatum, hippocampus, frontal cortex, and medulla, in a pattern consistent with the distribution of mGlu1 receptor in rat. At 30 min postinjection, the activity ratio of cerebellum to medulla was 4.5 for [(11) C]3, indicating a high degree of specific binding, while specific binding was lower for [(18) F]4 (cerebellum to medulla activity ratio of 2.0). Moreover, binding of the radioligands [(11) C]3 and [(18) F]4 in mGlu1 receptor-rich region such as cerebellum was blocked by pretreatment of the rats with their respective unlabeled compound or the selective mGlu1 antagonist (compound 5, 2 mg/kg each), but not by the selective mGlu2 antagonist LY341495, or the selective mGlu5 antagonist MPEP (2 mg/kg), thus indicating the binding specificity and selectivity of [(11) C]3 and [(18) F]4 to the mGlu1 receptor. However, in imaging experiments in baboons [(11) C]3 displayed a small specific binding signal only in the cerebellum, while the specific binding of [(18) F]4 was difficult to detect. Species differences in receptor density and affinity of the radioligands in large part account for the differences in the behavior of [(11) C]3 and [(18) F]4 in rats and baboons. Radioligands with higher affinity and/or lower lipophilicity are needed to successfully image the mGlu1 receptor in humans., (2012 Wiley Periodicals, Inc)

A recent single-site study (Fisher et al., 2009. Am J Psychiatry. 166 (7) 805-11) showed that repeated training with the Brain Fitness Program (BFP) improved performance on a battery of neuropsychological tasks. If replicated these data suggest an important non-pharmacological method for ameliorating cognitive impairment in schizophrenia. Our study evaluated the BFP training effects in an open-label, multi-site, multinational clinical trial. Fifty-five stable adult patients with schizophrenia on regular antipsychotic medication completed ≥ 32 BFP training sessions over 8-10 weeks. Training effects on cognitive performance and functional capacity outcome measures were measured using CogState® schizophrenia battery, UCSD Performance based Skills Assessment (UPSA-2) and Cognitive Assessment Interview (CAI). BFP training showed a large and significant treatment effect on a training exercise task (auditory processing speed), however this effect did not generalize to improved performance on independent CogState® assessment. There were no significant effects on UPSA-2 or CAI scores. Our study demonstrated the feasibility of implementing BFP training in a multi-site study. However, BFP training did not show significant treatment effects on cognitive performance or functional capacity outcome measures despite showing large and significant effects on a training exercise., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Purpose: We measured the whole-body distribution of IV-injected [¹¹C]GSK215083, a new 5-HT₆ antagonist PET tracer, as a function of time in adult subjects, in order to determine the radiation exposure., Procedures: After injection with a single bolus of [¹¹C]GSK215083 (range 330-367 MBq; mean 346 MBq), PET emission data were acquired for approximately 120 min in six subjects (three males and three females). Five organs were identified as exhibiting uptake above background. For these, regions of interest were delineated on emission images, and time-activity curves (TAC) generated. Residence times were calculated as the area under the curve of the TAC, normalized to injected activities and standard values of organ volumes. Dosimetry calculations were then performed using the computer program OLINDA/EXM 1.0., Results: The mean effective dose averaged over both males and females (deviation) was estimated to be 7.7 ± 1.0 μSv/MBq (male 7.0 ± 0.4; female 8.5 ± 0.6). For the effective dose equivalent, the corresponding values are 7.8 ± 1.2 μSv/MBq (male 6.8 ± 0.5; female 8.9 ± 0.1). The organ receiving the highest dose was the lung, with an average equivalent dose of 25.6 ± 6.9 μSv/MBq (male 20.8 ± 5.6; female 30.4 ± 4.4)., Conclusion: The estimated radiation dose for [¹¹C]GSK215083 is consistent with those for other neuroreceptor ligands labeled with carbon-11. The somewhat higher dose estimate for females compared to males may reflect the difference in observed residence times and representative differences in the male and female phantoms used for dosimetry calculations. Based on conventionally accepted dose limits, [¹¹C]GSK215083 may be used for multiple PET scans in the same subject.

Although [¹¹C]-(+)-PHNO has enabled quantification of the dopamine-D3 receptor (D3R) in the human brain in vivo, its selectivity for the D3R is not sufficiently high to allow us to disregard its binding to the dopamine-D2 receptor (D2R). We quantified the affinity of [¹¹C]-(+)-PHNO for the D2R and D3R in the living primate brain. Two rhesus monkeys were examined on four occasions each, with [¹¹C]-(+)-PHNO administered in a bolus + infusion paradigm. Varying doses of unlabeled (+)-PHNO were coadministered on each occasion (total doses ranging from 0.09 to 5.61 μg kg⁻¹). The regional binding potential (BP(ND) ) and the corresponding doses of injected (+)-PHNO were used as inputs in a model that quantified the affinity of (+)-PHNO for the D2R and D3R, as well as the regional fractions of the [¹¹C]-(+)-PHNO signal attributable to D3R binding. (+)-PHNO in vivo affinity for the D3R (K(d)/f(ND) ~0.23-0.56 nM) was 25- to 48-fold higher than that for the D2R (K(d)/f(ND) ~11-14 nM). The tracer limits for (+)-PHNO (dose associated with D3R occupancy ~10%) were estimated at ~0.02-0.04 μg kg⁻¹ injected mass for anesthetized primate and at 0.01-0.02 μg kg⁻¹ for awake human positron emission tomography (PET) studies. Our data enabled a rational design and interpretation of future PET studies with [¹¹C]-(+)-PHNO., (Copyright © 2011 Wiley Periodicals, Inc.)

D₁ receptors are the main mediators of dopamine transmission in the cortex and subserve cognitive functions that are affected in patients with schizophrenia. Prior imaging studies have suggested abnormalities in the expression of these receptors in schizophrenia, but no conclusive picture has emerged yet. One source of discrepancy may have been prior antipsychotic exposure. We used positron emission tomography (PET) and a D1 radiotracer, [¹¹C]NNC112, in drug naïve (DN, n = 12) and drug free (DF, n = 13) patients with schizophrenia and 40 healthy control subjects (HC, n = 40 total, n = 24 per comparison group) matched for age, gender, ethnicity, parental socioeconomic status and cigarette smoking. We measured the binding potential BPP, corrected for partial volume effects. The outcome measure was obtained in cortical and striatal subregions outlined on coregistered individual MRIs. Partial volume effect corrected BPP measures were significantly higher in DN vs controls in cortical regions. No such increases were found in the DF versus controls comparison. Furthermore, in the DF group, DF interval correlated positively with cortical BPP. We conclude that upregulation of D1 receptors in schizophrenia is related to the illness itself and may be corrected and normalized by chronic antipsychotic treatment.

3,4-Methylenedioxymethamphetamine (MDMA), the main psychoactive component of the recreational drug ecstasy, is a potent serotonin (5-HT) releaser. In animals, MDMA induces 5-HT depletion and toxicity in 5-HT neurons. The aim of this study was to investigate both presynaptic (5-HT transporter, SERT) and postsynaptic (5-HT(2A) receptor) markers of 5-HT transmission in recently abstinent chronic MDMA users compared with matched healthy controls. We hypothesized that MDMA use is associated with lower SERT density and concomitant upregulation of 5-HT(2A) receptors. Positron emission tomography studies using the SERT ligand [¹¹C]DASB and the 5-HT(2A) receptor ligand [¹¹C]MDL 100907 were evaluated in 13 current and recently detoxified MDMA users and 13 matched healthy controls. MDMA users reported a mean duration of ecstasy use of 8 years, regular exposure, and at least 2 weeks of abstinence before the scans. SERT and 5-HT(2A) receptor availability (binding potential, BP(ND)) were analyzed with a two-tissue compartment model with arterial input function. Current recreational MDMA use was significantly associated with lower SERT BP(ND) and higher 5-HT(2A) receptor BP(ND) in cortical, but not subcortical regions. Decreased SERT BP(ND) was regionally associated with upregulated 5-HT(2A) receptor BP(ND). In light of the animal literature, the most parsimonious interpretation is that repeated exposure to MDMA in humans, even in moderate amounts, leads to damage in 5-HT neuron terminals innervating the cortex. Alterations in mood, cognition, and impulse control associated with these changes might contribute to sustain MDMA use. The reversibility of these changes upon abstinence remains to be firmly established.

The passage of drugs in and out of the brain is controlled by the blood-brain barrier (BBB), typically, using either passive diffusion across a concentration gradient or active transport via a protein carrier. In-vitro and preclinical measurements of BBB penetration do not always accurately predict the in-vivo situation in humans. Thus, the ability to assay the concentration of novel drug candidates in the human brain in vivo provides valuable information for de-risking of candidate molecules early in drug development. Here, positron emission tomography (PET) measurements are combined with in-vitro equilibrium dialysis assays to enable assessment of transport and estimation of the free brain concentration in vivo. The PET and equilibrium dialysis data were obtained for 36 compounds in the pig. Predicted P-glycoprotein (P-gp) status of the compounds was consistent with the PET/equilibrium dialysis results. In particular, Loperamide, a well-known P-gp substrate, exhibited a significant concentration gradient consistent with active efflux and after inhibition of the P-gp process the gradient was removed. The ability to measure the free brain concentration and assess transport of novel compounds in the human brain with combined PET and equilibrium dialysis assays can be a useful tool in central nervous system (CNS) drug development.

Unlabelled: The development of a PET radioligand for imaging 5-hydroxytryptamine (5-HT) 6 receptors in the brain would, for the first time, enable in vivo imaging of this target along with assessment of its involvement in disease pathophysiology. In addition, such a tool would assist in the development of novel drugs targeting the 5-HT6 receptor., Methods: On the basis of in vitro data, GSK215083 was identified as a promising 5-HT6 radioligand candidate and was radiolabeled with (11)C via methylation. The in vivo properties of (11)C-GSK215083 were evaluated first in pigs (to investigate brain penetration and specific binding), second in nonhuman primates (to confirm brain penetration, specific binding, selectivity, and kinetics), and third in human subjects (to confirm brain penetration and biodistribution)., Results: (11)C-GSK215083 readily entered the brain in all 3 species, leading to a heterogeneous distribution (striatum > cortex > cerebellum) consistent with reported 5-HT6 receptor densities and distribution determined by tissue-section autoradiography in preclinical species and humans. In vivo saturation studies using escalating doses of GSK215083 in primates demonstrated saturable, dose-dependent binding to the 5-HT6 receptor in the striatum. Importantly, (11)C-GSK215083 also exhibited affinity for the 5-HT2A receptor; however, given the differential localization of these 2 receptors in the central nervous system, the discrete 5-HT6 binding properties of this radioligand were able to be determined., Conclusion: These data demonstrate the utility of (11)C-GSK215083 as a promising PET radioligand for probing the 5-HT6 receptor in vivo in both preclinical and clinical species.

Introduction: Scanning properties and analytic methodology of the 5-HT2A receptor-selective positron emission tomography (PET) tracer 11C-MDL100907 have been partially characterised in previous reports. We present an extended characterisation in healthy human subjects., Methods: 64 11C-MDL100907 PET scans with metabolite-corrected arterial input function were performed in 39 healthy adults (18-55 years). 12 subjects were scanned twice (duration 150 min) to provide data on plasma analysis, model order estimation, and stability and test-retest characteristics of outcome measures. All other scans were 90 min duration. 3 subjects completed scanning at baseline and following 5-HT2A receptor antagonist medication (risperidone or ciproheptadine) to provide definitive data on the suitability of the cerebellum as reference region. 10 subjects were scanned under reduced 5-HT and control conditions using rapid tryptophan depletion to investigate vulnerability to competition with endogenous 5-HT. 13 subjects were scanned as controls in clinical protocols. Pooled data were used to analyse the relationship between tracer injected mass and receptor occupancy, and age-related decline in 5-HT2A receptors., Results: Optimum analytic method was a 2-tissue compartment model with arterial input function. However, basis function implementation of SRTM may be suitable for measuring between-group differences non-invasively and warrants further investigation. Scan duration of 90 min achieved stable outcome measures in all cortical regions except orbitofrontal which required 120 min. Binding potential (BPP and BPND) test-retest variability was very good (7-11%) in neocortical regions other than orbitofrontal, and moderately good (14-20%) in orbitofrontal cortex and medial temporal lobe. Saturation occupancy of 5-HT2A receptors by risperidone validates the use of the cerebellum as a region devoid of specific binding for the purposes of PET. We advocate a mass limit of 4.6 μg to remain below 5% receptor occupancy. 11C-MDL100907 specific binding is not vulnerable to competition with endogenous 5-HT in humans. Paradoxical decreases in BPND were found in right prefrontal cortex following reduced 5-HT, possibly representing receptor internalisation. Mean age-related decline in brain 5-HT2A receptors was 14.0±5.0% per decade, and higher in prefrontal regions., Conclusions: Our data confirm and extend support for 11C-MDL100907 as a PET tracer with very favourable properties for quantifying 5-HT2A receptors in the human brain., (Copyright © 2011 Elsevier Inc. All rights reserved.)

[(11)C]PHNO is a D(2)/D(3) agonist positron emission tomography radiotracer, with higher in vivo affinity for D(3) than for D(2) receptors. As [(11)C]-(+)-PHNO is an agonist, its in vivo binding is expected to be more affected by acute fluctuations in synaptic dopamine than that of antagonist radiotracers such as [(11)C]raclopride. In this study, the authors compared the effects of an oral dose of the dopamine releaser amphetamine (0.3 mg/kg) on in vivo binding of [(11)C]-(+)-PHNO and [(11)C]raclopride in healthy subjects, using a within-subjects, counterbalanced, open-label design. In the dorsal striatum, where the density of D(3) receptors is negligible and both tracers predominantly bind to D(2) receptors, the reduction of [(11)C]-(+)-PHNO binding potential (BP(ND)) was 1.5 times larger than that of [(11)C]raclopride. The gain in sensitivity associated with the agonist [(11)C]-(+)-PHNO implies that ∼65% of D(2) receptors are in the high-affinity state in vivo. In extrastriatal regions, where [(11)C]-(+)-PHNO predominantly binds to D(3) receptors, the amphetamine effect on [(11)C]-(+)-PHNO BP(ND) was even larger, consistent with the higher affinity of dopamine for D(3). This study indicates that [(11)C]-(+)-PHNO is superior to [(11)C]raclopride for studying acute fluctuations in synaptic dopamine in the human striatum. [(11)C]-(+)-PHNO also enables measurement of synaptic dopamine in D(3) regions.

Evidence from biochemical, imaging, and treatment studies suggest abnormalities of the serotonin system in autism spectrum disorders, in particular in frontolimbic areas of the brain. We used the radiotracers [(11)C]MDL 100907 and [(11)C]DASB to characterize the 5-HT(2A) receptor and serotonin transporter in Asperger's Disorder. Seventeen individuals with Asperger's Disorder (age=34.3 ± 11.1 years) and 17 healthy controls (age=33.0 ± 9.6 years) were scanned with [(11)C]MDL 100907. Of the 17 patients, eight (age=29.7 ± 7.0 years) were also scanned with [¹¹C]DASB, as were eight healthy controls (age=28.7 ± 7.0 years). Patients with Asperger's Disorder and healthy control subjects were matched for age, gender, and ethnicity, and all had normal intelligence. Metabolite-corrected arterial plasma inputs were collected and data analyzed by two-tissue compartment modeling. The primary outcome measure was regional binding potential BP(ND). Neither regional [¹¹C]MDL 100907 BP(ND) nor [¹¹C]DASB BP(ND) was statistically different between the Asperger's and healthy subjects. This study failed to find significant alterations in binding parameters of 5-HT(2A) receptors and serotonin transporters in adult subjects with Asperger's disorder., (© 2011 Elsevier Ireland Ltd. All rights reserved.)

The current interest in developing Glycine transporter Type 1 (GlyT-1) inhibitors, for diseases such as schizophrenia, has led to the demand for a GlyT-1 PET molecular imaging tool to aid drug development and dose selection. We report on [(11) C]GSK931145 as a novel GlyT-1 imaging probe in primate and man. Primate PET studies were performed to determine the level of specific binding following homologous competition with GSK931145 and the plasma-occupancy relationship of the GlyT-1 inhibitor GSK1018921. Human PET studies were performed to determine the test-retest reproducibility of [(11) C]GSK931145 and the plasma-occupancy relationship of GSK1018921. [(11) C]GSK931145 entered primate and human brain and yielded a heterogeneous pattern of uptake which was similar in both species with highest uptake in midbrain, thalamus, and cerebellum. Homologous competition in primates indicated no viable reference region and gave binding potential estimates between 1.5 and 3 for midbrain, thalamus and cerebellum, While the distribution and binding potential values were similar across species, both the plasma free fraction (f(P) : 0.8 vs. 8%) and delivery (K(1) : 0.025 vs. 0.126 ml cm(-3) min(-1) ) were significantly lower in humans. Test-retest reproducibility in humans calculated using a two tissue compartmental model was poor (VAR(V(T) ): 29-38%), but was improved using a pseudo reference tissue model (VAR(BP(ND) ): 16-23%). GSK1018921 EC(50) estimates were 22.5 and 45.7 ng/ml in primates and humans, respectively., (Copyright © 2011 Wiley-Liss, Inc.)

[11 C] P943 is a recently developed PET radiotracer for serotonin 5-HT1B receptors. We characterized a number of its in vivo pharmacokinetic properties, including the evaluation of its two stereo-isomers, saturability of specific binding, selectivity for 5-HT1B and 5-HT1D receptors, and vulnerability to pharmacologically induced increases in endogenous 5-HT levels. Six isoflurane-anesthetized baboons were scanned with [11 C] P943 at baseline, and following various pharmacological manipulations. The interventions included the administration of pharmacological doses of P943, SB-616234-S (a 5-HT1B selective antagonist), SB-714786 (a 5-HT1D selective antagonist), as well as the administration of 5-HT releasing agents (fenfluramine, amphetamine) and 5-HT reuptake inhibitor (citalopram). [11 C] P943 was observed to bind saturably and specifically to 5-HT1B receptors and to be sensitive to all three challenges known to alter 5-HT levels in the proximity of receptors. [11 C] P943 shows promise as a tracer to image serotonin function in healthy subjects as well as subjects with psychiatric or neurologic conditions., (Copyright © 2011 Wiley-Liss, Inc.)

In a recent positron emission tomography (PET) study, we demonstrated the ability to measure amphetamine-induced dopamine (DA) release in the human cortex with the DA D₂/₃ radioligand [¹¹C]FLB 457. As previous studies in animals have shown that a relatively high fraction of the [¹¹C]FLB 457 signal in the cerebellum represents specific binding to D₂/₃ receptors, there was concern that the use of the cerebellum as a measure of nonspecific binding (i.e., reference region) to derive [¹¹C]FLB 457 binding potential (BP) (BP(ND) ) would bias cortical DA release measurements. Thus, we evaluated the fractional contribution of specific binding to D₂/₃ receptors in the human cerebellum for [¹¹C]FLB 457. Six healthy human subjects (5M/1F) were studied twice with [¹¹C]FLB 457, once at baseline and again following a single oral dose of 15 mg of aripiprazole, a D₂/₃ partial agonist. [¹¹C]FLB 457 distribution volume (V(T) ) was estimated using kinetic analysis in the cortical regions of interest and potential reference regions. The change in [¹¹C]FLB 457 V(T) following aripiprazole ranged from -33 to -42% in the cortical regions of interest (ROIs). The aripiprazole-induced change in [¹¹C]FLB 457 V(T) in three potential reference regions suggests significant specific binding the cerebellum (CER, -17 ± 12%), but not pons (PON, -10 ± 10%) and centrum semiovale (CESVL, -3 ± 12%). Nevertheless, a reanalysis of the published [¹¹C]FLB 457 test-retest and amphetamine studies suggests that the use of the PON V(T) and CESVL V(T) as an estimate of nonspecific binding to derive [¹¹C]FLB 457 BP(ND) in DA release studies is unlikely to be successful because it leads to less reproducible outcome measures, which in turn diminishes the ability to measure DA release in the cortex. D₂/₃ blocking studies with aripiprazole and [¹¹C]FLB 457 suggest specific binding to D₂/₃ receptors in the cerebellum. These data also suggest that the contribution of specific binding to D₂/₃ receptors in the cerebellum is lower than that in the cortical ROIs and that CER V(T) is mostly representative of nonspecific binding. Nevertheless, caution is advised when using reference tissue methods that rely solely on the cerebellum signal as an input function to quantify [¹¹C]FLB 457 BP(ND)., (Copyright © 2011 Wiley-Liss, Inc.)

Purpose: (11)C-GSK931145 is a novel radioligand suitable for imaging the glycine transporter 1 (GlyT-1) in brain. In the present study, human dosimetry is estimated from baboon and human biodistribution data., Procedures: Three baboons and eight healthy human volunteers underwent whole-body positron emission tomography (PET) scans. Human dosimetry was estimated using three different region-of-interest (ROI) delineation methods that ranged in their complexity and execution time: ROIs drawn on anterior-posterior compressed PET images, on subsamples of the organs, and covering the whole-organ. Residence times for each organ were calculated as the area under the time-activity curves divided by the injected activity. Radiation dose estimates were calculated from organ residence times using the OLINDA/EXM software package., Results: The overall distribution of activity was similar in baboons and humans. Early scans presented high activity in the liver, and moderate activity in the lungs and kidneys. The principal route of clearance was intestinal and no urinary excretion was observed. The limiting organ with the highest radiation-absorbed dose was the liver. The mean effective dose in humans was 4.02 μSv/MBq (male phantom) and 4.95 μSv/MBq (female phantom) (ROIs drawn on subsamples of the organs). The human effective dose estimated from baboon data was ~15% larger than the effective dose estimated from human data., Conclusion: Human PET imaging of the glycine transporter-1 with (11)C-GSK931145 results in a moderate effective human radiation dose, which allows for multiple PET examinations in the same individual. Among the three methods compared to delineate ROIs, the organ subsampling method shows the best balance between quantitative accuracy and practical application.

The aim of this study was to compare 5-HT(1A) availability in vivo in individuals with schizophrenia before and during treatment with the atypical antipsychotic ziprasidone. Six individuals with schizophrenia underwent two PET scans with [(11)C]WAY 100635; the first while medication-free (baseline) and the second while taking the atypical antipsychotic ziprasidone (on-medication). Regional volumes of distribution (V(T), mL g(-1)) were derived using a two-tissue compartment kinetic model. Outcome measures included binding potential relative to the plasma (BP(P), mL g(-1)) and the binding potential relative to the nonspecific distribution volume (BP(ND), unitless). No significant differences were observed in regional BP(P) or BP(ND) with ziprasidone treatment. A significant correlation was noted between BP(P) measured in the orbitofrontal cortex during the on-medication condition and degree of improvement in negative symptoms with treatment (r = 0.96, p = 0.004). Consistent with the published literature of changes in 5-HT(1A) binding during treatment with 5-HT(1A) receptor agonists, this study did not detect a significant reduction in 5-HT(1A) binding with ziprasidone. The finding of a relationship between 5-HT(1A) binding and the degree of improvement in negative symptoms provides further support for the role of the 5-HT(1A) receptor in the pathophysiology and treatment of this symptom domain.

Introduction: Development of agonist positron emission tomography (PET) radioligands for the 5-HT neurotransmitter system is an important target to enable the understanding of human 5-HT function in vivo. [(11)C]CUMI-101, proposed as the first 5-HT(1A) receptor agonist PET ligand, has been reported to behave as a potent 5-HT(1A) agonist in a cellular system stably expressing human recombinant 5-HT(1A) receptors. In this study, we investigate the agonist properties of CUMI-101 in rat brain tissue., Methods: [(35)S]-GTPγS binding studies were used to determine receptor function in HEK (human embryonic kidney) 293 cells transfected with human recombinant 5-HT(1A) receptors and in rat cortex and rat hippocampal tissue, following administration of CUMI-101 and standard 5-HT1A antagonists (5-HT, 5-CT and 8-OH-DPAT)., Results: CUMI-101 behaved as an agonist at human recombinant 5-HT(1A) receptors (pEC(50) 9.2). However, CUMI-101 did not show agonist activity in either rat cortex or hippocampus at concentrations up to 10 μM. In these tissues, CUMI-behaved as an antagonist with pK(B)s of 9.2 and 9.3, respectively., Conclusions: Our studies demonstrate that as opposed to its behavior in human recombinant system, in rat brain tissue CUMI-101 behaves as a potent 5-HT(1A) receptor antagonist., (Copyright © 2011 Elsevier Inc. All rights reserved.)

In a recent PET study, we demonstrated the ability to measure amphetamine-induced DA release in the human cortex with the relatively high affinity dopamine D₂/₃ radioligand [¹¹C]FLB 457 (Narendran et al., [2009] Synapse 63:447-461). The aim of this study was to evaluate the reproducibility and reliability of [¹¹C]FLB 457 in the same imaging paradigm we used to measure amphetamine-induced DA transmission. Six healthy human subjects (three males/three females)were studied twice with [¹¹C]FLB 457, once at baseline and again 3 h following the end of the baseline scan. D₂/₃ receptor binding parameters were estimated using a two-tissue compartment kinetic analysis in the cortical regions of interest and cerebellum (reference region). The test-retest variability and intraclass correlation coefficient were assessed for distribution volume (VT), binding potential relative to plasma concentration (BP(P)), and binding potential relative to non-displaceable uptake (BP(ND)) of [¹¹C]FLB 457. The test-retest variability of [¹¹C]FLB 457 VT, BPP, and BP(ND) were ≤15%, consistent with the published test-retest variability for this ligand in other brain regions (Sudo et al., [2001] Nucl Med Commun 22:1215-1221; Vilkman et al., [2000] Eur J Nucl Med 27:1666-1673). In addition, no significant decrease in [¹¹C]FLB457 BP(ND) was observed in the second scan compared to the first one. This suggests that the contribution of carryover mass of [¹¹C]FLB 457 to the measured reduction in[¹¹C]FLB 457 BP(ND) following amphetamine was relatively low. These data support the further validation of [¹¹C]FLB 457 as a tool to measure amphetamine-induced dopamine release in the human cortex., (Copyright © 2010 Wiley-Liss, Inc.)

[(11)C]-(+)-PHNO is a D3 preferring PET radioligand which has recently opened the possibility of imaging D3 receptors in the human brain in vivo. This imaging tool allows characterisation of the distribution of D3 receptors in vivo and further investigation of their functional role. The specific [(11)C]-(+)-PHNO signal is a mixture of D3 and D2 components with the relative magnitude of each component determined by the regional receptor densities. An accurate and reproducible delineation of regions of interest (ROI) is therefore important for optimal analysis of human PET data. We present a set of anatomical guidelines for the delineation of D3 relevant ROIs including substantia nigra, hypothalamus, ventral pallidum/substantia innominata, ventral striatum, globus pallidus and thalamus. Delineation of these structures using this approach allowed for high intra- and inter-operator reproducibility. Subsequently we used a selective D3 antagonist to dissect the total [(11)C]-(+)-PHNO signal in each region into its D3 and D2 components and estimated the regional fraction of the D3 signal (f(PHNO)(D3)). In descending order of magnitude the following results for the f(PHNO)(D3) were obtained: hypothalamus=100%, substantia nigra=100%, ventral pallidum/substantia innominata=75%, globus pallidus=65%, thalamus=43%, ventral striatum=26% and precommissural-ventral putamen=6%. An automated approach for the delineation of these anatomical regions of interest was also developed and investigated in terms of its reproducibility and accuracy., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Rising life expectancies coupled with an increasing awareness of age-related cognitive decline have led to the unwarranted use of psychopharmaceuticals, including acetylcholinesterase inhibitors (AChEIs), by significant numbers of healthy older individuals. This trend has developed despite very limited data regarding the effectiveness of such drugs on non-clinical groups and recent work indicates that AChEIs can have negative cognitive effects in healthy populations. For the first time, we use a combination of EEG and simultaneous EEG/fMRI to examine the effects of a commonly prescribed AChEI (donepezil) on cognition in healthy older participants. The short- and long-term impact of donepezil was assessed using two double-blind, placebo-controlled trials. In both cases, we utilised cognitive (paired associates learning (CPAL)) and electrophysiological measures (resting EEG power) that have demonstrated high-sensitivity to age-related cognitive decline. Experiment 1 tested the effects of 5 mg/per day dosage on cognitive and EEG markers at 6-hour, 2-week and 4-week follow-ups. In experiment 2, the same markers were further scrutinised using simultaneous EEG/fMRI after a single 5 mg dose. Experiment 1 found significant negative effects of donepezil on CPAL and resting Alpha and Beta band power. Experiment 2 replicated these results and found additional drug-related increases in the Delta band. EEG/fMRI analyses revealed that these oscillatory differences were associated with activity differences in the left hippocampus (Delta), right frontal-parietal network (Alpha), and default-mode network (Beta). We demonstrate the utility of simple cognitive and EEG measures in evaluating drug responses after acute and chronic donepezil administration. The presentation of previously established markers of age-related cognitive decline indicates that AChEIs can impair cognitive function in healthy older individuals. To our knowledge this is the first study to identify the precise neuroanatomical origins of EEG drug markers using simultaneous EEG/fMRI. The results of this study may be useful for evaluating novel drugs for cognitive enhancement.

Background: Alterations in dopamine D(2)/D(3) receptor binding have been reported in schizophrenia, and a meta-analysis of imaging studies has shown a modest elevation in striatum. Newer radioligands now allow the assessment of these receptors in extrastriatal regions. We used positron emission tomography with [(18)F]fallypride to evaluate D(2)/D(3) receptors in both striatal and extrastriatal regions in schizophrenia., Methods: Twenty-one patients with schizophrenia and 22 matched healthy control subjects were scanned with an ECAT EXACT HR+ camera. Two-tissue compartment modeling and the reference tissue method gave binding potentials relative to nondisplaceable uptake, total plasma concentration, and free plasma concentration. These were compared between groups in five striatal and eight extrastriatal regions. Several regional volumes were lower in the patient group, and positron emission tomography data were corrected for partial volume effects., Results: Binding potential values differed in three regions between groups. Values for binding potential relative to nondisplaceable uptake from two-tissue compartment modeling in patients and control subjects, respectively, were 28.7 ± 6.8 and 25.3 ± 4.3 in postcommissural caudate, 2.9 ± .7 and 2.6 ± .4 in thalamus, and 1.8 ± .5 and 2.1 ± .7 in uncus. Loss of D(2)/D(3) receptors with age was found in striatal and extrastriatal regions and was greater in neocortex., Conclusions: Our study found selective alterations in D(2)/D(3) receptors in striatal and extrastriatal regions, consistent with some but not all previously published reports. As previously shown for the striatum, a more sensitive imaging approach for studying the role of dopamine in the pathophysiology of schizophrenia might be assessment of neurotransmitter levels rather than D(2)/D(3) receptor levels in extrastriatal regions., (Copyright © 2010 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.)

Background: Dopamine D(3) receptors are involved in the pathophysiology of several neuropsychiatric conditions. [(11)C]-(+)-PHNO is a radiolabeled D(2) and D(3) agonist, suitable for imaging the agonist binding sites (denoted D(2HIGH) and D(3)) of these receptors with positron emission tomography (PET). PET studies in nonhuman primates documented that, in vivo, [(11)C]-(+)-PHNO displays a relative selectivity for D(3) compared with D(2HIGH) receptor sites and that the [(11)C]-(+)-PHNO signal is enriched in D(3) contribution compared with conventional ligands such as [(11)C] raclopride., Methods: To define the D(3) contribution (f(PHNO)(D3)) to [(11)C]-(+)-PHNO binding potential (BP(ND)) in healthy humans, 52 PET scans were obtained in 19 healthy volunteers at baseline and following oral administration of various doses of the selective D(3) receptor antagonist, GSK598809., Results: The impact of GSK598809 on [(11)C]-(+)-PHNO was regionally selective. In dorsal regions of the striatum, GSK598809 did not significantly affect [(11)C]-(+)-PHNO BP(ND) (f(PHNO)(D3) approximately 0%). Conversely, in the substantia nigra, GSK598809 dose-dependently reduced [(11)C]-(+)-PHNO binding to nonspecific level (f(PHNO)(D3) approximately 100%). In ventral striatum (VST), globus pallidus and thalamus (THA), [(11)C]-(+)-PHNO BP(ND) was attributable to a combination of D(2HIGH) and D(3) receptor sites, with f(PHNO)(D3) of 26%, 67% and 46%, respectively. D(3) receptor binding potential (BP(ND)(D3)) was highest in globus pallidus (1.90) and substantial nigra (1.39), with lower levels in VST (.77) and THA (.18) and negligible levels in dorsal striatum., Conclusions: This study elucidated the pharmacologic nature of the [(11)C]-(+)-PHNO signal in healthy subjects and provided the first quantification of D(3) receptor availability with PET in the living human brain., (Copyright 2010 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.)

Unlabelled: The histamine H(3) receptor is implicated in the pathophysiology of several central nervous system disorders. N-methyl-6-(3-cyclobutyl-2,3,4,5-tetrahydro-1H-benzo[d]azepin-7-yloxy)-nicotamide (GSK189254) is a highly potent, selective, and brain-penetrant H(3) receptor antagonist. Previous studies in the pig using PET have shown that (11)C-GSK189254 uptake in H(3)-rich regions of the brain can be blocked by the selective H(3) antagonist ciproxifan. The purpose of the present study was to evaluate (11)C-GSK189254 as a PET radioligand for human studies and to determine the dose-receptor occupancy relationship of GSK189254 in the human brain., Methods: Dynamic PET scans were obtained in healthy subjects over 90 min after intravenous administration of approximately 370 MBq of (11)C-GSK189254. Blood samples were taken throughout the scans to derive the arterial plasma parent input function. Each subject was scanned twice, either with tracer alone (test-retest) or before and after a single oral dose of GSK189254 (10-100 microg). Data were analyzed by compartmental analysis, and regional receptor-occupancy estimates were obtained by graphical analysis of changes in the total volumes of distribution (V(T)) of the radioligand., Results: (11)C-GSK189254 readily entered the brain; its regional brain distribution reflected the known distribution of H(3) receptors, with high binding in the caudate and putamen, intermediate binding in cortical regions, and low binding in the cerebellum. GSK189254 displayed a high receptor affinity, and a marked reduction in V(T) was apparent at all the doses tested. The oral dose equaling 50% occupancy of the available receptor sites (ED(50)) was estimated as 4.33 microg. Additional data on plasma pharmacokinetics after oral dosing and the plasma free fraction gave a corresponding estimate of the free concentration of GSK189254 required to occupy 50% of the available receptor sites (EC(50)) (0.011 nM). The test-retest data showed reductions in regional V(T) on the second scan in all subjects. A nonlinear compartmental analysis of this effect demonstrated that this reduction was consistent with carryover of a tracer mass dose effect with an estimated in vivo apparent dissociation constant of 0.010 nM, close to the independent estimate of the plasma EC(50)., Conclusion: (11)C-GSK189254 can be used to quantify H(3) receptor availability in humans in vivo using PET but requires high specific activity; the possibility of tracer mass dose effects should be carefully analyzed.

The type-1 glycine transporter (GlyT1) is an important target for the development of new medications for schizophrenia. A specific and selective positron emission tomography (PET) GlyT1 ligand would facilitate drug development studies to determine whether a drug reaches this target and help establish suitable doses for clinical trials. This article describes the evaluation of three candidate GlyT1 PET radioligands (GSK931145, GSK565710, and GSK991022) selected from a library of compounds based on favorable physicochemical and pharmacological properties. Each candidate was successfully labeled using [(11)C]methyl iodide or [(11)C]methyl triflate and administered to a pig pre- and postadministration with a pharmacological dose of a GlyT1 inhibitor to determine their suitability as PET ligands in the porcine brain in vivo. All three candidate ligands were analyzed quantitatively with compartment analyses employing a plasma input function. [(11)C]GSK931145 showed good brain penetration and a heterogeneous distribution in agreement with reported GlyT1 localization. Following pretreatment with GSK565710, uptake of [(11)C]GSK931145 was reduced to homogeneous levels. Although [(11)C]GSK565710 also showed good brain penetration and a heterogeneous distribution, the apparent level of specific binding was reduced compared to [(11)C]GSK931145. In contrast, [(11)C]GSK991022 showed a much lower brain penetration and resultant signal following pretreatment with GSK565710. Based on these findings [(11)C]GSK931145 was identified as the most promising ligand for imaging GlyT1 in the porcine brain, possessing good brain penetration, specific signal, and reversible kinetics. [(11)C]GSK931145 is now being progressed into higher species.

Background: Impulsive physical aggression is a common and problematic feature of many personality disorders. The serotonergic system is known to be involved in the pathophysiology of aggression, and multiple lines of evidence have implicated the serotonin 2A receptor (5-HT(2A)R). We sought to examine the role of the 5-HT(2A)R in impulsive aggression specifically in the orbitofrontal cortex (OFC), given that our own studies and an extensive literature indicate that serotonergic disturbances in the OFC are linked to aggression. We have previously hypothesized that increased 5-HT(2A)R function in the OFC is a state phenomenon that promotes impulsive aggression., Methods: Serotonin 2A receptor availability was measured with positron emission tomography and the selective 5-HT(2A)R antagonist radioligand [(11)C]MDL100907 in two groups of impulsively aggressive personality disordered patients-14 with current physical aggression, and 15 without current physical aggression-and 25 healthy control subjects. Clinical ratings of various symptom dimensions were also obtained., Results: Orbitofrontal 5-HT(2A)R availability was greater in patients with current physical aggression compared with patients without current physical aggression and healthy control subjects; no differences in OFC 5-HT(2A)R availability were observed between patients without current physical aggression and healthy control subjects. No significant differences in 5-HT(2A)R availability were observed in other brain regions examined. Among both groups of impulsively aggressive personality disordered patients combined, OFC 5-HT(2A)R availability was correlated, specifically, with a state measure of impulsive aggression., Conclusions: These findings are consistent with our previously described model in which impulsive aggression is related to dynamic changes in 5-HT(2A)R function in the OFC.

The amphetamine challenge, in which positron emission tomography (PET) or single photon emission computed tomography radioligand binding following administration of amphetamine is compared to baseline values, has been successfully used in a number of brain imaging studies as an indicator of dopaminergic function, particularly in the striatum. [(18)F] fallypride is the first PET radioligand that allows measurement of the effects of amphetamine on D2/D3 ligand binding in striatum and extra-striatal brain regions in a single scanning session following amphetamine. We scanned 15 healthy volunteer subjects with [(18)F] fallypride at baseline and following amphetamine (0.3 mg/kg) using arterial plasma input-based modeling as well as reference region methods. We found that amphetamine effect was robustly detected in ventral striatum, globus pallidus, and posterior putamen, and with slightly higher variability in other striatal subregions. However, the observed effect sizes in striatum were less than those observed in previous studies in our laboratory using [(11)C] raclopride. Robust effect was also detected in limbic extra-striatal regions (hippocampus, amygdala) and substantia nigra, but the signal-to-noise ratio was too low to allow accurate measurement in cortical regions. We conclude that [(18)F] fallypride is a suitable ligand for measuring amphetamine effect in striatum and limbic regions, but it is not suitable for measuring the effect in cortical regions and may not provide the most powerful way to measure the effect in striatum.

[(11)C]NNC112 (8-chloro-7-hydroxy-3-methyl-5-(7-benzofuranyl)-2,3,4,5-tetrahydro-IH-3-benzazepine), a selective positron-emission tomography (PET) ligand for the D(1) receptor (R) over the 5-HT(2A) R in vitro, has shown lower selectivity in vivo, hampering measurement of D(1) R in the cortex. [(11)C]NNC112 PET and intravenous (i.v) ketanserin challenge were used to (1) confirm the previous findings of [(11)C]NNC112 in vivo D(1) R selectivity, and (2) develop a feasible methodology for imaging cortical D(1) R without contamination by 5-HT(2A) R. Seven healthy volunteers underwent [(11)C]NNC112 PET scans at baseline and after a 5-HT(2A) R-blocking dose of ketanserin (0.15 mg/kg, i.v.). Percent BP(ND) change between the post-ketanserin and baseline scans was calculated. Irrespective of the quantification method used, ketanserin pretreatment led to significant decrease of BP(ND) in the cortical (approximately 30%) and limbic regions (approximately 20%) but not in the striatum, which contains a much lower amount of 5-HT(2A) R. Therefore, ketanserin allows D(1) R signal to be detected by [(11)C]NNC112 PET without significant 5-HT(2A) R contamination. These data confirm the presence of a significant 5-HT(2A) R contribution to cortical [(11)C]NNC112 signal, and call for caution in the interpretation of published [(11)C]NNC112 PET findings on cortical D(1) R in humans. In the absence of more selective ligands, [(11)C]NNC112 PET with ketanserin can be used for cortical D(1) R imaging in vivo.

Reported values of D(2) receptor occupancy (RO) achieved by antipsychotic drugs tend to be lower when measured with (123)I-IBZM SPECT than with (11)C-Raclopride PET. Image degrading factors such as attenuation, distance-dependent collimator response and scatter could account for this difference. While attenuation correction is routinely applied to SPECT images, the other degradations are not usually accounted for. The aim of this work was to assess the impact of scatter correction on D(2) RO quantification with (123)I-IBZM SPECT, and to compare the results of both corrected and un-corrected SPECT values with (11)C-Raclopride PET measurements. Phantom experiments as well as within-subject human data from a previous study were used for this purpose. SPECT images were reconstructed using filtered back-projection including attenuation correction (FBP(A)), ordered subsets expectation maximization including attenuation and point spread function corrections (OSEM(A+PSF)) and ordered subsets expectation maximization including attenuation, point spread function and scatter corrections (OSEM(A+PSF+SCT)). PET images were reconstructed using the FBP algorithm and corrected for attenuation, scatter, random coincidences and dead time. Quantification of receptor availability was performed using the tissue ratio at pseudoequilibrium for SPECT, and the simplified reference tissue model (SRTM) for PET. Analysis was performed using both occipital cortex (occ) and cerebellum (cer) as reference regions for both modalities. When images were reconstructed using FBP(A), SPECT D(2) RO values were significantly lower as compared with PET leading to a D(2) RO difference of -20% (CI(95%): -13, -27%) (occ) and -23% (CI(95%): -14, -31%) (cer). When images were reconstructed using OSEM(A+PSF), SPECT D(2) RO values were also lower as compared with PET leading to a D(2) RO difference of -21% (CI(95%): -14, -27%) (occ) and -24% (CI(95%): -18, -30%) (cer). When images were reconstructed using OSEM(A+PSF+SCT), the D(2) RO bias was reduced to -6% (CI(95%): 0, -13%) (occ) and -11% (CI(95%): -4, -18%) (cer). These data suggest that the scatter correction plays a major role in explaining the differences between D(2) RO measurements using (123)I-IBZM SPECT and (11)C-Raclopride PET., (Crown Copyright 2010. Published by Elsevier Inc. All rights reserved.)

Context: A long-standing version of the dopamine hypothesis of schizophrenia postulates that hyperactivity of dopaminergic transmission at D(2) receptors in the limbic striatum is associated with the illness and that blockade of mesolimbic D(2) receptors is responsible for the antipsychotic action of D(2) receptor antagonists., Objective: To localize dopaminergic hyperactivity within the striatum in schizophrenia., Design: Case-control study., Setting: Inpatient research unit., Participants: Eighteen untreated patients with schizophrenia and 18 healthy control subjects matched for age, sex, ethnicity, parental socioeconomic status, cigarette smoking, and weight., Main Outcome Measures: Percentage change in dopamine D(2) receptor availability in striatal subregions within each subject measured by positron emission tomography with carbon 11-labeled raclopride before and during pharmacologically induced dopamine depletion., Results: In the associative striatum, acute dopamine depletion resulted in a larger increase in D(2) receptor availability in patients with schizophrenia (mean [SD], 15% [7%]) than in control subjects (10% [7%], P = .045), suggesting higher synaptic dopamine concentration. Within the associative striatum, this effect was most pronounced in the precommissural dorsal caudate (15% [8%] in patients vs 9% [8%] in controls, P = .03). No between-group differences were observed in the limbic and sensorimotor striatum., Conclusions: These findings suggest that schizophrenia is associated with elevated dopamine function in associative regions of the striatum. Because the precommissural dorsal caudate processes information from the dorsolateral prefrontal cortex, this observation also suggests that elevated subcortical dopamine function might adversely affect performance of the dorsolateral prefrontal cortex in schizophrenia. On the other hand, the absence of a group difference in the limbic striatum brings into question the therapeutic relevance of the mesolimbic selectivity of second-generation antipsychotic drugs.

Synaptic dopamine (DA) levels seem to affect the in vivo binding of many D2 receptor radioligands. Thus, release of endogenous DA induced by the administration of amphetamine decreases ligand binding, whereas DA depletion increases binding. This is generally thought to be due to competition between endogenous DA and the radioligands for D2 receptors. However, the temporal discrepancy between amphetamine-induced increases in DA as measured by microdialysis, which last on the order of 2 h, and the prolonged decrease in ligand binding, which lasts up to a day, has suggested that agonist-induced D2 receptor internalization may contribute to the sustained decrease in D2 receptor-binding potential seen following a DA surge. To test this hypothesis, we developed an in vitro system showing robust agonist-induced D2 receptor internalization following treatment with the agonist quinpirole. Human embryonic kidney 293 (HEK293) cells were stably co-transfected with human D2 receptor, G-protein-coupled receptor kinase 2 and arrestin 3. Agonist-induced D2 receptor internalization was demonstrated by fluorescence microscopy, flow cytometry, and radioligand competition binding. The binding of seven D2 antagonists and four agonists to the surface and internalized receptors was measured in intact cells. All the imaging ligands bound with high affinity to both surface and internalized D2 receptors. Affinity of most of the ligands to internalized receptors was modestly lower, indicating that internalization would reduce the binding potential measured in imaging studies carried out with these ligands. However, between-ligand differences in the magnitude of the internalization-associated affinity shift only partly accounted for the data obtained in neuroimaging experiments, suggesting the involvement of mechanisms beyond competition and internalization.