Structural Characterization and Pharmaceutical Properties of Three Novel Cocrystals of Ethenzamide With Aliphatic Dicarboxylic Acids.

Ethenzamide (ET) was screened in cocrystallization experiments with pharmaceutically acceptable coformer molecules to discover materials of improved physicochemical properties, that is, higher solubility and better stability. Three novel cocrystals of ET with glutaric, malonic, and maleic acids were obtained by neat grinding and slow evaporation from solution. The purpose of the study was to notice the changes in the geometry and interactions of ET molecule in crystalline phase introduced by different acid and relate them to physicochemical properties of pure ET. Therefore, the crystal structure of the cocrystals was determined by single crystal X-ray diffraction analysis. The powder samples were characterized by differential scanning calorimetry, Fourier-transform infrared spectroscopy, and 13C and 15N solid-state nuclear magnetic resonance spectroscopy. Spectroscopic studies were supported by gauge including projector augmented wave calculations of chemical shielding constants. The high stability of cocrystals during direct compression was proved. The solubility in simulated gastric fluids for studied cocrystals appeared to be approximately 1.6 times-fold higher than ET. The dissolution rates of all ET cocrystals were not faster than the pure drug, but after 240 min, more drugs were released.

Phase 1 Study of Edasalonexent (CAT-1004), an Oral NF-κB Inhibitor, in Pediatric Patients with Duchenne Muscular Dystrophy.

BACKGROUND: Edasalonexent is an orally administered small molecule designed to inhibit NF-κB, which is activated from infancy in Duchenne muscular dystrophy and is central to causing muscle damage and preventing muscle regeneration. OBJECTIVE: Evaluate the safety, tolerability, pharmacokinetics and exploratory pharmacodynamics of three doses of edasalonexent in ambulatory males ≥4 to <8 years of age with genetically confirmed Duchenne muscular dystrophy. METHODS: This was a 1-week, open-label, multiple-dose study with 3 sequential ascending doses (33, 67 and 100 mg/kg/day) of edasalonexent administered under different dietary conditions to 17 males with a mean age of 5.5 years. RESULTS: All doses of edasalonexent were well tolerated, with no serious adverse events, no drug discontinuations and no dose reductions. The majority of adverse events were mild, and the most common adverse events were gastrointestinal (primarily diarrhea). Edasalonexent was rapidly absorbed with peak levels observed 2-6 hours after dosing and exposures appeared to increase nearly proportionally to dose for the 2 lower and all 3 doses under low-fat and high-fat meal conditions, respectively. Only minor plasma accumulation of edasalonexent was observed with 7 days of dosing. After treatment with edasalonexent for 7 days, levels of NF-κB-regulated genes and serum proteins were decreased. CONCLUSIONS: This first report of edasalonexent oral administration for one week in male pediatric patients with Duchenne muscular dystrophy showed that treatment was well tolerated and inhibited NF-kB pathways.

Failure to detect amphetamine-induced dopamine release in the cortex with [11 C]FLB 457 positron emission tomography (PET): Methodological considerations.

Studies in nonhuman primates and humans have demonstrated that amphetamine-induced dopamine release in the cortex can be measured with [11 C]FLB 457 and PET imaging. This technique has been successfully used in recent clinical studies to show decreased dopamine transmission in the prefrontal cortex in schizophrenia and alcohol dependence. Here, we present data from a cohort of twelve healthy controls in whom an oral amphetamine challenge (0.5 mg kg-1 ) did not lead to a significant reduction in [11 C]FLB 457 BPND (i.e., binding potential relative to non-displaceable uptake). Two factors that likely contributed to the inability to displace [11 C]FLB 457 BPND in this cohort relative to successful cohorts are: (a) the acquisition of the baseline and post-amphetamine scans on different days as opposed to the same day and (b) the initiation of the post-amphetamine [11 C]FLB 457 scan at ∼5 hours as opposed to ∼3 hours following oral amphetamine. Furthermore, we show [11 C]FLB 457 reproducibility data from a legacy dataset to support greater variability in cortical BPND when the test and retest scans are acquired on different days as compared to the same day. These results highlight the methodological challenges that continue to plague the field with respect to imaging dopamine release in the cortex.

Extrastriatal dopamine D2-receptor availability in social anxiety disorder.

Alterations in the dopamine system are hypothesized to influence the expression of social anxiety disorder (SAD) symptoms. However, molecular imaging studies comparing dopamine function between patients and control subjects have yielded conflicting results. Importantly, while all previous investigations focused on the striatum, findings from activation and blood flow studies indicate that prefrontal and limbic brain regions have a central role in the pathophysiology. The objective of this study was to investigate extrastriatal dopamine D2-receptor (D2-R) availability in SAD. We examined 12 SAD patients and 16 healthy controls using positron emission tomography and the high-affinity D2-R radioligand [11C]FLB457. Parametric images of D2-R binding potential were derived using the Logan graphical method with cerebellum as reference region. Two-tailed one-way independent ANCOVAs, with age as covariate, were used to examine differences in D2-R availability between groups using both region-based and voxel-wise analyses. The region-based analysis showed a medium effect size of higher D2-R levels in the orbitofrontal cortex (OFC) in patients, although this result did not remain significant after correction for multiple comparisons. The voxel-wise comparison revealed elevated D2-R availability in patients within OFC and right dorsolateral prefrontal cortex after correction for multiple comparisons. These preliminary results suggest that an aberrant extrastriatal dopamine system may be part of the disease mechanism in SAD.

A Novel NF-κB Inhibitor, Edasalonexent (CAT-1004), in Development as a Disease-Modifying Treatment for Patients With Duchenne Muscular Dystrophy: Phase 1 Safety, Pharmacokinetics, and Pharmacodynamics in Adult Subjects.

In Duchenne muscular dystrophy (DMD), NF-κB is activated in skeletal muscle from infancy regardless of the underlying dystrophin mutation and drives inflammation and muscle degeneration while inhibiting muscle regeneration. Edasalonexent (CAT-1004) is a bifunctional orally administered small molecule that covalently links 2 compounds known to inhibit NF-κB, salicylic acid and docosahexaenoic acid (DHA). Edasalonexent is designed to inhibit activated NF-κB upon intracellular cleavage to these bioactive components. Preclinical data demonstrate disease-modifying activity in DMD animal models. Three placebo-controlled studies in adult subjects assessed the safety, pharmacokinetics, and pharmacodynamics of single or multiple edasalonexent doses up to 6000 mg. Seventy-nine adult subjects received edasalonexent, and 25 received placebo. Pharmacokinetic results were consistent with the intracellular cleavage of edasalonexent to its active components. Food increased plasma exposures of edasalonexent and salicyluric acid, an intracellularly formed metabolite of salicylic acid. The NF-κB pathway and proteosome gene expression profiles in peripheral mononuclear cells were significantly decreased (P = .02 and P = .002, respectively) after 2 weeks of edasalonexent treatment. NF-κB activity was inhibited following a single dose of edasalonexent but not by equimolar doses of salicylic acid and DHA. Edasalonexent was well tolerated, and the most common adverse events were mild diarrhea and headache. In first-in-human studies, edasalonexent was safe, well tolerated, and inhibited activated NF-κB pathways, suggesting potential therapeutic utility in DMD regardless of the causative dystrophin mutation, as well as other NF-κB-mediated diseases.

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

PURPOSE: [(11)C]FLB 457, a radioligand with very high affinity and selectivity for dopamine D2/3 receptors, is used to measure receptor binding in extrastriatal regions showing low density of the receptors. The purpose of this study was to estimate the whole-body biodistribution of radioactivity and the radiation absorbed doses to organs after intravenous injection of [(11)C]FLB 457 in healthy human subjects. METHODS: Whole-body images were acquired for 2 h after an injection of [(11)C]FLB 457 in six healthy humans. Radiation absorbed doses were estimated by the MIRD scheme implemented in OLINDA/EXM 1.1 software. RESULTS: Organs with the longest residence time were the liver, lungs, and brain. The organs with the highest radiation doses were the kidneys, liver, and pancreas. The effective dose delivered by [(11)C]FLB 457 is 5.9 µSv/MBq, similar to those of other (11)C-labeled tracers. CONCLUSIONS: This effective dose would allow multiple scans in the same individual based on prevailing maximum recommended-dose guidelines in the USA and Europe.

Prefrontal dopaminergic receptor abnormalities and executive functions in Parkinson's disease.

The main pattern of cognitive impairments seen in early to moderate stages of Parkinson's disease (PD) includes deficits of executive functions. These nonmotor complications have a significant impact on the quality of life and day-to-day activities of PD patients and are not effectively managed by current therapies, a problem which is almost certainly due to the fact that the disease extends beyond the nigrostriatal system. To investigate the role of extrastriatal dopamine in executive function in PD, PD patients and a control group were studied with positron-emission-tomography using a high-affinity dopamine D2/D3 receptor tracer, [(11) C]FLB-457. All participants were scanned twice while performing an executive task and a control task. Patients were off medication for at least 12 h. The imaging analysis revealed that parkinsonian patients had lower [(11) C]FLB-457 binding than control group independently of task conditions across different brain regions. Cognitive assessment measures were positively correlated with [(11) C]FLB-457 binding in the bilateral dorsolateral prefrontal cortex and anterior cingulate cortex only in control group, but not in PD patients. Within the control group, during the executive task (as compared to control task), there was evidence of reduced [(11) C]FLB-457 binding (indicative of increased dopamine release) in the right orbitofrontal cortex. In contrast, PD patients did not show any reduction in binding during the executive task (as compared with control task). These findings suggest that PD patients present significant abnormalities in extrastriatal dopamine associated with executive processing. These observations provide important insights on the pathophysiology of cognitive dysfunction in PD.

Multi-scale hierarchical approach for parametric mapping: assessment on multi-compartmental models.

This paper investigates a new hierarchical method to apply basis function to mono- and multi-compartmental models (Hierarchical-Basis Function Method, H-BFM) at a voxel level. This method identifies the parameters of the compartmental model in its nonlinearized version, integrating information derived at the region of interest (ROI) level by segmenting the cerebral volume based on anatomical definition or functional clustering. We present the results obtained by using a two tissue-four rate constant model with two different tracers ([(11)C]FLB457 and [carbonyl-(11)C]WAY100635), one of the most complex models used in receptor studies, especially at the voxel level. H-BFM is robust and its application on both [(11)C]FLB457 and [carbonyl-(11)C]WAY100635 allows accurate and precise parameter estimates, good quality parametric maps and a low percentage of voxels out of physiological bound (<8%). The computational time depends on the number of basis functions selected and can be compatible with clinical use (~6h for a single subject analysis). The novel method is a robust approach for PET quantification by using compartmental modeling at the voxel level. In particular, different from other proposed approaches, this method can also be used when the linearization of the model is not appropriate. We expect that applying it to clinical data will generate reliable parametric maps.

Chronic quercetin feeding decreases plasma concentrations of salicylamide phase II metabolites in pigs following oral administration.

We investigated acute effects and effects after chronic intake of the orally administered flavonol quercetin on pharmacokinetics of salicylamide metabolites (SAM) after oral administration of salicylamide in pigs. Salicylamide (8 mg/kg body weight) was orally administered to seven pigs either without or with quercetin (10 mg/kg body weight). Additionally, salicylamide was administered to five pigs that had received a diet supplemented with the flavonol for 1 week. Daily quercetin intake was 10 mg/kg in these animals. Co-ingestion of quercetin with the drug did not alter area under the concentration-time curve (AUC(0→∞)), time to achieve maximum plasma concentration (t(max)), mean residence time (MRT) or half-life (t(1/2)) of SAM. However, maximum plasma concentration (c(max)) of SAM was lower when quercetin was administered concomitantly. After quercetin pre-treatment for 1 week AUC(0→∞), t(1/2) and MRT of SAM were decreased, while other parameters investigated were not affected. Co-ingestions and dietary pre-treatment with quercetin influenced SAM metabolism after oral salicylamide intake. But effects seen after acute concomitant intake are rather explained by induced salicylamide excretion from the intestinal mucosa, whereas quercetin pre-treatment seemed to induce hepatic enzymes involved in phase-II metabolism and thereby enhanced elimination of SAM.

New salicylamide and sulfonamide derivatives of quinoxaline 1,4-di-N-oxide with antileishmanial and antimalarial activities.

Continuing with our efforts to identify new active compounds against malaria and leishmaniasis, 14 new 3-amino-1,4-di-N-oxide quinoxaline-2-carbonitrile derivatives were synthesized and evaluated for their in vitro antimalarial and antileishmanial activity against Plasmodium falciparum Colombian FCR-3 strain and Leishmania amazonensis strain MHOM/BR/76/LTB-012A. Further computational studies were carried out in order to analyze graphic SAR and ADME properties. The results obtained indicate that compounds with one halogenous group substituted in position 6 and 7 provide an efficient approach for further development of antimalarial and antileishmanial agents. In addition, interesting ADME properties were found.

Thiazolides as novel antiviral agents. 1. Inhibition of hepatitis B virus replication.

We report the syntheses and activities of a wide range of thiazolides [viz., 2-hydroxyaroyl-N-(thiazol-2-yl)amides] against hepatitis B virus replication, with QSAR analysis of our results. The prototypical thiazolide, nitazoxanide [2-hydroxybenzoyl-N-(5-nitrothiazol-2-yl)amide, NTZ] 1 is a broad spectrum antiinfective agent effective against anaerobic bacteria, viruses, and parasites. By contrast, 2-hydroxybenzoyl-N-(5-chlorothiazol-2-yl)amide 3 is a novel, potent, and selective inhibitor of hepatitis B replication (EC(50) = 0.33 µm) but is inactive against anaerobes. Several 4'- and 5'-substituted thiazolides show good activity against HBV; by contrast, some related salicyloylanilides show a narrower spectrum of activity. The ADME properties of 3 are similar to 1; viz., the O-acetate is an effective prodrug, and the O-aryl glucuronide is a major metabolite. The QSAR study shows a good correlation of observed EC(90) for intracellular virions with thiazolide structural parameters. Finally we discuss the mechanism of action of thiazolides in relation to the present results.

Striatal and extrastriatal microPET imaging of D2/D3 dopamine receptors in rat brain with [¹8F]fallypride and [¹8F]desmethoxyfallypride.

In this study, we compared two different D(2/3) receptor ligands, [¹8F]fallypride and [¹8F]desmethoxyfallypride ([¹8F]DMFP) with respect to the duration of the scan, visualization of extrastriatal receptors, and binding potentials (BP(ND) ) in the rat brain. In addition, we studied the feasibility of using these tracers following a period of awake tracer uptake, during which the animal may perform a behavioral task. Male Sprague-Dawley rats were imaged with [¹8F]fallypride and with [¹8F]DMFP in four different studies using microPET. All scans were performed under isoflurane anesthesia. The first (test) and second (retest) study were 150-min baseline scans. No retest scans were performed with [¹8F]DMFP. A third study was a 60-min awake uptake of radiotracer followed by a 90-min scan. A fourth study was a 150-min competition scan with haloperidol (0.2 mg/kg) administered via tail vein at 90-min post-[¹8F]fallypride injection and 60-min post-[¹8F]DMFP. For the test-retest studies, BP(ND) was measured using both Logan noninvasive (LNI) method and the interval ratios (ITR) method. Cerebellum was used as a reference region. For the third study, the binding was measured only with the ITR method, and the results were compared to the baseline results. Studies showed that the average transient equilibrium time in the dorsal striatum (DSTR) was at 90 min for [¹8F]fallypride and 30 min for [¹8F]DMFP. The average BP(ND) for [¹8F]fallypride was 14.4 in DSTR, 6.8 in ventral striatum (VSTR), 1.3 in substantia nigra/ventral tegmental area (SN/VTA), 1.4 in colliculi (COL), and 1.5 in central gray area. In the case of [¹8F]DMFP, the average BP(ND) values were 2.2 in DSTR, 2.7 in VSTR, and 0.8 in SN/VTA. The haloperidol blockade showed detectable decrease in binding of both tracers in striatal regions with a faster displacement of [¹8F]DMFP. No significant changes in BP(ND) of [¹8F]fallypride due to the initial awake state of the animal were found, whereas BP(ND) of [¹8F]DMFP was significantly higher in the awake state compared to baseline. We were able to demonstrate that dynamic PET using MicroPET Inveon allows quantification of both striatal and extrastriatal [¹8F]fallypride binding in rats in vivo. Quantification of the striatal regions could be achieved with [¹8F]DMFP.

Extrastriatal dopamine D(2) receptor binding in Huntington's disease.

Huntington's disease (HD) is a neurodegenerative disorder, primarily affecting medium spiny neurones in the striatum. The density of striatal dopamine D(2) receptors is reduced in HD but there is little known about this biomarker in brain regions outside the striatum. The primary objective of this study was to compare extrastriatal dopamine D(2) receptor binding, in age-matched control subjects and patients with HD. All subjects were examined using a high-resolution positron emission tomography system and the high-affinity dopamine D(2) receptor radioligand [(11) C]FLB 457. A ROI based analysis was used with an atrophy correction method. Dopamine D(2) receptor binding potential was reduced in the striatum of patients with HD. Unlike the striatum, dopamine D(2) receptor binding in thalamic and cortical subregions was not significantly different from that in control subjects. A partial least square regression analysis which included binding potential values from all investigated cortical and subcortical regions revealed a significant model separating patients from controls, conclusively dependent on differences in striatal binding of the radioligand. Some clinical assessments correlated with striatal dopamine D(2) receptor binding, including severity of chorea and cognitive test performance. Hence, the present study demonstrates that dopamine D(2) receptors extrinsic to the striatum are well preserved in early to mid stage patients with HD. This observation may have implication for the development of therapy for HD.

Positron emission tomography measurement of dopamine D2 receptor occupancy in the pituitary and cerebral cortex: relation to antipsychotic-induced hyperprolactinemia.

OBJECTIVE: Hyperprolactinemia is a common side effect of antipsychotic drugs used in the treatment of schizophrenia. However, the magnitude of hyperprolactinemia differs among antipsychotics, and there is no reliable mechanism-related marker for the risk of hyperprolactinemia that would allow us to characterize antipsychotics. METHOD: In this study, 11 healthy male subjects taking different doses of sulpiride and 24 male patients with DSM-IV-diagnosed schizophrenia taking different antipsychotic drugs (risperidone, olanzapine, haloperidol, and sulpiride) participated. Positron emission tomography scanning using [¹¹C]FLB 457 was performed on all subjects. The dopamine D2receptor occupancy of antipsychotics in the pituitary and temporal cortex was calculated. Correlations between plasma concentration of prolactin and dopamine D2receptor occupancies were evaluated. The ratio of drug concentration of cerebral receptor site to that of pituitary receptor site (brain/plasma concentration ratio; B/P ratio) was calculated from the receptor occupancies in the 2 regions. Data were collected between November 2001 and September 2007. RESULTS: Significant positive correlation was observed between the plasma concentration of prolactin and dopamine D2receptor occupancy in the pituitary by all 4 antipsychotics (P = .001). Dopamine D2receptor occupancies of sulpiride were markedly different between the pituitary and temporal cortex, and the B/P ratio for sulpiride (0.34) was significantly lower than for olanzapine (P = .007) and risperidone (P = .015). Olanzapine had a relatively high B/P ratio (2.70), followed by haloperidol (2.40) and risperidone (1.61). CONCLUSIONS: Dopamine D2receptor occupancy in the pituitary is a good indicator of hyperprolactinemia. B/P ratio, indicating the penetrating capability across the blood-brain barrier, seems to be a good characteristic biomarker of each antipsychotic drug for the risk of hyperprolactinemia at therapeutic dose.

Endogenous competition against binding of [(18)F]DMFP and [(18)F]fallypride to dopamine D(2/3) receptors in brain of living mouse.

AIM: Molecular imaging studies with benzamide radioligands can reveal competition from endogenous binding at D(2/3)-receptors in living brain. However, single photon emission computed tomography (SPECT) methods suffer from limited spatial resolution, and [(11)C]-labeled ligands are only available at positron emission tomography (PET) research sites with cyclotron-radiochemistry facilities, whereas [(18)F] can be transported, due to its longer physical half-life. Therefore, we endeavored to characterize the vulnerabilities of the benzamide antagonist [(18)F]desmethoxyfallypride (DMFP) and its high-affinity congener [(18)F]fallypride (FP) to competition from endogenous dopamine in living mouse brain. METHODS: Groups of awake mice were pretreated with saline, amphetamine (10 mg/kg), or reserpine (5 mg/kg), followed by i.v. tracer injections. Mice were killed at 2.5-90 min (DMFP) or 2.5-180 min (FP) circulation times. Brains were dissected and regional radioactivity concentration measured by gamma counting. Other groups of mice were anesthetized for dynamic microPET recordings with DMFP or FP. Binding potentials (BP(ND)) were calculated using cerebellum as reference region. RESULTS: With 90-min circulation, DMFP BP(ND) in striatum was 2.4 by dissection and 2.2 by microPET, which showed a 62% decrease in response to amphetamine-evoked dopamine release and a 33% increase after reserpine-evoked dopamine depletion. With 120-min circulation, FP BP(ND) in striatum was 24.1 by dissection and 9.2 by microPET, which showed a 31% decrease in the amphetamine group, but no effect of reserpine. Dissection showed similar sensitivities for FP binding, but only a 29% amphetamine-evoked reduction for DMFP. CONCLUSIONS: Relative to gold standard ex vivo results, microPET estimates of DMFP BP(ND) were unbiased, whereas FP BP(ND) in striatum was substantially underestimated. Both tracers proved suitable for revealing pharmacologically evoked changes in competition at D(2/3)-receptors in striatum of living mice.

Extrastriatal dopamine D(2) receptor occupancy in olanzapine-treated patients with schizophrenia.

Olanzapine is described as a multi-acting receptor-targeted antipsychotic agent. Although regional differences of dopamine D(2) receptor occupancy, i.e., limbic selectivity, were reported for olanzapine, contradictory results were also reported. We measured dopamine D(2) receptor occupancy of olanzapine in extrastriatal regions in patients with schizophrenia using positron-emission tomography with [(11)C]FLB457 and the plasma concentrations of olanzapine. Ten patients with schizophrenia taking 5-20 mg/day of olanzapine participated. Dopamine D(2) receptor occupancy in the temporal cortex ranged from 61.1 to 85.8%, and plasma concentration was from 12.7 to 115.4 ng/ml. The ED(50) value was 3.4 mg/day for dose and 10.5 ng/ml for plasma concentration. The ED(50) values obtained in this study were quite similar to those previously reported in the striatum. In conclusion, although the subjects and methods were different from previous striatal occupancy studies, these results suggest that limbic occupancy by olanzapine may not be so different from that in the striatum.

Increased dopamine release in the right anterior cingulate cortex during the performance of a sorting task: a [11C]FLB 457 PET study.

There is clear evidence that the prefrontal cortex is strongly involved in executive processes and that dopamine can influence performance on working memory tasks. Although, some studies have emphasized the role of striatal dopamine in executive functions, the role played by prefrontal dopamine during executive tasks is unknown. In order to investigate cortical dopamine transmission during executive function, we used D(2)-dopamine receptor ligand [(11)C]FLB 457 PET in healthy subjects while performing the Montreal Card Sorting Task (MCST). During the retrieval with shift task of the MCST, the subjects had to match each test card to one of the reference cards based on a classification rule (color, shape or number) determined by comparing the previously viewed cue card and the current test card. A reduction in [(11)C]FLB 457 binding potential in the right dorsal anterior cingulate cortex (ACC) was observed when subjects performed the active task compared to the control task. These findings may suggest that right dorsal ACC dopamine neurotransmission increases significantly during the performance of certain executive processes, e.g., conflict monitoring, in keeping with previous evidence from fMRI studies showing ACC activation during similar tasks. These results may provide some insights on the origin of cognitive deficits underlying certain neurological disorders associated with dopamine dysfunction, such as Parkinson's disease and schizophrenia.

Error analysis for PET measurement of dopamine D2 receptor occupancy by antipsychotics with [11C]raclopride and [11C]FLB 457.

Dopamine D(2) receptor occupancy by antipsychotic drugs has been measured with positron emission tomography (PET) by comparing the binding potential (BP) values before and after drug administration. This occupancy has been found to be related to clinical effects and side effects. In this study, we evaluated the uncertainty of the quantitative analysis for estimating the dopamine D(2) receptor occupancy by antipsychotics in simulation and human studies of [(11)C]raclopride and for the high affinity ligand [(11)C]FLB 457. Time-activity curves of [(11)C]raclopride and [(11)C]FLB 457 were simulated, and the reliability of BP estimated by a simplified reference tissue model and the calculated occupancy were investigated for various noise levels, BP values, and scan durations. Then, in the human PET study with and without antipsychotics, the uncertainty of BP and occupancy estimates and the scan duration required for a reliable estimation were investigated by a bootstrap approach. Reliable and unbiased estimates of [(11)C]raclopride BP(ND) could be obtained with recording as short as 32 min, with the relative standard deviation (SD) of the striatal occupancy remaining less than 10%. Conversely, in [(11)C]FLB 457 studies, the mean value increased and SD of the temporal cortex and thalamus exceeded 10% when the scan duration was shorter than 60 min. These results demonstrated that dopamine D(2) receptor occupancy by antipsychotics can be estimated precisely with an optimal scan duration with [(11)C]raclopride and [(11)C]FLB 457.

Asymmetry in dopamine D(2/3) receptors of caudate nucleus is lost with age.

Molecular and functional imaging techniques reveal evidence for lateralization of human cerebral function. Based on animal data, we hypothesized that asymmetry in dopamine neurotransmission declines during normal aging. In order to test this hypothesis, we measured dopamine D2/3 receptor availability with [18F]desmethoxyfallypride-PET (DMFP) in putamen and caudate nucleus (NC) of 21 healthy, right-handed males (24-60 years; 35+/-10). For volumetric analysis, high-resolution T1-weighted MR-images were obtained in 18 of the PET-subjects in order to assess possible age-related decreases in NC and putamen volume. The calculated DMFP binding potentials (BP) showed a right-ward asymmetry in NC of young subjects that decreased with age (r = 0.577, p = 0.006; Pearson correlation; two-tailed). An age-independent analysis showed a right-ward asymmetry in NC of the whole subject group (left: 1.49+/-0.35; right: 1.65+/-0.43 [mean+/-S.D.]; p = 0.020). No such side lateralization or age-effects could be found in the putamen. Volumes tended to be asymmetric in the putamen (right: 4.85+/-0.56 cm3; left: 4.64+/-0.86 cm3 [mean+/-S.D.]; p = 0.063), but not in NC. The decline of putamen volume during aging was significant in the right putamen (r = -0.613; p = 0.007; Pearson correlation; two-tailed). There were no other significant correlations between striatal volumes and age or BP. Because ventral striatal dopamine neurotransmission is involved in cognitive processes, this loss of physiological asymmetry in NC dopamine transmission during aging might be involved in age-related declines of cognitive performance.

Time course of dopamine D2 receptor occupancy by clozapine with medium and high plasma concentrations.

Most antipsychotics were thought to induce antipsychotic action at an excess of 70% striatal dopamine D2 receptor occupancy, while the clinical dose of clozapine was reported to show less than 60% occupancy. High-dose clozapine could occupy as high as 80% of striatal dopamine D2 receptor in monkey PET studies. Although the time course of dopamine D2 receptor occupancy is an important property of antipsychotics, that by clozapine has not been investigated in a clinical setting. We measured the time course of extrastriatal dopamine D2 receptor occupancy with different doses of clozapine and evaluated whether the measured occupancies fitted the binding theory. Three consecutive PET scans with [11C]FLB 457 were performed for two patients with schizophrenia, chronically taking 600 mg/day and 200 mg/day of clozapine, respectively. Series of occupancies were also measured in combination with fluvoxamine or paroxetine in one patient. Dopamine D2 receptor occupancies were also simulated using individual clozapine plasma data and previously determined in vivo ED50 value. The occupancy of one patient with high plasma concentration (1207 ng/ml at peak time) was around 75% at peak and around 60% after 26 h. Another patient with medium plasma concentration (649 ng/ml at peak time) showed less than 50% occupancy at peak, decreasing to 15% after 25 h. The measured occupancy values fitted well with the simulated occupancy values. At high plasma concentration, clozapine can induce high extrastriatal dopamine D2 receptor occupancy in the human brain, and this finding fitted well with the theoretical estimation.