RESUMO
BACKGROUND: The serotonin system has been implicated in several psychiatric disorders. All major psychiatric disorders are associated with cognitive impairment, but treatment improving cognitive deficits is lacking, partly due to limited understanding of the neurobiology of cognitive functioning. Several markers for the serotonin system have been associated with cognitive functions. Our research group previously has reported a positive correlation between serotonin (5-HT1B) receptor availability in the dorsal brainstem and visuospatial memory in a pilot study of healthy individuals. Here, we aim to replicate our previous finding in a larger group of healthy volunteers as well as to investigate putative associations between 5-HT1B receptor availability and other cognitive domains. METHODS: Forty-three healthy individuals were examined with positron emission tomography using the 5-HT1B receptor radioligand [11C]AZ10419369 and a visuospatial memory test to replicate our previous finding as well as tests of verbal fluency, cognitive flexibility, reaction time, and planning ability to explore other domains potentially associated with the serotonin system. RESULTS: Replication analysis revealed no statistically significant association between 5-HT1B receptor availability in the dorsal brainstem and visuospatial memory performance. Exploratory analyses showed age-adjusted correlations between 5-HT1B receptor availability in whole brain gray matter and specific brain regions, and number of commission errors, reaction time, and planning ability. CONCLUSIONS: Higher 5-HT1B receptor availability was associated with more false-positive responses and faster reaction time but lower performance in planning and problem-solving. These results corroborate previous research supporting an important role of the serotonin system in impulsive behavior and planning ability.
Assuntos
Receptor 5-HT1B de Serotonina , Serotonina , Humanos , Radioisótopos de Carbono , Projetos Piloto , Morfolinas , Encéfalo/diagnóstico por imagem , Tomografia por Emissão de Pósitrons/métodos , CogniçãoRESUMO
BACKGROUND: The molecular actions underlying the clinical effects of inhaled anaesthetics such as sevoflurane and isoflurane are not fully understood. Unexpected observations in positron emission tomography (PET) studies with [11C]AZD9272, a metabotropic glutamate receptor 5 (mGluR5) radioligand with possible affinity for monoamine oxidase-B (MAO-B), suggest that its binding is sensitive to anaesthesia with sevoflurane. The objective of the present study was to assess the effects of sevoflurane anaesthesia on the binding of [11C]AZD9272 and of [11C]L-deprenyl-D2, a radioligand selective for MAO-B in non-human primates (NHPs). METHODS: Altogether, 12 PET measurements were conducted with a high-resolution research tomograph using the ligands [11C]AZD9272 or [11C]L-deprenyl-D2 in six cynomolgus monkeys anaesthetised with sevoflurane or ketamine/xylazine. RESULTS: The specific binding of [11C]AZD9272 and [11C]L-deprenyl-D2 was markedly reduced during anaesthesia with sevoflurane compared with ketamine/xylazine. The reduction was 80-90% (n=3) for [11C]AZD9272 and 77-80% (n=3) for [11C]L-deprenyl-D2. CONCLUSIONS: Sevoflurane anaesthesia inhibited radioligand binding to MAO-B in the primate brain. The observation of lower MAO-B binding at clinically relevant concentrations of sevoflurane warrants further exploration of the potential role of MAO-B related mechanisms in regulation of systemic blood pressure during anaesthesia.
Assuntos
Anestésicos Inalatórios/farmacologia , Encéfalo/efeitos dos fármacos , Monoaminoxidase/efeitos dos fármacos , Sevoflurano/farmacologia , Animais , Encéfalo/diagnóstico por imagem , Encéfalo/metabolismo , Macaca fascicularis , Modelos Animais , Monoaminoxidase/metabolismo , Tomografia por Emissão de Pósitrons/métodos , Ensaio Radioligante/métodosRESUMO
Synaptic vesicle glycoprotein 2A (SV2A) has been previously characterized as an imaging biomarker for assessment of synaptic density in positron emission tomography (PET) studies of patients with neurological conditions. To provide detailed maps of the brain localization of SV2A autoradiography studies were carried out using the SV2A radioligand [11 C]UCB-J and whole hemisphere sections of non-human primate (NHP) and human brain. Binding of [11 C]UCB-J was observed in all evaluated grey matter structures of the primate brain, with highest density in the caudate nucleus and cortex and lowest density in pons and globus pallidus. The density of [11 C]UCB-J binding sites in human brain showed a good correlation with that in NHP brain. Binding of [11 C]UCB-J in the white matter was very low relative to that in grey matter containing structures and was only inhibited to a minor extent by co-incubation with a saturating concentration of unlabelled UCB-J. The high-resolution images obtained in the present study may aid the interpretation of data acquired in human subjects examined using [11 C]UCB-J in PET studies. In addition, observation of low binding for [11 C]UCB-J in white matter (centrum semiovale) supports that this structure can be used as a reference region for quantitative analysis of [11 C]UCB-J PET data.
Assuntos
Encéfalo/metabolismo , Glicoproteínas de Membrana/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Adulto , Animais , Encéfalo/crescimento & desenvolvimento , Feminino , Substância Cinzenta/diagnóstico por imagem , Substância Cinzenta/metabolismo , Humanos , Macaca fascicularis , Masculino , Pessoa de Meia-Idade , Tomografia por Emissão de Pósitrons , Ligação Proteica , Piridinas/farmacocinética , Pirrolidinas/farmacocinética , Compostos Radiofarmacêuticos/farmacocinética , Substância Branca/diagnóstico por imagem , Substância Branca/metabolismoRESUMO
PURPOSE: To examine the hypothesis that cerebral binding to the 18 kDa translocator protein (TSPO), a marker of microglia activation, is elevated in Parkinson's disease (PD), and to assess the relationship between brain TSPO binding and dopaminergic pathology in PD. METHODS: The radioligand [11C]PBR28 was used for quantitative assessment of brain TSPO in 16 control subjects and 16 PD patients. To analyse the relationship between dopaminergic pathology and brain TSPO binding, PET studies of the dopamine transporter (DAT) were undertaken in PD patients using the DAT radioligand [18F]FE-PE2I. The total distribution volume of [11C]PBR28 was quantified in nigrostriatal regions, limbic cortices and thalamus, and the binding potential of [18F]FE-PE2I was quantified in nigrostriatal regions. RESULTS: Based on genotype analysis of the TSPO rs6971 polymorphism, 16 subjects (8 control subjects and 8 PD patients) were identified as high-affinity binders, and the remaining subjects were identified as mixed-affinity binders. A two-way ANOVA showed a strong main effect of TSPO genotype on the cerebral binding of [11C]PBR28, whereas no statistically significant main effect of diagnostic group, or a group by genotype interaction was found for any of the regions analysed. [18F]FE-PE2I PET studies in patients indicated a marked reduction in nigrostriatal binding to DAT. However, no correlations between the binding parameters were found for [11C]PBR28 and [18F]FE-PE2I. CONCLUSION: The findings do not support the hypothesis of elevated cerebral TSPO binding or a relationship between TSPO binding and dopaminergic pathology in PD.
Assuntos
Proteínas da Membrana Plasmática de Transporte de Dopamina/metabolismo , Doença de Parkinson/diagnóstico por imagem , Doença de Parkinson/metabolismo , Tomografia por Emissão de Pósitrons , Pirimidinas/metabolismo , Receptores de GABA/metabolismo , Idoso , Encéfalo/diagnóstico por imagem , Encéfalo/metabolismo , Estudos de Casos e Controles , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Ligação ProteicaRESUMO
Carbon-11 labeled SL25.1188 is a promising reversible monoamine oxidase-B (MAO-B) radioligand that was recently translated for human positron emission tomography (PET) imaging. Herein, we report the development of a novel fluorinated derivative, namely, [18F](S)-3-(6-(3-fluoropropoxy)benzo[d]isoxazol-3-yl)-5-(methoxymethyl)oxazolidin-2-one ([18F]FSL25.1188; [18F]6), as a candidate 18F-labeled MAO-B radioligand, and, its subsequent preclinical evaluation in non-human primates (NHP). [18F]6 was produced and isolated (>6â¯GBq) with high radiochemical purity (>99%), and molar activity (>100â¯GBq/µmol at time of injection). Autoradiography studies conducted in post-mortem human brain sections revealed [18F]6 binding in MAO-B rich regions. PET imaging study of [18F]6 in NHP showed high brain uptake (SUVâ¯>â¯2.5) as well as a regional brain radioactivity distribution in accordance with MAO-B expression. [18F]6 displayed favorable in vivo kinetics, with an early peak in the time-activity curve followed by progressive wash-out from the NHP brain. Specificity of [18F]6 was investigated in a pre-treatment study with l-deprenyl (1.0â¯mg/kg) wherein reduced radioligand uptake was observed in all MAO-B rich regions. Results from the current preclinical investigation suggests [18F]6 is a promising MAO-B PET radioligand. Further evaluation of [18F]6 and structurally related 18F-analogs are underway to identify an optimized candidate for clinical research studies.
Assuntos
Monoaminoxidase/metabolismo , Tomografia por Emissão de Pósitrons/métodos , Compostos Radiofarmacêuticos/síntese química , HumanosRESUMO
Positron emission tomography (PET) is widely applied in central nervous system (CNS) drug development for assessment of target engagement in vivo. As the majority of PET investigations have addressed drug interaction at a single binding site, findings of multitarget engagement have been less frequently reported and have often been inconsistent with results obtained in vitro. AZD3676 [N,N-dimethyl-7-(4-(2-(pyridin-2-yl)ethyl)piperazin-1-yl) benzofuran-2-carboxamide] is a novel combined serotonin (5-hydroxytryptamine) 5-HT1A and 5-HT1B receptor antagonist that was developed for the treatment of cognitive impairment in Alzheimer's disease. Here, we evaluated the properties of AZD3676 as a CNS drug by combining in vitro and ex vivo radioligand binding techniques, behavioral pharmacology in rodents, and PET imaging in nonhuman primates. Target engagement in the nonhuman primate brain was assessed in PET studies by determination of drug-induced occupancy using receptor-selective radioligands. AZD3676 showed preclinical properties consistent with CNS drug potential, including nanomolar receptor affinity and efficacy in rodent models of learning and memory. In PET studies of the monkey brain, AZD3676 inhibited radioligand binding in a dose-dependent manner with similar affinity at both receptors. The equally high affinity at 5-HT1A and 5-HT1B receptors as determined in vivo was not predicted from corresponding estimates obtained in vitro, suggesting more than 10-fold selectivity for 5-HT1A versus 5-HT1B receptors. These findings support the further integrated use of PET for confirmation of multitarget occupancy of CNS drugs. Importantly, earlier introduction of PET studies in nonhuman primates may reduce future development costs and the requirement for animal experiments in preclinical CNS drug development programs.
Assuntos
Benzofuranos/metabolismo , Benzofuranos/farmacologia , Piperazinas/metabolismo , Piperazinas/farmacologia , Tomografia por Emissão de Pósitrons , Psicotrópicos/metabolismo , Psicotrópicos/farmacologia , Quinazolinas/metabolismo , Quinazolinas/farmacologia , Animais , Proteínas Sanguíneas/metabolismo , Encéfalo/diagnóstico por imagem , Encéfalo/efeitos dos fármacos , Encéfalo/metabolismo , Encéfalo/fisiologia , Humanos , Macaca fascicularis , Memória/efeitos dos fármacos , Camundongos , Receptor 5-HT1A de Serotonina/metabolismo , Receptor 5-HT1B de Serotonina/metabolismo , Antagonistas do Receptor 5-HT1 de Serotonina/metabolismo , Antagonistas do Receptor 5-HT1 de Serotonina/farmacologiaRESUMO
BACKGROUND: Previous autoradiography studies have suggested a marked interspecies variation in the neuroanatomical localization and expression levels of the neurokinin 3 receptor, with high density in the brain of rat, gerbil, and guinea pig, but at the time offered no conclusive evidence for its presence in the human brain. Hitherto available radioligands have displayed low affinity for the human neurokinin 3 receptor relative to the rodent homologue and may thus not be optimal for cross-species analyses of the expression of this protein. METHODS: A novel neurokinin 3 receptor radioligand, [(18)F]Lu AF10628 ((S)-N-(cyclobutyl(3-fluorophenyl)methyl)-8-fluoro-2-((3-[(18)F]-fluoropropyl)amino)-3-methyl-1-oxo-1,2-dihydroisoquinoline-4-carboxamide), was synthesized and used for autoradiography studies in cryosections from guinea pig, monkey, and human brain as well as for positron emission tomography studies in guinea pig and monkey. RESULTS: The results confirmed previous observations of interspecies variation in the neurokinin 3 receptor brain localization with more extensive distribution in guinea pig than in primate brain. In the human brain, specific binding to the neurokinin 3 receptor was highest in the amygdala and in the hypothalamus and very low in other regions examined. Positron emission tomography imaging showed a pattern consistent with that observed using autoradiography. The radioactivity was, however, found to accumulate in skull bone, which limits the use of this radioligand for in vivo quantification of neurokinin 3 receptor binding. CONCLUSION: Species differences in the brain distribution of neurokinin 3 receptors should be considered when using animal models for predicting human neurokinin 3 receptor pharmacology. For positron emission tomography imaging of brain neurokinin 3 receptors, additional work is required to develop a radioligand with more favorable in vivo properties.
Assuntos
Encéfalo/metabolismo , Receptores da Neurocinina-3/metabolismo , Animais , Autorradiografia , Osso e Ossos/metabolismo , Cobaias , Humanos , Macaca fascicularis , Tomografia por Emissão de Pósitrons , Ensaio Radioligante , Especificidade da EspécieRESUMO
Impaired mitochondrial function, oxidative stress and formation of excessive levels of reactive oxygen species play a key role in neurodegeneration in Parkinson's disease. Myeloperoxidase is a reactive oxygen generating enzyme and is expressed by microglia. The novel compound AZD3241 is a selective and irreversible inhibitor of myeloperoxidase. The hypothesized mechanism of action of AZD3241 involves reduction of oxidative stress leading to reduction of sustained neuroinflammation. The purpose of this phase 2a randomized placebo controlled multicentre positron emission tomography study was to examine the effect of 8 weeks treatment with AZD3241 on microglia in patients with Parkinson's disease. Parkinson patients received either AZD3241 600 mg orally twice a day or placebo (in 3:1 ratio) for 8 weeks. The binding of (11)C-PBR28 to the microglia marker 18 kDa translocator protein, was examined using positron emission tomography at baseline, 4 weeks and 8 weeks. The outcome measure was the total distribution volume, estimated with the invasive Logan graphical analysis. The primary statistical analysis examined changes in total distribution volume after treatment with AZD3241 compared to baseline. Assessments of safety and tolerability of AZD3241 included records of adverse events, vital signs, electrocardiogram, and laboratory tests. The patients had a mean age of 62 (standard deviation = 6) years; 21 were male, three female and mean Unified Parkinson's Disease Rating Scale III score (motor examination) ranged between 6 and 29. In the AD3241 treatment group (n = 18) the total distribution volume of (11)C-PBR28 binding to translocator protein was significantly reduced compared to baseline both at 4 and 8 weeks (P < 0.05). The distribution volume reduction across nigrostriatal regions at 8 weeks ranged from 13-16%, with an effect size equal to 0.5-0.6. There was no overall change in total distribution volume in the placebo group (n = 6). AZD3241 was safe and well tolerated. The reduction of (11)C-PBR28 binding to translocator protein in the brain of patients with Parkinson's disease after treatment with AZD3241 supports the hypothesis that inhibition of myeloperoxidase has an effect on microglia. The results of the present study provide support for proof of mechanism of AZD3241 and warrant extended studies on the efficacy of AZD3241 in neurodegenerative disorders.
Assuntos
Inibidores Enzimáticos/uso terapêutico , Microglia/efeitos dos fármacos , Doença de Parkinson , Tomografia por Emissão de Pósitrons , Idoso , Relação Dose-Resposta a Droga , Método Duplo-Cego , Feminino , Radioisótopos de Flúor , Seguimentos , Humanos , Masculino , Microglia/diagnóstico por imagem , Pessoa de Meia-Idade , Doença de Parkinson/diagnóstico por imagem , Doença de Parkinson/tratamento farmacológico , Doença de Parkinson/patologia , Polimorfismo de Nucleotídeo Único/genética , Ligação Proteica/efeitos dos fármacos , Pirimidinas/sangue , Pirimidinonas/farmacologia , Pirimidinonas/uso terapêutico , Pirróis/farmacologia , Pirróis/uso terapêutico , Receptores de GABA/genética , Índice de Gravidade de DoençaRESUMO
BACKGROUND: Positron emission tomography microdosing of radiolabeled drugs allows for noninvasive studies of organ exposure in vivo. The aim of the present study was to examine and compare the brain exposure of 12 commercially available CNS drugs and one non-CNS drug. METHODS: The drugs were radiolabeled with (11)C (t 1/2 = 20.4 minutes) and examined using a high resolution research tomograph. In cynomolgus monkeys, each drug was examined twice. In rhesus monkeys, a first positron emission tomography microdosing measurement was repeated after preadministration with unlabeled drug to examine potential dose-dependent effects on brain exposure. Partition coefficients between brain and plasma (KP) were calculated by dividing the AUC0-90 min for brain with that for plasma or by a compartmental analysis (VT). Unbound KP (KP u,u) was obtained by correction for the free fraction in brain and plasma. RESULTS: After intravenous injection, the maximum radioactivity concentration (C max, %ID) in brain ranged from 0.01% to 6.2%. For 10 of the 12 CNS drugs, C max, %ID was >2%, indicating a preferential distribution to brain. A lower C max, %ID was observed for morphine, sulpiride, and verapamil. K P ranged from 0.002 (sulpiride) to 68 (sertraline) and 7 of 13 drugs had KP u,u close to unity. For morphine, sulpiride, and verapamil, K P u,u was <0.3, indicating impaired diffusion and/or active efflux. Brain exposure at microdosing agreed with pharmacological dosing conditions for the investigated drugs. CONCLUSIONS: This study represents the largest positron emission tomography study on brain exposure of commercially available CNS drugs in nonhuman primates and may guide interpretation of positron emission tomography microdosing data for novel drug candidates.
Assuntos
Encéfalo/efeitos dos fármacos , Encéfalo/diagnóstico por imagem , Fármacos do Sistema Nervoso Central/farmacocinética , Morfina/farmacocinética , Sulpirida/farmacocinética , Verapamil/farmacocinética , Animais , Encéfalo/metabolismo , Radioisótopos de Carbono , Fármacos do Sistema Nervoso Central/administração & dosagem , Relação Dose-Resposta a Droga , Feminino , Macaca fascicularis , Macaca mulatta , Modelos Biológicos , Modelos Químicos , Morfina/administração & dosagem , Tomografia por Emissão de Pósitrons , Compostos Radiofarmacêuticos , Sulpirida/administração & dosagem , Verapamil/administração & dosagemRESUMO
AIM: The simplified reference tissue model (SRTM) is used for estimation of receptor occupancy assuming that the non-displaceable binding in the reference region is identical to the brain regions of interest. The aim of this work was to extend the SRTM to also account for inter-regional differences in non-displaceable concentrations, and to investigate if this model allowed estimation of receptor occupancy using white matter as reference. It was also investigated if an apparent higher affinity in caudate compared with other brain regions, could be better explained by a difference in the extent of non-displaceable binding. METHODS: The analysis was based on a PET study in six healthy volunteers using the 5-HT1B receptor radioligand [(11)C]-AZ10419369. The radioligand was given intravenously as a tracer dose alone and following different oral doses of the 5-HT1B receptor antagonist AZD3783. Non-linear mixed effects models were developed where differences between regions in non-specific concentrations were accounted for. The properties of the models were also evaluated by means of simulation studies. RESULTS: The estimate (95% CI) of Ki(PL) was 10.2 ng ml(-1) (5.4, 15) and 10.4 ng ml(-1) (8.1, 13.6) based on the extended SRTM with white matter as reference and based on the SRTM using cerebellum as reference, respectively. The estimate (95% CI) of Ki(PL) for caudate relative to other brain regions was 55% (48, 62%). CONCLUSIONS: The extended SRTM allows consideration of white matter as reference region when no suitable grey matter region exists. AZD3783 affinity appears to be higher in the caudate compared with other brain regions.
Assuntos
Benzopiranos/metabolismo , Encéfalo/metabolismo , Modelos Biológicos , Morfolinas/metabolismo , Piperazinas/metabolismo , Ensaio Radioligante , Receptor 5-HT1B de Serotonina/metabolismo , Adulto , Radioisótopos de Carbono/metabolismo , Neuroimagem Funcional , Humanos , Masculino , Tomografia por Emissão de PósitronsRESUMO
BACKGROUND: The neurotransmitter norepinephrine has been implicated in psychiatric and neurodegenerative disorders. Examination of synaptic norepinephrine concentrations in the living brain may be possible with positron emission tomography (PET), but has been hampered by the lack of suitable radioligands. METHODS: We explored the use of the novel α2C-adrenoceptor antagonist PET tracer [(11)C]ORM-13070 for measurement of amphetamine-induced changes in synaptic norepinephrine. The effect of amphetamine on [(11)C]ORM-13070 binding was evaluated ex vivo in rat brain sections and in vivo with PET imaging in monkeys. RESULTS: Microdialysis experiments confirmed amphetamine-induced elevations in rat striatal norepinephrine and dopamine concentrations. Regional [(11)C]ORM-13070 receptor binding was high in the striatum and low in the cerebellum. After injection of [(11)C]ORM-13070 in rats, mean striatal specific binding ratios, determined using cerebellum as a reference region, were 1.4±0.3 after vehicle pretreatment and 1.2±0.2 after amphetamine administration (0.3mg/kg, subcutaneous). Injection of [(11)C]ORM-13070 in non-human primates resulted in mean striatal binding potential (BP ND) estimates of 0.65±0.12 at baseline. Intravenous administration of amphetamine (0.5 and 1.0mg/kg, i.v.) reduced BP ND values by 31-50%. Amphetamine (0.3mg/kg, subcutaneous) increased extracellular norepinephrine (by 400%) and dopamine (by 270%) in rat striata. CONCLUSIONS: Together, these results indicate that [(11)C]ORM-13070 may be a useful tool for evaluation of synaptic norepinephrine concentrations in vivo. Future studies are required to further understand a potential contribution of dopamine to the amphetamine-induced effect.
Assuntos
Anfetamina/farmacologia , Encéfalo/efeitos dos fármacos , Estimulantes do Sistema Nervoso Central/farmacologia , Tomografia por Emissão de Pósitrons , Receptores Adrenérgicos alfa 2/metabolismo , Inibidores da Captação Adrenérgica/farmacologia , Antagonistas de Receptores Adrenérgicos alfa 2/farmacologia , Animais , Cloridrato de Atomoxetina , Dioxanos/metabolismo , Feminino , Humanos , Imidazóis/farmacologia , Macaca fascicularis , Masculino , Piperazinas/metabolismo , Propilaminas/farmacologia , Ligação Proteica/efeitos dos fármacos , Compostos Radiofarmacêuticos/metabolismo , Ratos , Ratos Sprague-Dawley , Fatores de TempoRESUMO
Both central and peripheral cannabinoid receptor type 1 (CB1R) have been considered to be among the key targets for obesity treatment. First generation CB1R antagonists/inverse agonists such as rimonabant and taranabant exhibited severe CNS side effects such as anxiety and depression, which are considered to be related to the compounds' ability to access central CB1R. Recently, several compounds have been developed as second generation antagonists with a profile of restriction to peripheral CB1R. We evaluated the distribution of TM38837, a second generation CB1R antagonist, using brain and whole body PET in three cynomolgus monkeys, and established the relationship between CB1R occupancy and dose/plasma concentration of TM38837 in comparison with rimonabant. A brain PET study was performed using [(11) C]MePPEP, a PET radioligand for CB1R, to evaluate the brain CB1R occupancy of TM38837 at various plasma concentrations in comparison with rimonabant at known efficacious plasma concentrations. A whole body PET study was performed to investigate the change of peripheral distribution of [(11) C]MePPEP by TM38837 administration, which indirectly estimated the effects to the peripheral CB1R by TM38837. CB1R occupancy by both TM38837 and rimonabant increased in a dose/plasma concentration-dependent manner. However, in vivo affinity by plasma level was more than 100 times lower for TM38837. Peripherally, [(11) C]MePPEP accumulation decreased in gall bladder and brown adipose tissue by TM38837 administration. TM38837 showed rather lower CB1R occupancy than rimonabant at the expected therapeutic plasma level, which is expected to reduce CNS side effects in clinical situations. Further clinical development of TM38837 is warranted.
Assuntos
Encéfalo/efeitos dos fármacos , Agonistas de Receptores de Canabinoides/farmacocinética , Piperidinas/farmacocinética , Pirazóis/farmacocinética , Receptor CB1 de Canabinoide/antagonistas & inibidores , Tecido Adiposo Marrom/efeitos dos fármacos , Tecido Adiposo Marrom/metabolismo , Animais , Autorradiografia , Encéfalo/metabolismo , Agonistas de Receptores de Canabinoides/administração & dosagem , Agonistas de Receptores de Canabinoides/sangue , Vesícula Biliar/efeitos dos fármacos , Vesícula Biliar/metabolismo , Macaca fascicularis , Imageamento por Ressonância Magnética , Piperidinas/administração & dosagem , Piperidinas/sangue , Tomografia por Emissão de Pósitrons , Pirazóis/administração & dosagem , Pirazóis/sangue , Pirrolidinonas/metabolismo , Receptor CB1 de Canabinoide/metabolismo , RimonabantoRESUMO
The metabotropic glutamate receptor 2 (mGluR2) has emerged as a potential therapeutic target for the treatment of various neurological diseases, prompting substantial interest in the development of mGluR2-targeted drug candidates. As part of our medicinal chemistry program, we synthesized a series of isoindolone derivatives and assessed their potential as mGluR2 positive allosteric modulators (PAMs). Notably, AZ12559322 exhibited high affinity (K i mGluR2 = 1.31 nM) and an excellent in vitro binding specificity of 89% while demonstrating selectivity over other mGluR subtypes (>4000-fold). Autoradiography with the radiolabeled counterpart, [3H]AZ12559322, revealed a heterogeneous accumulation with the highest binding in mGluR2-rich brain regions. Radioligand binding was significantly reduced by pretreatment with nonradioactive mGluR2 PAMs in brains of rats and nonhuman primates. Although positron emission tomography imaging of [11C]AZ12559322 (6a) revealed low brain uptake in a nonhuman primate, this study provides valuable guidance to further design novel isoindolone-based mGluR2 PAMs with improved brain exposure.
RESUMO
AZD2066 is a new chemical entity pharmacologically characterized as a selective, negative allosteric modulator of the metabotropic glutamate receptor subtype 5 (mGluR5). Antagonism of mGluR5 has been implicated in relation to various diseases such as anxiety, depression, and pain disorders. To support translation from preclinical results and previous experiences with this target in man, a positron emission tomography study was performed to estimate the relationship between AZD2066 plasma concentrations and receptor occupancy in the human brain, using the mGluR5 radioligand [(11)C]-ABP688. The study involved PET scans on 4 occasions in 6 healthy volunteers. The radioligand was given as a tracer dose alone and following oral treatment with different doses of AZD2066. The analysis was based on the total volume of distribution derived from each PET-assessment. A non-linear mixed effects model was developed where ten delineated brain regions of interest from all PET scans were included in one simultaneous fit. For comparison the analysis was also performed according to a method described previously by Lassen et al. (1995). The results of the analysis showed that the total volume of distribution decreased with increasing drug concentrations in all regions with an estimated Kipl of 1170 nM. Variability between individuals and occasions in non-displaceable volume of distribution could explain most of the variability in the total volume of distribution. The Lassen approach provided a similar estimate for Kipl, but the variability was exaggerated and difficult to interpret.
Assuntos
Analgésicos/farmacocinética , Ansiolíticos/farmacocinética , Encéfalo/efeitos dos fármacos , Encéfalo/diagnóstico por imagem , Isoxazóis/farmacocinética , Receptor de Glutamato Metabotrópico 5/antagonistas & inibidores , Triazóis/farmacocinética , Adulto , Radioisótopos de Carbono , Voluntários Saudáveis , Humanos , Masculino , Pessoa de Meia-Idade , Oximas , Tomografia por Emissão de Pósitrons , Piridinas , Compostos Radiofarmacêuticos , Adulto JovemRESUMO
PURPOSE: The aim of this study was to evaluate AZD2995 side by side with AZD2184 as novel PET radioligands for imaging of amyloid-ß in Alzheimer's disease (AD). METHODS: In vitro binding of tritium-labelled AZD2995 and AZD2184 was studied and compared with that of the established amyloid-ß PET radioligand PIB. Subsequently, a first-in-human in vivo PET study was performed using [(11)C]AZD2995 and [(11)C]AZD2184 in three healthy control subjects and seven AD patients. RESULTS: AZD2995, AZD2184 and PIB were found to share the same binding site to amyloid-ß. [(3)H]AZD2995 had the highest signal-to-background ratio in brain tissue from patients with AD as well as in transgenic mice. However, [(11)C]AZD2184 had superior imaging properties in PET, as shown by larger effect sizes comparing binding potential values in cortical regions of AD patients and healthy controls. Nevertheless, probably due to a lower amount of nonspecific binding, the group separation of the distribution volume ratio values of [(11)C]AZD2995 was greater in areas with lower amyloid-ß load, e.g. the hippocampus. CONCLUSION: Both AZD2995 and AZD2184 detect amyloid-ß with high affinity and specificity and also display a lower degree of nonspecific binding than that reported for PIB. Overall [(11)C]AZD2184 seems to be an amyloid-ß radioligand with higher uptake and better group separation when compared to [(11)C]AZD2995. However, the very low nonspecific binding of [(11)C]AZD2995 makes this radioligand potentially interesting as a tool to study minute levels of amyloid-ß. This sensitivity may be important in investigating, for example, early prodromal stages of AD or in the longitudinal study of a disease modifying therapy.
Assuntos
Doença de Alzheimer/diagnóstico por imagem , Peptídeos beta-Amiloides/análise , Tomografia por Emissão de Pósitrons , Compostos Radiofarmacêuticos , Idoso , Idoso de 80 Anos ou mais , Doença de Alzheimer/diagnóstico , Doença de Alzheimer/genética , Aminopiridinas/farmacocinética , Compostos de Anilina , Animais , Benzotiazóis/farmacocinética , Benzoxazóis/farmacocinética , Sítios de Ligação , Encéfalo/diagnóstico por imagem , Radioisótopos de Carbono , Estudos de Casos e Controles , Feminino , Humanos , Imageamento por Ressonância Magnética , Masculino , Camundongos , Camundongos Transgênicos , Pessoa de Meia-Idade , Ligação Proteica , Ensaio Radioligante , Compostos Radiofarmacêuticos/farmacocinética , Sensibilidade e Especificidade , TiazóisRESUMO
AIM: To investigate the occupancy at brain 5-hydroxytryptamine (5-HT) 1B receptors in human subjects after administration of the antimigraine drug zolmitriptan. METHODS: Positron emission tomography (PET) studies were undertaken using the radioligand [(11)C]AZ10419369 in eight control subjects at baseline and after administration of zolmitriptan orodispersible tablets. The subjects were examined after two consecutive administrations of 10 mg zolmitriptan, approximately 1 week apart. Two of the subjects were subsequently examined after administration of 5 mg zolmitriptan. One week after the last administration of zolmitriptan five of the subjects underwent additional PET measurements without drug pretreatment. RESULTS: After administration of 10 mg zolmitriptan, mean receptor occupancy was 4-5%. No consistent changes in 5-HT1B receptor binding were observed for subjects who received 5 mg zolmitriptan. There was a statistically significant negative relationship between binding potential ( BP ND) and plasma concentration of zolmitriptan and the active metabolite 183C91, respectively. All of the five subjects who were examined 1 week after dosing with zolmitriptan showed higher BP ND post drug administration compared with baseline. CONCLUSION: This is the first demonstration of CNS 5-HT1B receptor occupancy of a triptan. The findings are consistent with the low receptor occupancy previously reported in PET studies with agonists at other G protein coupled receptors.
Assuntos
Benzopiranos/metabolismo , Encéfalo/metabolismo , Morfolinas/metabolismo , Oxazolidinonas/metabolismo , Piperazinas/metabolismo , Tomografia por Emissão de Pósitrons , Receptor 5-HT1B de Serotonina/metabolismo , Agonistas do Receptor 5-HT1 de Serotonina/metabolismo , Triptaminas/metabolismo , Adulto , Encéfalo/diagnóstico por imagem , Radioisótopos de Carbono/metabolismo , Humanos , Masculino , Tomografia por Emissão de Pósitrons/métodos , Adulto JovemRESUMO
Positron emission tomography (PET) is increasingly used in drug discovery and development for evaluation of CNS drug disposition and for studies of disease biomarkers to monitor drug effects on brain pathology. The quantitative analysis of PET data is based on kinetic modeling of radioactivity concentrations in plasma and brain tissue compartments. A number of quantitative methods of analysis have been developed that allow the determination of parameters describing drug pharmacokinetics and interaction with target binding sites in the brain. The optimal method of quantification depends on the properties of the radiolabeled drug or radioligand and the binding site studied. We here review the most frequently used methods for quantification of PET data in relation to CNS drug discovery and development. The utility of PET kinetic modeling in the development of novel CNS drugs is illustrated by examples from studies of the brain kinetic properties of radiolabeled drug molecules.
Assuntos
Encéfalo/metabolismo , Fármacos do Sistema Nervoso Central/farmacocinética , Descoberta de Drogas/métodos , Modelos Biológicos , Tomografia por Emissão de Pósitrons/métodos , Animais , Encéfalo/diagnóstico por imagem , Fármacos do Sistema Nervoso Central/sangue , Simulação por Computador , Humanos , Distribuição TecidualRESUMO
Positron emission tomography (PET) using radioligands for the enzyme monoamine oxidase B (MAO-B) is increasingly applied as a marker for astrogliosis in neurodegenerative disorders. In the present study, a novel reversible fluorine-18 labeled MAO-B compound, [18F]GEH200449, was evaluated as a PET radioligand in non-human primates. PET studies of [18F]GEH200449 at baseline showed brain exposure (maximum concentration: 3.4-5.2 SUV; n = 5) within the range of that for suitable central nervous system radioligands and a regional distribution consistent with the known localization of MAO-B. Based on the quantitative assessment of [18F]GEH200449 data using the metabolite-corrected arterial plasma concentration as input function, the Logan graphical analysis was selected as the preferred method of quantification. The binding of [18F]GEH200449, as calculated based on regional estimates of the total distribution volume, was markedly inhibited (occupancy >80%) by the administration of the selective MAO-B ligands L-deprenyl (0.5 and 1.0 mg/kg) or rasagiline (0.75 mg/kg) prior to radioligand injection. Radioligand binding was displaceable by the administration of L-deprenyl (0.5 mg/kg) at 25 min after radioligand injection, thus supporting reversible binding to MAO-B. These observations support that [18F]GEH200449 is a reversible MAO-B radioligand suitable for applied studies in humans.
Assuntos
Monoaminoxidase , Selegilina , Animais , Tomografia por Emissão de Pósitrons , Encéfalo , PrimatasRESUMO
The serotonin 1B (5-HT1B) receptor has lately received considerable interest in relation to psychiatric and neurological diseases, partly due to findings based on quantification using Positron Emission Tomography (PET). Although the brainstem is an important structure in this regard, PET radioligand binding quantification in brainstem areas often shows poor reliability. This study aims to improve PET quantification of 5-HT1B receptor binding in the brainstem.Volumes of interest (VOIs) were selected based on a 3D [3H]AZ10419369 Autoradiography brainstem model, which visualized 5-HT1B receptor distribution in high resolution. Two previously developed VOI delineation methods were tested and compared to a conventional manual method. For a method based on template data, a [11C]AZ10419369 PET template was created by averaging parametric binding potential (BPND) images of 52 healthy subjects. VOIs were generated based on a predefined volume and BPND thresholding and subsequently applied to test-retest [11C]AZ10419369 parametric BPND images of 8 healthy subjects. For a method based on individual subject data, VOIs were generated directly on each individual parametric image.Both methods showed improved reliability compared to a conventional manual VOI. The VOIs created with [11C]AZ10419369 template data can be automatically applied to future PET studies measuring 5-HT1B receptor binding in the brainstem.
Assuntos
Tronco Encefálico , Compostos Radiofarmacêuticos , Receptor 5-HT1B de Serotonina , Autorradiografia , Encéfalo/diagnóstico por imagem , Encéfalo/metabolismo , Tronco Encefálico/diagnóstico por imagem , Humanos , Tomografia por Emissão de Pósitrons/métodos , Compostos Radiofarmacêuticos/metabolismo , Receptor 5-HT1B de Serotonina/metabolismo , Reprodutibilidade dos TestesRESUMO
BACKGROUND: Electroconvulsive therapy (ECT) is an effective treatment for depressive disorders, although its molecular mechanism of action is unknown. The serotonin 1B (5-HT1B) receptor is a potential target for treatment of depression and low 5-HT1B receptor binding in limbic regions has been reported in previous positron emission tomography (PET) studies of depression. METHODS: The objective of this longitudinal PET study was to examine the effect of ECT for depression on 5-HT1B receptor binding. Fifteen hospitalized patients with major depressive episodes were examined with PET and the 5-HT1B receptor selective radioligand [11C]AZ10419369, before and after ECT. Fifteen controls matched for age and sex were examined. Limbic regions with previously reported low 5-HT1B receptor binding in depression and a dorsal brain stem region were selected. RESULTS: Thirteen patients completed the study according to protocol. Eleven out of thirteen patients responded to ECT. 5-HT1B receptor binding in hippocampus increased with 30 % after ECT (p=0.021). Using linear mixed effects modelling, we observed increases in 5-HT1B receptor binding following ECT with a moderate to large effect size, which did not differ significantly between regions. In an exploratory analysis, strong correlations between changes in 5-HT1B receptor binding and agitation scores on the Hamilton Depression Rating Scale after ECT were observed. LIMITATIONS: Albeit representative of a PET study, the sample size is still small and there are potential confounding effects of medication. CONCLUSIONS: Increased 5-HT1B receptor binding was observed following ECT for depression, corresponding to previous findings of increased 5-HT1B receptor binding in hippocampus after rapid acting ketamine for treatment resistant depression.