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DPA-C5yne, the lead compound of a novel series of DPA-714 derivatives in which the fluoroethoxy chain linked to the phenylpyrazolopyrimidine scaffold has been replaced by a fluoroalkyn-1-yl moiety, is a high affinity (Ki: 0.35 nM) and selective ligand targeting the translocator protein 18 kDa. In the present work, DPA-C5yne was labelled with no-carrier-added [18F]fluoride based on a one-step tosyloxy-for-fluorine nucleophilic substitution reaction, purified by cartridge and HPLC, and formulated as an i.v. injectable solution using a TRACERLab FX N Pro synthesizer. Typically, 4.3-5.2 GBq of [18F]DPA-C5yne, ready-to-use, chemically and radiochemically pure (> 95%), was obtained with specific radioactivities ranging from 55 to 110 GBq/µmol within 50-60 min, starting from a 30 GBq [18F]fluoride batch (14-17%). LogP and LogD of [18F]DPA-C5yne were measured using the shake-flask method and values of 2.39 and 2.51 were found, respectively. Autoradiography studies performed on slices of ((R,S)-α-amino-3-hydroxy-5-methyl-4-isoxazolopropionique (AMPA)-lesioned rat brains showed a high target-to-background ratio (1.9 ± 0.3). Selectivity and specificity of the binding for the translocator protein was demonstrated using DPA-C5yne (unlabelled), PK11195 and Flumazenil (central benzodiazepine receptor ligand) as competitors. Furthermore, DPA-C5yne proved to be stable in plasma at 37°C for at least 90 min. [ABSTRACT FROM AUTHOR]

As part of our ongoing research for molecular structures binding to the translocator protein (TSPO 18 kDa), we investigated the preparation of a number of new 2,4,5-trisubstituted pyridines as novel . In particular, 5-amino-2-halo-4-phenoxypyridines ( 11, 12, 13) were designed as key intermediates for the synthesis of the recently developed TSPO ligand 6-F-PBR28 and its fluorine-18-labeled version for positron emission tomography, 6-[18F]F-PBR28. We hereby report the chemical preparation as well as the 1H and 13C NMR spectroscopic data of polysubstituted pyridines 2, 3, 4, 5, 6, 7, 7b, 8, 9, 10, 11, 12, 13, 14. The latter demonstrates dramatic changes in electron density repartition of the aromatic ring upon substitution. [ABSTRACT FROM AUTHOR]

Abstract: Carbon-11-labeled acetate ([1-11C]acetate) is a radiopharmaceutical of importance in clinical practice as well as in preclinical research in cardiology and oncology. Its preparation is based on the [11C]carboxylation reaction of a Grignard reagent with [11C]CO2. Most of the commercially available synthesizers are only dedicated to the preparation of [11C]methyl iodide (or [11C]methyl triflate) for the radiomethylation of an appropriate precursor but not for the direct use of cyclotron-produced [11C]CO2. Based on the classical [11C]carboxylation reaction and SPE purification, we propose in this technical note a detailed, simple, easy-to-handle and fully reversible modification of the TRACERLab FX C Pro to operate, on demand, [11C]carboxylation reactions, exemplified herein by the production of [1-11C]acetate, or [11C]radiomethylation reactions. This also opens new prospects to other type of radiochemical reactions involving [11C]CO2. [Copyright &y& Elsevier]

The development of dyskinesias following chronic L-DOPA replacement therapy remains a major problem in the long-term treatment of Parkinson's disease. This study aimed at evaluating the effect of IRC-082451 (base of BN82451), a novel multitargeting hybrid molecule, on L-DOPA-induced dyskinesias (LIDs) and hypolocomotor activity in a non-human primate model of PD. IRC-082451 displays multiple properties: it inhibits neuronal excitotoxicity (sodium channel blocker), oxidative stress (antioxidant) and neuroinflammation (cyclooxygenase inhibitor) and is endowed with mitochondrial protective properties. Animals received daily MPTP injections until stably parkinsonian. A daily treatment with increasing doses of L-DOPA was administered to parkinsonian primates until the appearance of dyskinesias. Then, different treatment regimens and doses of IRC-082451 were tested and compared to the benchmark molecule amantadine. Primates were regularly filmed and videos were analyzed with specialized software. A novel approach combining the analysis of dyskinesias and locomotor activity was used to determine efficacy. This analysis yielded the quantification of the total distance travelled and the incidence of dyskinesias in 7 different body parts. A dose-dependent efficacy of IRC-082451 against dyskinesias was observed. The 5 mg/kg dose was best at attenuating the severity of fully established LIDs. Its effect was significantly different from that of amantadine since it increased spontaneous locomotor activity while reducing LIDs. This dose was effective both acutely and in a 5-day sub-chronic treatment. Moreover, positron emission tomography scans using radiolabelled dopamine demonstrated that there was no direct interference between treatment with IRC-082451 and dopamine metabolism in the brain. Finally, post-mortem analysis indicated that this reduction in dyskinesias was associated with changes in cFOS, FosB and ARC mRNA expression levels in the putamen. The data demonstrates the antidyskinetic efficacy of IRC-082451 in a primate model of PD with motor complications and opens the way to the clinical application of this treatment for the management of LIDs. [ABSTRACT FROM AUTHOR]

Purpose: Here, we report a new and rapid radiosynthesis of F- N-[2-(diethylamino)ethyl]-6-fluoro-pyridine-3-carboxamide ([F]ICF01006), a molecule with a high specificity for melanotic tissue, and its evaluation in a murine model for early specific detection of pigmented primary and disseminated melanoma. Methods: [F]ICF01006 was synthesized using a new one-step bromine-for-fluorine nucleophilic heteroaromatic substitution. Melanoma models were induced by subcutaneous (primary tumour) or intravenous ( lung colonies) injection of B16BL6 melanoma cells in C57BL/6J mice. The relevance and sensitivity of positron emission tomography (PET) imaging using [F]ICF01006 were evaluated at different stages of tumoural growth and compared to F-fluorodeoxyglucose ([F]FDG). Results: The fully automated radiosynthesis of [F]ICF01006 led to a radiochemical yield of 61 % and a radiochemical purity >99 % (specific activity 70-80 GBq/μmol; total synthesis time 42 min). Tumours were visualized before they were palpable as early as 1 h post-injection with [F]ICF01006 tumoural uptake of 1.64 ± 0.57, 3.40 ± 1.47 and 11.44 ± 2.67 percentage of injected dose per gram of tissue (%ID/g) at days 3, 5 and 14, respectively. [F]ICF01006 PET imaging also allowed detection of melanoma pulmonary colonies from day 9 after tumour cell inoculation, with a lung radiotracer accumulation correlated with melanoma invasion. At day 21, radioactivity uptake in lungs reached a value of 5.23 ± 2.08 %ID/g (versus 0.41 ± 0.90 %ID/g in control mice). In the two models, comparison with [F]FDG showed that both radiotracers were able to detect melanoma lesions, but [F]ICF01006 was superior in terms of contrast and specificity. Conclusion: Our promising results provide further preclinical data, reinforcing the excellent potential of [F]ICF01006 PET imaging for early specific diagnosis and follow-up of melanin-positive disseminated melanoma. [ABSTRACT FROM AUTHOR]

Purpose: In recent years there has been an increase in the development of radioligands targeting the 18-kDa translocator protein (TSPO). TSPO expression is well documented in activated microglia and serves as a biomarker for imaging neuroinflammation. In addition, TSPO has also been reported to be overexpressed in a number of cancer cell lines and human tumours including glioma. Here we investigated the use of [F]DPA-714, a new TSPO positron emission tomography (PET) radioligand to image glioma in vivo. Methods: We studied the uptake of [F]DPA-714 in three different rat strains implanted with 9L rat glioma cells: Fischer (F), Wistar (W) and Sprague Dawley (SD) rats. Dynamic [F]DPA-714 PET imaging, kinetic modelling of PET data and in vivo displacement studies using unlabelled DPA-714 and PK11195 were performed. Validation of TSPO expression in 9L glioma cell lines and intracranial 9L gliomas were investigated using Western blotting and immunohistochemistry of brain tissue sections. Results: All rats showed significant [F]DPA-714 PET accumulation at the site of 9L tumour implantation compared to the contralateral brain hemisphere with a difference in uptake among the three strains (F > W > SD). The radiotracer showed high specificity for TSPO as demonstrated by the significant reduction of [F]DPA-714 binding in the tumour after administration of unlabelled DPA-714 or PK11195. TSPO expression was confirmed by Western blotting in 9L cells in vitro and by immunohistochemistry ex vivo. Conclusion: The TSPO radioligand [F]DPA-714 can be used for PET imaging of intracranial 9L glioma in different rat strains. This preclinical study demonstrates the feasibility of employing [F]DPA-714 as an alternative radiotracer to image human glioma. [ABSTRACT FROM AUTHOR]

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the CNS. Activated microglia/macrophages play a key role in the immunopathogenesis of MS and its corresponding animal models, experimental autoimmune encephalomyelitis (EAE). Microglia activation begins at early stages of the disease and is associated with elevated expression of the 18 kDa mitochondrial translocator protein (TSPO). Thus, positron emission tomography (PET) imaging of microglial activation using TSPO-specific radioligands could be valuable for monitoring disease-associated neuroinflammatory processes. EAE was induced in rats using a fragment of myelin basic protein, yielding acute clinical disease that reflects extensive spinal cord inflammation. Enhanced TSPO expression in spinal cords of EAE rats versus those of controls was confirmed by Western blot and immunohistochemistry. Biodistribution studies in control and EAE rats were performed using the TSPO radioligand [ 18F]DPA-714 [N,N-diethyl-2-(2-(4-(2-fluoroethoxy)phenyl)-5,7-dimethylpyrazolo[1,5- a]pyrimidin-3-yl)acetamide]. At 1 h after injection, almost fivefold higher levels of [ 18F]DPA-714 were measured in spinal cords of EAE rats versus controls. The specific binding of [ 18F]DPA-714 to TSPO in spinal cords was confirmed in competition studies, using unlabeled (R,S)-PK11195 [(R,S)-N-methyl-N-(1-methylpropyl)-1-(2-chlorophenyl)isoquinoline-3-carboxamide)] or DPA-714 in excess. MicroPET studies affirm that this differential radioactivity uptake in spinal cords of EAE versus control rats could be detected and quantified. Using [ 18F]DPA-714, neuroinflammation in spinal cords of EAE-induced rats could be visualized by PET, offering a sensitive technique for monitoring neuroinflammatory lesions in the CNS and particularly in the spinal cord. In addition to current MRI protocols, this approach could provide molecular images of neuroinflammation for detection, monitoring, and research in MS. [ABSTRACT FROM AUTHOR]

Purpose: Neuroinflammation is involved in neurological disorders through the activation of microglial cells. Imaging of neuroinflammation with radioligands for the translocator protein (18 kDa) (TSPO) could prove to be an attractive biomarker for disease diagnosis and therapeutic evaluation. The indoleacetamide-derived 7-chloro- N, N,5-trimethyl-4-oxo-3-phenyl-3,5-dihydro-4 H-pyridazino[4,5- b]indole-1-acetamide, SSR180575, is a selective high-affinity TSPO ligand in human and rodents with neuroprotective effects. Methods: Here we report the radiolabelling of SSR180575 with C and in vitro and in vivo imaging in an acute model of neuroinflammation in rats. Results: The image contrast and the binding of [C]SSR180575 are higher than that obtained with the isoquinoline-based TSPO radioligand, [C]PK11195. Competition studies demonstrate that [C]SSR180575 has high specific binding for the TSPO. Conclusion: [C]SSR180575 is the first PET radioligand for the TSPO based on an indoleacetamide scaffold designed for imaging neuroinflammation in animal models and in the clinic. [ABSTRACT FROM AUTHOR]

The key role of neuroinflammation in acute and chronic neurological disorders has stimulated the search for specific radiotracers targeting the peripheral benzodiazepine receptor (PBR)/18 kDa translocator protein (TSPO), a hallmark of neuroinflammation. Here we evaluate the new radiotracer for positron emission tomography (PET) [18F]PBR111 in a rodent model of acute inflammation and compare it with [11C]CLINME, an 11C-labelled tracer of the same chemical family, and with the isoquinolinic carboxamide [11C]PK11195. We studied radiometabolites by HPLC, in vitro binding by autoradiography and in vivo brain kinetics as well as in vivo specificity of binding using PET imaging. We show that this radiotracer has a high in vitro specificity for PBR/TSPO versus central benzodiazepine receptors, as reflected by the drastic reduction of its binding to target tissue by addition of PK11195 or PBR111, while addition of flumazenil does not affect binding. Only intact [18F]PBR111 is detected in brain up to 60 min after i.v. injection, and PET imaging shows an increased uptake in the lesion as compared to the contralateral side as early as 6 min after injection. Administration of an excess of PK11195 and PBR111, 20 min after [18F]PBR111 administration, induces a rapid and complete displacement of [18F]PBR111 binding from the lesion. Modelling of the PET data using the simplified reference tissue model showed increased binding potential (BP) in comparison to [11C]PK11195. [18F]PBR111 is a metabolically stable tracer with a high specific in vitro and in vivo binding to TSPO. In addition, considering the longer half-life of 18F over 11C, these results support [18F]PBR111 as a promising PET tracer of the PBR/TSPO for neuroinflammation imaging. [ABSTRACT FROM AUTHOR]

[11C]befloxatone is a high-affinity, reversible, and selective radioligand for the in vivo visualization of the monoamine oxidase A (MAO-A) binding sites using positron emission tomography (PET). The multi-injection approach was used to study in baboons the interactions between the MAO-A binding sites and [11C]befloxatone. The model included four compartments and seven parameters. The arterial plasma concentration, corrected for metabolites, was used as input function. The experimental protocol—three injections of labeled and/or unlabeled befloxatone—allowed the evaluation of all the model parameters from a single PET experiment. In particular, the brain regional concentrations of the MAO-A binding sites (B′max) and the apparent in vivo befloxatone affinity (Kd) were estimated in vivo for the first time. A high binding site density was found in almost all the brain structures (170±39 and 194±26 pmol/mL in the frontal cortex and striata, respectively, n=5). The cerebellum presented the lowest binding site density (66±13 pmol/mL). Apparent affinity was found to be similar in all structures (KdVR=6.4±1.5 nmol/L). This study is the first PET-based estimation of the Bmax of an enzyme. [ABSTRACT FROM AUTHOR]

6-[18F]Fluoro-3,4-dihydroxy- L-phenylalanine (6-[18F]F- L-DOPA) is increasingly used for PET imaging of neuroendocrine tumours. In this study, we investigated the use of 6-[18F]F- L-DOPA to detect and to monitor the progression of medullary thyroid carcinoma (MTC) in a genetically engineered mouse model of multiple endocrine neoplasia type 2A (MEN2A). Dynamic [18F]FDG and 6-[18F]F- L-DOPA small animal PET scans were acquired during 60 or 90 min in 8- to 20-month-old MEN2A transgenic mice. The kinetics of 6-[18F]F- L-DOPA, standardized uptake values (SUV) at 60 min and tumour volumes were recorded. The detection of MTCs using PET was confirmed by autopsy and histological analysis. 6-[18F]F- L-DOPA performs better than [18F]FDG for MTC detection in this transgenic mouse model. Uptake kinetics of 6-[18F]F- L-DOPA in MTCs are very different between mice but, in all cases, high contrast could be observed. Furthermore, 6-[18F]F- L-DOPA can detect tumours with sizes (1.8 mm3) that are near the resolution limit of PET, whereas they were undetectable by autopsy at the macroscopic level. 6-[18F]F- L-DOPA PET imaging can monitor the progression of MTCs in a genetically engineered mouse model. [ABSTRACT FROM AUTHOR]

[11C]SL-25.1188 [(S)-5-methoxymethyl-3-[6-(4,4,4-trifluorobutoxy)-benzo[ d]isoxazol-3-yl]-oxazolidin-2-one], an oxazolidinone derivative, was characterized in baboons as a radioligand for the in vivo visualization of MAO-B using positron emission tomography (PET). After i.v. injection, [11C]SL25.1188 presented a rapid phase of distribution in blood (about 5 min), followed by a T1/2 elimination of 85 ± 14 min. Plasma metabolism analysis showed that [11C]SL25.1188 is stable in vivo at least for 30 min. Brain uptake was rapid with the highest one observed in the striatum and thalamus, and the lowest in the pons. Calculated distribution volumes ( VT) were as follows: striatum = 10.3, thalamus = 10.9, hippocampus = 8.9, temporal cortex = 7.7, occipital cortex = 7.2, parietal cortex = 7.4, frontal cortex = 7.4, white matter = 7.4, and pons = 6.1. Pretreatment with deprenyl (2 mg/kg, i.v.) or lazabemide (0.5 mg/kg, i.v.) reduced VT values in all brain areas up to 50%. In displacement experiments, injection of SL25.1188 or deprenyl (1 and 2 mg/kg, i.v., respectively) strongly reduced the specific uptake of [11C]SL25.1188 in all brain areas (85-100%), while a lesser displacement was observed with lazabemide (0.5 mg/kg, i.v.) (55-70% of specific binding depending on the brain area). Therefore, [11C]SL25.1188 is characterized in vivo by reversible binding, high brain uptake and very slow plasma metabolism, strongly suggesting that this radioligand is a potent tool for the in vivo study of brain MAO-B. Synapse 64:61-69, 2010. © 2009 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Focal cerebral ischemia leads to an inflammatory reaction involving an overexpression of the peripheral benzodiazepine receptor (PBR)/18-kDa translocator protein (TSPO) in the cerebral monocytic lineage (microglia and monocyte) and in astrocytes. Imaging of PBR/TSPO by positron emission tomography (PET) using radiolabeled ligands can document inflammatory processes induced by cerebral ischemia. We performed in vivo PET imaging with [18F]DPA-714 to determine the time course of PBR/TSPO expression over several days after induction of cerebral ischemia in rats. In vivo PET imaging showed significant increase in DPA (N,N-diethyl-2-(2-(4-(2-fluoroethoxy)phenyl)-5,7-dimethylpyrazolo[1,5-a]pyrimidin-3-yl)acetamide) uptake on the injured side compared with that in the contralateral area on days 7, 11, 15, and 21 after ischemia; the maximal binding value was reached 11 days after ischemia. In vitro autoradiography confirmed these in vivo results. In vivo and in vitro [18F]DPA-714 binding was displaced from the lesion by PK11195 and DPA-714. Immunohistochemistry showed increased PBR/TSPO expression, peaking at day 11 in cells expressing microglia/macrophage antigens in the ischemic area. At later times, a centripetal migration of astrocytes toward the lesion was observed, promoting the formation of an astrocytic scar. These results show that [18F]DPA-714 provides accurate quantitative information of the time course of PBR/TSPO expression in experimental stroke. [ABSTRACT FROM AUTHOR]

In vivo gene transfer using viral vectors is an emerging therapy for neurodegenerative diseases with a clinical impact recently demonstrated in Parkinson's disease patients. Recombinant adeno-associated viral (rAAV) vectors, in particular, provide an excellent tool for long-term expression of therapeutic genes in the brain. Here we used the [11C]raclopride [(S)-(-)-3,5-dichloro-N-((1-ethyl-2-pyrrolidinyl)methyl)-2-hydroxy-6-methoxybenzamide] micro-positron emission tomography (PET) technique to demonstrate that delivery of the tyrosine hydroxylase (TH) and GTP cyclohydrolase 1 (GCH1) enzymes using anrAAV5vector normalizes the increased [11C]raclopride binding in hemiparkinsonian rats. Importantly, we show in vivo by microPET imaging and postmortem by classical binding assays performed in the very same animals that the changes in [11C]raclopride after viral vector-based enzyme replacement therapy is attributable to a decrease in the affinity of the tracer binding to the D2 receptors, providing evidence for reconstitution of a functional pool of endogenous dopamine in the striatum. Moreover, the extent of the normalization in this non-invasive imaging measure was highly correlated with the functional recovery in motor behavior. The PET imaging protocol used in this study is fully adaptable to humans and thus can serve as an in vivo imaging technique to followTH+GCH1 gene therapy in PD patientsandprovideanadditionalobjectivemeasuretoapotentialclinicaltrialusingrAAVvectorstodeliver ʟ-3,4-dihydroxyphenylanalineinthebrain. [ABSTRACT FROM AUTHOR]

Neurodegenerative, inflammatory and neoplastic brain disorders involve neuroinflammatory reactions, and a biomarker of neuroinflammation would be useful for diagnostic, drug development and therapy control of these frequent diseases. In vivo imaging can document the expression of the peripheral benzodiazepine receptor (PBR)/translocator protein 18 kDa (TSPO) that is linked to microglial activation and considered a hallmark of neuroinflammation. The prototype positron emission tomography tracer for PBR, [11C]PK11195, has shown limitations that until now have slowed the clinical applications of PBR imaging. In recent years, dozens of new PET and SPECT radioligands for the PBR have been radiolabelled, and several have been evaluated in imaging protocols. Here we review the new PBR ligands proposed as challengers of [11C]PK11195, critically analyze preclinical imaging studies and discuss their potential as neuroinflammation imaging agents. [ABSTRACT FROM AUTHOR]

In vivo pharmacokinetic and brain binding characteristics of (+)-[11C]A-69024, a high-affinity-D1-selective dopamine receptor antagonist, were assessed with micro-PET and β-microprobes in the rat and PET in the baboon. The biodistribution of (+)-[11C]A-69024 in rats and baboons showed a rapid brain uptake (reaching a maximal value at 5 and 15 min postinjection in rats and baboons, respectively), followed by a slow wash out. The region/cerebellum concentration ratio was characterized by a fourfold higher uptake in striatum and a twofold higher uptake in cortical regions, consistent with in vivo specific binding of the radiotracer in these cerebral regions. Furthermore, this specific (+)-[11C]A-69024 binding significantly correlated with the reported in vitro distribution of dopamine D1-receptors. Finally, the specific uptake of the tracer in the striatum and cortical regions was completely prevented by either a pretreatment with large doses of nonradioactive (±)A-69024 or of the D1-selective antagonist SCH23390, resulting in a similar uptake in the reference region (cerebellum) and in other brain regions. Thus, (+)-[11C]A-69024 appears to be a specific and enantioselective radioligand to visualize and quantify brain dopamine D1 receptors in vivo using positron emission tomography. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:2811–2819, 2008 [ABSTRACT FROM AUTHOR]

The radioligand 2-[18F]fluoro-A-85380 has been developed for imaging α4β2 nAChRs with PET. However, it has slow kinetics and a large fraction of bound activity is nondisplaceable. In an attempt to address these problems, two epibatidine-based α4β2 nicotinic antagonists, coded FPhEP and F2PhEP, were evaluated in vivo in baboons. They were radiolabeled with fluorine-18 from the corresponding N-Boc-protected bromo-derivatives and the no-carrier-added K[18F]F-Kryptofix®222 complex. Radiochemically pure [18F]FPhEP or [18F]F2PhEP was obtained in 80 min in amounts of 1.11-2.22 GBq (111-185 GBq/μmol). After injection of 215 MBq of [18F]FPhEP or [18F]F2PhEP, dynamic PET data were acquired. Thalamic radioactivity peaked at 20 min (4.9% ± 0.2% ID/100 mL tissue) for [18F]FPhEP. For [18F]F2PhEP, the peak was at 45 min (3.3% ± 0.1% ID/100 mL tissue). Regional distribution of both radiotracers was in accordance with the known distribution of nAChRs. In presaturation experiments, nicotine, cytosine, or FPhEP reduced brain radioactivity of [18F]FPhEP. In a displacement experiment with nicotine only a small amount of [18F]F2PhEP was dislodged. In spite of a moderate to high in vitro affinity, both ligands do not fulfill the widely adopted criteria for a PET radioligand. Synapse 61:764-770, 2007. © 2007 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Abstract: LBT-999 (8-((E)-4-fluoro-but-2-enyl)-3β-p-tolyl-8-aza-bicyclo[3.2.1]octane-2β-carboxylic acid methyl ester), a cocaine derivative belonging to a new generation of highly selective dopamine transporter (DAT) ligands, and its corresponding carboxylic acid derivative, the latter used as precursor for labelling both with tritium and the positron-emitter carbon-11 (half-life: 20.38min), were synthesized from (R)-cocaine. [3H]LBT-999 (>99% radiochemically pure, specific radioactivity of 3.1TBq/mmol) was prepared from [3H]methyl iodide, allowing its in vitro pharmacological evaluation (K D: 9nM for DAT and IC50 >1000nM for SERT and NET). Routine production batches of 4.5–9.0GBq of iv injectable solutions of [11C]LBT-999 (with specific radioactivities ranging from 30 to 45GBq/μmol) were prepared in 25–30min (HPLC purification and formulation included) using the efficient methylation reagent [11C]methyl triflate. The preliminary in vivo pharmacological evaluation of [11C]LBT-999, using both biodistributions in rats and brain imaging in monkeys with positron emission tomography (PET), clearly illustrates that this ligand is an excellent candidate for quantification with PET of DAT in humans. [Copyright &y& Elsevier]

Purpose: This study reports on the whole-body biodistribution and radiation dosimetry of [11C]raclopride, a dopamine D2 receptor antagonist. Methods: In three healthy male volunteers, whole-body scans were performed up to 2 h following i.v. injection of 320±65 MBq [11C]raclopride. Transmission scans (3 mm per step, eight or nine steps according to the height of the subject) in 2D mode were used for subsequent attenuation correction of emission scans. Emission scans (1 mm per step, eight or nine steps) were acquired over 2 h. Venous blood samples and urine were collected up to 2 h after injection of the radiotracer. For each subject, the percentage of injected activity measured in regions of interest over brain, intestine, lungs, kidneys and liver was fitted to a mono-exponential model, as an uptake phase followed by a mono-exponential washout, for urinary bladder to generate time-activity curves. Using the MIRD method, several source organs were considered in estimating residence time and mean effective radiation absorbed doses. Results: Blood pressure and ECG findings remained unchanged after tracer injection. The analysed blood and urine pharmacological parameters did not change significantly after [11C]raclopride injection. The primary routes of clearance were renal and intestinal. Ten minutes after injection, high activities were observed in the gall-bladder, kidneys and liver. High activity was observed in the gall-bladder during the whole study. The kidneys, urinary bladder wall, liver and gall-bladder received the highest absorbed doses. The average effective dose of [11C]raclopride was estimated to be 6.7±0.4 μSv/MBq. Conclusion: The amount of [11C]raclopride required for adequate dopamine D2 receptor imaging results in an acceptable effective dose equivalent, permitting two or three repeated clinical PET imaging studies, with the injection of 222 M Bq for each study. [ABSTRACT FROM AUTHOR]

2-[18F]fluoro-3-[2(S)-2-azetidinylmethoxy]pyridine ([18F]fluoro-A-85380) is an α4β2 subtype selective nicotinic cholinergic agonist with potential suitability for studying changes in endogenous acetylcholine synaptic concentration. Physostigmine, a potent AChE inhibitor, and galantamine, an allosteric modulator of nAChRs, are widely used for the treatment of Alzheimer's disease. Before studying patients with this neurodegenerative disease, positron emission tomography (PET) studies in monkeys were performed to assess the impact of these two compounds on the radiotracer distribution volumes. Physostigmine was administered i.v. at two dosages: 150 μg/kg/h and 37.5 μg/kg/h for 160 min. Galantamine was administered i.v. at two dosages: 2 or 4 mg over 20 min. For PET data analysis, a model with one tissue (radioactivity of the parent compound in plasma and radioactivity in brain tissue) compartment was chosen because reliable parameter estimates could not be obtained with a more complex model. The higher dose of physostigmine produced a 40%, 23%, and 30% reduction of distribution volumes in the putamen, the temporal, and frontal cortices, respectively. The lower dose of physostigmine produced a reduction of 33%, 31%, and 24% in the same structures, respectively. Galantamine (4 mg or 2 mg) produced no significant change of distribution volumes in the basal ganglia, the temporal and frontal cortex. The effects of physostigmine, a more potent AChE inhibitor than galantamine, could be interpreted as a desensitization of nAChRs, due to a prolonged exposure to high synaptic concentration of acetylcholine or as a competition with acetylcholine. Synapse 56:217-221, 2005. © 2005 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]