Evaluation and improvement of CuI-mediated 11 C-cyanation.

CuI-mediated 11 C-cyanation was evaluated by synthesizing [11 C]perampanel ([11 C]5) as a model compound and compared with previous reports. To a DMF solution with 5'-(2-bromophenyl)-1'-phenyl-[2,3'-bipyridin]-6'(1'H)-one (4) and CuI, [11 C]NH4 CN in a stream of ammonia/nitrogen (5:95, v/v) gas was bubbled. Subsequently, the reaction mixture was heated at 180°C for 5 min. After HPLC purification, [11 C]5 was obtained in 7.2 ± 1.0% (n = 4) non-decay corrected radiochemical yield with >99% radiochemical purity and a molar activity of 98 ± 28 GBq/µmol. In vivo evaluations of [11 C]5 were performed using small animals. PET scans to check the kinetics of [11 C]5 in the whole body of mice suggested that [11 C]5 spreads rapidly into the brain, heart, and lungs and then accumulates in the small intestine. To evaluate the performance of CuI-mediated 11 C-cyanation reaction, bromobenzene (6a) was selected as the model compound; however, it failed. Therefore, optimization of the reaction conditions has been performed, and consequently, the addition of K2 CO3 and prolonging the reaction time improved the radiochemical yield about double. With this improved method, CuI-mediated 11 C-cyanation of various (hetero)aromatic bromides was performed to exhibit the tolerance of most functional groups and to provide 11 C-cyanated products in good to moderate radiochemical yields.

11C-Labeled Radiotracer for Noninvasive and Quantitative Assessment of the Thiocyanate Efflux System in the Brain.

Thiocyanate (SCN-) alters the potency of certain agonists for the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor, and dysfunctions in AMPA receptor signaling are considered to underlie a number of neurological diseases. While humans may be exposed to SCN- from the environment, including food sources, a carrier-mediated system transports SCN- from the brain into the blood and is an important regulator of SCN- distribution in the central nervous system. The assessment of this SCN- efflux system in the brain would thus be useful for understanding the mechanisms underlying the neurotoxicity of SCN- and for elucidating the relationship between the efflux system and brain diseases. However, the currently available technique for studying SCN- efflux is severely limited by its invasiveness. Here, we describe the development of a SCN- protracer, 9-pentyl-6-[11C]thiocyanatopurine ([11C]1), to overcome this limitation. [11C]1 was synthesized by the reaction of the iodo-precursor and [11C]SCN- or the reaction of the disulfide precursor with [11C]NH4CN. The protracer [11C]1 entered the brain after intravenous injection into mice and was rapidly metabolized to [11C]SCN-, which was then eliminated from the brain. The efflux of [11C]SCN- was dose-dependently inhibited by perchlorate, a monovalent anion, and the highest dose caused an 82% reduction in the efflux rate. Our findings demonstrate that [11C]1 can be used for the noninvasive and quantitative assessment of the SCN- efflux system in the brain.

Automated radiosynthesis of [11 C]MTP38-a phosphodiesterase 7 imaging tracer-using [11 C]hydrogen cyanide for clinical applications.

We have developed 8-amino-3-(2S,5R-dimethyl-1-piperidyl)-[1,2,4]triazolo[4,3-a]pyrazine-5-[11 C]carbonitrile ([11 C]MTP38) as a positron emission tomography (PET) tracer for the imaging of phosphodiesterase 7. For the fully automated production of [11 C]MTP38 routinely and efficiently for clinical applications, we determined the radiosynthesis procedure of [11 C]MTP38 using [11 C]hydrogen cyanide ([11 C]HCN) as a PET radiopharmaceutical. Radiosynthesis of [11 C]MTP38 was performed using an automated 11 C-labeling synthesizer developed in-house within 40 min after the end of irradiation. [11 C]MTP38 was obtained with a relatively high radiochemical yield (33 ± 5.5% based on [11 C]CO2 at the end of irradiation, decay-corrected, n = 15), radiochemical purity (>97%, n = 15), and molar activity (47 ± 12 GBq/µmol at the end of synthesis, n = 15). All the results of the quality control (QC) testing for the [11 C]MTP38 injection complied with our in-house QC and quality assurance specifications. We successfully automated the radiosynthesis of [11 C]MTP38 for clinical applications using an 11 C-labeling synthesizer and sterile isolator. Taken together, this protocol provides a new radiopharmaceutical [11 C]MTP38 suitable for clinical applications.

Radiosynthesis and quality control testing of the tau imaging positron emission tomography tracer [18 F]PM-PBB3 for clinical applications.

Recently, we produced 11 C-labeled 2-((1E,3E)-4-(6-(methylamino)pyridin-3-yl)buta-1,3-dienyl)benzo[d]thiazol-6-ol ([11 C]PBB3) as a clinically useful positron emission tomography (PET) tracer for in vivo imaging of tau pathologies in the human brain. To overcome the limitations (i.e., rapid in vivo metabolism and short half-life) of [11 C]PBB3, we further synthesized 18 F-labeled 1-fluoro-3-((2-((1E,3E)-4-(6-(methylamino)pyridine-3-yl)buta-1,3-dien-1-yl)benzo[d]thiazol-6-yl)oxy)propan-2-ol ([18 F]PM-PBB3). [18 F]PM-PBB3 is also a useful tau PET tracer for imaging tau pathologies. In this study, we developed a routine radiosynthesis and quality control testing of [18 F]PM-PBB3 for clinical applications. [18 F]PM-PBB3 was synthesized by direct 18 F-fluorination of the tosylated derivative, followed by removal of the protecting group. [18 F]PM-PBB3 was obtained with sufficient radioactivity (25 ± 6.0% of the nondecay-corrected radiochemical yield at the end of synthesis, EOS), radiochemical purity (98 ± 0.6%), and molar activity (350 ± 94 GBq/µmol at EOS; n = 53). Moreover, [18 F]PM-PBB3 consistently retained >95% of radiochemical purity for 60 min without undergoing photoisomerization using a new UV-cutoff light (yellow light) fixed in the hot cell to monitor the synthesis. All the results of the quality control testing for the [18 F]PM-PBB3 injection complied with our in-house quality control and quality assurance specifications. We have accomplished >200 production runs of [18 F]PM-PBB3 in our facility for various research purposes.

3-(Cyclopropylmethyl)-7-((4-(4-[11C]methoxyphenyl)piperidin-1-yl)methyl)-8-(trifluoromethyl)-[1,2,4]triazolo[4,3-a]pyridine: Synthesis and preliminary evaluation for PET imaging of metabotropic glutamate receptor subtype 2.

Selective metabotropic glutamate receptor 2 (mGluR2) inhibitors have been demonstrated to show therapeutic effects by improving alleviating symptoms of schizophrenic patients in clinical studies. Herein we report the synthesis and preliminary evaluation of a 11C-labeled positron emission tomography (PET) tracer originating from a mGluR2 inhibitor, 3-(cyclopropylmethyl)-7-((4-(4-methoxyphenyl)piperidin-1-yl)methyl)-8-(trifluoromethyl)-[1,2,4]triazolo[4,3-a]pyridine (CMTP, 1a). [11C]CMTP ([11C]1a) was synthesized by O-[11C]methylation of desmethyl precursor 1b with [11C]methyl iodide in 19.7 ± 8.9% (n = 10) radiochemical yield (based on [11C]CO2) with >98% radiochemical purity and >74 GBq/µmol molar activity. Autoradiography study showed that [11C]1a possessed moderate in vitro specific binding to mGluR2 in the rat brain, with a heterogeneous distribution of radioactive accumulation in the mGluR2-rich brain tissue sections, such as the cerebral cortex and striatum. PET study indicated that [11C]1a was able to cross the blood-brain barrier and enter the brain, but had very low specific binding in the rat brain. Further optimization for the chemical structure of 1a is necessary to increase binding affinity to mGluR2 and then improve in vivo specific binding in brain.

Radiosynthesis of [thiocarbonyl-11C]disulfiram and its first PET study in mice.

[Thiocarbonyl-11C]disulfiram ([11C]DSF) was synthesized via iodine oxidation of [11C]diethylcarbamodithioic acid ([11C]DETC), which was prepared from [11C]carbon disulfide and diethylamine. The decay-corrected isolated radiochemical yield (RCY) of [11C]DSF was greatly affected by the addition of unlabeled carbon disulfide. In the presence of carbon disulfide, the RCY was increased up to 22% with low molar activity (Am, 0.27 GBq/µmol). On the other hand, [11C]DSF was obtained in 0.4% RCY with a high Am value (95 GBq/µmol) in the absence of carbon disulfide. The radiochemical purity of [11C]DSF was always >98%. The first PET study on [11C]DSF was performed in mice. A high uptake of radioactivity was observed in the liver, kidneys, and gallbladder. The uptake level and distribution pattern in mice were not significantly affected by the Am value of the [11C]DSF sample used. In vivo metabolite analysis showed the rapid decomposition of [11C]DSF in mouse plasma.

Radiosynthesis and evaluation of new PET ligands for peripheral cannabinoid receptor type 1 imaging.

Cannabinoid receptor type 1 (CB1) is mainly expressed in the brain, as well as being expressed in functional relevant concentrations in various peripheral tissues. 1-(4-Chlorophenyl)-3-(3-(6-(pyrrolidin-1-yl)pyridin-2-yl)phenyl)urea (PSNCBAM-1, 1) was developed as a potent allosteric antagonist for CB1 and its oral administration led to reductions in the appetite and body weight of rats. Several analogs of 1 (compounds 2 and 3) were recently identified through a series of structure-activity relationship studies. Herein, we report the synthesis of radiolabeled analogs of these compounds using [11C]COCl2 and an evaluation of their potential as PET ligands for CB1 imaging using in vitro and in vivo techniques. [11C]2 and [11C]3 were successfully synthesized in two steps using [11C]COCl2. The radiochemical yields of [11C]2 and [11C]3 were 17±8% and 20±9% (decay-corrected to the end of bombardment, based on [11C]CO2). The specific activities of [11C]2 and [11C]3 were 42±36 and 37±13GBq/µmol, respectively. The results of an in vitro binding assay using brown adipose tissue (BAT) homogenate showed that the binding affinity of 2 for CB1 (KD=15.3µM) was much higher than that of 3 (KD=26.0µM). PET studies with [11C]2 showed a high uptake of radioactivity in BAT, which decreased in animals pretreated with AM281 (a selective antagonist for CB1). In conclusion, [11C]2 may be a useful PET ligand for imaging peripheral CB1 in BAT.

[11C]BCTC: Radiosynthesis and in vivo binding to transient receptor potential vanilloid subfamily member 1 (TRPV1) receptor in the mouse trigeminal nerve.

The purpose of this study was to synthesize a new positron emission tomography radiotracer, N-(4-tertiarybutylphenyl)-4-(3-chloropyridin-2-yl)tetrahydropyrazine-1(2H)-[11C]carboxamide ([11C]BCTC, [11C]1), and assess its in vivo binding to the transient receptor potential vanilloid subfamily member 1 (TRPV1) receptor in mice. [11C]BCTC was synthesized by reacting the hydrochloride of 4-tertiarybutylaniline (2·HCl) with [11C]phosgene ([11C]COCl2) to give isocyanate [11C]4, followed by reaction with 4-(3-chloropyridin-2-yl)tetrahydropyrazine (3). [11C]BCTC was obtained at a 16-20% radiochemical yield, based on the cyclotron-produced [11C]CO2 (decay-corrected to the end of bombardment), with >98% radiochemical purity and 65-110GBq/µmol specific activity at the end of synthesis. An ex vivo biodistribution study in mice confirmed the specific binding of [11C]BCTC to TRPV1 in the trigeminal nerve, which is a tissue with high TRPV1 expression.

Radiosynthesis and evaluation of 5-methyl-N-(4-[(11)C]methylpyrimidin-2-yl)-4-(1H-pyrazol-4-yl)thiazol-2-amine ([(11)C]ADX88178) as a novel radioligand for imaging of metabotropic glutamate receptor subtype 4 (mGluR4).

ADX88178 (1) has been recently developed as a potent positive allosteric modulator for metabotropic glutamate receptor 4 (mGluR4). The aim of this study was to develop [(11)C]1 as a novel positron emission tomography ligand and to evaluate its binding ability for mGluR4. Using stannyl precursor 3, [(11)C]1 was efficiently synthesized by introducing an [(11)C]methyl group into a pyrimidine ring via C-(11)C coupling and deprotection reactions, in 16±6% radiochemical yield (n=10). At the end of synthesis, 0.54-1.10GBq of [(11)C]1 was acquired with >98% radiochemical purity and 90-120GBq/µmol of specific activity. In vitro autoradiography and ex vivo biodistribution study in rat brains showed specific binding of [(11)C]1 in the cerebellum, striatum, thalamus, cerebral cortex, and medulla oblongata, which showed dose-dependent decreases by administration with multi-dose of unlabeled 1.

[(11)C-carbonyl]CEP-32496: radiosynthesis, biodistribution and PET study of brain uptake in P-gp/BCRP knockout mice.

CEP-32496 is a novel, orally active serine/threonine-protein kinase B-raf (BRAF) (V600E) kinase inhibitor that is being investigated in clinical trials for the treatment of some cancers in patients. In this study, we developed [(11)C-carbonyl]CEP-32496 as a novel positron emission tomography (PET) probe to study its biodistribution in the whole bodies of mice. [(11)C]CEP-32496 was synthesized by the reaction of 5-(1,1,1-trifluoro-2-methylpropan-2-yl)isoxazol-3-amine hydrochloride (1·HCl) with [(11)C]phosgene, followed by treatment with 3-(6,7-dimethoxyquinozolin-4-yloxy)aniline (2). Small-animal PET studies with [(11)C]CEP-32496 indicated that radioactivity levels (AUC0-90 min, SUV×min) accumulated in the brains of P-gp/BCRP knockout mice at a 8-fold higher rate than in the brains of wild-type mice.

Synthesis and evaluation of new (18)F-labelled acetamidobenzoxazolone-based radioligands for imaging of the translocator protein (18 kDa, TSPO) in the brain.

The visualization of the activated microglia/TSPO is one of the main aspects of neuroimaging. Here we describe two new (18)F-labelled molecules, 2-[5-(4-[(18)F]fluoroethoxyphenyl)- ([(18)F]2) and 2-[5-(4-[(18)F]fluoropropyloxyphenyl)- ([(18)F]3) -2-oxo-1,3-benzoxazol-3(2H)-yl]-N-methyl-N-phenylacetamide as novel PET ligands for imaging the translocator protein (18 kDa, TSPO) in the brain. The three-D pharmacophore evaluation and docking studies suggested their high affinity for the TSPO and in vitro binding assays of the TSPO showed binding affinities 6.6 ± 0.7 nM and 16.7 ± 2.5 nM for 2 and 3, respectively. The radiochemical yields for [(18)F]2 and [(18)F]3 were found to be 22 ± 4% (n = 8) and 5 ± 2% (n = 5), respectively at EOB. The radiochemical purity for both was found ≥98% and the specific activity was in the range of 98-364 GBq µmol(-1) at EOS. In vitro autoradiography with an ischemic rat brain showed significantly increased binding on the ipsilateral side compared to the contralateral side. The specificity of [(18)F]2 and [(18)F]3 for binding TSPO was confirmed using the TSPO ligands PK11195 and MBMP. The biodistribution patterns of both PET ligands were evaluated in normal mice by 1 h dynamic PET imaging. In the brain, regional radioactivity reached the maximum very rapidly within 0-4 min for both ligands, similar to (R)[(11)C]PK11195. The metabolite study of [(18)F]2 also favoured a more favourable profile for quantification in comparison to (R)[(11)C]PK11195. In summary, these data indicated that [(18)F]2 and [(18)F]3 have good potential to work as PET ligands, therefore there are merits to use these radioligands for the in vivo evaluation in animal models to see their efficacy in the living brain.

Improved synthesis of 6-bromo-7-[11C]methylpurine for clinical use.

BACKGROUND: Multidrug resistance-associated protein 1 (MRP1), an energy-dependent efflux pump, is expressed widely in various tissues and contributes to many physiological and pathophysiological processes. 6-Bromo-7-[11C]methylpurine ([11C]7m6BP) is expected to be useful for the assessment of MRP1 activity in the human brain and lungs. However, the radiochemical yield (RCY) in the synthesis of [11C]7m6BP was low, limiting its clinical application, because the methylation of the precursor with [11C]CH3I provided primarily the undesired isomer, 6-bromo-9-[11C]methylpurine ([11C]9m6BP). To increase the RCY of [11C]7m6BP, we investigated conditions for improving the [11C]7m6BP/[11C]9m6BP selectivity of the methylation reaction. RESULTS: [11C]7m6BP was manually synthesized via the methylation of 6-bromopurine with [11C]CH3I in various solvents and at different temperatures in the presence of potassium carbonate for 5 min. Several less polar solvents, including tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), and ethyl acetate (AcOEt) improved the [11C]7m6BP/[11C]9m6BP selectivity from 1:1 to 2:1, compared with the conventionally used solvents for the alkylation of 6-halopurines, acetone, acetonitrile, and N,N-dimethylformamide. However, a higher temperature (140 °C or 180 °C) was needed to progress the 11C-methylation in the less polar solvents, and the manual conditions could not be directly translated to an automated synthesis. [11C]Methyl triflate ([11C]CH3OTf) was thus used as a methylating agent to increase the conversion at a lower temperature. The 11C-methylation using [11C]CH3OTf at 100 °C proceeded efficiently in THF, 2-MeTHF, and AcOEt with maintenance of the improved selectivity. Starting from 28 to 34 GBq [11C]CO2, [11C]7m6BP was produced with 2.3-2.6 GBq for THF, 2.7-3.3 GBq for AcOEt, and 2.8-3.9 GBq for 2-MeTHF at approximately 30 min after the end of bombardment (n = 3 per solvent). The isolated RCYs (decay corrected) for THF, 2-MeTHF, and AcOEt were 24-28%, 29-35%, and 22-31% (n = 3), respectively. CONCLUSIONS: The use of THF, 2-MeTHF, and AcOEt improved the [11C]7m6BP/[11C]9m6BP selectivity in the methylation reaction, and the improved method provided [11C]7m6BP with sufficient radioactivity for clinical use.

Synthesis and evaluation of 1-[2-(4-[(11)C]methoxyphenyl)phenyl]piperazine for imaging of the serotonin 5-HT7 receptor in the rat brain.

1-[2-(4-Methoxyphenyl)phenyl]piperazine (4) is a potent serotonin 5-HT7 receptor antagonist (Ki=2.6nM) with a low binding affinity for the 5-HT1A receptor (Ki=476nM). As a potential positron emission tomography (PET) radiotracer for the 5-HT7 receptor, [(11)C]4 was synthesized at high radiochemical yield and specific activity, by O-[(11)C]methylation of 2'-(piperazin-1-yl)-[1,1'-biphenyl]-4-ol (6) with [(11)C]methyl iodide. Autoradiography revealed that [(11)C]4 showed in vitro specific binding with 5-HT7 in the rat brain regions, such as the thalamus which is a region with high 5-HT7 expression. Metabolite analysis indicated that intact [(11)C]4 in the brain exceeded 90% of the radioactive components at 15min after the radiotracer injection, although two radiolabeled metabolites were found in the rat plasma. The PET study of rats showed moderated uptake of [(11)C]4 in the brain (1.2SUV), but no significant regional difference in radioactivity in the brain. Pretreatment with 5-HT7-selective antagonist SB269970 (3) did not decrease the uptake of [(11)C]4 in the rat brain. Further studies are warranted that focus on the development of PET ligand candidates with higher binding affinity for 5-HT7 and higher in vivo stability in brain than 4.

Automated radiosynthesis and in vivo evaluation of 18F-labeled analog of the photosensitizer ADPM06 for planning photodynamic therapy.

BACKGROUND: A family of BF2-chelated tetraaryl-azadipyrromethenes was developed as non-porphyrin photosensitizers for photodynamic therapy. Among the developed photosensitizers, ADPM06 exhibited excellent photochemical and photophysical properties. Molecular imaging is a useful tool for photodynamic therapy planning and monitoring. Radiolabeled photosensitizers can efficiently address photosensitizer biodistribution, providing helpful information for photodynamic therapy planning. To evaluate the biodistribution of ADPM06 and predict its pharmacokinetics on photodynamic therapy with light irradiation immediately after administration, we synthesized [18F]ADPM06 and evaluated its in vivo properties. RESULTS: [18F]ADPM06 was automatically synthesized by Lewis acid-assisted isotopic 18F-19F exchange using ADPM06 and tin (IV) chloride at room temperature for 10 min. Radiolabeling was carried out using 0.4 µmol of ADPM06 and 200 µmol of tin (IV) chloride. The radiosynthesis time was approximately 60 min, and the radiochemical purity was > 95% at the end of the synthesis. The decay-corrected radiochemical yield from [18F]F- at the start of synthesis was 13 ± 2.7% (n = 5). In the biodistribution study of male ddY mice, radioactivity levels in the heart, lungs, liver, pancreas, spleen, kidney, small intestine, muscle, and brain gradually decreased over 120 min after the initial uptake. The mean radioactivity level in the thighbone was the highest among all organs investigated and increased for 120 min after injection. Upon co-injection with ADPM06, the radioactivity levels in the blood and brain significantly increased, whereas those in the heart, lung, liver, pancreas, kidney, small intestine, muscle, and thighbone of male ddY mice were not affected. In the metabolite analysis of the plasma at 30 min post-injection in female BALB/c-nu/nu mice, the percentage of radioactivity corresponding to [18F]ADPM06 was 76.3 ± 1.6% (n = 3). In a positron emission tomography study using MDA-MB-231-HTB-26 tumor-bearing mice (female BALB/c-nu/nu), radioactivity accumulated in the bone at a relatively high level and in the tumor at a moderate level for 60 min after injection. CONCLUSIONS: We synthesized [18F]ADPM06 using an automated 18F-labeling synthesizer and evaluated the initial uptake and pharmacokinetics of ADPM06 using biodistribution of [18F]ADPM06 in mice to guide photodynamic therapy with light irradiation.

The Glutaminase-1 Inhibitor [11C-carbony]BPTES: Synthesis and Positron Emission Tomography Study in Mice.

Bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl)ethyl sulfide (BPTES) is a selective inhibitor of glutaminase-1 (GLS1), consequently inhibiting glutaminolysis. BPTES is known for its potent antitumor activity and plays a significant role in senescent cell removal. In this study, we synthesized [11C-carbonyl]BPTES ([11C]BPTES) as a positron emission tomography (PET) probe for the first time and assessed its biodistribution in mice using PET. [11C]BPTES was synthesized by the reaction of an amine precursor () with [11C-carbonyl]phenylacetyl acid anhydride ([11C]2), which was prepared from [11C]CO2 and benzyl magnesium chloride, followed by in situ treatment with isobutyl chloroformate. The decay-corrected isolated radiochemical yield of [11C]BPTES was 9.5% (based on [11C]CO2) during a synthesis time of 40 min. A PET study with [11C]BPTES showed high uptake levels of radioactivity in the liver, kidney, and small intestine of mice.

Small-animal PET study for noninvasive quantification of transmembrane AMPA receptor regulatory protein γ-8 (TARP γ-8) in the brain.

Transmembrane AMPA receptor regulatory protein γ-8 (TARP γ-8) mediates various AMPA receptor functions. Recently, [11C]TARP-2105 was developed as a PET ligand for TARP γ-8 imaging. We performed a full kinetic analysis of [11C]TARP-2105 using PET with [11C]TARP-2105 for the first time. The distribution volume (VT), which is a macro parameter consisting of the K1-k4 rate constants in the two-tissue compartment model analysis, exhibited the following rank order: hippocampus (1.4 ± 0.3) > amygdala (1.0 ± 0.2) > frontal cortex (0.9 ± 0.2) > striatum (0.8 ± 0.2) ≫ cerebellum (0.5 ± 0.1) ≈ thalamus (0.5 ± 0.1) > pons (0.4 ± 0.1 mL/cm3). These heterogenous VT values corresponded with the order of biological distribution of TARP γ-8 in the brain. To validate the reference tissue model, the binding potential (BPND) of [11C]TARP-2105 for TARP γ-8 was estimated using general methods (SRTM, MRTM0, Logan reference model, and ratio method). These BPNDs based on reference models indicated excellent correlation (R2 > 0.9) to the indirect BPNDs based on 2TCM with moderate reproducibility (%variability ≈ 10). PET with [11C]TARP-2105 enabled noninvasive BPND estimation and visual mapping of TARP γ-8 in the living rat brain.

Utilization of [11C]phosgene for radiosynthesis of N-(2-{3-[3,5-bis(trifluoromethyl)]phenyl[11C]ureido}ethyl)glycyrrhetinamide, an inhibitory agent for proteasome and kinase in tumors.

N-(2-{3-[3,5-Bis(trifluoromethyl)]phenylureido}ethyl)glycyrrhetinamide (2), an ureido-substituted derivative of glycyrrhetinic acid (1), has been reported to display potent inhibitory activity for proteasome and kinase, which are overexpressed in tumors. In this study, we labeled this unsymmetrical urea 2 using [(11)C]phosgene ([(11)C]COCl(2)) as a labeling agent with the expectation that [(11)C]2 could become a positron emission tomography ligand for the imaging of proteasome and kinase in tumors. The strategy for the radiosynthesis of [(11)C]2 was to react hydrochloride of 3,5-bis(trifluoromethyl)aniline (4·HCl) with [(11)C]COCl(2) to possibly give isocyanate [(11)C]6, followed by the reaction of [(11)C]6 with N-(2-aminoethyl)glycyrrhetinamide (3).

Radiosynthesis of [13N]dantrolene, a positron emission tomography probe for breast cancer resistant protein, using no-carrier-added [13N]ammonia.

Dantrolene (1) is a substrate for breast cancer resistant protein, which is widely distributed in the blood-brain-barrier, intestine, gall bladder, and liver. PET study with 1 labeled with a positron emitter can be used to visualize BCRP and to elucidate the effect of BCRP on the pharmacokinetics of drugs. The objective of this study was to label 1 using nitrogen-13 ((13)N, a positron emitter; half-life: 9.9min). Using no-carrier-added [(13)N]NH(3) as the labeling agent, we synthesized [(13)N]dantrolene ([(13)N]1) for the first time. The reaction of carbomyl chloride 2b with [(13)N]NH(3) gave an unsymmetrical urea [(13)N]3, followed by cyclization of [(13)N]3 to afford [(13)N]1. Due to its instability, 2b was prepared in situ by treating amine 5 with triphosgene in a ratio of 4 to 1 and used for subsequent [(13)N]ammonolysis without purification.

Rapid 'on-column' preparation of hydrogen [11C]cyanide from [11C]methyl iodide via [11C]formaldehyde.

Hydrogen [11C]cyanide ([11C]HCN) is a versatile 11C-labelling agent for the production of 11C-labelled compounds used for positron emission tomography (PET). However, the traditional method for [11C]HCN production requires a dedicated infrastructure, limiting accessibility to [11C]HCN. Herein, we report a simple and efficient [11C]HCN production method that can be easily implemented in 11C production facilities. The immediate production of [11C]HCN was achieved by passing gaseous [11C]methyl iodide ([11C]CH3I) through a small two-layered reaction column. The first layer contained an N-oxide and a sulfoxide for conversion of [11C]CH3I to [11C]formaldehyde ([11C]CH2O). The [11C]CH2O produced was subsequently converted to [11C]HCN in a second layer containing hydroxylamine-O-sulfonic acid. The yield of [11C]HCN produced by the current method was comparable to that of [11C]HCN produced by the traditional method. The use of oxymatrine and diphenyl sulfoxide for [11C]CH2O production prevented deterioration of the molar activity of [11C]HCN. Using this method, compounds labelled with [11C]HCN are now made easily accessible for PET synthesis applications using readily available labware, without the need for the 'traditional' dedicated cyanide synthesis infrastructure.

Visualization of early infarction in rat brain after ischemia using a translocator protein (18 kDa) PET ligand [11C]DAC with ultra-high specific activity.

The aim of this study was to visualize early infarction in the rat brain after ischemia using a translocator protein (TSPO) (18 kDa) PET ligand [(11)C]DAC with ultra-high specific activity (SA) of 3670-4450 GBq/µmol. An infarction model of rat brain was prepared by ischemic surgery and evaluated 2 days after ischemia using small-animal PET and in vitro autoradiography. Early infarction with a small increase of TSPO expression in the brain was visualized using PET with high SA [(11)C]DAC (average 4060 GBq/µmol), but was not distinguished clearly with usually reported SA [(11)C]DAC (37 GBq/µmol). Infarction in the rat brain 4 days after ischemia was visualized using high and usually reported SAs [(11)C]DAC. Displacement experiments with unlabeled TSPO-selective AC-5216 or PK11195 diminished the difference in radioactivity between ipsilateral and contralateral sides, confirming that the increased uptake on the infracted brain was specific to TSPO. In vitro autoradiography with high SA [(11)C]DAC showed that the TSPO expression increased on early infarction in the rat brain. High SA [(11)C]DAC is a useful and sensitive biomarker for the visualization of early infarction and the characterization of TSPO expression which was slightly elevated in the infarcted brain using PET.