Masanao Ogawa

[18F]FMDAA1106 and [18f]FEDAA1106: Two positron-emitter labeled ligands for peripheral benzodiazepine receptor (PBR)

We synthesized and evaluated N-(5-fluoro-2-phenoxyphenyl)-N-(2-[(18)F]fluoromethyl-5-methoxybenzyl)acetamide ([(18)F]-FMDAA1106) and N-(5-fluoro-2-phenoxyphenyl)-N-(2-[(18)F]fluoroethyl-5-methoxybenzyl)acetamide ([(18)F]FEDAA1106) as two potent radioligands for peripheral benzodiazepine receptors (PBR). [(18)F]FMDAA1106 and [(18)F]FEDAA1106 were respectively synthesized by fluoroalkylation of the desmethyl precursor DAA1123 with [(18)F]FCH(2)I and [(18)F]FCH(2)CH(2)Br. Ex vivo autoradiograms of [(18)F]FMDAA1106 and [(18)F]FEDAA1106 binding sites in the rat brains revealed that a high radioactivity was present in the olfactory bulb, the highest PBR density region in the brain.

[11C]sorafenib: radiosynthesis and preliminary PET study of brain uptake in P-gp/Bcrp knockout mice.

Sorafenib (Nexavar, BAY43-9006, 1) is a second-generation, orally active multikinase inhibitor that is approved for the treatment of some cancers in patients. In this Letter, we developed [(11)C]1 as a novel positron emission tomography (PET) probe, and evaluated the influence of ABC transporters-mediated efflux on brain uptake using PET with [(11)C]1 in P-glycoprotein (P-gp)/breast cancer resistance protein (Bcrp) knockout mice versus wild-type mice. [(11)C]1 was synthesized by the reaction of hydrochloride of aniline 2 with [(11)C]phosgene ([(11)C]COCl(2)) to give isocyanate [(11)C]6, followed by reaction with another aniline 3. Small-animal PET study with [(11)C]1 indicated that the radioactivity level (AUC(0-60 min), SUV×min) in the brains of P-gp/Bcrp knockout mice was about three times higher than in wild-type mice.

Synthesis and evaluation of 6-[1-(2-[18F]fluoro-3-pyridyl)-5-methyl-1H-1,2,3-triazol-4-yl]quinoline for positron emission tomography imaging of the metabotropic glutamate receptor type 1 in brain

The purpose of this study was to synthesize 6-[1-(2-[(18)F]fluoro-3-pyridyl)-5-methyl-1H-1,2,3-triazol-4-yl]quinoline ([(18)F]FPTQ, [(18)F]7a) and to evaluate its potential as a positron emission tomography ligand for imaging metabotropic glutamate receptor type 1 (mGluR1) in the rat brain. Compound [(18)F]7a was synthesized by [(18)F]fluorination of 6-[1-(2-bromo-3-pyridyl)-5-methyl-1H-1,2,3-triazol-4-yl]quinoline (7b) with potassium [(18)F]fluoride. At the end of synthesis, 1280-1830MBq (n=8) of [(18)F]7a was obtained with >98% radiochemical purity and 118-237GBq/μmol specific activity using 3300-4000MBq of [(18)F]F(-). In vitro autoradiography showed that [(18)F]7a had high specific binding with mGluR1 in the rat brain. Biodistribution study using a dissection method and small-animal PET showed that [(18)F]7a had high uptake in the rat brain. The uptake of radioactivity in the cerebellum was reduced by unlabeled 7a and mGluR1-selective ligand JNJ-16259685 (2), indicating that [(18)F]7a had in vivo specific binding with mGluR1. Because of a low amount of radiolabeled metabolite present in the brain, [(18)F]7a may have a limiting potential for the in vivo imaging of mGluR1 by PET.

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.

PET Imaging of Lung Inflammation with [18F]FEDAC, a Radioligand for Translocator Protein (18 kDa)

Purpose The translocator protein (18 kDa) (TSPO) is highly expressed on the bronchial and bronchiole epithelium, submucosal glands in intrapulmonary bronchi, pneumocytes and alveolar macrophages in human lung. This study aimed to perform positron emission tomography (PET) imaging of lung inflammation with [18F]FEDAC, a specific TSPO radioligand, and to determine cellular sources enriching TSPO expression in the lung. Methods An acute lung injury model was prepared by intratracheal administration of lipopolysaccharide (LPS) to rat. Uptake of radioactivity in the rat lungs was measured with small-animal PET after injection of [18F]FEDAC. Presence of TSPO was examined in the lung tissue using Western blot and immunohistochemical assays. Results The uptake of [18F]FEDAC increased in the lung with the progress of inflammation by treatment with LPS. Pretreatment with a TSPO-selective ligand PK11195 showed a significant decrease in the lung uptake of [18F]FEDAC due to competitive binding to TSPO. TSPO expression was elevated in the inflamed lung section and its level responded to the [18F]FEDAC uptake and severity of inflammation. Increase of TSPO expression was mainly found in the neutrophils and macrophages of inflamed lungs. Conclusion From this study we conclude that PET with [18F]FEDAC may be a useful tool for imaging TSPO expression and evaluating progress of lung inflammation. Study on human lung using [18F]FEDAC-PET is promising.

Synthesis and evaluation of novel radioligands for positron emission tomography imaging of metabotropic glutamate receptor subtype 1 (mGluR1) in rodent brain.

We designed three novel positron emission tomography ligands, N-(4-(6-(isopropylamino)pyrimidin-4-yl)-1,3-thiazol-2-yl)-4-[(11)C]methoxy-N-methylbenzamide ([(11)C]6), 4-[(18)F]fluoroethoxy-N-[4-[6-(isopropylamino)pyrimidin-4-yl]-1,3-thiazol-2-yl]-N-methylbenzamide ([(18)F]7), and 4-[(18)F]fluoropropoxy-N-[4-[6-(isopropylamino)pyrimidin-4-yl]-1,3-thiazol-2-yl]-N-methylbenzamide ([(18)F]8), for imaging metabotropic glutamate receptor type 1 (mGluR1) in rodent brain. Unlabeled compound 6 was synthesized by benzoylation of 4-pyrimidinyl-2-methylaminothiazole 10, followed by reaction with isopropylamine. Removal of the methyl group in 6 gave phenol precursor 12 for radiosynthesis. Two fluoroalkoxy analogues 7 and 8 were prepared by reacting 12 with tosylates 13 and 14. Radioligands [(11)C]6, [(18)F]7, and [(18)F]8 were synthesized by O-[(11)C]methylation or [(18)F]fluoroalkylation of 12. Compound 6 showed high in vitro binding affinity for mGluR1, whereas 7 and 8 had weak affinity. Autoradiography using rat brain sections showed that [(11)C]6 binding is aligned with the reported distribution of mGluR1 with high specific binding in the cerebellum and thalamus. PET study with [(11)C]6 in rats showed high brain uptake and a similar distribution pattern to that in autoradiography, indicating the usefulness of [(11)C]6 for imaging brain mGluR1.

Synthesis and in vivo evaluation of 18F-fluoroethyl GF120918 and XR9576 as positron emission tomography probes for assessing the function of drug efflux transporters

The purpose of this study was to synthesize two new positron emission tomography (PET) probes, N-(4-(2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl)phenyl)-9,10-dihydro-5-[¹⁸F]fluoroethoxy-9-oxo-4-acridine carboxamide ([¹⁸F]3) and quinoline-3-carboxylic acid [2-(4-{2-[7-(2-[¹⁸F]fluoroethoxy)-6-methoxy-3,4-dihydro-1H-isoquinolin-2-yl]ethyl}phenylcarbamoyl)-4,5-dimethoxyphenyl]amide ([¹⁸F]4), and to evaluate the potential of these PET probes for assessing the function of two major drug efflux transporters, P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP). [¹⁸F]3 and [¹⁸F]4 were synthesized by ¹⁸F-alkylation of each O-desmethyl precursor with [¹⁸F]2-fluoroethyl bromide for injection as PET probes. In vitro accumulation assay showed that treatment with P-gp/BCRP inhibitors (1 and 2) enhanced the intracellular accumulation capacity of P-gp- and BCRP-overexpressing MES-SA/Dx5 cells. In PET studies, the uptake (AUC(brain[0-)₆₀ (min])) of [¹⁸F]3 and [¹⁸F]4 in wild-type mice co-injected with 1 were approximately sevenfold higher than that in wild-type mice, and the uptake of [¹⁸F]3 and [¹⁸F]4 in P-gp/Bcrp knockout mice were eight- to ninefold higher than that in wild-type mice. The increased uptake of [¹⁸F]3 and [¹⁸F]4 was similar to that of parent compounds ([¹¹C]1 and [¹¹C]2) previously described, indicating that radioactivity levels in the brain after injection of [¹⁸F]3 and [¹⁸F]4 are related to the function of drug efflux transporters. Also, these results suggest that the structural difference between parent compounds ([¹¹C]1 and [¹¹C]2) and fluoroethyl analogs ([¹⁸F]3 and [¹⁸F]4) do not obviously affect the potency against drug efflux transporters. In metabolite analysis of mice, the unchanged form in the brain and plasma at 60 min after co-injection of [¹⁸F]4 plus 1 were higher (95% for brain; 81% for plasma) than that after co-injection of [¹⁸F]3 plus 1. [¹⁸F]4 is a promising PET probe to assess the function of drug efflux transporters.

Evaluation of the P-glycoprotein- and breast cancer resistance protein-mediated brain penetration of 11C-labeled topotecan using small-animal positron emission tomography

INTRODUCTION Topotecan (TPT) is a camptothecin derivative and is an anticancer drug working as a topoisomerase-I-specific inhibitor. But TPT cannot penetrate through the blood-brain barrier. In this study, we synthesized a new positron emission tomography (PET) probe, [(11)C]TPT, to evaluate the P-glycoprotein (Pgp)- and breast cancer resistance protein (BCRP)-mediated brain penetration of [(11)C]TPT using small-animal PET. METHODS [(11)C]TPT was synthesized by the reaction of a desmethyl precursor with [(11)C]CH(3)I. In vitro study using [(11)C]TPT was carried out in MES-SA and doxorubicin-resistant MES-SA/Dx5 cells in the presence or absence of elacridar, a specific inhibitor for Pgp and BCRP. The biodistribution of [(11)C]TPT was determined using small-animal PET and the dissection method in mice. RESULTS The transport of [(11)C]TPT to the extracellular side was determined in MES-SA/Dx5 cells exhibiting the expressions of Pgp and BCRP at high levels. This transport was inhibited by coincubation with elacridar. In Mdr1a/b(-/-)Bcrp1(-/-) mice, PET results indicated that the brain uptake of [(11)C]TPT was about two times higher than that in wild-type mice. Similarly, the brain penetration of [(11)C]TPT in wild-type mice was increased by treatment with elacridar. The radioactivity in the brain of elacridar-treated mice was maintained at a certain level after the injection of [(11)C]TPT, although the radioactivity in the blood decreased with time. CONCLUSIONS We demonstrated the increase of brain penetration of [(11)C]TPT by deficiency and inhibition of Pgp and BCRP functions using small-animal PET in mice.

Simple and effective method for producing [11C]phosgene using an environmental CCl4 gas detection tube.

INTRODUCTION Carbon-11-labeled phosgene is an important labeling precursor for PET molecular probes. Despite the usefulness of [(11)C]phosgene, some difficulties, especially in the formation of [(11)C]phosgene process from [(11)C]CCl(4), hamper its use. The present article shows a simple preparation method for [(11)C]phosgene. METHOD [(11)C]CCl(4) was obtained using the conventional method by passing a mixture of [(11)C]CH(4) and Cl(2) through a heated quartz tube. The [(11)C]CCl(4) was transformed to [(11)C]phosgene simply by passing through a pretreatment tube of a Kitagawa gas detection system for the working-environmental CCl(4) concentration measurement at room temperature with a flow rate of 50 ml/min. RESULT This tube successfully transformed [(11)C]CCl(4) to [(11)C]phosgene at room temperature. [(11)C]Phosgene was obtained at nearly 80% radiochemical yield (EOB) in a short synthesis time with high reproducibility. CONCLUSION A high yield and reliable [(11)C]phosgene production method using a gas detector tube system for working-environmental CCl(4) concentration measurement was developed.

Radiosynthesis of novel carbon-11-labeled triaryl ligands for cannabinoid-type 2 receptor.

Two novel triaryl ligands 2 and 5 with potent in vitro binding affinities for the cannabinoid subtype-2 (CB2) receptor were labeled with a positron-emitting radioactive nuclide (11)C. Radioligands [(11)C]2, [(11)C]5, and their analogs [(11)C]3 and [(11)C]4 were synthesized by O-[(11)C]methylation of their corresponding phenol precursors with [(11)C]CH(3)I. [(11)C]2-5 had relatively high uptakes (>1.2% injected dose/g tissue) in mouse brains.