• Nuclear Medicine and Molecular Imaging
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• v.43 no.4
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• pp.337-343
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• 2009

Purpose: ((R)-1-(2-chlorophenyl)-N-1-[$^{11}$C]methyl-N(1-propyl)-3-isoquinoline carboxamide ((R)-PK11195) is a specific ligand for the peripheral type benzodiazepine receptor and a marker of activated microglia, used to measure inflammation in neurologic disorders. We report here that a direct and simple radiosynthesis of [$^{11}$C](R)-PK11195 in mild condition using NaH suspension in DMF and one-step loop method. Materials and Methods: (R)-N-Desmethyl-PK11195 (1 mg) in DMSO (0.1 mL) and NaH suspension in DMF (0.1 mL) were injected into a semi-prep HPLC loop. [$^{11}$C]methyl iodide was passed through HPLC loop at room temperature. Purification was performed using semi-preparative HPLC. Aliquots eluted at 11.3 min were collected and analyzed by analytical HPLC and mass spectrometer. Results: The labeling efficiency of [$^{11}$C](R)-PK11195 was 71.8$\pm$8.5%. The specific activity was 11.8:$\pm$6.4 GBq/$\mu$mol and radiochemical purity was higher than 99.2%. The mass spectrum of the product eluted at 11.3 min showed m/z peaks at 353.1 (M+1), indicating the mass and structure of (R)-PK11195. Conclusion: By the one-step loop method with the [$^{11}$C]CH3l automated synthesis module, [$^{11}C$](R)-PK11195 could be easily prepared in high radiochemical yield using NaH suspension in DMF.

• Korean Journal of Bronchoesophagology
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• v.4 no.1
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• pp.64-72
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• 1998

This study aimed at observing the effect of diazepam on the contractility of trachealis muscle isolated from canine trachea, possible involvement of central or peripheral type benzodiazepine receptor, and the calcium related mechanism of action of diazepam. Trachealis muscle strips of 15 mm long were suspended in an isolated organ bath containing 1 ml of physiologic salt solution maintained at $37^{\circ}C$, and aerated with 95% $O_2$ /5% $CO_2$. Isometric myography was performed. Diazepam reduced the basal tone concentration dependently, and this inhibitory action was not affected by neither flumazenil, a central benzodiazepine receptor antagonist, nor PK11195, a peripheral benzodiazepine receptor antagonist. Pretreatment with diazepam showed the inhibitory effect on the concentration-response curves to agonists such as bethanechol, 5-hydroxytryptamine and histamine. Diazepam also caused concentration-related inhibition of contraction with potassium chloride 30 mM. The effect of diazepam on the basal tone and potassium chloride-induced contraction with calcium channel blockers were compared. Similar results were obtained in canine trachealis with verapamil, nifedipine and diltiazem. These results suggest that diazepam relax an airway muscle not via specific receptors but by a similar action as calcium channel blockers in canine trachealis muscle.

• The Korean Journal of Physiology and Pharmacology
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• v.1 no.6
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• pp.769-774
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• 1997

Non-neuronal high affinity binding sites for benzodiazepines have been found in many peripheral tissues including cardiac muscle and vascular smooth muscle, and have been designated as 'peripheral benzodiazepine receptor'. Benzodiazepines have been shown to induce relaxation of the ileal, vesical, and uterine smooth muscles. However, it is still unclear about possible involvement of peripheral benzodiazepine receptor on the contractility of trachealis muscle. This study was performed to investigate the role of the peripheral benzodiazepine receptor on the contractility of canine trachealis muscle. Canine trachealis muscle strips of 15 mm long were suspended in an isolated organ bath containing 1 ml of physiological salt solution maintained at $37^{\circ}C$, and aerated with $95%\;O_2/5%\;CO_2$. Isometric myography was performed, and the results of the experiments were as follows: Ro5-4684, FGIN-1-27 and clonazepam reduced a basal tone of isolated canine trachealis muscle strip concentration dependently, relaxant actions of RoS-4684 and FGIN-1-27 were antagonized by PK11195, a peripheral benzodiazepine receptor antagonist. Flumazenil, a central type antagonist, did not antagonize the relaxant action of Peripheral type agonists. Saturation binding assay of [3H]Ro5-4864 showed a high affinity$(Kd=5.33{\pm}1.27nM,\;Bmax=\;867.3{\pm}147.2\;fmol/mg\;protein)$ binding site on the canine trachealis muscle. Ro 5-4684 suppressed the bethanechol-, 5-hydroxyoyptamine- and histamine- induced contractions. Platelet activating factor (PAF) exerted strong and prolonged contraction in trachealis muscle strip. Strong tonic contraction by PAE was attenuated by Ro 5-4684, but not by WEB 2086, a PAF antagonist. Based on these results, it is concluded that the peripheral benzodiazepine receptor mediates the inhibitory regulation of contractilty of canine trachealis muscle.

• Journal of Radiopharmaceuticals and Molecular Probes
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• v.5 no.2
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• pp.89-100
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• 2019

In our previous studies, we developed a ¹⁸F-labeled TSPO-binding ligand, named [¹⁸F]CB251, which has been proved to be a promising TSPO-binding PET radiotracer for the detection and monitoring of TSPO expression in pathological diseases. (Ki = 0.27 nM for TSPO, 1.96% ID/g of tumor uptake at 1h post-injection) Based on these results, we utilized 6,8-dichloro-2-phenylimidazo[1,2-a]pyridineacetamide analogs, CB185 (1) as a targeting moiety for the selective delivery of probes and anticancer molecules to TSPO-overexpressed tissues. In this study, we designed CB185 derivatives contains different PEG chains (n = 1, 3 and 5) and fluorescence dye (Cy5) to identify the necessary space between a TSPO-binding ligand and an anticancer agent. Three CB185 derivatives (11a-c) which contains Cy5 and PEG chain, were synthesized and the effect of PEG additive on their TSPO-binding affinities were evaluated using in vitro assays. The binding affinity for compounds 11a-c was lower than that of PK11195 (Ki = 3.2 nM), but still characterized by nanomolar binding affinity for TSPO (Ki = 46.5 nM for 11a, 51.0 nM for 11b, and 388.5 nM for 11c). These results showed that the conjugates are characterized by a moderate binding affinity toward TSPO except for compound 11c, which PEG chain consist of five PEG monomers. Our finding might add useful information to decide the appropriate PET chain length for developing new TSPO-targeting drug carriers.