ABSTRACT
PURPOSE: Lipophilic cations including tetraphenylphosphonium (TPP) salts penetrate the hydrophobic barriers of the plasma and mitochondrial membranes, resulting in accumulation in mitochondria in response to the negative inner transmembrane potentials. The development of radiolabeled phosphonium cations as a noninvasive imaging agent may serve as a new molecular "voltage sensor" probe to investigate the role of mitochondria in the pathophysiology and diagnosis of cancer. MATERIALS AND METHODS: We have synthesized a reference compound (4-fluorophenyl)triphenylphosphonium (TPP) and a labeled compound [18F]TPP via two step nucleophilic substitution of no-carrier-added [18F]fluoride with the precursor, 4-iodophenyltrimethylammonium iodide, in the presence of Kryptofix-2.2.2 and K2CO3. RESULT: The reference compound (4-fluorophenyl)triphenylphosphonium (TPP) was synthesized in 60% yield. The radiolabeled compound [18F]TPP was synthesized in 10~15% yield. The radiochemical purity of the [18F]TPP was 95.57+/-0.51% (n=11). CONCLUSION: [18F]TPP was successfully synthesized that might have a potential to be utilized as a novel myocardial or cancer imaging agent for PET. However, it is required to improve the radiochemical yield to apply [18F]TPP in preclinical or clinical researches.
Subject(s)
Cations , Diagnosis , Membrane Potential, Mitochondrial , Membrane Potentials , Mitochondria , Mitochondrial Membranes , Plasma , SaltsABSTRACT
PURPOSE: Several radioisotope-labeled thymidine derivatives such as [11C]thymidine was developed to demonstrate cell proliferation in tumor. But it is difficult to track metabolism with [11C]thymidine due to rapid in vivo degradation and its short physical half-life. 3'-[18F]fluoro-3'-deoxythymidine ([18F]FLT) was reported to have the longer half life of fluorine-18 and the lack of metabolic degradation in vivo. Here, we described the synthesis of the 3'-[18F]fluoro-3'-deoxythymidine ([18F]FLT) and compared with [18F]FET and [18F]FDG in cultured 9L cell and obtained the biodistribution and PET image in 9L tumor bearing rats. MATERIAL AND METHOD: For the synthesis of [18F]FLT, 3-N-tert-butoxycarbonyl-(5'-O-(4,4'-dimethoxytriphenylmethyl)-2'-deoxy-3'-O-(4-nitrobenzenesulfonyl)-beta-D-threopentofuranosyl)thymine was used as a FLT precursor, on which the tert-butyloxycarbonyl group was introduced to protect N3-position and nitrobenzenesulfonyl group. Radiolabeling of nosyl substitued precursor with 18F was performed in acetonitrile at 120 degrees C and deproteced with 0.5 N HCl. The cell uptake was measured in cultured 9L glioma cell. The biodistribution was evaluated in 9L tumor bearing rats after intravenous injection at 10 min, 30 min, 60 min and 120 min and obtained PET image 60 minutes after injection. RESULTS: The radiochemical yield was about 20-30% and radiochemical purity was more than 95% after HPLC purification. Cellular uptake of [18F]FLT was increased as time elapsed. At 120 min post-injection, the ratios of tumor/blood, tumor/muscle and tumor/brain were 1.61+/-0.34, 1.70+/-0.30 and 9.33+/-2.22, respectively. The 9L tumor was well visualized at 60 min post injection in PET image. CONCLUSION: The uptake of [18F]FLT in tumor was higher than in normal brain and PET image of [18F]FLT was acceptable. These results suggest the possibility of [18F]FLT as an imaging agent for brain tumor.
Subject(s)
Animals , Rats , Brain , Brain Neoplasms , Cell Proliferation , Chromatography, High Pressure Liquid , Glioma , Half-Life , Injections, Intravenous , Metabolism , ThymidineABSTRACT
The antiarrhythmic clofilium is an efficient blocker of hERG1 potassium channels that are strongly expressed in the heart. Therefore, derivatives of clofilium that emit positrons might be useful tools for monitoring hERG1 channels in vivo. Fluoroclofilium (F-clofilium) was synthesized and its channel-blocking properties were determined for hERG1 and hEAG1 channels expressed in HEK 293 cells and in Xenopus oocytes. When applied extracellularly in the whole-cell patch-clamp configuration, F-cloflium exhibited a slower onset of block when compared with clofilium, presumably owing to its lower membrane permeability. When applied in the inside-out configuration at the intracellular membrane side, it blocked hEAG1 channels almost as efficiently as clofilium (IC50 1.37 nM and 0.83 nM, respectively). Similar results were obtained for hERG1, showing Fclofilium is a potent hERG1 and hEAG1 channel blocker once it has reached the intracellularly accessible target site at the channel. Using the 18Flabeled analog we studied the in vivo binding and distribution of F-clofilium in mice and a dog. Greatest activity was found in kidneys and bones. A small but significant enrichment of activity in the dog myocardium known for its expression of cERG1 channels allowed to depict the myocardium of a living dog by PET. Thus, F-clofilium is a useful tool for imaging hERG channels in living organisms.
Subject(s)
Animals , Dogs , Female , Mice , Anti-Arrhythmia Agents/pharmacokinetics , Cell Line , Electrons , Ether-A-Go-Go Potassium Channels/antagonists & inhibitors , Inhibitory Concentration 50 , Kidney/metabolism , Mice, Inbred BALB C , Myocardium/metabolism , Positron-Emission Tomography , Potassium Channel Blockers/pharmacokinetics , Quaternary Ammonium Compounds/pharmacokinetics , Tissue Distribution , XenopusABSTRACT
PURPOSE: Thallous-201 chloride produced at Korea Cancer Center Hospital(KCCH) is used in detecting cardiovascular disease and cancer. Thallium impurity can cause emesis, catharsis and nausea, so the presence of thallium and other metal impurities should be determined. According to USP and KP, their amounts must be less than 2 ppm in thallium and 5 ppm in total. In this study, the detection method of trace amounts of metal impurities in [201Tl]TlCl injection with polarography was optimized without environmental contamination. MATERALS AND METHODS: For the detection of metal impurities, Osteryoung Square Wave Stripping Voltammetry method was used in Bio-Analytical System (BAS) 50W polarograph. The voltammetry was composed of Dropping Mercury Electrode (DME) as a working electrode, Ag/AgCl as a reference electrode and Pt wire as a counter electrode. Square wave stripping method, which makes use of formation and deformation of amalgam, was adopted to determine the metal impurities, and pH 7 phosphate buffer was used as supporting electrolyte. RESULTS: T1, Cu and Pb in thallous-201 chloride solution were detected by scanning from 300 mV to -800 mV. Calibration curves were made by using TlNO3, CuSO4 and Pb(NO3)2 as standard solutions. Tl was confirmed at -450 mV peak potential and Cu at -50 mV. Less than 2 ppm of Tl and Cu was detected and Pb was not detected in KCCH-produced thallous-201 chloride injection. CONCLUSION: Detection limit of thallium and copper is approximately 50 ppb with this method. As a result of this experiment, thallium and other metal impurities in thallous-201 chloride injection, produced at Korea Cancer Center Hospital, are in the regulation of USP and KP. Polarograph could be applied for the determination of metal impurities in the quality control of radiopharmaceuticals conveniently without environmental contamination.