HPLC investigation of the radiochemical purity of <Superscript>99m</Superscript>Tc-MIBI

Technetium-99m-sestamibi (^99mTc-MIBI) is a small, lipophilic and cationic compound used for myocardial perfusion imaging. In addition, ^99mTc-MIBI has been shown to be useful in identifying several types of tumors, such as breast, lung and thyroid cancers. The high quality of this radiopharmaceutical and its uniformity are very important facts for application of this preparation in clinical practice. The monograph for ^99mTc-MIBI recommends at least 90% radiochemical purity (RCP) for clinical use. Various factors may influence the RCP of certain reagent kits. Some of these include the amount of activity added to the reagent kit, heating time and the age of the formulated kit. The effect of these factors on RCP of ^99mTc-MIBI has been investigated using high performance liquid chromatography (HPLC) and instant thin layer chromatography.     

Formulation of a freeze-dried kit for the preparation of <Superscript>99m</Superscript>Tc-tetrofosmin

A new formulation of a freeze-dried kit for the labeling of tetrofosmin with technetium-99m has been developed. The kit contains lyophilized mixture of 0.320 mg tetrofosmin [6,9-bis(2-ethoxyethyl)-3,12-dioxa-6,9-diphosphatetradecane], 0.025 mg stannous chloride dihydrate, 5 mg sodium tartrate and 5 mg sodium hydrogen carbonate. The product contains no antimicrobial preservative. When ^99mTc pertechnetate up to 6 mL saline containing 200 mCi is added to lyophilized mixture, a lipophilic, cationic ^99mTc complex is formed, ^99mTc-tetrofosmin. The performance of newly developed kit is compared with commercially available MYOVIEW kit for heart imaging. The patient studies show that the images of heart obtained by ^99mTc-tetrofosmin prepared by new formulation are equally good to MYOVIEW.     

Synthesis and biological evaluation of <Superscript>99m</Superscript>Tc labeled aryl piperazine derivatives as cerebral radiotracers

The aim of this study is to develop cerebral radiotracers for central nervous system receptors imaging. The synthesis, characterization and biological evaluation of two aryl piperazine ^99mTc-radiocomplexes based on the piano stool motif [CpM(CO₃)] (Cp = cyclopentadienyl, M = ^99mTc/Re) is reported. The ^99mTc-radiocomplexes were obtained quickly (time < 5 min) with high radiochemical yields. The ^99mTc-radiocomplexes characterized by high performance liquid chromatography comparison with the rhenium surrogates have both a suitable lipophilicity and are able to cross the blood brain barrier with 0.43 ± 0.05 and 1.96 ± 0.06% ID/g of brain uptake, at 10 min post injection.     

Preparation,quality control and physico-chemical properties of <Superscript>99m</Superscript>Tc-BAT-AV-45

One novel styrylpyridine derivatives(AV-45) coupled with ^99mTc complex was synthesized. ^99mTc-BAT-AV-45 was prepared by a ligand exchange reaction employing sodium glucoheptonate, and effects of the amount of ligand, stannous chloride, sodium glucoheptonate and pH value of reaction mixture on the radiolabeling yield were studied in details. Quality control was performed by thin layer chromatography and high performance liquid chromatography. Besides the stability, partition coefficient and electrophoresis of ^99mTc-BAT-AV-45 were also investigated. The results showed that the average radiolabeling yield was (95 ± 1%) and ^99mTc-BAT-AV-45 with suitable lipophilicity was stable and uncharged at physiological pH.     

A novel electrochemical <Superscript>99</Superscript>Mo/<Superscript>99m</Superscript>Tc generator

A novel electrochemical process to avail clinical grade ^99mTc from (n,γ)⁹⁹Mo has been demonstrated. The electrochemical parameters were optimized to maximize the ^99mTc yield with minimal ⁹⁹Mo contamination. ⁹⁹Mo/^99mTc generators containing up to 29.6 GBq (800 mCi) ⁹⁹Mo were developed and their performance were extensively evaluated for 10 days without changing the operating conditions. Very high radioactive concentration of ^99mTcO₄ ⁻ of acceptable quality, commensurate with hospital radiopharmacy requirements could be availed from the system with >90% yield. The compatibility of the product for the formulation of ^99mTc labeled radiopharmaceuticals such as ^99mTc-DMSA and ^99mTc-EC was found to be satisfactory in terms of high labeling yields. The proposed route represents an important step for enhancing the scope of accessing clinical grade ^99mTc from low specific activity (n, γ)⁹⁹Mo.     

Combined determination of <Superscript>99</Superscript>Tc and <Superscript>108m</Superscript>Ag in L/ILW liquid wastes

The low- and intermediate-activity level liquid wastes produced by the Paks Nuclear Power Plant (NPP) contain routinely measureable gamma-emitting (e.g., ⁵⁴Mn, ⁶⁰Co, ^110mAg, and ¹³⁷Cs) as well as many so-called “difficult-to-measure” radionuclides. Despite of their low specific activity compared to the total, the reliable determination of these radionuclides is an important issue of nuclear waste management. The increasing amount of waste samples to be qualified yearly by our laboratory put a pressure on revising the existing procedure of ⁹⁹Tc separation applied. We have managed to halve the initial amount of the sample required to achieve the same level of detection of technetium. Furthermore, one of the new purifying steps introduced have proved to be able to separate ^108mAg (and ^110mAg) better than 99% keeping the ⁹⁹Tc content of the product almost intact. Means of separation of ⁹⁹Tc from ¹⁰⁶Ru and ^124+125Sb have also been successfully investigated. As intended, this new procedure has a major impact on the chemical reagent as well as the electricity requirement of the separation making it more cost-effective.     

Synthesis and biodistribution of the <Superscript>99m</Superscript>Tc(CO)<Subscript>3</Subscript>-DEDT complex as a potential new radiopharmaceutical for brain imaging

The ^99mTc(CO)₃(H₂O)-DEDT complex was prepared by a two-step procedure involving the preparation of the precursor fac-[^99mTc(CO)₃(H₂O)₃]⁺, followed by the addition of sodium salt of diethyl dithiocarbamate (DEDT). The radiochemical purity (RCP) of the product was over 90% as measured by thin layer chromatography (TLC). No decomposition of the complex at room temperature was observed over a period of 6 hours. Its partition coefficient indicated that it was a lipophilic complex. The electrophoresis results showed the complex was neutral. Biodistribution in mice demonstrated that the complex can penetrate the intact blood-brain barrier (BBB) and the brain uptake (ID%/g) was 4.22 at 5-minute post-injection, suggesting the complex may lead to a further development of the radiopharma ceutical as a brain perfusion tracer.     

Preparation,quality control and stability of <Superscript>99m</Superscript>Tc-cefuroxime axetil

Cefuroxime axetil, a cephalosporin antibiotic used to treat bacterial infections, was investigated to label with ^99mTc. Radiolabeling of cefuroxime axetil was carried out by using stannous chloride method. Effects of pH and stannous chloride amount on the radiolabeling yield were investigated. The radiochemical purity of ^99mTc-cefuroxime axetil was determined by thin layer radio chromatography (TLRC), electrophoresis and high performance liquid chromatography. The maximum radiolabeling yield was 98±1%.     

The interaction of <Superscript>99m</Superscript>Tc with pyrimidine compounds

The reaction of ^99mTc of different oxidation states (+7, +4) with 2-thiouracil and 5-nitrobarbituric acid have been studied at different temperatures, pH and concentrations. The reaction mixtures have been analyzed at different times using thin layer chromatography (TLC) and a radio detector to show the peaks at the plates. ^99mTc is obtained from the Mo generators with oxidation state (+7). The use of SnCl₂ as a reducing agent gave ^99mTc with oxidation state (+4). It is very difficult to separate the complexes formed from the reactions in very small concentration. The percentage of ^99mTc and its oxidation state involved in the complexes can be determined. The labeling efficiencies (percentage of complex) in the reaction of ^99mTc⁺⁷ with 5-nitro-barbituric-acid increases mostly at pH  10. Both oxidation states of ^99mTc(+7, +4) can be detected at pH’s 4 and 10, but at pH  4, the reduced form ^99mTCO₂, is more pronounced. At pH  7 no complexes were detected and most of ^99mTc remains as ^99mTCO₄ ⁻ . By increasing the ligand concentration, the labeling efficiencies of the complex increases. For the reaction of ^99mTc of oxidation states (+4, +7) with 2-thiouracil at different temperatures and analytical times it is concluded that several complexes with different R_f values were observed in equilibrium and most of these complexes were unstable.     

Synthesis and biological evaluation of <Superscript>99m</Superscript>Tc-DHPM complex: a potential new radiopharmaceutical for lung imaging studies

In the recent years interests on dihydropyrimidinone and their analogues have increased potentially due to their wide range of pharmacological/biological activities. Synthesis, radiolabeling with technetium-99 m (^99mTc) and biological evaluation of 5-etoxycarbonyl-4-phenyl-6-methyl-3,4-dihydro-(1H)-pyrimidine-2-one (DHPM) were studied in this present work. After synthesis complexation of DHPM with ^99mTc was carried out using stannous chloride as the reducing agent. The complex (^99mTc-DHPM) was characterized by thin layer chromatography, radio-HPLC technique and determination of partition co-efficient. Radiochemical stability and particle size distribution of the complex were also measured. Biodistribution/scintigraphy studies were performed in rats and rabbits to evaluate the pharmacological characteristics of this complex. The radiochemical purity of the complex was over 95% as studied by thin layer chromatography and radio-HPLC. It was stable over 24 h at room temperature. Its partition coefficient indicated that it was a lipophilic complex. According to the European Pharmacopeia, >80% of ^99mTc labeled radiopharmaceutical (^99mTc-MAA) in the size range 10–50 μm, must be accumulated in the lungs 15 min after intravenous administration. In this study >85% of the ^99mTc-DHPM complex in the average size of 40 μm. Biodistribution studies of ^99mTc-DHPM in rat revealed that the complex accumulated in the lung with high uptake and good retention after intravenous administration. Scintigraphic studies in rabbit also revealed that most of the administered radiolabeled complex was accumulated in the lungs and after 1 h slowly excreted through the renal system. The lung uptake (ID%/g) was 10.12, 9.67, 8.60 and 5.01 and the lung/liver ratio was 7.49, 2.88, 2.62 and 1.87 at 2, 15, 30 and 60 min post-injection, respectively. These results suggested that ^99mTc-DHPM could be suitable as a potential lung perfusion imaging agent. Further studies with ^99mTc-DHPM and its derivatives are warranted to develop new ^99mTc-labeled imaging agents for clinical applications.     

Synthesis and biodistribution of <Superscript>99m</Superscript>TcN-isopentyl xanthate as a potential myocardial perfusion imaging agent

A novel ^99mTc nitrido xanthate complex ^99mTcN(IPEXT)₂ (IPEXT: isopentyl xanthate) has been synthesized by the reduction of ^99mTcO₄ ⁻ into [^99mTcN]²⁺ with stannous chloride in the presence of succinic dihydrazide and propylenediamine tetraacetic acid, followed by the addition of the corresponding xanthate ligand. The radiochemical purity of the complex was over 90% as measured by thin layer chromatography (TLC). No decomposition of the complex at room temperature was observed over a period of 6 hours. Its partition coefficient indicated that it was a lipophilic complex. The electrophoresis results showed the complex was neutral. Biodistribution in mice showed that the ^99mTcN(IPEXT)₂ complex accumulated in the heart with high uptake. The heart uptake (%IDg) was 8.00% at 5-minute post-injection, but the heart/lung, heart/liver and heart/blood ratios were not high, thereby, restricting the use of the complex as a good myocardial imaging agent.     

<Superscript>99</Superscript>Mo/<Superscript>99m</Superscript>Tc generators based on aluminum molybdate gel matrix prepared by nano method

A procedure for preparation of ⁹⁹Mo/^99mTc radioisotope generator based on low specific activity neutron activated ⁹⁹Mo was developed. Aluminum molybdate(VI)-⁹⁹Mo of high Mo(VI) content (~?364 mg/g Al⁹⁹Mo) was prepared by mixing low specific activity molybdate(VI)-⁹⁹Mo and aluminum mixture solution with isoamyl alcohol. Al⁹⁹Mo gel matrix was precipitated when the pH of the mixture solution was raised to ~?5 by addition of NaOH to the mixture. Radiometric measurements indicate the strong fixation of Molybdate(VI)-⁹⁹Mo species in the form of the sparingly insoluble Al⁹⁹Mo gel matrix. The prepared AlMo gel matrix was physiochemically characterized. Al⁹⁹Mo gel matrix was used as a base material for preparation of ⁹⁹Mo/^99mTc generator. The ^99mTc eluted from ⁹⁹Mo/^99mTc radioisotope generator was found to have relatively high elution yield (84?±?2.3%), radionuclidic (≥?99.99%), radiochemical (98.1?±?0.9%) and chemical purity.     

Radiosynthesis and biological evaluation of <Superscript>99m</Superscript>TcN-sitafloxacin dithiocarbamate as a potential radiotracer for <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> infection

Sitafloxacin dithocarbamate (SFDE) was synthesized, radiolabeled with technetium-99m (^99mTc) using [^99mTc-N]²⁺ core and evaluated its biological efficacy as a potential radiotracer for Staphylococcus aureus (S. aureus) infection in artificially infected rats (AIRT) and rabbits (AIRB). The radiochemical stability of the ^99mTc labeled SFDE (^99mTcN-SFDE) in saline and serum was determined by radio-HPLC and TLC methods, respectively. After, 1 min of reconstitution the value of radiochemical purity (RCP) was 99.00 ± 0.20% and was remained more than 90% unwavering even after 240 min of the radiolabeling. The ^99mTcN-SFDE complex showed similar radiochemical permanence behavior in serum at 37 °C. The complex showed almost six fold higher specific in vitro binding with living than heat killed S. aureus. Biodistribution behavior was evaluated in S. aureus AIRT and whole body imaging (WBI) in AIRB, respectively. Seven fold up take was observed in infected muscle of the AIRT as compared to inflamed and normal muscles. The disappearance of activity from blood and appearance in urinary system indicated normal route of excretion of the complex. Scintigraphically, it was confirmed that the labeled SFDE was higher accumulated in the infected muscle higher than in inflamed and normal muscle. The high radiochemical stability in saline and serum, specific in vitro binding with S. aureus, precise in vivo distribution in S. aureus AIRT and targeted WBI in AIRB confirmed the possibility of the ^99mTcN-SFDE complex as a potential and promising S. aureus infection radiotracer.     

Determination of radionuclidic impurities in <Superscript>99m</Superscript>Tc eluate from <Superscript>99</Superscript>Mo/<Superscript>99m</Superscript>Tc generator for quality control

Technetium-99m is the principal radioisotope used in medical diagnostics; radionuclidic impurity is the major concern of its quality. This work presents a analytical method for sequential determination of all radionuclidic impurities listed in pharmacopoeia including gamma emitters, alpha emitters, ⁸⁹Sr and ⁹⁰Sr. Radioactive decay for removal of ^99mTc, ion exchange and extraction chromatography for removal of ⁹⁹Mo and ⁹⁹Tc are effective for separation of interferences. Gamma spectrometry, LSC with alpha/beta discrimination, and Cherenkov counting using LSC are sensitive methods for measurement of the impurity radionuclides. The detection limits of this method are well meet the requirement of the quality control according to the limitation of the pharmacopoeia.     

Synthesis of <Superscript>99m</Superscript>Tc-pefloxacin: A new targeting agent for infectious foci

Summary This investigation focused on the labeling of pefloxacin, a fluoroquinolone antibacterial agent, with ^99mTc to form ^99mTc-pefloxacin complex. The labeling process was done by direct addition of pertechnetate in isotonic solution to Sn-pefloxacin solution. The labeling technique is effective, as a high labeling yield (98%) was obtained after 30-minute reaction time. Different factors were found that influenced this labeling reaction: 0.5 mg pefloxacin or more must be used to prevent the formation of colloids in the reaction medium. Fifty micrograms of stannous chloride dihydrate were found to be sufficient to reduce all pertechnetate with activity ranging from 37 to 3700 MBq without the detection of free pertechnetate or colloids in the reaction mixture. The pH of the reaction medium was found to play an important role in the labeling process. The labeling reaction proceeds well at neutral pH (pH 6) but at acidic pH value (pH 4 or below) the yield of ^99mTc-pefloxacin complex decreased markedly to a labeling yield of 5%. The reaction mixture must be heated to 100 °C in an oil bath to enhance the formation of the ^99mTc-pefloxacin complex. The biodistribution data show that ^99mTc labeled pefloxacin was retained in infectious focus. The retention was specific since the abscess uptake of ^99mTc-pefloxacin remained high as compared to the uptake of aseptic foci at 24-hour post injection. Also, the clearance of the tracer from other tissues is rapid on the contrary to its clearance from the septic focus. This supports the hypothesis that ^99mTc-pefloxacin is retained at the infectious site because of its specific binding to the gyrase enzymes of bacterial cells.     

Determination of calibration curves for <Superscript>131</Superscript>I in thyroid tumour metabolic radiotherapy and other radionuclides used in SPECT imaging

Large columns containing aluminum oxide (Al₂O₃) or gel (e.g. zirconium molybdate) are needed to prepare ⁹⁸Mo(n,γ)⁹⁹Mo→^99mTc column chromatographic generators that results in large elution volumes containing relatively high ⁹⁹Mo impurity and low concentrations of ^99mTc. The decrease in radioactive concentration or specific volume concentration of ^99mTc places a limitation on some pharmaceutical kits (DTPA, MIBI, ECD, etc.) or clinical procedures. We report on the post elution concentration of ^99mTc using in house prepared lead cation-exchange and alumina columns. Using these columns high bolus volumes (10–60 mL 0.02M sodium sulfate) of ^99mTc can conveniently be concentrated in 1 mL of physiological saline. This approach also works very effectively to prepare high specific volume solutions of ^99mTc-pertechnetate from a fission based ⁹⁹Mo/^99mTc generator in the second week of its normal working life.     

Preparation of <Superscript>99m</Superscript>Tc-metronidazole as a model for tumor imaging

Metronidazole (MTNZ) is an antiprotozoa drug, could be labeled with the ^99mTc. MTZL could be used as an ideal vehicle to deliver radioactive decay energy of ^99mTc to the sites of tumor, thus facilitate tumor imaging. The process of labeling was done using tin chloride as reducing agent. The optimum conditions required to label 25 μg MTZL were 100 μg stannous chloride, 30 min reaction time, room temperature at pH 7–9 using 0.5 M phosphate buffer. The radiochemical purity of the labeled compound, at the above conditions, was determined using paper chromatography. The yield was about 93%. About 2.5 × l0⁶ of Ehrlich Ascites Carcinoma (EAC) was injected intrapritoneally (i.p) to produce ascites and intramuscularly (i.m) in the right thigh to produce solid tumor in female mice. Biodistribution studies were carried out by injecting solution of ^99mTc-MTZL in normal and tumor bearing mice. The uptake in ascites was over 5% of the injected dose per gram tissue body weight, at 4 h post injection and above 4% in solid tumor. These data revealed localization of the tracer in the tumor tissues with high percentage sufficient to use ^99 mTc MTZL as promising tool for diagnosis of tumor.     

Systematic radiochemical separation for the determination of <Superscript>99</Superscript>Tc, <Superscript>90</Superscript>Sr, <Superscript>94</Superscript>Nb, <Superscript>55</Superscript>Fe and <Superscript>59,63</Superscript>Ni in low and intermediate radioactive waste samples

A simple and rapid separation procedure was systemized for the determination of ⁹⁹Tc, ⁹⁰Sr, ⁹⁴Nb, ⁵⁵Fe and ^59,63Ni in low and intermediate level radioactive wastes. The integrated procedure involves precipitation, anion exchange and extraction chromatography for the separation and purification of individual radionuclide from sample matrix elements and from other radionuclides. After separating Re (as a surrogate of ⁹⁹Tc) on an anion change resin column, Sr, Nb, Fe and Ni were sequentially separated as follows; Sr was separated as Sr (Ca-oxalate) co-precipitates from Nb, Fe and Ni followed by purification using Sr-Spec extraction chromatographic resin. Nb was separated from Fe and Ni by anion exchange chromatography. Fe was separated from Ni by anion exchange chromatography. Ni was separated as Ni-dimethylglyoxime precipitates after the removal of ^134,137Cs and ^110mAg by Cs-phosphotungstate and AgCl precipitation, respectively. Finally, the radionuclide sources were prepared by precipitation for their radioactivity measurements. The reliability of the procedure was evaluated by measuring the recovery of chemical carriers added to a synthetic radioactive waste solution.     

Synthesis and biodistribution of a novel <Superscript>99m</Superscript>Tc nitrido dithiocarbamate complex containing ether group as a potential myocardial and brain imaging agent

In the present study, a novel ^99mTc nitrido dithiocarbamate complex containing ether group, the bis(2-ethoxyethyl dithiocarbamato) nitrido ^99mTc complex ^99mTcN(EOEDTC)₂ has been synthesized by the reduction of ^99mTcO₄ ⁻ into [^99mTcN]²⁺ with stannous chloride in the presence of succinic dihydrazide and propylenediamine tetraacetic acid, followed by the addition of the corresponding dithiocarbamate ligand. The radiochemical purity of the complex was over 90% as measured by thin layer chromatography (TLC). In vitro studies showed that the complex possessed good stability. Its partition coefficient indicated that it was lipophilic complex. The electrophoresis results showed the complex was neutral. Biodistribution in mice showed that the complex accumulated in the heart and brain with high initial uptake, suggesting the complex may lead to a further development of the radiopharmaceutical as a heart and brain perfusion tracer.     

Preparation of <Superscript>99m</Superscript>Tc-PQQ and preliminary biological evaluation for the NMDA receptor

Pyrroloquinoline quinone (PQQ), an essential nutrient, antioxidant, redox modulator and nerve growth factor found in a class of enzymes called quinoproteins, was labeled with ^99mTc by using stannous fluoride (SnF₂) method. Radiolabeling qualification, quality control and characterization of ^99mTc-PQQ and its biodistribution studies in mice were performed and discussed. Effects of pH values, temperature, time and reducing agents concentration on the radiolabeling yield were investigated. The quality control procedure of ^99mTc-PQQ was determined by thin layer chromatography (TLC), radio high-performance liquid chromatography (RHPLC) and paper electrophoresis methods. The average radiolabeling yield was 94 ± 1% under optimum conditions of 0.99 mg of PQQ, 30 μg of SnF₂, 0.5 mg of ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) and 18.5 MBq of Na^99mTcO₄ at pH 6 and 25 °C with a response volume of 1 ± 0.1 mL. ^99mTc-PQQ was stable and anionic. Lipid–water partition coefficient of ^99mTc-PQQ was −1.49 ± 0.16. The pharmacokinetics parameters of ^99mTc-PQQ were t _1/2α = 18.16 min, t _1/2β = 100.45 min, K ₁₂ = 0.013 min⁻¹, K ₂₁ = 0.017 min⁻¹, K _e = 0.016 min⁻¹, AUC (area under the curve) = 1040.78 ID% g⁻¹ min and CL (plasma clearance) = 0.096 mL min⁻¹. The dual-exponential equation was Y = 10.88e^−0.038t  + 5.21e^−0.0069t . The biodistribution of ^99mTc-PQQ was studied in ICR (Institute for Cancer Research 7701 Burhelme Are., Fox Chase, Philadelphia, PA 1911 USA) mice. In vitro autoradiographic studies clearly showed that the ^99mTc-PQQ radioactivity accumulated predominantly in the hippocampus and cortex, which had a high density of N-methyl-d-aspartate Receptor (NMDAR). The enrichment can be blocked by NMDAR redox modulatory site antagonists-ebselen (EB) and ^99mTc-PQQ is therefore a promising candidate for the molecular imaging of NMDAR. To date, however, there have been no studies characterizing ^99mTc-PQQ.