Synthesis and evaluation of 99m Tc-NIDA and 99m Tc-DMIDA complexes for hepatobiliary imaging

1-Naphthylcarbamoylmethyliminodiacetic acid (NIDA) and diphenylmethylcarbamoylmethyliminodiacetic acid (DMIDA) were synthesized, characterized, and labeled with ^99m Tc using SnCl₂ as reducing agent. The parameters affecting the yield of ^99m Tc-NIDA and ^99m Tc-DMIDA were studied in detail. The optimum conditions ensuring high yield of ^99m Tc-NIDA (94.2 ± 2%) and ^99m Tc-DMIDA (93.1 ± 2%) are as follows: 30 mg of NIDA or DMIDA, 0.3 mg of SnCl₂·H₂O, pH 6, 15 min. The biodistribution in mice injected with ^99m Tc-NIDA and ^99m Tc-DMIDA showed high liver uptake at 10 min post injection, with fast biliary excretion. Accumulation of the activity in kidneys was negligible, especially after a long time post injection. Both ^99m Tc-NIDA and ^99m Tc-DMIDA can be applied as hepatobiliary imaging agents for the evaluation of the functional status of the hepatocytes and the patency of the biliary duct.     

Preclinical evaluation of <Superscript>99<Emphasis Type="Italic">m</Emphasis> </Superscript>Tc-histidine as a possible tumor imaging agent

Radiolabeling of histidine (Hist), an essential amino acid, with ^99mTc was performed. The radiochemical yield higher than 95% was achieved with stannous chloride as a reducing agent. Factors affecting the radiochemical yield (histidine amount, stannous chloride amount, reaction time, pH of the reaction mixture) were studied in detail, and the reaction conditions were optimized. In vitro stability of the radiolabeled complex was checked, and it was found to be stable for up to 6 h. ^99mTc-Hist was injected intravenously into normal and tumor-bearing mice. Biodistribution studies revealed that the ^99mTc-Hist uptake in tumor sites was 10 and 16% ID/g in ascites and 7 and 9.2% ID/g in thigh solid tumor at 60 and 120 min post injection, respectively. The amount of ^99mTc-Hist in ascites and solid tumor increased with time and then decreased slowly. Thus, ^99mTc-Hist can be used as a potential agent for imaging tumor sites.     

Labeling of omeprazole with technetium-99m for diagnosis of stomach

Omeprazole, a proton pump inhibitor, was labeled with ^99m Tc to obtain ^99m Tc-omeprazole in ～96% yield in basic media. The optimum conditions were as follows: pH 9, 50 μg of SnCl₂·2H₂O, 30 min, and 3 mg of the substrate. ^99m Tc-omeprazole was stable for 6 h. Intravenous biodistribution of ^99m Tc-omeprazole showed that it concentrated in the stomach ulcer to reach about 22% of the total injected dose at 1 h post injection. This concentration of ^99m Tc-omeprazole in stomach ulcer may be sufficient for ulcer imaging.     

Radiolabeling,quality control,and biodistribution of <Superscript>99m</Superscript>Tc-sulfadiazine as an infection imaging agent

Abstract—Sulfadiazine (antibiotic used for treating bacterial infections) was labeled with ^99mTc with the aim of the development of a new radiopharmaceutical for infection imaging. The influence of the reaction parameters such as the substrate and SnCl₂·2H₂O concentrations, pH of the reaction mixture, and reaction time on the labeling yield was examined, and the labeling conditions were optimized. The maximum radiochemical yield of ^99mTc-sulfadiazine (94.7%) was obtained by using 50 µg of SnCl₂·2H₂O and 1 mg of sulfadiazine at pH 5. The radiochemical purity of the labeled compound was evaluated by ITLC and HPLC. The biological distribution of ^99mTc-sulfadiazine in mice with experimentally induced Staphylococcus aureus infection in the right thigh was studied, and the bacterial infected thigh/normal thigh (target-to-nontarget, T/NT) ratio was evaluated. The T/NT ratio for ^99mTc-sulfadiazine was found to be 3.6, which is comparable to the commercially available ^99mTc-ciprofloxacin (3.8), indicating that ^99mTc-sulfadiazine can be used for infection imaging.     

99m Tc-sulfadimidine as a potential radioligand for differentiation between septic and aseptic inflammations

Sulfadimidine, a bacteriostatic drug blocking folic acid synthesis, was labeled with ^99m Tc producing a yield of about 90%. The optimum conditions required to obtain 90% yield of the ^99m Tc complex were as follows: 500 μg of sulfadimidine, 100 μg of SnCl₂·2H₂O, 5 min, room temperature (25 ± 1°C), pH 4 (0.5 M citrate buffer). The radiochemical purity of the labeled compound was determined using paper and thin-layer chromatography. Biodistribution study in normal mice showed high uptake of the ^99m Tc complex in stomach and intestine. The ratio of the uptake of the ^99m Tc complex in muscles infected with E. coli to that in normal mice was about 2, 1.5 and 1.4 at 15, 90, and 180 min post injection, respectively, whereas for the muscles inflamed with heat-killed E. coli or sterile turpentine oil the difference from the normal muscles was insignificant.     

99m Tc-labeled teicoplanin and its biological evaluation in experimental animals for detection of bacterial infection

Labeling of teicoplanin with ^99m Tc using SnCl₂·2H₂O as reducing agent was performed. The dependence of the ^99m Tc-teicoplanin yield on the concentrations of teicoplanin and reducing agent, pH of the reaction mixture, reaction time, and reaction temperature was studied. Under optimum conditions (2 mg of teicoplanin, 5 μg of SnCl₂·2H₂O, pH 9, 30 min, 25°C), the labeling yield of ^99m Tc-teicoplanin of 87.7 ± 1.3% was achieved. ^99m Tc-teicoplanin is stable for 4 h after labeling; then its relative content decreased gradually to reach 81.7 ± 1.1% in 8 h. Biodistribution studies in mice with infection induced in the left thigh by Staphylococcus aureus were carried out. The bacterial infected thigh/contralateral thigh uptake ratio (T/NT) was evaluated. The time for the maximum accumulation of ^99mTc-teicoplanin in the infection site was 2 h after administration of the labeled compound. The abscess-to-muscle ratio for ^99m Tc-teicoplanin was 4.33 ± 0.3, while that for commercially available ^99m Tc-ciprofloxacin was 3.8 ± 0.5 under similar conditions. Thus, ^99m Tc-teicoplanin can be used for infection imaging.     

Radiolabeling and biological evaluation of losartan as a possible cardiac imaging agent

A procedure was developed for preparing high radiochemical purity ^99m Tc-Losartan in a yield of about 90%. The optimal reaction conditions are as follows: 100 μg of Losartan, 50 μg of SnCl₂·2H₂O, 150 μL of phosphate buffer (pH 7), room temperature (25 ± 1°C), reaction time 5 min. Under these conditions, the radiochemical yield up of ^99m Tc-Losartan reaches 98%. The radiochemical yield and purity of the labeled product were determined by electrophoresis and paper chromatography. Biodistribution studies were carried out in normal Albino Swiss mice at different time intervals after administration of ^99m Tc-Losartan. The labeled compound cleared from the systematic circulation within 3 h after administration, and the majority of organs showed significant decrease in the uptake of ^99m Tc-Losartan. The heart uptake of ^99m Tc-Losartan was sufficiently high for using this agent as myocardial imaging agent.     

Synthesis and biodistribution of 99m Tc-PyDA as a potential marker for tumor hypoxia imaging

The ^99m Tc-pyrimidine-4,5-diamine (^99m Tc-PyDA) complex was prepared. The yield under the optimum conditions (5 mg of PyDA, pH 8, 25 μg of SnCl₂·2H₂O) was 96 ± 3%. The complex is stable in vitro for 24 h. The complex was tested on mice as potential marker for tumor hypoxia imaging. The complex showed high tumor hypoxia uptake with the target/nontarget (T/NT) ratio as high as ～3.     

Synthesis,Characterization, and Radiolabeling of Heterocyclic Bisphosphonate Derivative as a Potential Agent for Bone Imaging

1-Hydroxy-2-(2-pyridyl)ethanedisphosphonic acid monosodium salt (HPEDP) was prepared and labeled with ^99mTc using two different reducing agents: SnCl₂·2H₂O and NaBH₄; NaBH₄ gave better results. The radiochemical purity of ^99mTc(NaBH₄)-HPEDP was 96 ± 4%, and the complex was stable in vitro for 6 h. The in vivo biodistribution studies performed in mice show highly selective uptake of the labeled compound in the skeletal system and rapid elimination via the urinary pathway. The maximum bone uptake was 32.3 ± 2.1% ID/organ.     

Labeling and biological evaluation of 99m Tc-azithromycin for infective inflammation diagnosis

Azithromycin, an antibiotic used to treat bacterial infections, was labeled with ^99m Tc. The maximum radiochemical yield of ^99m Tc-azithromycin, 97.5 ± 0.9%, was attained under the following conditions: addition of ^99m Tc to 2 mg of azithromycin in the presence of 50 μg of SnCl₂·2H₂O at pH 4, reaction time 30 min. ^99m Tc-azithromycin complex was stable for 6 h. Biological distribution of ^99m Tc-azithromycin was studied in mice infected with Staphylococcus aureus in the left thigh. The ratio of ^99mTc-azithromycin uptake in the bacterially infected and contralateral thighs, T/NT, for was found to be 6.20 ± 0.12 at 2 h after intravenous injection (higher than the ratio obtained with the commercially available ^99m Tc-ciprofloxacin), which was followed by gradual decline. The results obtained show that ^99m Tc-azithromycin can be used for infection imaging and allows differentiation between bacterial infection and sterile inflammation.     

Synthesis, labeling, and biological evaluation of 2-{[benzyl(cyanomethyl)amino]methyl}-3-(ethoxycarbonyl)-quinoxaline 1,4-dioxide in ascites bearing mice

Quinoxaline 1,4-dioxide derivative, 2-{[benzyl(cyanomethyl)amino]methyl}-3-(ethoxycarbonyl) quinoxaline 1,4-dioxide (Q₃D), was synthesized and labeled with radioiodine via direct electrophilic substitution giving labeling yield above 90%. The product was examined by paper electrophoresis. ¹²⁵I-Q₃D was prepared using Chloramine T as oxidizing agent. ¹²⁵I-Q₃D was stable for up to 72 h post labeling, in contrast to ^99m Tc-AQCD which is stable only for a short time. Biodistribution study of ¹²⁵I-Q₃D in ascites tumor bearing mice revealed large uptake of the labeled compound in tumor sites. In addition, in vitro incubation of the labeled compound with Ehrlich cells indicated incorporation of these compounds in DNA of tumor cells. This uptake of ¹²⁵I-Q₃D in DNA of tumor cells may be helpful in tumor diagnosis and therapy.     

Radiochemical and biological characterization of <Superscript>99<Emphasis Type="Italic">m</Emphasis></Superscript>Tc-oxiracetam as a model for brain imaging

^99mTc-oxiracetam was prepared. It can be used as a radiotracer for brain imaging. Under the optimum conditions (0.5 mg of oxiracetam, 50 μg of SnCl₂·2H₂O, pH 7, room temperature, 30 min), the radio-chemical yield determined by chromatographic methods reached 96%. Biodistribution studies with mice showed that the brain uptake of the complex was 5.1% injected dose per gram (% ID/g) at 5 min post injection. In this parameter, the complex surpasses the commercially available ^99mTc-ECD (4.7% ID/g) and ^99mTc-HMPAO (2.25% ID/g).     

Synthesis of 99m Tc-erythromycin complex as a model for infection sites imaging

Labeling of erythromycin with ^99m Tc using SnCl₂·2H₂O as a reducing agent was investigated. Dependence of the yield of ^99m Tc-erythromycin complex on the concentrations of erythromycin and reducing agent, on pH, and on the reaction time was studied. 97% labeling yield of ^99m Tc-erythromycin complex was achieved by performing the reaction with 1.5 mg of erythromycin and 15 μg of SnCl₂·2H₂O at pH 4 for 15 min. ^99m Tc-erythromycin complex was stable for 6 h. Biodistribution studies in Albino mice bearing septic and aseptic inflammation models showed that ^99m Tc-erythromycin does not allow differentiation between septic (Staphylococcus aureus) and aseptic inflammation. The maximum accumulation of ^99m Tc-erythromycin at the infection site was observed in 30 min after administration and was followed by gradual decline. The abscess-tomuscle ratio for ^99m Tc-erythromycin was 5 ± 0.6, whereas that for the commercially available ^99m Tc ciprofloxacin was 3.8 ± 0.8.     

Synthesis of <Superscript>99<Emphasis Type="Italic">m</Emphasis></Superscript>Tc-Radiolabeled Uridine as a Potential Tumor Imaging Agent

Uridine, a pyrimidine nucleoside essential for the synthesis of RNA and biomembranes, was radiolabeled with ^99mTc to obtain a potential tumor imaging agent. The maximal radiochemical yield of about 96.5%, as determined by paper chromatography and instant thin-layer chromatography, was reached under the following optimum conditions: 1 mg of uridine, 20 μg of SnCl₂·2H₂O as reducing agent, 20 mg of mannitol as a stabilizer, and pH 8. ^99mTc-uridine is stable in vitro at room temperature for up to 6 h post labeling. The biodistrbution study in tumor-bearing mice shows high target-to-nontarget ratio. These results match with the high docking score of the complex on uridine phosphorylase enzyme. ^99mTc-uridine shows promise as a tumor imaging agent.     

Radiochemical and biological characterization of 99m Tc-piracetam for brain imaging

Experiments on piracetam labeling with ^99m Tc were performed. The radiochemical yield of 97% was obtained under the optimum conditions: pH 6, SnCl₂·2H₂O as reducing agent, room temperature, 30 min. In vivo biodistribution studies showed that the initial brain uptake correlated fairly well with the brain binding affinity of the compound. The brain uptake of ^99m Tc-piracetam was as high as 6, 12.3, 5.3, and 3.3% per gram tissue at 5, 30, 60, and 120 min post injection, respectively. ^99m Tc-piracetam shows promise in radioreceptor assays of neuroleptic drug levels and, in the labeled form, for brain imaging.     

Preparation, quality control, and biodistribution of 99mTc-rufloxacin complex as a model for detecting sites of infection

With the aim of the development of a new radiopharmaceutical for infection imaging, able to differentiate between septic and aseptic inflammations, ^99m Tc-rufloxacin was obtained. Its radiochemical yield reaches 93.4 ± 3% under optimum conditions (addition of ^99m TcO₄ — to a solution containing 50 mg of rufloxacin and 50 μg of SnCl₂·2H₂O at pH 6). ^99m Tc-rufloxacin biodistribution studies in Albino mice bearing septic and aseptic inflammation models showed that ^99m Tc-rufloxacin is able to differentiate between septic and aseptic inflammations.     

Optimized chromatographic separation and biological evaluation of <Superscript>99<Emphasis Type="Italic">m</Emphasis> </Superscript>Tc-clarithromycin for infective inflammation diagnosis

Clarithromycin antibiotic was labeled with technetium-99m by adding ^99mTc to clarithromycin in the presence of SnCl₂·2H₂O. The radiochemical yield of ^99mTc-clarithromycin was determined by chromatographic methods. Gel chromatographic method was investigated for separation of the reaction mixture using different eluents including NaCl and phosphate, citrate, and carbonate buffer solutions. Also, free ^99mTcO₄^- and ^99mTc-clarithromycin were efficiently separated by reversed-phase HPLC on RP18 column. The maximum radiochemical yield reached 98 ± 0.2%. ^99mTc-clarithromycin is stable for 6 h. Biological distribution of ^99mTc-clarithromycin was studied for mice with the infection in the left thigh induced using Staphylococcus aureus. The target-to-nontarget (T/NT) ratio for ^99mTc-clarithromycin was found to be 7.33 ± 0.13 at 2 h after intravenous injection, with the subsequent gradual decline. This value is higher than that of commercially available ^99mTc-ciprofloxacin. The abscess to normal muscle ratio shows that ^99mTc-clarithromycin can be successfully used for infection imaging, allowing differentiation between bacterial infection and sterile inflammation.     

Radiodiagnosis of peptic ulcer with technetium-99<Emphasis Type="Italic">m</Emphasis>-labeled esomeprazole

Esomeprazole was labeled with ^99m Tc in high (up to ~98.0%) radiochemical yield. The optimum conditions are as follows: pH 8, 50 μg of SnCl₂·2H₂O, 30 min, and 2 mg of the substrate. The complex is stable for 8 h. The reaction mixture was separated by gel chromatography using such eluents as NaCl solution and, phosphate, citrate, and carbonate buffer solutions. Free ^99m TcO ₄ ^– and the complex were also efficiently separated by reversed-phase HPLC, paper chromatography, and electrophoreses. Intravenous biodistribution studies of ^99m Tc-esomeprazole complex showed high uptake in the stomach ulcer, reaching about 30.5% ID/g at 1 h post injection. Such a high ^99m Tc-esomeprazole uptake makes this agent promising for stomach ulcer imaging.     

Preparation and biological evaluation of <Superscript>99<Emphasis Type="Italic">m</Emphasis></Superscript>Tc-timonacic acid as a new complex for hepatobiliary imaging

Timonacic acid (TCA) was successfully labeled with ^99m Tc. The influence exerted on the reaction by the substrate and reducing agent concentrations, pH of the reaction mixture, and reaction time was examined, and in vitro stability of ^99m Tc-TCA was evaluated. The maximum labeling yield was 98.5 ± 0.6%. The complex was stable throughout the working period (6 h). A study of in-vivo biodistribution in mice showed that the maximum uptake of ^99m Tc-TCA in the liver was 22.3 ± 0.3% of the injected activity per gram of the tissue or organ (% ID/g) at 30 min post injection. The clearance from the mice appeared to proceed via the circulation mainly through the kidneys and urine (approximately 56% of the injected dose at 1 h after injection). The liver uptake of ^99m Tc-TCA is higher than that of ^99m Tc-UDCA (ursodeoxycholic acid); therefore, ^99m Tc-TCA shows more promise for liver SPECT.     

Synthesis and Stability of New Nitrophenol Complexes of <Superscript>99<Emphasis Type="Italic">m</Emphasis></Superscript>Tc as Possible Hypoxia Imaging Radiopharmaceuticals

Seven new nitrophenol derivatives were synthesized; their ^99mTc complexes (N₂OS chelates), which are possible hypoxia tumor imaging agents, were prepared by the reaction with [^99mTc]NaTcO₄ in the presence of SnCl₂ at pH 10. The in vitro biostabilty of the complexes was evaluated. The purity and stability (in human and rat serum) of the complexes were evaluated by chromatographic methods (TLC, HPLC). The most stable (for more than 6 h) is the complex of ^99mTc with 3-[3′-N-(2″-hydroxy-5″-nitrobenzylamino)-2′-hydroxypropyl]-1-methylthiourea.