Synthesis,radiochemical and biological characteristics of <Superscript>99m</Superscript>Tc-8-hydroxy-7-substituted quinoline complex: a novel agent for infection imaging

2,2′-[(8-hydroxyquinolin-7-yl)methylazanediyl]diacetic acid (HQMADA) was synthesized via reaction of 8-hydroxyquinoline with iminodiacetic acid in presence of paraformaldehyde with a yield of 27%. The obtained compound was well characterized via different analytical techniques. Labeling of the synthesized compound with technetium-99m in pertechnetate form (^99mTcO₄ ⁻) in the presence of stannous chloride dihydrate was carried out via chelation reaction. The reaction parameters that affect the labeling yield such as HQMADA concentration, stannous chloride dihydrate concentration, pH of the reaction mixture, and reaction time were studied to optimize the labeling conditions. Maximum radiochemical yield of ^99mTc-HQMADA complex (91.9%) was obtained by using 1.5 mg HQMADA, 50 μg SnCl₂·2H₂O, pH 8 and 30 min reaction time. Biodistribution studies in mice were carried out in experimentally induced infection in the left thigh using E. coli. ^99mTc-HQMADA complex showed higher uptake (T/NT = 5.5 ± 0.3) in the infectious lesion than the commercially available ^99mTc-ciprofloxacin (T/NT = 3.8 ± 0.8). Biodistribution studies for ^99mTc-HQMADA complex in Albino mice bearing septic and aseptic inflammation models showed that ^99mTc-HQMADA complex able to differentiate between septic and aseptic inflammation.     

Recovery of plutonium from nitric acid containing oxalate and fluoride by a macroporous bifunctional phosphinic acid resin (MPBPA)

Summary Piroxicam was labeled effectively with ^99mTc due to the presence of electron donating atoms such as sulfur, nitrogen, and oxygen in its structure. The labeling yield was found to be influenced by different factors such as the amount of piroxicam, stannous chloride dihydrate, pH of the reaction mixture, reaction time and reaction temperature. The suitable amount of stannous chloride dihydrate required to produce high labeling yield of ^99mTc-piroxicam was 50 μg, above this quantity (200 μg) a colloidal solution was formed. Another factor which plays a significant role in this labeling reaction is the pH of the reaction medium. The labeling reaction was done only at alkaline pH range from 9-11, because piroxicam was not soluble at acidic or neutral pH. The labeling reaction proceeded well at room temperature and the complex was decomposed by heat. The labeled piroxicam (^99mTc-piroxicam ) showed good localization in inflamed foci and good imaging must be taken at 24-hour post injection, as the ratio of both types of inflammation (sterile and septic) to the background are 10.6 and 8.7, respectively.     

Study on the preparation and biological evaluation of <Superscript>99m</Superscript>Tc–gatifloxacin and <Superscript>99m</Superscript>Tc–cefepime complexes

The aim of this work is the development of new radiopharmaceuticals for imaging infection and inflammation in human. Gatifloxacin (fluoroquinolone derivative) and cefepime (cephalosporine derivative) are antibiotics used to treat bacterial infections were investigated to label with one of the most important radioactive isotopes (technetium-99m). The reaction parameters that affect the labeling yield such as substrate concentration, stannous chloride dihydrate concentration, pH of the reaction mixture, and reaction time were studied to optimize the labeling conditions. Maximum radiochemical yield of ^99mTc–gatifloxacin (90  ± 1.8%) complex was obtained by using 50 μg SnCl₂·2H₂O and 2.5 mg gatifloxacin at pH 10 while ^99mTc–cefepime was prepared at pH 8 with a maximum radiochemical yield of 98  ± 1.4% by adding ^99mTc to 5 mg cefepime in the presence of 50 μg SnCl₂·2H₂O. Biological distribution of ^99mTc–gatifloxacin and ^99mTc–cefepime was carried out in experimentally induced infection rats, in the left thigh, using Escherichia coli. Both thighs of the rats were dissected and counted and the ratio of bacterial infected thigh/contralateral thigh was then evaluated. T/NT for both ^99mTc–gatifloxacin and ^99mTc–cefepime was found to be 4.5  ± 0.3 and 8.4  ± 0.1, respectively, which was higher than that of the commercially available ^99mTc–ciprofloxacin. The abscess to normal muscle ratio indicated that ^99mTc–cefepime could be used for infection imaging. Besides, in vitro studies showed that ^99mTc–cefepime can differentiate between bacterial infection and sterile inflammation.     

Labeling bombesin-like peptide with <Superscript>99m</Superscript>Tc via hydrazinonicotinamide: description of optimized radiolabeling conditions

Bombesin (BNN)-like peptides have very high binding affinity for the gastrin-releasing peptide (GRP) receptor. The goal of the current study was to optimize the labeling conditions of a new ^99mTc-radiolabeled BNN-like peptide based on the bifunctional chelating ligand HYNIC using different co-ligands (EDDA and tricine). The radiolabeling conditions (pH, amount of co-ligand, amount of stannous chloride, temperature and reaction time) for newly-formed ^99mTc-tricine-HYNIC-Q-Litorin and ^99mTc-EDDA-HYNIC-Q-Litorin were optimized and evaluated by RHPLC and RTLC. Radiochemical yields for ^99mTc-tricine-HYNIC-Q-Litorin and ^99mTc-EDDA-HYNIC-Q-Litorin were 98.0 ± 1.7 and 97.5 ± 2.5%, respectively. When EDDA was used as co-ligand, the labeling of ^99mTc-EDDA-HYNIC-Q-Litorin was optimal in the following reaction mixture: HYNIC-peptide: EDDA: 10 μg/5 mg, pH 3, SnCl₂ concentration: 12 μg/0.1 mL, reaction temperature: 100 °C, reaction time: 15 min. Besides, the optimum conditions were HYNIC-peptide:tricine: 10 μg/50 mg, pH 5, SnCl₂ concentration: 12 μg/0.1 mL, reaction temperature: 100 °C, reaction time: 15 min for preparing ^99mTc-tricine-HYNIC-Q-Litorin. The manufactured ^99mTc-HYNIC-Q-Litorin conjugates may offer new possibilities for imaging cancer cells expressing bombesin receptors.     

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.     

Synthesis,labeling and biodistribution of <Superscript>99m</Superscript>Tc-3-amino-2-quinoxalin-carbonitrile 1,4-dioxide in tumor bearing mice

3-Amino-2-quinoxalincarbonitrile 1,4-dioxide (AQCD) is a quinoxaline derivative, which was synthesized by condensation method. AQCD was labeled with ^99mTc with labeling yield above 90% investigated by paper chromatography. ^99mTc-AQCD was prepared using stannous chloride as reducing agent at pH 7 and 10 min reaction time. ^99mTc-AQCD should be freshly prepared, otherwise the yield significantly decreased after 15 min post labeling. Stability study of ^99mTc-AQCD reflected the short time stability of Biodistribution study of ^99 mTc-AQCD in tumor bearing mice reflected that its uptake in tumor sites in both ascites and solid tumor sites. This uptake of ^99mTc-AQCD in tumor sites was sufficient to radioimage the inoculated sites.     

Labeling and biodistribution of 99mTc-7-bromo-1,4-dihydro-4-oxo-quinolin-3-carboxylic acid complex

7-Bromo-1,4-dihydro-4-oxo-quinolin-3-carboxylic acid (BDOQCA), was synthesized with a yield of 93% and well characterized. The obtained compound was investigated to label with one of the most important radioactive isotopes (technetium-99m). Effect of BDOQCA concentration, stannous chloride dihydrates (SnCl₂.2H₂O) concentration, pH and reaction time on the percent labeling yield of ^99mTc-BDOQCA complex was studied in details. ^99mTc-BDOQCA complex was obtained at a maximum yield of 97.3% by mixing 2.5 mg of BDOQCA with 25 μg SnCl₂.2H₂O at pH 6 and 30 min reaction time and the formed complex was stable for a time up to 8 h with a maximum yield of 97.3%. Biodistribution studies in mice were carried out using experimentally induced infection in the left thigh using E. coli. Both thighs of the mice were dissected and counted to evaluate the ratio of bacterial infected thigh/contralateral thigh. Higher uptake in the infected thigh was observed after 2 h of IV administration of ^99mTc-BDOQCA complex (T/NT = 7.6 ± 0.6%) than that of the commercially available ^99mTc-ciprofloxacin complex (T/NT = 3.8 ± 1%). The in vitro binding and biodistribution of ^99mTc-BDOQCA complex in the septic and aseptic inflammation bearing mice showed that, ^99mTc-BDOQCA complex is a promising agent for infection imaging and can differentiate between infected and inflamed muscle.     

Synthesis, biodistribution and evaluation of 99mTc-sitafloxacin kit: a novel infection imaging agent

Radiosynthesis of ^99mTc-sitafloxacin (^99mTc-STF) complex and its efficacy as a potential infection imaging agent was evaluated. Effect of sitafloxacin (STF) concentration, sodium pertechnetate (Na^99mTcO₄), stannous chloride dihydrate (SnCl₂·2H₂O), and pH on the % radiochemical purity yield (RCP) of ^99mTc-STF complex was studied. A stable ^99mTc-STF complex up to 120 min with maximum %RCP yield was observed by mixing 2 mg of STF with 3 mCi of Na^99mTcO₄ and 150 μL of SnCl₂·2H₂O (1 μg/μL in 0.01 N HCl) at a pH 5.5. Artificially infected rats with Staphylococcus aureus were used for studying the biodistribution behavior of the ^99mTc-STF complex. After 30 min of the intravenous (I.V.) administration of the ^99mTc-STF complex, 7.50 ± 0.10% was absorbed in the infected thigh of the rats and the uptake gradually increased to 18.50 ± 0.20% within 90 min. Rabbits with artificially induced infection were used for evaluating the scintigraphic accuracy. Higher uptake in the infected thigh was observed after 2 h of I.V. administration of the ^99mTc-STF complex. Target to non-target organ ratio of the % absorbed dose incase of infected/normal muscle was 6.82 ± 0.40, 17.11 ± 0.60, and 23.13 ± 1.00% at 30, 60 and 90 min of administration. Stable and higher %RCP, higher uptake in the infected thigh, and spectral studies, recommend the ^99mTc-STF for routine infection imaging.     

Radiolabeling of anti-carcinoembryonic antigen (CEA) monoclonal antibody (MAb BW 431/26) for clinical applications

A method for labeling of anti-carcinoembryonic antigen (CEA) monoclonal antibody (MAb) BW 431/26 is described. For preparations of^99mTc-anti-CEA complex, a solution (1 ml) of tetrasodium-1,1,3,3-propanetetetraphosphate dihydrate (2.7 mg), stannous chloride dihydrate (0.12 mg) and sodium chloride (0.2 mg) in 5 ml of 0.9% saline was added to a vial containing monoclonal antibody (2 mg) from mouse (MAb BW 431/26), D-glucitol (2 mg) and sodium sulfate (2 mg) to obtain a clear solution. A quantitative labeling yield of the MAb BW 431/26 was achieved by addition of 5 ml (40.5 mCi, 1.5 Gbq) technetium-99m-pertechnetate (^99mTcO₄) generator eluate at room temperature within 10 minutes. The radiochemical purity determined by ITLC (Gelman, SG) plates was >95%.     

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.     

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%.     

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.     

Labeling of scorpion venom with 99mTc and its biodistribution

Labeling of scorpion venom (SV) was successfully achieved with ^99mTc using direct chelating method. Venom was labeled with ^99mTc using stannous chloride as reducing agent. Preliminary studies were done to establish the optimum conditions for obtaining the highest yield of the labeled venom. The labeling technique is effective, as a maximum labeling yield (97 %) was obtained after 30-min reaction time by using 80 μg SV in phosphate buffer of pH 7 and 25 μg Sncl₂·2H₂O at room temperature. Venom was injected into normal mice to determine the excretion pathway. Biodistribution studies in normal mice with SV shows rapid clearance of the venom from blood and tissue except for kidneys. The improvement of the immunotherapeutic treatment of envenomation requires a better knowledge of the biological actions of the SV since tissue distribution studies are very important for clinical purpose.     

Formulation and preclinical evaluation of 99mTc–gemcitabine as a novel radiopharmaceutical for solid tumor imaging

The aim of this study is the formulation of a new radiopharmaceutical for imaging solid tumor bearing. Gemcitabine is a nucleoside analogue used as chemotherapeutic agent. Gemcitabine was formulated and radiolabeled with one of the most important diagnostic radioactive isotopes (technetium-99m) to be investigated in solid tumor imaging. The labeling parameters such as gemcitabine amount, stannous chloride amount, pH of the reaction mixture, and reaction time were optimized. ^99mTc–gemcitabine was prepared at pH 9 with a maximum labeling yield of 96 ± 0.3 % without any notable decomposition at room temperature over a period of 8 h. The preclinical evaluation and biodistribution in solid tumor bearing mice showed that ^99mTc–gemcitabine had solid tumor selectivity, preclinical high biological accumulation in tumor cells and high retention. Tumor/normal muscle (T/NT) ratios increased with time showing high T/NT ratio (T/NT = 4.9 ± 0.27 at 120 min post injection) and high Tumor/Blood ratio (3.4 ± 0.06), suggesting ^99mTc–gemcitabine as a novel solid tumor imaging agent.     

Exchange labeling of proteins:99mTc labeled transferrin

^99mTc-labeled transferrin was prepared by reduction of^99mTcO ₄ ⁻ ; with stannous DTPA or stannous citrate followed by equilibration of the technetium chelate with human transferrin. The rate of transfer of^99mTc to transferrin in the presence of 0.015M citrate buffer was dependent on pH in the order pH 2.1> pH 7.2> pH 4.1> pH 5.9. The incorporation rate was inversely proportional to the concentration of DTPA and citrate buffer. The replacement of citrate buffer by acetate buffer or oxalate buffer reduced drastically the formation of^99mTc-labeled transferrin at pH 4.1. The formation of^99mTc-labeled transferrin prepared from the reduction of^99mTcO ₄ ⁻ with stannous citrate was faster than that from the reduction with stannous DTPA in the presence of 0.015M citrate buffer and pH 2.5. Equilibration of transferrin with^99mTc-labeled pyrophosphate did not produce^99mTc-labeled transferrin at pH 4.5. The ligand exchange labeling of^99mTc to transferrin in 0.015M citrate did not cause appreciable denaturation of the protein at all pH values. This method also enabled labeling of the protein in a low concentration (2.6·10⁻⁴ M) via tin reduction. Sequential external imaging of the^99mTc-labeled transferrin in Sprague-Dawley rats bearing Walker-256 carcinosarcoma showed optimal tumor localization occurred at 3 hr after injection. In spite of this,^99mTc-labeled transferrin does not appear to be a suitable imaging agent because of the low tumor to blood ratio of^99mTc (0.50±0.17) at 3 hr post injection. This is similar to that of^{6 7}Ga-citrate (0.43±0.15%).     

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.     

Radioiodinated paroxetine, a novel potential radiopharmaceutical for lung perfusion scan

Paroxetine (a selective serotonin reuptake inhibitor) was successfully labeled with ¹²⁵I via direct electrophilic substitution reaction at ambient temperature. The reaction parameters studied were paroxetine amount, CAT amount, pH of the reaction mixture, reaction temperature, reaction time and in vitro stability of ¹²⁵I-paroxetine. ¹²⁵I-paroxetine was obtained with a maximum labeling yield of 94 ± 0.23% and in vitro stability up to 24 h. Biodistribution studies showed that maximum in vivo uptake of ¹²⁵I-paroxetine in lungs was 27.89 ± 1.03% injected activity/g tissue at 15 min post-injection and retention in lungs remained high up to 1 h, whereas the clearance from mice appeared to proceed mainly via the hepatobiliary pathway. ¹²⁵I-paroxetine is not a blood product and so it is more safe than the currently available ^99mTc-macroaggregated albumin (^99mTc-MAA), and its lung uptake is higher than that of the recently discovered ^99mTc(CO)₅I and ^99mTc-DHPM. As a conclusion, radioiodinated paroxetine could be used as a novel radiopharmaceutical for lung perfusion scan safer than the currently available ^99mTc-MAA and more potential than the recently discovered ^99mTc(CO)₅I and ^99mTc-DHPM.     

Synthesis,biological evaluation and biodistribution of the <Superscript>99m</Superscript>Tc–Garenoxacin complex in artificially infected rats

The labeling of garenoxacin (GXN) with technetium-99m (^99mTc) using different concentrations of GXN, sodium pertechnetate (Na^99mTcO₄), stannous chloride dihydrate (SnCl₂·2H₂O) at different pH was investigated and evaluated in terms of in-vitro stability in saline, serum, binding with multi-resistant Staphylococcus aureus (MDRSA) and penicillin-resistant Streptococci (PRSC) and its biodistribution in artificially MDRSA and PRSC infected rats. ^99mTc–GXN complex with 97.45 ± 0.18% radiochemical stability was prepared by mixing 3 mg of GXN with 3 mCi of Na^99mTcO₄ in the presence of 150 μL of SnCl₂·2H₂O (1 μg/μL in 0.01 N HCl) at a pH 5.6. The radiochemical stability of the complex was evaluated in normal saline up to 240 min of reconstitution. It was observed that the complex showed maximum RCP values after 30 min of the reconstitution and remained more than 90% up to 240 min. The complex showed radiochemical stability in normal saline at 37 °C up to 16 h with a 17.80% de-tagging. The complex showed saturated in-vitro binding with living MDRSA and PRSC as compared to the insignificant binding with heat killed MDRSA and PRSC. Biodistribution behavior of the complex was assessed in artificially infected with living and heat killed MDRSA and PRSC rats. It was observed that the accumulation of the complex in the infected (live MDRSA and PRSC) tissue of the rats was almost five fold than in the inflamed and normal tissue. The high radiochemical stability in normal saline at room temperature, promising in-vitro stability in serum at 37 °C, saturated in-vitro binding with living MDRSA and PRSC, specific biodistribution behavior and high infected (target) to normal (non-target) tissue and low inflamed (non-target) to normal (non-target) tissue ratios we recommend ^99mTc–GXN complex for in-vivo localization of infection caused by MDRSA and PRSC effective stains.     

Synthesis of 99mTc-oxybutynin for M3-receptor-mediated imaging of urinary bladder

Radiolabeling of oxybutynin, a muscarinic acetylcholine (mACh) receptor antagonist agent with ^99mTc is of considerable interest for imaging of urinary bladder. This study is aimed to optimize radiolabeling yield of oxybutynin with ^99mTc using SnCl₂·2H₂O as a reducing agent with respect to factors that affect the reaction conditions such as oxybutynin amount, stannous chloride amount, reaction time and pH of the reaction mixture. In vitro stability of the radiolabeled complex was checked and it was found to be stable for up to 8 h. ^99mTc-oxybutynin was injected via subcutaneous and intravenous administration routes into normal Sprague?CDawley rats. Biodistribution studies have revealed that ^99mTc-oxybutynin exhibits high affinity and specificity for the muscarinic M₃ subtype located on the smooth muscle of urinary bladder relative to the M₁ and M₂ subtypes of the G protein coupled receptor (GPCR) superfamily. In vivo uptake of subcutaneous ^99mTc-oxybutynin in urinary bladder was 19.6 ± 0.42% ID at 0.5 h, whereas in intravenous administration route the accumulation in the urinary bladder was found to be 9.4 ± 0.31% ID at 0.5 h post injection. Administration of cold oxybutynin effectively blocked urinary bladder uptake and further confirms the high specificity of this complex for the M₃ receptor.     

Reaction of [TcNCl4]− with ethylenediamine-N,N'-diacetic acid ligand

The reaction of [^99mTcNCl₄]^– with ethylenediamine-N,N'-diacetic acid (ENDA) has been studied. Starting from [^99mTcNCl₄]^– prepared according to the method of Apparu et al.6, the exchange reaction with ENDA in the presence of stannous tartrate led to the formation of an anionic^99mTcN-ENDA complex. The labeling yield was about 90% at pH values of 10.5 and 6.5. In the absence of the reducing agent the formation of^99mTcO₄ ^– is reflected in the decrease of the complex yield. The exchange reaction of [⁹⁹TcNCl₄]^– with ENDA at pH 6.5 and in the absence of a reducing agent resulted in the formation of the anionic⁹⁹TcN-ENDA complex and⁹⁹TcO₄ ^–. The spectrophotometric characteristics (UV-vis. and IR) of the pure complex are similar to those of some tcN²⁺-complexes with amine ligands. The electrophoretic and chromatographic behaviors of^99mTcN- and⁹⁹TcN-ENDA anions are identical; this proves the formation of the same complex with both radionuclides.