Preparation of99mTc complexes with compounds structurally related to ethylene diamine tetraacetic acid

The preparation of^99mTc-Sn-DOTA,^99mTc-Sn-DDDTA and^99mTc-Sn-DHDTA is described. The labelling efficiency of all samples was checked by paper chromatography, thin layer chromatography and paper electrophoresis. Preliminary results of the biodistribution studies performed in white rats are given.     

Labeling of polyaminomacrocyclic ligands BY99mTcO 4 − reduction and exchange reactions

The cationic^99mTc-complexes of 1,4,8,12-tetraazacyclopentadecane (15-ane-N₄), 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (Me₄cyclam) and 1,4,7,10,13,16-hexaazacyclooctadecane (hexacyclen) are obtained in yields higher than 80% by^99mTcO ₄ ^– reduction at pH 12. The electrophoretic and chromatographic analyses show that these ligands form structurally similar complexes. Efficient labeling of 15-ane-N₄ (>95%) is obtained by the exchange reaction with^99mTc-citrate,^99mTc-ENDA and^99mTc-HBA at pH 12. The labeling yield of hexacyclene is 70% and 85% following the reaction with^99mTc-ENDA and^99mTc-HBA and^99mTc-citrate, respectively. The labeling of Me₄cyclam is very poor (about 10%) except starting from^99mTc-citrate (55%). The results are compared wint the available data for well characterized [TcO₂L]⁺ complexes.     

Evaluation of labelling conditions,quality control and biodistribution study of 99mTc-5-aminolevulinic acid (5-ALA): a potential liver imaging agent

Labelling of 5-aminolevulinic acid (5-ALA) with ^99mTc was achieved by using SnCl₂·2H₂O as reducing agent. Radiochemical purity and labelling efficiency was determined by instant thin layer chromatography/paper chromatography. Efficiency of labelling was dependent on many parameters such as amount of ligand, reducing agent, pH, and time of incubation. ^99mTc labelled 5-ALA remained stable for 24 h in human serum. Tissue biodistribution of ^99mTc-5-ALA was evaluated in Sprague–Dawley rats. Biodistribution study (% ID/g) in rats revealed that ^99mTc-5-ALA was accumulated significantly in liver, spleen, stomach and intestine after half hour, 4 and 24 h. Significant activity was noted in bladder and urine at 4 h. High liver uptake of ^99mTc-5-ALA makes it a promising liver imaging agent.     

A ready-to-use kit for the preparation of99mTc-phytate for liver scanning

Kits were developed-for the sterile labelling of phytate with^99mTc. The effect of molar ratio of phytate to stannous chloride, pH, dilution of the Sn-phytate with^99mTc-generator eluate, time of incubation, the shelf life of^99mTc-phytate and the storage time of Sn-phytate on the labelling yield of phytate with^99mTc was investigated using paper chromatography and gel chromatography column scanning method (GCS). Organ distribution was performed in rabbits and mice. Excellent human liver scans were obtained.     

Radiochemical quality control of99mTc-phytate

Several chromatographic methods have been used for determining the radiochemical purity of^99mTc-phytate. Good separation of^99mTc-phytate from radiochemical impurities was performed using gel column chromatography packed with Sephadex G-10. Reduced^99mTc-complexes and^99mTc-phytate were not separated by paper and thin layer chromatography.This work has been presented at the Fifth International Symposium on Radiopharmaceutical Chemistry, Tokyo, July 9–12, 1984.     

Studies on the porphine labeled with <Superscript>99m</Superscript>Tc–pertechnetate

The aim of this research is to use acetylacetonate as a ^99mTc chelating agent label with porphyrin and evaluate its radiochemical and biological characteristics. Stannous chloride was used as a reductant to determine the chemical and biological characterization of ^99mTc-complexes from labeling porphine{4′,4′′,4′′′-(2lH,23H-Porphine-5,10,15,20-terayl)tetrakis-(benzoic acid), TPPB} with ^99mTc–pertechnetate. Instant thin layer chromatography (ITLC), size exclusion chromatography (SEC), paper electrophoresis, and UV/Vis spectrophotometry were used to evaluate chemical characterization. Finally, biodistribution and liver function tests were applied to evaluate biological characteristics. The results of this study show that the labeling efficiency of ^99mTc(acac)–TPPB was nearly 100% when using acetylacetone (acac) as a conjugator. Three major ^99mTc(acac)–TPPB complexes were separated by SEC, and all of them were hydrophilic. The UV-Vis spectra of ^99mTc(acac)–TPPB complexes closely resembled those of the TPPB, but the wave lengths of their peaks changed 430, 521, 556, 591 and 647 nm after complexation. The biodistribution study selected the liver as the target organ. The ^99mTc(acac)–TPPB complex may cause short-term liver injury. However, this injury can be repaired, and the reagent is quickly metabolized. Hence, the toxicity of the ^99mTc(acac)–TPPB complex is within an acceptable range, and making it a promising liver imaging agent.     

99mTc-DMSA complex preparation: the effect of pH and tin(II) chloride amount on reaction

Labelling of meso-2,3-dimercaptosuccinic acid (DMSA) with technetium-99m was reinvestigated. Dependence of the ^99mTc-DMSA complex formation on the molar ratio of DMSA:reducing agent (SnCl₂·2H₂O) and pH was studied. Five different types of ^99mTc-DMSA complexes were determined. Especially three different complexes were established in the clinically used and prepared DMSA kit labelled with ^99mTc under alkaline condition. This radiopharmaceutical is used as imaging agent of the primary medullary carcinoma in the thyroid gland and different metastasis types. The existence of all complexes was observed by paper chromatography, paper electrophoresis and high performance liquid chromatography.     

Luminescent determination of neptunium and plutonium in the environment

The preparation of^99mTc-complexes with nine derivatives of (4R)-1,3-thiazolidine-4-carboxylic acid over a broad pH range is described. The labeling efficiency of all compounds was checked by paper- and thin layer chromatography. Paper electrophoresis and gel chromatography indicated the presence of two types of^99mTc-complexes differing in charge and molecular size. Preliminary results of the biodistribution of anionic complexes in mice are given. The structure of both types of the Tc-complexes is also discussed.     

Separation of99mTc from neutron-irradiated MoO3 by precipitation as CaMoO4

A method is discussed for separating^99mTc from⁹⁹Mo by dissolution and reprecipitation of CaMoO₄ containing⁹⁹Mo-^99mTc.^99mTc can be obtained successfully with a yield of about 80% and with a radionuclidic purity as high as over 99.7%. On the other hand, by agitating Ca⁹⁹ MoO₄ solid with 0.9% NaCl aqueous solution,^99mTc can directly be obtained with a yield of about 30% without any impurities.     

The preparation of99mTc-labelled methionine

^99mTc-labelled methionine was prepared by ligand substitution reaction. Methionine was reacted with^99mTc-citrate under physiological conditions, to form a radiochemically pure, neutral Tc complex. Labelling parameters involving incubation period of methionine in^99mTc-citrate solution were studied by paper and thin-layer chromatography.     

Analytical procedures for radiochemical control of water-soluble99mTc-labelled radiopharmaceuticals

In this paper chromatographic systems for the accurate and reliable determination of the percentage of different species (free pertechnetate, particulate^99mTc and labelled^99mTc) in^99mTc-labelled radiopharmaceuticals are described. The procedures are based on the simultaneous run of two different chromatograms, one in 85% CH₃OH and the other in 15% H₃PO₄. Also, 0.9% NaCl can be used instead of 15% H₃PO₄ for the second chromatogram. Alternative procedures applying two dimensional chromatography on Whatman No. 1 paper or silica G plates with 85% CH₃OH for the first run and 15% H₃PO₄ for the second are given. The applicability of these procedures is limited to water-soluble radiopharmaceuticals.     

Chromatographic and biological comparison of99mTc-DMSA prepared by direct labelling and ligand exchange reaction

^99mTc-dimercaptosuccinic acid /DMSA/ is one of the most favourable agents used for renal scintigraphy. This radiopharmaceutical was prepared in two different ways: by direct labelling of tin/II/-dimercaptosuccinic acid and by ligand exchange reaction from^99mTc-gluconate at tracer concentration of technetium under acidic condition. The complexes formed were compared using paper chromatography, thin layer chromatography, gel filtration and electrophoresis. Their biodistribution was studied on rats.     

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.     

Radiochemical quality control of99mTc-labelled radiopharmaceuticals

Two methods for the determination of radiochemical purity of preparations labeled with^99mTc are described. Paper chromatography was used for separation of reduced^99mTc and free pertechnetate from the labeled radiopharmaceutical. Whatman 3MM paper was used first with a acetone and then with 1N NaCl, as the mobile phase. Instant thin layer chromatography was performed for comparison. The electrophoretic method was also applied, using 0.05 M Na-acetate and 0.017 M NaCl. Biodistribution of^99mTc-DMSA in the organs of experimental animals was followed in order to verify chemical control methods.     

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.     

Kinetic examination of ligand exchange reaction between99mTc-gluconate and dimercaptosuccinic acid

^99mTc-dimercaptosuccinic acid is one of the most widely applied radiopharmaceutical for renal scintigraphy. This complex was prepared by ligand exchange reaction from^99mTc-gluconate at tracer concentration of technetium under acidic conditions. The exchange yield was determined by paper chromatography and reaction rate constants were calculated at different pH values.     

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.     

Quality control and statistical analysis of biodistribution of commercial99mTc-IDA derivatives

The results obtained for radiochemical purity of ITLC (SA) and (SG) using different solvent systems and low voltage electrophoresis are presented in the paper. Radiochemical purities obtained for^99mTc-dimethyl IDA (^99mTc-HIDA) and^99mTc-diethyl IDA (^99mTc-EHIDA) are 98.1±0.6% and 98.7±0.5%, respectively. Variable^99mTc hydrolyzate contents, depending on the ionic strength of the eluents and on the time interval between labelling and analysis, have been obtained by Sephadex chromatography. The eluent containing Sn-EHIDA inhibits dissociation of^99mTc-EHIDA due to dilution of the preparation during elution of the column and yielding only a small percent of Sephadex bound fraction, as compared to other investigated eluents. The range of normal^99mTc-IDA biodistribution values in the organs of experimental animals and statistical significance of the difference between these two preparations have also been determined. The results obtained for^99mTc-HIDA and^99mTc-EHIDA in the liver are 33.9±5% and 25.7±4.7%, respectively p<0.01.     

99mTc-labeling and in vitro characterization of N4- and N3S-RGDS-derivative peptides

The aim of this work was to characterize the in vitro behavior of N4- and N3S-RGDS-derivative peptides labeled with ^99mTc. Peptides AGGG-Abu-GRGDSPK-NH₂ (F22) and C(acm)-GGG-Abu-GRGDSPK-NH₂ (SMA1) were synthesized by solid phase. The stability of ^99mTc-labeled peptides was assessed in a 30-fold molar excess of cysteine and in plasma. The affinity for plasma proteins was also evaluated. Labeling yield was >95% for both peptides. ^99mTc-F22 was not stable in presence of cysteine, but 63% of ^99mTc remained chelated to SMA1 up to 24 hours. Both peptides showed low affinity to plasma proteins. N3S-RGDS-derivative peptide (SMA1) showed more stable coordination binding with ^99mTc and a higher stability in plasma with regard to N4-RGDS-derivative peptide (F22).     

Statistical analysis of the results of99mTc-MDP quality control

The methods used for control of radiochemical purity of^99mTc-MDP are presented. TLC method on silica gel, developed with methanol and acetone (11 v/v), was convenient for determination of^99mTcO ₄ ^– with the content of 2.6±1.2%. The reliable results on detection of^99mTc hydrolyzate (2.2±1.3%) and for another^99mTc-MDP complex (13.2±2.8%) were obtained by application of ITLC (SA), developed with Sn-MDP. By Sephadex G-25 column chromatography (1.5 cm×5 cm) the separation of^99mTcO ₄ ^– was not achieved. The range of normal^99mTc-MDP biodistribution values in the organs of experimental animals have been determined. The mean value of bone distribution was 8.4±1.13%/g, in muscles 0.071±0.033%/g, while uptake in liver and kidneys was below 5%. Chi-square test and P show that the results on biodistribution of^99mTc-MDP in liver, bones and muscles are arranged around their mean values, which is statistically allowed.