Síntese da DISIDA: produçäo de conjuntos de reativos liofolizados para obtençäo da DISIDA - 99mTC

A DISIDA-99mTc mostrou ser o melhor readiofármaco entre os diversos derivados do ácido iminodiacético para a aquisiçäo de imagens hepatobiliares. O custo elevado do conjunto de reativos para sua marcaçäo com 99mTc nos levou a optar por sua síntese. Apresentamos a síntese e a caracterizaçäo físico-química da DISIDA e o preparo de conjunto de reativos liofilizados para a obtençäo da DISIDA-99mTc. Os controles de qualidade realizados mostraram a alta estabilidade dos conjuntos de reativos produzidos e sua aplicaçäo em Medicina Nuclear, mesmo naqueles pacientes com alta bilirrubinemia

Síntese e preparaçäo de conjuntos de reativos liofilizados do ácido p-(Bis-carboximetil) Aminometil Carboxiamino Hippúrico / The synthesis and preparation of lyophilized kit of p-(Bis-Carboxymethyl)-Aminomethyl Carboxyamino Hippuric acid

Tendo em vista o crescente interesse da Medicina Nuclear em utilizar um agente marcado com 99mTc cuja eficiência seja semelhante a do Hippurato de Sódio 131I para fultraçäo glomerular, preparou-se por síntese química um análogo do ácido Amino Hippúrico: Acido p-(bis-carboximetil)-aminometil carboxiamino hippúrico (PAHIDA). A pureza físico química foi determinada por ponto de fusäo e espectros de Ressonância Nuclear Magnética e Infra-vermelho. Prepararam-se Conjuntos de Reativos Liofilizados destinados à maracaçiao com 99mTc. Cada frasco contendo 10 mg de PAHIDA e 0,25 mg de Cloreto Estanoso foi submetido a análises cromatográficas em ITLC para determinaçäo de pureza radioquímica e estabilidade do produto liofilizado. Realizaram-se também estudos de distribuiçäo biológica em ratos: houve concordância entre a eliminaçäo urinária e o clareamento do produto no plasma

[A new sterile generator of Tc 99m. Quality control]. / Un nuovo generatore sterile di 99mTc. Controlli di qualità.

Production has started on a new Tc 99m sterile generator in Italy. We give the results of a series of quality controls in order to have a first evaluation of the product. The elution profile and the volume, activity, pH, aluminium concentration, 99 Mo content and radiochemical purity of the eluate were examined. Radiochemical purity tests were also carried out with some of the more widely used "in vivo" radiopharmaceuticals. The results are in line with the Official Pharmacopeia and good technical standards.

Technetium-99m d,l-HM-PAO: a new radiopharmaceutical for SPECT imaging of regional cerebral blood perfusion.

Following investigation of a large number of new ligands based upon propylene amine oxime (PnAO) the d,l-diastereoisomer of hexamethyl propyleneamine oxime (HM-PAO) was selected as the preferred ligand for 99mTc as a tracer for cerebral perfusion imaging. The neutral, lipophilic 99mTc complex of d,l-HM-PAO was formed in high yield by stannous reduction of 99Mo/99mTc generator eluate using a kit formulation of the ligand. Two minutes following i.v. administration of this complex in rats, 2.25% of the injected dose appears in the brain. Little washout of the tracer is observed up to 24 hr postinjection. By qualitative autoradiographic comparison with iodoantipyrine this new radiopharmaceutical displays blood flow dependent brain uptake with little redistribution of the tracer over time. The lipophilic 99mTc complex converts slowly in vitro to a secondary complex. This conversion process may account for the ability of [99mTc]d,l-HM-PAO to be retained within the brain without redistribution.

In the procurement of a neutral and compact monomeric complex of dithiosemicarbazone (DTS) derivative: 99mTc-KTS.

As a basic structure of a bifunctional radiopharmaceutical (BR), dithiosemicarbazone (DTS) enables the formation of a small conjugated chelating ring with divalent metals (Cu2+, Zn2+, Ni2+), yielding stable and compact complexes. In the development of a neutral and compact monomeric DTS complex of technetium (99mTc), a DTS containing ligand, kethoxal-bis(thiosemicarbazone) (KTS) was selected. A well known monomeric Cu-KTS complex (or 64Cu-KTS) is taken as a model compound, and in vitro (TLC, EP, HPLC) and in vivo (mice biodistribution) studies were compared. Using the stannous chloride method, under conditions to avoid the hydrolytic polynucleation of technetium, a good yield of 99mTc-KTS with characteristics resembling the non-charged, compact and stable Cu-KTS is obtained, in in vitro as well as in vivo studies. The importance of DTS as the constituent of a BR is discussed.

Synthesis and biological evaluation of technetium-99m MAG3 as a hippuran replacement.

A new technetium-chelating agent based on a triamide monomercaptide tetradentate set of donor groups, mercaptoacetylglycylglycylglycine (MAG3), was synthesized and evaluated. Chelation with 99mTc resulted in a single radiochemical product as expected. Studies in mice of [99mTc]MAG3 indicated excretion rates faster than omicron-iodohippurate (OIH) both in normal and in probenecid treated animals. Specificity for renal excretion was essentially complete. Clearance studies in rats resulted in 2.84 ml/min/100 g for [99mTc]MAG3, 2.17 for OIH, and 1.29 for [125I]iothalamate. Extraction efficiencies were 85% for [99mTc]MAG3, 69% for OIH and 39% for [125I]iothalamate. Probenicid depressed the clearance both of [99mTc]MAG3 and OIH at 25 and 50 mg/kg/hr, but to a greater extent with [99mTc]MAG3. The greater effect is offset, however, by the larger fraction secreted by the renal tubular cells. The animal results suggest that [99mTc]MAG3 may be a useful alternative to [131I]OIH.

In vivo skeletal localization properties of 99mTc complexes of large phosphonate ligands.

Tetramethylenephosphonate derivatives of norborane (TPNB) and dicyclopentadiene (TPDCPD) were shown to readily form stable chelates with 99mTc that had high and selective bone uptake. The skeletal uptake and blood clearance properties of 99mTc-TPNB were similar to 99mTc-MDP in both rats and rabbits. This suggests additional studies to further evaluate 99mTc-TPNB or perhaps other large-organic based multidentate phosphonate ligands as potential bone imaging agents is warranted.

Preparation and biodistribution of 99mTc chelate of strophanthidin--a cardiac aglycone.

Cardiac glycosides are well known to exert a specific and powerful effect on myocardial tissue, and there is a possibility that this class of compound with a 99mTc radiolabel may behave as a superior myocardial imaging agent in comparison to 201Tl which is at present used clinically. Because of the extreme chemical complexity of cardiac glycosides a simpler aglycone, strophanthidin was selected as the pilot compound for preliminary labelling and in vivo distribution studies. Strophanthidin was converted to 19-thiosemicarbazone which nicely accommodated 99mTc to produce a pure radiopharmaceutical of high specific activity. The distribution pattern in animal models was studied which is in accordance with the metabolic studies performed earlier with the ligand itself.

Technetium-99m APD compared with technetium-99m MDP as a bone scanning agent.

We have investigated the possibilities of technetium-99m-(-3-aminohydroxypropylidene)-1-1-bisphosphon ate ([99mTc]APD) as a bone scanning agent in 14 normal subjects and 28 patients. Similar studies in the same normal subjects and patients were carried out with 99mTc-methylene-bisphosphonate ([99mTc]MDP). The compounds were labeled with 99mTc by means of an electrolytical method; the free pertechnetate content was always under 1%. The [99mTc]APD T1/2 of the third component of the disappearance plasma curve in six normal subjects was 152 +/- 46 min (mean +/- s.d.), while the 24-hr whole-body retention (WBR) was 17.6% +/- 4.6. The [99mTc]MDP value of the 24-hr WBR was 28.6% +/- 3.9 (p less than 0.001). The bone/soft-tissue ratio (B/ST) was investigated in eight control subjects on the eleventh thoracic and the fourth lumbar vertebrae. The B/ST ratios were similar for both APD and MDP studies. In 28 patients with suspected bone metastasis or primary bone disease, bone scintigraphy was carried out; both compounds showed similar findings and the same number of positive results. In five of these patients, the lesion/normal bone ratio was determined with values of 4.6 +/- 2.0 in APD studies and 4.8 +/- 2.3 with MDP. APD was also used in 126 patients; no adverse reactions were observed. The APD dose used i.v. for bone scanning was 200-fold less than those employed by mouth per day, for the treatment of bone disease for long periods. In our experience, APD appears to be an adequate agent for bone scintigraphy.

Technetium-99m galactosyl-neoglycoalbumin: preparation and preclinical studies.

Technetium-99m galactosyl-neoglycoalbumin ([Tc] NGA), a labeled analog ligand to the hepatocyte-specific receptor, hepatic binding protein (HBP), was prepared and tested for labeling yield, stability, biodistribution, toxicity, and dosimetry. The ligand was synthesized by the covalent coupling of a carbohydrate bifunctional reagent, 2-imino-2-ethyloxymethyl-1-thiogalactose, to human serum albumin. Testing in mice and rabbits revealed the product to be nontoxic and apyrogenic. Technetium labeling yields in excess of 95%, by the electrolytic method, did not alter the molecular weight profile of the neoglycoalbumin. The NGA-bound activity remained stable for at least 4 hr. Biodistribution studies in rabbits demonstrated the liver as the single focus of tracer uptake. Dosimetry was based on kinetic studies in three baboons. Absorbed doses to liver, small intestine, urinary bladder wall, and uterus were 0.089, 0.28, 0.56, and 0.88 rad/mCi, respectively. Total body, lens of the eye, red marrow, ovaries, and testes were less than 0.06 rad/mCi. High liver specificity imparted by receptor binding combined with high labeling yield, stability, acceptable dosimetry, and safety provide [Tc]NGA with the attributes required for routine clinical assessment of hepatocyte function.

Exposure to fingers while handling a solvent extraction-type technetium-99m generator.

Technetium-99m-labeled compounds are routinely used for various diagnostic procedures in nuclear medicine. In India, most of the nuclear medicine centers use 99mTc obtained from a solvent extraction-type generator. As a result of the long procedure involved in the separation of 99mTc from 99mMo in this type of generator compared to the elution of 99mTc from a column-type generator, the likelihood of exposure to fingers of technicians is high. The measurement of radiation exposure was done on 16 workers at seven major nuclear medicine centers in India. The maximum exposure to any of the fingers per MBq of 99mTc extracted was found to vary from 1.46 X 10(-9) to 22.38 X 10(-9) C-kg-1. With the existing work load, the exposures to the fingers were found to be within the permissible limits.

Synthesis and quality control of 99mTc-p-butyl IDA.

A procedure is described for synthesis of p-butyl IDA and for identification of the product by i.r. and NMR spectroscopy and by chemical analysis. A method for preparing this compound by "instant" technique and for its labelling with 99mTc is also given, as well as a procedure for control of the chemical and biological properties of the radiopharmaceutical. Radiochemical study shows a high labelling yield of 95%. Investigation of the biodistribution proves that this preparation is a good hepatobiliary reagent, suitable for use in investigation of the liver functions and for quantitative visualization of the hepatobiliary system.

Preparation, quality control and application of 99mTc-gluco-ene-diolate for renal scanning.

A one-step freeze-dried Sn-glucose kit was developed to be labelled with technetium-99m. TLC, paper chromatography and gel chromatography column scanning techniques (GCS) were used for the determination of the labelling yield of the complex. High radiochemical purity was obtained (98%). In vivo distribution studies were performed in white rats. Maximum uptake in kidneys (28%) was achieved in 15-90 min. The blood disappearance curve studies of the labelled Sn(II)-gluco-ene-diolate in rabbits have shown two disappearance phases of activity from blood with biological half-times of 10 and 150 min for the fast and slow component respectively.

Preparation and biokinetic studies of 99mTc-p-butyl-IDA for hepatobiliary scintigraphy.

A freeze-dried powder of tin-p-butyl-IDA to be labelled with 99mTc for hepatobiliary scintigraphy has been developed. Gel chromatography column scanning has been applied for evaluating the labeling efficiency of the complex under different conditions. The results of organ distribution studies in mice and of clinical investigations in human beings showed the stability of the radiopharmaceutical. The preparative 99mTc-p-butyl-IDA concentrates moderately well in the bile with a rapid blood clearance into hepatocytes, very low excretion in the urine and slow clearance into the bile.

The design of a pentavalent 99mTc-dimercaptosuccinate complex as a tumor imaging agent.

In our search for a technetium-tumor seeking agent, the chemical characteristic of polynuclear Ga-citrate attracted our attention. On this basis, we selected the ligand dimercaptosuccinic acid (DMS) and appropriate labeling conditions in the design of 99mTc(V)-DMS. Chemical characterization was performed by thin layer chromatography, electrophoresis, Sephadex column chromatography and spectrophotometric studies at the chemical concentration (99Tc). Biodistribution in mice bearing Ehrlich ascites tumor and scintigraphic images in VX-2 tumor-bearing rabbit, indicated the great applicability of 99mTc(V)-DMS as a new tumor imaging agent. Its distinctive characteristic, different from the kidney imaging agent (99mTc-DMSA) is demonstrated and the biological implication of hydrolytic polynucleation of pentavalent technetium, through an anionic specie Tc(V)O3-(4), in the tumor cell is discussed.

99mTc bone scanning agents--I. Influence of experimental conditions on the formation and gel chromatography of 99mTc(Sn)pyrophosphate complexes.

The conversion of 99mTcO4- to 99mTc(Sn)pyrophosphate complexes was investigated under various experimental conditions. An increase of the Sn(II) concentration had a beneficial effect, whereas the ligand concentration had little effect. The pH had only a small influence over the range 2-8. Raising the pH to 10 resulted in the partial decomposition of the complexes, which could be reversed by lowering the pH. Furthermore, the occurrence of various complexes was investigated by means of gel chromatography on Biogel P-4 as a function of pH and of the Sn(II) and pyrophosphate concentrations. Four major fractions were found. A single preparation contained, however, no more than two major fractions. The formation of the different complexes was mainly governed by the pH and the ligand concentration. The influence of the eluent on the decomposition and interconversion of the complexes during chromatography was also studied. It appeared to be necessary that the eluent should have the same composition (except for 99mTcO4-) as the reaction mixture.

Technetium thiodiglycollic acid (99mTc-TDG). A new radiopharmaceutical with the potential for the assessment of renal function.

A mixture of hydrophilic complexes is formed on the reduction (employing tin metal as a reductant) of sodium pertechnetate 99mTc in the presence of the ligand thiodiglycollic acid (TDG). When administered to rats, the mixture demonstrated a renal clearance rate marginally greater than Glomerular filtration rate (GFR). HPLC analysis indicated the formation of two technetium complexes of TDG. After isolation of the complexes and their administration to rats, one (complex 1) showed renal clearance similar to that of 99mTc Diethylenetriamine pentaacetic acid (DTPA), while the other (complex 2) demonstrated renal clearance similar to that of 125I o-iodo hippuric acid. On heating the mixture of complexes, the proportion of the faster-clearing 99mTc TDG complex increased to 92% of the total activity, and the biodistribution of the material following heat rearrangement was equivalent to that of isolated complex 2.

Bromine-82 contamination in fission product 99mTc-generator eluate.

Following receipt of fission product 99mTc-generators, results of radionuclide purity analysis, performed within 30 min after the first elution, demonstrated detectable levels of a contaminate radionuclide not previously reported. Gamma spectroscopy and half-life determinations confirmed the presence of 82Br. Bromine-82 activity, in eluates from the first elution of 30 generators, received weekly during a 7-month period, ranged from 0.22 microCi (8.235 kBq) to 0.67 microCi (24.68 kBq) per eluate. The ratio of 99Mo to 99mTc ranged from 0.13 nCi to 0.39 nCi per mCi 99mTc. The presence of 82Br in 99mTc-generator eluate resulted in falsely elevated 99Mo assay determinations using whole vial 99Mo assay procedures. For every 0.1 microCi 82Br present in 99mTc eluate the 99Mo assay results were elevated by 1 microCi. Gamma spectroscopy of eluates from additional elutions of these generators failed to detect the presence of 82Br demonstrating the displacement of monovalent bromine anions from the alumina column during the first elution.