Direct 99mTc labeling of human immunoglobulin with an insoluble macromolecular Sn(II) complex

Preincubation with Sn-complexes causes intensive intracellular retention of 99mTc in thyroid cells in vitro

Technetium radiopharmaceuticals are well established in nuclear medicine. Besides its well-known gamma radiation, 99mTc emits an average of five Auger and internal conversion electrons per decay. The biological toxicity of these low-energy, high-LET (linear energy transfer) emissions is a controversial subject. One aim of this study was to estimate in a cell model how much 99mTc can be present in exposed cells and which radiobiological effects could be estimated in 99mTc-overloaded cells. Methods: Sodium iodine symporter (NIS)- positive thyroid cells were used. 99mTc-uptake studies were performed after preincubation with a non-radioactive (cold) stannous pyro - phosphate kit solution or as a standard 99mTc pyrophosphate kit preparation or with pure pertechnetate solution. Survival curves were analyzed from colony-forming assays. Results: Preincubation with stannous complexes causes irreversible intracellular radioactivity retention of 99mTc and is followed by further pertechnetate influx to an unexpectedly high 99mTc level. The uptake of 99mTc pertechnetate in NIS-positive cells can be modified using stannous pyrophosphate from 3–5% to >80%. The maximum possible cellular uptake of 99mTc was 90 Bq/cell. Compared with nearly pure extracellular irradiation from routine 99mTc complexes, cell survival was reduced by 3–4 orders of magnitude after preincubation with stannous pyrophosphate. Conclusions: Intra cellular 99mTc retention is related to reduced survival, which is most likely mediated by the emission of low-energy electrons. Our findings show that the described experiments constitute a simple and useful in vitro model for radiobiological investigations in a cell model.

Direct technetium-99m labeling of anti-hepatoma monoclonal antibody fragment: a radioimmunoconjugate for hepatocellular carcinoma imaging

AIM: To directly radiolabel an anti-hepatoma mAb fragment HAb18 F(ab')₂ with ^99mTc by stannous-reduced method, and assess the stability, biodistribution and radioimmun oimaging (R II).

METHODS: Immunoreactive fraction was determined according to Lin dmo's method. Ellman's reagent was used to determine the number of thiols in the reduced F(ab')₂. Labeling efficiency and homogeneity were measured by paper chromatography, sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) and autora diography. Challenge assay involved the incubation of aliquots of labeled antibody in ethylenediaminetetraacetate (EDTA) and L-cysteine (L-cys) solutions with different molar ratio at 37 °C for 1 h, respectively. Investigations in vivo utilized nude mice bearing human hepatocellular carcinoma (HHCC) xenografts with gamma camera imaging and tissue biodistribution studies at regular intervals.

RESULTS: The labeling procedure was finished within 1.5 h compared with the "pretinning" method which would take at least 21 h. In vitro studies demonstrated that the radiolabeled mAb fragment was homogen eous and retained its immunoreactivity. Challenge studies indicated that ^99mTc-labeled HAb18 F(ab')₂ in EDTA is more stable than in L-cys. Imaging and biodistribution showed a significant tumor uptake at 24 h post-injection of ^99mTc-labeled HAb18 F(ab')₂. The blood, kidney, liver and tumor uptakes at 24 h were 0.56 ± 0.09, 56.45 ± 11.36, 1.43 ± 0.27 and 6.57 ± 3.01 (%ID/g), respectively.

CONCLUSION: ^99mTc-HAb18 F(ab')₂ conjugate prepare d by this direct method appears to be an effective way to detect hepatoma in nude mice model.

Cellular inactivation induced by a radiopharmaceutical kit: role of stannous chloride

Stannous chloride (SnCl2) has been used in many sectors of human activities such as food manufacturing and in nuclear medicine to produce radiopharmaceuticals labeled with technetium-99m (99mTc). Due to its importance and genotoxic potentiality, we decided to evaluate the biological effect induced by a nuclear medicine kit, which includes SnCl2, in association with glucoheptonic acid (GHA) which is employed for brain and renal scintigraphies. These studies were carried out with the Escherichia coli AB1157 strain and the deoxyribonucleic acid (DNA) plasmid pUC 9.1. The experiments, with different concentrations of SnCl2 and GHA, show an inverse relationship between both agents. When the GHA concentration was increased, the cellular inactivation induced by SnCl2 was reduced, as measured by the number of viable cells. Moreover, GHA protects the DNA molecule against the damage induced by SnCl2.