99MTc-Dextran-Antibody Conjugates : Labelling procedures

Abstract

Dextran forms stable chelates with ^99mTc, a radionuclide with ideal properties for planar scintigraphic and tomographic imaging. This study investigates some of the factors of importance to the formation of ^99mTc-dextran. The complex was used for the technetium labelling of a monoclonal antibody. Two radiolabelling methods were studied: direct dextran labelling with the reductant dissolved in HCl and labelling via a weak ‘transfer’ chelator (tartaric acid) with the reductant dissolved in ethanol. Different conditions during the labelling reaction were studied. Finally, dextran was coupled to a monoclonal anticytokeratin antibody and the conjugate was subsequently radiolabeled with ^99mTc. Gel filtration (GFR) and thin layer chromatography (TLC) were compared as methods for estimation of the labelling efficiency. When using 10-500μM of Ugand, 5-100μM SnCl₂ with 10-500 MBq of technetium at pH7 incubated for 10-15 min, the radiolabelling seemed optimal (70-75% labelling efficiency). It was found that 100 μM tartaric acid used as a weak intermediate chelator with SnCl₂ dissolved in ethanol improved the reproducibility of the labelling. The labelling efficiency was not affected by either the presence of oxygen or the addition of an oxygen scavenger during the labelling incubation. In general, TLC showed higher labelling efficiencies than GFR, indicating inadequate separation of the different moieties.