TC-99M-DEXTRAN-ANTIBODY CONJUGATES - LABELING PROCEDURES

Dextran forms stable chelates with Tc-99m, a radionuclide with ideal p roperties for planar scintigraphic and tomographic imaging. This study investigates some of the factors of importance to the formation of Tc -99m-dextran. The complex was used for the technetium labelling of a m onoclonal antibody, Two radiolabelling methods were studied: direct de xtran labelling with the reductant dissolved in HCl and labelling via a weak 'transfer' chelator (tartaric acid) with the reductant dissolve d in ethanol, Different conditions during the labelling reaction were studied. Finally, dextran was coupled to a monoclonal anticytokeratin antibody and the conjugate was subsequently radiolabelled with Tc-99m. Gel filtration (GFR) and thin layer chromatography (TLC) were compare d as methods for estimation of the labelling efficiency, When using 10 -500 mu M of ligand, 5-100 mu M SnCl2 with 10-500 MBq of technetium at pH 7 incubated for 10-15 min, the radiolabelling seemed optimal (70-7 5% labelling efficiency). It was found that 100 mu M tartaric acid use d as a weak intermediate chelator with SnCl2 dissolved in ethanol impr oved the reproducibility of the labelling, The labelling efficiency wa s not affected by either the presence of oxygen or the addition of an oxygen scavenger during the labelling incubation, In general, TLC show ed higher labelling efficiencies than GFR, indicating inadequate separ ation of the different moieties.