Stability, targeting, and biodistribution of scandium-46- and gallium-67-labeled monoclonal antibody in erythroleukemic mice

Using a monoclonal antibody specific for the Mr 70,000 glycoprotein of Rauscher erythroleukemia virus, the authors have determined the optimal conditions for conjugation with the cyclic anhydride of diethylene triamine pentaacetic acid and subsequent labeling with 46Sc. The conjugates were shown to retain their specificity and activity in vitro and to target specifically to virus-infected spleen cells in vivo. The stability of the 46Sc:diethylene triamine pentaacetic acid-antibody conjugates in vivo was studied using immunoaffinity chromatography; 25% of the isotope bound to transferrin, and 75% remained bound to the antibody conjugates. These results are discussed with respect to the potential for labeling antibodies with 47Sc for use in imaging and therapy. Studies with 111In-labeled antibody were used for comparison. Labeling with 67Ga was also performed; these labeled conjugates showed adventitious binding of the isotope to the antibody and lack of stability of diethylene triamine pentaacetic acid-chelated gallium. Free EDTA was shown to stably incorporate 67Ga