EVALUATION OF THE IN-111 (SN)-CITRATE METHOD TO LABEL ANTIBODIES FOR RADIOIMMUNOTARGETING STUDIES

Monoclonal antibody against carcinoembryonic antigen (CEA) was labeled by the In-111-(Sn)-citrate technique and its characteristics were determined from the point of radioimmunotargeting studies. Antibodies of high specific radioactivity could be labeled with a high labeling yield of greater than 90% without any further purification step, and without loss of immunoreactivity. In biodistribution studies using nude mice bearing CEA-producing tumors, an extremely high tumor-to-blood ratio (40 on day 6) was obtained since In-111 in the blood cleared very rapidly, but nonspecific In-111 localized in the liver and spleen should be seriously considered.