The immunoreactivity and affinity of seven kinds of
monoclonal antibody raised against human
gastric cancer (MKN-45) secreted
carcinoembryonic antigen (CEA) were determined with the method of cell binding assay in vitro.
Tumor localization and biodistribution of radiolabeled
antibodies were performed in athymic mice implanted MKN-45 xenografts. Results obtained were as follows: 1) The affinity constant of CEA-specific three
antibodies (1A4, 1B2, 4H11) was the same approximately, whereas the immunoreactivity found to be quite different among them. While CEA-nonspecific four
antibodies (7D1, 6C7, 2C3, 5H7) showed the much higher affinity constant than that of the former. 2) In an animal model on
tumor localization and biodistribution studies, CEA-specific
antibodies obtained more highly
tumor targeting and cleared more rapidly from the blood and non-
tumor organs than CEA-nonspecific
antibodies did, so that
tumor to nontumor ratios was increased. 3) In this model system it is the immunoreactivity preparation of
antibodies that improved
tumor targeting and
tumor activity retention, on the other side, the affinity constant of
antibodies were associated with rapid clearance from the blood and non
tumor sites. In conclusion, this studies would also be beneficial for practical use and clinical application of radiolabeled
monoclonal antibodies.