Monoclonal antibody radioimmunodetection of human-derived colon cancer

This study was designed to determine whether monoclonal antibody directed against carcinoembryonic antigen could successfully be used in the scintigraphic localization of a human-derived colon carcinoma in a hamster model. An immunoglobulin G (IgG)-1 kappa monoclonal antibody, prepared in this laboratory, against carcinoembryonic antigen (CEA) was radiolabeled with iodine-131 (131I). Four Syrian hamsters bearing GW-39 human colon cancers received intracardiac injections of 50 mu Ci of 131I (14 micrograms of antibody). Gamma camera images were obtained at 24-hour intervals. Animals were sacrificed at 11 days, and the tumors and entire animals were counted. A double-label antibody experiment was conducted with 131I anti-CEA and nonspecific MOPC 21 IgG iodine-125 (125I) to assess localization specificity. The scintiphotos clearly showed the tumor at 24 hours, but there was significant background (blood-pool activity). Later images at six and 11 days showed a gradual decrease in background activity and more clear definition of the tumor. Animals sacrificed at 11 days showed 48-80% of residual whole body radioactivity to be present in the tumor. However, these tumors were large at sacrifice, weighing 8.9 to 12.4 g. Specific localization was confirmed by the double-label experiments where specific localization was twice nonspecific accretion of IgG in the tumor. This study has shown that a specific monoclonal antibody can successfully be used to scintigraphically localize a colon tumor of human origin. Although clearance of background activity is a gradual process, eventually most radioactivity left in the animal is localized in the tumor. This study illustrates that the potential radiolabeled monoclonal antibodies hold as immunodiagnostic agents.