ADJUVANT I-131 ANTI-CEA-ANTIBODY RADIOIMMUNOTHERAPY INHIBITS THE DEVELOPMENT OF EXPERIMENTAL COLONIC-CARCINOMA LIVER METASTASES

Adjuvant radioimmunotherapy (RIT) for human colonic cancer was perform ed in a nude rat model of experimental liver metastases. Thirty-three rats were injected intraportally through a mesenteric vein with 5 x 10 (6) cells from the human colonic cancer cell line LS174T. Within half an hour 20 MBq (n=2), 75 MBq (n=5), or 150 MBq (n=10) of the I-131-lab elled anti-carcinoembryonic antigen (CEA) monoclonal antibody (MAb) 38 S1 was administered intravenously (i.v.), whereas control groups recei ved either i.v. saline injections (n=12) or 150 MBq of the irrelevant I-131-labelled MAb 79C (n=4). Decay corrected whole-body data showed t hat more than 80% of the initially MAb-bound radioiodine was excreted during the first 2 weeks. Whole-body clearance and blood clearance of I-131-38S1 and I-131-79C were essentially similar: At sacrifice 5-7 we eks after administration, neither 20 MBq nor 75MBq I-131-38S1 38S1 sig nificantly prevented the development of liver metastases. By contrast with 150 MBq, no metastases formed in the animals treated with MAb I-1 31-38S1 or I-131-79C. A radiation induced effect on the haematopoietic system was found in the 150MBq dosage groups. It is concluded that th e inhibition of tumour induction was not strictly dependent on a radia tion dose delivered by a tumour-specific MAb. Since a non-tumour-speci fic specific I-131-MAb, in a smaller group of animals, proved equally efficacious in preventing tumour growth, the total body I-131 dose was probably the major contributing factor.