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Radioactive iodine-labeled rabbit antibodies to beta 1-MA antigen (the marker of human colon cancer) were injected iv to BALB/c mice as well as to nude mice with xenografts of various human tumors. Preparations of iodinated antibodies contained an admixture of protein-unbound radionuclide 2-4% of total radioactivity. Part of the recipient animals were given per os 0.1% solution of KI to block the thyroid from radioactive iodine. A comparative study was made of the distribution of radioactivity in the tissues of recipients in the time course of 7 days. The thyroid of nude mice with tumors was shown to uptake much more radioactivity than that of immunologically intact mice. In addition to its protective effect of the thyroid from radioactive iodine, KI also enhanced the excretion of the preparation of labeled antibodies. Possible mechanisms of the revealed phenomena were analyzed.

131I labeled rabbit antibodies to the human epithelial intestinal antigen beta 1-MA was administered intravenously to nude mice together with human tumor grafts: colon cancer (CC), breast cancer, Ewing's sarcoma and hepatoma. Antibodies to beta 1-MA were selectively accumulated in CC only, excluding the other tumors. Iodinated nonspecific rabbit IgG in mice with CC were distributed like antibodies to beta 1-MA in the body of mice with control heterografts. A conclusion was made of the promising use of labeled antibodies to beta 1-MA in radioimmuno-scintigraphy of CC and its metastases.

131I-antibodies (Ab) to human organ-specific intestinal antigen--beta 1-MA (maconial antigen) were injected intravenously to nude mice to whom various human tumors including colon tumors had been transplanted. Ab distribution in recipient tissues and in tumors was determined over time with the help of a gamma-counter. Ab to beta 1-MA was shown to localize specifically in colon tumors. 131I-Ab accumulation in this tumor exceeded the background level in tumor-bearing tissues. The excess increased with time as a result of slower Ab clearance of colon tumors as compared to normal tissues. beta 1-MA was detected immunohistochemically in the mouse colon epithelium however elevated accumulation of Ab to beta 1-MA injected into the blood flow in the intestine was undetectable.

The results of experiments using 131I-labelled monoclonal antibody (131I-MoAb) were described. The experiments were staged on nude male mice with transplanted human colon adenocarcinoma of the 34th generation (RTK-12). Tumor sizes by the time of 131I-MoAb administration varied from 1 to 3 cm. 131I-MoAb specific radioactivity was 456.6 kBq/micrograms in the volume of 0.3 ml. The same amount of 131I-Na was administered to control animals. Scanning on the Scintimat-2F (Siemens) was performed 1, 2, 3 and 4 days after injection of 131I-MoAb. Three days before scanning 0.2% KI was added to the drinking water. Some animals were decapitated on the 2nd-3rd day for radiometry of organs and tissues. After the injection of 131I-MoAb 10-fold less than the CEA serum concentration and with specific radioactivity of 370-444 kBq its tumor accumulation in 48 h was 10-15-fold higher than that in the surrounding tissues resulting in better tumor scans. Intensive dehalogenation of 131I-MoAb in vivo and related 131I accumulation in the thyroid and adrenal glands (in the medullary layer) required the administration of stable iodine not only before but also after injection of the radioactive agent.