title: Prolonged binding of a radiolabeled monoclonal antibody (B72.3) used for the in situ radioimmunodetection of human colon carcinoma xenografts.
abstract: Monoclonal antibody B72.3 binds to a glycoprotein complex with a molecular weight of 220,000 to 400,000. B72.3 reacts with approximately 50% of human mammary carcinomas and to 80% of the colon carcinomas tested but does not react appreciably with normal mammary tissue, with normal colon, or to a variety of normal adult human tissues tested using immunohistochemical techniques. B72.3 immunoglobulin G was purified and radiolabeled with 125I without significant loss in its reactivity to tumor extracts. The radiolabeled B72.3 immunoglobulin G was shown to efficiently localize human colon carcinoma xenografts in athymic mice. Tumor:tissue ratios of the localized antibody rose over the 7-day period studied, with tumor:liver, tumor:spleen, or tumor:kidney ratios of approximately 18:1 at Day 7 and a tumor:blood ratio of approximately 5:1 at Day 7. Tumor:muscle or tumor:brain ratios rose to over 100:1. The amount of radioactivity in the tumor increased for the first 2 days postinoculation of antibody and stayed constant over a 19-day period of study. Thus, there was no appreciable loss of radioiodine from the tumor over the study interval. No localization was seen in mice bearing a B72.3 antigen-negative human melanoma xenograft or with an isotype-identical control immunoglobulin G in mice bearing colon tumor xenografts. Gamma camera imaging with a pinhole collimator confirmed the ability of the radiolabeled antibody to detect the presence of colon carcinoma xenografts less than 0.5 cm in diameter over a 19-day period. The potential use of this system as a model for radioimmunotherapy will be discussed.
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000302:isolation & purification; D000951:Antigens, Neoplasm / Q000032:analysis*; D002460:Cell Line; D003110:Colonic Neoplasms / Q000000981:diagnostic imaging / Q000276:immunology*; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006023:Glycoproteins / Q000032:analysis; D006801:Humans; D007457:Iodine Radioisotopes; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D011863:Radioimmunoassay / Q000379:methods; D011877:Radionuclide Imaging; D014183:Transplantation, Heterologous
chemical_list: D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm; D006023:Glycoproteins; D007457:Iodine Radioisotopes