Localization of human osteogenic sarcoma xenografts in nude mice by a monoclonal antibody labeled with radioiodine and indium-111.

Monoclonal antibody OST7 reacts specifically with human osteogenic sarcoma. Whole immunoglobulin G (IgG) and the F(ab')2 fragment of OST7 were labeled with radioiodine and indium-111 (111I), and injected into athymic nude mice bearing xenografts of human osteogenic sarcoma (KT005). All radiolabels retained their antigen-binding activities allowing clear visualization of transplanted tumors. Tissue distribution, however, varied. The net tumor concentration of 111In-lableled whole IgG was higher and was retained longer than that of radioiodinated one, but 111In-labeled antibody showed a lower tumor-to-liver and tumor-to-kidney ratio. In radioiodinated OST7, F(ab')2 fragments provided much better images with much higher tumor-to-tissue ratios than whole IgG. Using F(ab')2 fragments as a carrier for 111In, little image improvement was obtained due to the high radioactivity in the liver and kidney. The different distributions among these radiolabels suggest that the choice between intact igG and F(ab')2 fragments and between radioiodine and 111In depends on the intended use.