Localization of Sarcoma Xenografts in Nude Mice with Indium-111-Labeled Monoclonal Antibodies

A labeling method utilizing modified carbohydrate moieties in antibody heavy chains as radionucleotide binding sites was evaluated. Murine anti-sarcoma monoclonal antibody (MAb 19-24) was labeled with Indium-111 (111In) using this technique and subcutaneous human sarcoma xenografts were successfully localized in nude mice. A nonspecific monoclonal antibody BL-3 was used as a negative control. Tumor-to-blood ratios of radioactivity in the mice injected with 111Inlabeled MAb 19-24 were significantly (P < 0.05) higher than those obtained with nonspecific MAb BL-3. Calculations of percentage injected dose of radioactivity per gram tissue showed relatively high specific uptake of MAb 19-24 in sarcoma xenografts. Radioactivity cleared from the blood rapidly and hepatic uptake of 111In-labeled antibodies was found to be relatively low. Biodistribution studies in normal mice with 111In-labeled antibodies showed only blood pool activity with no significant concentration of activity into organs. Therefore, immunoreactivity of the antibodies was retained after 111In-labeling utilizing this new technique, allowing specific binding of radiolabeled MAb to tumor xenografts with relatively low hepatic uptake.