Comparative biodistributions of yttrium- and indium-labeled monoclonal antibody B72.3 in athymic mice bearing human colon carcinoma xenografts.

The biodistribution of yttrium- and indium-labeled monoclonal antibody (MAb) B72.3 IgG using three different chelate conjugates (SCN-Bz-EDTA, CA-DTPA, and SCN-Bz-DTPA) was compared in athymic mice bearing LS-174T tumors. The 88Y-SCN-Bz-DTPA-B72.3 yielded 40% ID/g at 5-7 days in the tumors, while the 88Y-SCN-Bz-EDTA-B72.3 and 88Y-CA-DTPA-B72.3 showed only 6-8% ID/g. The yttrium uptake in the bone with the SCN-Bz-EDTA and CA-DTPA conjugated IgG was over 14 and 11% ID/g, respectively, while 88Y-SCN-Bz-DTPA-B72.3 showed only 3% ID/g. In contrast, the 111In-labeled B72.3 uptake in the bone with all three chelate conjugates was 2-3% ID/g. The differences in yttrium- versus indium-labeled MAb biodistributions demonstrate the difficulty in using 111In-labeled MAbs to predict the biodistribution and dosimetry of 90Y-labeled MAbs unless chelate conjugates such as SCN-Bz-DTPA are used.