Radioimmunoscintigraphy of human colon cancer xenografts in mice with radioiodinated monoclonal antibody B72.3

Monoclonal antibody B72.3 reacts with a tumor-associated antigen that is found on human breast and colon carcinomas in significantly higher concentration than in normal adult tissues. Intact B72.3 lgG was labeled with I-131 or I-125 and injected into athymic mice bearing xenografts of human colon cancer. Whole-body scintiphotos obtained with a pinhole collimator demonstrated tumor localization within 24 hr after intravenous administration, and the tumor-to-background ratio rose continuously for at least 14 days. Progressive antibody accumulation was observed in the tumor during the first 3 days, but no significant normal organ localization was observed at any time. No localization was seen in control tumors, a human melanoma xenograft that lacks the antigen recognized by B72.3. The pharmacokinetics of this antibody in tumor-bearing mice suggest that I-131 B72.3 may be useful for radioimmunotherapy as well as radioimmunoscintigraphy of colon cancer in man