Localization of colorectal carcinoma by rhenium-188-labeled B72.3 antibody in xenografted mice

In order to evaluate the feasibility of 188Re-labeled antibodies for radioimmunotargeting, monoclonal antibody B72.3, recognizing TAG-72, expressed on the surface membranes of colorectal cancer cells, was directly labeled with 188Re, obtained from a 188W/188Re generator, using stannous tartrate and compared with 125I-labeled B72.3. As a control, a human IgG was also radiolabeled with 188Re and 125I. Prepared antibodies for 188Re labeling could be stored as kits. Biodistribution was determined in nude mice inoculated with human colorectal carcinoma LoVo. Labeling efficiency and immunoreactivity of 188Re-B72.3 were 80.3% and 64.7%, respectively. 188Re-B72.3 localized specifically in the LoVo tumors. Although the absolute tumor accumulation level of 188Re-B72.3 was lower than 125I-B72.3, 188Re-B72.3 demonstrated higher tumor-to-blood contrast than the 125I-labeled counterpart, 2.04±0.44 vs. 1.05±0.28 at 96 hours, because of fast clearance from the blood. 188Re-B72.3 seemed efficient for the imaging and therapy of colorectal carcinoma. (author)