RADIOLABELED CHIMERIC ANTI-CEA MONOCLONAL-ANTIBODY COMPARED WITH THE ORIGINAL MOUSE MONOCLONAL-ANTIBODY FOR SURGICALLY TREATED COLORECTAL-CARCINOMA

Biodistribution and tumor uptake of a chimeric human-mouse monoclonal antibody (MAb) and the original mouse MAb have been comparatively stud ied. Methods: Eighteen patients with suspected colorectal cancer sched uled for surgery underwent immunoscintigraphy with I-123-labeled chime ric anti-CEA MAb. iodine-125 and I-131 trace-labeled chimeric and orig inal mouse MAb were simultaneously injected for biodistribution studie s. Results: Similar serum kinetics and a low immunogenicity were obser ved for both antibodies. Mean binding capacity to CEA measured in PBS after radiolabeling was identical for both MAbs and it was slightly de creased when measured in serum 1-4 hr after injection. Radiochromatogr ams of patients sera showed immune complex formation related to the am ount of circulating CEA. Postoperative ex vivo radioactivity counting in tissue samples revealed similar antibody distributions with notably similar antibody uptakes in tumors. High tumor uptakes (between 0.02 to 0.06% injected dose per g) were observed in 3 of 13 patients operat ed for primary or metastatic colorectal cancer. Conclusion: In this du al-label technique, the radioiodinated anti-CEA IgG(4) chimeric MAb an d the original mouse IgG(1) MAb were shown to have very similar behavi or in colorectal cancer patients.