Metastatic colorectal cancer: radioimmunoscintigraphy with a stabilized In-111-labeled F(ab')2 fragment of an anti-CEA monoclonal antibody.

Metastatic colorectal cancer was detected with stabilized F(ab')2 fragments of ZCE-025, an anti-carcino-embryonic antigen (CEA) monoclonal antibody (MoAb). The fragments were prepared by cross-linking Fab' with a bifunctional cross-linking agent, bis-(maleimido)methyl ether. The authors labeled 2 mg of ZCE-025 with 5 mCi (185 MBq) of indium-111 and injected the material intravenously, either alone or with unlabeled F(ab')2, into 16 patients. Lesion detection, pharmacokinetics, and relative body distribution were evaluated and compared with those of the intact immunoglobulin (IgG1) antibody. Stabilized F(ab')2 fragments were more useful than the intact antibody in detection of lesions: Overall sensitivity of F(ab')2 fragments for all the patients was 79.4%, whereas overall sensitivity of the intact IgG1 antibody was 32%. This anti-CEA-stabilized F(ab')2 fragment may be a powerful diagnostic tool that can achieve higher sensitivity at smaller protein doses than the intact IgG1 antibody.