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.