Site-specific radiolabeling of monoclonal antibodies with biotin/streptavidin

Sulfhydryl groups of a murine IgG2a monoclonal antibody, 5G6.4, were site-specifically biotinylated with N-iodo-acetyl- N′-biotinylhexylenediamine (compound 1) following partial reduction of disulfide bonds. Antibody labeling using fluoresceinated or [ 125I]streptavidin were consistent with sulfhydryl group-specific incorporation of label with good retention of immunoreactivity, mainly in the form of high molecular weight oligomers (molecular weight ≈ > 400,000). In vivo localization of the radioantibody complex to xenografts of ovarian carcinoma was achieved. This approach appears to be a promising method of labeling monoclonal antibodies.