LYSINE-DIRECTED CONJUGATION OF ETHIDIUM HOMODIMER TO B72.3 MAB - RETENTION OF IMMUNOREACTIVITY AND ALTERED TUMOR TARGETING

Ethidium homodimer (EHD) was conjugated to the anti-TAG monoclonal ant ibody B72.3 via random thiopropionylation of the lysine residues of th e antibody and its reaction with maleimido-functionalized EHD. Three t o four EHD were bound per protein molecule, and they retained their ca pacity to intercalate effectively with DNA (85-90%). Compared with the native antibody, the conjugate maintained full chemical integrity and immunoreactivity, but its targeting of LS174T tumors declined 3-4-fol d and its electrophoretic mobility decreased. While the testing of che mical integrity and immunoreactivity in vitro is important in assessin g the efficacy of an immunoconjugate, these parameters do not necessar ily predict the extent of tumor targeting in vivo.