[Cytotoxicity to hepatoma BEL-7402 cells of an antitumor monoclonal antibody-streptonigrin conjugate].

Streptonigrin, a highly active antitumor antibiotic, was covalently conjugated to anti-human hepatoma monoclonal antibody 3A5 via the active ester method. The conjugate showed biological activities and UV spectra characteristics of streptonigrin and McAb 3A5. The molar ratio of streptonigrin to 3A5 was 2-6:1, with protein recovery of 76%. The conjugate retained 12.5% of drug activity and nearly full antibody activity, though as the number of streptonigrin molecules in the conjugate increased, the antibody activity of the conjugate decreased. As determined by clonogenic assay with human hepatoma BEL-7402 cells in vitro, the inhibitory potency of the conjugate was 63-fold stronger than that of free streptonigrin. For KB cells (which react weakly with 3A5) the cytotoxicity was 11-fold weaker. The results indicate that the McAb 3A5-streptonigrin conjugate is selective for target cells.