Production, Binding and Cytotoxicity of Human/Mouse Chimeric Monoclonal Antibody-Neocarzinostatin Conjugate

A human/mouse chimeric Fab monoclonal antibody A7 (chFabA7) was covalently coupled to neocarzinostatin (NCS) by the SPDP method at various chFabA7:NCS substitution ratios. The antigen-binding activity of the conjugate, examined by ELISA using fixed antigen-positive colon cancer cells, was identical to that of the parent chFabA7 when one mole of NCS was conjugated, but was reduced with 2 or 3 moles of conjugated NCS. By means of a colony-forming assay, the cytocidal effect of the conjugate on antigen-positive cancer cells was found to be stronger than that of free NCS, whereas in antigen-negative cancer cells it was similar to that of free NCS. This effect was attenuated by adding an excess amount of monoclonal antibody A7. These findings indicate that the conjugate has an antigen-specific cytocidal action, and thus chFabA7-NCS is a promising tool for targeting cancer chemotherapy.