Effect of a monoclonal anti-carcinoembryonic antigen antibody-ricin A-chain conjugate on human carcinoembryonic antigen-producing tumor cells.

For the development of therapeutic agents that are coupled to tumor specific carriers, an artificial protein hybrid conjugate (immunotoxin) containing monoclonal anti-carcinoembryonic antigen (CEA) antibody which binds specifically to the cell surface of CEA-producing tumor cells and a toxic subunit of ricin (A-chain) was prepared. This conjugate exerted strong cytotoxicity specifically toward CEA-producing tumor cells in vitro. In vivo, it has anti-tumor effects on ascitic tumor cells, and on free tumor cells before the solid tumor has been established. However, for the established solid tumor, a significant decrease of tumor growth was not seen even after repeated intravenous administrations of the antibody-ricin A-chain conjugate. Furthermore, the conjugate was found to be stable in both mouse and human serum in vitro, but after intravenous injection, it was inactivated in vivo quickly.