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

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Abstract
For the development of therapeutic agents that are coupled to tumor specific cariers, an artificial protein hybrid conjugate (immunotoxin) containing monoclonal anticarcinoembryonic 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.