Preparation and characterization of immunotoxin with blocked galactose-binding sites of ricin

In the present study,a specific cytotoxic agent was prepared by linking intact ricin to antibody,in a manner that the galactose-binding sites on the B chain of the ricin were blocked.The ricin was iodoacetyla-ted by N-hydroxy-succinimidyl ester of iodoacetic acid and then treated with thiolated McAb,a murine monoclonal antibody against gastric cancer.The fraction of the conjugate with reduced galactose-binding capacity were separated by affinity chromatography on Sepharose 4B.The binding activity of the antibody in the conjugate retained well at theconcentration of 2 nmol/L.The conjugate showed highly selective cytotoxicity on a gastric cancer cell line KATOⅢ The cytotoxic activity of McAb-ricin was much higher than that of McAb-ricin A chain,suggesting that this conjugate has both high potency,which is often lacked in antibody-A chain conjugate,and high specificity,which is lacked in intact ricin.