Recombinant Immunotoxin 4D5scFv-PE40 for Targeted Therapy of HER2-Positive Tumors.

Recombinant immunotoxins are extremely promising agents for the targeted therapy of tumors with a certain molecular profile. In this work, we studied the properties of a new recombinant HER2-specific immunotoxin composed of the scFv antibody and a fragment of Pseudomonas exotoxin A (4D5scFv-PE40). High affinity of the immunotoxin for the HER2 tumor marker, its selective cytotoxicity against HER2-overexpressing cells, and its storage stability were demonstrated. The 50% inhibitory concentration (IC50) of the 4D5scFv-PE40 immunotoxin for HER2-overexpressing cancer cells was 2.5-3 orders of magnitude lower compared to that for CHO cells not expressing this tumor marker and was 2.5-3 orders of magnitude lower than IC50 of free PE40 for HER2-overexpressing cancer cells. These findings provide a basis for expecting in the long run high therapeutic index values of the 4D5scFv-PE40 immunotoxin for its use in vivo.