Humanization and directed evolution of the selenium-containing scFv phage abzyme

According to the binding site structure and the catalytic mechanism of the native glutathione peroxidase (GPX), three glutathione derivatives, GSH-S-DNP butyl ester (hapten Be), GSH-S-DNP hexyl ester (hapten He) and GSH-S-DNP hexamethylene ester (hapten Hme) were synthesized. By a four-round panning with a human synthetic scFv phage library against three haptens, the enrichment of the scFv phage particles with specific binding activity could be determined. Three phage particles were selected binding to each glutathione derivative, respectively. After a two-step chemical mutation to convert the serine residues of the scFv phage particles into selenocysteine residues, GPX activity could be observed and determined upto 3000 U μmol^-1 in the selenium-containing scFv phage abzyme which was isolated by affinity capture against the hapten Be. Also the scFv phage abzymes elicited by different antigens displayed different catalytic activities. After a directed evolution by DNA shuffling to improve the affinity to the hapten Be, a secondary library with GPX activity was created in which the catalytic activity of the selenium-containing scFv phage abzyme could be increased 17%. This study might be helpful for new haptens or antigens design to optimize the abzymes with high binding activities and might also provide a novel scheme for GPX mimic candidates for drug development.

Antibody-enzyme fusion proteins for cancer therapy

Advances in biomolecular technology have allowed the development of genetically fused antibody-enzymes. Antibody-enzyme fusion proteins have been used to target tumors for cancer therapy in two ways. In one system, an antibody-enzyme is pretargeted to the tumor followed by administration of an inactive prodrug that is converted to its active form by the pretargeted enzyme. This system has been described as antibody-directed enzyme prodrug therapy. The other system uses antibody-enzyme fusion proteins as direct therapeutics, where the enzyme is toxic in its own right. The key feature in this approach is that the antibody is used to internalize the toxic enzyme into the tumor cell, which activates cell-death processes. This antibody-enzyme system has been largely applied to deliver ribonucleases. This article addresses these two antibody-enzyme targeting strategies for cancer therapy from concept to (pre)clinical trials.