HIGH-AFFINITY RECOMBINANT PHAGE ANTIBODIES TO THE PAN-CARCINOMA MARKER EPITHELIAL GLYCOPROTEIN-2 FOR TUMOR TARGETING

The tumour-associated antigen epithelial glycoprotein-2 (EGP-2) is a p romising target for detection and treatment of a variety of human carc inomas. Antibodies to this antigen have been successfully used in pati ents for imaging of small-cell lung cancer and for adjuvant treatment of minimal residual disease of colon cancer. We describe here the isol ation and complete characterization of high-affinity single-chain vari able fragments (scFv) to the EGP-2 antigen. First, the binding kinetic s of four murine whole antibodies directed to EGP-2 (17-1A, 323/A3, MO C-31 and MOC-161) were determined using surface plasmon resonance (SPR ). The MOC-31 antibody has the lowest apparent off-rate, followed by M OC-161 and 323/A3. The V-genes of the two MOC hybridomas were cloned a s scFv in a phage display vector and antigen-binding phage were select ed by panning on recombinant antigen. The scFvs compete with the origi nal hybridoma antibodies for binding to antigen and specifically bind to human carcinomas in immunohistochemistry. MOC-31 scFv has an off-ra te which is better than those of the bivalent 17-1A and 323/A3 whole a ntibodies, providing it with an essential characteristic for tumour re tention in vivo. The availability of these high-affinity anti-EGP-2 an tibody fragments and of their encoding V-genes creates a variety of po ssibilities for their future use as tumour-targeting vehicles.