Construction, expression, and characterization of an anti-tumor immunotoxin containing the human anti-c-Met single-chain antibody and PE38KDEL.

Recombinant immunotoxins consisting of small antibody fragments fused to cytotoxic moieties are being evaluated for use in prospective antibody-targeted cancer therapies. A receptor tyrosine kinase known as c-Met is overexpressed in a vast range of human malignancies, making it an ideal target for antibody-mediated delivery of numerous cytotoxic agents. A single Fab molecule capable of binding to human c-Met with high affinity and specificity was previously identified using antibody phage-display technology. In order to develop a molecule to increase both the cytotoxicity and anti-tumor activity of the anti-c-Met molecule, a recombinant immunotoxin anti-c-Met/PE38KDEL was constructed and expressed by fusing the human anti-c-Met single-chain variable fragment (ScFv) with a modified Pseudomonas exotoxin A (PE38KDEL). Purified anti-c-Met/PE38KDEL was demonstrated to specifically bind to cells of c-Met-positive human hepatoma cell lines, causing a proliferation defect by inducing caspase-3/8-mediated apoptosis, as observed by in vitro assays. Furthermore, anti-c-Met/PE38KDEL administration was shown to inhibit the growth of hepatocellular carcinoma xenografts in vivo through suppression of Ki-67 expression and enhancement of tumor cell apoptosis rates. Cumulatively, the current findings demonstrate the successful construction of a recombinant immunotoxin capable of accurately targeting c-Met-positive human hepatoma cell lines both in vitro and in vivo, providing a novel compound with potential for applications as an alternative therapy for c-Met-positive cancer management.