Targeted anticancer therapy by a recombinant monovalent antibody against the MET oncogene

The Met oncogene encodes the high affinity receptor for Hepatocyte Growth Factor (HGF), one of the most frequently activated tyrosine kinases in human cancer and a validated target for cancer therapy. We previously developed a mouse monoclonal antibody directed against the extracellular portion of Met (DN-30) that induces Met proteolytic cleavage (receptor ‘shedding’) followed by proteasome-mediated receptor degradation. This translates into inhibition of HGF/Met-mediated biological responses. To safely harness the therapeutic potential of DN-30, the shedding activity must be disassociated from agonistic activity. This was achieved by chemical modification of a genetically engineered DN-30 Fab fragment that (a) maintains high affinity Met binding, (b) elicits efficient receptor shedding and down-regulation, without promoting kinase activation and (c) displays potent cytostatic and cytotoxic activity in vitro, in a dose-dependent fashion. In mouse transplantation assays using Met-’addicted’ carcinoma cells, intra-tumor administration of native DN-30 Fab, or systemic delivery of its chemically stabilized form, results in reduction of Met phosphorylation and inhibition of tumor growth. As an autocrine-loop of HGF and MET is present in a sub-type of glioblastoma, a gene therapy approach was explored. Lentiviral vector transfer in mice harbouring a transplanted U-87MG glyoblastoma of the recombinant DN-30 gene, under a Tet-inducible promoter, resulted in suppression of tumor growth (if the antibody gene was turned-on at time zero of the transplant) and complete (22% of mice) or significant (55% of mice) inhibition (if the antibody was turned on in animals harboring 50 mm3 tumors). These data provide proofs-ofconcept about the therapeutic potential of the DN-30 antibody for Met-target therapy.