ABSTRACT
Met, the high affinity receptor for hepatocyte growth factor, is 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 hepatocyte growth factor/Met-mediated biological activities. However, DN-30 binding to Met also results in partial activation of the Met kinase due to antibody-mediated receptor homodimerization. To safely harness the therapeutic potential of DN-30, its shedding activity must be disassociated from its agonistic activity. Here we show that the DN-30 Fab fragment maintains high affinity Met binding, elicits efficient receptor shedding and down-regulation, and does not promote kinase activation. In Met-addicted tumor cell lines, DN-30 Fab displays potent cytostatic and cytotoxic activity in a dose-dependent fashion. DN-30 Fab also inhibits anchorage-independent growth of several tumor cell lines. In mouse tumorigenesis assays using Met-addicted carcinoma cells, intratumor administration of DN-30 Fab or systemic delivery of a chemically stabilized form of the same molecule results in reduction of Met phosphorylation and inhibition of tumor growth. These data provide proof of concept that monovalency unleashes the full therapeutic potential of the DN-30 antibody and point at DN-30 Fab as a promising tool for Met-targeted therapy.
Subject(s)
Antibodies, Anti-Idiotypic/pharmacology , Antibodies, Monoclonal/pharmacology , Neoplasms/drug therapy , Proto-Oncogene Proteins c-met/immunology , Animals , Antibodies, Anti-Idiotypic/immunology , Antibodies, Anti-Idiotypic/metabolism , Antibodies, Monoclonal/immunology , Antibodies, Monoclonal/metabolism , Antibody Affinity/immunology , Apoptosis/drug effects , Binding, Competitive , Blotting, Western , Cell Adhesion/drug effects , Cell Line, Tumor , Cell Proliferation/drug effects , Female , HCT116 Cells , Humans , Immunoglobulin Fab Fragments/immunology , Immunoglobulin Fab Fragments/metabolism , Immunoglobulin Fab Fragments/pharmacology , Immunoprecipitation , Mice , Mice, Nude , Neoplasms/metabolism , Neoplasms/pathology , Protein Binding , Proto-Oncogene Proteins c-met/metabolism , Signal Transduction/drug effects , Tumor Burden/drug effects , Xenograft Model Antitumor AssaysABSTRACT
Matriptase, also known as membrane-type-serine-protease 1 (MT-SP 1), is a type II transmembrane serine protease involved in the activation of the precursor form of hepatocyte growth factor/scatter factor (pro-HGF/SF). Since HGF/SF is a well-known extracellular signal, which plays a key role in the control of invasive growth, we investigated the effects of matriptase inhibition in cell lines derived from colon (DLD-1) or prostate (PC-3) carcinomas. Biochemical analysis showed that matriptase was very efficient in the proteolytic conversion of the inactive HGF/SF precursor into HGF/SF. Inhibition of endogenous matriptase synthesis in DLD-1 or PC-3 cells by specific small interfering RNAs impaired the conversion of pro-HGF/SF into HGF/SF at the cell surface and inhibited cell scattering upon pro-HGF/SF stimulation. The same effect was observed after treatment of these cells with matriptase inhibitors of the 3-amidinophenylalanine-type, CJ-697 or CJ-730. Inhibition of matriptase significantly reduced invasion of the extracellular matrix as well. Interestingly, this reduction was observed even in the presence of pre-activated HGF/SF. It is concluded that matriptase plays a dual-role in the events unleashing the invasive phenotype, one 'upstream' from the HGF/SF signalling cascade and one 'downstream', most likely at the level of the plasminogen activation system. These data provide a proof of concept for the targeting of matriptase in the search for anti-invasive drugs.
