Abstract 2448: h224G11, a humanized whole antibody targeting the c-Met receptor, induces c-Met down-regulation and triggers ADCC functions

Abstract

Abstract c-Met is the prototypic member of a sub-family of receptor tyrosine kinases (RTK) which also includes RON and SEA. The c-Met RTK family is structurally different from other RTK families and is the only known high-affinity receptor for hepatocyte growth factor (HGF), also called scatter factor (SF). While the controlled regulation of c-Met and HGF are essential for in mammalian development, tissue maintenance and repair, their deregulation is implicated in the progression of cancers. Aberrant signalling of c-Met can arise by ligand-dependent and independent mechanisms such as over-expression of c-Met, paracrine or autocrine activations, or through gain of function mutations. However, an oligomerization of the c-Met receptor, either in the presence or absence of the ligand, is required to regulate the binding affinity and binding kinetics of the kinase toward ATP and tyrosine-containing peptide substrates. An inappropriate c-Met activation plays a crucial role in tumorigenesis and metastasis. We have generated, a humanized anti-c-Met IgG1 monoclonal antibody (h224G11) that displays fully antagonist activities when used as a whole antibody. The h224G11 Mab exhibits a high affinity for the receptor, blocks HGF binding, inhibits c-Met phosphorylation and c-Met dimerization. These effects are presumably responsible for the inhibition of the major functions of c-Met including cell proliferation, migration, invasion but also cell scattering and angiogenesis, observed in vitro with different cell lines. In addition to these in vitro properties, h224G11 dramatically inhibits in vivo growth of autocrine (U87-MG), partially autophosphorylated (NCI-H441) and c-Met amplified cell lines (MKN45, EBC1 and Hs746T). Recent in vitro experiments demonstrate that h224G11 down-regulates c-Met on many cells including A549 and NCI-H441. Using an ELISA immunoassay, it has been shown that this down-regulation does not result from a shedding process but that h224G11 induces c-Met internalization and degradation. Similar results were obtained in ex-vivo experiments using Hs764T tumors from xenografted mice. In addition to its direct effect on c-Met modulation, the humanized antibody also triggers effector functions. A549, NCI-H441 and Hs746T were used as target cells in an ADCC chromium-released assay with human purified NK cells. In these assays, the h224G11 demonstrates a significant ADCC activity. Taken together the in vitro and in vivo data suggest that the h224G11 antibody targeting c-Met is a promising candidate for the treatment of ligand-dependent and ligand-independent tumors as a single or combined therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2448.