Receptor tyrosine kinases (RTKs) are key regulators of critical cellular processes such as cell growth, differentiation, neo-vascularization, and tissue repair. In addition to their importance in normal physiology, aberrant expression of certain RTKs has been implicated in the development and progression of many types of cancer. These RTKs have emerged as promising drug targets for cancer therapy.
The RTK c-Met is the cell surface receptor for hepatocyte growth factor (HGF), also known as scatter factor (Cooper et al. Nature 1984; 311:29-33; Bottaro et al. Science 1991; 251:802-4). HGF is a 90 kD multidomain glycoprotein that is highly related to members of the plasminogen serine protease family. It is secreted as a single-chain, inactive polypeptide by mesenchymal cells and is cleaved to its active a/3 heterodimer extracellular form by a number of proteases (Birchmeier et al. Nat Rev Mol Cell Biol 2003; 4:915-25). The α chain NH2-terminal portion contains the high-affinity c-Met receptor-binding domain, but the β chain is required to interact with the c-Met receptor for receptor activation (Matsumoto & Nakamura Cancer Sci 2003; 94:321-7). The c-Met receptor, like its ligand, is a disulfide-linked heterodimer consisting of extracellular α and β chains. The α chain, heterodimerized to the amino-terminal portion of the β chain, forms the major ligand-binding site in the extracellular domain. The carboxy-terminal tail of c-Met includes tyrosines Y1349 and Y1356, which, when phosphorylated, serve as docking sites for intracellular adaptor proteins, leading to downstream signaling (Ponzetto et al. Mol Cell Biol 1993; 13:4600-8). The c-Met/HGF pathway is the main driver of the invasive growth program, a series of events including cell proliferation, scattering, migration, survival, and invasion of tissues. Under normal circumstances, the invasive growth program is essential for correct organ formation during embryogenesis and in adult homeostasis. Importantly, it is also involved in tumorigenesis, tumor angiogenesis and metastasis.
The use of HGF- or c-Met-specific antibodies that prevent ligand/receptor binding result in growth inhibition and tumor regression by inhibiting proliferation and enhancing apoptosis. A combination of three monoclonal antibodies displayed high neutralizing activity to HGF in vitro and in vivo and showed significant tumor growth inhibition against autocrine HGF-Met-expressing glioma xenograft tumors (Cao et al. Proc Natl Acad Sci USA 2001; 98:7443-8). The strategy of using monoclonal antibodies allows for exclusive specificity against HGF/c-Met, a relatively long half-life compared to small-molecule kinase inhibitors, and the potential to elicit a host immune response against tumor cells (Liu et al. Expert Opin Investig Drugs 2008; 17:997-1011).
AMG102 (Amgen, Inc.) is a fully human IgG2 monoclonal antibody that selectively binds and neutralizes HGF, thereby preventing its binding to c-Met and subsequent activation (Kakkar et al. Pharm Res 2007; 24:1910-8; Burgess et al. Cancer Res 2006; 66:1721-9).
One-armed 5D5 (OA5D5, MetMAb; Genentech) is a humanized, monovalent, antagonistic anti-c-Met antibody derived from the agonistic monoclonal antibody 5D5 (Nguyen et al. Cancer Gene Ther 2003; 10:840-9). MetMAb binds to c-Met with high affinity and remains on the cell surface with c-Met, preventing HGF binding and subsequent c-Met phosphorylation as well as downstream signaling activity and cellular responses.
Unfortunately, the use of large monoclonal and/or heavily engineered antibodies also carries a high manufacturing cost and results in suboptimal tumor penetration compared to other strategies.
According to the current biomedical understanding, drug resistance is caused by a complex network of proteins responsible for the regulation of cell proliferation, apoptosis, migration and invasion. Currently, no systematic description of growth factor receptor dependent signaling pathways is available. Indeed, the molecular pathways by which c-Met abnormalities drive cancer development are extremely complex and involve many interconnected signaling pathways, including both signaling molecules (such as Ras and PI3K), receptors (such as EGFR), and growth factors (such as VEGF).
Targeting serum albumin to extend the half-life of biological molecules such as e.g. immunoglobulin single variable domains has been described e.g. in WO2008/028977, WO04/041865 and WO08/122787, and non-published US application U.S. 61/500,464 of 23 Jun. 2011.