Abstract B234: Dual targeting of the tyrosine kinase receptors EGFRvIII and c-Met in glioblastoma multiforme

Abstract

Abstract The most common mutation of the epidermal growth factor receptor (EGFR) in glioblastoma multiforme (GBM) is an extracellular truncation of 267 amino acids known as EGFRvIII (or de2-7 EGFR). While the EGFRvIII is unable to bind any known ligand, it displays a low level of constitutive activation that is enhanced by its inability to undergo downregulation. HGF/SF is the ligand for the receptor tyrosine kinase c-Met, both of which are often co-expressed in GBM. The presence of the HGF/c-Met axis or expression of EGFRvIII each independently enhances GBM growth, angiogenesis capacity, migration and invasiveness. Using tyrosine kinase array technology, we now show that expression of EGFRvIII in U87MG glioblastoma cells (U87MG. 2-7 cells) leads to co-activation of several receptor tyrosine kinases, including PDGFR and c-Met. A fully human neutralizing antibody directed to HGF (AMG 102) did not inhibit this EGFRvIII mediated activation of c-Met in vitro, demonstrating that it is ligand independent. We examined if this transactivation of c-Met influenced the efficacy of therapies targeting the HGF:c-Met axis. Treatment of parental U87MG xenografts with low doses of AMG 102 resulted in significant inhibition of tumor growth (see Burgess et al. 2006), while U87MG. 2-7 xenografts (see Johns et al 2007) were profoundly resistant to AMG 102 treatment. Treatment with Panitumumab, a fully human antibody directed to the EGFR and EGFRvIII, was able to inhibit the EGFRvIII mediated activation of c-Met and significantly reversed the resistance to AMG 102 observed in U87MG. 2-7 xenografts. Indeed, combination therapy with Panitumumab and AMG 102 resulted in a marked increase in tumor cell apoptosis, especially in the central parts of the xenograft. An EGFRvIII molecule with an active kinase but incapable of autophosphorylation at the five major autophosphorylation sites (tyrosine changed to phenylalanine) involved in signal transduction was also able to mediate resistance to AMG 102, suggesting that the activation of c-Met by EGFRvIII occurs via a direct interaction rather than through these docking sites. These studies show that expression of EGFRvIII leads to the promiscuous activation of several kinases, causing resistance to ligand inhibitory based strategies. Since Panitumumab can reverse this process, the combination of this antibody with AMG 102 may be an effective treatment for GBM patients positive for EGFRvIII. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B234.