Antitumor activity of cetuximab against malignant glioma cells overexpressing EGFR deletion mutant variant III.

Anti-epidermal growth factor receptor (EGFR) monoclonal antibody, cetuximab, is a promising targeted drug for EGFR-expressing tumors. Glioblastomas frequently overexpress EGFR including not only the wild type but also a deletion mutant form called 'variant III (vIII)', which lacks exon 2-7, does not bind to ligands, and is constitutively activated. In this study, we investigated the antitumor activity of cetuximab against malignant glioma cells overexpressing EGFRvIII. For this purpose, we transfected human malignant glioma cell lines with the retroviral vector containing cDNA for EGFRvIII, and analyzed the mode of cetuximab-induced action on the EGFRvIII in the cells. Immunoprecipitation and immunofluorescence revealed binding of cetuximab to EGFRvIII. Notably, immunoblotting analyses showed that cetuximab treatment resulted in reduced expression levels of the EGFRvIII. However, cetuximab alone did not exhibit a growth-inhibitory effect against the EGFRvIII-expressing cells. On the other hand, an assay for antibody-dependent cell-mediated cytotoxicity (ADCC) demonstrated cetuximab-induced cytolysis in the presence of human peripheral blood mononuclear cells in a dose-dependent manner. These results suggest that deletion mutant EGFRvIII can be a target of cetuximab and that ADCC activity substantially contributes to the antitumor efficacy of cetuximab against the EGFRvIII-expressing glioma cells. Thus, cetuximab could be a promising therapy in malignant gliomas that express EGFRvIII.