Epidermal Growth Factor Receptor Activation in Glioblastoma through Novel Missense Mutations in the Extracellular Domain

Abstract

BackgroundProtein tyrosine kinases are important regulators of cellular homeostasis with tightly controlled catalytic activity. Mutations in kinase-encoding genes can relieve the autoinhibitory constraints on kinase activity, can promote malignant transformation, and appear to be a major determinant of response to kinase inhibitor therapy. Missense mutations in the EGFR kinase domain, for example, have recently been identified in patients who showed clinical responses to EGFR kinase inhibitor therapy.Methods and FindingsEncouraged by the promising clinical activity of epidermal growth factor receptor (EGFR) kinase inhibitors in treating glioblastoma in humans, we have sequenced the complete EGFR coding sequence in glioma tumor samples and cell lines. We identified novel missense mutations in the extracellular domain of EGFR in 13.6% (18/132) of glioblastomas and 12.5% (1/8) of glioblastoma cell lines. These EGFR mutations were associated with increased EGFR gene dosage and conferred anchorage-independent growth and tumorigenicity to NIH-3T3 cells. Cells transformed by expression of these EGFR mutants were sensitive to small-molecule EGFR kinase inhibitors.ConclusionsOur results suggest extracellular missense mutations as a novel mechanism for oncogenic EGFR activation and may help identify patients who can benefit from EGFR kinase inhibitors for treatment of glioblastoma.

Comparison of automated silver enhanced in situ hybridization and fluorescence in situ hybridization for evaluation of epidermal growth factor receptor status in human glioblastomas

“…The incidence of EGFR amplification detected with silver enhanced in situ hybridization was 28% (fluorescence in situ hybridization 30%), according to previous literature. 25,26 The concordance rate between fluorescence in situ hybridization and silver enhanced in situ hybridization was 98% (k ¼ 0.95, 95% CI), demonstrating that silver enhanced in situ hybridization is a valid alternative testing method for the determination of EGFR-amplification status in glioblastoma. These results are consistent with previous studies reporting on concordance rates for HER2 silver enhanced in situ hybridization vs. fluorescence in situ hybridization of 96% (k ¼ 0.75, 95% CI) and 99%.…”

Epidermal growth factor receptor activation in prostate cancer by three novel missense mutations

“…In lung cancer, cells whose growth depends on EGFR with mutations in exons 19 and 21 are sensitive to tyrosine kinase inhibitors of EGFR (Lynch et al, 2004;Paez et al, 2004;Pao et al, 2004;Bell et al, 2005;Choi et al, 2007). Glioblastoma cells transformed by expression of these EGFR mutants were sensitive to small-molecule EGFR kinase inhibitors (Lee et al, 2006). We are in the process of testing anti-EGFR drugs, including several classes of EGFR inhibitors (small molecules, monoclonal antibodies and the HSP90 inhibitor 17AAG) to determine whether these mutations in prostate cancer have differential responses to EGFR inhibitors.…”

“…Recently, either point or deletion mutations of the EGFR kinase domain have been associated with a number of human cancers, including lung, head/neck and brain tumors (Paez et al, 2004;Pao et al, 2004;Bell et al, 2005;Lee et al, 2005Lee et al, , 2006Nagahara et al, 2005). The L858R EGFR mutation, also alternatively identified as L834R for the human EGFR sequence occuring in lung and head neck cancer, has been extensively studied and serves as a prototype for EGFR kinase domain mutational studies in many other cancers.…”

Autophosphorylation of the carboxyl‐terminal domain is not required for oncogenic transformation by lung‐cancer derived EGFR mutants

“…Aberrant activation of EGFR is among the most common oncogenic driving events in human cancer, which is mediated largely through different classes of genomic alterations within the EGFR gene 2. These genomic events include somatic EGFR mutations within regions of either the extracellular domain, in glioblastoma, or the kinase domain in lung adenocarcinoma,3, 4 as well as through gene amplification as observed in many other types of solid tumors 5, 6. In addition, several intragenic deletions within either the extracellular or C‐terminal domain of EGFR have also been reported to be oncogenic in a subset of glioblastoma and lung adenocarcinoma 7, 8, 9…”