Epidermal Growth Factor Receptor Activation in Glioblastoma through Novel Missense Mutations in the Extracellular Domain (original) (raw)
Pathology oncology research : POR, 2009
Gefitinib and erlotinib are both selective EGFR tyrosine kinase inhibitors (EGFR-TKIs) that have produced responses in a small subgroup of lung cancer patients. The strongest evidence for a role of EGFR in the biology of glioblastoma stems from clinical trials in which 15-20% of recurrent glioblastoma patients experienced significant tumour regression in response to these small-molecule EGFR kinase inhibitors. We examined the protein-kinase domain of the EGFR gene, EGFR protein expression and EGFR gene amplification in 20 cases of recurrent GBMs. EGFR protein over-expression was found in 65% of cases. EGFR protein over-expression was associated with EGFR gene amplification in 35% of cases, and with high polysomy in 15% of cases. No mutations were found in the TK domain of the EGFR gene. Our results confirm that mutations in the kinase domain are absent in recurrent GBM, and this might be a preponderant factor in the lack of major clinical responses of TKIs in GBM, recent studies hav...
Cancer Research, 2011
Genomic alterations of the epidermal growth factor receptor (EGFR) gene play a crucial role in pathogenesis of glioblastoma multiforme (GBM). By systematic analysis of GBM genomic data, we have identified and characterized a novel exon 27 deletion mutation occurring within the EGFR carboxyl-terminus domain (CTD) in addition to identifying additional examples of previously reported deletion mutations in this region. We show that the GBM-derived EGFR CTD deletion mutants are able to induce cellular transformation in vitro and in vivo in the absence of ligand and receptor autophosphorylation. Treatment with the EGFR-targeted monoclonal antibody, cetuximab, or the small molecule EGFR inhibitor, erlotinib, effectively impaired tumorigenicity of oncogenic EGFR CTD deletion mutants. Cetuximab in particular prolonged the survival of intracranially xenografted mice with oncogenic EGFR CTD deletion mutants, compared to untreated control mice. Therefore, we propose that erlotinib and especially cetuximab treatment may be a promising therapeutic strategy in GBM patients harboring EGFR CTD deletion mutants.
Cancer research, 2015
Epidermal growth factor receptor (EGFR) is highly amplified, mutated and overexpressed in human malignant gliomas. Despite its prevalence and growth-promoting functions, therapeutic strategies to inhibit EGFR kinase activity have not been translated into profound beneficial effects in glioma clinical trials. To determine the roles of oncogenic EGFR signaling in gliomagenesis and tumor maintenance, we generated a novel glioma mouse model driven by inducible expression of a mutant EGFR (EGFR*). Using combined genetic and pharmacological interventions, we revealed that EGFR*-driven gliomas were insensitive to EGFR tyrosine kinase inhibitors although they could efficiently inhibit EGFR* auto-phosphorylation in vitro and in vivo. This is in contrast to genetic suppression of EGFR* induction which led to significant tumor regression and prolonged animal survival. But in spite of their initial response to genetic EGFR* extinction, all tumors would relapse and propagate independent of EGFR*...
Nuclear Signaling of EGFR and EGFRvIII in Glioblastoma
The pivotal role of kinases in signal transduction and cellular regulation has lent them considerable appeal as therapeutic targets across a broad spectrum of cancers. The epidermal growth factor receptor (EGFR) was the first receptor tyrosine kinase to be discovered and remains the most investigated. Most of the mechanistic principles of receptor tyrosine kinases were first established with the EGFR family as a model.
2001
Amplification of the epidermal growth factor receptor (EGFR) gene is found in about 40% of glioblastomas (GBMs) but is rarely detected in GBM cell lines. We confirmed that the exceptional SKMG-3 GBM cell line retained amplified EGFR genes in vitro, and found that these sequences were concentrated on extra-chromosomal DNA particles similar to double-minute chromosomes. The cells contained two other gene mutations that are associated with high-grade astrocytic tumors: extrachromosomal amplification of the cyclin-dependent kinase-4 (CDK4) gene and a homozygous mutation within the PTEN tumor suppressor gene. Immunoblots revealed very high levels of EGFR, moderately increased expression of CDK4, and no detectable PTEN protein. The overexpressed SKMG-3 EGFRs responded to exogenous ligand and resembled normal rather than mutant receptors. A heterozygous mutation of the p53 gene (p53 R282W) correlated with failure of radiation to induce the expression of cyclin-dependent kinase inhibitor p21 waf1 or an early G1 cell cycle arrest. Although each of these gene mutations occurs in GBMs, SKMG-3 cells had an unusual genotype in that a p53 gene mutation co-existed with amplified EGFR genes. Nonetheless, the SKMG-3 cell line can be exploited as a model to study how oncogenic EGFR signals in GBM cells interact with over-expressed CDK4 and loss of PTEN to confer the malignant phenotype.
Molecular Cancer Research, 2012
Aberrations in epidermal growth factor receptor (EGFR/ErbB1) are the most common oncogenic alterations in glioblastoma multiforme (GBM), the most common primary brain tumor. Interactions between wild-type (wt) and mutant EGFRs and their subsequent activation are of biologic and potential therapeutic importance in GBMs. We recently showed that in situ proximity ligation assay (PLA) allows for quantitative evaluation of EGFR dimerization and activation in intact cells. Using this in situ platform, we show the aberrant homo-/heterodimeric properties of EGFRvIII and EGFRc958 mutants, the two most common EGFR mutants in GBMs. In addition, dimer phosphoactivation status could be detected by PLA with superior signal-noise ratio (>17-fold) and sensitivity (>16-fold) than immunofluorescence-based phospho-EGFR measurements. Dimer activation analysis indicated quantitative activation differences of mutant dimers. These aberrant features were not overexpression dependent but appeared independent of cellular expression levels, suggesting inherent properties of the mutant receptors. Moreover, we observed in situ detection of EGFRwt-EGFRvIII heterodimerization in GBM specimens, supporting our cell line observations. Notably, currently used anti-EGFR therapeutics, such as cetuximab, matuzumab, and panitumumab, could effectively block EGFRwt dimerization and activation but did not equally impair EGFRvIII homodimers, EGFRwt-EGFRvIII, or EGFRvIII-EGFRc958 heterodimers. EGFRvIII appears to have intrinsic phosphoactivation independent of dimerization as matuzumab blockade of homodimerization had no effect on receptor phosphorylation levels. These data suggest differences in the dimerization-blocking efficacy of EGFR monoclonal antibodies as mutant EGFR dimer configurations prevalent in GBMs can evade blockade by anti-EGFR treatments. Further studies are warranted to evaluate whether this evasion contributes to poor therapeutic response or resistance. Mol Cancer Res; 10(3); 428-40. Ó2012 AACR.
Targeting EGFR for Treatment of Glioblastoma: Molecular Basis to Overcome Resistance
Current Cancer Drug Targets, 2012
Glioblastoma (glioblastoma multiforme; GBM; WHO Grade IV) accounts for the majority of primary malignant brain tumors in adults. Amplification and mutation of the epidermal growth factor receptor (EGFR) gene represent signature genetic abnormalities encountered in GBM. A range of potential therapies that target EGFR or its mutant constitutively active form, EGFR, including tyrosine kinase inhibitors (TKIs), monoclonal antibodies, vaccines, and RNA-based agents, are currently in development or in clinical trials for the treatment of GBM. Data from experimental studies evaluating these therapies have been very promising; however, their efficacy in the clinic has so far been limited by both upfront and acquired drug resistance. This review discusses the current status of anti-EGFR agents and the recurrent problem of resistance to these agents that strongly indicates that a multiple target approach will provide a more favorable future for these types of targeted therapies in GBM.
Amplification and overexpression of the EGF receptor gene in primary human glioblastomas
1985
The expression of epidermal growth factor (EGF) receptor in brain tumours of glial origin was studied at the protein, mRNA and genomic levels. Four out of 10 glioblastomas that overexpress EG F receptor also have gene amplification. The amplified genes appear to be rearranged, generating an aberrant mRNA in at least one of these tumours. Such receptor defects may be relevant to tumorigenesis of human glioblastomas.