Fyn and SRC are effectors of oncogenic epidermal growth factor receptor signaling in glioblastoma patients

Activating epidermal growth factor receptor (EGFR) mutations are common in many cancers including glioblastoma. However, clinical responses to EGFR inhibitors are infrequent and short-lived. We show that the Src family kinases (SFK) Fyn and Src are effectors of oncogenic EGFR signaling, enhancing invasion and tumor cell survival in vivo. Expression of a constitutively active EGFR mutant, EGFRvIII, resulted in activating phosphorylation and physical association with Src and Fyn, promoting tumor growth and motility. Gene silencing of Fyn and Src limited EGFR- and EGFRvIII-dependent tumor cell motility. The SFK inhibitor dasatinib inhibited invasion, promoted tumor regression, and induced apoptosis in vivo, significantly prolonging survival of an orthotopic glioblastoma model expressing endogenous EGFRvIII. Dasatinib enhanced the efficacy of an anti-EGFR monoclonal antibody (mAb 806) in vivo, further limiting tumor growth and extending survival. Examination of a large cohort of clinical samples showed frequent coactivation of EGFR and SFKs in glioblastoma patients. These results establish a mechanism linking EGFR signaling with Fyn and Src activation to promote tumor progression and invasion in vivo and provide rationale for combined anti-EGFR and anti-SFK targeted therapies.

Inhibition of glioblastoma growth in a highly invasive nude mouse model can be achieved by targeting epidermal growth factor receptor but not vascular endothelial growth factor receptor-2

PURPOSE

Major shortcomings of traditional mouse models based on xenografted human glioblastoma cell lines are that tumor cells do not invade and that genetic alterations, such as amplification of the epidermal growth factor receptor (EGFR) gene, are not maintained. Such models are thus of limited value for preclinical studies. We established a highly invasive model to evaluate the effect of antibodies against EGFR (cetuximab) and vascular endothelial growth factor receptor-2 (antibody DC101).

EXPERIMENTAL DESIGN

After short-term culture, glioblastoma spheroids were implanted into the brains of nude mice. Animals were treated either i.c. with cetuximab or i.p. with DC101. Tumor burden was determined histologically using image analysis of 36 different landmark points on serial brain sections.

RESULTS

Invasive xenografts were obtained from nine different glioblastomas. Three of seven cases treated with cetuximab responded with significant tumor growth inhibition, whereas four did not. All responsive tumors were derived from glioblastomas exhibiting EGFR amplification and expression of the truncated EGFRvIII variant, which were maintained in the xenografts. All nonresponsive tumors lacked EGFR amplification and EGFRvIII expression. The proportion of apoptotic cells was increased, whereas proliferation and invasion were decreased in responsive tumors. None of four xenograft cases treated with DC101 responded to treatment, and the diffusely invading tumors grew independent of angiogenesis.

CONCLUSIONS

Inhibition of glioblastoma growth and invasion can be achieved using i.c. delivery of an anti-EGFR antibody, but tumor response depends on the presence of amplified and/or mutated EGFR. Antiangiogenic treatment with DC101 is not effective against diffusely invading tumors.

Inhibition of the epidermal growth factor receptor increases expression of genes that stimulate inflammation, apoptosis, and cell attachment

The epidermal growth factor receptor (EGFR) is overexpressed in several types of human cancer, and inhibition of EGFR function is a promising strategy for cancer therapy. We used cDNA microarrays to examine alterations in gene expression after treatment of carcinoma cells with PD153035, a specific and reversible inhibitor of EGFR function. When human cervical carcinoma cells were grown on a collagen substrate in three-dimensional organotypic culture, untreated cells expressed high levels of EGFR RNA and invaded the underlying collagen. Blocking EGFR function decreased DNA synthesis and inhibited invasion in a dose-dependent manner. Microarray analyses identified 312 genes that were significantly increased or decreased in expression after EGFR inhibition. Many could be classified into one of four functional groups including genes that (a) stimulate inflammation and innate immunity, (b) promote cell attachment, (c) enhance apoptosis, and (d) inhibit cell cycle progression. PD153035 induced a dose-dependent activation of nuclear factor kappaB, a transcription factor that stimulates proinflammatory gene expression. Our results identify alterations in gene expression caused by EGFR inhibition and show that this response varies significantly in different cell lines.