Use of an Orthotopic Xenograft Model for Assessing the Effect of Epidermal Growth Factor Receptor Amplification on Glioblastoma Radiation Response

Abstract

Purpose:The influence of epidermal growth factor receptor (EGFR) amplification on glioblastoma patient prognosis following definitive radiotherapy has been extensively investigated in clinical studies, and yet the relationship between EGFR status and radiation response remains unclear. The intent of the current study was to address this relationship using several EGFRamplified glioblastoma xenografts in an orthotopic athymic mouse model. Experimental Design: We examined the effect of radiation on the survival of nude mice with intracranial xenografts derived from 13 distinct patient tumors, 7 of which have amplified EGFR. Mice with established intracranial tumors were randomized to sham treatment or 12-Gy radiation in six fractions delivered over 12 days. Results: For six of the xenografts, radiation of mice with intracranial tumor significantly extended survival, and four of these xenografts had EGFR amplification. For seven other xenografts, radiation treatment did not significantly extend survival, and three of these, including GBM12, had EGFR amplification. Similar to EGFR, the tumor genetic status of p53 or PTEN did not show preferential association with radiation-sensitive or radiation-resistant xenografts whereas hyperphosphorylation of Akt on Ser 473 was associated with increased radioresistance. To specifically investigate whether inhibition of EGFR kinase activity influences radiation response, we examined combined radiation and EGFR inhibitor treatment in mice with intracranial GBM12. The combination of oral erlotinib administered concurrently with radiation resulted only in additive survival benefit relative to either agent alone. Conclusions: Our results indicate that EGFR amplification, as a biomarker, is not singularly predictive of glioblastoma response to radiation therapy, nor does the inhibition of EGFR enhance the intrinsic radiation responsiveness of glioblastoma tumors. However, efficacious EGFR inhibitor and radiation monotherapy regimens can be used in combination to achieve additive antitumor effect against a subset of glioblastoma.

Quantitative Phosphoproteomics Reveals Wee1 Kinase as a Therapeutic Target in a Model of Proneural Glioblastoma

“…Induction of apoptosis with MK-1775 in primary cells derived from the engineered mouse model of proneural GBM led us to test our theory in a different GBM system, human GBM PDX tumors and cell lines (13, 34). We chose three PDX lines: GBM6, GBM36, and GBM38.…”

“…Xenografts GBM6, GBM36, and GBM 38 were established in athymic mice (Harlan) as previously described (12). Briefly, xenografts and cell line models were established from resected tumor tissue of patients with GBM, descriptions in Table 1 (12, 13). Athymic female mice were inoculated subcutaneously with 2E6 cells.…”

“… Adapted with permission from from Carlson et al 2011, Current Protocols in Pharmacology, copyright 2011 John Wiley & Sons, Inc (12) and Sarkaria et al 2006, Clinical Cancer Research, copyright 2006 American Association for Cancer Research (13). Tumors were classified by GBM subtype as defined by TCGA (6).…”

Stimulated PI3K-AKT Signaling Mediated through Ligand or Radiation-Induced EGFR Depends Indirectly, but not Directly, on Constitutive K-Ras Activity

“…signaling is an important cascade to promote cell survival in response to exogenous stress factors such as exposure to ionizing radiation (38,40,47). It has been shown for both in vitro and in vivo systems that radiation sensitivity of various tumor xenografts or cell lines overexpressing EGFR can efficiently be enhanced by blocking EGFR with the monoclonal anti-EGFR antibody C225 (48-51).…”

“…It seems to be clear that activation of AKT via PI3K occurs through phosphorylation by phosphoinositide-dependent kinase-1 and/or phosphoinositide-dependent kinase-2 at serine and threonine residues (Ser 472/473 , Thr 308 ). Several authors reported that especially phosphorylation of AKT at Ser 473 is associated with resistance to chemotherapy/ radiotherapy (36)(37)(38)(39)(40), and it has been proposed that activated AKT promotes survival of cells exposed to ionizing radiation through inhibition of apoptosis (41,42) or enhancement of DNA double-strand break repair (31).…”