EGFRvIII and DNA double-strand break repair: a molecular mechanism for radioresistance in glioblastoma.
Glioblastoma multiforme (GBM) is the most lethal of brain tumors and is highly resistant to ionizing radiation (IR) and chemotherapy. Here, we report on a molecular mechanism by which a key glioma-specific mutation, epidermal growth factor receptor variant III (EGFRvIII), confers radiation resistance. Using Ink4a/Arf-deficient primary mouse astrocytes, primary astrocytes immortalized by p53/Rb suppression, as well as human U87 glioma cells, we show that EGFRvIII expression enhances clonogenic survival following IR. This enhanced radioresistance is due to accelerated repair of DNA double-strand breaks (DSB), the most lethal lesion inflicted by IR. The EGFR inhibitor gefitinib (Iressa) and the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 attenuate the rate of DSB repair. Importantly, expression of constitutively active, myristylated Akt-1 accelerates repair, implicating the PI3K/Akt-1 pathway in radioresistance. Most notably, EGFRvIII-expressing U87 glioma cells show elevated activation of a key DSB repair enzyme, DNA-dependent protein kinase catalytic subunit (DNA-PKcs). Enhanced radioresistance is abrogated by the DNA-PKcs-specific inhibitor NU7026, and EGFRvIII fails to confer radioresistance in DNA-PKcs-deficient cells. In vivo, orthotopic U87-EGFRvIII-derived tumors display faster rates of DSB repair following whole-brain radiotherapy compared with U87-derived tumors. Consequently, EGFRvIII-expressing tumors are radioresistant and continue to grow following whole-brain radiotherapy with little effect on overall survival. These in vitro and in vivo data support our hypothesis that EGFRvIII expression promotes DNA-PKcs activation and DSB repair, perhaps as a consequence of hyperactivated PI3K/Akt-1 signaling. Taken together, our results raise the possibility that EGFR and/or DNA-PKcs inhibition concurrent with radiation may be an effective therapeutic strategy for radiosensitizing high-grade gliomas.
Department of Radiation Oncology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390, USA.
Bipasha
B
Mukherjee
Brian
B
McEllin
Cristel V
CV
Camacho
Nozomi
N
Tomimatsu
Shyam
S
Sirasanagandala
Suraj
S
Nannepaga
Kimmo J
KJ
Hatanpaa
Bruce
B
Mickey
Christopher
C
Madden
Elizabeth
E
Maher
David A
DA
Boothman
Frank
F
Furnari
Webster K
WK
Cavenee
Robert M
RM
Bachoo
Sandeep
S
Burma
D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D001932:Brain Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000401:mortality / Q000473:pathology / Q000532:radiotherapy; D045744:Cell Line, Tumor; D003131:Combined Modality Therapy; D004249:DNA Damage / Q000528:radiation effects; D004260:DNA Repair / Q000528:radiation effects; D004273:DNA, Neoplasm / Q000235:genetics* / Q000528:radiation effects; D003606:Dacarbazine / Q000031:analogs & derivatives / Q000627:therapeutic use; D019008:Drug Resistance, Neoplasm; D066246:ErbB Receptors / Q000235:genetics*; D005347:Fibroblasts / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D005909:Glioblastoma / Q000188:drug therapy / Q000235:genetics* / Q000401:mortality / Q000473:pathology / Q000532:radiotherapy; D006801:Humans; D051379:Mice; D011839:Radiation, Ionizing; D016019:Survival Analysis; D017741:Survivors; D000077204:Temozolomide
D004273:DNA, Neoplasm; C410723:epidermal growth factor receptor VIII; D003606:Dacarbazine; D066246:ErbB Receptors; D000077204:Temozolomide