Radiosensitization of malignant glioma cells through overexpression of dominant-negative epidermal growth factor receptor.
The epidermal growth factor receptor (EGFR) plays an important role in neoplastic growth control of malignant gliomas. We have demonstrated that radiation activates EGFR Tyr-phosphorylation (EGFR Tyr-P) and the proliferation of surviving human carcinoma cells, a likely mechanism of accelerated cellular repopulation, a major cytoprotective response after radiation. We now investigate the importance of radiation-induced activation of EGFR on the radiosensitivity of the human malignant glioma cells U-87 MG and U-373 MG. The function of EGFR was inhibited through a genetic approach of transducing cells with an Adenovirus (Ad) vector containing dominant-negative (DN) EGFR-CD533 (Ad-EGFR-CD533) at efficiencies of 85-90%. The resulting cells are referred to as U-87-EGFR-CD533 and U-373-EGFR-CD533. After irradiation at 2 Gy, both of the cell lines exhibited a mean 3-fold increase in EGFR Tyr-P. The expression of EGFR-CD533 completely inhibited the radiation-induced activation of EGFR. In clonogenic survival assays after a single radiation exposure, the radiation dose for a survival of 37% (D37) for U-87-EGFR-CD533 cells was 1.4- to 1.5-fold lower, relative to cells transduced with AdLacZ or untransduced U-87 MG cells. This effect was amplified with repeated radiation exposures (3 x 2 Gy) yielding a D37 ratio of 1.8-2.0. In clonogenic survival studies with U-373 MG cells, the radiosensitizing effect of EGFR-CD533 was similar. Furthermore, in vivo studies with U-87 MG xenografts confirmed the effect of EGFR-CD533 on tumor radiosensitization (dose enhancement ratio, 1.8). We conclude that inhibition of EGFR function via Ad-mediated gene transfer of EGFR-CD533 results in significant radiosensitization. As underlying mechanism, we suggest the disruption of a major cytoprotective response involving EGFR and its downstream effectors, such as mitogen-activated protein kinase. The experiments demonstrate for the first time that radiosensitization of malignant glioma cells through disruption of EGFR function may be achieved by genetic therapy approaches.
Lammering
G
G
Department of Radiation Oncology, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298-0058, USA.
Valerie
K
K
Lin
P S
PS
Mikkelsen
R B
RB
Contessa
J N
JN
Feden
J P
JP
Farnsworth
J
J
Dent
P
P
Schmidt-Ullrich
R K
RK
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D015153:Blotting, Western; D001932:Brain Neoplasms / Q000532:radiotherapy*; D002455:Cell Division; D002470:Cell Survival; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D066246:ErbB Receptors / Q000235:genetics*; D005260:Female; D005799:Genes, Dominant; D015316:Genetic Therapy; D005910:Glioma / Q000532:radiotherapy*; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D010766:Phosphorylation; D011836:Radiation Tolerance; D014161:Transduction, Genetic; D014407:Tumor Cells, Cultured
D066246:ErbB Receptors