Epidermal growth factor receptor as a genetic therapy target for carcinoma cell radiosensitization.
BACKGROUND
Exposure of human cancer cells to ionizing radiation activates the epidermal growth factor receptor (EGFR), which, in turn, mediates a cytoprotective response that reduces the cells' sensitivity to ionizing radiation. Overexpression of a dominant-negative EGFR mutant, EGFR-CD533, disrupts the cytoprotective response by preventing radiation-induced activation of the receptor and its downstream effectors. To investigate whether gene therapy with EGFR-CD533 has the potential to increase tumor cell radiosensitivity, we introduced an adenoviral vector containing EGFR-CD533 into xenograft tumors in nude mice and evaluated the tumor response to ionizing radiation.


METHODS
Xenograft tumors established from the human mammary carcinoma cell line MDA-MB-231 were transduced via infusion with the adenoviral vector Ad-EGFR-CD533 or a control vector containing the beta-galactosidase gene, Ad-LacZ. The transduced tumors were then exposed to radiation in the therapeutic dose range, and radiation-induced EGFR activation was assessed by examining the tyrosine phosphorylation of immunoprecipitated EGFR. Radiosensitization was determined in vitro by colony-formation assays. All statistical tests were two-sided.


RESULTS
The transduction efficiency of MDA-MB-231 tumors by Ad-LacZ was 44%. Expression of EGFR-CD533 in tumors reduced radiation-induced EGFR activation by 2.94-fold (95% confidence interval [CI] = 2.23 to 4.14). The radiosensitivity of Ad-EGFR-CD533-transduced tumors was statistically significantly higher (46%; P<.001) than that of Ad-LacZ-transduced tumors, yielding a dose-enhancement ratio of 1.85 (95% CI = 1.54 to 2.51).


CONCLUSIONS
Transduction of MDA-MB-231 xenograft tumors with Ad-EGFR-CD533 conferred a dominant-negative EGFR phenotype and induced tumor radiosensitization. Therefore, disruption of EGFR function through overexpression of EGFR-CD533 may hold promise as a gene therapeutic approach to enhance the sensitivity of tumor cells to ionizing radiation.
Lammering
G
G
Department of Radiation Oncology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, VA, USA.
Hewit
T H
TH
Hawkins
W T
WT
Contessa
J N
JN
Reardon
D B
DB
Lin
P S
PS
Valerie
K
K
Dent
P
P
Mikkelsen
R B
RB
Schmidt-Ullrich
R K
RK
D000818:Animals; D001943:Breast Neoplasms / Q000473:pathology / Q000532:radiotherapy / Q000628:therapy*; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D004318:Doxycycline / Q000633:toxicity; D066246:ErbB Receptors / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000528:radiation effects; D015316:Genetic Therapy; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D011836:Radiation Tolerance; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured; D014410:Tumor Stem Cell Assay
D066246:ErbB Receptors; D004318:Doxycycline