Inhibition of radiation-induced EGFR nuclear import by C225 (Cetuximab) suppresses DNA-PK activity.
OBJECTIVE
Inhibition of EGFR-function can induce radiosensitization in tumor cells. Purpose of our investigation was to identify the possible molecular mechanism of radiosensitization following treatment with anti-EGFR-antibody C225 (Cetuximab).


METHODS
The effect of C225 on radiation response was determined in human cell lines of bronchial carcinoma (A549) and breast adenoma cells (MDA MB 231). The molecular effects of C225 on EGFR-function after irradiation were analyzed applying western blotting, immune-precipitation and kinase assays. Effects on DNA-repair were detected by quantification of gamma-H2AX positive foci 24h after irradiation.


RESULTS
The EGFR specific antibody C225 induced radiosensitization in A549 and also in MDA MB 231 cells. Radiosensitization in A549 was associated with blockage of radiation-induced EGFR transport into the nucleus, and immobilized the complex of EGFR with DNA-dependent protein kinase (DNA-PK) in the cytoplasm. As a consequence radiation-induced DNA-PK activation was abolished, a process that is essential for DNA-repair after radiation exposure. Likewise C225 treatment increased the residual amount of gamma-H2AX-positive foci 24h after irradiation in A549 and in MDA MB 231 cells.


CONCLUSIONS
Our results suggest that irradiation induced DNA-PK activation-essential for DNA repair-may be hampered specifically by use of the anti-EGFR-antibody C225. This process is associated with radiosensitization.
Dittmann
Klaus
K
Division of Radiobiology and Molecular Environmental Research, Department of Radiation Oncology, University of Tübingen, Germany. klaus.dittmann@uni-tuebingen.de
Mayer
Claus
C
Rodemann
Hans-Peter
HP
D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor / Q000378:metabolism* / Q000528:radiation effects*; D002467:Cell Nucleus / Q000378:metabolism*; D000068818:Cetuximab; D003593:Cytoplasm / Q000378:metabolism; D004260:DNA Repair; D051747:DNA-Activated Protein Kinase / Q000378:metabolism*; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000528:radiation effects*; D006801:Humans; D011836:Radiation Tolerance; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D066246:ErbB Receptors; D051747:DNA-Activated Protein Kinase; D000068818:Cetuximab