Mutagen sensitivity and DNA repair of the EGFR gene in oropharyngeal cancer

SummaryEpidermal growth factor receptor (EGFR) is overexpressed in several epithelial malignancies, including head and neck squamous cell cancer. Up to 90% of the tumour cases in this area exhibit EGFR overexpression. The reasons for overexpression are still not clear. Mutagen sensitivity, pre-existing conditions for genotoxic damage, gene amplification, and reduced DNA repair of the EGFR gene are possible causes for EGFR protein overexpression. DNA damage in macroscopically healthy pharyngeal mucosal tissue of 30 patients with (15) and without cancer (15) of the oropharynx was evaluated after incubation with Benz[a]pyren-7,8-diol-9,10-epoxid (BPDE), a tobacco-associated carcinogen. Emerging DNA fragmentation of the EGFR gene located on chromosome 7 was evaluated. The centromere of the chromosome served as a reference gene. Comet FISH was applied to assess the mutagen sensitivity in these regions. The extent of DNA repair was evaluated in the same samples after a 24-h repair-period. Differences in gene amplification and protein expression between the two groups were analysed by Interphase-FISH (I-FISH) and immunohistochemistry (IHC), respectively. BPDE caused significant DNA damage compared to the negative control in oropharyngeal mucosa cells of patients with- and without carcinoma. DNA fragmentation of the EGFR gene in the two groups was comparable. Mutagen sensitivity was significantly higher in the EGFR gene than in the reference gene, but fragmentation of the EGFR gene was not enhanced compared to the DNA damage of the entire DNA. The DNA repair period led to a significant reduction in DNA damage levels in all groups, without preference for any of the groups or genes. EGFR amplification was found in 7.7% of the tumour patients but not in control patients. Of the patients with oropharyngeal carcinoma, 66.6% showed enhanced expression of EGFR protein (grades 2 and 3), whereas only 13% of tumour-free patients showed such protein expression. No significant differences in either mutagen sensitivity or DNA repair were shown between the two groups. Therefore, both factors do not seem to have any major impact on protein overexpression. Gene amplification might have moderate effects on protein expression, but other reasons such as dysregulation at transcriptional- and posttranscriptional levels require further investigation.