Enhanced radiosensitivity by 6-thio-dG via increasing telomere dysfunction and ataxia telangiectasia mutated inhibition in non-small cell lung cancer

Objective

To investigate the radiosensitivity of 6-thio-dG and its underlying molecular mechanisms in non-small cell lung cancer (NSCLC).

Methods

H1299 and A549 NSCLC cells were pretreated with 6-thio-dG for one week and then exposed to γ-irradiation. Cell proliferation and survival were quantified using clonogenic assays. DNA damage was assessed using immunofluorescence for γH2AX. Telomere dysfunction-induced foci analysis was performed by the co-localization of telomere signals (FISH) and γH2AX. Telomere fusion was defined as two telomere signals merged into one at the chromosome by immuno-FISH in metaphase spreads. Proteins related to the DNA damage response were detected using Western blot analysis. Apoptosis wasanalyzed using flow cytometry and Western blot.

Results

The presence of 6-thio-dG increased the radio sensitivity of H1299 and A549 ​cells (P<0.05), but had no effect on the normal human lung fibroblast line, MRC5. 6-thio-dG pretreatment significantly reduced the clonogenic potential induced by γ-ray irradiation and aggravated genomic DNA and telomeric DNA damage (P<0.05). In addition, 6-thio-dG pretreatment effectively increased γ-ray irradiation induced telomere dysfunction (P<0.05), resulting in disruption of chromosome stability and inhibition of the ATM pathway, thereby impairing genomic DNA and telomeric DNA repair, which was closely associated with enhanced drug-mediated radiation-induced apoptosis.

Conclusions

6-thio-dG increases the radiosensitivity of NSCLC by inhibiting ATM and inducing telomere dysfunction, which can potentially be used as a strategy for radiotherapy for NSCLC.