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 toγ-irradiation.Cell proliferation and survival were quantified using clonogenic assays.DNA damage was assessed using immunofluorescence forγH2AX.Telomere dysfunction-induced foci analysis was performed by the colocalization of telomere signals(FISH)andγH2AX.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 byγ-ray irradiation and aggravated genomic DNA and telomeric DNA damage(P<0.05).In addition,6-thio-dG pretreatment effectively increasedγ-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.