Defective repair signalling in oral SCC cell-lines following DNA damage

Comparative evaluation of double strand break (DSB) dynamics in progression of potentially malignant oral disorders to oral squamous cell carcinoma (OSCC).

Methods:

Two discrete approaches were used to induce DSB in cell lines derived from normal through dysplastic to OSCC tissues. Hydrogen peroxide induces DSB via indiscriminate oxidative damage whereas camptothecin induces DSB by specifically intercalating to the DNA/topoisomerase1 interface. Camptothecin induced DSB are cumulative, reversible and consequent to cell cycle interruption at S phase. After optimization, γH2Ax foci were counted manually and confirmed by image analysis software and Western blot.

Results:

Dynamics of DSB repair in response to hydrogen peroxide and camptothecin was observed over 24 hours. Maximal number of γH2Ax foci was detected immediately and 2 hours post exposure to camptothecin and hydrogen peroxide respectively; the repair was linear onwards. When adjusted for the baseline number of γH2Ax, neoplastic cell lines showed the lowest number of maximal DSB and slowest rate of repair compared to other cell lines. Severely dysplastic cell lines also showed a significantly lower increase in the number of γH2Ax foci when compared to mildly dysplastic and normal oral cell lines (P<0.008).

Conclusions:

There is a difference in efficiency of DSB repair pathways in different cell lines derived from different stages of oral carcinogenesis with neoplastic cell lines having the most defective DSB repair system.