Objective To investigate the effect of 5-azacytidine (5-Aza) on the radiation sensitivity of human nasopharyngeal carcinoma cell line C666-1 and its underlying mechanism.

Methods C666-1 cells were treated by 5-azacytidine with different concentrations (0, 500, 1000, 3000, 5000nmol/L). Cell growth was determined by MTT, cell cycle was detected using flow cytometry, and the expression of apoptosis-related proteins, such as cleaved Caspase-3, cleaved PARP and DNA damage related protein gamma H2AX were assayed by Western blot.

Results With the increase of drug concentration, 5-azacytidine enhanced the inhibition of C666-1 cells growth gradually. We further studied the radiation sensitivity of nasopharyngeal carcinoma cells using 1000nmol/L 5-azacytidine. SF2 (cell survival rate after radiation of 2Gy) of C666-1 cells after receiving radiation alone was 48%, SF2 was decreased to 31% after treated by 5-azacytidine combined radiation, and the radiotherapy sensitization ratio was 1.37. 5-azacytidine increased the expression of apoptosis-related proteins cleaved Caspase-3 and cleaved PARP.

Conclusion 5-azacytidine could enhance the radiation sensitivity of nasopharyngeal carcinoma C666-1 cells and the possible mechanism is that 5-azacytidine may increase the radiation-induced apoptosis.