OBJECTIVEThe aim of this study was to investigate the effect of 5-aza-2'-deoxycytidine (5-Aza-dc), a methylation inhibitor, on cisplatin-resistance in non-small cell lung cancer cell line A549/DDP and to explore its possible mechanism.

METHODSMTT assay was used to test the cytotoxicity of 5-Aza-dc on A549/DDP cells, and the IC(50) and cisplatin resistance index of A540/DDP cells at 48 hours after 5-Aza-dc (0 µmol/L, 20 µmol/L, 40 µmol/L) treatment at different concentrations. MSP, fluorescence quantitative RT-PCR (real-time RT-PCR) and Western blot were used to detect the hMLH1 methylation status, mRNA and protein expressions, respectively.

RESULTSThe IC(50) value of cisplatin in A549/DDP cells was 30.15 ± 0.76 µmol/L. The MTT assay results demonstrated that during the 5-Aza-dc treatment for 48 hours, the dose of 20 µmol/L was non-toxic and 40 µmol/L was low-toxic. 5-Aza-dc at those two doses reduced IC(50) value of cisplatin to 16.54 ± 0.35 µmol/L (RI = 1.82) and 6.82 ± 0.16 µmol/L (RI = 4.42), respectively. MSP, real-time RT-PCR and Western blot showed that 5-Aza-dc at non-toxic and low-toxic doses removed the partial hMLH1-hypermethylation, and up-regulated hMLH1 mRNA and protein expressions.

CONCLUSIONSLow dose 5-Aza-dc can partially reverse the cisplatin-resistance in A549/DDP cells, which may be achieved through removal of hMLH1 hypermethylation and increased expression of hMLH1 gene. 5-Aza-dc may have a role in increasing the efficacy of chemotherapy for patients whose tumors are lack of hMLH1 expression because of hMLH1 promoter hypermethylation.