Hypermethylation ofATP‐binding cassette B1 (ABCB1) multidrug resistance 1 (MDR1) is associated with cisplatin resistance in the A549 lung adenocarcinoma cell line

-PCR) and Western blot methods. Cell viability, DDP resistance and apoptosis of A549 cells were evaluated using the Cell Counting Kit-8 and fluorescence-activated cell sorter analysis. Our results showed that the onset of resistance to the cisplatin analogue, DDP, was associated with hypermethylation of the ABCB1 gene. Expression of the ABCB1 gene was enhanced at both mRNA and protein levels. Treatment with 5-Aza-C contributed to the hypomethylation of the ABCB1 gene and decreased ABCB1 protein expression in A549 cells. In conclusion, this in vitro and human tissue study of lung adenocarcinoma cells demonstrated that hypermethylation of the ABCB1 gene correlated with increased gene expression and was associated with the acquisition of resistance to the cisplatin analogue, DDP in human lung adenocarcinoma cells. Taken together, our study highlighted the connection between increased ABCB1 methylation level and upregulated expression of the gene in lung cancer. Moreover, the abnormally high expression of ABCB1 in A549 cells contributed to the development of the DDP resistance.