Abstract: ObjectiveTo explore the changes of micro RNA 155 (miR-155), BTB and CNC homologous protein 1 (BACH1), quinone oxidoreductase 1 (NQO1) and heme-oxygenase-1 (HO-1) in the process of arsenic trioxide-induced cell death, and to clarify the relationship between miR-155 and BACH1, providing experimental basis for the sensitivity of arsenic trioxide (ATO) treatment. MethodsHuman lung adenocarcinoma cell line A549 cells were treated with different concentrations of ATO. MTT assay and total antioxidant capacity detection kit were used to determine cell viability and total antioxidant capacity, respectively. BACH1, NQO1 and HO-1 protein expression were probed by Western blot and real-time fluorescence quantitative (qRT-PCR) was utilized to test the miR-155 level. A549 cells were transfected with miR-155 mimic and its negative control, then the expression level of miR-155 was detected by qRT-PCR, and these cells were treated with 20 μmol/L for 24 h followed by MTT and Western blot detection. Results10 μmol/L ATO significantly reduced the cell viability in A549 cells. 10 μmol/L and 20 μmol/L ATO treatment activated BACH1 expression and inhibited miR-155, NQO1 and HO-1 expression, leading to decreased total antioxidant capacity. Importantly, the cell death induced by 20 μmol/L ATO was significantly decreased in miR-155 mimic transfection cells in comparison with non-transfected cells and miR-155 mimic negative control transfected cells. Moreover, high expression of miR-155 reduced BACH1 activation and increased NQO1 and HO-1 expression in cells treated with 20 μmol/L ATO ( P<0.05). ConclusionRestraining total antioxidant capacity contributes to ATO induced cell death, the underlying mechanisms may be that ATO can activate BACH1 expression through inhibition of the miR-155 level, leading to subsequent inhibition of NQO1 and HO-1 expression. Taken together, these data suggest that miR-155 and BACH1 could be used as sensitivity targets for ATO treatment in lung cancer.