Arsenic trioxide inhibits the growth of Calu-6 cells via inducing a G2 arrest of the cell cycle and apoptosis accompanied with the depletion of GSH

Arsenic trioxide (ATO) can regulate many biological functions such as apoptosis and differentiation in various cells. We evaluated the effects of ATO on the viability, cell cycle and apoptosis of human pulmonary adenocarcinoma, Calu-6 and A549 cells. ATO reduced the viability of Calu-6 cells with an IC₅₀ of approximately 3 or 4 μM. However, A549 cells were very resistant to ATO. Calu-6 cells treated with 1, 3 or 5 μM ATO showed a G2 phase arrest of the cell cycle at 72 h. The G2 phase arrest was accompanied with the down-regulation of cdc2 protein. Treatment with ATO-induced apoptosis in Calu-6 cells. The apoptotic process was accompanied by the down-regulation of Bcl-2 protein, the activation of caspase-3, and the loss of the mitochondrial membrane potential (ΔΨ_m). All of the caspase inhibitors, especially pan-caspase inhibitor (Z-VAD), markedly rescued Calu-6 cells from ATO-induced cell death. Caspase inhibitors also prevented the loss of mitochondrial membrane potential (ΔΨ_m). The inhibitors significantly increased the number of G2 phase cells in 10 μM ATO-treated cells. In addition, the levels of O₂^{{radical dot} -} were significantly increased in 10 μM ATO-treated cells. However, the changes of ROS by 10 μM ATO are not correlated with apoptosis in Calu-6 cells. Treatment with 10 μM ATO depleted GSH content in Calu-6 cells and caspase inhibitors significantly prevented the GSH depletion in these cells. In conclusion, we have demonstrated that ATO inhibits the growth of Calu-6 cells by inducing a G2 arrest of the cell cycle and by triggering apoptosis accompanied with the depletion of GSH.