Auranofin inhibits the proliferation of lung cancer cells via necrosis and caspase-dependent apoptosis

Auranofin, an inhibitor of thioredoxin reductase (TrxR), inhibits the growth of a variety of cancer cells. In the present study, various lung cancer cells were used to investigate the molecular basis of anti-cancer effects of auranofin, including cell death via apoptosis or necrosis and cell cycle arrest. Generally, auranofin inhibited the growth of the tested lung cancer cell lines in a dose-dependent manner with an IC50 of 3-4 μM at 24 h. This agent significantly decreased the activity of TrxR in Calu-6 and A549 lung cancer cells. In addition, auranofin (3-5 μM) triggered necrosis in lung cancer cells measured by the release of lactate dehydrogenase (LDH) into culture media. Auranofin increased the percentages of sub-G1 cells in Calu-6 and A549 cells. DNA flow cytometry showed that auranofin induced G2/M phase arrest of Calu-6 cells. This agent also efficiently induced apoptosis, accompanied by loss of mitochondrial membrane potential (MMP; ΔΨm), increases in cleavage forms of caspase-3 and poly (ADP-ribose) polymerase (PARP), and a high ratio of BAX to Bcl-2 proteins. Furthermore, various caspase inhibitors reduced apoptosis and MMP (ΔΨm) loss in auranofin-treated Calu-6 cells. In particular, the pan-caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (Z-VAD), decreased cleavage forms of caspase-3, -8, and -9 in these cells. In conclusion, auranofin inhibited the proliferation of lung cancer cells, especially Calu-6 cells, via cell cycle arrest and cell death due to necrosis or caspase-dependent apoptosis.