Synergism between thioredoxin reductase inhibitor ethaselen and sodium selenite in inhibiting proliferation and inducing death of human non-small cell lung cancer cells.

New effective treatment for human non-small cell lung cancer (NSCLC) is needed. The thioredoxin (Trx) system composes of thioredoxin reductase (TrxR), Trx and NADPH. In this study, we combined an organic selenium compound--TrxR inhibitor ethaselen (BBSKE) with low dosage sodium selenite to inhibit proliferation and induce death of NSCLC cells, and identified underlying mechanisms. Synergistic anti-proliferation effect of BBSKE and selenite was found in human NSCLC cell lines, A549, NCI-H1299 and NCI-1266. A significant increase of apoptosis, necrosis and autophagy were observed in the group of BBSKE plus selenite in A549 cells. The autophagy induced by BBSKE and selenite inhibited apoptosis and necrosis. In addition, BBSKE plus selenite induced G2/M arrest, which was verified by the alteration of gene and protein expression of cell cycle regulatory complexes. The intracellular enzyme activity of TrxR was remarkably decreased by cotreatment of BBSKE and selenite. Besides, the mRNA and protein level of TrxR1 and Trx1 were significantly inhibited by cotreatment of BBSKE and selenite. HEK 293 cells overexpressing TrxR1 were more sensitive to BBSKE plus selenite. The nuclear translocation of Trx1 and Ref-1, as well as expression of Ref-1 and AP-1 were inhibited by combination treatment. In short, BBSKE synergizes selenite in inhibiting proliferation and inducing death of NSCLC cells; BBSKE combined with selenite may be a treatment strategy for NSCLC.