Additional evidence validating thioredoxin reductase as the major mechanistic target producing synergy with the cyst(e)inase and auranofin combination was provided by the fact that natural compound inhibitors of thioredoxin reductase (curcumin, myricetin, and quercetin39,40) also produced a synergistic inhibition of cell survival when combined with cyst(e)inase (Supplementary Fig. 6c, d). This evidence concerns the gene PRDX5 and cyst.