TXNRD1 and cancer: Exposure to AgNPs or Ag ions decreases TrxR1 activity in A549 cells. The active site selenocysteine residue of TrxR has been shown to be sensitive to arsenic and gold compounds in recent years, and this reactivity has generated a great deal of interest in this enzyme as a target for cancer research and toxicology (Cox et al. 2008; Ganyc et al. 2007; Jackson-Rosario and Self 2010; Lu et al. 2007; Meno et al. 2009; Prast-Nielsen et al. 2011; Santini et al. 2011; Talbot et al. 2008).