An orally bioavailable organoselenium inhibitor of thioredoxin reductase 1 (TrxR1), with potential antineoplastic activity. Upon oral administration, ethaselen specifically binds to the selenocysteine-cysteine redox pair in the C-terminal active site of TrxR1 and inhibits its activity, which may result in growth inhibition and the induction of apoptosis in TrxR1-overexpressing tumor cells. TrxR1, upregulated in many cancer cell types, plays a key role in various redox-dependent cellular pathways, regulates transcription factor activity, inhibits apoptosis, and promotes cell growth and survival. Check for active clinical trialsusing this agent.