TXN and cancer: However, in cancer cells with higher levels of ROS and concomitant expanded antioxidant arsenal such as aberrantly accumulated Nrf2 and overexpression of DJ1, thioredoxin (Trx) and thioredoxin reductase (TrxR) [10,11,12,13], melatonin no longer plays antioxidant roles but in turn becomes a prooxidant agent to heighten oxidant stress to cause cell death [4,5].