GSR and neoplasm: Different from Fe2+, Cu+, or Mn2+, Zn2+ breaks down the antioxidant system and increases endogenous ROS via inhibiting the glutathione reductase (GR) and thioredoxin reductase (TrxR) activities, enhancing ROS‐mediated therapeutic effects of tumor cells.[119] Also, Zn2+ leads to mitochondrial dysfunction by inhibiting their oxidative respiration, thus decreasing intracellular ATP levels.