Maintaining moderate levels of intracellular ROS under physiological conditions, for keeping redox balance as well as cell proliferation are extremely important.23 ROS is a key regulator of ER stress which generally triggers unfolded protein reaction to protect cancer cells away from cell death.24, 25 We found that the p‐eIF2a and ATF4 protein levels were increased in a dose‐dependent manner after CHE treatment. The gene discussed is ATF4; the disease is cancer.