Western blot analysis of ERstress biomarkers PERK, BiP, calnexin, and Ero-1-Lα revealedER stress activation which finally led to breast cancer cell death.The ability of 4 to produce ROS in the presence of hydrogenperoxide was confirmed by an independent EPR spin-trapping experiment,as well as fluorescent microscopy. The gene discussed is CANX; the disease is breast cancer.