3.6. NQO1 Activity Assays

The NQO1 activity assays kit (#ab184867) was purchased from Abcam (Cambridge, MA, USA). According to the manufacturer’s instructions, OC3-IV2 cells were lysed with 1X extraction buffer containing 1 mM phenylmethylsulfonyl fluoride for 15 min on ice, and then centrifuged at 17,000 × g at 4 °C for 20 min. The supernatant was collected, and then, the protein concentration of each sample was determined by bicinchoninic acid assays (Santa Cruz Biotechnology). A diluted sample and reaction buffer were added into 96-wells plate containing menadione or isoplumbagin with cofactor NADH and water-soluble tetrazolium salt (2-(4-iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, a highly sensitive tetrazolium reagent). The absorbance of reduced water-soluble tetrazolium salt was measured at 450 nm wavelengths by a spectrophotometer.