MTT Assay and Oxidative Stress Analysis

S4 was synthesized as previously described [23 (link)]. 3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide (MTT) was purchased from the USB Corporation (Cleveland, OH, USA). L-ascorbic acid, dimethyl sulfoxide, 2′,7′-dichlorofluorescin diacetate (DCFDA), leupeptin, phenylmethylsulfonyl fluoride, and paraformaldehyde were obtained from the Sigma-Aldrich Corporation (St. Louis, MO, USA). Dulbecco’s modified Eagle’s medium (DMEM), fetal bovine serum (FBS), penicillin, and streptomycin were purchased from Gibco, Invitrogen (Carlsbad, CA, USA). Enhanced chemiluminescence (ECL)™ Western blotting detection reagent was obtained from Amersham Biosciences (England). ProLong^® Gold antifade reagent with 4′,6-diamidino-2-phenylindole (DAPI) was purchased from Invitrogen (Carlsbad, CA, USA). Mitogen-activated protein (MAP) kinase inhibitors, including c-Jun N-terminal kinases (JNK) inhibitor II, PD98059, and SB203580, were obtained from Calbiochem (Darmstadt, Germany). Tris, sodium dodecyl sulfate (SDS), and Tween 20 were purchased from the USB Corporation (Cleveland, OH, USA). Other reagents and chemicals used in this study were reagent grade.