Hydrogen peroxide induces cell death in human TRAIL-resistant melanoma through intracellular superoxide generation

Intracellular reactive oxygen species (ROS) such as hydrogen peroxide (H2O2) are thought to mediate apoptosis induced by death receptor ligands, including tumornecrosis factor-related apoptosis-inducing ligand (TRAIL). However, the role of H2O2 is controversial, since some evidence suggests that H2O2 acts as an anti-apoptotic factor. Here, we show that exogenously applied H2O2 (30-100 JIM) induces cell death in TRAIL-resistant human melanoma cells via intracellular superoxide (O-2(-)) generation. H2O2 induced apoptotic or necrotic cell death, depending on the concentration of the oxidant applied; low concentrations of H2O2 preferentially activated the caspase-dependent apoptotic pathway, while high concentrations of H2O2 induced apoptotic and necrotic cell death in a caspase-independent manner. The H2O2-induced cell death was associated with increased mitochondrial membrane potential collapse and caspase-3/7 activation and ER stress responses including caspase-12 and X-box-binding protein-1 (XBP-1) activation. H2O2 induced intracellular O-2(-) generation even within the mitochondria, while TRAIL did not. The superoxide dismutase mimetic antioxidant MnTBaP [Mn (III) tetrakis (4-benzonic acid) porphyrin chloride] inhibited the H2O2-induced O-2(-) generation, apoptosis and XBP-1 and caspase-12 activation at comparable concentrations. Importantly, H2O2 treatment caused minimal O-2(-) generation and apoptosis in normal primary melanocytes. These data show that H2O2 induces endoplasmic reticulum-associated cell death via intracellular O-2(-) generation and that malignant melanoma cells are more susceptible than normal cells to this oxidative cell death. The findings suggest that H2O2 has therapeutic potential in the treatment of TRAIL-resistant melanoma.