Molecular and Cellular PharmacologyInterruption of mitochondrial complex IV activity and cytochrome c expression activated O2∙−-mediated cell survival in silibinin-treated human melanoma A375-S2 cells via IGF-1R-PI3K-Akt and IGF-1R-PLC γ-PKC

Silibinin was reported to have high cyto-toxicity in many malignant cell lines, however, it showed low cyto-toxicity in treatment of human melanoma A375-S2 cells and even protected these cells against certain stress insults. Reactive oxygen species was reported to have controversial effects on cancer chemotherapy. In this study we investigated the mechanism of reactive oxygen species generation and the role of reactive oxygen species in protecting cells against silibinin induced cyto-toxicity in A375-S2 cells. We found that silibinin induced the generation of large amount of superoxide anion (O2∙−) and small amount of hydrogen peroxide (H2O2) through down-regulating the activity of mitochondrial complex IV and the protein level of cytochrome c. We also discovered that O2∙− generation activated insulin like growth factor-1 receptor (IGF-1R) and its down-stream phosphatidylinositol 3-kinases-Akt (PI3K-Akt) and phospholipase C γ-protein kinase C (PLC γ-PKC) signaling pathways, which were augmented by H2O2 scavenger catalase. Scavenging O2∙− by superoxide dismutase (SOD) or inhibition of IGF-1R-PI3K-Akt and IGF-1R-PLC γ-PKC signaling pathways increased cell apoptosis. Therefore, O2∙− mediated cell resistance to silibinin via activating IGF-1R-PI3K-Akt and IGF-1R-PLC γ-PKC pathways in silibinin treated A375-S2 cells.