This study is the first to investigate the anticancer effect of plumbagin in 
human melanoma A375.S2 cells. Plumbagin exhibited effective cell growth 
inhibition by inducing cancer cells to undergo S-G2/M phase arrest and 
apoptosis. Further investigation revealed that plumbagin's inhibition of cell 
growth was also evident in a nude mice model. Blockade of cell cycle was 
associated with increased levels of p21, and reduced amounts of cyclin B1, 
cyclin A, Cdc2, and Cdc25C. Plumbagin also enhanced the levels of inactivated 
phosphorylated Cdc2 and Cdc25C. Plumbagin triggered the mitochondrial apoptotic 
pathway indicated by a change in Bax/Bcl-2 ratios, resulting in caspase-9 
activation. We also found the generation of ROS is a critical mediator in 
plumbagin-induced cell growth inhibition. Plumbagin increased the activation of 
apoptosis signal-regulating kinase 1, JNK and extracellular signal-regulated 
kinase 1/2 (ERK1/2), but not p38. In addition, antioxidants vitamin C and 
catalase significantly decreased plumbagin-mediated c-Jun N-terminal kinase 
(JNK) activation and apoptosis. Moreover, blocking ERK and JNK by specific 
inhibitors suppressed plumbagin-triggered mitochondrial apoptotic pathway. Taken 
together, these results imply a critical role for ROS and JNK in the plumbagin's 
anticancer activity.