Abstract
PURPOSE: Treatment with arsenic trioxide (As(2)O(3)) results in a wide range of cellular effects that includes induction of apoptosis, inhibition of cell growth, promotion or inhibition of cellular differentiation, and inhibition of angiogenesis through a variety of mechanisms. The mechanisms of As(2)O(3)-induced cell death have been mainly studied in hematological cancers, and those mechanisms in solid cancers have yet to be clearly defined. In this study, the mechanisms by which As(2)O(3) induces apoptosis in human colorectal adenocarcinoma HT-29 cells were investigated. MATERIALS AND METHODS: To examine the levels of apoptosis, HT-29 cells were treated with As(2)O(3) and then we measured the percentage of Annexin V binding cells, the amount of ROS production and the mitochondrial membrane potential. Western blot analysis was performed to identify the activated caspases after As(2)O(3) exposure, and we compared the possible target molecules of apoptosis. As(2)O(3) treatment induced the loss of the mitochondrial membrane potential and an increase of ROS, as well as activation of caspase-3, -7, -9 and -10. RESULTS: As(2)O(3) induced apoptosis via the production of reactive oxygen species and the loss of the mitochondrial membrane potential. As(2)O(3) induced the activation of caspase-3, -7, -9 and -10. Furthermore, As(2)O(3) treatment downregulates the Mcl-1 and Bcl-2 expressions, and the release of cytochrome c and an apoptosis-inducing factor (AIF). Pretreating the HT-29 cells with N-acetyl-L-cysteine, which is a thiol-containing antioxidant, inhibited the As(2)O(3)-induced apoptosis and caspase activation. CONCLUSION: Taken together, these results suggest that the generation of reactive oxygen species (ROS) by As(2)O(3) might play an important role in the regulation of As(2)O(3)-induced apoptosis. This cytotoxicity is mediated through a mitochondria-dependent apoptotic signal pathway in HT-29 cells.