1740

Salvicine (SAL) is a novel topoisomerase II inhibitor, synthesized by the structural modification of natural product lead isolated from a Chinese medicinal plant Salvia prionitis. It exerts potent in vitro and in vivo anti-tumor effects, and is in phase I clinical trial in China. In the present study, we explored the roles of reactive oxygen species (ROS) and glutathione (GSH) in SAL-mediated apoptosis in K562 cells. Our data revealed that SAL stimulated intracellular H2O2 generation and GSH depletion, and subsequently elicited notable DNA double-strand breaks (DSBs) and the apoptotic cell death in K562 cells. SAL resulted in activation of ROS-related proteins JNK and p38 MAPK, and mitochondrial-dependent apoptosis. SAL also down-regulated DSBs repair proteins Ku70, Ku86 and Rad51 levels through its apoptotic pathway. Furthermore, SAL mediated DSBs in a concentration-dependent manner. The DSBs of SAL was much prior to apoptosis induction. SAL significantly stimulated intracellular H2O2 generation and GSH depletion in the early stage. Thiol antioxidants, such as N-Acetylcysteine (NAC) and GSH, and a special H2O2 inhibitor, catalase (CAT), but not other antioxidants, such as SOD, Trolox, BHA, ascorbic acid, EGCG and diphenylene iodonium (DPI), significantly inhibited SAL-mediated H2O2 level increase, DSBs and apoptosis. These thiol antioxidants also attenuated SAL-mediated JNK and p38 MAPK activation, and the change of apoptosis-related proteins and DSBs repair proteins. These results identify a novel mechanism that H2O2 generation and GSH depletion play critical roles in SAL-mediated DSBs and apoptosis in K562 cells. Additionally, we propose that GSH relox systems are associated with SAL mediated-H2O2 generation and GSH depletion. Recently, we have reported that SAL is cytotoxic for multidrug resistance (MDR) tumor cells and down-regulates mdr-1expression in MDR K562/A02 cells (Miao Z. H. and Ding J. (2003) Cancer Res. 63, 4527-4532). In this study, we also investigated the roles of ROS and GSH in SAL-mediated DSBs and apoptosis in MDR K562/A02 cells. SAL provided similar effects and mechanisms in both MDR and parental K562 cells, further demonstrating the effects of SAL against MDR tumor cells.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]