The Study Of Anti-tumor Effects And Its Related Mechanism Of JS-K On The Gastric Cancer Cells

Background: In China,gastric cancer is a common malignant tumor in the digestive tract. Due to the large population and the imbalance of economy and social development,many patients with early gastric cancer are not diagnosed, while many gastric cancers are diagnosed as advanced cancers, which sharply reduces the patients' 5-year survival rate. To date, the main treatment for gastric cancer is gastrectomy with D2 lymphadenectomy plus postoperative chemotherapy. Because of the severe complications and the uncertainty of the commonly used chemotherapy drugs, novel drugs are urgently needed. JS-K is a newly synthesised NO prodrug which can kill many kinds of tumor cells. However, the anti-tumor efficacy and the specific mechanisms of JS-K on gastric cancer have not been elucidated.Methods: In this study, by using a series of in vitro and in vivo experiments, we assessed the anti-tumor efficacy of JS-K in gastric cancer and explored its specific mechanisms. MTT assays, flow cytometry, isolation of mitochondria, targeted gene overexpression via plasmid transfection, siRNA, Western blot and subcutaneous tumor xenograft models were used to evaluate the effects of JS-K on gastric cancer and its specific mechanisms.Results: JS-K could kill gastric cancer cells by inducing apoptosis in a time- and dose-dependent manner. The apoptosis induced by JS-K in gastric cancer cells is caspase-dependent, and Z-VAD-FMK (a pan-caspase inhibitor) could completely reverse these effects, while Z-DEVD-FMK (a caspase 3 inhibitor) and Z-LEHD-FMK (a caspase 3 inhibitor) could only partially protect gastric cancer cells from being killed by JS-K. JS-K inhibited the activities of Complex I and Complex IV in the mitochondrial respiratory chain, thus increased the production of reactive oxygen species (ROS ). At the same time,JS-K decreased the amount of SOD1 and catalase that were responsible for clearing away reactive oxygen species (ROS ) in cells. Increase in ROS production and decrease in ROS clearing away together resulted in the accumulation of reactive oxygen species (ROS ) in cells. The accumulation of reactive oxygen species (ROS ) in cells impaired the mitochondrial function, and decreased mitochondrial membrane potential (??m),cytochrome C went into the cytoplasm from the mitochodria. Cytochrome C in the cytoplasm activated caspase 9' precursor, and activated caspase 9 triggered the activation of caspase 3 and cleavage of PARP, finally leading to apoptosis. JS-K induced apoptosis in gastric cancer cells via reactive oxygen species (ROS ), but N-acetyl-L-cysteine (NAC),a reactive oxygen species scavenger, could reverse these effects. JS-K decreased the expression of Bcl-2 and Bcl-xL, while the overexpression of Bcl-2 and Bcl-xL via plasmid transfection protected gastric cancer cells from being killed by JS-K. By using siRNA, we found apoptosis inducing factor (AIF) and endonuclease G (Endo G) were not involved in the JS-K-induced apoptosis in gastric cancer cells. In vivo tests showed JS-K significantly inhibited the tumor growth in the subcutaneous tumor xenograft models, but showed little influence in the body weights of the tumor-bearing mice, indicating fine biological tolerance.Conclusions: JS-K could impair the mitochondria via the accumulation of reactive oxygen species (ROS ), and induce caspase-dependent apoptosis through the mitochondrial pathways in gastric cancer cells; JS-K had good anti-tumor efficacy in gastric cancer and fine biological tolerance, which made JS-K a potential novel drug for the treatment of gastric cancer, and it deserved our further investigation.