Inhibition of autophagy enhances cinobufagin‑induced apoptosis in gastric cancer.

Cinobufagin is a cardiotoxic bufanolide steroid secreted by the Asiatic toad Bufo gargarizans. Cinobufagin is one of the active ingredients in the anticancer Chinese medicine called Chan Su, which was demonstrated to be an effective treatment for gastric cancer. Increasing evidence shows that inhibition of autophagy has a pro-apoptotic effect on human gastric cancer cells. The aim of the present study was to investigate the relationship between cinobufagin, autophagy and apoptosis in gastric cancer. Autophagy was induced or inhibited in the human gastric cancer cell line SGC-7901 by incubation in HBSS media or by treatment with 3-methyladenine or ATG5 siRNA, respectively. Following treatment, the levels of apoptosis, apoptotic proteins, reactive oxygen species (ROS), and mitochondrial membrane potential were compared between the conditions. As anticipated, we found that cinobufagin increased apoptosis in SGC-7901 cells. Notably, inhibition of autophagy, monitored by the absence of the autophagosome marker LC3-II, also enhanced cell apoptosis. This effect was reversed when autophagy was induced by incubation in HBSS media. Enhanced expression of pro-apoptotic indicators, including BAX, cytosolic cytochrome c, cleaved PARP, caspase-3 and caspase-9, was detected when autophagy was suppressed. Increased pro-apoptotic protein expression was accompanied by disrupted mitochondrial membrane potential and elevated ROS production. Altogether, these data suggest that inhibition of autophagy enhances the anticancer action of cinobufagin through increased apoptosis of gastric cancer cells. Moreover, these effects may be partly mediated by ROS generation and the activation of the mitochondrial programmed cell death pathway.