Autophagy inhibition promotes 5-fluorouraci-induced apoptosis by stimulating ROS formation in human non-small cell lung cancer A549 cells.

Chemotherapy is an important option for the treatment of various cancers including lung cancer. However, tumor resistance towards cytotoxic chemotherapy has become more common. It has been reported that autophagy is one of the processes contributing to this resistance. In the present study, we found that the anti-cancer drug 5-fluorouraci(5-FU) could induce autophagy in A549 cells. 5-FU treatment could lead to the conversion of LC3 I/II, the up-regulation of Beclin-1, the down-regulation of p62 and the formation of acidic vesicular organelles (AVOs) in A549 cells. Pre-treatment of cancer cells with 3-MA or siAtg7 could enhance 5-FU-induced apoptosis through the activation of caspases, and the caspase inhibitor z-VAD-fmk rescued the cell viability reduction. Furthermore, the inhibition of autophagy also stimulated ROS formation and scavenging of ROS by antioxidant NAC inhibited caspase-3 activity, prevented the release of cyt-c from mitochondria and eventually rescued cancer cells from 5-FU-mediated apoptosis. These results suggest that 5-FU-elicited autophagic response plays a protective role against cell apoptosis and the inhibition of autophagy could sensitize them to 5-FU-induced caspase-dependent apoptosis through the stimulation of ROS formation.