Autophagy is induced by 3β-O-succinyl-lupeol (LD9-4) in A549 cells via up-regulation of Beclin 1 and down-regulation mTOR pathway

The purpose of this study is to investigate the antitumor activity of a new derivative of lupeol-3β-O-succinyl-lupeol (LD9-4) and the molecular mechanism underlying cell death in human non-small cell lung cancer A549 cells. The results revealed that LD9-4 inhibited A549 cell proliferation in a time- and dose-dependent manner, with an IC50 value of 5.78 ± 0.48 μM after cells exposed to LD9-4 for 72 h. Markers indicative of apoptosis (cell cycle arrest, phosphatidylserine externalization and Hoechst33258 staining) were uniformly negative in LD9-4 exposed cells. Interestingly, transmission electron microscope, MDC staining and LC3 level determination all confirmed that autophagy was induced in LD9-4 treated A549 cells. Furthermore, we found that LD9-4-induced autophagy in A549 cells was associated with the increase of intracellular reactive oxygen species and the decrease of phosphorylated mTOR and p70S6K levels. In the meanwhile, both mRNA and protein levels of Beclin 1 were up-regulated in a time-dependent manner. Our data suggest that autophagy is induced by LD9-4 in A549 cells, and the accumulating reactive oxygen species, up-regulation of Beclin 1 and inhibition of the mTOR signaling pathway are involved in this process.