The role of usnic acid-induced apoptosis and autophagy in hepatocellular carcinoma.

Usnic acid (UA) is a multifunctional bioactive lichen secondary metabolite with potential anti-cancer properties. Although the promising therapeutic effects of UA have been investigated in different cancer cell lines, the mechanism driving UA-induced cell death has yet to be elucidated. As the type of cell death (apoptosis or autophagy) induced by UA may vary depending on the cancer cell type, we first studied the cytotoxic effects of UA in HEPG2 (HBV(-)) and SNU-449(HBV(+)) hepatocellular carcinoma (HCC) cell lines. HCC cell viability was considerably reduced in a dose-dependent manner at 12, 24, and 48 h after treatment with UA ( p < 0.05). However, SNU-449 cells were more sensitive to UA than HEPG2 cells. UA also induced apoptotic cell death in HCC cells with cell cycle arrest at G0/G1 and G2/M phase depending on the genetic profile of each cell type. On the other hand, we observed acidic vesicular organelles in HCC cells after 36 h of UA treatment. Taken together, these findings suggest that UA stimulates apoptosis and autophagy in HEPG2 and SNU-449 cells without damaging normal control cells. Thus, UA might be a potential therapeutic compound for HCC treatment. However, there is a need for further studies investigating the death-promoting or preventing roles for autophagy and the molecular signaling mechanisms induced by UA treatment.