EHHM, a novel phenolic natural product from Livistona chinensis, induces autophagy-related apoptosis in hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) ranks the second cause of cancer-associated mortality worldwide. In the present study, the effects and mechanisms of a new phenolic natural product E-[6′-(5′-hydroxypentyl)tricosyl]-4-hydroxy-3-methoxycinnamate (EHHM) isolated from Livistona chinensis on the growth of HCC cells were investigated. It was observed that EHHM treatment significantly suppressed cell proliferation and colony formation, and induced cell apoptosis via a mitochondria-dependent caspase pathway in HepG2 cells in a time- and dose-dependent manner. Meanwhile, EHHM treatment also led to upregulated expression of autophagy protein 5 (Atg5), Beclin 1 and light chain 3 (LC3)-II proteins, and accumulation of green fluorescent protein-LC3 punctate florescent foci in HCC cells, suggesting that EHHM-induced apoptosis is accompanied by autophagy induction. Western blotting revealed that EHHM-induced autophagy is related to the inhibition of the Akt/mechanistic target of rapamycin/p70 ribosomal protein S6 kinase signaling pathway. Furthermore, treatment with Atg5 small interfering RNA or autophagy inhibitors significantly enhanced EHHM-mediated growth inhibition and apoptotic cell death, indicating that autophagy serves as a self-protective mechanism in EHHM-treated HCC cells, and that combined treatment with EHHM and autophagy inhibitors may be an effective therapeutic strategy for HCC.