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

Abstract

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 <i>Livistona chinensis</i> 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.