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 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.
Hepatocellular carcinoma (HCC) is the most frequently diagnosed cancer and the second major cause of cancer mortality worldwide (1-3). Infection with hepatitis B or C virus is the leading cause of HCC (4). Surgical resection is mostly selected in HCC treatment, followed by radiation therapy and chemotherapy; however, the 5-year survival rates following resection are very low, and the recurrence rates, mainly due to primary tumor metastasis and formation of new tumors, exceed 70% (5,6). Therefore, it is necessary and urgent to develop new effective chemotherapeutic agents for the treatment of HCC.
Livistona chinensis, a species of subtropical palm tree in eastern Asia, is widely distributed and cultivated in tropical and temperate regions, including several islands in the South China Sea, Southern Japan and Taiwan (7). The extract from the fruit of L. chinensis has been shown to exhibit antibacterial activity (8), and was traditionally used for folk remedy for various tumors, including chorionic carcinoma, esophageal carcinoma, leukemia and nasopharyngeal carcinoma (9,10). E-[6'-(5'-hydroxypentyl) tricosyl]-4-hydroxy-3-methoxycinnamate (EHHM), a new phenolic compound isolated from the L. chinensis fruit, has been shown to have antioxidant activity and a potent anticancer activity by inhibiting cancer cell proliferation (9,11). However, the antitumor effects and possible mechanisms of EHHM against human HCC have not yet been investigated. In the present study, it was demonstrated that EHHM can inhibit the proliferation and induce the apoptosis of HCC cells. In addition, EHHM induced autophagy in HCC cells.
The induction of cancer cell apoptosis is the main consideration in anticancer compound research (12-15). Cell morphology shrinkage, nuclear fragmentation, chromatin condensation and chromosomal DNA fragmentation are typically observed during apoptosis (16). However, to escape from apoptosis, cancer cells may also trigger various other pathways such as autophagy in order to overcome the adverse environment (17-19).
Autophagy is an intracellular degradation process, through which, a portion of the cytoplasmic components is delivered to lysosomes to be...