16-O-caffeoyl-16-hydroxylhexadecanoic acid, a medicinal plant-derived phenylpropanoid, induces apoptosis in human hepatocarcinoma cells through ROS-dependent endoplasmic reticulum stress

Background: Hepatocellular carcinoma (HCC) is the leading cause of cancer death, and novel chemotherapeutic drugs for treating HCC are urgently needed. 16-O-caffeoyl-16-hydroxylhexadecanoic acid (CHHA) is a new phenylpropanoid isolated by our group from Euphorbia nematocypha which is commonly used to treat solid tumors. However, the underlying mechanisms responsible for the CHHA-induced apoptosis in cancer cells, particularly in HCC, remain unknown. Purpose: In the present work, we evaluated the growth inhibitory effect of CHHA on HCC cells and explored the underlying molecular mechanisms. Methods/Study designs: The anti-proliferative activity of CHHA was evaluated by MTT assay. Cell cycle, apoptosis, reactive oxygen species and mitochondrial membrane potential were determined by flow cytometry. ER localization was performed by ER-tracker red staining. The effect of CHHA on the expression of mRNA in HCC cells was detected by RT-PCR. The potential mechanisms for proteins level in ER pathway and apoptosis were analyzed by Western blot. Results: Our results showed that CHHA exerted strong anti- proliferative activity against both HepG2 and Bel7402 cells in a concentration-and time-dependent manner. Mechanistic studies demonstrated that CHHA induced apoptosis through mitochondrial apoptotic pathway, and arrested the cell cycle at G1 phase. CHHA was also found to induce endoplasmic reticulum (ER) stress, accompanied by ROS production, increase of intracellular calcium and up-regulation of GRP78, CHOP, caspase-12 and p-PERK. Inhibition of endoplasmic reticulum stress by salubrinal pretreatment could suppress both apoptosis and ER stress, indicating that ER stress induction contributes to apoptosis and is required for the latter. Besides, the ROS scavenger N-acetyl cysteine (NAC) significantly attenuated apoptosis induced by CHHA and reversed CHHA-stimulated the expression of ER markers. Conclusion: In conclusion, CHHA inhibited HCC cell growth and induced apoptosis through mitochondriamediated pathway and ROS-mediated endoplasmic reticulum stress. This provides molecular bases for developing CHHA into a drug candidate for the treatment of HCC.