Background and purpose: The previous work of this study has showed that the treatment of liver cancer cells with emodin could induce endoplasmic reticulum (ER) stress and apoptosis. Given the cross-talk between ER stress and autophagy

this study aimed to investigate whether blockage of autophagy

a defense mechanism against environmental stress

could improve the killing effect of emodin on liver cancer cells. Methods: The CYTO-ID autophagy detection kit and Western blot were used to determine autophagy in liver cancer cells. After combined treatment with chloroquine (CQ) and emodin

cancer cell survival was analyzed by ATPlite assay and clonogenic assay. Apoptosis was detected by both flow cytometry analysis and Western blot. Results: Autophagy could be induced in liver cancer cells after treatment with emodin. Inhibition of autophagy significantly increased growth-inhibitory effect of emodin on both HepG2 and Huh7 cancer cells. The combination treatment with CQ and emodin promoted remarkable apoptosis in liver cancer cells

evidenced by the increase in the percentage of cells in sub-G1 phase and the higher expression lever of cleaved caspase-3. Conclusion: Therapeutically targeting autophagy is capable of enhancing cytotoxicity of emodin in liver cancer cell lines.