Background and Aims: Chloroquine is a widely used agent for the treatment of malaria and rheumatoid disorders, and it is also an autophagy inhibitor. Moreover, several studies have demonstrated that chloroquine exerts inhibitory effect on a variety of cancer cells, including the liver cancer cells. This study was designed to further observe the inhibitory effect of chloroquine on liver cancer cells in vitro and in tumor-bearing mice, and the connection with autophagy.  
Methods: Liver cancer Huh7 cells were exposed to different concentrations of chloroquine (0, 25 and 50 μmol/L) in vitro, and then the cell proliferation was determined by MTT assay. Tumor xenograft models were established in 75 nude mice by subcutaneous inoculation of Huh7 cells, and then the mice were equally randomized into 3 groups, and at 7 d after inoculation (tumor formation established), were intraperitoneally administrated with saline (control group), 25 mg/kg chloroquine (low-dose chloroquine group) and 50 mg/kg chloroquine (high-dose chloroquine group) respectively, once per day for 30 d. The tumor growth in each group was recorded. The xenografts were harvested at end of the experiment, and the expressions of autophagy-related proteins (LC3, p62) were determined by immunochemical staining and Western blot, respectively. 
Results: The results of MTT assay showed that the proliferation of Huh7 cells was significantly inhibited by either concentration of chloroquine compared with control (0 μmol/L), with a time- and concentration-dependent manner (all P<0.05). In the tumor-bearing mice, the xenograft growths in both chloroquine treated groups were significantly suppressed compared with control group, and the tumor growth suppression in high-dose chloroquine group was more evident than that in low-dose chloroquine group (all P<0.05); the results of immunohistochemical staining and Western blot showed that the expression levels of LC3 and p62 in the tumor tissues in both chloroquine treated groups were significantly increased compared with control group, and  the increasing amplitudes in high-dose chloroquine group were greater than those in low-dose chloroquine group (all P<0.05). 
Conclusion: Chloroquine can inhibit the growth of liver cancer cells both in vitro and in vivo, and the mechanism may be related to its regulating the expressions of autophagy-related proteins and then inhibiting the autophagy of the liver cancer cells.