Abstract
Quercetin (QCT) has been shown to have anticancer activities associated with apoptosis and autophagy induction. However, whether autophagy is functionally responsible for the inhibitory effect of QCT on hepatocellular carcinoma (HCC) remains elusive. This study aims to investigate if QCT inhibits HCC growth via autophagy induction. The in vitro experiments showed that QCT inhibited the growth of human HCC cells in dose- and time-dependent manners and had minimal cytotoxicity to normal hepatocytes. QCT increased both autophagosomes and autolysosomes in HCC cells, as determined by electron microscopy, GFP-RFP-LC3 fluorescence confocal microscopy and Western blot analysis of autophagy-related biomarkers. Functional assays using pathway-specific inhibitors, activators or siRNAs indicated that QCT stimulated autophagy in part via inhibiting the AKT/mTOR pathway and activating the MAPK pathways. Further functional experiments using autophagy inhibitors demonstrated that QCT induced apoptosis of HCC cells in part via stimulating autophagy. The in vivo studies showed that QCT significantly inhibited tumor growth associated with apoptosis induction and autophagy stimulation, and that inhibition of autophagy significantly alleviated the QCT effect on tumor growth inhibition and apoptosis induction. To the best of our knowledge, this is the first in vivo report to demonstrate that QCT inhibits HCC tumor growth and induces apoptosis in part via stimulation of autophagy. Our results provide strong experimental evidence to support that autophagy stimulation may be an important mechanism by which QCT induces cancer cell apoptosis, and pave the way for further clinical investigations by applying QCT or QCT-rich foods for HCC intervention.