Inhibition of hypoxia-induced HIF-1α-mediated autophagy enhances the in vitro antitumor activity of rhein in pancreatic cancer cells

A hypoxic microenvironment results in significantly elevated hypoxia-inducible factor-1 (HIF-1) level in pancreatic cancer. HIF-1 functions to maintain the survival of cancer cells. The present study was performed to investigate whether inhibition of HIF-1 alpha expression was involved in the in vitro antitumor effect of rhein in pancreatic cancer cells and to explore the underlying mechanism. sh-RNA knockout technique and western blotting were used to investigate the role of HIF-1 alpha in autophagy activation in MiaPaCa-2 and PANC-1 cells. The survival and glycolysis were assessed using MTT assay and colorimetric kits, respectively. Apoptosis was evaluated by detecting the levels of apoptosis-related proteins using western blotting. Among the five pancreatic cancer cell lines, MiaPaCa-2 and PANC-1 cells were more sensitive to hypoxia-induced autophagy. HIF-1 alpha regulated hypoxia-induced autophagy in MiaPaCa-2 and PANC-1 cells. Treatment with rhein inhibited the survival and suppressed glycolysis in MiaPaCa-2 and PANC-1 cells exposed to hypoxia. Bafilomycin A1 enhanced the suppressive effects of rhein on cell survival and glycolysis under hypoxia. Treatment with rhein, but not bafilomycin A1, significantly reduced HIF-1 alpha expression. In conclusion, inhibition of HIF-1 alpha-mediated autophagy enhances the in vitro antitumor activity of rhein in pancreatic cancer cells under hypoxia.