Silymarin suppresses proliferation of human hepatocellular carcinoma cells under hypoxia through downregulation of the HIF-1α/VEGF pathway

Background: Hypoxia is a significant feature of many solid tumors and can activate hypoxia-inducible factor 1a (HIF-1a)/vascular epidermal growth factor (VEGF) signaling pathway, which is closely related to the occurrence and development of primary liver cancer (PLC). Silymarin (SM) had been used as a traditional liver protective drug for decades. Recent studies have found that SM has chemopreventive and chemosensitizing effects on multiple cancers. In this study, we investigated the effects of SM on HIF-1a/VEGF signaling in human hepatocellular carcinoma cells under hypoxia conditions.Methods: HepG2 and Hep3B cells were divided into different experimental groups according to different culture conditions (aerobic or anaerobic) and the concentration of SM in the culture medium. The cellular proliferation, migration, invasion, colony formation, and apoptosis were observed by using methyl thiazolyl tetrazolium (MTT) assay, cell migration assay, in vitro invasion assay, soft agar colony formation assay, and Annexin V apoptosis assay, respectively. The cellular expressions of HIF-1a and VEGF were determined by real-time reverse transcription-polymerase chain reaction (RT-PCR) and western blot (WB) analyses.Results: SM reduced cellular proliferation, migration, invasion, and colony formation, but induced apoptosis in HepG2 and Hep3B cells under hypoxia conditions. The half inhibitory concentrations (IC50) of SM on HepG2 and Hep3B cells were 58.46 and 75.13 umol/L, respectively. SM also suppressed cellular expressions of HIF-1a and VEGF in HepG2 and Hep3B cells under hypoxia conditions at the mRNA and protein levels. All these effects of SM were dose dependent.Conclusions: The inhibitory effect of SM on HepG2 and Hep3B cells under hypoxia is partially via downregulating HIF-1a/VEGF signaling, which may serve as a potential drug therapy target for liver cancer based on SM.