The mTOR inhibition in concurrence with ERK1/2 activation is involved in excessive autophagy induced by glycyrrhizin in hepatocellular carcinoma

Autophagy is a life phenomenon in which autophagosomes remove damaged or aging organelles and long-lived circulating proteins to maintain the cell's stability. However, disorders of excessive autophagy are a response of cancer cells to a variety of anticancer treatments which lead to cancer cell death. The Akt/mammalian target of rapamycin (mTOR) and the extracellular signal-regulated kinase 1/2 (ERK1/2) pathways are both involved in nutrient-induced autophagic phenomenon and exhibit vital relevance to oncogenesis in various cancer cell types, including hepatocellular carcinoma (HCC). However, the influence of autophagy for cancer cell death remains controversial and few scientists have investigated the variation of these two signaling pathways in cancer cell autophagic phenomenon induced by anticancer treatment simultaneously. Here, we explored the anticancer efficacy and mechanisms of glycyrrhizin (GL), a bioactive compound of licorice with little toxicity in normal cells. It is interesting that inhibition of Akt/mTOR signaling in concurrence with enhanced ERK1/2 activity exists in GL-induced autophagy and cytotoxicity in HepG2 and MHCC97-H hepatocellular carcinoma cells. These results imply that the GL-related anticancer ability might correlate with the induction of autophagy. The influence of induced autophagic phenomenon on cell viability might depend on the severity of autophagy and be pathway specific. In the subsequent subcutaneous xenograft experiment in vivo with MHCC97-H cells, GL obviously exhibited its inhibitory efficacy in tumor growth via inducing excess autophagy in MHCC97-H cells (P<0.05). Our data prompt that GL possesses a property of excess autophagic phenomenon induction in HCC and exerts high anticancer efficacy in vitro and in vivo. This warrants further investigation toward possible clinical applications in patients with HCC.