Plantamajoside promotes metformin-induced apoptosis, autophagy and proliferation arrest of liver cancer cells via suppressing Akt/GSK3β signaling

Metformin, a well-known antidiabetic drug, exhibits anticancer effect in a variety of cancers, including liver cancer. Plantamajoside (PMS), a phenylethanoid glycoside compound isolated from Plantago asiatica, is proved to possess anticancer effects, too. In our study, we hypothesized that PMS might promote metformin mediated anticancer effects on liver cancer. The half maximal inhibitory concentration (IC50) of metformin was evaluated by cell viability assay. The influence of PMS on proliferation, migration, invasion and apoptosis of metformin-treated cells was evaluated by BrdU incorporation assay, flow cytometry, western blot, wound scratch healing assay, transwell cell migration assay and immunofluorescence. A fasting/feeding mouse model was built to evaluate the influence of PMS on metformin sensitivity in vivo. PMS (2.5, 10 or 40 μg/mL) treatment reduced the IC50 of metformin under different glucose concentrations. PMS (10 μg/mL) promoted metformin (5 mm) induced apoptosis and autophagy, and inhibition on proliferation, migration and invasion of HepG2 and HuH-7 cells. In the fasting/feeding mouse model, PMS (50 mg/kg) promoted metformin (200 mg/kg) induced proliferation arrest and apoptosis in vivo. Meanwhile, PMS reduced the level of pAkt(ser473) and GSK3β(ser9) in HepG2 and HuH-7 cells. Restoration of Akt/GSK3β signaling by a constitutively activated myr-Akt1 abrogated the effects of PMS on metformin-treated liver cancer cells. Our results demonstrated that PMS promoted the anticancer effects of metformin on liver cancer in vitro and in vivo.