Chrysin-induced ERK1/2 Phosphorylation Enhances the Sensitivity of Human Hepatocellular Carcinoma Cells to Sorafenib.

Sorafenib is now standard treatment for advanced hepatocellular carcinoma (HCC). However, therapeutic efficacy is not as good as was predicted. Many efforts are being made to improve HCC sensitivity to sorafenib. Our previous study demonstrated that co-treatment with chrysin enhanced sorafenib sensitivity through inhibition of ATP-binding cassette super-family G member 2 (ABCG2). Whether there is another mechanism other than inhibition of ABCG2 underlying chrysin-mediated synergistic effect is still not completely elucidated. Phosphorylation of extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) was examined by western blot. Cell viability was examined by crystal violet staining. The importance of ERK1/2 phosphorylation was assessed by overexpression and blockage of mitogen-activated protein kinase kinase 1 (MEK1). Chrysin induced sustained ERK1/2 phosphorylation of HCC cells in both time- and dose-dependent manners. Overexpression of MEK1 enhanced, whereas blockage of MEK1 led to loss of chrysin-synergized sorafenib effect, through modulating ERK1/2 phosphorylation level. These results identify another novel mechanism underlying chrysin-mediated synergistic effect on sorafenib activity in HCC cells.