Radiosensitivity enhancement of human hepatocellular carcinoma cell line SMMC-7721 by sorafenib through the MEK/ERK signal pathway

Purpose: Sorafenib, an oral multikinase inhibitor, is the first agent that has demonstrated an improved overall survival benefit in advanced hepatocellular carcinoma, setting a new standard for first-line treatment. However, the association between radiosensitivity and sorafenib remains unclear. The purpose of this study was to investigate whether sorafenib could enhance radiosensitivity and the possible mechanisms of sorafenib-mediated radiosensitization in human hepatocellular carcinoma cell line SMMC-7721. Experimental design: The cell viability of human hepatocellular carcinoma cell line SMMC-7721 was determined by the 3-(4, 5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. The radiosensitization of sorafenib in SMMC-7721 cells was evaluated by clonogenic assays, and immunofluorescence for DNA double-strand break detection, and Western blotting for protein detection. Results: The MTT results clearly showed that sorafenib affected cell viability in human hepatocellular cell line SMMC-7721. Sorafenib administered 1 h before the radiation treatment resulted in radiosensitization with a sensitivity enhancement ratio (SER) of 1.65 as shown by clonogenic assays. Furthermore, sorafenib pretreatment led to decreased phosphorylation levels of extracellular signal-regulated kinase (ERK) and protein kinase B (AKT) in SMMC-7721 cells. Interestingly, pretreatment of mitogen-activated protein kinase kinases/extracellular signal-regulated kinase (MEK/ERK) signaling inhibitor U0126 had a similar effect as that of sorafenib pretreatment in hepatocellular carcinoma cells, whereas pretreatment of phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) signaling inhibitor LY294002 in the same cells had no effect on radiosensitization. The group treated with sorafenib and radiation was more sensitive to irradiation alone as demonstrated by the results of the DNA double-strand break detection. Conclusions: The combination of sorafenib and radiation affected cell viability more effectively than radiation alone. Sorafenib significantly enhanced the sensitivity of SMMC-7721 cells to radiation showing significantly reduced repair of DNA double-strand breaks. The MEK/ERK signaling pathway may be a pathway responsible for the radiosensitivity enhancement of sorafenib. Our data provided experimental support for the possible combination of sorafenib with radiation for the treatment of hepatocellular carcinoma and other cancers.