Radiosensitivity Enhancement of Human Hepatocellular Carcinoma Cell Line SMMC-7721 by Sorafenib Through the MEK/ERK Signal Pathway

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 is to investigate whether sorafenib can enhance radiosensitivity and the possible mechanisms of sorafenib-mediated radiosensitization in hepatocellular cell line SMMC-7721. The radiosensitization of sorafenib in human hepatocellular carcinoma cell line SMMC-7721 was evaluated by clonogenic assays. The cell proliferation was determined by the MTT assay, and immunofluorescence for DNA double-strand break detection, western blotting for protein detection. Our results clearly showed that sorafenib inhibited cell proliferation in human hepatocellular cell line SMMC-7721. Sorafenib injection resulted in radiosensitization both 24-hours and 1-hour before the radiation treatment with an enhancement ratio of 1.52 and 1.57, respectively. Furthermore, sorafenib pretreatment led to decreased phosphorylation levels of ERK and AKT in SMMC-7721 cells. Interestingly, pretreatment of MEK/ERK signaling inhibitor U0126 has a similar effect as that of sorafenib pretreatment in hepatocellular carcinoma cells, whereas pretreatment of PI3K/Akt signaling inhibitor LY294002 in the same cells has no effect on radiosensitization. The group treated with sorafenib and radiation was more sensitive to irradiation as demonstrated by the results of the DNA double-strand break detection. Sorafenib plus radiation can inhibit cell proliferation more effectively than radiation alone. Sorafenib significantly increased the sensitivity of SMMC-7721 cells to radiation by delaying the repair of DNA double-strand breaks. The MEK/ERK signaling pathway may be the critical pathway responsible for radiosensitivity of sorafenib. Our data provided experimental support for the possible combination of sorafenib with radiation for the treatment of hepatocellular carcinoma and other cancers.