Saikosaponin-d Increases the Radiosensitivity of Hepatocellular Carcinoma Cell line SMMC-7721 via activation of p53 Level in Ox

Background: Saikosaponin-d (SSd) is a monomer terpenoid, purified from Chinese herbal drug Radix bupleuri, with multiple effects including anticancer. But the effect of SSd on the tumor exposed to radiation is largely unknown. To investigate the radiosensitive effect of SSd and its possible mechanism, we combined SSd with radiation therapy to treat hepatocarcinoma cell SMMC-7721 under oxia and hypoxia. Methods: The cell growth, cell apoptosis and cell cycle distribution were examined after treatment with SSd or radiation alone and their combinations in oxia and hypoxia. The protein and mRNA levels of p53, Bcl2 and BAX were measured by Western blot and RT-PCR respectively. Results: In either oxia or hypoxia, SSd and radiation alone exposure resulted in a cell growth inhibition and increased apoptosis rate at the concentration used. And when treated with the combination of SSd and radiation, these effects were enhanced. Moreover, SSd not only potentiated the effects of radiation to induce Go/G1 arrest in SMMC-7721 cells, but also reduced the G2/M-phase population in hypoxia. However, in oxia, SSd only potentiated the effects of radiation to induce Go/G1 arrest,but not in G2/M-phase. In addition, these effects resulting from SSd or radiation and their combinations were companied with up-regulated expression of p53 and BAX, a down-regulation of Bcl2 in either oxia or hypoxia. Conclusion: It is demonstrated unambiguously that SSd potentiated the effect of radiation in this cell line and would be a promising radiosensitizer. Radiosensitizing effect of SSd may contribute to its function to affect Go/G1 and G2/M checkpoints of cell cycle