HS-1200, a synthetic chenodeoxycholic acid derivative, has cytotoxic activity in various human cancer cells. The present study was undertaken to examine whether HS-1200 sensitizes radiation-induced apoptosis in MCF-7 human breast carcinoma cells. Clonogenic assay elucidated that the combination treatment with HS-1200 and radiation induced more cytotoxic effects than the radiation treatment alone. Nuclear staining, DNA electrophoresis and Western blot analysis for poly(ADP-ribose) polymerase revealed that the increased cytotoxic effect by the combination treatment resulted from the augmentation of apoptosis. There was an increase in the expression level of Bax and its translocation onto the mitochondria, a reduction in the mitochondrial membrane potential in the earlier time-points, and the release of cytochrome c into the cytosol increased in the MCF-7 cells treated with radiation and HS-1200 compared to the cells treated only with radiation. Therefore, the synthetic bile acid derivative, HS-1200, could have the therapeutic potential as a radiosensitizer in MCF-7 cells.

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