Radiotherapy is the most common treatment of human cancer. Its ability to cure cancer is depending on
the response of cancer cells to radiation damage. In order to increase the therapeutic efficacy,
radiosensitizers had been used in combination with irradiation. Success of a strategy in improving
cancer radiotherapy relies on achieving the increased tumor cytotoxicity and at the same time, had no
adverse effect on normal tissue. Although many compounds that modify the radiation response of
mammalian cells had been discovered over the years but most offer no practical gain in radiotherapy
because they do not show a differential effect between tumors and normal tissue. The aim of this study
is to evaluate the potential effects of Thai medicinal plants extract on enhancement of radiosensitivity in
human epithelial colon cancer cells (HT29) and normal retinal pigment epithelial cells (RPE). The
radiosensitizer capacity was evaluated from cell survival analysis, micro-nuclei determination, and cell
cycle analysis. The result shown that extract from the stem of Derris scandens Benth strongly enhanced
radiosensitivity of human epithelial colon cancer cells (HT29) but had no effect on the radiosensitivity
of normal retinal pigment epithelial cells (RPE). Our finding demonstrated for the first time that D.
scandens extract holds radiosensitization activity. This will provide preliminary information for
developing a new potential radiosensitzer, with the ultimate goal of improving clinical outcomes for
cancer patients.