Radiosensitization of human tumor cells by gemcitabine in vitro.

Gemcitabine is a novel nucleoside analog that has shown clinical activity in a variety of solid tumors. The use of gemcitabine in combination with radiation was investigated in vitro using HT-29 colon carcinoma cells. Gemcitabine was demonstrated to be a potent radiosensitizer even at noncytotoxic concentrations. Increasing the concentration of gemcitabine and/or the duration of exposure increased the radiosensitization of cells. Biochemical studies indicated that a reduction in the dATP pool was the most likely mechanism of radiosensitization by gemcitabine. This effect is of great clinical importance and should be investigated in vivo.