RESUMO
PURPOSE: To determine the effect of cellular proliferation and cell cycle stage on the ability of postirradiation 5-fluorouracil (5-FU) to radiosensitize cultured human colon adenocarcinoma Clone A cells. METHODS AND MATERIALS: Cell survival curves were generated for irradiated: (a) log- and plateau-phase Clone A cells; and (b) Clone A cells separated by centrifugal elutriation into the various phases of the cell cycle; with and without postirradiation treatment with 100 micrograms/ml 5-FU. RESULTS: Postirradiation treatment with 5-FU sensitized proliferating cells to a greater degree than it sensitized cells growing in plateau phase. The beta component of cell kill in log-phase cells was increased by a factor of 1.5 with a sensitizer enhancement ratio of 1.21 at the 0.01 survival level. Plateau-phase cells showed less radiosensitization (sensitizer enhancement ratio of 1.13 at the 0.01 survival level); however, there was a mild increase in both alpha and beta kill in plateau-phase cells. Elutriated G1 cells were the most radiosensitive, independent of treatment with 5-FU. The phase of the cell cycle had little effect on the ability of fluorouracil to radiosensitize Clone A cells. CONCLUSION: Proliferating cells are more susceptible to radiosensitization with 5-FU than plateau-phase cells are, but this effect appears to be independent of the phase of the cell cycle.
