Effect of combined treatment with radiation and low dose etoposide on cellsurvival

Background: To improve the radiotherapy results, we evaluated etoposide as an effective radiosensitizer by using cultured cell-lines. Materials and Me thods: Forts cell fines having different doubling times (DT) were used: V79 (Chinese hamster fibroblasts, DT=9 hours), (1), T24 (human bladder cancer; DT=19 hours) (2), MDA-MB231 (human breast cancel; DT=25-30 hours) (3) and RMG1 (human ovarian cancer; DT=50 hours) (4). Cell survival was determined by colony assay and cell cycle analysis was performed by flow-cytometry. Re sults; The survival curves showed RMG1 to be the most radiosensitive, follo wed by MDA-MB231, T24, and V79. V79 was most che mosensitive to etoposide, followed by T24, MDA-MB231 and RMG1. Neither 24-hours exposure to etoposide (less than or equal to0.05 mug/ml) ol 0.5-h exposure (less than or equal t o1.0 mug/ml) had any cell killing effect on any of the cell lines used. Whe n the cells were irradiated after exposure to 1 mug/ml of etoposide fos 0.5 hours, no radiosensitization was observed in any of the cell lines Except V79. Enhanced radiosensitivity was observed in V79 and T24 cells (which hav e a relatively short DT) when they wt re incubated with 0.05 mug/ml etoposi de for 23 hours brat no enhanced effect was seen in MDA-MB231 ol RMG1 cells (which have a relatively long DT). Conclusion: It is suggested that a comb ination of radiation and etoposide may be useful in the treatment of rapidl y growing cancel.