The effect of two topoisomerase inhibitors on low-dose hypersensitivity and increased radioresistance in Chinese hamster V79 cells.

A preliminary investigation of the effect of topoisomerase inhibitors on the structure of the survival curve at low doses has been carried out in Chinese hamster V79 cells, where there is a deviation from the predicted response to radiation (Marples and Joiner, Radiat. Res. 113, 41-51, 1993). Cells were treated with one representative drug for each enzyme (topoisomerase I or II) prior to X irradiation in air and assessed for cell survival using automated microscopic location of cells. VP-16 causes little or no effect, while camptothecin has a measurable effect up to 2 Gy. The results are discussed in terms of the role of DNA damage and cell cycle in increased radioresistance, which encourage further investigation of the effects of this class of drugs at low doses.