[Computation of a radiodosage equivalent of the effect of bleomycin]

The responses of in vitro cultured mammalian cells to X-rays and bleomycin were compared for establishing a general rule to convert X-ray dose to bleomycin dose for a given biological effect. There was no significant difference in the radiosensitivities according to cell lines used in this experiment, while the responses of cells to bleomycin varied from cell to cell. The X-ray dose-response curves for the cells were convex upward if plotted on a semilogarithmical scale, while bleomycin dose-response curves were convex downward. These results indicated that the ratio of X-ray dose and bleomycin dose required for a comparable biological effect would vary with the X-ray dose and from cell to cell. Preliminary treatment with bleomycin sensitized mammalian L5 cells to X-rays. When the cells were exposed to bleomycin following irradiation, no significant synergestic effect was observed, in spite of the fact that the bleomycin dose was sufficient to result in a survival of 4.5%.