Modification of Radiation Effect on Mammalian Tumour Cells by Pharmacological Agents

Abstract

IN an earlier communication it was demonstrated that the effect of X-irradiation on the reproductive capacity of mammalian tumour cells could be modified by the incorporation of relatively small amounts of halogenated pyrimidine deoxyribosides into the DNA of these cells¹. Additional work has now been completed in which the time and dose relationships of administration of the drugs and variation in the ionization density of the radiation have been examined. The P–388 lymphocytic leukæmia of the DBA/2 mouse and its use by serial dilution assay to examine cell reproductive capacity have been reported in detail² ; the TD₅₀ is defined as the mean number of cells necessary to produce 50 per cent tumour ‘takes’ in a group of recipient animals of the same strain, and the ‘surviving fraction’ is the result of control TD₅₀ divided by experimental TD₅₀.