The Importance of Cellular Energy Metabolism for the Sparing Effect of Dose Fractionation with Electrons and Ultra-violet Light

SummaryThe sparing effect of dose fractionation with electron and u.v. exposure was investigated in diploid yeast Saccharomyces cerevisiae. Sparing was observed at the same rate and to the same extent in air or under hypoxia if the cells were held in a glucose-containing nutrient medium. With non-fermentable substrates, e.g. lactate or acetate, the process was slower in the aerated sample, and absent in hypoxia. The action of some metabolic inhibitors known to interfere with cellular energy production was also studied. The sparing effect was diminished if ATP production was inhibited at an early stage of the metabolic pathway. The results are interpreted by assuming that energy-rich metabolites are essential for the sparing effect. Implications for radiotherapy are discussed.