Nuclear genotype, growth phase, and the presence of metal ions all proved to be important in controlling the lethal effects of phleomycin in eukaryotic Saccharomyces cerevisiae. Among 120 normal and radiation-sensitive strains compared for their sensitivities to lethal effects of phleomycin, all mutant strains exhibiting enhanced sensitivities to phleomycin killing were also sensitive to killing by ionizing radiation. Mutants exhibiting sensitivities to phleomycin similar to normal strains of the same ploidy were sensitive to ultraviolet radiation. We conclude that cellular recovery from phleomycin-induced damage in yeast depends upon the function of some or all of 13 independent genes and upon at least some of the same steps in cellular pathways for the biological repair of damage by ionizing radiation. In this respect, the action of phleomycin is similar to the action of its structurally similar analog, bleomycin, even though phleomycin was substantially more cytotoxic. Stationary-phase haploid yeast cells were more sensitive than exponentially growing cells to killing by phleomycin. Survival of stationary-phase yeast was reduced to 0.3 ± 0.07% (S.E.) after 20-min exposures to phleomycin (1 µg/ml; approximately 6.7 × 10-7 m), but lethal effects of phleomycin were completely eradicated (98% survival) by the presence of 0.05 m ethylenediaminetetraacetate during the treatment period. The inactivation indicates an important role for one or more metal ion(s) in the in vivo toxicity of the phleomycin-bleomycin group of anticancer antibiotics.
This research was supported by the United Cancer Council, Inc., of Rochester, N. Y., Grants CA25609 from the NIH and VC-190 from the American Cancer Society, and United States Department of Energy Contract DE-AC02-76EV03490 at the University of Rochester Department of Radiation Biology and Biophysics. This paper has been assigned Report No. UR-3490-1698.