Phleomycin, isolated from the culture filtrate of Streptomyces verticillus by Maeda et al.^2,3), is a water-soluble copper-containing antibiotic complex, effective against a variety of bacteria. Recent investigation by Lein et al.⁴⁾ and Umezawa et al.⁵⁾ revealed that it exhibits a significant tumor-inhibitory activity against Ehrlich carcinoma, sarcoma 180 and adenocarcinoma 755 of mice. Lein et al.⁴⁾and reported introduction of lysogenic bacteria by phleomycin.

In this connection, the mode of action of phleomycin has been investigated and the results are presented in this publication. It was observed that this antibiotic selectively inhibits the DNA synthesis in E. coli and in HeLa cells, as reported by Shiba et al.⁶⁾ with mitomycin C in E. coli. However, phleomycin was found to show much less activity of depolymerizing DNA to acid-soluble products than mitomycin C.