MECHANISM OF ACTION OF ACLACINOMYCIN A

I. THE EFFECT ON MACROMOLECULAR SYNTHESES

Abstract

The mechanism of action of aclacinomycin A was investigated with mouse tumor cells and Escherichia coli. The antibiotic inhibited growth of mouse lymphoblastoma L5178Y cells completely at a concentration of 0.0125 μg/ml, and partially at 0.0063-0.0031 μg/ml. A greater inhibition of RNA than DNA synthesis was found in the intact cells of L5178Y: i.e. , approximately 50% inhibition of the former occurred at an antibiotic concentration of 0.07 μg/ml, and that of the latter at 1.0 μg/ml. The degree of preferential inhibition by aclacinomycin A was more pronounced than that by adriamycin. Protein synthesis was not significantly affected. RNA synthesis by RNA polymerase II, from EHRLICH mouse carcinoma cells, was sensitive to aclacinomycin A. By the method employed, approximately 50% inhibition was observed at an antibiotic concentration of 1 μg/ml, with calf thymus DNA or poly(dAdT) as a template. In contrast, RNA polymerase reaction with poly (dIdC) was resistant to the antibiotic. The inhibition of RNA polymerase reaction with poly(dAdT) as template was apparently competitively reversed by increasing concentrations of the template but not of the enzyme, suggesting a direct interaction of the antibiotic with the template. Growth and macromolecular biosyntheses of E. coli were rather resistant to aclacinomycin A. RNA and DNA polymerase reactions with toluenized cells of E. coli P3478 (polA^-) were prevented by the antibiotic. RNA synthesis was inhibited by ca. 60% and DNA synthesis by ca. 25% at an antibiotic concentration of 10 μg/ml. RNA polymerase reaction, using E. coli enzyme and calf thymus DNA as a template, was blocked by aclacinomycin A: approximately 50% inhibition was observed at an antibiotic oncentration of 10 μg/ml; whereas DNA polymerase I reaction was not significantly affected by the antibiotic.