Mechanism of action of macromomycin: DNA strand scission, inhibition of DNA synthesis and mitosis.

The effects of macromomycin (MCR), a high molecular weight peptide antibiotic, on cell division, DNA synthesis and DNA fragmentation were examined in cultured mammalian tumor cells. When MCR was added to HeLa cell culture simultaneously with [3H]thymidine, inhibition of DNA synthesis was observed depending on the amount of the drug present, although the inhibition was partial even at a high concentration of the drug. Preincubation of cells with MCR for 2 hours before assay was required for the complete inhibition of DNA synthesis. Cell division of synchronized L5178Y cells, arrested at metaphase, was strongly inhibited by MCR, indicating that the inhibition of cell mitosis by the drug was not dependent on the inhibition of DNA synthesis. Strand scission of DNA in MCR-treated cells was observed by alkaline sucrose gradient centrifugation. The fragmentation of cellular DNA occurred at low concentration of the drug and within a very short incubation time (37 degrees C, 5 minutes). At high concentrations of the drug, however, the size of the fragmented DNA remained constant. DNA polymerase activity in isolated nuclei from HeLa and L5178Y cells was stimulated by MCR. These data suggest that MCR works directly on cell nuclei and strand scission of DNA is one of the more important actions of the drug.