Molecular Pharmacology, Vol 18, 491-496, Copyright © 1980 by the American Society for Pharmacology and Experimental Therapeutics

Inhibition of DNA Replication in HeLa S₃ Cells by Macromomycin-I, an Antitumor Protein Antibiotic

¹ Department of Experimental Therapeutics, Roswell Park Memorial Institute, Buffalo, New York 14263

Macromomycin-I, a chromophore-containing form of an antitumor protein antibiotic macromomycin, was found to be a potent inhibitor of [³H]thymidine incorporation into DNA in intact nonsynchronous and G₁/S-synchronized HeLa S₃ cells. This inhibitory effect depended on the drug dose and duration of treatment, but was essentially independent of the cell cycle position, within the G₁ through S phases. A parallel inhibition of DNA synthesis was observed in lysates and purified nuclei from drug-treated cells (as measured by incorporation of radioactive dTTP into DNA), indicating that the drug interferes with DNA biosynthesis after formation of deoxynucleoside triphosphates. The addition of a cytoplasmic fraction from untreated cells to purified nuclei from drug-treated cells failed to overcome the inhibition of DNA synthesis, while a cytoplasmic fraction from drug-treated cells was able to stimulate efficiently DNA synthesis in purified nuclei from untreated cells. Moreover, the inhibition of DNA synthesis in nuclei from drug-treated cells could be overcome by the addition of exogeneous DNA. These data demonstrate that macromomycin-I acts on DNA replication by interfering with the template and probably does not affect DNA polymerase or other factors involved in replication. In addition, macromomycin-I was found to enhance the incorporation of [³H]thymidine into DNA in HeLa S₃ cells in the presence of hydroxyurea; thus, the drug seems to stimulate DNA repair. Both findings, inhibition of DNA replication and stimulation of repair synthesis, probably arise from the drug’s damage to DNA and support the assumption that this damage is a primary event in the cytotoxic action of macromomycin.

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ACKNOWLEDGMENTS The authors would like to thank Jeffrey LaDuca for his excellent technical assistance and Nina Ruth Wright for her aid in editing the manuscript.