TY - JOUR T1 - Inhibition of DNA Replication in HeLa S<sub>3</sub> Cells by Macromomycin-I, an Antitumor Protein Antibiotic JF - Molecular Pharmacology JO - Mol Pharmacol SP - 491 LP - 496 VL - 18 IS - 3 AU - JAN M. WOYNAROWSKI AU - TERRY A. BEERMAN Y1 - 1980/11/01 UR - http://molpharm.aspetjournals.org/content/18/3/491.abstract N2 - 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. 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. ER -