Our earlier studies have shown that gossypol is a specific inhibitor of DNA synthesis in cultured cells at low doses. In an attempt to determine the mechanism for the inhibition of DNA synthesis by gossypol we observed that gossypol does not interact with DNA per se but may affect some of the enzymes involved in DNA replication. These studies indicated that gossypol inhibits both in vivo and in vitro the activity of DNA polymerase alpha (EC 2.7.7.7), a major enzyme involved in DNA replication, in a time- and dose-dependent manner. Kinetic analysis revealed that gossypol acts as a noncompetitive inhibitor of DNA polymerase alpha with respect to all four deoxynucleotide triphosphates and to the activated DNA template. Inhibition of DNA polymerase alpha does not appear to be due to either metal chelation or reduction of sulfhydryl groups on the enzyme. Gossypol also inhibited HeLa DNA polymerase beta in a dose-dependent manner, but had no effect on DNA polymerase gamma. These results suggest that inhibition of DNA polymerase alpha may account in part for the inhibition of DNA synthesis and the S-phase block caused by gossypol. The data also raise the possibility that gossypol may interfere with DNA repair processes as well.
DNA Polymerase I DNA Polymerase II