DNA topoisomerases as targets for the anticancer drug TAS-103: DNA interactions and topoisomerase catalytic inhibition

Academic Article


  • TAS-103 is a novel anticancer drug that kills cells by increasing levels of DNA cleavage mediated by topoisomerase II. While most drugs that stimulate topoisomerase II-mediated DNA scission (i.e., topoisomerase II poisons) also inhibit the catalytic activity of the enzyme, they typically do so only at concentrations above the clinical range. TAS-103 is unusual in that it reportedly inhibits the catalytic activity of both topoisomerase I and II and does so at physiologically relevant concentrations [Utsugi, T., et al. (1997) Jpn. J. Cancer Res. 88, 992-1002]. Without a topoisomerase activity to relieve accumulating torsional stress, the DNA tracking systems that promote the action of TAS-103 as a topoisomerase II poison would be undermined. Therefore, the effects of TAS-103 on the catalytic activity of topoisomerase I and II were characterized. DNA binding and unwinding assays indicate that the drug intercalates into DNA with an apparent dissociation constant of ~2.2 μM. Furthermore, DNA strand passage assays with mammalian topoisomerase I indicate that TAS-103 does not inhibit the catalytic activity of the type I enzyme. Rather, the previously reported inhibition of topoisomerase I-catalyzed DNA relaxation results from a drug-induced alteration in the apparent topology of the nucleic acid substrate. TAS-103 does inhibit the catalytic activity of human topoisomerase IIα, apparently by blocking the DNA religation reaction of the enzyme. The lack of inhibition of topoisomerase I catalytic activity by TAS-103 explains how the drug is able to function as a topoisomerase II poison in treated cells.
  • Published In

  • Biochemistry  Journal
  • Digital Object Identifier (doi)

    Author List

  • Fortune JM; Velea L; Graves DE; Utsugi T; Yamada Y; Osheroff N
  • Start Page

  • 15580
  • End Page

  • 15586
  • Volume

  • 38
  • Issue

  • 47