Dual inhibition of topoisomerase II and tubulin polymerization by azatoxin, a novel cytotoxic agent

Biochem Pharmacol. 1993 Jun 22;45(12):2449-56. doi: 10.1016/0006-2952(93)90226-m.


Azatoxin (NSC 640737) is a synthetic molecule that was rationally designed as a topoisomerase II inhibitor (Leteurtre et al., Cancer Res 52: 4478-4483, 1992). The present study was undertaken in order to investigate the molecular pharmacology and the cytotoxic activity of azatoxin in human tumor cells. Alkaline elution experiments performed in HL-60 cells demonstrated that: (1) azatoxin induces DNA-protein cross-links and protein-linked DNA single- and double-strand breaks characteristics of topoisomerase II inhibition in HL-60 cells; and (2) the potency of azatoxin is comparable to that of etoposide (VP-16). Testing of azatoxin in 45 human cell lines in the National Cancer Institute (NCI) in vitro Drug Screening Program indicated that azatoxin was potent (mean IC50 = 0.13 microM), but that its cell line sensitivity profile was correlated with that of tubule inhibitors rather than that of topoisomerase II inhibitors. These data led us to investigate the anti-tubulin activity of azatoxin. We found that azatoxin inhibited tubulin polymerization in vitro and was a mitotic inhibitor at 1 microM and above in the human colon cancer cell line KM20L2. In these cells topoisomerase II inhibition, as detected by the induction of protein-linked DNA strand breaks, required azatoxin concentrations of at least 10 microM. In summary, azatoxin is a potent cytotoxic agent that inhibited both tubulin and topoisomerase II. At lower azatoxin concentrations the former activity prevailed whereas at higher concentrations topoisomerase II inhibition became prominent.

Publication types

  • Comparative Study

MeSH terms

  • Cell Death / drug effects
  • Cell Division / drug effects
  • Cell Line / drug effects
  • DNA Damage
  • Dose-Response Relationship, Drug
  • Drug Screening Assays, Antitumor
  • Etoposide / pharmacology
  • Humans
  • Indoles / pharmacology*
  • Mitosis / drug effects
  • Topoisomerase II Inhibitors*
  • Tubulin / chemistry
  • Tubulin Modulators*
  • Tumor Cells, Cultured / drug effects


  • Indoles
  • Topoisomerase II Inhibitors
  • Tubulin
  • Tubulin Modulators
  • azatoxin
  • Etoposide