Dual inhibition of topoisomerase II and tubulin polymerization by azatoxin, a novel cytotoxic agent.
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.
Laboratory of Molecular Pharmacology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.
E
E
Solary
F
F
Leteurtre
K D
KD
Paull
D
D
Scudiero
E
E
Hamel
Y
Y
Pommier
D016923:Cell Death / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line / Q000187:drug effects; D004249:DNA Damage; D004305:Dose-Response Relationship, Drug; D004354:Drug Screening Assays, Antitumor; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D008938:Mitosis / Q000187:drug effects; D059005:Topoisomerase II Inhibitors; D014404:Tubulin / Q000737:chemistry; D050257:Tubulin Modulators; D014407:Tumor Cells, Cultured / Q000187:drug effects
D007211:Indoles; D059005:Topoisomerase II Inhibitors; D014404:Tubulin; D050257:Tubulin Modulators; C075996:azatoxin; D005047:Etoposide