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.
Solary
E
E
Laboratory of Molecular Pharmacology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.
Leteurtre
F
F
Paull
K D
KD
Scudiero
D
D
Hamel
E
E
Pommier
Y
Y
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