Abstract
Topoisomerase (topo) II poisons have been categorized into ATP-independent and -dependent drugs based on in vitro studies. We investigated drug-induced topoII-DNA complexes in intact cells almost completely depleted of ATP. Virtually no DNA single-strand breaks (SSBs), as measured by alkaline elution, were detected in energy-depleted cells treated with the topoII poisons etoposide, teniposide, daunorubicin, doxorubicin, mitoxantrone, or clerocidin. This inhibition was reversible; subsequent incubation with glucose restored the level of DNA SSBs. The effect of ATP depletion was specific for topoII, because topoI-mediated cleavable complexes induced by camptothecin were unaffected by ATP depletion. Furthermore, etoposide-induced DNA-protein complexes and DNA double-strand breaks, as measured by filter elution techniques, and topoIIα and -β trapping, as measured by a band depletion assay, were completely inhibited by energy depletion. Differences in drug transport could not explain the effect of ATP depletion. The topoII poison amsacrine (m-AMSA) was unique with respect to ATP dependence. In ATP-depleted cells, m-AMSA-induced DNA SSBs, DNA double-strand breaks, DNA-protein complexes, topoIIα and -β trapping were only modestly reduced. The accumulation ofm-AMSA was reduced in ATP-depleted cells, which indicates that drug transport could contribute to the modest decrease in m-AMSA-induced cleavable complexes. In conclusion, drug-induced topoII-DNA complexes were completely antagonized in ATP-depleted cells, except in the case of m-AMSA. One possible interpretation is that m-AMSA mainly produces prestrand passage DNA lesions, whereas the other topoII poisons tested exclusively stabilize poststrand passage DNA lesions in intact cells.
Footnotes
-
Send reprint requests to: Dr. Morten Sorensen, Laboratory of Experimental Medical Oncology, The Finsen Center, 5074, Rigshospitalet, 9 Blegdamsvej, DK-2100 Copenhagen, Denmark. E-mail:msorensen{at}dadlnet.dk
-
This work was supported financially by the Faculty of Health, University of Copenhagen, and by the Danish Cancer Society.
- Abbreviations:
- topo
- topoisomerase
- SSBs
- single-strand breaks
- DPCs
- DNA protein complexes
- DSBs
- double-strand-breaks
- FCS
- fetal calf serum
- DMSO
- dimethyl sulfoxide
- m-AMSA
- amsacrine
- VP-16
- etoposide
- DNP
- 2,4-dinitro-phenol
- Received August 27, 1998.
- Accepted November 30, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|