Vol. 55, Issue 3, 424-431, March 1999

Effect of Cellular ATP Depletion on Topoisomerase II Poisons. Abrogation of Cleavable-Complex Formation by Etoposide But Not by Amsacrine

M. Sorensen, M. Sehested, and P. B. Jensen

Laboratory of Experimental Medical Oncology, The Finsen Center (M.So., P.B.J.), and Department of Pathology, The Laboratory Center (M.So., M.Se.), Rigshospitalet, Copenhagen, Denmark

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 topoII and - 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, topoII and - trapping were only modestly reduced. The accumulation of m-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.