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Protein-associated deoxyribonucleic acid strand breaks produced in mouse leukemia L1210 cells by ellipticine and 2-methyl-9-hydroxyellipticinium

1982; Elsevier BV; Volume: 31; Issue: 20 Linguagem: Inglês

10.1016/0006-2952(82)90560-3

1873-2968

Leonard A. Zwelling, Stephen Michaels, Donna Kerrigan, Yves Pommier, Kurt W. Kohn,

DNA Repair Mechanisms

DNA intercalating agents, including ellipticine, had been found previously to produce protein-associated DNA single-strand breaks and double-strand breaks in mammalian cells. The relationship between these effects on DNA and cytotoxicity could not be determined reliably for ellipticine, because of the poor solubility characteristics of this compound. Studies were therefore carried out using the cationic derivative, 2-methyl-9-hydroxyellipticinium (2-Me-9-OH-E+), which has adequate water solubility and retains antitumor activity. DNA single-strand breaks (SSB) and DNA-protein crosslinks (DPC) were measured using the alkaline elution (pH 12) technique, and double-strand breaks (DSB) were measured by the neutral elution (pH 10) method. The effects of ellipticine and 2-Me-9-OH-E+ were compared in mouse leukemia L1210 cells. Like ellipticine, moderate concentrations of 2-Me-9-OH-E+ produced protein-associated SSB, indicated by the appearance of SSB and DPC at approximately equal frequencies and localized with respect to each other. Below 20 μM (1-hr treatments), the effects of the two drugs were comparable in magnitude. At higher concentrations, ellipticine produced extensive DNA breakage not associated with protein; this is perhaps secondary to an action on membranes or other non-DNA targets. However, 2-Me-9-OH-E+ produced only protein-associated strand breaks, even at 4-fold higher concentrations. The two compounds produced similar and relatively large extents of double-strand scission. The measured DSB/SSB ratio was higher than that produced by X-ray or certain other intercalators that have been similarly studied. The DNA effects of 2-Me-9-OH-E+, unlike those of ellipticine, were readily reversible and, therefore, permitted a meaningful correspondence between the magnitudes of the DNA effects and the inhibition of colony-forming ability. Comparison with two other types of intercalating agents indicated that neither the SSB nor the DSB predicts the magnitude of cell killing.