SEQUENCE SELECTIVITY OF TOPOISOMERASE-II DNA CLEAVAGE STIMULATED BY MITOXANTRONE DERIVATIVES - RELATIONSHIPS TO DRUG-DNA BINDING AND CELLULAR EFFECTS

Mitoxantrone, a DNA intercalator, is an effective antitumor drug known to interfere with topoisomerase II function through stimulation of en zyme-mediated DNA cleavage. To clarify the drug structural requirement s for stimulation of topoisomerase II DNA cleavage, the cytotoxic acti vity and molecular effects of mitoxantrone, ametantrone, and a new der ivative (BBR2577), bearing a modification on one of the side chains, w ere examined in relation to their DNA binding affinities and modes of drug-DNA interaction. The results showed a good correlation between cy totoxicity and topoisomerase II DNA cleavage. The modification of one side chain did not influence the cytotoxic potency or the ability of t he drug to stimulate DNA cleavage. In contrast, removal of the hydroxy l substituents in the planar aromatic moiety (ametantrone) markedly af fected the efficacy of the drug. Ametantrone showed a markedly lower c apacity, compared with the other two compounds, to induce cleavable co mplexes both in intact cells and in SV40 DNA, which suggests a critica l role of these substituents in the formation of the ternary topoisome rase II-DNA-drug complex. The poor efficacy of ametantrone is likely d ue to low stability of the ternary complex. This is possibly related t o a different orientation of the drug chromophore intercalated into DN A, compared with those of mitoxantrone and BBR2577. The DNA cleavage e fficiencies of the tested drugs at low concentrations correlated with the DNA binding affinity. Identical DNA cleavage patterns were observe d with the three compounds, which suggests that all tested drugs share a similar specificity for interaction with sites recognized by the en zyme.