Similar sequence specificity of mitoxantrone and VM-26 stimulation of in vitro DNA cleavage by mammalian DNA topoisomerase II.

The molecular mechanism of topoisomerase II trapping by antitumor drugs probably involves the formation of a ternary complex DNA-drug-topoisomerase II. Recent studies support the view that a drug molecule might be placed at the DNA cleavage site interacting with the two flanking base pairs and amino acid residues of the enzyme. In this work, the DNA sequence-dependent action of mitoxantrone on topoisomerase II DNA cleavage was investigated in SV40 DNA fragments and short oligonucleotides, in comparison to VM-26, 4-demethoxydaunorubicin, and mAMSA. Mitoxantrone and VM-26 had a much lower degree of selectivity than 4-demethoxydaunorubicin and mAMSA in stimulating DNA cleavage. DNA cleavage at sites that were always stimulated also by VM-26. In contrast, mitoxantrone and 4-demethoxydaunorubicin shared only 7% of cleavage sites, and about 70% of the 4-demethoxydaunorubicin-stimulated sites were also stimulated by VM-26. Unlike what is generally seen with anthracyclines, the structurally related drug, mitoxantrone, stimulated cleavage also at DNA sites observed without drugs. Local base preferences at the cleavage site as determined by statistical analysis showed that mitoxantrone preferentially cleaved the DNA at sites with a cytosine or a thymine at position-1. However, strong DNA cleavage stimulation by mitoxantrone was favored by specific base pairs at the next positions flanking the cleaved bond (positions -2 and +2) and at positions +8 and +9. Effects of base mutations on drug stimulation of DNA cleavage in short DNA oligonucleotides independently showed that a pyrimidine at position -1 is required for mitoxantrone action.(ABSTRACT TRUNCATED AT 250 WORDS)