INTERACTION OF THE ANTITUMOR ANTIBIOTIC STREPTONIGRIN WITH DNA AND OLIGONUCLEOTIDES

The interaction of the aminoquinone antitumour antibiotic streptonigri n with plasmid DNA, calf thymus DNA and oligonucleotides, in the prese nce and absence of metal ions, has been studied using circular dichroi sm, NMR spectroscopy and gel electrophoresis experiments. In the absen ce of metal ions, streptonigrin does not interact with DNA. Incubation of the two enantiomers of streptonigrin with calf thymus DNA, in the presence of excess zinc(II), showed no evidence of selective interacti on of the natural enantiomer, (R)-streptonigrin, with the DNA by circu lar dichroism. The interaction of streptonigrin with the hexanucleotid e d(GCATGC)(2) was studied by H-1- and P-31-NMR spectroscopy. In the p resence of four equivalents of zinc(II) nitrate and one equivalent of streptonigrin, small changes in chemical shifts of the proton resonanc es associated with T-4 and G(5) were detected as well as P-4 and P-5, consistent with a weak interaction of the zinc(II)-streptonigrin compl ex with the most accessible binding sites, involving the phosphate gro ups and guanine N7, at either end of the duplex. In contrast, no signi ficant interaction between the metal complex and d(ATGCAT)(2) was dete cted. Gel electrophoresis experiments were carried out to probe the se quence specificity of the interaction of the non-covalent streptonigri n-metal complexes with DNA, the DNA cleavage reaction of supercoiled D NA, and the specificity of the cleavage reaction. DNase I footprinting showed no sequence specific interactions. Zinc(II), copper(II) and ma nganese(II) enhanced the cleavage of supercoiled DNA into nicked and l inear forms of DNA, while magnesium showed no cleavage reactions under identical conditions. The DNA cleavage reaction of streptonigrin and NADH in the presence and absence of metal ions was studied. Overall, l ittle sequence specificity was observed, but slightly different cleava ge patterns suggest that the DNA cleavage can be influenced by the nat ure of the metal ions.