Instability of the monofunctional adducts in cis-[Pt(NH3)2(N7-N-methyl-2-diazapyrenium)CI]2+;-modified DNA: rates of cross-linking reactions in cis-platinummodified DNA

摘要

Single- and double-stranded oligonucleotides containing a single monofunctional cis-[Pt(NH₃)₂(dG)(N7-N-methyl-2-diazapyrenium)]3+ adduct have been studied at two NaCI concentrations. In 50 mM and 1 M NaCI, the adducts within the single-stranded oligonucleotides are stable. In contrast, they are unstable within the corresponding double-stranded oligonucleotides. In 50 mM NaCI, the bonds between platinum and guanine or N-methyl-2,7-diazapyrenium residues are cleaved and subsequently, intra- or interstrand cross-links are formed as in the reaction between DNA and cis-DDP. In 1 M NaCI, the main reaction is the replacement of N-methyl-2,7-diazapyrenium residues by chloride which generates double-stranded oligonucleotides containing a single monofunctional cis-[Pt(NH₃)₂(dG)CI]+ adduct. The rates of closure of these monofunctional adducts to bifunctional cross-links have been studied in 60 mM NaCIO₄. Within d(TG CT/AGCA), d(CG CT/AGCG) and d(AGCT/AGCT) (the symbol' indicates the location of the adducts in the central sequences of oligonucleotides), the half-lifes (t_1/2) of the cis-[Pt(NH₃)₂(dG)CI]+ adducts are respectively 12, 6 and 2.8 hr and the crosslinking reactions occur between guanine residues on the opposite strands. Within d(AG TC/GACT), d(CG AT/ATCG) and d(TGTG 7CACA) or d(TG TG/CACA) t_1/2, are respectively 1.6, 8 and larger than 20 hr and the intrastrand cross-links are formed at the d(AG), d(GA) and d(GTG) sites, respectively. The conclusion is that the rates of conversion of cis-platinum - DNA monofunctional adducts to minor bifunctional crosslinks are dependent on base sequence. The potential use of the instability of cis-[Pt(NH₃)₂(dG)(N7-N-methyl-2-diazapyrenium)]3+ adducts is discussed in the context of the antisense strategy.