Similar rates for platination of hairpin loops and single-stranded DNA

The presence of ribonucleic acid hairpin structures is important for proper processing of the genetic information in living cells. Recent studies indicate that interactions between platinum based anticancer active metal complexes and hairpin motifs result in a change of their three-dimensional structure combined with a decrease of the melting temperature. We here report a study of the reaction between two platinum complexes, cis-[PtCl(NH3)(2)(OH2)](+) I and, cis-[PtCl(NH3)(c-NH2C6H11)(OH2)](+) II, and a series of short DNA hairpins which all exhibit a documented preference for adduct formation with donor groups located in the loop region; d(CGCGTTXTTCGCG), where X = G-N7, p(S), I-s6 or U-s4. The binding kinetics of adduct formation with the hairpins have been compared with that of binding to similar size single-stranded DNA; d(T6XT6), where X = G, p(S), I-s6 or U-s4. The overall picture reveals rather similar reactivity of the platinum complexes towards these two DNA secondary structures. However, the smaller complex I exhibits a tendency for preferential interaction with the hairpins, whereas the more bulky complex II shows a higher reactivity towards the single-stranded structures.