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Mitoxantrone (MXT), an anti-tumor antibiotic, shows irreversible electrochemical behavior at a waxed graphite electrode in a 0.05 M Tris-HCl buffer (pH 7.4) solution. The interaction between MXT and calf thymus DNA (ctDNA) in solution has been studied using cyclic voltammetry. An electrochemical equation suitable for examining the binding of irreversibly electroactive molecules to DNA is established. Determination of diffusion coefficients of both free and binding MXT (D(f), D(b)), the binding constant (K) and binding site size (s base pairs per molecule, bp) of MXT with DNA was performed on the basis of the equation. A nonlinear fit analysis of the experimental data yielded: D(f)=3.76 x 10(-5) cm(2)s(-1), D(b)=2.73 x 10(-7) cm(2)s(-1), K=8.7 x 10(9) cm(3)mol(-1), s=2.8 bp. The results demonstrate that MXT binds tightly to ctDNA and covers three base pairs. The anthraquinone of MXT, which is a planar heterocyclic ring, intercalates between the DNA's base pairs. The two aminoethylamino side-chains of the drug fit to the major groove reinforce the combination of MXT and DNA. The results show that MXT is a DNA intercalator with a high binding constant compared to those of other anthraquinones.

A rapid method for investigation of the interaction of DNA and electroactive ligands based on an electrochemical equation for irreversible processes is presented. The binding constant (K) and the size of binding site (s) are simultaneously obtained from the dependence of the current on the amount of added DNA in voltammetry. A non-intercalative binder (Hoechst 33258) and two DNA-intercalators (mitoxantrone (MXT) and actinomycin D (AMD)) were examined in experiments. It was found that the binding constant of Hoechst 33258, mitoxantrone and actinomycin D, were 2.1 x 10(8), 8.9 x 10(9) and 9.1 x 10(9) cm(3) mol(-1); and the size of their binding sites were 4, 3 and 8, respectively. The study provides a convenient and sensitive approach for estimating affinity parameters and outlining the interaction between DNA and electroactive targeting compounds.

An electrochemical method was used to probe the interaction of actinomycin D (AMD) and calf thymus DNA (ctDNA) in phosphate buffer solution (pH 7.0) at an oxidized waxed graphite electrode. AMD showed a pair of nonsymmetric peaks at −0.51 and 0.19 V in cyclic voltammetry. As a result of reaction with ctDNA, the voltammetric peaks of AMD disappeared. The diffusion coefficient of free AMD (Df=1.9×10−5 cm2 s−1), binding constant (K=7.54×109 cm3 mol−1) and binding site size (s=8.1) of the AMD–DNA complex were obtained simultaneously by nonlinear fit analysis of voltammetric data based on an electrochemical equation, which was derived to examine the interaction of DNA and irreversibly electroactive compounds. The results demonstrate that AMD binds tightly to ctDNA. The AMD phenoxazone ring intercalates between the DNA base pairs. The two side chains of the depsipeptide extend along the minor groove of DNA and cover eight base pairs. The study provides a convenient and sensitive approach to estimate affinity parameters of the interaction between DNA and targeting compounds. [Copyright &y& Elsevier]