Voltammetric study of doxorubicin interaction with single-stranded and double-stranded DNA

The interaction of doxorubicin (DOX) - anthracycline antibiotic routinely used in the cancer treatment - with single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) has been studied by electroanalysis. As a part of the study, the redox behavior of DOX on carbon screen printed electrodes was thoroughly investigated by cyclic and square wave voltammetry. Preparations of DNA differing in molecular size and secondary structure, PCR-generated dsDNA fragments, and synthetic oligonucleotides and their duplex were employed as examples of ssDNA and dsDNA. Prior to studying, DNA samples were carefully characterized to verify DNA structure. The binding strength of DOX to both ssDNA and dsDNA under physiological pH and close to physiological ionic strength was found to be rather weak (with the binding constants of the order of 10³-10⁴ L/mol) and undistinguishable in practical terms. That suggests the electrostatic attraction between positively charged molecules of DOX and the negatively charged phosphate groups of DNA chains as a major driving force for the DOX-DNA interactions. Other modes of interaction such as the specific binding into minor and major grooves of dsDNA and the DOX insertion between paired nucleobases may be secondary in relation to electrostatic interactions of DOX with DNA phosphate groups. The use of ssDNA as a special control in a study of drug-DNA interaction mechanisms appears as an essential requirement to correctly evaluate the contributions of various modes of binding to the overall binding strength.