Determination of the level of DNA modification with cisplatin by catalytic hydrogen evolution at mercury-based electrodes.

Electrochemical methods proved useful as simple and inexpensive tools for the analysis of natural as well as chemically modified nucleic acids. In particular, covalently attached metal-containing groups usually render the DNA well-pronounced electrochemical activity related to redox processes of the metal moieties, which can in some cases be coupled to catalytic hydrogen evolution at mercury or some types of amalgam electrodes. In this paper we used voltammetry at the mercury-based electrodes for the monitoring of DNA modification with cis-diamminedichloroplatinum (cisplatin), a representative of metallodrugs used in the treatment of various types of cancer or being developed for such purpose. In cyclic voltammetry at the mercury electrode, the cisplatin-modified DNA yielded catalytic currents the intensity of which reflected DNA modification extent. In square-wave voltammetry, during anodic polarization after prereduction of the cisplatinated DNA, a well-developed, symmetrical signal (peak P) was obtained. Intensity of the peak P linearly responded to the extent of DNA modification at levels relevant for biochemical studies (rb = 0.01-0.10, where rb is the number of platinum atoms bound per DNA nucleotide). We demonstrate a correlation between the peak P intensity and a loss of sequence-specific DNA binding by tumor suppressor protein p53, as well as blockage of DNA digestion by a restriction endonuclease Msp I (both caused by the DNA cisplatination). Application of the electrochemical technique in studies of DNA reactivity with various anticancer platinum compounds, as well as for an easy determination of the extent of DNA platination in studies of its biochemical effects, is discussed.