Abstract

Nucleic acids are the biological target for many antimicrobial, antitumor and antiviral drugs. Ligand-DNA interactions can be classified into two major categories: 1. covalent binding, which can provide to intermolecular adducts, 2. physico-chemical interactions, which can be divided into intercalation (e.g. adriamycin) or groove binding (e.g. dystamycin). There are several methods to investigate interactions between drug and DNA. Some of them measure changes in DNA structures, such as lengthening and untwisting of DNA helix. Other techniques measure changes in drug environment. With the increasing availability of sensitive microcalorimeters, particular interest has arisen in the thermodynamics of drug-DNA interaction.Microcalorimetry ITC (Isothermal Titration Calorimetry) is the only technique, that directly measures the enthalpy changes associated with interactions between molecules. When we have only one thermal process, we can obtain almost complete thermodynamic profile of reaction in one experiment using ITC technique. This profile helps to understand which molecular forces drive the complex formation. However during titration of DNA by concentrated ligand solution, for some ligands occur an additional process - deaggregation of the ligand. The deaggregation is a strong endothermic process, in which heat energy is absorbed. So in the experiment we have two parallel thermal processes with two opposite thermal effects - ligand deaggregation and its physico-chemical binding into DNA. These two processes are difficult to distinguish using ITC technique and it might provide to improper interpretation of results. In our poster we propose an experimental procedure, by which the thermodynamic profiles of the two processes could be determined. The procedure was used to investigate the interaction of DNA with a few reference dyes, which aggregate in water solution. Almost complete thermodynamic profiles of this reaction have been obtained by proposed procedure.

Authors (3)