Poster Presenter

Physical Parameters As A Criterion Of Efficacy Of DNA-Anticancer Antibiotics Complexation On The Molecular Level
Anna Victorovna Shestopalova
Ukraine

One of the important trends in the present drug design is prediction of pharmacological action of drugs on the molecular level. The aims of such investigations are to describe correlations of physical parameters of interaction in the system of nucleic acid/drug and biological activity of the drugs; to obtain the most probable molecular models of nucleic acid/biologically active substance complexes on the basis of results of experimental physical techniques and molecular simulations; to determine the complexes containing the biologically active substances with maximal biological effectiveness. It is well known that the biological testing of new pharmaceuticals is a rather expensive and time-consuming procedure. Therefore, making prognoses of biological activity of pharmaceutical compounds on a molecular level could result in reducing of the time lapse between the synthesis of the new medicines and their applications as well as to give a basis for recommendation about synthesis of drugs with effective and focused pharmacological action.

The present work describes the results of the study of physical mechanisms of DNA interaction with a new series of biologically active substances, namely dimethylaminoalkylamino derivatives of anticancer antibiotic Actinomycin D (AMD). The main goal of this study is to acquire the structure and thermodynamic characteristics of drug/DNA complexes and compare these parameters with the biological activity of the drugs measured in the cell culture.

The following experimental physical methods are used to solve this problem: UV-visible spectrophotometry to study the different modes of ligand binding with DNA; infrared and Raman spectroscopy to disclose the interacting groups and hydration centers of the drug and DNA and follow the structural transitions of DNA upon the drug binding; piezogravimetry, to obtain the information on the influence of water on formation of DNA-drug complexes; differential scanning calorimetry to get the direct data on the thermostability of such complexes. Optimal molecular models of DNA-ligand interactions are built with the help of the methods of computational analysis (Monte Carlo simulations and molecular dynamics). Biological activity of the drugs that is measured by the rate of the drug-induced apoptosis and cell cycle perturbations in human leukemia MOLT-3 cells.

The results obtained have shown a direct correlation between the spectroscopic and thermal parameters of complexation of the drugs and DNA, and its biological activity. It is found that stability of all drug/DNA complexes mainly results from intercalation interactions, while additional stabilization for the most active against MOLT-3 cell lines dimethylaminoethylamino derivative of AMD is caused by stronger interactions between side chain of the drug and DNA and formation of specific water structure around this complex. Water molecules act as bridges between the hydration centers of drugs and DNA moieties providing additional stabilization of intercalation complexes of all drugs in the series and are most pronounced for dimethylaminoethylamino derivative of AMD. Formation of hydrogen bonds between side chains of this AMD derivative intercalated into GC-sites and sugar phosphate backbone of DNA observed in the molecular model of the complex could explain its substantial energetic preference established by calorymetric studies. On the basis of these results we have selected the optimal molecular models of complexes of all investigated drugs and DNA among those constructed by the computational approaches.

The results of the study enable us to conclude that the association constants, free energy of binding, the melting parameters, formation of hydrogen bonds and water bridges in binding sites of drugs and target may be recommended as a reliable quantitative data for prediction of the biological activity of drugs on the molecular level.