Thermodynamic and spectrographic studies on the interactions of ct-DNA with 5-fluorouracil and tegafur

The interactions of calf thymus deoxyribonucleic acid (ct-DNA) with two antitumour drugs (5-fluorouracil and tegafur) in aqueous buffer solution (pH 7.40) have been investigated using nano-watt-scale isothermal titration calorimetry (ITC), circular dichroism (CD), ultraviolet absorption (UV) and fluorescence spectroscopy. Thermodynamic parameters, i.e., binding proportions and constants, standard changes of enthalpy (ΔHo), Gibbs free energy (ΔGo) and entropy (ΔSo) have been derived from the calorimetric data. The binding ratios of 5-fluorouracil and tegafur with base pairs in ct-DNA are 1:3 and 1:4, respectively. The thermodynamic parameters have been discussed according to the influence of drugs on molecular structure of the DNA shown spectrogram. The results indicate that molecule of 5-fluorouracil or tegafur can intercalate itself into the intra-molecular space formed by DNA double helix and cause some changes in the secondary structure of DNA molecule.