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 (ΔH°), Gibbs free energy (ΔG°) and entropy (ΔS°) 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.