Thermodynamic characterization of the multivalent binding of chartreusin to DNA

Characterization of the thermodynamics of DNA- drug interactions is a very useful part in rational drug design. Isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC) and UV melting experiments have been used to analyze the multivalent (intercalation plus minor groove) binding of the antitumor antibiotic chartreusin to DNA. Using DNA UV melting studies in the presence of the ligand and the binding enthalpy determined by ITC, we determined that the binding constant for the interaction was 3.6 x 10(5) M(-1) at 20 degrees C, in a solution containing 18 mM Na(+). The DNA-drug interaction was enthalpy driven, with a DeltaH(b) of -7.07 kcal/mol at 20 degrees C. Binding enthalpies were determined by ITC in the 20-35 degrees C range and used to calculate a binding-induced change in heat capacity (DeltaCp) of -391 cal/mol K. We have obtained a detailed thermodynamic profile for the interaction of this multivalent drug, which makes possible a dissection of DeltaG(obs) into the component free energy terms. The hydrophobic transfer of the chartreusin chromophore from the solution to the DNA intercalating site is the main contributor to the free energy of binding.