Targeting of 1-Naphthyl acetyl spermine to DNA: A calorimetric and spectroscopic investigation

Abstract

Isothermal titration calorimetry, UV optical melting, differential scanning calorimetry, circular dichroism and ethidium bromide displacement experiments were employed to study the interaction of the polyamine analogue 1-naphthyl acetyl spermine with DNA. The mode of binding was evaluated by hoechst 33258 displacement assay. Calorimetric studies divulged the binding of 1-naphthyl acetyl spermine to DNA to be endothermic with affinity (7.10±0.20)·105mol−1·dm3. The interaction was entropy driven with a small enthalpy contribution that was unfavourable. The binding was characterised by total enthalpy–entropy compensation and high standard molar heat capacity values. The interaction led to strong stabilization of the DNA melting. Circular dichroism studies revealed significant structural perturbation of the DNA on binding of 1-naphthyl acetyl spermine. Displacement assay with hoechst 33258 proved the minor groove binding mechanism of the analogue. Ethidium bromide displacement assay corroborated the ability of the spermine analogue to displace ethidium bromide from the DNA scaffold. Salt dependent studies reiterated the involvement of electrostatic interaction in the binding along with the strong involvement of hydrophobic interactions.