Interaction of indomethacin with calf thymus DNA: a multi-spectroscopic, thermodynamic and molecular modelling approach

Indomethacin belongs to the acetic acid derivative class of non-steroidal anti-inflammatory drugs with diverse pharmacological and biological activities. Understanding the mechanism of interaction of drugs with possible target and off-target biomolecules can prove useful in the development of a rational drug designing system. In this paper, we have attempted to ascertain the mode of binding of indomethacin with calf thymus DNA (Ct-DNA) through various biophysical techniques and in silico molecular docking. Analysis of the UV-visible absorbance spectra and fluorescence emission profile of indomethacin upon addition of Ct-DNA indicates the formation of a drug-DNA complex. UV-visible absorbance and steady state fluorescence experiments revealed a binding constant on the order of 10(3) L mol(-1), which is consistent with those of well-known groove binders. Competitive displacement studies with ethidium bromide, acridine orange and Hoechst 33258 further suggested that indomethacin binds to the minor groove of the Ct-DNA. The above observations were further confirmed by KI induced quenching experiments, DNA melting studies, CD spectral analysis and viscosity measurements. The thermodynamic parameters like spontaneous free energy (Delta G < 0) and large favourable enthalpy (Delta H < 0) obtained from isothermal calorimetry indicated the involvement of hydrogen bonding and van der Waals forces in the binding process. Molecular docking further corroborated the experimental results.