Biophysical and nuclear magnetic resonance spectroscopic studies of the binding of baicalein to DNA sequence d(CACGTG)2 and its cytotoxicity evaluation

Abstract

This paper reports the interaction of baicalein with a hexamer nucleic acid sequence d(CACGTG)2, present in the promoter region of various transcription factors, using biophysical techniques and nuclear magnetic resonance spectroscopy. UV–Visible absorption and fluorescence titration data implied partial intercalative binding of baicalein with a binding constant of 105 M−1. Continuous variation analysis using fluorescence data revealed a 1:1 stoichiometry of the baicalein and DNA in the solution. Circular dichroism data displayed a structural change of DNA upon baicalein binding. Thermal denaturing studied using circular dichroism showed that the melting temperature of the system does not significantly vary with the addition of baicalein. The spectral features suggest a partial intercalation of baicalein. Differential scanning calorimetric data exhibited two two-state transitions for alone DNA and its 1:1 complex with subtle changes in the melting temperatures supporting the non-intercalative binding of baicalein. Nuclear magnetic resonance data showed baicalein binding to the region near the C3pG4 base step, evidenced by the intermolecular nuclear overhauser effect cross peaks. Distance restrained molecular dynamics was employed to obtain the lowest energy structure. Biological evaluation of the effect of baicalein displayed excellent apoptotic effect on different cancer cell lines. IC50 values of 72.55, 79.9 and 96.7 µM were obtained in MCF-7, DU-145 and HCT-15 cell lines. The results uphold its chemotherapeutic potential.