Biophysical and Spectroscopic Studies of Anthraquinone Derivatives with G Quadruplex DNAs

Abstract

Anthraquinone compounds posseses an important position in cancer therapy owing to their distinguishable binding characteristics to DNA. In the present study, 1,4-bis[(3-Diethylamino) propanamide]anthracen-9,10-dione (D1) and 1,4-bis[(3-Piperidino)propanamide]anthracen-9,10-dione (D2), Chrysophanol (D3), Rhein (D4), Aloe-emodin (D5) and Emodin (D6) were selected for binding studies with Wild Type Human Telomeric DNA (26-mer sequence) wHTel26: [d-TTAGGG(TTAGGG)3-TT] in K+ and Human Telomeric DNA (22-mer sequence) HTel22: [d-AGGG(TTAGGG)3] in Na+ rich solution. A combination of biophysical and structural studies has been used for studying the interaction and to establish the binding sites by UV absorbance, Fluorescence, Circular Dichroism (CD) spectroscopy and Molecular Docking. Thermal melting profiles using CD/ Differential Scanning calorimetry (DSC) has been obtained. Determination of anti-cancer activity via MTT assay has been done. From different independent techniques, the binding affinity values for D1, D2, D3 and D4 complexes with quadruplex DNAs lies in the range of 107 M-1 - 108 M-1,106 M-1- 107 M-1, 105 M-1 106 M-1 and 103 M-1 104 M-1, respectively. While for D5 and D6, the complexes with similar binding affinity (104 M-1 105 M-1) values are observed. Partial stacking was found as preferential binding mode for D1 and D2. External binding may be due to electrostatic, van der Waals, hydrogen bonding or hydrophobic interactions were observed in case of D4 and D5 upon complexation and comparably D4 has shown very weak binding affinity. However, drug D3 depicts external binding at lower concentration of DNA while partial stacking at higher concentration of DNA. Similar, binding for drug D6 observed in Na+ solution while in K+ solution only external binding mode was found. Slope changes in absorbance, fluorescence and ellipticity variation with D/N ratios suggested the formation of complexes with well-defined stoichiometries. MTT assay has depicted cell death. Thermal denaturation profile gave distinct results in both the solutions with significant thermal stabilization in K+ rich solution and practically no thermal stabilization in Na+ solution. These results are encouraging since the conformations present in K+ solution are biologically more relevant therefore, has immense therapeutic potential. newline