Binding investigation of chrysin and flavone with promoter DNA sequence d(CACGTG)2: Multi spectroscopic studies and cytotoxic evaluation

Abstract

Interactions of chrysin and flavone with d(CACGTG)₂ DNA sequence were explored using multi spectroscopic techniques. Absorption and fluorescence spectroscopic results indicated the partial intercalation for chrysin, and flavone interact externally. The binding coefficient (K_b) values of chrysin and flavone are 10⁵ and 10⁴ M^-1, respectively. Job plots using fluorescence data confirmed the 1:1 stoichiometry for the chrysin DNA complex, while multiple stoichiometries for the flavone DNA complex in solutions. Fluorescence lifetime analysis data showed that the average lifetime of chrysin increased while the average lifetime of flavone decreased upon complexation with DNA. Competitive displacement studies with EtBr and Hoechst 33258 data suggest partial intercalation. Circular dichroism results showed that DNA structures were perturbed upon chrysin and flavone binding. Circular dichroism and differential scanning calorimetry thermal data showed minute changes in melting temperature at 1:1 complex for chrysin-DNA, while there was no significant change in flavone DNA complex. These slight changes in melting temperatures support the non-intercalative binding of chrysin and flavone. The heat enthalpy changes of the free d(CACGTG)₂ DNA increased significantly upon interaction with both chrysin and flavone. Specifically, for chrysin, ΔH₁ increased from 88.07 to 196.40 kcal/mol and ΔH₂ from 41.14 to 104.00 kcal/mol. In the case of flavone, ΔH₁ rose from 88.07 to 127.40 kcal/mol and ΔH₂ from 41.14 to 180.70 kcal/mol. The van der Waals forces and hydrophobic interactions are key contributors to the binding between d(CACGTG)₂ DNA and both chrysin and flavone. The cytotoxic effect of chrysin and flavone was analyzed using an MTT assay and AO/EtBr staining. MTT data showed that they exhibited a significant antiproliferation effect against MCF-7, DU-145, and HCT-15 cancer cell lines, where flavone is most effective against DU-145 prostate cancer cells, and chrysin has more effects against MCF-7 breast cancer cells. The IC₅₀ values of chrysin and flavone are 74.97 µM, 95.15 µM, 88.66 µM, 78.62 µM and 149.45 µM, 45.17 µM against MCF-7, HCT-15, and DU-145 respectively. Flavone compounds induced apoptosis substantially in all three cancer cell lines compared to the control cells. This study recognizes flavones as potential proapoptotic agents.