Design, synthesis and investigation of the interaction behavior between two acridone derivatives, 8-chloro acridone and nitrile cyanide acridone with calf thymus DNA, by different spectroscopic techniques

Evaluating the binding interaction between biomacromolecules and various chemical compounds is one of the most biologically researched topics. The present experimental study attempted to investigate the binding interaction between two types of acridone derivative, namely 8-chloro acridone (CA) and nitrile cyanide acridone (NCA) as antineoplastic agents and calf thymus DNA (ctDNA) by applying various spectroscopic techniques. The binding interactions were first characterized by fluorescence quenching experiments, and it was demonstrated that NCA had higher affinity to ctDNA and bound to it more tightly. Further analysis indicated that the quenching process between CA and ctDNA was controlled by a dynamic mechanism, while the dominant process in ctDNA–NCA interaction was static. Analysis of thermodynamic parameters showed that hydrophobic forces played a key role in the interaction between ctDNA and CA, whereas ctDNA–NCA complex was mainly stabilized by van der Waals interactions. In terms of the latter interaction, external binding also contributed to the stabilization of the formed complex. On the basis of RLS results, we concluded that CA had stronger potential toxicity on ctDNA than NCA. Fluorescence competition studies aimed at uncovering the mode of binding and indicated that CA and NCA probably intercalated into ctDNA. Thermal denaturation studies confirmed the displacement experiments and showed that CA brought about a stronger effect on the ctDNA stabilization. Data gathered by spectroscopy studies were further supported by viscosity experiments. These studies also showed that CA and NCA intercalated into ctDNA by a non-classical and classical mode, respectively. The results of circular dichroism experiments revealed no considerable conformational transition occurred in ctDNA upon the binding interactions and ctDNA remained in B-form. Based on the spectroscopic results and the binding affinity of CA to double-strand and single-strand ctDNA, we inferred that although CA predominantly intercalated into ctDNA, a small population of its molecules might bind to the grooves of ctDNA. In case of NCA, all the experimental results confirmed that NCA molecules intercalated into ctDNA by a classical mode.