Study On The Interaction Between Active Small Drug Molecules And DNA

DNA which is the material basis of life inheritance controls the structure and function of cells. It is aduplex molecule with two self complementary strands held together by Watson-Crick base pairs, and itplays an important role in the life process. DNA is a major target for antiviral, anticancer and antibioticdrugs, it could be damaged under various conditions especially interact with some molecules, so it could beapplied in various type of therapy. The study on the interaction between drug small molecules and DNAhas become an active research area in biochemistry and life science in recent years. The interactions ofnatural and synthetically small drug molecules with DNA are worth studying because they are the base ofcarcinogenic and therapeutic properties of many carcinogenic species, antivirus and antitumor drugs, andare helpful to elucidate the mechanism of these compounds’ effects on the structure and physical propertiesof DNA and drug toxicity and pharmacokinetics. Understanding the modes of small molecules binding toDNA and DNA binding affinity and cleavage mechanism would be useful in the design of newDNA-targeted drugs. Anthracyclines are considered to be some of the most effective anticancer drugs forcancer therapy. However, drug resistance and cardiotoxicity of anthracyclines limit their clinicalapplication. Naproxen is a nonsteroidal anti-inflammatory drug and belongs to the group of antalgic andantipyrotic drugs, and exhibits anti-inflammatory, analgesic and antipyretic properties. It is usually used inclinics to ease pain and diminish inflammation like osteoarthritis, rheumatoid arthritis, and spondylitis. Inthis study, we investigated the interaction of4′-O-(α-L-Oleandrosyl)daunorubicin (ODNR), aglycon ofdaunorubicin (DNR-A), neodymium-naproxen complex (Nd-NAP) and dysprosium-naproxen complex(Dy-NAP) with calf thymus DNA (ctDNA).Part1: IntroductionThis section introduced the important role of DNA in life activities, the structures and functions ofDNA, the methods which were exploited to investigate the interaction of small molecules with DNA andthe prospects of this study.Part2: Study of the interaction between ODNR and ctDNAThe interaction of ODNR with ctDNA was studied through UV absorption, fluorescence spectroscopy, effect of ionic strength, potassium iodide quenching study and denatured DNA study. The experimentalresults showed that ODNR intercalated into the ctDNA base pairs. The quenching mechanism was static.The binding constants and the number of binding sites were calculated at different temperatures.Thermodynamic parameters suggested that hydrophobic force was the predominant intermolecular forces,but the electrostatic interaction could not be eliminated.Part3: Study of the interaction between DNR-A and ctDNAThe interaction between DNR-A and ctDNA was studied by spectroscopy. Hypochromic effect wasfounded in the absorption spectra of DNR-A in the presence of ctDNA. Stern-Volmer plots at differenttemperatures proved that the quenching mechanism was a static quenching type. The viscositymeasurement, effect of ionic strength, potassium iodide quenching study, fluorescence polarizationexperiment, denatured DNA studies and DNA melting experiment were all indicated that DNR-Aintercalated into ctDNA base pairs. The thermodynamic parameters suggested that hydrophobic force mightplay a major role in the binding process.Part4: Study of the interaction between Nd-NAP and ctDNAFluorescence spectroscopy in combination with UV absorption spectroscopy was carried out in orderto investigate the interaction between Nd-NAP and ctDNA. The experimental results showed that Nd-NAPintercalated into the ctDNA base pairs. Analysis of fluorescence quenching data of Nd-NAP by ctDNA atdifferent temperatures using Stern-Volmer equation revealed that dynamic and static quenching occurredsimultaneously. The binding constants and the number of binding sites at293and310K were obtained as2.904×104L·mol-1,1.172and2.432×104L·mol-1,1.143, respectively. The thermodynamic parametersΔG, ΔH and ΔS calculated at different temperatures indicated that hydrogen bond and van der Waals forcewere the main binding forces.Part5: Study of the interaction between Nd-NAP and ctDNAThe interacting mode and mechanism of the binding between Dy-NAP and ctDNA were studied inphysiological buffer (pH7.4). The analysis of fluorescence quenching data at four different temperaturesmade use of Stern-Volmer equation revealed that not only one type of quenching process occurred. Thebinding constants and the number of binding sites were obtained using the modified Stern-Volmer equation.Hypochromic effect and red shift were found in the absorption spectra which suggested that there was a strong interaction between Dy-NAP and ctDNA. The results of effect of ionic strength, iodide quenchingmeasurement in combination with fluorescence polarization indicated that the binding mode of Dy-NAPand ctDNA was intercalation.