Spectroscopic studies on the interaction of aspartame with human serum albumin.

In this work the binding of artificial sweetener aspartame with human serum albumin (HSA) was studied at physiological pH. Binding studies of aspartame (APM) with HSA are useful to understand APM -HSA interaction, mechanism and providing guidance for the application and design of new and more efficient artificial sweeteners. The interaction was investigated by spectrophotometric, spectrofluorometric competition experiment and circular dichroism (CD) techniques. The results indicated that the binding of APM to HSA caused fluorescence quenching of HSA through static quenching mechanism with binding constant 1.42 × 10+4 M-1 at 298 K and the number of binding sites is approximately one. Thermodynamic parameters, enthalpy changes (ΔH) and entropy changes (ΔS) were calculated to be -41.20 kJ mol-1 and -58.19 J mol-1 K-1, respectively, according to van't Hoff equation, which indicated that reaction is enthalpically driven. Quenching of the fluorescence of HSA was found to be a static quenching process. The binding constants and number of binding sites were obtained at three different temperatures (298, 308 and 318 K). Combining above results and those of spectrofluorometric competition experiment and circular dichroism (CD), indicated that APM binds to HSA via Sudlow's site I. Furthermore, the study of molecular docking on HSA binding also indicated that APM can strongly bind to the site I (subdomain IIA) of HSA mainly by hydrophobic interaction and hydrogen bond interactions exist between APM and HSA.

The Use of Molecular Docking and Spectroscopic Methods for Investigation of The Interaction Between Regorafenib with Human Serum Albumin (HSA) and Calf Thymus DNA (Ct-DNA) In The Presence Of Different Site Markers.

BACKGROUND: Interactions of drugs with DNA and proteins may modify their biological activities and conformations, which effect transport and biological metabolism of drugs. OBJECTIVE: In this study the interaction of anticancer drug regorafenib (REG) with calf thymus-DNA (ct-DNA) and human serum albumin (HSA) has been investigated Methods: Hence, for the first time, it was discovered interaction between REG with DNA and HSA using multi-spectroscopic, zeta potential measurements and molecular docking method. RESULTS AND DISCUSSION: DNA displacement studies showed that REG does not have any effect on acridine orange and methylene blue bound DNA, though it was substantiated by displacement studies with Hoechst (as groove binder). Furthermore, the different concentrations of REG induce slight changes in the viscosity of ct-DNA. Zeta potential parameters indicated that hydrophobic interaction plays a major role in the DNA-REG complex. Results obtained from molecular docking demonstrate that the REG prefers to bind on the minor groove of DNAs than that of the major groove. Binding properties of HSA reveal that intrinsic fluorescence of HSA could be quenched by REG in a static mode. The competitive experiments in the presence of warfarin and ibuprofen (as site markers) suggested that the binding site of REG to HSA was most probably located in the subdomain IIA. Measurements of the zeta potential indicated that REG bound to HSA mainly by both electrostatic and hydrophobic interactions. It was found on docking procedures that REG could fit well into HSA subdomain IIA, which confirmed the experimental results. CONCLUSION: In conclusion, REG can be delivered by HSA in a circulatory system and affect DNA as potential target.

Multi-spectroscopic and molecular docking studies on the interaction of neotame with calf thymus DNA.

In this paper, we have studied the in vitro binding of neotame (NTM), an artificial sweetener, with native calf thymus DNA using different methods including spectrophotometric, spectrofluorometric, competition experiment, circular dichroism (CD), and viscosimetric techniques. From the spectrophotometric studies, the binding constant (Kb) of NTM-DNA was calculated to be 2 × 103 M-1. The quenching of the intrinsic fluorescence of NTM in the presence of DNA at different temperatures was also used to calculate binding constants (Kb) as well as corresponding number of binding sites (n). Moreover, the obtained results indicated that the quenching mechanism involves static quenching. By comparing the competitive fluorimetric studies with Hoechst 33258, as a known groove probe, and methylene blue, as a known intercalation probe, and iodide quenching experiments it was revealed that NTM strongly binds in the grooves of the DNA helix, which was further confirmed by CD and viscosimetric studies. In addition, a molecular docking method was employed to further investigate the binding interactions between NTM and DNA, and confirm the obtained results.

Binding site identification of anticancer drug gefitinib to HSA and DNA in the presence of five different probes.

This study was carried out to evaluate the binding interaction of gefitinib (GEF) with human serum albumin (HSA) and calf thymus DNA (ct-DNA) using fluorescence, UV-Visible, zeta potential measurements and molecular docking methods in order to understand its pharmacokinetic mechanism. By increasing the temperature, a steady decrease in Stern-Volmer quenching constants was observed for HSA binding properties; this indicates a static type of fluorescence quenching. Negative values were calculated for Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) changes, indicating that the reaction is spontaneous and enthalpy-driven. Probe competitive experimental results showed that GEF contains the same binding site as warfarin and are consistent with modeling results. The zeta potential of the HSA increased with increasing GEF, which represents the presence of electrostatic interactions in the system. DNA binding properties were investigated in the presence of three probes. The experimental results showed that by increasing GEF to DNA-AO (acridine-orange) and DNA-MB (methylene-blue) system, the fluorescence intensity and absorbance spectra had no considerable change. Furthermore, with the addition of GEF to DNA, the zeta potential decreased gradually, indicating that the hydrophobic interaction between the GEF and the bases of DNA is the major factor. Thus, GEF can bind to DNA via a groove binding mode. It was also found that GEF entered into the minor groove in the A-T rich region of DNA fragment and bind via van der-Waals forces and three H-bond with double strands of DNA. This is in good agreement with experimental results.

In vitro cytotoxicity and DNA/HSA interaction study of triamterene using molecular modelling and multi-spectroscopic methods.

The anticancer activity of triamterene on HCT116 and CT26 colon cancer cells lines was investigated. Furthermore, the mechanism of interaction between triamterene and calf thymus DNA (ct-DNA) and also human serum albumin (HSA) was conducted using spectroscopic and molecular docking techniques. In vitro cytotoxicity of triamterene against HCT116 and CT26 cells showed promising anticancer effects with IC50 values of 31.30 and 24.45 µM, respectively. Competitive studies of the triamterene with NR (neutral red) and MB (methylene blue) as intercalator probes showed that triamterene can be replaced by these probes. The viscosity data also confirmed that triamterene binds to calf-thymus DNA through intercalation binding mode. Binding properties of triamterene with HSA in the presence of warfarin and ibuprofen showed that triamterene competes with warfarin for the site I of human serum albumin (HSA). In addition, the binding modes of triamterene with DNA and HSA were verified by molecular docking technique. Abbreviations ct-DNA calf thymus DNA CV cyclic voltammetry DNA deoxyribonucleic acid DPV differential pulse voltammetry FBS fetal bovine serum HSA human serum albumin NR neutral red MB methylene blue MTT 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazoliumbromide Communicated by Ramaswamy H. Sarma.

Anticancer activity, calf thymus DNA and human serum albumin binding properties of Farnesiferol C from Ferula pseudalliacea.

In this study, Farnesiferol C was introduced as an anti-colon cancer agent. Its cytotoxicity was investigated on two cancer cell lines, HCT116 and CT26, and mesenchymal stem cells (MSCs) as normal cells employing MTT assay. Moreover, Farnesiferol C interactions with ct-DNA and HSA were investigated by various techniques. The IC50 values of Farnesiferol C on HCT116 and CT26 cells were 42 and 46 µM, respectively, while its IC50 value on MSCs cells was 92 µM, indicating that Farnesiferol C was more efficacious against cancer cell lines than normal cells. DNA competitive binding studies, viscosity and zeta potential measurements confirmed that Farnesiferol C bound to DNA through intercalation binding. HSA binding investigations revealed that there were two different binding sites for Far C on HSA with higher binding affinity in site 2 compared to site 1. Furthermore, Farnesiferol C could bind to HSA and quench its intrinsic fluorescence in a static quenching mechanism, with a distance of 2.54 nm. Competitive binding in the presence of warfarin and ibuprofen was carried out and the resulting quenching constant was strongly changed in the presence of warfarin. Consequently, Farnesiferol C most probably will be located within sub-domain IIA. In this study, molecular modeling buttressed and confirmed our laboratory results. Conclusively, we proposed that DNA is an appropriate target for Farnesiferol C. Therefore, Farnesiferol C and its semisynthetic analogues can be one of the priority innovations in research on anticancer drugs.

Improving antiproliferative effect of the nevirapine on Hela cells by loading onto chitosan coated magnetic nanoparticles as a fully biocompatible nano drug carrier.

The freshly prepared magnetic iron oxide nanoparticles (MIONPs) were coated with SiO2 and then modified with a Si-based linker (SiL) having chlorine atom at the end of its chain. The resulting chlorine functionalized MIONPs were bonded to chitosan (CT) in trimethylamine solution. Then nevirapine (Nev) drug was loaded into above CT-SiL-MIONPs system and resulting Nev-loaded magnetic nanoparticles, Nev@CT-SiL-MIONPs, studied using different techniques. Furthermore, the value of Nev loading efficiency and also controlled delivery effect of Nev@CT-SiL-MIONP particles was determined by UV-vis spectrometer. Interestingly, the above nanomaterial showed a superparamagnetic property with a saturation magnetization value of 35.66 emu/g, indicating that it has an excellent potential application in the treatment of cancer using magnetic targeting drug delivery technology. Furthermore, the in-vitro antiproliferative activity of Nev@CT-SiL-MIONPs against cancer cell line (Hela) was compared with nevirapine using MTT colourimetric assay. The Nev-loaded magnetic nanoparticles were shown to be more effective antiproliferative on Hela cancer cell lines than nevirapine itself. Moreover, in vitro ct-DNA binding studies were investigated by UV-Vis and competitive fluorescence spectroscopies. The results showed that DNA aggregated on Nev-loaded nanoparticles via groove binding mode.

Binding Studies of Isoxsuprine Hydrochloride to Calf Thymus DNA Using Multispectroscopic and Molecular Docking Techniques.

In the present work, the interaction of Isoxsuprine (ISX) with Calf thymus DNA (ct-DNA) under physiological conditions (Tris-HCl buffer of pH 7.4) was investigated by using electronic absorption, circular dichroism, viscosity, electrochemical studies, fluorescence techniques, salt effect studies and computational studies. Competitive fluorimetric studies with Hoechst 33258 have shown that ISX exhibit the ability to displace the DNA-bound Hoechst 33258, indicating that it binds to ct-DNA in strong competition with Hoechst 33258 for the minor groove binding. Furthermore, the resulting data showed that ISX cannot displace methylene blue or acridine orange, which are the common intercalator molecules. The viscosity of ct-DNA solution was almost unchanged on addition of ISX and circular dichroism (CD) spectra of ct-DNA showed small changes in the presence of ISX which is in agreement with groove binding mode of interaction. Thus all above studies showed that the ISX drug binds to ct-DNA in a groove binding mode.The salt-effect studies showed the non-electrostatic nature of binding of ISX to ct-DNA. Moreover, molecular docking results support the above experimental data and suggest that ISX prefers to bind on the minor groove of ct-DNA.

Spectroscopic and molecular docking studies on the interaction of antiviral drug nevirapine with calf thymus DNA.

The interaction of calf thymus DNA with nevirapine at physiological pH was studied by using absorption, circular dichroism, viscosity, differential pulse voltammetry, fluorescence techniques, salt effect studies and computational methods. The drug binds to ct-DNA in a groove binding mode, as shown by slight variation in the viscosity of ct-DNA. Furthermore, competitive fluorimetric studies with Hoechst 33258 indicate that nevirapine binds to DNA via groove binding. Moreover, the structure of nevirapine was optimized by DFT calculations and was used for the molecular docking calculations. The molecular docking results suggested that nevirapine prefers to bind on the minor groove of ct-DNA.

A multi-spectroscopic and molecular docking approach to investigate the interaction of antiviral drug oseltamivir with ct-DNA.

The possible interaction between the antiviral drug oseltamivir and calf thymus DNA at physiological pH was studied by spectrophotometry, competitive spectrofluorimetry, differential pulse voltammogram (DPV), circular dichroism spectroscopy (CD), viscosity measurements, salt effect, and computational studies. Intercalation of oseltamivir between the base pairs of DNA was shown by a sharp increase in specific viscosity of DNA and a decrease of the peak current and a positive shift in differential pulse voltammogram. Competitive fluorescence experiments were performed using neutral red (NR) as a probe for the intercalation binding mode. The studies showed that oseltamivir is able to release the NR.

Experimental and computational studies on the effects of valganciclovir as an antiviral drug on calf thymus DNA.

DNA-binding properties of an antiviral drug, valganciclovir (valcyte) was studied by using emission, absorption, circular dichroism, viscosity, differential pulse voltammetry, fluorescence techniques, and computational studies. The drug bound to calf thymus DNA (ct-DNA) in a groove-binding mode. The calculated binding constant of UV-vis, Ka, is comparable to groove-binding drugs. Competitive fluorimetric studies with Hoechst 33258 showed that valcyte could displace the DNA-bound Hoechst 33258. The drug could not displace intercalated methylene blue from DNA double helix. Furthermore, the induced detectable changes in the CD spectrum of ct-DNA as well as changes in its viscosity confirm the groove-binding mode. In addition, an integrated molecular docking was employed to further investigate the binding interactions between valcyte and calf thymus DNA.

DNA interaction studies of a novel Cu(II) complex as an intercalator containing curcumin and bathophenanthroline ligands.

A new copper(II) complex; [Cu(Cur)(DIP)](+2) in which Cur=curcumin and DIP=4,7-diphenyl-1,10-phenanthroline, was synthesized and characterized using different physico-chemical methods. Binding interaction of this complex with calf thymus (CT-DNA) has been investigated by emission, absorption, circular dichroism, viscosity, and differential pulse voltammetry and fluorescence techniques. The complex displays significant binding properties to the CT-DNA. In fluorimeteric studies, the binding mode of the complex with CT-DNA was investigated using methylene blue as a fluorescence probe. Fluorescence of methylene blue-DNA solution increased in the presence of increasing amounts of the complex. It was found that the complex is able to displace the methylene blue completely. This indicate intercalation of the complex between base pairs of DNA. The cleavage of plasmid DNA by the complex was also studied. We found that the copper(II) complex can cleave puC18 DNA. Furthermore, mentioned complex induces detectable changes in the CD spectrum of CT-DNA, a decrease in absorption spectrum, and an increase in its viscosity. All of the experimental results showed that the Cu(II) complex bound to DNA by an intercalative mode of binding.

Determining the mode of interaction of calf thymus DNA with the drug sumatriptan using voltammetric and spectroscopic techniques.

The interaction of native calf thymus DNA with sumatriptan(1-[3-(2-dimethylaminoethyl)-1H-indol-5-yl]-N-methyl-methanesulfonamide) at physiological pH was studied by spectrophotometry, circular dichroism, voltammetry and viscosimetric techniques. Sumatriptan molecule intercalated between base pairs of DNA, showed by a sharp increase in specific viscosity of DNA. In cyclic voltammetry, decrease of the peak current and positive shift indicated that this drug is able to intercalate between the DNA base pairs. In addition, the drug induced changes in the CD spectrum of CT-DNA, as well as hypochromism changes in its UV-vis spectrum.

DNA interaction studies of a platinum (II) complex containing an antiviral drug, ribavirin: the effect of metal on DNA binding.

The water-soluble Pt (II) complex, [PtCl (DMSO)(N(4)N(7)-ribavirin)]· H(2)O (ribavirin is an antiviral drug) has been synthesized and characterized by physico-chemical and spectroscopic methods. The binding interactions of this complex with calf thymus DNA (CT-DNA) were investigated using fluorimetry, spectrophotometry, circular dichroism and viscosimetry. The complex binds to CT-DNA in an intercalative mode. The calculated binding constant, K(b), was 7.2×10(5) M(-1). In fluorimetric studies, the enthalpy (ΔH<0) and entropy (ΔS>0) changes of the reaction between the Pt (II) complex with CT-DNA showed hydrophobic interaction. In addition, CD study showed stabilization of the right-handed B form of CT-DNA. All these results prove that the complex interacts with CT-DNA via intercalative mode of binding. In comparison with the previous study of the DNA interaction with ribavirin, these results show that platinum complex has greater affinity to CT-DNA.