Interaction of 6 mercaptopurine with calf thymus DNA--deciphering the binding mode and photoinduced DNA damage

Synthesis, characterisation, and in vitro antiparasitic activity of new flavanoidal tetrazinan-6'-ones and their binding study with calf thymus DNA using molecular modelling and spectroscopic techniques

With the developing resistance to traditional antiparasitic medications, the purpose of this study was to efficiently develop a series of six noble flavanoidal tetrazinane-6'-one derivatives by a one-pot reaction pathway. FT-IR, 1HNMR, 13CNMR, and Mass spectra were employed for the structural elucidation of the synthesized compounds (7-12). Clinostomum complanatum, a parasite infection model that has been well-established, demonstrated that all the synthesized compounds are potent antiparasitic agents. DNA is the main target for various medicinal compounds. As a result, thestudy of how small molecules attach to DNA has received a lot of attention. In the present study, we have performed various biophysical techniques to determine the mode of binding of synthesized compounds (7-12) with calf thymus DNA (ct-DNA). It was observed from the UV-visible absorbance and fluorescence spectra that all synthesized compounds (7-12) form complexes with the ct-DNA. The value of binding constant (Kb) was obtained to be in the range of 4.36---24.50 × 103 M - 1 at 298 K. Competitive displacement assay with ethidium bromide (EB), CD spectral analysis, viscosity measurements, and in silico molecular docking confirmed that ligands (7-12) incorporate with ct-DNA through groove binding only. Molecular docking studies were performed for all synthesized compounds with the calf thymus DNA and it was found that all the newly synthesized compounds strongly bind with the chain B of DNA in the minor groove with the value of binding energy in the range of -8.54 to -9.04 kcal per mole and several hydrogen bonding interactions.

Multi-spectroscopic, thermodynamic and molecular simulation studies on binding of pyrroloquinoline quinone with DNA: coexistence of intercalation and groove binding modes

The interaction between enzyme-like pyrroloquinoline quinone (PQQ) and calf-thymus DNA (CT-DNA) has been investigated by means of multi-spectroscopic (UV-Vis, fluorescence and circular dichroism), isothermal titration calorimetric (ITC), viscometry and molecular docking and metadynamics simulation techniques. Absorption spectral data suggested the formation of a PQQ/CT-DNA complex, which quenched the fluorescence of PQQ via the dynamic quenching process. The results of CD spectral studies coupled with viscosity measurements, competitive binding assays with Hoechst 33258 and ethidium bromide (EB), KI quenching experiments, gel electrophoresis and DNA melting studies indicated groove binding mode of interaction of PQQ with CT-DNA. ITC experiment revealed that the complex formation is a spontaneous process (ΔGo < 0) with a binding constant of 1.05 × 104 M-1. The observed ΔHo < 0 and ΔSo < 0 pointed out that the complex is stabilized by van der Waals forces along with H-bonding interactions. The outcomes of molecular docking and simulation studies confirmed the binding of PQQ with DNA. The free energy surface (FES) analysis pointed out the existence of an equilibrium between partial intercalation and groove binding modes, which is in good agreement with the competitive binding assays.Communicated by Ramaswamy H. Sarma.

Genotoxicity and metabolic changes induced via ingestion of virgin and UV-aged polyethylene microplastics by the freshwater fish Perca fluviatilis

The present study aims to compare and assess the toxicity induced by aged (irradiated with ultraviolet radiation for 120 days) polyethylene microplastics (PE-MPs) in comparison to virgin (non-irradiated) ones, after feeding the freshwater fish Perca fluviatilis. To this end, MPs mediated genotoxicity was assessed by the investigation of micronucleus nuclear abnormalities frequency in fish blood, and the degree of DNA damage in the liver and muscle tissues, while metabolic alterations were also recorded in both tissues. Results showed that both virgin and aged PE-MPs induced signaling pathways leading to DNA damage and nuclear abnormalities, as well as metabolites changes in all tissues studied. Metabolic changes revealed that the metabolism of nucleic acids, energy, amino acids, and neurotransmitters was more disrupted in the liver and by aged PE-MPs compared to muscles. Fish fed with aged PE-MPs exhibited greater DNA damage, while blood cells of fish fed with virgin PE-MPs seemed to be more vulnerable to nuclear abnormalities in relation to those fed with aged PE-MPs. Moreover, aged PE-MPs induced more acute overall effects on the metabolic profiles of fish tissues, and initiated stronger stress responses, inflammation, and cellular damages in fish tissues in relation to virgin ones. Characterization of both virgin and aged MPs revealed that the latter exhibited lower crystallinity and melting point, more irregular shapes and higher moiety of oxygen and carbonyl groups, which could be attributed for their observed higher toxicity. The research outcomes provide significant insights for advancing toxicological investigations in this field.

QbD Assisted Systematic Review for Optimizing the Selection of PVP as a Ternary Substance in Enhancing the Complexation Efficiency of Cyclodextrins: a Pilot Study

Inclusion complexes require higher concentration of Beta cyclodextrins (βCD) resulting in increased formulation bulk, toxicity, and production costs. This systematic review offers a comprehensive analysis using Quality by design (QbD) as a tool to predict potential applications of Polyvinylpyrrolidone (PVP) as a ternary substance to address issues of inclusion complexes. We reviewed 623 documents from 2013 to 2023 and Eighteen (18) research papers were selected for statistical and meta-analysis using the QbD concept to identify the most critical factors for selecting drugs and effect of PVP on inclusion complexes. The QbD analysis revealed that Molecular weight (MW), Partition coefficient (Log P), and the auxiliary substance ratio directly affected complexation efficiency (CE), thermodynamic stability in terms of Gibbs free energy (ΔG), and percent drug release. However, Stability constant (Ks) remained unaffected by any of these parameters. The results showed that low MW (250), median Log P (6), and a βCD: PVP ratio of 2:3 would result in higher CE, lower G, and improved drug release. PVP improves drug solubility, enhances delivery and therapeutic outcomes, and counteracts increased drug ionization due to decreased pH. In certain cases, its bulky nature and hydrogen bonding with CD molecules can form non-inclusion complexes. The findings of the study shows that there is potential molecular interaction between PVP and β-cyclodextrins, which possibly enhances the stability of inclusion complexes for drug with low MW and log P values less than 9. The systematic review shows a comprehensive methodology based on QbD offers a replicable template for future investigations into drug formulation research.

Multispectroscopic and computational techniques to study the interaction of anthraquinone appended sensor with calf thymus DNA

An anthraquinone based derivative (AQ) has been designed and synthesized to find its applications for the interactions with calf thymus DNA (ctDNA) involving various spectroscopic techniques, thermodynamic and computational approaches. The UV-vis studies pointed to interaction of AQ with ctDNA via groove binding mode, which has been further supported well by the ionic strength studies, viscosity measurement, circular dichroism and melting temperature (Tm) curves. These findings have been further validated by dye-displacement assay and molecular docking studies. The analysis of thermodynamic parameters supports that the AQ-ctDNA binding is entropy favoured and enthalpy disfavoured and main acting binding interaction is hydrophobic interaction. The outcomes of the molecular modelling suggested that AQ might have entered the A-T abundant area of the ctDNA.Communicated by Ramaswamy H. Sarma.

Astaxanthin Binding Affinity to DNA: Studied By Fluorescence, Surface Plasmon Resonance and Molecular Docking Methods

Carotenoid astaxanthin (Ax), a pink-red pigment, with its anti-oxidative feature, is useful as a therapeutic element for numerous diseases. The purpose of this study is to investigate the binding affinity of Ax to double strand (ds) DNA evaluated by using the fluorescence spectroscopy, surface plasmon resonance (SPR) and docking approaches. The fluorescence results show that Ax can quench the intensity of DNA fluorescence via a static quenching way. In the SPR method, for affinity evaluation, DNA molecules were attached on a gold sensor surface. Using different amounts of ds DNA, the kinetic values KD, KA, and Ka were calculated. The Van't Hoff equation was used to estimate thermodynamic parameters including enthalpy (∆H), entropy (∆S) and Gibbs free energy (∆G) changes. The obtained results for KD in SPR (6.89×10-5 M) and fluorescence (KD=0.76×10-5 M) methods were in line with each other. Thermodynamic studies were carried out at four different temperatures, and the resulted negative data for ΔH and ΔS displayed that the main binding strength in the interaction of Ax with DNA was hydrogen bonding. ΔG value calculated by fluorescence method was near -38 kJ. mol-1 and using the docking method, estimated -9.95 kcal. mol-1 (-41.63 kJ. mol-1) which shows the binding behavior has an exothermic and spontaneous mechanism. Molecular docking results confirmed that the side chains of Ax interact specifically with base pairs and the DNA backbone.

Antiproliferative activity of platinum(II) and copper(II) complexes containing novel biquinoxaline ligands

Nowadays, cancer represents one of the major causes of death in humans worldwide, which renders the quest for new and improved antineoplastic agents to become an urgent issue in the field of biomedicine and human health. The present research focuses on the synthesis of 2,3,2',3'-tetra(pyridin-2-yl)-6,6'-biquinoxaline) and (2,3,2',3'-tetra(thiophen-2-yl)-6,6'-biquinoxaline) containing copper(II) and platinum(II) compounds as prodrug candidates. The binding interaction of these compounds with calf thymus DNA (CT-DNA) and human serum albumin were assessed with UV titration, thermal decomposition, viscometric, and fluorometric methods. The thermodynamical parameters and the temperature-dependent binding constant (K'b) values point out to spontaneous interactions between the complexes and CT-DNA via the van der Waals interactions and/or hydrogen bonding, except Cu(ttbq)Cl2 for which electrostatic interaction was proposed. The antitumor activity of the complexes against several human glioblastomata, lung, breast, cervix, and prostate cell lines were investigated by examining cell viability, oxidative stress, apoptosis-terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, in vitro migration and invasion, in vitro-comet DNA damage, and plasmid DNA interaction assays. The U87 and HeLa cells were investigated as the cancer cells most sensitive to our complexes. The exerted cytotoxic effect of complexes was attributed to the formation of the reactive oxygen species in vitro. It is clearly demonstrated that Cu(ttbq)Cl2, Pt(ttbq)Cl2, and Pt(tpbq)Cl2 have the highest DNA degradation potential and anticancer effect among the tested complexes by leading apoptosis. The wound healing and invasion analysis results also supported the higher anticancer activity of these two compounds.

Biophysical insights on the interaction of anticoagulant drug dicoumarol with calf thymus-DNA: deciphering the binding mode and binding force with thermodynamics

The biological activity of drugs is exhibited due to their interactions with bio-receptors. Dicoumarol (DIC) is a natural hydroxycoumarin and a well-known anticoagulant. DNA is the genetic material and one of the targets of numerous drugs. The interaction of DIC with calf-thymus DNA (ct-DNA) has been studied using different biophysical techniques and docking studies. The binding constant in the order of 103 to 104 M-1 was observed from spectroscopic studies. Thermodynamic studies at 4 different temperatures revealed the spontaneity of the interaction with the entropy-driven process. Marker displacement studies with competitive markers of intercalators (ethidium bromide) and groove binders (Hoechst 33258) confirmed the groove-binding nature of DIC in DNA. The groove-binding mode of DIC was complemented by different studies like viscosity measurements, DNA melting, and the effect of KI on the binding. A minor perturbation in the DNA viscosity and no significant change in the DNA melting temperature (Tm) after binding with DIC further confirms the groove binding mode. The effect of KI on the DIC and DIC-DNA system suggested the absence of DIC intercalation. The absence of significant electrostatic force was revealed from the ionic-strength effect study. Binding-induced conformational variation in ct-DNA was absent in circular dichroism studies. Molecular docking studies suggested the position of DIC within the minor groove of ct-DNA, covering three base pairs long. The outcome of this report may help in understanding the pharmacodynamics and pharmacokinetics of dicoumarol analogs and related molecules.Communicated by Ramaswamy H. Sarma.

Ruthenium-Cyclopentadienyl-Cycloparaphenylene Complexes: Sizable Multicharged Cations Exhibiting High DNA-Binding Affinity and Remarkable Cytotoxicity

Two novel sizable multicharged cationic complexes, of the formulae [(η6--[12]CPP)[Ru(η5--Cp)]12]Χ12 and [(η6--[11]CPP)[Ru(η5--Cp)]11]Χ11, CPP = cycloparaphenylene, Cp = cyclopentadienyl, X = [PF6]-, (1), (3) and [Cl]-, (2), (4), were synthesized and characterized using NMR techniques, high-resolution mass spectrometry, and elemental analyses. Complexes (1) and (3) were stable in acetone and acetonitrile solutions over 48 h. In contrast, the water-soluble (2) and (4) begin to decompose in aqueous media after 1 h, due to the [Cl]- tendency for nucleophilic attack on ruthenium of the {Ru(η5--Cp)} units. Fluorescence quenching experiments conducted during the stability window of (2) with the d(5'-CGCGAATTCGCG-3')2-EtBr adducts revealed remarkably high values for Ksv = 1.185 × 104 ± 0.025 M-1 and Kb = 3.162 × 105 ± 0.001 M-1. Furthermore, the cytotoxic activity of (2) against A2780, A2780res, and MCF-7 cancer cell lines shows that it is highly cytotoxic with IC50 values in the range of 4.76 ± 1.85 to 16 ± 0.81 μΜ.

Synthesis and Characterization of Ruthenium-Paraphenylene-Cyclopentadienyl Full-Sandwich Complexes: Cytotoxic Activity against A549 Lung Cancer Cell Line and DNA Binding Properties

Novel full-sandwich (η5-Cp)-Ru-paraphenylene complexes with the general formula [(η5-Cp)nRu(η6-L)](PF6)n where n = 1-3 and L = biphenyl, p-terphenyl and p-quaterphenyl, were synthesized and characterized by means of spectroscopic and analytical techniques. The structures of the complexes [(η5-Cp)Ru(η6-biphenyl)](PF6) (1), [(η5-Cp)Ru(η6-terphenyl)](PF6) (3) and [(η5-Cp)2Ru(η6-terphenyl)](PF6)2 (4) was determined by X-ray single crystal methods. The interaction of the complexes [(η5-Cp)Ru(η6-quaterphenyl)]Cl, (6)Cl, and [(η5-Cp)2Ru(η6-quaterphenyl)]Cl2, (7)Cl2, with the DNA duplex d(5'-CGCGAATTCGCG-3')2 was studied using NMR techniques. The results showed that both complexes interacted non-specifically with both the minor and major grooves of the helix. Specifically, (6)Cl exhibited partial binding through intercalation between the T7 and T8 bases of the sequence without disrupting the C-G and A-T hydrogen bonds. Fluorometric determination of the complexes' binding constants revealed a significant influence of the number of connected phenyl rings in the paraphenylene ligand (L) on the binding affinity of their complexes with the d(5'-CGCGAATTCGCG-3')2. The complexes (6)Cl and (7)Cl2 were found to be highly cytotoxic against the A549 lung cancer cell line, with complex (6) being more effective than (7) (IC50 for (6)Cl: 17.45 ± 2.1 μΜ, IC50 for (7)Cl2: 65.83 ± 1.8 μΜ) and with a selectivity index (SI) (SI for (6)Cl: 1.1 and SI for (7)Cl2: 4.8).

Synthesis of water-soluble novel bioactive pyridine-based azo coumarin derivative and competitive cytotoxicity, DNA binding, BSA binding study, and in silico analysis with coumarin

The diazo coupliling reaction of 3- amino pyridine with coumarin in water medium produces water soluble 6-[3-pyridyl]azocoumarin. The synthesised compound has been fully charecterised by IR, NMR, and Mass spectroscopy. The frontier molecular orbital calculations reveal that 6-[3-pyridyl]azocoumarin is more biologically and chemically active in comparison to coumarin. The cytotoxicity evaluation confirms that 6-[3-pyridyl]azocoumarin is more active than coumarin against human brain glioblastoma cell lines, LN-229 with IC50 value 9.09 μM (IC50 value for coumarin is 9.9 μM). The compound (I) has been synthesized by coupling of diazotized solution of 3-aminopyridine with coumarin in an aqueous medium at ∼ pH 10. The structure of the compound (I) has been characterized using UV-vis, IR, NMR, and Mass spectral studies. Frontier molecular orbital calculations reveal that 6-[3-pyridyl]azocoumarin (I) is more active chemically and biologically in comparison to coumarin. IC50 value 9.09 and 9.9 μM of 6-[3-pyridyl]azocoumarin and coumarin respectively obtained in cytotoxicity evaluation confirms the enhanced activity of the synthesized compound against human brain glioblastoma cell lines, LN-229. The synthesized compound also shows strong binding interactions with DNA and BSA in comparison with coumarin. The DNA binding study shows groove binding interaction of the synthesized compound with CT-DNA. The nature of interaction, binding parameters and structural variations of BSA in the presence of the synthesized compound and coumarin have been evaluated using several usefull spectroscopy approaches such as UV -Vis, time resolved and stady state flurescence. The molecular docking interaction has been carried out to justify the experimental binding interaction with DNA and BSA.

Insight into the binding interactions of fluorenone-pendent Schiff base with calf thymus DNA

A novel fluorenone appended Schiff base (L) has been synthesized and utilized for studying the binding interactions with Calf Thymus DNA (ct-DNA). The mechanism of binding with ct-DNA was explored by employing various spectroscopic techniques viz. UV-Vis absorption spectroscopy, fluorescence emission spectroscopy, gel-electrophoresis, circular dichroism (CD), melting studies, viscosity arrays and molecular modelling methodology. The interpretation of UV-vis absorbance spectra pointed to binding of L within minor groove of ct-DNA with the binding constant of K_b = 0.15 × 10⁴ M^-1. Dye-displacement studies with Rhodamine-B (RhB) and Ethylene Bromide (EB) in fluorescence spectroscopy verified the groove binding mode of interaction between L and ct-DNA. Melting studies, circular dichroism, and viscosity studies further elucidated the binding modes of L with ct-DNA. Thermodynamic variable measurements taken at various temperatures such as ΔG^⁰, ΔH^⁰, and ΔS^⁰ revealed that hydrophobic forces played a significant role in the binding process. The meticulous computational interaction demonstrated by molecular docking confirmed the minor groove binding of L with ct-DNA.

Binding of dicoumarol analog with DNA and its antioxidant studies: A biophysical insight by in-vitro and in-silico approaches

DNA is the major target for a number of pharmaceutical drugs. The interaction of drug molecules with DNA plays a major role in pharmacokinetics and pharmacodynamics. Bis-coumarin derivatives have diverse biological properties. Here, we have explored the antioxidant activity of 3,3'-Carbonylbis (7-diethylamino coumarin) (CDC) using DPPH, H₂O_2, and superoxide scavenging studies followed by its binding mode in calf thymus-DNA (CT-DNA) using several biophysical methods including molecular docking. CDC exhibited comparable antioxidant activity to standard ascorbic acid. The UV-Visible and fluorescence spectral variations indicate the CDC-DNA complex formation. The binding constant in the range of 10⁴ M^-1 was obtained from spectroscopic studies at room temperature. The fluorescence quenching of CDC by CT-DNA suggested a quenching constant (K_SV) of 10³ to 10⁴ M^-1 order. Thermodynamic studies at 303, 308, and 318 K revealed the observed quenching as a dynamic process besides the spontaneity of the interaction with negative free energy change. Competitive binding studies with site markers like ethidium bromide, methylene blue, and Hoechst 33258 reflect CDC's groove mode of interaction. The result was complemented by DNA melting study, viscosity measurement, and KI quenching studies. The ionic strength effect was studied to interpret the electrostatic interaction and found its insignificant role in the binding. Molecular docking studies suggested the binding location of CDC within the minor groove of CT-DNA, complementing the experimental result.

Targeting genomic DNAs and oligonucleotide on base specificity: A comparative spectroscopic, computational and in vitro study

Drug discovery in targeted nucleic acid therapeutics encompass several stages and rigorous challenges owing to less specificity of the DNA binders and high failure rate in different stages of clinical trials. In this perspective, we report newly synthesized ethyl 4-(pyrrolo[1,2-a]quinolin-4-yl)benzoate (PQN) with minor groove A-T base pair binding selectivity and encouraging in cell results. This pyrrolo quinolin derivative has shown excellent groove binding ability with three of our inspected genomic DNAs (cpDNA 73 % AT, ctDNA58% AT and mlDNA 28 % AT) with varying A-T and G-C content. Notably in spite of similar binding patterns PQN have strong binding preference with A-T rich groove of genomic cpDNA over the ctDNA and mlDNA. Spectroscopic experiments like steady state absorption and emission results have established the relative binding strengths (K_abs = 6.3 × 10⁵ M^-1, 5.6 × 10⁴ M^-1, 4.3 × 10⁴ M^-1 and K_emiss = 6.1 × 10⁵ M^-1, 5.7 × 10⁴ M^-1 and 3.5 × 10⁴ M^-1 for PQN-cpDNA, PQN-ctDNA and PQN-mlDNA respectively) whereas circular dichroism and thermal melting studies have unveiled the groove binding mechanism. Specific A-T base pair attachment with van der Waals interaction and quantitative hydrogen bonding assessment were characterized by computational modeling. In addition to genomic DNAs, preferential A-T base pair binding in minor groove was also observed with our designed and synthesized deca-nucleotide (primer sequences 5^/-GCGAATTCGC-3^/ and 3^/-CGCTTAAGCG-5^/). Cell viability assays (86.13 % in 6.58 μM and 84.01 % in 9.88 μM concentrations) and confocal microscopy revealed low cytotoxicity (IC₅₀ 25.86 μM) and efficient perinuclear localization of PQN. We propose PQN with excellent DNA-minor groove binding capacity and intracellular permeation properties, as a lead for further studies encompassing nucleic acid therapeutics.

Assessment of binding interaction to salmon sperm DNA of two antiviral agents and ecofriendly nanoparticles: comprehensive spectroscopic study

The direct binding of antiviral agents; Daclatasvir and valacyclovir and green synthesized nanoparticles to salmon sperm DNA have been assessed in a comparative study. The nanoparticles were synthesized by the hydrothermal autoclave method and have been fully characterized. The interactive behavior and competitive binding of the analytes to DNA in addition to the thermodynamic properties were deeply investigated by the UV-visible spectroscopy. The binding constants were monitored in the physiological pH conditions to be 1.65 × 10⁶, 4.92 × 10⁵ and 3.12 × 10⁵ for daclatasvir,valacyclovir and quantum dots, respectively. The significant changes in the spectral features of all analytes have proven intercalative binding. The competitive study has confirmed that, daclatasvir, valacyclovir, and the quantum dots have exhibited groove binding. All analytes have shown good entropy and enthalpy values indicating stable interactions. The electrostatic and non-electrostatic kinetic parameters have been determined through studying the binding interactions at different concentrations of KCl solutions. A molecular modelling study has been applied to demonstrate the binding interactions and their mechanisms. The obtained results were complementary and afforded new eras for the therapeutic applications.

Tumor Microenvironment-Responsive 6-Mercaptopurine-Releasing Injectable Hydrogel for Colon Cancer Treatment

Colon cancer is a significant health concern. The development of effective drug delivery systems is critical for improving treatment outcomes. In this study, we developed a drug delivery system for colon cancer treatment by embedding 6-mercaptopurine (6-MP), an anticancer drug, in a thiolated gelatin/polyethylene glycol diacrylate hydrogel (6MP-GPGel). The 6MP-GPGel continuously released 6-MP, the anticancer drug. The release rate of 6-MP was further accelerated in an acidic or glutathione environment that mimicked a tumor microenvironment. In addition, when pure 6-MP was used for treatment, cancer cells proliferated again from day 5, whereas a continuous supply of 6-MP from the 6MP-GPGel continuously suppressed the survival rate of cancer cells. In conclusion, our study demonstrates that embedding 6-MP in a hydrogel formulation can improve the efficacy of colon cancer treatment and may serve as a promising minimally invasive and localized drug delivery system for future development.

Interaction of bifunctional peptide-carbazole complexes with DNA and antimicrobial activity

Two peptide-carbazole conjugates, CTAT and CNLS, were designed and synthesized using carbazole Schiff base to modify the cell membrane penetrating peptide TAT (47-57) and the nuclear localization peptide NLS at the N terminus. The interaction with ctDNA was investigated by multispectral and agarose gel electrophoresis. And the effects of CNLS and CTAT on the G-quadruplex structure were explored by circular dichroism titration experiments. The results show that both CTAT and CNLS interact with ctDNA in a minor groove binding manner. Both conjugates bind more tightly to DNA than the individual substances CIBA, TAT and NLS. In addition, CTAT and CNLS are capable of unfolding parallel G-quadruplex structures and are potential G-quadruplex unfolding agents. Finally, broth microdilution was performed to test the antimicrobial activity of the peptides. The results showed that CTAT and CNLS had a 4-fold increase in antimicrobial activity compared with the parent peptides TAT and NLS. They could exert antimicrobial activity by disrupting the integrity of cell membrane bilayer and binding to DNA, and could be used as novel antimicrobial peptides for the development of novel antimicrobial antibiotics.

Ru(II) Complexes with Enaminone Structures for Rapid Sterilization of Staphylococcus aureus and MRSA with Little Accumulation of Drug Resistance

Drug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), pose a serious threat to human life. Therefore, there is urgent need to develop antibiotics with new chemical structures and antibacterial mechanisms, especially those that elicit little drug resistance after long-term use. Herein we synthesized three novel ruthenium complexes (Ru1-Ru3) containing the enaminone structures for the first time. At a concentration of 5 μM, Ru1-Ru3 can lead to a CFU reduction of about 5 log units towards S. aureus and MRSA. Interestingly, Ru3 displayed rapid bactericidal effects and could decrease the CFU numbers of both pathogens by 5 log units within 40 min. The control compounds (Ru4 and Ru5) without the enaminone structures displayed very poor antibacterial activity under the same conditions. Moreover, S. aureus did not show apparent drug resistance towards Ru3 after 20 passages incubation with a sublethal concentration. These results highlight the critical role of enaminone structures for antibacterial applications.

Influence of the Photodegradation of Azathioprine on DNA and Cells

Azathioprine (AZA) is a pharmacologic immunosuppressive agent administrated in various conditions such as autoimmune disease or to prevent the rejection of organ transplantation. The mechanism of action is based on its biologically active metabolite 6-mercaptopurine (6-MP), which is converted, among others, into thioguanine nucleotides capable of incorporating into replicating DNA, which may act as a strong UV chromophore and trigger DNA oxidation. The interaction between azathioprine and DNA, before and after exposure to solar simulator radiation, was investigated using UV-vis spectrometry and differential pulse voltammetry at a glassy carbon electrode. The results indicated that the interaction of AZA with UV radiation was pH-dependent and occurred with the formation of several metabolites, which induced oxidative damage in DNA, and the formation of DNA-metabolite adducts. Moreover, the viability assays obtained for the L929 cell culture showed that both azathioprine and degraded azathioprine induced a decrease in cell proliferation.

Synthesis, characterization, interactions with the DNA duplex dodecamer d(5'-CGCGAATTCGCG-3')2 and cytotoxicity of binuclear η6-arene-Ru(II) complexes

The novel binuclear η⁶-arene-Ru(II) complexes with the general formula {[(η⁶-cym)Ru(L)]₂(μ-BL)}(PF₆)₄, and their corresponding water soluble {[(η⁶-cym)Ru(L)]₂(μ-BL)}Cl₄, where cym = p-cymene, L = 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen), BL = 4,4'-bipyridine (BL-1), 1,2-bis(4-pyridyl)ethane (BL-2) and 1,3-bis(4-pyridyl)propane (BL-3), were synthesized and characterized. The structure of {[(η⁶-cym)Ru(phen)]₂(μ-BL-1)}(PF₆)₄ was determined by X-ray single crystal methods. The interaction of {[(η⁶-cym)Ru(phen)]₂(μ-BL-i)}Cl₄ (i = 1, 2, 3; (4), (5) and (6) correspondingly) with the DNA duplex d(5'-CGCGAATTCGCG-3')₂ was studied by means of NMR techniques and fluorescence titrations. The results show that complex (4) binds with a K_b = 12.133 × 10³ M^-1 through both intercalation and groove binding, while (5) and (6) are groove binders (K_b = 2.333 × 10³ M^-1 and K_b = 3.336 × 10³ M^-1 correspondingly). Comparison with the mononuclear complex [(η⁶-cym)Ru(phen)(py)]²⁺ reveals that it binds to the d(5'-CGCGAATTCGCG-3')₂ with a K_b value two orders of magnitude lower than (4) (K_b = 0.158 × 10³ M^-1), indicating that for the binuclear complexes both ruthenium moieties participate in the binding. The complexes were found to be cytotoxic against the A2780 and A2780 res. cancer cell line with a selectivity index (SI) in the range of 3.0-5.9.

Deciphering the nature of binding of dexlansoprazole with DNA: Biophysical and docking approaches

Drugs, in general, exhibit their pharmacological activity in binding with intracellular targets. Numerous anticancer and antibacterial drugs target DNA as one of their primary intracellular targets. Dexlansoprazole (DLP) is a heterocyclic compound containing benzimidazole moiety and a proton pump inhibitor used to treat gastroesophageal reflux disease. The interaction of dexlansoprazole with calf thymus DNA (ct-DNA) has been studied using biophysical methods. The UV-Visible studies revealed a binding constant of 2.15 ± 0.3 × 104 M^-1 which is close to the value of 2.44 ± 0.3 × 10⁴ M^-1 obtained from the fluorescence studies. Competitive displacement studies using the fluorescence spectroscopic method with ethidium bromide and Hoechst as DNA markers suggested the groove binding mode of DLP in ct-DNA. The groove binding mode of DLP in ct-DNA was complemented by the results of viscosity and DNA melting studies. Further studies on the effect of ionic strength and potassium iodide on DLP binding with ct-DNA supported the observed binding mode. Circular dichroism studies reflected no significant conformational variation in ct-DNA after the interaction. The binding mode obtained from the experimental studies was corroborated by the molecular docking studies that showed the position of DLP in the minor groove of ct-DNA along with the receptor interface restudies involved in the interaction.

Comparative Studies on DNA-Binding Mechanisms between Enantiomers of a Polypyridyl Ruthenium(II) Complex

A pair of ruthenium(II) complex enantiomers, Δ- and Λ-[Ru(bpy)₂MBIP]²⁺ (bpy = 2,2'-bipyridine, MBIP = 2-(3-bromophenyl)imidazo[5,6-f]phenanthroline), were designed, synthesized, and characterized. Comparative studies between the enantiomers on their binding behaviors to calf thymus DNA (CT-DNA) were conducted using UV-visible, fluorescence, and circular dichroism spectroscopies, viscosity measurements, isothermal titration calorimetry, a photocleavage experiment, and molecular simulation. The experimental results indicated that both the enantiomers spontaneously bound to CT-DNA through intercalation stabilized by the van der Waals force or the hydrogen bond and driven by enthalpy and that Δ-[Ru(bpy)₂MBIP]²⁺ intercalated into DNA more deeply than Λ-[Ru(bpy)₂MBIP]²⁺ did and exhibited a better DNA photocleavage ability. Molecular simulation further indicated that Δ-[Ru(bpy)₂MBIP]²⁺ more preferentially intercalated between the base pairs of CT-DNA to the major groove, and Λ-[Ru(bpy)₂MBIP]²⁺ more favorably intercalated to the minor groove. These research findings should be very helpful to the understanding of the stereoselectivity mechanism of DNA-bindings of metal complexes, and be useful for the design of novel metal-complex-based antitumor drugs with higher efficacy and lower toxicity.

Decrypting the interaction pattern of Piperlongumine with calf thymus DNA and dodecamer d(CGCGAATTCGCG)2 B-DNA: Biophysical and molecular docking analysis

The mechanisms of interaction of DNA with pharmacological molecules are critical to understanding their therapeutic actions on physiological systems. Piperlongumine is widely studied for its anticancer potential. Multi-spectrometry, calorimetry and in silico studies were employed to study the interaction of piperlongumine and calf thymus DNA. UV-Vis spectroscopy illustrated a hyperchromic pattern in spectra of the calf thymus DNA-piperlongumine complex, while fluorescent quenching was observed in emission spectral studies. Competitive displacement assay demonstrated higher displacement and binding constant for DNA-rhodamine B complex by piperlongumine than DNA-methylene blue complex. Differential scanning calorimetry presented non-significant changes in melting temperature and molecular docking presented the precise interaction site of piperlongumine with calf thymus DNA at minor groove. Further, piperlongumine treatment did not result in pBluescript KS plasmid DNA cleavage as revealed from the DNA topology assay. All these experiments confirmed the binding of piperlongumine with DNA through minor groove binding mode.

Spectroscopic and theoretical evidences for the surface binding of voglibose drug with DNA

Binding of voglibose (VOG), an alpha glucosidase inhibitor, with CT-DNA has been investigated using various spectroscopic techniques including UV-Vis, fluorescence and circular dichroism (CD) coupled with relative viscosity. Isothermal titration calorimetric studies have been used to calculate the thermodynamic parameters such as ΔH (0.0188 cal/mol), ΔS (63.3 cal/mol/K) and ΔG (-18.8 kcal/mol), which reveal that the binding is a spontaneous process and hydrophobic and H-bonding interactions play major roles in the binding process. Effect of ionic strength confirms the existence of hydrophobic interaction between VOG and CT-DNA. Competitive displacement assays with ethidium bromide (EB) and Hoechst 33258 suggest that VOG possibly binds on the surface of CT-DNA. Viscosity measurements also disclose that the binding could be mainly surface binding. Corroborating the experimental observations, metadynamics molecular simulation studies confirm that VOG binding on the surface of the DNA molecule through hydrophobic interactions and direct and water molecule mediated H-bonding.

A study of structure-activity relationship and anion-controlled quinolinyl Ag(I) complexes as antimicrobial and antioxidant agents as well as their interaction with macromolecules

In this communication, we feature the synthesis and in-depth characterization of a series of silver(I) complexes obtained from the complexation of quinolin-4-yl Schiff base ligands ((E)-2-((quinolin-4-ylmethylene)amino)phenol L_a, 2-(quinolin-4-yl)benzo[d]thiazole L_b, (E)-N-(2-fluorophenyl)-1-(quinolin-4-yl)methanimine L_c, (E)-N-(4-chlorophenyl)-1-(quinolin-4-yl)methanimine L_d, (E)-1-(quinolin-4-yl)-N-(p-tolyl)methanimine L_e, (E)-1-(quinolin-4-yl)-N-(thiophen-2-ylmethyl)methanimine L_f) and three different silver(I) anions (nitrate, perchlorate and triflate). Structurally, the complexes adopted different coordination geometries, which included distorted linear or distorted tetrahedral geometry. The complexes were evaluated in vitro for their potential antibacterial and antioxidant activities. In addition, their interactions with calf thymus-DNA (CT-DNA) and bovine serum albumin (BSA) were evaluated. All the complexes had a wide spectrum of effective antibacterial activity against gram-positive and gram-negative bacterial and good antioxidant properties. The interactions of the complexes with CT-DNA and BSA were observed to occur either through intercalation or through a minor groove binder, while the interaction of the complexes with BSA reveals that some of the complexes can strongly quench the fluorescence of BSA through the static mechanism. The molecular docking studies of the complexes were also done to further elucidate the modes of interaction with CT-DNA and BSA.

Binding and thermodynamic study of thalidomide with calf thymus DNA: Spectroscopic and computational approaches

The thalidomide-DNA interactions have been investigated in detail by numerous biophysical techniques such as UV-vis, dye displacement assay, viscosity, cyclic voltammetry, circular dichroism, molecular docking, molecular dynamic simulation, FT-IR and ¹H NMR spectroscopy. CD spectroscopy, thermal denaturation and viscosity measurement explained that thalidomide is groove binder. Molecular docking analysis highlighted that thalidomide binds trough minor groove of calf thymus DNA which also confirmed from dye displacement experiment. To our knowledge, this is the first instance thalidomide was shown to binds with calf thymus DNA. Molecular dynamic simulation indicated that the thalidomide-DNA system was stabilized by electrostatic attraction as the main interaction and mode of binding is minor groove. Our study provides a better understanding to the DNA-thalidomide binding affinity and it mechanism. Overall, all these in formations can be used for further understanding the pharmacological effects of thalidomide.

Visible-Light-Prompted Synthesis and Binding Studies of 5,6-Dihydroimidazo[2,1-b]thiazoles with BSA and DNA Using Biophysical and Computational Methods

Fused heterocyclic systems containing a bridgehead nitrogen atom have emerged as imperative pharmacophores in the design and development of new drugs. Among these heterocyclic moieties, the imidazothiazole scaffold has long been used in medicinal chemistry for the treatment of various diseases. In this study, we have established a simplistic and environmentally safe regioselective protocol for the synthesis of 5,6-dihydroimidazo[2,1-b]thiazole derivatives from easily available reactants. The reaction proceeds through in situ formation of the α-bromodiketones ensuing trap with imidazolidine-2-thione to provide these versatile bicyclic heterocycles in excellent yields. The synthesized compounds were screened through the molecular docking approach for the most stable complex formation with bovine serum albumin (BSA) and calf thymus deoxyribonucleic acid (ctDNA). The selected compound was further studied using ex vivo binding studies, which revealed moderate interactions with BSA and ctDNA. The binding studies were performed using biophysical approaches including UV-visible spectroscopy, steady-state fluorescence, circular dichroism (CD), and viscosity parameters.

Studying the interaction of scopolamine with calf-thymus DNA: An in-vitro and in-silico approach and genotoxicity

Scopolamine is used to treat various CNS disorder like urinary incontinence, motion sickness, spasmic movements. Despite its pharmaceutical properties, its interaction with DNA is not yet reported. In this article, the interaction between scopolamine and ct-DNA is reported using a combination of biophysical techniques. UV-visible and steady-state fluorescence spectroscopy were used to study interaction and complex formation. Competitive displacement assays and potassium iodide quenching confirmed the mode of binding between scopolamine and DNA. Structural changes induced in the ct-DNA in the presence of scopolamine were evaluated by CD spectroscopy. The plasmid nicking and NBT assay confirmed the genotoxic effect of scopolamine. In-silico study by molecular docking and molecular dynamics simulation revealed the mode of interaction, major stabilizing forces as well as the nucleotide sequences to which the scopolamine binds.

Deciphering the sensing of α-amyrin acetate with hs-DNA: a multipronged biological probe

In this study, we focus on the biomimetic development of small molecules and their biological sensing with DNA. The binding of herring sperm deoxyribonucleic acid (hs-DNA) with naturally occurring bioactive small molecule α-amyrin acetate (α-AA), a biomimetic - isolated from the leaves of Ficus (F.) arnottiana is investigated. Collective information from various imaging, spectroscopic and biophysical experiments provides evidence that α-AA is a minor groove sensor of hs-DNA and preferentially binds to the A-T-rich regions. Interactions of different concentrations of small molecule α-AA with hsDNA were evaluated via various analytical techniques such as UV-Vis, circular dichroism (CD) and fluorescence emission spectroscopy. Fluorescence emission spectroscopy results suggest that α-AA decreases the emission level of hsDNA. DNA minor groove sensor Hoechst 33258 and intercalative sensor EB, melting transition analysis (T M) and viscosity analysis clarified that α-AA binds to hs-DNA via a groove site. Biophysical chemistry and molecular docking studies show that hydrophobic interactions play a major role in this binding. The present research deals with a natural product biosynthesis-linked chemical-biology interface sensor as a biological probe for α-AA: hs-DNA.

Discovery of a 2,4-diphenyl-5,6-dihydrobenzo(h)quinolin-8-amine derivative as a novel DNA intercalating topoisomerase IIα poison

Several anticancer agents have been developed and innovative approaches have been made toward cancer type-specific medicines for cancer treatment. As a continuous effort to develop potential chemotherapeutic agents, a novel series of 2,4-diphenyl-5,6-dihydrobenzo(h)quinolin-8-amines containing amino groups, hydroxyphenyl and fluorine functionalities were designed and synthesized. The compounds were evaluated for topo IIα inhibitory and cytotoxicity against HCT15, and HeLa human cancer cell lines. Among synthesized thirty compounds, the majority exhibited strong topo IIα inhibition and anti-proliferation against HCT15 colorectal adenocarcinoma cell line. The structure-activity relationship study revealed that compounds with -CF₃ and -OCF₃ substituents at 4- position and 3' or 4'-hydroxyphenyl at 2-position attached to the central pyridine ring displayed potent topo IIα and anti-proliferative activity in colorectal and cervix cancer cell line. In vitro studies provided the evidence that compounds 16, 19, 22, and 28 possess excellent topo IIα inhibition and antiproliferative activity. For a better understanding, topo IIα cleavage complex, EtBr displacement, KI quenching assays and molecular docking of compound 19 was performed and the results revealed the mode of action as a DNA intercalative topo IIα poison inhibitor. The results obtained from this study provide insight into the DNA binding mechanism of 2,4-diphenyl-5,6-dihydrobenzo(h)quinolin-8-amines and alteration in topo IIα inhibitory and antiproliferative activity with modifications in the rigid structure.

The interaction of proanthocyanidins with DNA molecules studied by atomic force microscopy and spectroscopic method

The interactions of the naturally available botanicals with DNA molecules have received considerable attention owing to the potential to develop for medicinal agents. In this study, the interaction of proanthocyanidins with DNA molecules was studied by atomic force microscopy (AFM) and spectroscopic method. The AFM observation indicated that proanthocyanidins induced DNA molecules from double helix chains to the thick rope and toroids. The heights of the formed DNA structures are more than eight times than that of DNA double helix. Spectroscopic measurement results revealed that proanthocyanidins intercalated between the base pairs of DNA in the intercalative binding mode, which resulted in unwinding the DNA helix, twisting the DNA strands and finally transforming into the supercoiled DNA structures. All these results implied that DNA molecule is an important interaction target of proanthocyanidins, and the formed compact DNA structures have biological significance on the gene expression and regulation.

Anticancer Activity of Indeno[1,2-b]-Pyridinol Derivative as a New DNA Minor Groove Binding Catalytic Inhibitor of Topoisomerase IIα

Topoisomerase IIα has been a representative anti-cancer target for decades thanks to its functional necessity in highly proliferative cancer cells. As type of topoisomerase IIα targeting drugs, topoisomerase II poisons are frequently in clinical usage. However, topoisomerase II poisons result in crucial consequences resulted from mechanistically induced DNA toxicity. For this reason, it is needed to develop catalytic inhibitors of topoisomerase IIα through the alternative mechanism of enzymatic regulation. As a catalytic inhibitor of topoisomerase IIα, AK-I-191 was previously reported for its enzyme inhibitory activity. In this study, we clarified the mechanism of AK-I-191 and conducted various types of spectroscopic and biological evaluations for deeper understanding of its mechanism of action. Conclusively, AK-I-191 represented potent topoisomerase IIα inhibitory activity through binding to minor groove of DNA double helix and showed synergistic effects with tamoxifen in antiproliferative activity.

Complexation of uranyl (UO2)2+ with bidentate ligands: XRD, spectroscopic, computational, and biological studies

Three new uranyl complexes [(UO₂)(OAc)₂(CMZ)], [(UO₂)(OAc)₂(MP)] and [(UO₂)(OAc)₂(SCZ)] were synthesized and characterized by elemental analysis, FT-IR, UV-Vis spectroscopy, powder XRD analysis, and molar conductivity. The IR analysis confirmed binding to the metal ion by the sulfur and ethoxy oxygen atoms in the carbimazole (CMZ) ligand, while in the 6-mercaptopurine (MP) ligand, the sulfur and the N7 nitrogen atom of a purine coordinated binding to the metal ion. The third ligand showed a 1:1 molar ratio and bound via sulfonamide oxygen and the nitrogen of the pyrimidine ring. Analysis of the synthesized complexes also showed that acetate groups had monodentate binding to the (UO₂²⁺). Density Functional Theory (DFT) calculations at the B3LYP level showed similar structures to the experimental results. Theoretical quantum parameters predicted the reactivity of the complexes in the order, [(UO₂)(OAc)₂(SCZ)] > [(UO₂)(OAc)₂(MP)]> [(UO₂)(OAc)₂(CMZ)]. DNA binding studies revealed that [(UO₂)(OAc)₂(SCZ)] and [(UO₂)(OAc)₂(CMZ)] have the highest binding constant (K_b) among the uranyl complexes. Additionally, strong binding of the MP and CMZ metal complexes to human serum albumin (HSA) were observed by both absorbance and fluorescence approaches. The antibacterial activity of the complexes was also evaluated against four bacterial strains: two gram-negative; Escherichia coli and Klebsiella pneumonia, and two gram-positive; Staphylococcus aureus and Streptococcus mutans. [(UO₂)(OAc)₂(MP)] had the greatest antibacterial activity against Klebsiella pneumonia, the gram-positive bacteria, with even higher activity than the standard antibiotic. In vitro cytotoxicity tests were also performed against three human cancer lines, and revealed the most cytotoxic complexes to be [(UO₂)(OAc)₂(SCZ)], which showed moderate activity against a colon cancer cell line. Thus, uranyl addition enhances the antibacterial and anticancer properties of the free ligands.

Effect of Net Charge on DNA-Binding, Protein-Binding and Anticancer Properties of Copper(I) Phosphine-Diimine Complexes

The syntheses of [Cu(PPh3)2(L)]NO3 and [Cu(PPh3)2(L-SO3Na)]NO3 were achieved through the reaction of Cu(PPh3)2NO3 and equimolar amount of the ligands (L = 5,6-diphenyl-3-[2-pyridyl]-1,2,4-triazine; LSO3Na = 5,6-diphenyl-3-[2-pyridyl]-1,2,4-triazine-4,4′-disulfonic acid disodium salt). The complexes were characterized by NMR and IR spectroscopy and mass spectrometry. The compounds exhibit similar absorption and emission spectra, suggesting a similar electronic structure. Ct-DNA binding studies show the strong influence of the net charge as Cu-L (positively charged) is able to bind to ct-DNA while Cu-LSO3Na (negatively charged) is not. The net charge of the complexes affects the thermodynamic and kinetic binding parameters toward human serum albumin. HSA-binding of the complexes was further investigated by molecular docking, revealing different binding sites on the HSA protein as a function of the net charge. The different anticancer activities of the complexes towards ovcar-3 and hope-62 cancer cell lines are suggestive of a role for the overall charge of the complexes. Interaction with the DNA is not the major mechanism for this class of complexes. The overall net charge of the pharmacophore (anticancer agent) should be a key consideration in the design of anticancer metal complexes.

Insights into the toxicity of biomaterials microparticles with a combination of cellular and oxidative biomarkers

Considering that the extensive biomedical, pharmaceutics, cosmetic and other industrial applications of biomaterials (BMs) is of great concern nowadays, regarding their environmental risk, the present study aimed to investigate the effects of four BMs, poly(ε-caprolactone) (PCL), poly(butylene succinate) (PBSu), chitosan (CS) and modified chitosan (succinic acid grafted chitosan) (CS-Suc) in the form of microplastics (particle sizes less than 1 mm) on biochemical parameters of snails Cornu aspersum hemocytes. Due to the absence of knowledge about the environmentally relevant concentrations of BMs, snails were initially treated through their food with a wide range of nominal concentrations of each BM to define the half maximal effective concentration (NRRT₅₀), according to the destabilization degree of hemocytes' lysosomal membranes (by mean of neutral red retention time/NRRT assay). Thereafter, snails were treated with each BM, at concentrations lower than the estimated NRRT₅₀ values in all cases, for periods up to 15 days. After the end of the exposure period, a battery of stress indices were measured in hemocytes of challenged snails. According to the results, all parameters tested in BMs-treated snails statistically differed from those measured in BMs-free snails, thus indicating the pro-oxidant potential of BMs, as well as their ability to affect animals' physiology. The most considerable effect in most cases seems to be caused by modified chitosan and PCL, while chitosan appears to be the least toxic. A common response mechanism of snails' blood cells against the 4 BMs used in the present study was shown. After exposure to each of the studied BMs a significant augmentation in protein carbonyls, MDA equivalents and DNA damage, while a significant reduction in NRRT values was determined in the snails hemocytes, in relation to the unexposed animals. From the biochemical parameters examined, MDA equivalents and DNA damage seem to be more susceptible than the other parameters studied, to respond to BMs effect, with MDA to react with more sensitivity to PCL and CS, while DNA damage to CS-Suc and PBSu. Our results could suggest the simultaneous use of the latter biomarkers in biomonitoring studies of terrestrial ecosystems against the specific BMs.

Concentration-dependent mode of binding of drug oxatomide with DNA: multi-spectroscopic, voltammetric and metadynamics simulation analysis

The interaction between antihistaminic drug oxatomide (OXT) and calf-thymus DNA (CT-DNA) has been investigated in a physiological buffer (pH 7.4) using UV-Vis, fluorescence, ¹H NMR and circular dichroism spectral techniques coupled with viscosity measurements, KI quenching, voltammetry and in silico molecular modeling studies. OXT binds with CT-DNA in a concentration-dependent manner. At a lower [Drug]/[CT-DNA] molar ratio (0.6-0.1), OXT intercalates into the base pairs of CT-DNA, while at a higher [Drug]/[CT-DNA] molar ratio (13-6), the drug binds in the minor grooves of CT-DNA. The binding constants for the interaction are found to be in the order of 10³-10⁵ M^-1, and the groove binding mode of interaction exhibits a slightly higher binding constant than that of intercalative mode. Thermodynamic analysis of binding constants at three different temperatures suggests that both these modes of binding are mainly driven by hydrophobic interactions (ΔH^o > 0 and ΔS^o > 0). Voltammetric investigations indicate that the electro-reduction of OXT is an adsorption controlled process and shifts in reduction peak potentials reiterate the concentration-dependent mode of binding of the drug with CT-DNA. The free energy landscape obtained at the all-atom level, using metadynamics simulation studies, revealed two major binding forces: partial intercalation and minor groove binding, which corroborate well with the experimental results.Communicated by Ramaswamy H. Sarma.

Textile dyes Maxilon blue 5G and Reactive blue 203 induce acute toxicity and DNA damage during embryonic development of Danio rerio

Common textile dyes used in various industrial sectors are organic compounds and considered for the aquatic environment as pollutants. The textile dye industry is one of the main sectors that have serious impacts on the environment due to a large amount of wastewater released into the ecosystem. Maxilon blue 5G (MB-5G) and Reactive Blue 203 (RB-203) are widely used textile dyes. However, their potential toxicity on living organisms remains to be elucidated. Here, we investigate the acute toxicity and genotoxicity of MB-5G and RB-203 dyes using the zebrafish embryos/larvae. Embryos treated with each dye for 96 h revealed LC₅₀ values of acute toxicity as 166.04 mg L^-1 and 278.32 mg L^-1 for MB-5G and RB 203, respectively. When exposed to MB-5G and RB-203 at different concentrations (1, 10, and 100 mg L^-1) for 96 h, the expression of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage, significantly increased in brain tissues as compared to control. MB-5G and RB-203 resulted in common developmental abnormalities including tail malformation, microphthalmia, pericardial edema, curved body axis, and yolk sac/pericardial edemas. Moreover, at its highest dose (100 mg L^-1), RB-203 caused premature hatching after 48 h, while MG-5G did not. Our results collectively reveal that the textile dyes MB-5G and RB-203 cause genotoxicity and teratogenicity during embryonic and larval development of zebrafish. Thus, it is necessary to eliminate these compounds from wastewater or reduce their concentrations to safe levels before discharging the textile industry wastewater into the environment.

Studies to explore the UVA photosensitizing action of 9-phenylacridine in cells by interaction with DNA

Acridine and its derivatives are well known for their DNA binding properties. In this report, we present our findings on evaluating different binding parameters of the interaction of 9-phenylacridine (ACPH) with DNA. Absorption spectroscopic studies including standard and reverse titration, the effects of ionic strength and temperature on titration, and Job plot analysis were done to calculate the binding constant and determine the different thermodynamic parameters and stoichiometry of the binding. Spectrofluorimetry and circular dichroism (CD) spectral titration were also utilized to confirm these findings. The results indicated that ACPH binds to DNA reversibly through non-electrostatic interactions by hydrogen bonding and van der Waals interactions. The binding constant and the number of binding sites were of the order 10³ M^-1 and ≈2, respectively with a binding stoichiometry of 1:4. The binding of ACPH with DNA was spontaneous, exothermic and enthalpy-driven. The extent of uptake of ACPH in B16 melanoma cells was estimated. As this compound absorbs in the UVA region, the effect of treatment with ACPH prior to UVA exposure was assessed to evaluate its phototoxicity in these cells. Our results indicated that the binding to DNA enhanced damage to sensitize cells to killing through apoptosis. Our findings indicated its potential to act as a photosensitizer.

Influence of position of hydroxyl group of flavonoids on their binding with single stranded polyriboadenylic acid: A spectroscopic evaluation

Single stranded polyriboadenylic acid [poly (rA)] has been accepted widely as a suitable drug target owing to its vital role in the development of cancer since it controls gene expression during cell growth and differentiation. The biological properties of poly (rA) depend on its structural morphology. Pharmacologically active flavonoids can act as suitable binders to poly (rA) and significantly change its biophysical properties. Different factors favour flavonoid-poly (rA) binding. In our present work we have explored the role played by the position of hydroxyl groups in the flavonoids namely 3, 5, 6 and 7 hydroxyflavones in their course of interaction with poly (rA). A range of spectroscopic experiments reveal that 3HF binds best to poly (rA) among the four chosen flavonoids. This is probably due to the presence of a hydroxyl group in '3' position that enables it to exhibit ESIPT phenomenon which is missing for the other used flavonoids.

Insight into the binding mechanism of macrolide antibiotic; erythromycin to calf thymus DNA by multispectroscopic and computational approaches

In the present study, the interactions between Erythromycin drug and calf thymus deoxyribonucleic acid (ct-DNA) were explored by multi spectroscopic techniques (UV-Visible, fluorescence, circular dichroism spectroscopies), viscosity, molecular docking simulation, and atomic force microscopy (AFM). In addition, the values of binding constant were calculated by the UV-Visible and fluorescence spectroscopy. Competitive fluorescence study with methylene blue (MB), acridine orange (AO), and Hoechst 33258 were indicated that the Erythromycin drug could displace the DNA-bound Hoechst, which displays the strong competition of Erythromycin with Hoechst to interact with the groove binding site of DNA. In addition, the observed complexes in AFM analysis comprise the chains of ct-DNA and Erythromycin with an average size of 314.05 nm. The results of thermodynamic parameter calculations (ΔS° = -332.103 ± 14 J mol^-1 K^-1 and ΔH° = -115.839 ± 0.02 kJ mol^-1) approved the critical role of van der Waals forces and hydrogen bonds in the complexation of Erythromycin-DNA. Fluorescence spectroscopy results demonstrate the existence of a static enhancement mechanism in the interaction of Erythromycin-DNA. According to the obtained results, Erythromycin drug interacts with the major groove of ct-DNA. These consequences were further supported by the molecular docking study, and it could be determined that DNA-Erythromycin docked model was in a rough correlation with our experimental results.Communicated by Ramaswamy H. Sarma.

Biophysical and theoretical studies of the interaction between a bioactive compound 3,5-dimethoxy-4-hydroxycinnamic acid with calf thymus DNA

3,5-Dimethoxy-4-hydroxycinnamic acid commonly known as Sinapic acid is a well-known derivative of hydroxycinnamic acids, is commonly present in human diet. Due to its wide variety of pharmacological activities like antioxidant, antimicrobial, anti-inflammatory, anticancer, and anti-anxiety, it has attracted much attention for the researchers. In our previous published work we have already analyzed the interaction between sinapic acid (SA) with a model transport protein. In this work our aim is to demonstrate a detailed investigation of the binding interaction between sinapic acid with another carrier of genetic information in a living cell, the DNA. Here we have used calf thymus DNA (ct-DNA) as a model. The binding characteristic of SA with ct-DNA was investigated by different spectroscopic and theoretical tools. The spectroscopic investigation revealed that quenching of intrinsic fluorescence of SA by ct-DNA occurs through dynamic quenching mechanism. The thermodynamic parameters established the involvement of hydrogen bonding and weak van der Waals forces in the interaction. Further, the circular dichroism, competitive binding experiment with ethidium bromide and potassium iodide quenching experiment suggested that SA possibly binds to the groove position of the ct-DNA. Finally, molecular docking analysis established the SA binds to minor groove position of ct-DNA in G-C rich region through hydrogen bonding interaction. Additionally, gel electrophoresis analysis has been performed to determine the protective efficacy of SA against UVB induced DNA damage and 50 μM of SA was found to protect the DNA from UVB induced damage. We hope that our study could provide the validation of SA on behalf of therapeutics and development of next generation therapeutic drug as well as designing new efficient drug molecule and methodology for the interaction study of the drug with DNA.

Luminescent terpyridine appended geminal bisazide and bistriazoles: multinuclear Pt(II) complexes and AIPE-based DNA detection with the naked eye

We report square planar Pt(ii) complexes as luminescent biosensors for DNA detection in solution. The sensing is attributed to the aggregation induced bright red photoluminescence (AIPE) of the complexes in the presence of DNA that can be seen with the naked eye using only a 360 nm light source. Terpyridine appended luminescent geminal bistriazoles (L1-L4, from geminal bisazide A through azide-alkyne 'click' cycloaddition) with versatile chelating sites were explored for metal coordination and reaction with Pt(dmso)2Cl2 yielding tetranuclear and dinuclear complexes of Pt(ii) with different N∩N ligand environments. Thermally stable gem-bisazide and bistriazoles are hardly reported in the literature and this is the first report of terpyridine appended geminal bisazide and bistriazoles.

Probing the Strength and Mechanism of Binding Between Amifampridine and Calf Thymus DNA

In this work, we have investigated the strength and mechanism of amifampridine (3,4-Diaminopyridine/3,4-DAP) interaction with calf thymus DNA (ct-DNA). The existence and the strength of interaction are evaluated using circular dichroism (CD), UV-vis absorption, and differential pulse voltammogram studies. Results from UV-vis absorption technique indicate that amifampridine can significantly interact with DNA through a binding constant of Kb = 1.66 × 105 M-1 at 298 K. The mechanism of the interaction between amifampridine and DNA is also studied using ionic effect investigations, competitive fluorescence experiments, viscosity measurements, and molecular docking studies. The viscosity results indicate that amifampridine can bind to DNA via intercalation binding mode. Competitive fluorescence experiments using Acridine Orange (AO) and Hoechst 33258 (HO) probes also reveal that amifampridine binds to DNA via an intercalation mode of binding. Finally, the molecular docking studies also suggest that amifampridine tends to bind with the G-C rich region of DNA.