Contrasting enantioselective DNA preference: chiral helical macrocyclic lanthanide complex binding to DNA

A Novel Fluorescent DNA Sensor for Acrylamide Detection in Food Samples Based on Single-Stranded DNA and GelRed

The presence of acylamide (AA) in large group of food products and its health hazards have been confirmed by scientists. In this study, a simple and innovative biosensor for AA determination was designed based on single-stranded DNA (ssDNA) with partial guanine and GelRed. The idea of this biosensor is based on the formation of AA-ssDNA adduct through the strong binding interaction between AA and guanine base of ssDNA, which subsequently inhibits the interaction of ssDNA and GelRed, leading to a weak fluorescence intensity. The binding interaction between AA and ssDNA was confirmed by UV-Vis absorption spectrometry and fluorescence intensity. Under optimum conditions, the designed biosensor exhibited excellent linear response in range of 0.01-95 mM, moreover it showed high selectivity toward AA. The limit of detection was 0.003 mM. This biosensor was successfully applied for the determination of AA in water extract of potato fries and coffee in the range of 0.05-100 mM with LOD of 0.01 mM and 0.05-95 mM with LOD of 0.004 mM, respectively.

Chirality-Dependent Reprogramming of Macrophages by Chiral Nanozymes

It is known that extracellular free radical reactive oxygen species (ROS) rather than intracellular ROS plays a non-substitutable role in regulation of tumor-suppressing (M1) tumor-associated macrophages (TAMs) polarization. However, most therapeutic nanoplatforms mainly provide intracellular ROS and exhibit insufficient accumulation near TAMs, which strongly limits the macrophage-based immunotherapeutic effects. Here we design and synthesize chiral MoS2 /CoS2 nanozymes with peroxidase (POD)-like and catalase (CAT)-like activities to efficiently modulate TAMs polarization and reverse tumor immunosuppression by harnessing their chirality-specific interactions with biological systems. MoS2 /CoS2 nanoparticles coordinated with d-chirality (d-NPs, right-handed) show improved pharmacokinetics with longer circulating half-life and higher tumor accumulation compared with their l (left-handed)- and dl (racemate)-counterparts. Further, d-NPs can escape from macrophage uptake in the tumor microenvironment (TME) with the aid of cell-unpreferred opposite chirality and act as extracellular hydroxyl radicals (⋅OH) and oxygen (O2 ) generators to efficiently repolarize TAMs into M1 phenotype. On the contrary, l-NPs showed high cellular uptake due to chirality-driven homologous adhesion between l-NPs and macrophage membrane, leading to limited M1 polarization performance. As the first example for developing chiral nanozymes as extracellular-localized ROS generators to reprogram TAMs for cancer immunotherapy, this study opens an avenue for applications of chiral nanozymes in immunomodulation.

Small Molecule Interactions with Biomacromolecules: DNA Binding Interactions of a Manganese(III) Schiff Base Complex with Potential Anticancer Activities

A manganese(III) complex, [MnIII(L)(SCN)(enH)](NO3)·H2O (1•H2O) (H2L = 2-((E)-(2-((E)-2-hydroxy-3-methoxybenzylidene-amino)-ethyl-imino)methyl)-6-methoxyphenol), has been synthesized and characterized by single-crystal X-ray diffraction analysis. The interaction of 1•H2O with DNA was studied by monitoring the decrease in absorbance of the complex at λ = 324 nm with the increase in DNA concentration, providing an opportunity to determine the binding constant of the 1•H2O-ct-DNA complex as 5.63 × 103 M-1. Similarly, fluorescence titration was carried out by adding ct-DNA gradually and monitoring the increase in emission intensity at 453 nm on excitation at λex = 324 nm. A linear form of the Benesi-Hildebrand equation yields a binding constant of 4.40 × 103 M-1 at 25 °C, establishing the self-consistency of our results obtained from absorption and fluorescence titrations. The competitive displacement reactions of dyes like ethidium bromide, Hoechst, and DAPI (4',6-diamidine-2'-phenylindole dihydrochloride) from dye-ct-DNA conjugates by 1•H2O were analyzed, and the corresponding KSV values are 1.05 × 104, 1.25 × 104, and 1.35 × 104 M-1 and the Kapp values are 2.16 × 103, 8.34 × 103, and 9.0 × 103 M-1, from which it is difficult to infer the preference of groove binding over intercalation by these DNA trackers. However, the molecular docking experiments and viscosity measurement clearly indicate the preference for minor groove binding over intercalation, involving a change in Gibbs free energy of -8.56 kcal/mol. The 1•H2O complex was then evaluated for its anticancer potential in breast cancer MCF-7 cells, which severely abrogates the growth of the cells in both 2D and 3D mammospheres, indicating its promising application as an anticancer drug through a minor groove binding interaction with ct-DNA.

Detection of Glucose Based on Noble Metal Nanozymes: Mechanism, Activity Regulation, and Enantioselective Recognition

Glucose monitoring is essential to evaluate the degree of glucose metabolism disorders. The enzymatic determination has been the most widely used method in glucose detection because of its high efficiency, accuracy, and sensitivity. Noble metal nanomaterials (NMs, i.e., Au, Ag, Pt, and Pd), inheriting their excellent electronic, optical, and enzyme-like properties, are classified as noble metal nanozymes (NMNZs). As the NMNZs are often involved in two series of reactions, the oxidation of glucose and the chromogenic reaction of peroxide, here the chemical mechanism by employing NMNZs with glucose oxidase (GOx) and peroxidase (POD) mimicking activities is briefly summarized first. Subsequently, the regulation strategies of the GOx-like, POD-like and tandem enzyme-like activities of NMNZs are presented in detail, including the materials, size, morphology, composition, and the reaction condition of the representative NMs. In addition, in order to further mimic the enantioselectivity of enzyme, the design of NMNZs with enantioselective recognition of d-glucose and l-glucose by using different chiral compounds (DNA, amino acids, and cyclodextrins) and molecular imprinting is further described in this review. Finally, the feasible solutions to the existing challenges and a vision for future development possibilities are discussed.

Imine- and Amine-Type Macrocycles Derived from Chiral Diamines and Aromatic Dialdehydes

The condensation of aromatic dialdehydes with chiral diamines, such as 1,2-trans-diaminocyclohexane, leads to various enantiopure or meso-type macrocyclic Schiff bases, including [2 + 2], [3 + 3], [4 + 4], [6 + 6] and [8 + 8] condensation products. Unlike most cases of macrocycle synthesis, the [3 + 3] macrocycles of this type are sometimes obtained in high yields by direct condensation without a metal template. Macrocycles of other sizes from this family can often be selectively obtained in high yields by a suitable choice of metal template, solvent, or chirality of the building blocks. In particular, the application of a cadmium(II) template results in the expansion of the [2 + 2] macrocycles into giant [6 + 6] and [8 + 8] macrocycles. These imine macrocycles can be reduced to the corresponding macrocyclic amines which can act as hosts for the binding of multiple cations or multiple anions.

Designing lanthanide coordination nanoframeworks as X-ray responsive radiosensitizers for efficient cancer therapy

A series of three-dimensional Ln-based coordination nanoframeworks were designed and shown potential as efficient and low toxic X-ray responsive radiosensitizers for the treatment of cervical cancer.

Recognizing and stabilizing miR-21 by chiral ruthenium(II) complexes

MiR-21, a non-coding miRNA with 22 nucleotides, plays an important part in the proliferation, invasion, and metastasis of tumor cells. The present study demonstrates that isomers of chiral ruthenium(II) complexes with alkynes (Λ-1 and Δ-1) were synthesized by Songogashira coupling reaction by using microwave-assisted synthetic technology. The isomers can recognize and stabilize miR-21, with the Λ-isomer showing a stronger binding capacity than the Δ-isomer. Further studies showed that both isomers can be uptaken by MDA-MB-231 cells and enriched in the nucleus. Treatment with the Λ-/Δ-isomer downregulated the expression of miR-21. In a word, the development of chiral ruthenium(II) complexes act as potential inhibitors against tumor cells by recognizing, stabilizing, and regulating the expression of miR-21.

Nucleic acid binding mechanism of flavone derivative, riviciclib: Structural analysis to unveil anticancer potential

Despite burgeoned knowledge about the origin, growth, tissue interactions, and spread of cancer in recent years, the functional complexity and unique survival ability of cancer cells still make it difficult to target them. Riviciclib is a semi-synthetic derivative of rohitukine and possesses anticancer potential. Inhibition of nucleic acid activity in an uncontrolled dividing cell can form the basis for the development of new-age cancer therapeutics. The present study reports the molecular interaction between riviciclib and nucleic acid (DNA/tRNA) using spectroscopic and molecular docking studies in an attempt to comprehend its cellular toxicity as well as the nature and mode of binding between them. Vibrational spectroscopic results suggest that riviciclib intercalates DNA duplex and primarily binds with guanine, adenine, and thymine nucleobases. While in the case of riviciclib-tRNA complexation, riviciclib interacts mostly with uracil residues of the tRNA molecule. Besides nucleobases, riviciclib interacts with the sugar-phosphate backbone of both biomacromolecules. Conformationally, DNA alters from B-form to C-form, whereas tRNA shows no change in its native A-form. The order (10⁴ M^-1) of binding constant for riviciclib-nucleic acid complexation infer moderate to strong affinity of riviciclib with DNA and tRNA, respectively. Molecular docking explorations are further in corroboration with our spectroscopic outcomes.

Discriminating between negative cooperativity and ligand binding to independent sites using pre-equilibrium properties of binding curves

Negative cooperativity is a phenomenon in which the binding of a first ligand or substrate molecule decreases the rate of subsequent binding. This definition is not exclusive to ligand-receptor binding, it holds whenever two or more molecules undergo two successive binding events. Negative cooperativity turns the binding curve more graded and cannot be distinguished from two independent and different binding events based on equilibrium measurements only. The need of kinetic data for this purpose was already reported. Here, we study the binding response as a function of the amount of ligand, at different times, from very early times since ligand is added and until equilibrium is reached. Over those binding curves measured at different times, we compute the dynamic range: the fold change required in input to elicit a change from 10 to 90% of maximum output, finding that it evolves in time differently and controlled by different parameters in the two situations that are identical in equilibrium. Deciphering which is the microscopic model that leads to a given binding curve adds understanding on the molecular mechanisms at play, and thus, is a valuable tool. The methods developed in this article were tested both with simulated and experimental data, showing to be robust to noise and experimental constraints.

Effect of magnetic anisotropy on direct chiral discrimination in paramagnetic NMR spectroscopy

We have studied the effect of thermally populated crystal field states on room temperature chiral discrimination in NMR spectroscopy.

Chirality transfer between hexaazamacrocycles in heterodinuclear rare earth complexes

Both the chiral hexaazamacrocyle L1 based on trans-1,2-diaminocyclohexane and the achiral hexaazamacrocyle L2 based on ethylenediamine form lanthanide(iii) dinuclear μ-hydroxo bridged complexes which have been characterized by NMR and CD spectroscopy. The homodinuclear complexes of the type [Ln₂(L1)₂(μ-OH)₂](NO₃)₄ (Ln = Nd^III, Eu^III, Tb^III and Yb^III) have been synthesized in the enantiopure form and the X-ray crystal structures of Nd^III, Eu^III and Yb^III derivatives have been determined. The heterodinuclear cationic complexes [Ln(L1)Ln'(L2)(μ-OH)₂X₂]ⁿ⁺ have been generated and characterized in solution by using the mononuclear complexes of L1 and L2 as substrates. While the formation of [LnLn'(L1)₂(μ-OH)₂X₂]ⁿ⁺ dinuclear complexes is accompanied by chiral narcissistic self-sorting, the formation of [Ln(L1)Ln'(L2)(μ-OH)₂X₂]ⁿ⁺ dinuclear complexes is accompanied by the sizable sociable self-sorting of macrocyclic units. The homodinuclear complexes [Y₂(L1)₂(μ-OH)₂X₂]ⁿ⁺ and [Ln₂(L2)₂(μ-OH)₂X₂]ⁿ⁺ (Ln = Dy^III, Pr^III and Nd^III) are CD silent in the visible region due to the lack of f-f transitions and the presence of an achiral ligand, respectively. In contrast, the heterodinuclear [Y(L1^S)Ln(L2)(μ-OH)₂X₂]ⁿ⁺ complexes give rise to CD signals arising from the f-f transitions because of the chirality transfer from the L1 macrocyclic unit to the L2 macrocyclic unit.

Binding and thermodynamics of REV peptide-ctDNA interaction

The thermodynamics of DNA-ligand binding is important as it provides useful information to understand the details of binding processes. HIV-1 REV response element (RRE) located in the env coding region of the viral genome is reported to be well conserved across different HIV-1 isolates. In this study, the binding characteristics of Calf thymus DNA (ctDNA) and REV peptide from HIV-1 were investigated using spectroscopic (UV-visible, fluorescence, and circular dichroism (CD)) and isothermal titration calorimetric (ITC) techniques. Thermal stability and ligand binding properties of the ctDNA revealed that native ctDNA had a T_m of 75.5 °C, whereas the ctDNA-REV peptide complex exhibited an incremental shift in the T_m by 8 °C, indicating thermal stability of the complex. CD data indicated increased ellipticity due to large conformational changes in ctDNA molecule upon binding with REV peptide and two binding stoichiometric modes are apparent. The ctDNA experienced condensation due to large conformational changes in the presence of REV peptide and positive B→Ψ transition was observed at higher molar charge ratios. Fluorescence studies performed at several ligand concentrations revealed a gradual decrease in the fluorescence intensity of EtBr-bound ctDNA in response to increasing ligand concentrations. The fluorescence data further confirmed two stoichiometric modes of binding for ctDNA-REV peptide complex as previously observed with CD studies. The binding enthalpies were determined using ITC in the temperature range of 293 K-308 K. The ITC binding isotherm was exothermic at all temperatures examined, with low ΔH values indicating that the ctDNA-REV peptide interaction is driven largely by entropy. The heat capacity change (ΔC_p ) was insignificant, an unusual finding in the area of DNA-peptide interaction studies. The variation in the values obtained for ΔH, ΔS, and ΔG with temperature further suggests that ctDNA-REV peptide interaction is entropically driven. ITC based analysis of salt dependence of binding constant gave a charge value (Z) = +4.01, as determined for the δlnK/δln[Na⁺ ] parameter, suggesting the participation of only 3-4 Arg out of 11 Arg charge from REV peptide. The stoichiometry observed for the complex was three molar charge of REV peptide binding per molar charge of ctDNA. ITC based analysis further confirmed that the binding between ctDNA and REV peptide is governed by electrostatic interaction. Molecular interactions including H-bonding, van der Waals forces, and solvent molecules rearrangement, underlie the binding of REV peptide to ctDNA.

Catalytic Capacity of Diaza-Crown Ether Lanthanum Complexes with Varied Ligands for Phosphate Ester Hydrolysis in Different Media

Two diaza-crown ether compounds, 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (L0) and its derivative with double acetamide side arms 2,2'-(1,4,10,13-teteaoxa-7,16-diazacyclooctadecane-7,16-diyl)diacetamide (L), and the corresponding two lanthanum complexes were synthesised and characterised. The catalytic capacity of the lanthanum complexes was investigated for the hydrolysis of bis(4-nitrophenyl) phosphate ester (BNPP) in aqueous solution and in CTAB micelles. Kinetic studies show that the catalytic efficiency of complex LaL is obviously higher than that of complex LaL0, and introducing acetamide into the ring of the diaza-crown ether can improve the catalytic ability of the complexes for BNPP hydrolysis. A rate enhancement of about two times was observed for the complex–micelle in contrast with the complex–water system for BNPP catalytic hydrolysis. The optimal pH for the catalytic reaction in the two kinds of media systems show an approximately 0.4 pH unit difference. The two complexes possess higher thermostability, and are more stable in the micelle than in aqueous solution. Based on the results and their analysis, a catalytic mechanism with cooperation of acetamide is proposed.

DNA Recognition by a Novel Bis-Intercalator, Potent Anticancer Drug XR5944

XR5944 is a potent anticancer drug with a novel DNA binding mode: DNA bisintercalationg with major groove binding. XR5944 can bind the estrogen response element (ERE) sequence to block ER-ERE binding and inhibit ERα activities, which may be useful for overcoming drug resistance to currently available antiestrogen treatments. This review discusses the progress relating to the structure and function studies of specific DNA recognition of XR5944. The sites of intercalation within a native promoter sequence appear to be different from the ideal binding site and are context- and sequence- dependent. The structural information may provide insights for rational design of improved EREspecific XR5944 derivatives, as well as of DNA bis-intercalators in general.

Room Temperature Chiral Discrimination in Paramagnetic NMR Spectroscopy

A recently proposed theory of chiral discrimination in NMR spectroscopy based on the detection of a molecular electric polarization P rotating in a plane perpendicular to the NMR magnetic field [A. D. Buckingham, J. Chem. Phys. 140, 011103 (2014)] is generalized here to paramagnetic systems. Our theory predicts new contributions to P, varying as the square of the inverse temperature. Ab initio calculations for ten Dy^{3+} complexes, at 293 K, show that, in strongly anisotropic paramagnetic molecules, P can be more than 1000 times larger than in diamagnetic molecules, making paramagnetic NMR chiral discrimination amenable to room temperature detection.

Multinuclear Ni(ii), Cu(ii) and Zn(ii) complexes of chiral macrocyclic nonaazamine

Herein, we report the preparation and crystal structures of Ni(ii), Cu(ii) and Zn(ii) complexes. For both the Ni(ii) and Cu(ii) compounds, a magnetostructural correlation was established.

SOD mimetic activity and antiproliferative properties of a novel tetra nuclear copper (II) complex

The search for novel anticancer therapeutic agents is an urgent and important issue in medicinal chemistry. Here, we report on the biological activity of the copper-based bioinorganic complex Cu4 (2,4-di-tert-butyl-6-(1H-imidazo- [1, 10] phenanthrolin-2-yl)phenol)4]·10 CH3CN (2), which was tested in rat L6 myotubes, mouse NSC-34 motor neurone-like cells, and HepG-2 human liver carcinoma. Upon 96 h incubation, 2 exhibited a significant cytotoxic effect on all three types of cells via activation of two cell death mechanisms (apoptosis and necrosis). Complex 2 exhibited better potency and efficacy than the canonical cytotoxic drug cisplatin. Moreover, during shorter incubations, complex 2 demonstrated a significant SOD mimetic activity, and it was more effective and more potent than the well-known SOD mimetic TEMPOL. In addition, complex 2 was able to interact with DNA and, cleave DNA in the presence of sodium ascorbate. This study shows the potential of using polynuclear redox active compounds for developing novel anticancer drugs through SOD-mimetic redox pathways.

DNA Cleavage Activity: Comparison of two Lanthanum Complexes Based on Aza-Crown Ethers with Different Numbers of Nitrogen Atoms

Based on the unique characteristics of lanthanum ion and aza-crown ethers, the lanthanum complexes of two aza-crown ether (L1: 1,10-Dioxa-4,7,13,16-tetraazacyclo-octadecane and L2: 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane) were designed and synthesised. The interaction between these two complexes and DNA was measured by UV-Vis spectroscopy and gel electrophoresis. Moreover, a series of experiments of cleavage of pUC19 DNA were conducted to illustrate the acidity, time and concentration effects. The results indicated that the two metal complexes can accelerate the breakage of DNA from its supercoiled form (form I) to the nicked form (form II) at near-physiological conditions, and the optimum acidity of DNA catalytic cleavage is pH=6.5 and pH=7.0 for LaL1 and LaL2, respectively. Furthermore, the LaL1 exhibited better cleavage activity than LaL2 under the same conditions, thus supercoiled DNA was thoroughly cleaved to the nicked form under the appropriate conditions. The hydrolytic mechanism was verified by applying several oxygen-scavengers to the DNA catalytic cleavage.

Development of the aza-crown ether metal complexes as artificial hydrolase

Hydrolases play a crucial role in the biochemical process, which can catalyze the hydrolysis of various compounds like carboxylic esters, phosphoesters, amides, nucleic acids, peptides, and so on. The design of artificial hydrolases has attracted extensive attention due to their scientific significance and potential applications in the field of gene medicine and molecular biology. Numerous macrocyclic metal complexes have been used as artificial hydrolase in the catalytic hydrolysis of the organic substrate. Aza-crown ether for this comment is a special class of the macrocyclic ligand containing both the nitrogen atoms and oxygen atoms in the ring. The studies showed that the aza-crown complexes exhibited high activity of hydrolytic enzyme. However, the aza-crown ether metal complex as artificial hydrolase is still very limited because of its difficulty in synthesis. This review summarizes the development of the aza-crown ether metal complexes as the artificial hydrolase, including the synthesis and catalysis of the transition metal complexes and lanthanide metal complexes of aza-crown ethers. The purpose of this review is to highlight: (1) the relationship between the structure and hydrolytic activity of synthetic hydrolase; (2) the synergistic effect of metal sites and ligands in the course of organic compound hydrolysis; and (3) the design strategies of the aza-crown ethers as hydrolase.

Chiral resolution capabilities of DNA oligonucleotides

Herein, we studied the chiral resolution properties of a repertoire of arbitrarily chosen DNA oligonucleotides (ON). Ten oligonucleotidic sequences characterized by diverse base compositions, sizes, and structural features, ranging from secondary structure-free homo-oligonucleotides to duplex, hairpin, and three-way junction architectures, were investigated as potential chiral selectors. Their enantioselective features were assessed by using ONs as running buffer additives in partial-filling capillary electrophoresis. It was shown that all the screened sequences displayed enantiodiscrimination capabilities toward small aromatic compounds. Under (sub)millimolar DNA concentration conditions, the combination of only three oligonucleotidic sequences provided the chiral resolution of around 20 racemates, including drugs, illegal drugs, amino-acids, and nucleosides. This work represents the first demonstration of such analyte selectivity spectrum for nucleic acid-based chiral separation tools.

Lanthanide(iii) and lead(ii) complexes of a chiral nonaaza macrocyclic amine based on 1,2-diaminocyclopentane

We report the synthesis, spectroscopic characterization and X-ray crystal structures of a series of helical complexes of a new chiral macrocycle based on diaminocyclopentane fragments. In the case of a Pb(ii) derivative the NMR data indicate a dynamic process corresponding to partial wrapping and unwrapping of the macrocycle resulting in the switching of the helix axis.

Interaction of human telomeric G-quadruplex DNA with thymoquinone: a possible mechanism for thymoquinone anticancer effect

BACKGROUND

Thymoquinone (TQ) has been documented to possess chemo-preventive and chemotherapeutic antitumor effects. Studies reported that TQ inhibits the growth of cancer cells in animal models, culture and xenografted tumors. Molecular mechanisms underlying these anticancer effects were attributed to inductions of cell cycle arrest, apoptosis, oxidative damage of cellular macromolecules, blockade of tumor angiogenesis and inhibitions in migration, invasion and metastasis of cancer cells. On the other hand, human telomere DNA plays a role in regulating genes' transcriptions. It folds up into G-quadruplex structures that inhibit telomerase enzyme over-expressed in cancerous cells. Molecules that selectively stabilize G-quadruplex are potential anticancer agents. Therefore, this work aimed to explore the interaction of TQ with G-quadruplex DNA as a possible underlying mechanism for the anticancer effect of TQ.

METHODS

Interactions of TQ with telomeric G-quadruplex (5'-AGGG(TTAGGG)3-3') and duplex DNAs were studied using UV-vis, fluorescence, circular dichroism, liquid and solid NMR (1H and 13C), melting temperature and docking simulation.

RESULTS

Changes in UV-vis, CD, fluorescence, 1H NMR and 13C NMR, spectra as well as melting temperatures and docking simulations provided evidences for TQ's interactions with G-quadruplex. TQ was found to interact with G-quadruplex on two binding sites adjacent to the TTA loop with binding constants 1.80×10(5) and 1.12×10(7) M(-1). Melting temperatures indicated that TQ stabilized G-quadruplex by 5.6 °C and destabilized ct-DNA by 5.1 °C. Selectivity experiment indicated that TQ is preferentially binding to G-quadruplex over duplex with selectivity coefficients of 2.80-3.33×10(-3). Results suggested an intercalation binding mode based on π-π stacking.

CONCLUSION

Our results propose that TQ can possibly act as a G-quadruplex DNA stabilizer and subsequently contribute to the inhibition of telomerase enzyme and cancer's proliferation.

GENERAL SIGNIFICANCE

Our results represent a change in the paradigms reported for structural features of G-quadruplex's stabilizers and anticancer mechanisms of TQ.

A structural insight into major groove directed binding of nitrosourea derivative nimustine with DNA: a spectroscopic study

Nitrosourea therapeutics occupies a definite place in cancer therapy but its exact mechanism of action has yet to be established. Nimustine, a chloroethyl nitrosourea derivative, is used to treat various types of malignancy including gliomas. The present work focuses on the understanding of nimustine interaction with DNA to delineate its mechanism at molecular level. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) has been used to determine the binding sites of nimustine on DNA. Circular dichroism (CD) spectroscopy has been used to confirm conformational variations in DNA molecule upon nimustine-DNA interaction. Thermodynamic parameters of nimustine-DNA reaction have been calculated by isothermal titration calorimetry. Results of the present study demonstrate that nimustine is not a simple alkylating agent rather it causes major grove-directed-alkylation. Spectroscopic data suggest binding of nimustine with nitrogenous bases guanine (C6 = O6) and thymine (C4 = O4) in DNA major groove. CD spectra of nimustine-DNA complexes point toward the perturbation of native B-conformation of DNA and its partial transition into C-form. Thermodynamically, nimustine-DNA interaction is an entropy driven endothermic reaction, which suggests hydrophobic interaction of nimustine in DNA-major groove pocket. Spectral results suggest base binding and local conformational changes in DNA upon nimustine interaction. Investigation of drug-DNA interaction is an essential part of rational drug designing that also provides information about the drug's action at molecular level. Results, demonstrated here, may contribute in the development of new nitrosourea therapeutics with better efficacy and fewer side effects.

Enantioselective recognition mechanism of ofloxacin via Cu(II)-modulated DNA

The specific interactions of Cu(2+) with self-complementary DNA sequences involving d[G4C4(GC)2G4C4], d[(GC)10], and d[(AT)10], as well as the chiral recognition mechanism of ofloxacin enantiomers via the Cu(II)-modulated DNAs, were investigated using characterizations of circular dichroism, gel electrophoresis, FT-IR spectroscopy, UV melting measurement, electron paramagnetic resonance, and HPLC. The Cu(II)-coordinated GC-rich DNAs exhibit amplified enantioselectivity toward the S-enantiomer of ofloxacin. Especially in the case of d[G4C4(GC)2G4C4], ofloxacin enantiomers intercalate into the two adjacent guanine bases through the minor groove mediated by Cu(2+), which leads to a more favorable binding between S-ofloxacin and DNA. The highest ee value of ofloxacin enantiomers in the permeate after being adsorbed by the Cu(II)-DNA complex is obtained as 49.2% in the R-enantiomer at the [Cu(2+)]/[base] molar ratio of 0.25, while at the [Cu(2+)]/[base] molar ratio of 0.05 the highest ee value of ofloxacin enantiomers in the retentate reaches 26.3% in the S-enantiomer. This work illustrates a novel promising route to construct DNA-based chiral selectors toward certain drug enantiomers through the programmable enantioselective recognition on the basis of DNA chirality and the specific binding of transition metal ions.

Anion and solvent induced chirality inversion in macrocyclic lanthanide complexes

A series of the lanthanide(III) or yttrium(III) complexes of the type [LnL(NO3)(H2O)2](NO3)2, [LnL(NO3)(H2O)](NO3)2, [LnL(H2O)2](NO3)3, and [LnLCl(H2O)2]Cl2 where L is an all-R or all-S enantiomer (L(R) or L(S)) of the chiral hexaaza macrocycle, 2(R),7(R),18(R),23(R)- or 2(S),7(S),18(S),23(S)-1,8,15,17,24,31-hexaazatricyclo[25.3.1.1.0.0]-dotriaconta-10,12,14,26,28,30-hexaene, and Ln(III) = Sm(III), Tb(III), Ho(III), Er(III), Tm(III), Yb(III), Lu(III), or Y(III), have been synthesized and structurally characterized. The crystal structure of the free macrocycle shows a highly twisted molecule, preorganized for the formation of helical complexes. The crystal structures of the lanthanide(III) complexes show two different diastereomeric forms of the macrocycle with different configurations at the stereogenic amine nitrogen atoms: (RRRR) or (RSRS) (denoted as L(RI) and L(RII), respectively). The L(RI) diastereomeric form of the nitrate derivatives [LnL(NO3)(H2O)](NO3)2 (Ln = Ho, Er) and [LnL(H2O)2](NO3)3 (Ln = Tm, Yb, Lu) convert slowly to the L(RII) form in methanol or acetonitrile solutions, while this process is not observed for the L(RI) diastereomers of analogous chloride derivatives [LnL(H2O)2]Cl3 (Ln = Tm, Yb, Lu). On the other hand, the L(RI) → L(RII) conversion for these Tm(III), Yb(III), and Lu(III) chloride derivatives can be triggered by the addition of external nitrate anions. The circular dichroism (CD) and (1)H NMR data indicate initial fast exchange of axial chloride for axial nitrate ligand, followed by slow chirality inversion of the equatorial macrocyclic ligand.

An insulin-like growth factor-II intronic variant affects local DNA conformation and ovarian cancer survival

Insulin-like growth factor-II (IGF-II) may be a prognostic marker in ovarian cancer, and its intronic single nucleotide polymorphism (SNP) rs4320932 has been associated with risk of the disease. We determined whether rs4320932 is associated with IGF-II expression and patient survival in ovarian cancer, and explored whether the SNP variation affects DNA conformation both in the absence of and presence of carboplatin. IGF-II genotype (rs4320932) and phenotype were analyzed in 212 primary invasive epithelial ovarian cancer tissue samples with Taqman® SNP genotyping assays, quantitative reverse transcription-polymerase chain reaction and commercial enzyme-linked immunosorbent assay. DNA conformation was evaluated by circular dichroism (CD) spectra. Kaplan-Meier survival curves and Cox proportional hazard regression models were used to analyze the SNP associations with patient survival. The C allele of rs4320932, previously associated with decreased risk of ovarian cancer development, was here associated with significantly elevated risks of relapse (Ptrend = 0.0002) and death (Ptrend = 0.0006), remaining significant in multivariate analyses. The adjusted hazard ratios were 3.05 (95% confidence interval [CI]: 1.47-6.37) for relapse and 3.28 (95% CI: 1.64-6.57) for death, respectively. The variant was also significantly associated with chemotherapy response, but not with other clinicopathologic variables or with IGF-II expression. DNA with genotypes TT and CC had distinct CD spectra in both the absence of and presence of carboplatin. These findings suggest that the intronic SNP rs4320932 affects patient survival and chemotherapy response via alteration of DNA conformation, but not through regulation of IGF-II expression. This novel finding may have implications in individualized medicine for the design of specific molecules targeting DNA of specific conformations.