Characterization, modes of interactions with DNA/BSA biomolecules and anti-tumor activity of newly synthesized dinuclear platinum(II) complexes with pyridazine bridging ligand.

Platinum-based drugs are widely recognized efficient anti-tumor agents, but faced with multiple undesirable effects. Here, four dinuclear platinum(II) complexes, [{Pt(1,2-pn)Cl}2(µ-pydz)]Cl2 (C1), [{Pt(ibn)Cl}2(µ-pydz)]Cl2 (C2), [{Pt(1,3-pn)Cl}2(µ-pydz)]Cl2 (C3) and [{Pt(1,3-pnd)Cl}2(µ-pydz)]Cl2 (C4), were designed (pydz is pyridazine, 1,2-pn is ( ±)-1,2-propylenediamine, ibn is 1,2-diamino-2-methylpropane, 1,3-pn is 1,3-propylenediamine, and 1,3-pnd is 1,3-pentanediamine). Interactions and binding ability of C1-C4 complexes with calf thymus DNA (CT-DNA) has been monitored by viscosity measurements, UV-Vis, fluorescence emission spectroscopy and molecular docking. Binding affinities of C1-C4 complexes to the bovine serum albumin (BSA) has been monitored by fluorescence emission spectroscopy. The tested complexes exhibit variable cytotoxicity toward different mouse and human tumor cell lines. C2 shows the most potent cytotoxicity, especially against mouse (4T1) and human (MDA-MD468) breast cancer cells in the dose- and time-dependent manner. C2 induces 4T1 and MDA-MD468 cells apoptosis, further documented by the accumulation of cells at sub-G1 phase of cell cycle and increase of executive caspase 3 and caspase 9 levels in 4T1 cells. C2 exhibits anti-proliferative effect through the reduction of cyclin D3 and cyclin E expression and elevation of inhibitor p27 level. Also, C2 downregulates c-Myc and phosphorylated AKT, oncogenes involved in the control of tumor cell proliferation and death. In order to measure the amount of platinum(II) complexes taken up by the cells, the cellular platinum content were quantified. However, C2 failed to inhibit mouse breast cancer growth in vivo. Chemical modifications of tested platinum(II) complexes might be a valuable approach for the improvement of their anti-tumor activity, especially effects in vivo.

Docking Studies, Cytotoxicity Evaluation and Interactions of Binuclear Copper(II) Complexes with S-Isoalkyl Derivatives of Thiosalicylic Acid with Some Relevant Biomolecules.

The numerous side effects of platinum based chemotherapy has led to the design of new therapeutics with platinum replaced by another transition metal. Here, we investigated the interactions of previously reported copper(II) complexes containing S-isoalkyl derivatives, the salicylic acid with guanosine-5'-monophosphate and calf thymus DNA (CT-DNA) and their antitumor effects, in a colon carcinoma model. All three copper(II) complexes exhibited an affinity for binding to CT-DNA, but there was no indication of intercalation or the displacement of ethidium bromide. Molecular docking studies revealed a significant affinity of the complexes for binding to the minor groove of B-form DNA, which coincided with DNA elongation, and a higher affinity for binding to Z-form DNA, supporting the hypothesis that the complex binding to CT-DNA induces a local transition from B-form to Z-form DNA. These complexes show a moderate, but selective cytotoxic effect toward colon cancer cells in vitro. Binuclear complex of copper(II) with S-isoamyl derivative of thiosalicylic acid showed the highest cytotoxic effect, arrested tumor cells in the G2/M phase of the cell cycle, and significantly reduced the expression of inflammatory molecules pro-IL-1ß, TNF-α, ICAM-1, and VCAM-1 in the tissue of primary heterotopic murine colon cancer, which was accompanied by a significantly reduced tumor growth and metastases in the lung and liver.

Dinuclear platinum(II) complexes as the pattern for phosphate backbone binding: a new perspective for recognition of binding modes to DNA.

The mechanism of action of most approved drugs in use today is based on their binding to specific proteins or DNA. One of the achievements of this research is a new perspective for recognition of binding modes to DNA by monitoring of changes in measured and stoichiometric values of absorbance at 260 nm. UV-Vis and IR spectroscopy, gel electrophoresis and docking study were used for investigation of binding properties of three dinuclear platinum(II) complexes containing different pyridine-based bridging ligands, [{Pt(en)Cl}2(µ-4,4'-bipy)]Cl2·2H2O (Pt1), [{Pt(en)Cl}2(µ-bpa)]Cl2·4H2O (Pt2) and [{Pt(en)Cl}2(µ-bpe)]Cl2·4H2O (Pt3) to DNA (4,4'-bipy, bpa and bpe are 4,4'-bipyridine, 1,2-bis(4-pyridyl)ethane and 1,2-bis(4-pyridyl)ethene, respectively). In contrast to the system with well-known intercalated ligand (EtBr), covalently bound ligand (cis-Pt) and with minor groove binder (Hoechst 33258), which do not have significant differences in measured and stoichiometric values, the most pronounced deviations are recorded for two dinuclear platinum(II) complexes (Pt1 and Pt2), as a consequence of complex binding to the phosphate backbone and bending of DNA helix. The hydrolysis of complexes and changes in DNA conformation were also analysed as phenomena that may have an impact on the changes in absorbance.

New minor groove covering DNA binding mode of dinuclear Pt(II) complexes with various pyridine-linked bridging ligands and dual anticancer-antiangiogenic activities.

New anticancer platinum(II) compounds simultaneously targeting tumor cells and tumor-derived neoangiogenesis, with new DNA interacting mode and large therapeutic window are appealing alternative to improve efficacy of clinical platinum chemotherapeutics. Herein, we describe three novel dinuclear [{Pt(en)Cl}2(µ-L)]2+ complexes with different pyridine-like bridging ligands (L), 4,4'-bipyridine (Pt1), 1,2-bis(4-pyridyl)ethane (Pt2) and 1,2-bis(4-pyridyl)ethene (Pt3), which highly, positively charged aqua derivatives, [{Pt(en)(H2O)}2(µ-L)]4+, interact with the phosphate backbone forming DNA-Pt adducts with an unique and previously undescribed binding mode, called a minor groove covering. The results of this study suggested that the new binding mode of the aqua-Pt(II) complexes with DNA could be attributed to the higher anticancer activities of their chloride analogues. All three compounds, particularly complex [{Pt(en)Cl}2(µ-4,4'-bipy)]Cl2·2H2O (4,4'-bipy is 4,4'-bipyridine) (Pt1), overcame cisplatin resistance in vivo in the zebrafish-mouse melanoma xenograft model, showed much higher therapeutic potential than antiangiogenic drug sunitinib malate, while effectively blocking tumor neovascularization and melanoma cell metastasis. Overall therapeutic profile showed new dinuclear Pt(II) complexes could be novel, effective and safe anticancer agents. Finally, the correlation with the structural characteristics of these complexes can serve as a useful tool for developing new and more effective anticancer drugs.

The influence of oxo-bridged binuclear gold(III) complexes on Na/K-ATPase activity: a joint experimental and theoretical approach.

The in vitro effects of oxo-bridged binuclear gold(III) complexes, i.e., [(bipy2Me)2Au2(µ-O)2][PF6]2 (Auoxo6), Au2[(bipydmb-H)2(µ-O)][PF6] (Au2bipyC) and [Au2(phen2Me)2(µ-O)2](PF6)2 (Au2phen) on Na/K-ATPase, purified from the porcine cerebral cortex, were investigated. All three studied gold complexes inhibited the enzyme activity in a concentration-dependent manner achieving IC50 values in the low micromolar range. Kinetic analysis suggested an uncompetitive mode of inhibition for Auoxo6 and Au2bipyC, and a mixed type one for Au2phen. Docking studies indicated that the inhibitory actions of all tested complexes are related to E2-P enzyme conformation binding to ion channel and intracellular part between N and P sub-domain. In addition, Au2phen was able to inhibit the enzyme by interacting with its extracellular part as well. Toxic effects of the gold(III) complexes were evaluated in vitro by following lactate dehydrogenase activity in rat brain synaptosomes and incidence of micronuclei and cytokinesis-block proliferation index in cultivated human lymphocytes. All investigated complexes turned out to induce cytogenetic damage consisting of a significant decrease in cell proliferation and an increase in micronuclei in a dose-dependent manner. On the other hand, lactate dehydrogenase activity, an indicator of membrane integrity/viability, was not affected by Auoxo6 and Au2bipyC, while Au2phen slightly modified its activity.

Nature of the water/aromatic parallel alignment interactions.

The water/aromatic parallel alignment interactions are interactions where the water molecule or one of its O-H bonds is parallel to the aromatic ring plane. The calculated energies of the interactions are significant, up to ΔE(CCSD)(T)(limit) = -2.45 kcal mol(-1) at large horizontal displacement, out of benzene ring and CH bond region. These interactions are stronger than CH···O water/benzene interactions, but weaker than OH···π interactions. To investigate the nature of water/aromatic parallel alignment interactions, energy decomposition methods, symmetry-adapted perturbation theory, and extended transition state-natural orbitals for chemical valence (NOCV), were used. The calculations have shown that, for the complexes at large horizontal displacements, major contribution to interaction energy comes from electrostatic interactions between monomers, and for the complexes at small horizontal displacements, dispersion interactions are dominant binding force. The NOCV-based analysis has shown that in structures with strong interaction energies charge transfer of the type π → σ*(O-H) between the monomers also exists.

Parallel water/aromatic interactions of non-coordinated and coordinated water.

The parallel interactions of non-coordinated and coordinated water molecules with an aromatic ring were studied by analyzing data in the Cambridge structural database (CSD) and by using quantum chemical calculations. The CSD data show that water/aromatic contacts prefer parallel to OH/π interactions, which indicates the importance of parallel interactions. The results reveal the influence of water coordination to a metal ion; the interactions of aqua complexes are stronger. Coordinated water molecules prefer a parallel-down orientation in which one OH bond is parallel to the aromatic ring, whereas the other OH bond points to the plane of the ring. The interactions of aqua complexes with parallel-down water/benzene orientation are as strong as the much better known OH/π orientations. The strongest calculated interaction energy is -14.89 kcal mol(-1) . The large number of parallel contacts in crystal structures and the quite strong interactions indicate the importance of parallel orientation in water/benzene interactions.

What are preferred water-aromatic interactions in proteins and crystal structures of small molecules?

The distribution of water molecules around aromatic rings in the protein structures and crystal structures of small molecules shows quite a small number of the strongest OH-π interactions, a larger number of parallel interactions, and the largest number of the weakest CH-O interactions.

Stacking interactions of Ni(acac) chelates with benzene: calculated interaction energies.

Piling 'em up: The stacking energy of the [Ni(acac)2]/benzene system is calculated at local CCSD(T) level and is in good agreement with the values obtained with the SCS-MP2 method. Energies calculated with several DFT-D methods are somewhat overestimated. The calculated stacking energy of the [Ni(acac)2]/benzene system is significantly stronger than that of the benzene dimer.

Degradation of tartrazine by Oxone® in the presence of cobalt based catalyst supported on pillared montmorillonite - Efficient technology even in extreme conditions.

The catalytic degradation of hazardous organic contaminants in industrial wastewater is a promising technology. Reactions of tartrazine, the synthetic yellow azo dye, with Oxone® in the presence of catalyst in strong acidic condition (pH 2), were detected by using UV-Vis spectroscopy. In order to extend the applicability profile of Co-supported Al-pillared montmorillonite catalyst an investigation of Oxone® induced reactions were performed in extreme acidic environment. The products of the reactions were identified by liquid chromatography-mass spectrometry (LC-MS). Along with the catalytic decomposition of tartrazine induced by radical attack (confirmed as unique reaction path under neutral and alkaline conditions), the formation of tartrazine derivatives by reaction of nucleophilic addition was also detected. The presence of derivatives under acidic conditions slowed down the hydrolysis of tartrazine diazo bond in comparison to the reactions in neutral environment. Nevertheless, the reaction in acidic conditions (pH 2) is faster than the one conducted in alkaline conditions (pH 11). Theoretical calculations were used to complete and clarify the mechanisms of tartrazine derivatization and degradation, as well as to predict the UV-Vis spectra of compounds which could serve as predictors of certain reaction phases. ECOSAR program, used to estimate toxicological profile of compounds to aquatic animals, indicated an increase in the harmfulness of the compounds identified by LC-MS as degradation products from the reaction conducted for 240min. It could be concluded that an intensification of the process parameters (higher concentration of Oxone®, higher catalyst loading, increased reaction time, etc.) is needed in order to obtain only biodegradable products.

The influence of water molecule coordination to a metal ion on water hydrogen bonds.

The geometry of hydrogen bonds in the crystal structures from the Cambridge Structural Database and calculated data show that water coordination to a metal ion has a remarkable influence on hydrogen bonds. The calculated energies of hydrogen bonds of coordinated water are much stronger, even if the aqua complex is neutral.

Cytotoxic activity and influence on acetylcholinesterase of series dinuclear platinum(II) complexes with aromatic nitrogen-containing heterocyclic bridging ligands: Insights in the mechanisms of action.

Herein, the stability, lipophilicity, in vitro cytotoxicity, and influence on acetylcholinesterase of five dinuclear platinum(II) complexes with the general formula [{Pt(en)Cl}2(µ-L)]2+ (L is a different aromatic nitrogen-containing heterocyclic bridging ligands pyrazine (pz, Pt1), pyridazine (pydz, Pt2), quinoxaline (qx, Pt3), phthalazine (phtz, Pt4) and quinazoline (qz, Pt5), while en is bidentate coordinated ethylenediamine) were evaluated. The most active analyzed platinum complexes induced time-dependent growth inhibition of A375, HeLa, PANC-1, and MRC-5 cells. The best efficiency was achieved on HeLa and PANC-1 cells for Pt1, Pt2, and Pt3 at the highest concentration, while Pt1 was significantly more potent than cisplatin at a lower concentration. Additionally, a lower effect on normal cells was observed compared to cisplatin, which may indicate potentially fewer side effects of these complexes. Selected complexes induce reactive oxygen species and apoptosis on tumor cell lines. The most potent reversible acetylcholinesterase (AChE) inhibitors were Pt2, Pt4, and Pt5. Pt1 showed similar inhibitory potential toward AChE as cisplatin, but a different type of inhibition, which could contribute to lower neurotoxicity. Docking studies revealed that Pt2 and Pt4 were bound to the active gorge above the catalytic triad. In contrast, the other complexes were bound to the edge of the active gorge without impeding the approach to the catalytic triad. According to this, Pt1 represents a promising compound with potent anticancer properties, high selectivity, and low neurotoxicity.

Na, K-ATPase as a Biological Target for Gold(III) Complexes: A Theoretical and Experimental Approach.

BACKGROUND: Gold-based complexes represent a new class of potential metallodrugs. Although their action mechanism is not entirely understood, it was shown that gold complexes inhibit some enzymes' activities. Among them, Na,K-ATPase is emerging as an essential target for various anticancer drugs. The functionalization of nanoparticles by gold(III) complexes could facilitate their delivery into the cells and enable the following of their distribution in the target tissues. OBJECTIVE: The paper presents an overview of Na,K-ATPase interaction with representative and structurally related cytotoxic gold(III) complexes. The results obtained by the employment of theoretical methods (DFT and docking studies) combined with the experimental approach involving a variety of nanotechnology-base techniques (UV/Vis, Raman and fluorescence spectroscopy, CD, AFM, DLS) are discussed. Detailed information was obtained on the enzyme's conformational and structural changes upon binding the gold(III) complexes. The experimentally determined reaction parameters (constants of dissociation and the reaction stoichiometry) were predicted theoretically. CONCLUSION: The presented results offer further support to the view that Na,K-ATPase may be a relevant biomolecular target for cytotoxic gold(III) compounds of medicinal interest.

A novel approach in revealing mechanisms and particular step predictors of pH dependent tartrazine catalytic degradation in presence of Oxone®.

The degradation of tartrazine in the presence of cobalt activated Oxone® (potassium peroxymonosulfate) was investigated at different initial pH values. Aluminum pillared clay had the role of a support for catalytically active cobalt oxide species. The degradation of tartrazine and the formation of a mixture of degradation products were monitored using the Ultraviolet-Visible (UV-Vis) spectroscopy and gas chromatography-mass spectrometry (GC-MS). The exact qualitative composition of this mixture and the determination of the most probable mechanism of degradation (the primary goal) were obtained using GC-MS. Besides, the main reaction pathway (reaction with SO4˙- radical anion) and secondary pathways were proposed depending on the pH value. At pH = 6 the reaction with HO˙ radical was proposed. At pH = 11 decarboxilation was suggested as the first step of the secondary proposed reaction pathway. The combination of results acquired from the deconvolution of UV-Vis spectra and the theoretical UV-Vis spectra of degradation products, whose occurrence was predicted by quantum-chemical calculations, was proven to be beneficial for the identification of tartrazine degradation products and for defining UV-Vis predictors of particular degradation steps. An additional contribution of this paper, from the reactivity aspect, was the establishment of the critical structural demand for the radical degradation of any diazo compound. The existence of a hydrogen atom bound to a diazo group was found to be the essential prerequisite for the radical cleavage of diazo compounds.

Supramolecular insight into the substitution of sulfur by selenium, based on crystal structures, quantum-chemical calculations and biosystem recognition.

Statistical analysis of data from crystal structures extracted from the Cambridge Structural Database (CSD) has shown that S and Se atoms display a similar tendency towards specific types of interaction if they are part of a fragment that corresponds to the side chains of cysteine (Cys), methionine (Met) selenocysteine (Sec) and selenomethionine (Mse). The most numerous are structures with C-H...Se and C-H...S interactions (∼80%), notably less numerous are structures with Se...Se and S...S interactions (∼5%), and Se...π and S...π interactions are the least numerous. The results of quantum-chemical calculations have indicated that C-H...Se (∼-0.8 kcal mol-1) and C-H...S interactions are weaker than the most stable parallel interaction (∼-3.3 kcal mol-1) and electrostatic interactions of σ/π type (∼-2.6 kcal mol-1). Their significant presence can be explained by the abundance of CH groups compared with the numbers of Se and S atoms in the crystal structures, and also by the influence of substituents bonded to the Se or S atom that further reduce their possibilities for interacting with species from the environment. This can also offer an explanation as to why O-H...Se (∼-4.4 kcal mol-1) and N-H...Se interactions (∼-2.2 kcal mol-1) are less numerous. Docking studies revealed that S and Se rarely participate in interactions with the amino acid residues of target enzymes, mostly because those residues preferentially interact with the substituents bonded to Se and S. The differences between Se and S ligands in the number and positions of their binding sites are more pronounced if the substituents are polar and if there are more Se/S atoms in the ligand.

Self-Assembly and Biorecognition of a Spirohydantoin Derived from α-Tetralone: Interplay between Chirality and Intermolecular Interactions.

A racemic spirohydantoin derivative with two aromatic substituents, a tetralin and a 4-methoxybenzyl unit, was synthesized and its crystal structure was determined. To define the relationship between molecular stereochemistry and spatial association modes, development of the crystal packing was analyzed through cooperativity of intermolecular interactions. Homo and heterochiral dimeric motifs were stabilized by intermolecular N-H⋅⋅⋅O, C-H⋅⋅⋅O, C-H⋅⋅⋅π interactions and parallel interactions at large offsets (PILO), thus forming alternating double layers. The greatest contribution to the total stabilization came from a motif of opposite enantiomers linked by N-H⋅⋅⋅O bonds (interaction energy=-13.72 kcal/mol), followed by a homochiral motif where the 4-methoxybenzyl units allowed C-H⋅⋅⋅π, C-H⋅⋅⋅O interactions and PILO (interaction energy=-11.56 kcal/mol). The number of the contact fragments in the environment of the tetralin unit was larger, but the 4-methoxybenzyl unit had greater contribution to the total stabilization. The statistical analysis of the data from the Cambridge Structural Database (CSD) showed that this is a general trend. The compound is a potential inhibitor of kinase enzymes and antigen protein-coupled receptors. A correlation between the docking study and the results of the CSD analysis can be drawn. Due to a greater flexibility, the 4-methoxybenzyl unit is more adaptable for interactions with the biological targets than the tetralin unit.

A new acetylcholinesterase allosteric site responsible for binding voluminous negatively charged molecules - the role in the mechanism of AChE inhibition.

Acetylcholinesterase (AChE) inhibitors are important in the treatment of neurodegenerative diseases. Two inhibitors, 12-tungstosilicic acid (WSiA) and 12-tungstophosphoric acid (WPA), which have polyoxometalate (POM) type structure, have been shown to inhibit AChE activity in nM concentration. Circular dichroism and tryptophan fluorescence spectroscopy demonstrated that the AChE inhibition was not accompanied by significant changes in the secondary structure of the enzyme. The molecular docking approach has revealed a new allosteric binding site, termed ß-allosteric site (ß-AS), which is considered responsible for the inhibition of AChE by POMs. To the best of our knowledge, this is the first study reporting a new allosteric site that is considered responsible for AChE inhibition by voluminous and negatively charged molecules such as POMs. The selected POMs were further subjected to genotoxicity testing using human peripheral blood cells as a model system. It was shown that WSiA and WPA induced a mild cytostatic but not genotoxic effects in human lymphocytes, which indicates their potential to be used as medicinal drugs. The identification of non-toxic compounds capable of binding to an allosteric site that so far has not been considered responsible for enzyme inhibition could be fundamental for the development of new drug design strategies and the discovery of more efficient AChE modulators.

Theoretical modeling of sorption of metal ions on amino-functionalized macroporous copolymer in aqueous solution.

With regard to the harmful effects of heavy metals on human health and the environment, the demand for synthesis and investigation of macromolecules with large capacity of harmful substances sorption is ever greater. Quantum-chemical methods may be applied in structural modeling, prediction, and characterization of such molecules and reactions. Sorption of metal ions (Cu2+, Cd2+, Co2+, and Ni2+) to triethylenetetramine-functionalized copolymer poly(GMA-co-EGDMA)-teta was successfully modeled by quantum chemical calculations, at the B3LYP//6-311++G**/lanl2dz level. Optimized structures of metal complexes were used for calculation of real binding energy of metal ion within the complex (ΔEr). Solvent and hydrolyzation effects were essential for obtaining the objective values. Solvent effect was included in ΔEr by using the total solvation energy for reaction of formation of tetaOH complex (ΔEs1, the first approach) or by using dehydration energy of free metal ion (ΔEs2, the second approach). Experimental results were confirmed in our theoretical analyses (using the second approach). Graphical abstract Theoretical modeling of divalent metal ions sorption on triethylenetetramine-functionalized copolymer poly(GMA-co-EGDMA)-teta.

Parallel alignment of water and aryl rings-crystallographic and theoretical evidence for the interaction.

Analysis of crystal structures from the Cambridge Structural Database (CSD) that involve close contact between water and aryl rings revealed the existance of conformations where the water molecule or one of its O-H bonds is parallel to the aromatic ring plane at distances typical for stacking interactions; attractive interaction energies obtained from ab initio calculations performed on model systems are significant (e.g.DeltaE(CCSD(T)) = -1.60 kcal mol(-1)) and consistent with the observed structures.

Influence of hydrogen bonds on edge-to-face interactions between pyridine molecules.

Edge-to-face interactions between two pyridine molecules and the influence of simultaneous hydrogen bonding of one or both of the pyridines to water on those interactions were studied by analyzing data from ab initio calculations. The results show that the edge-to-face interactions of pyridine dimers that are hydrogen bonded to water are generally stronger than those of non-H-bonded pyridine dimers, especially when the donor pyridine forms a hydrogen bond. The binding energy of the most stable edge-to-face interacting H-bonded pyridine dimer is -5.05 kcal/mol, while that for the most stable edge-to-face interacting non-H-bonded pyridine dimer is -3.64 kcal/mol. The interaction energy data obtained in this study cannot be explained solely by the differences in electrostatic potential between pyridine and the pyridine-water dimer. However, the calculated cooperative effect can be predicted using electrostatic potential maps.