Remarkable photocytotoxicity in hypoxic HeLa cells by a dipyridophenazine copper(II) Schiff base thiolate

Binding mechanism, photo-induced cleavage and computational studies of interaction cefepime drug with Human serum albumin

The binding interaction of cefepime to human serum albumin (HSA) in aqueous solution was investigated by molecular spectroscopy (UV spectra, fluorescence spectra and CD spectra), photo-cleavage and modeling studies under simulative physiological conditions. Spectrophotometric results are rationalized in terms of a static quenching process and binding constant (Kb) and the number of binding sites (n ≈ 1) were calculated using fluorescence quenching approaches at three temperature settings. Thermodynamic data of ΔG, ΔH and ΔS at different temperatures were evaluated. The results showed that the electrostatic and hydrogen bonding interactions play a major role in the binding of cefepime to HSA. The value of 3.4 nm for the distance r between the donor (HSA) and acceptor (cefepime) was derived from the fluorescence resonance energy transfer (FRET). FTIR and CD measurements has been reaffirmed HSA-cefepime association and demonstrated reduction in α-helical content of HSA. Furthermore, the study of molecular modeling also indicated that cefepime could strongly bind to the site I (subdomain IIA) of HSA. Additionally, cefepime shows efficient photo- cleavage of HSA cleavage. Our results may provide valuable information to understand the pharmacological profile of cefepime drug delivery in blood stream.Communicated by Ramaswamy H. Sarma.

Oxoperoxovanadium Complexes of Hetero Ligands: X-Ray Crystal Structure, Density Functional Theory, and Investigations on DNA/BSA Interactions, Cytotoxic, and Molecular Docking Studies

Oxoperoxovanadium (V) complexes [VO (O)2 (nf) (bp)] (1) and [VO (O)2 (ox) (bp)] (2) based on 5-nitro-2-furoic acid (nf), oxine (ox) and 2, 2' bipyridine (bp) bidentate ligands have been synthesized and characterized by FT-IR, UV-visible, mass, and NMR spectroscopic techniques. The structure of complex 2 shows distorted pentagonal-bipyramidal geometry, as confirmed by a single-crystal XRD diffraction study. The interactions of complexes with bovine serum albumin (BSA) and calf thymus DNA (CT-DNA) are investigated using UV-visible and fluorescence spectroscopic techniques. It has been observed that CT-DNA interacts with complexes through groove binding mode and the binding constants for complexes 1 and 2 are 8.7 × 103 M-1 and 8.6 × 103 M-1, respectively, and BSA quenching constants for complexes 1 and 2 are 0.0628 × 106 M-1 and 0.0163 × 106 M-1, respectively. The ability of complexes to cleave DNA is investigated using the gel electrophoresis method with pBR322 plasmid DNA. Furthermore, the cytotoxic effect of the complexes is evaluated against the HeLa cell line using an MTT assay. The complexes are subjected to density functional theory calculations to gain insight into their molecular geometries and are in accordance with the results of docking studies. Furthermore, based on molecular docking studies, the intermolecular interactions responsible for the stronger binding affinities between metal complexes and DNA are discussed.

Synthesis, Characterization, Crystal Structure, DNA and HSA Interactions, and Anticancer Activity of a Mononuclear Cu(II) Complex with a Schiff Base Ligand Containing a Thiadiazoline Moiety

A mononuclear Cu(II) complex [Cu(HL)(o-phen)]·H₂O (1) [H₃L =, o-phen = 1,10-phenanthroline] was isolated from methanol, and its X-ray single-crystal structure was determined. Frozen glass X-band EPR of 1 in dimethylformamide (DMF) at LNT showed a spectrum that is characteristic of a monomeric tetragonal character with g _∥ = 2.164, g _⊥ = 2.087, A _∥ = 19.08 mT, and A _⊥ ≤ 4 mT. Electronic spectroscopic studies using calf thymus DNA (CT-DNA) showed strong binding affinity of 1 as reflected from its intrinsic binding constant (K _b) value of 2.85 × 10⁵ M^-1. Competitive behavior of 1 with ethidium bromide (EB) displayed intercalative binding of DNA (K _app = 1.3 × 10⁶ M^-1). The compound displayed significant oxidative cleavage of pUC19 DNA. The interaction between HSA and complex 1 was examined by employing fluorescence and electronic absorption spectroscopic experiments. The secondary and tertiary structures of HSA were found to be altered as suggested by three-dimensional (3D) fluorescence experiments. The affinity of 1 to bind to HSA was found to be strong as indicated from its value of the binding constant (K _a = 2.89 × 10⁵ M^-1). Intrinsic fluorescence of the protein was found to be reduced through a mechanism of static quenching as suggested from the k _q (2.01 × 10¹³ M^-1 s^-1) value, the bimolecular quenching constant. The Förster resonance energy transfer (FRET) process may also be accounted for such a high k _q value. The r value (2.85 nm) calculated from FRET theory suggested that the distance between complex 1 (acceptor) and HSA (donor) is quite close. Complex 1 primarily bound to HSA in subdomain IIA as suggested by molecular docking studies. IC₅₀ values (0.80 and 0.43 μM, respectively) obtained from the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay with HeLa and MCF7 cells suggested remarkable in vitro anticancer activity of 1. Nuclear dual staining assays revealed that cell death occurred via apoptosis in HeLa cells and reactive oxygen species (ROS) accumulation caused apoptosis induction. On treatment with a 5 μM dose of 1 in HeLa cells, the cell population significantly increased in the G2/M phase, while it was decreased in G0/G1 and S phases as compared to the control, clearly indicating G2/M phase arrest.

Targeting an Artificial Metal Nuclease to DNA by a Simple Chemical Modification and Its Drastic Effect on Catalysis

A novel metal complex was synthesized containing a purine derived ligand in order to increase its binding to DNA. We observed a huge increase in nuclease activity and, quite interestingly, an improvement on DNA sequence selectivity. A potential site of specific cleavage in the presence of a reductant in the reaction medium is suggested. We were able to synthesize a novel metal nuclease with improved activity on DNA, and with sequence specificity when exposed to a coreactant, this opens up new possibilities to create site specific and redox status modulated artificial nucleases.

Theoretical study on the DNA interaction properties of copper(II) complexes

Theoretical studies on DNA-cleavage and DNA-binding properties of a series of Cu(II) complexes [Cu(bimda)(diimine)] 1-5 have been carried out by density functional theory (DFT). The optimized structures of Cu(II) complexes were docked into parallel, antiparallel and mixed G-quadruplexes, with which the binding energies of complexes 1-5 were obtained. The cytotoxicities of these complexes can be predicted preliminarily by the binding energies. To explore the energy changes of Cu(II) complexes in duplex DNA, the optimized structures of these complexes were docked into the duplex DNA, and the obtained docking models were further optimized using QM/MM method. The DNA-cleavage abilities of complexes 1-5 can be predicted accurately and explained reasonably by the computed intra-molecular reorganization energies of these complexes. This work reported here has implications for the understanding of the interaction Cu(II) complexes with the DNA, which might be helpful for the future directing the design of novel anticancer Cu(II) complexes.

Biomolecular Interaction, Anti-Cancer and Anti-Angiogenic Properties of Cobalt(III) Schiff Base Complexes

Two cobalt(III) Schiff base complexes, trans-[Co(salen)(DA)₂](ClO₄) (1) and trans-[Co(salophen)(DA)₂](ClO₄) (2) (where salen: N,N'-bis(salicylidene)ethylenediamine, salopen: N,N'-bis(salicylidene)-1,2-phenylenediamine, DA: dodecylamine) were synthesised and characterised using various spectroscopic and analytical techniques. The binding affinity of both the complexes with CT-DNA was explored adopting UV-visible, fluorescence, circular dichroism spectroscopy and cyclic voltammetry techniques. The results revealed that both the complexes interacted with DNA via intercalation as well as notable groove binding. Protein (BSA) binding ability of these complexes was investigated by absorption and emission spectroscopy which indicate that these complexes engage in strong hydrophobic interaction with BSA. The mode of interaction between these complexes and CT-DNA/BSA was studied by molecular docking analysis. The in vitro cytotoxic property of the complexes was evaluated in A549 (human small cell lung carcinoma) and VERO (African green monkey kidney cells). The results revealed that the complexes affect viability of the cells. AO and EB staining and cell cycle analysis revealed that the mode of cell death is apoptosis. Both the complexes showed profound inhibition of angiogenesis as revealed in in-vivo chicken chorioallantoic membrane (CAM) assay. Of the two complexes, the complex 2 proved to be much more efficient in affecting the viability of lung cancer cells than complex 1. These results indicate that the cobalt(III) Schiff base complexes in this study can be potentially used for cancer chemotherapy and as inhibitor of angiogenesis, in general, and lung cancer in particular, for which there is need for substantiation at the level of signalling mechanisms and gene expressions.

A long-lived cuprous bis-phenanthroline complex for the photodynamic therapy of cancer

An earth-abundant cuprous bis-phenanthroline photosensitizer showed potential use in the photodynamic therapy of cancer.

Mixed-ligand copper(ii) Schiff base complexes: the vital role of co-ligands in DNA/protein interactions and cytotoxicity

Four new mixed-ligand copper(ii) complexes display an antibacterial mechanism of cell death via cell-wall rupture and cytotoxicity via apoptotic cell death.

Mixed-ligand copper(ii)-phenolate complexes: structure and studies on DNA/protein binding profiles, DNA cleavage, molecular docking and cytotoxicity

Copper(ii) complexes with simple and mixed ligands, [Cu(L)(ClO₄)] and [Cu(L)(diimine)]ClO₄ were synthesized and characterized by elemental analysis, UV-vis, FT-IR, electrospray ionization-mass spectrometry (ESI-MS) and electrochemical studies.

Theoretical studies on binding modes of copper-based nucleases with DNA

In the present work, molecular simulations were performed for the purpose of predicting the binding modes of four types of copper nucleases (a total 33 compounds) with DNA. Our docking results accurately predicted the groove binding and electrostatic interaction for some copper nucleases with B-DNA. The intercalation modes were also reproduced by "gap DNA". The obtained results demonstrated that the ligand size, length, functional groups and chelate ring size bound to the copper center could influence the binding affinities of copper nucleases. The binding affinities obtained from the docking calculations herein also replicated results found using MM-PBSA approach. The predicted DNA binding modes of copper nucleases with DNA will ultimately help us to better understand the interaction of copper compounds with DNA.

DNA binding, photoactivated DNA cleavage and cytotoxic activity of Cu(II) and Co(II) based Schiff-base azo photosensitizers

A new class of Cu(II) and Co(II) complexes of azo-containing Schiff base of the type [Cu(L1)2] and [Co(L1)2], where L1=4-[(E)-{2-hydroxy-3-[(E)-(4-bromophenyl)diazenyl]benzylidene}amino]benzoic acid have been synthesized and characterized. Extension of conjugation and the presence of free carboxylic acid group of the ligand L1 increased the wavelength of the complexes from visible region to the near IR region (620-850 nm). The Cu(II) and Co(II) complexes interacted with CT-DNA via intercalative mode with the respective Kb value of 3.2×10(4) M(-1) and 2.9×10(4) M(-1) and acted as proficient photocleavers of SC pUC19 DNA in UV-A light, forming (1)O2 as the reactive oxygen species with the quantum yield of 0.38 and 0.36, respectively. Furthermore, the Cu(II) and Co(II) complexes showed photocytotoxicity toward two selected tumor cell lines MCF-7 and A549 by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) method, and the Cu(II) complex exhibits higher photocytotoxicity than Co(II) complex against each of the selected cell lines, this result is identical with their DNA binding ability order.