A novel benzothiazole-based mononuclear platinum(II) complex displaying potent antiproliferative activity in HepG-2 cells via mitochondrial-mediated apoptosis

A novel mononuclear platinum(II) complex, [Pt(L-H)Cl] (1, where L= N-(4-(benzo[d]thiazol-2-yl)phenyl)-2-((2-pyridylmethyl)(2-hydroxyethyl)-amino)acetamide), was obtained by covalently tethering a benzothiazole derivative 2-(4-aminophenyl)benzothiazole to the 2-pyridylmethyl-2-hydroxyethylamine chelating PtII center. In vitro tests indicated that complex 1 displayed excellent antiproliferative activity against the tested cancer cell lines, especially liver cancer HepG-2 and SMMC-7221 cells. Importantly, the complex possessed 4.33-fold higher antiproliferative activity as compared with cisplatin against HepG-2 cells, but was less toxic to the normal cell line L02 with the selectivity index (SI = IC50(L02)/IC50(HepG-2)) value of 8.36 compared to cisplatin (SI, 1.40). The results suggested that 1 might have the potential to act as a candidate for the treatment of hepatocellular carcinoma (HCC). Cellular uptake and distribution studies showed that 1 could effectively pass through the membrane of cells, enter the nuclei and mitochondria, induce the platination of cellular DNA. The interaction of 1 with CT-DNA demonstrated that 1 could effectively bind to DNA in a dual binding mode, i.e., the intercalation of the 2-(4-aminophenyl)benzothiazole unit plus monofunctional platination of the platinum(II) moiety. In addition, Hoechst 33342 staining and flow cytometry analysis illustrated that 1 arrested the cell cycle in HepG-2 cancer cells at G2/M phases, induced mitochondrial membrane depolarization, increased ROS generation, and caused obvious cell apoptosis. Further cellular mechanism studies elucidated that 1 triggered HepG-2 cell apoptosis via the mitochondrial-mediated pathway by upregulating the gene and protein expression levels of Bax, downregulating the gene and protein expression levels of Bcl-2, and activating the caspase cascade.

Transition metal complexes as self-activating chemical nucleases: proficient DNA cleavage without any exogenous redox agents

Chemical nucleases have found potential applications in the research fields of chemistry, biotechnology and medicine. A variety of metal complexes have been explored as good to outstanding therapeutic agents for DNA cleavage activity most likely via hydrolytic, oxidative or photoinduced cleavage pathways. However, most of these DNA cleaving agents lack their utility in in vivo applications due to their dependence on exogenous oxidants or reductants to achieve successful DNA damage. In view of addressing these issues, the development of metal complexes/organic molecules serving as self-activating chemical nucleases has received growing attention from researchers. In only the last decade, this field has dramatically expanded for the usage of chemical nucleases as therapeutic agents for DNA damage. The present study provides an overview of the opportunities and challenges in the design and development of self-activating chemical nucleases as improved DNA therapeutic candidates in the absence of an external redox agent. The reports on DNA nuclease activity via self-activation, especially with copper, zinc and iron complexes, and their mechanistic investigation have been discussed in this review article.

Syntheses, Structural Characterization, and Cytotoxicity Assessment of Novel Mn(II) and Zn(II) Complexes of Aroyl-Hydrazone Schiff Base Ligand

This work describes the syntheses, structural characterization, and biological profile of Mn(II)- and Zn(II)-based complexes 1 and 2 derived from the aroyl-hydrazone Schiff base ligand (L1). The synthesized compounds were thoroughly characterized by elemental analysis, Fourier transform infrared spectroscopy (FTIR), UV-vis, electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), and single-crystal X-ray diffraction (s-XRD). Density functional theory (DFT) studies of complexes 1 and 2 were performed to ascertain the structural and electronic properties. Hirshfeld surface analysis was used to investigate different intermolecular interactions that define the stability of crystal lattice structures. To ascertain the therapeutic potential of complexes 1 and 2, in vitro interaction studies were carried out with ct-DNA and bovine serum albumin (BSA) using analytical and multispectroscopic techniques, and the results showed more avid binding of complex 2 than complex 1 and L1. The antioxidant potential of complexes 1 and 2 was examined against the 2,2-diphenyl picrylhydrazyl (DPPH) free radical, which revealed better antioxidant ability of the Mn(II) complex. Moreover, the antibacterial activity of synthesized complexes 1 and 2 was tested against Gram-positive and Gram-negative bacteria in which complex 2 demonstrated more effective bactericidal activity than L1 and complex 1 toward Gram-positive bacteria. Furthermore, the in vitro cytotoxicity assessment of L1 and complexes 1 and 2 was carried out against MDA-MB-231 (triple negative breast cancer) and A549 (lung) cancer cell lines. The cytotoxic results revealed that the polymeric Zn(II) complex exhibited better and selective cytotoxicity against the A549 cancer cell line as was evidenced by its low IC₅₀ value.

Mixed Ni(II) and Co(II) complexes of nalidixic acid drug: Synthesis, characterization, DNA/BSA binding profile and in vitro cytotoxic evaluation against MDA-MB-231 and HepG2 cancer cell lines

In this work, herein we report the synthesis, structural characterization and in vitro cytotoxic evaluation of two mixed Co(II)/Ni(II)-nalidixic acid-bipyridyl complexes (1 and 2). The structural analysis of metal complexes 1 and 2 was carried out by analytical and multispectroscopic techniques (FT-IR, UV-vis, EPR, sXRD). The crystallographic details of complexes 1 and 2 revealed a monoclinic crystal system with P21/c space group. DFT studies of complexes were performed to get electronic structure and localization of HOMO and LUMO electron densities. Hirshfeld surface analysis of metal complexes 1 and 2 was employed to understand the various intermolecular interactions (C-H···O, N-H···H and O-H···O) that define the stability of crystal lattice structures. The comparative interaction studies of complex 1 and complex 2 with DNA/BSA were performed by diverse multispectroscopic and analytical techniques to evaluate their chemotherapeutic potential. The magnitude of the DNA binding propensity and binding mode was verified by calculating K_b, K and K_sv values. Higher binding affinity was observed in case of complex 2via intercalative mode. Furthermore, the cytotoxic assessment of complexes 1 and 2 was examined against MDA-MB-231 (triple negative human breast cancer cell line) and HepG2 (liver carcinoma cell line) employing MTT assay which revealed remarkably effecient and specific cytotoxic activity of complex 2.

Structure elucidation, in vitro binding studies and ROS-dependent anti-cancer activity of Cu(II) and Zn(II) phthaloylglycinate(phen) complexes against MDA-MB-231 cells

New mononuclear Cu(II) and Zn(II)-based complexes 1 [Cu(L)2(diimine)HOCH3] and 2 [Zn(L)2(diimine)] have been synthesized as anti-cancer chemotherapeutics targeted to tRNA. The structure elucidation of complexes 1 and 2 was carried out by spectroscopic and single X-ray diffraction studies. In vitro interaction studies of complexes 1 and 2 with ct-DNA/tRNA were performed by employing various biophysical techniques to evaluate and predict their interaction behavior and preferential selectivity at biomolecular therapeutic targets. The corroborative results of the interaction studies demonstrated that complexes 1 and 2 exhibited avid binding propensity via intercalative mode of binding toward ct-DNA/tRNA. Electrophoretic assay revealed that the complexes 1 and 2 were able to promote single- and double-strand cleavage of the plasmid DNA at low micromolar concentrations under physiological conditions in the absence of an additional oxidizing or reducing agent. RNA hydrolysis studies revealed that the complexes 1 and 2 could promote tRNA cleavage in a concentration and time-dependent manner. The cytotoxic potential of complexes 1 and 2 was evaluated against the MDA-MB-231 cell line, which showed that the complexes were able to inhibit the cell growth in a dose-dependent manner. The intracellular ROS production and mitochondrial superoxide anion assay revealed that the complexes 1 and 2 induce a dose-dependent activity, suggesting the involvement of ROS-mediated mitochondrial apoptotic pathway leading to cell death.

Zinc(II) complexes of 3,5-dibromo-salicylaldehyde and α-diimines: Synthesis, characterization and in vitro and in silico biological profile

The synthesis of five neutral zinc(II) complexes of 3,5-dibromo-salicyladehyde (3,5-diBr-saloH) in the presence of nitrogen-donor co-ligands 2,2'-bipyridine (bipy), 1,10-phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (neoc), or 2,2'-bipyridylamine (bipyam) was undertaken and complexes [Zn(3,5-diBr-salo)₂(H₂O)₂] (1), [Zn(3,5-diBr-salo)₂(bipy)] (2), [Zn(3,5-diBr-salo)₂(phen)]^.3,5-diBr-saloΗ (3), [Zn(3,5-diBr-salo)₂(neoc)] (4) and [Zn(3,5-diBr-salo)₂(bipyam)] (5) were characterized by various techniques. The crystal structures of complexes 3 and 5 were determined by X-ray crystallography, revealing the co-existence of two different coordination modes of 3,5-diBr-salo^- ligands. The new complexes show selective in vitro antibacterial activity against two Gram-positive and two Gram-negative bacterial strains. The complexes may scavenge 1,1-diphenyl-picrylhydrazyl and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radicals and reduce H₂O₂. The complexes may intercalate in-between the calf-thymus DNA-bases and have exhibited low-to-moderate ability to cleave supercoiled circular pBR322 plasmid DNA. The complexes may bind tightly and reversibly to bovine and human serum albumins. In order to explain the in vitro activity of the compounds, molecular docking studies were adopted on the crystal structure of calf-thymus DNA, human and bovine serum albumin, Escherichia coli and Staphylococcus aureus DNA-gyrase, 5-lipoxygenase, and 5-lipoxygenase activating protein. The employed in silico studies aimed to explore the ability of the compounds to bind to these target biomacromolecules, establishing a possible mechanism of action and were in accordance with the in vitro studies.

Copper(ii) complexes of 2-methyl-8-hydroxyquinoline and tri/diimine co-ligand: DFT calculations, DNA and BSA binding, DNA cleavage, cytotoxicity and induction of apoptosis

Four-coordinate copper(ii) complex cleaves supercoiled ϕX174 RF DNA without reductant while five-coordinate complex cleaves with reductant. The cytotoxicity against cancer cells are higher than cisplatin, less-toxic to normal cells and induce apoptosis.

Antiproliferative Activities of Diimine-Based Mixed Ligand Copper(II) Complexes

A series of Cu(diimine)(X-sal)(NO₃) complexes, where the diimine is either 2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen) and X-sal is a monoanionic halogenated salicylaldehyde (X = Cl, Br, I, or H), have been synthesized and characterized by elemental analysis and X-ray crystallography. Penta-coordinate geometries copper(II) were observed for all cases. The influence of the diimine coligands and different halogen atoms on the antiproliferative activities toward human cancer cell lines have been investigated. All Cu(II) complexes were able to induce a loss of A2780 ovarian carcinoma cell viability, with phen derivatives more active than bpy derivatives. In contrast, no in vitro antiproliferative effects were observed against the HCT116 colorectal cancer cell line. These cytotoxicity differences were not due to a different intracellular concentration of the complexes determined by inductively coupled plasma atomic emission spectroscopy. A small effect of different halogen substituents on the phenolic ring was observed, with X = Cl being the most highly active toward A2780 cells among the phen derivatives, while X = Br presented the lowest IC₅₀ in A2780 cells for bpy analogs. Importantly, no reduction in normal primary fibroblasts cell viability was observed in the presence of bpy derivatives (IC₅₀ > 40 μM). Mechanistically, complex 1 seems to induce a stronger apoptotic response with a higher increase in mitochondrial membrane depolarization and an increased level of intracellular reactive oxygen species (ROS) compared to complex 3. Together, these data and the low IC₅₀ compared to cisplatin in A2780 ovarian carcinoma cell line demonstrate the potential of these bpy derivatives for further in vivo studies.

Structural characterization and pharmacological assessment in vitro/in vivo of a new copper(II)-based derivative of enrofloxacin

Enrofloxacin (EFX) was selected as the medicinal ligand to afford a new copper(ii)-based complex, EFX-Cu, which was structurally characterized by spectroscopic analyses including X-ray single crystal diffraction. It was also stable and could retain the coordination state in aqueous solution. The in vitro antibacterial activity of EFX-Cu against a panel of pathogenic bacteria was about the same as that of EFX, except that it was twice as active against E. coli. The in vivo test on mice gave a LD50 value of 8148 mg kg-1 for EFX-Cu, which was much lower than those for EFX (LD50, 5312 mg kg-1) and its clinically used sodium salt, EFX-Na (LD50, 1421 mg kg-1). In addition, no obvious lesions in the organs of the dead mice were found by histopathological examination. Pharmacokinetic studies on rats suggested similar pharmacokinetics between EFX-Cu and EFX. On the other hand, EFX-Cu showed higher acute toxicity than EFX-Na in zebrafish, which was inconsistent with that in mice. The ROS-related inflammation and anti-inflammatory assay of EFX-Cu, respectively, in normal cells and zebrafish could be ascribed to its ROS-related redox property. Unfortunately, the final in vivo therapeutic assay in the E. coli-infected mouse model indicated that the therapeutic effect of EFX-Cu, mainly in terms of mortality in mice, was found to be lower than that of EFX-Na at the same dosage (800 mg kg-1, continuous gavage), although the contradictory factors between toxicity and antibacterial activity could not be excluded in this trial.

Octahedral copper(ii)-diimine complexes of triethylenetetramine: effect of stereochemical fluxionality and ligand hydrophobicity on CuII/CuIredox, DNA binding and cleavage, cytotoxicity and apoptosis-inducing ability

Stereochemical fluxionality of octahedral [Cu(trien)(diimine)]²⁺complexes determines the Cu^II/Cu^Iredox potential, DNA binding affinity, ROS generation, cytotoxicity and apoptosis-inducing ability.

Solvent induced mononuclear and dinuclear mixed ligand Cu(ii) complex: structural diversity, supramolecular packing polymorphism and molecular docking studies

Phenolate bridged dinuclear and solvent induced mononuclear supramolecular isomers of Cu(ii) complex have been reported to explore the structural diversity and their antibacterial activity supported by molecular docking studies.

Molecular docking, QSAR properties and DNA/BSA binding, anti-proliferative studies of 6-methoxy benzothiozole imine base and its metal complexes

The molecular and QSAR (Quantitative Structure-Activity Relationship) properties of title compound 2-((6-Methoxybenzo[d]thiazol-2-ylimino)methyl)-6-ethoxyphenol (HL) were evaluated employing HyperChem 7.5 tools. The interaction of the 1a-1e complexes of HL with calf thymus DNA (CT-DNA) was investigated by absorption titrations, Fluorescence quenching and viscosity measurements. The experimental data suggest that these complexes bind to CT-DNA through an intercalative mode, wherein DNA-binding affinity of 1e is found to be greater compared to other complexes. The tryptophan emission-quenching with bovine serum albumin (BSA) experiment revealed stronger binding of 1e than other complexes in the hydrophobic region of protein. The photocleavage of plasmid pBR322 DNA investigated in the presence of the title complexes inferred conversion of supercoiled form of DNA plasmid to circular nicked form. Free-radical scavenging activity studies of HL and its metal complexes determined by their interaction with the stable free-radical DPPH have shown promising antioxidant property. Further cytotoxicity studies with HeLa and MCF-7 cell lines indicated that the compounds can efficiently inhibit the cell proliferation in a dose dependent manner. The DAPI staining assay studies revealed the higher potency of 1e to induce apoptosis. AbbreviationsBSABovine serum albumin proteinCT-DNACalf thymus DNADMSODimethyl sulfoxideDAPI4',-6-Diamidino-2-phenylindole dihydrochlorideESI-MSElectrospray ionization mass spectrometryIC₅₀Half-maximal inhibitory concentrationMBTYE2-((6-methoxybenzo[d]thiazol-2-ylimino) methyl)-6-ethoxyphenolMTT3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromidePBSPhosphate-buffered salineTrisTris(hydroxymethyl)aminomethaneCommunicated by Ramaswamy H. Sarma.

Structure, DNA/proteins binding, docking and cytotoxicity studies of copper(II) complexes with the first quinolone drug nalidixic acid and 2,2'‑dipyridylamine

This work presents the synthesis, structural characterization and biological affinity of the newly synthesized copper(II) complexes with the first antibacterial quinolone drug nalidixic acid (nal) or N-donor ligand 2,2'‑dipyridylamine (bipyam). [Cu(II)(nal)(bipyam)Cl], (2) reveals a distorted square pyramidal based geometry in Cu(II) atom confirmed by X-ray crystallography technique. The theoretical stabilities and optimized structures of the complex were obtained from DFT calculations. The ability of the complexes to bind with calf thymus DNA (CT DNA) were investigated by electronic absorption, fluorescence, circular dichroism, and viscosity measurements techniques. The experimental results reveal that the complexes strongly interact with CT DNA via intercalative mode but complex 2 exhibits the highest affinity giving K_b=3.91±0.13×10⁶, M^-1. The fluorescence spectroscopy measurements show that both complexes have the superior ability to the replacement of EtBr from DNA-bound EtBr solution and bind to DNA through intercalative mode. Both complex also shows the superior affinity towards proteins with comparatively high binding constant values which have been further revealed by fluorescence spectroscopy measurements. Molecular docking analysis indicates that the interaction of the complexes and proteins are stabilized by hydrogen bonding and hydrophobic interaction. Furthermore, the results of in vitro cytotoxicity reveal that the complex 2 has excellent cytotoxicity than 1 against human breast cancer cell lines (MCF-7).

Thioether sulfur-bound [Cu2] complexes showing catechol oxidase activity and DNA cleaving behaviour

Ligand backbone alteration leads to different mechanisms for catecholase activity and order of interaction with DNA molecules.

Design, synthesis and characterization of novel chromone based-copper(ii) antitumor agents with N,N-donor ligands: comparative DNA/RNA binding profile and cytotoxicity

A series of new chromone based-Cu(ii) complexes 1-3 derived from bioactive pharmacophore, 3-formylchromone and N,N-donor ligands viz., 1,10-phenanthroline, 2,2'-bipyridine and 1R,2R-DACH were synthesized as potential antitumor agents and thoroughly characterized by UV-vis, FT-IR, EPR, ESI-MS and elemental analysis. Single X-crystal diffraction studies of complex 2 revealed triclinic P1̄ space group with square pyramidal geometry around the Cu(ii) center. Comparative in vitro binding studies with ct-DNA and tRNA were carried out using absorption and emission titration experiments which revealed intercalative mode of binding with higher binding propensity of complexes 1-3 towards tRNA as compared to ct-DNA. Additionally, complex 1 exhibited high binding affinity among all the three complexes due to the involvement of phen co-ligands via π-stacking interactions in between nucleic acid base pairs. Furthermore, Hirshfeld surface analysis was carried out for complex 2 to investigate various intra and intermolecular non-covalent interactions (H-bonding, C-H⋯π etc.) accountable for stabilization of crystal lattice. The cleavage activity of complex 1 was performed by gel electrophoretic assay with pBR322 DNA and tRNA which revealed efficient DNA/tRNA cleaving ability of complex, suggesting tRNA cleavage both concentration and time dependent. Furthermore, in vitro cytotoxic activity of complexes 1-3 on a selected panel of human cancer cell lines was performed which revealed that all three complexes exhibited remarkably good cytotoxic activity with GI50 value < 10 μg mL-1 (<20 μM).

Single X-ray crystal structure, DFT studies and topoisomerase I inhibition activity of a tailored ionic Ag(i) nalidixic acid–piperazinium drug entity specific for pancreatic cancer cells

DFT studies, Topo I inhibition assay and cytotoxic activity of novel ionic Ag(i) nalidixic acid–piperazinium molecular entity.

Copper(II) complexes of N3O tripodal ligands appended with pyrene and polyamine groups: Anti-proliferative and nuclease activities

A series of tripodal ligands based on the 2-tert-butyl-4-R-6-phenol was synthesized, where R=aldehyde (HL¹), R=putrescine-pyrene (HL²) and R=putrescine (HL³). A dinucleating ligand wherein a putrescine group connects two tripodal moieties was also prepared (H₂L⁴). The corresponding copper complexes (1, 2, 3, and 4, respectively) were prepared and characterized. We determined the phenol's pKas in the range 2.47-3.93. The DNA binding constants were determined at 6×10⁶, 5.5×10⁵ and 2.7×10⁶ for 2, 3 and 4, respectively. The complexes display a metal-centered reduction wave at E_p^c,red=-0.45 to -0.5V vs. saturated calomel electrode, as well as a ligand-centered oxidation wave above 0.57V at pH7. In the presence of ascorbate they promote an efficient cleavage of DNA, with for example a concentration required to cleave 50% of supercoiled DNA of 1.7μM for 2. The nuclease activity is affected by the nature of the R group: putrescine-pyrene≈bis-ligating>putrescine>aldehyde. The species responsible for strand scission is the hydroxyl radical. The cytotoxicity of the complexes was evaluated on bladder cancer cell lines sensitive or resistant to cis-platin. The IC₅₀ of complexes 2 and 4 span over a short range (1.3-2μM) for the two cell lines. They are lower than those of the other complexes (3.1-9.7μM) and cis-platin. The most active compounds block the cell cycle at the G0/1 phase and promote apoptosis.