Antiproliferative activity of heterometallic sodium and potassium-dioxidovanadium(V) polymers

Vanadium complex as a potential modulator of the autophagic mechanism through proteins PI3K and ULK1: development, validation and biological implications of a specific force field for [VO(bpy)2Cl]

The modulation of autophagy has been presented as a very useful strategy in anticancer treatments. In this sense, the vanadium complex (VC) bis(2,2'-bipyridine)chlorooxovanadium(IV), [VO(bpy)2Cl], is known for its ability to induce autophagy in triple-negative breast cancer cells (TNBC). An excellent resource to investigate the role of VC in the induction of autophagy is to make use of Molecular Dynamics (MD) simulations. However, until now, the scarcity of force field parameters for the VC prevented a reliable analysis. The autophagy signaling pathway starts with the PI3K protein and ends with ULK1. Therefore, in the first stage of this work, we developed a new AMBER force field for the VC (VCFF) from a quantum structure, obtained by DFT calculations. In the second stage, the VCFF was validated through structural analyses. From this, it was possible to investigate, through docking and MD (200 ns), the performance of the PI3K-VC and ULK1-VC systems (third stage). The analyses of this last stage involved RMSD, hydrogen bonds, RMSF and two pathways for the modulation of autophagy. In general, this work fills in the absence of force field parameters (FF) for VC by proposing an efficient and new FF, in addition to investigating, at the molecular level, how VC is able to induce autophagy in TNBC cells. This study encourages new parameterizations of metallic complexes and contributes to the understanding of the duality of autophagic processes.Communicated by Ramaswamy H. Sarma.

In Vitro and In Vivo Biological Activities of Dipicolinate Oxovanadium(IV) Complexes

The work is focused on anticancer properties of dipicolinate (dipic)-based vanadium(IV) complexes [VO(dipic)(N^∩N)] bearing different diimines (2-(1H-imidazol-2-yl)pyridine, 2-(2-pyridyl)benzimidazole, 1,10-phenanthroline-5,6-dione, 1,10-phenanthroline, and 2,2'-bipyridine), as well as differently 4,7-substituted 1,10-phenanthrolines. The antiproliferative effect of V(IV) systems was analyzed in different tumors (A2780, HCT116, and HCT116-DoxR) and normal (primary human dermal fibroblasts) cell lines, revealing a high cytotoxic effect of [VO(dipic)(N^∩N)] with 4,7-dimethoxy-phen (5), 4,7-diphenyl-phen (6), and 1,10-phenanthroline (8) against HCT116-DoxR cells. The cytotoxicity differences between these complexes can be correlated with their different internalization by HCT116-DoxR cells. Worthy of note, these three complexes were found to (i) induce cell death through apoptosis and autophagy pathways, namely, through ROS production; (ii) not to be cytostatic; (iii) to interact with the BSA protein; (iv) do not promote tumor cell migration or a pro-angiogenic capability; (v) show a slight in vivo anti-angiogenic capability, and (vi) do not show in vivo toxicity in a chicken embryo.

Evaluation of autophagy inhibition to combat cancer: (vanadium complex)-protein interactions, parameterization, and validation of a new force field

Autophagy has drawn attention from the scientific community, mainly because of its significant advantages over chemotherapeutic processes. One of these advantages is its direct action on cancer cells, avoiding possible side effects, unlike chemotherapy, which reaches tumor cells and affects healthy cells in the body, leading to a great loss in the quality of life of patients. In this way, it is known that vanadium complex (VC) [VO(oda)(phen)] has proven inhibition effect on autophagy process in pancreatic cancer cells. Keeping that in mind, molecular dynamics (MD) simulations can be considered excellent strategies to investigate the interaction of metal complexes and their biological targets. However, simulations of this type are strongly dependent on the appropriate choice of force field (FF). Therefore, this work proposes the development of AMBER FF parameters for VC, having a minimum energy structure as a starting point, obtained through DFT calculations with B3LYP/def2-TZVP level of theory plus ECP for the vanadium atom. An MD simulation in vacuum was performed to validate the developed FF. From the structural analyses, satisfying values of VC bond lengths and angles were obtained, where a good agreement with the experimental data and the quantum reference was found. The RMSD analysis showed an average of only 0.3%. Finally, we performed docking and MD (120 ns) simulations with explicit solvent between VC and PI3K. Overall, our findings encourage new parameterizations of metal complexes with significant biological applications, as well as allow to contribute to the elucidation of the complex process of autophagy.

Equilibria of complexes in the aqueous cobalt(II)-N-(2-hydroxybenzyl)phenylalanine system and their biological activity compared to analogous Schiff base structures

Due to their excellent prospects in biological applications, Schiff bases and their complexes are a source of continuing interest. The present study examines the formation of four cobalt(II) complexes with the reduced Schiff base N-(2-hydroxybenzyl)phenylalanine (PhAlaSal) in alkaline aqueous solution by pH-metry. UV-Vis and ESI-MS studies confirmed the model of proposed species. Kinetic analysis indicated that the single- and bi-ligand cobalt(II) complexes transitioned from octahedral to tetrahedral structures. The Schiff base and its complexes detected under physiological pH were tested for antimicrobial abilities and compared with analogous structures of the Schiff base derivative, N-(2-hydroxybenzyl)alanine (AlaSal). The ability of these structures to influence cell growth was tested on L929 mouse fibroblasts and on cervix and gastric adenocarcinoma cancer cell lines. N-(2-hydroxybenzyl)phenylalanine demonstrates greater antimicrobial efficacy than N-(2-hydroxybenzyl)alanine but also higher cytotoxicity; however, it is nonetheless effective against cancer cells. In turn, AlaSal demonstrates low cytotoxicity for fibroblasts and high cytotoxicity for gastric adenocarcinoma epithelial cells at bacteriostatic concentration for Helicobacter pylori and Candida strains. The presence of these microorganisms in the gastric milieu supports the development of gastritis and gastric cancer; AlaSal therapy may be simultaneously effective against both. Due to their cytotoxicity, Schiff base complexes are not suitable for use against fungal and bacterial infections, but may effectively prevent cancer cell growth.

Data availability

Data will be made available on request.

Chemical Characterization and Biological Evaluation of New Cobalt(II) Complexes with Bioactive Ligands, 2-Picolinehydroxamic Acid and Reduced Schiff Base N-(2-Hydroxybenzyl)alanine, in Terms of DNA Binding and Antimicrobial Activity

Five new heteroligand cobalt(II) complexes with 2-picolinehydroxamic acid and reduced Schiff base, N-(2-hydroxybenzyl)alanine, were formed in an aqueous solution over a wide pH range. The coordination properties of ligands towards the metal ion were determined using a pH-metric method, and then the speciation model was confirmed by UV–Vis studies. A stacking interaction between the Schiff base phenol ring and the 2-picolinehydroxamic acid pyridine ring was found to improve the stability of the heteroligand species, indicating more effective coordination in mixed-ligand complexes than in their respective binary systems. The antimicrobial properties of heteroligand complexes were determined against Gram-negative and Gram-positive bacteria, as well as fungal strains. The formulation demonstrated the highest bacteriostatic and bactericidal activity (3.65 mM) against two strains of Gram-negative Helicobacter pylori bacteria and towards Candida albicans and Candida glabrata; this is important due to the potential co-existence of these microorganisms in the gastric milieu and their role in the development of gastritis. The binary complexes in the cobalt(II)—2-picolinehydroxamic acid system and 2-picolinehydroxamic acid were not cytotoxic against L929 mouse fibroblasts, neither freshly prepared solutions or after two weeks’ storage. By comparison, the heteroligand complexes within the range 0.91–3.65 mM diminished the metabolic activity of L929 cells, which was correlated with increased damage to cell nuclei. The concentration of the heteroligand species increased over time; therefore, the complexes stored for two weeks exhibited stronger anticellular toxicity than the freshly prepared samples. The complexes formed in an aqueous solution under physiological pH effectively bound to calf thymus DNA in an intercalative manner. This DNA-binding ability may underpin the antimicrobial/antifungal activity of the heteroligand complexes and their ability to downregulate the growth of eukaryotic cells.

Vanadium(IV) Complexes with Methyl-Substituted 8-Hydroxyquinolines: Catalytic Potential in the Oxidation of Hydrocarbons and Alcohols with Peroxides and Biological Activity

Methyl-substituted 8-hydroxyquinolines (Hquin) were successfully used to synthetize five-coordinated oxovanadium(IV) complexes: [VO(2,6-(Me)₂-quin)₂] (1), [VO(2,5-(Me)₂-quin)₂] (2) and [VO(2-Me-quin)₂] (3). Complexes 1-3 demonstrated high catalytic activity in the oxidation of hydrocarbons with H₂O₂ in acetonitrile at 50 °C, in the presence of 2-pyrazinecarboxylic acid (PCA) as a cocatalyst. The maximum yield of cyclohexane oxidation products attained was 48%, which is high in the case of the oxidation of saturated hydrocarbons. The reaction leads to the formation of a mixture of cyclohexyl hydroperoxide, cyclohexanol and cyclohexanone. When triphenylphosphine is added, cyclohexyl hydroperoxide is completely converted to cyclohexanol. Consideration of the regio- and bond-selectivity in the oxidation of n-heptane and methylcyclohexane, respectively, indicates that the oxidation proceeds with the participation of free hydroxyl radicals. The complexes show moderate activity in the oxidation of alcohols. Complexes 1 and 2 reduce the viability of colorectal (HCT116) and ovarian (A2780) carcinoma cell lines and of normal dermal fibroblasts without showing a specific selectivity for cancer cell lines. Complex 3 on the other hand, shows a higher cytotoxicity in a colorectal carcinoma cell line (HCT116), a lower cytotoxicity towards normal dermal fibroblasts and no effect in an ovarian carcinoma cell line (order of magnitude HCT116 > fibroblasts > A2780).

Preparation, Antimicrobial Activity and Docking Study of Vanadium Mixed Ligand Complexes Containing 4-Amino-5-hydrazinyl-4H-1,2,4-triazole-3-thiol and Aminophenol Derivatives

The synthesis of mixed-ligand complexes is considered an important strategy for developing new metal complexes of enhanced biological activity. This paper presents the synthesis, characterization, in vitro antimicrobial assessment, and theoretical molecular docking evaluation for synthesized oxidovanadium (V) complexes. The proposed structures of the synthesized compounds were proved using elemental and different spectroscopic analysis. The antimicrobial tests showed moderate activity of the compounds against the Gram-positive bacterial strains and the fungal yeast, whereas no activity was observed against the Gram-negative bacterial strains. The performance of density functional theory (DFT) was conducted to study the interaction mode of the targeted compounds with the biological system. Calculating the quantitative structure-activity relationship (QSPR) was performed depending on optimization geometries, frontier molecular orbitals (FMOs), and chemical reactivities for synthesized compounds. The molecular electrostatic potentials (MEPs) that were plotted link the interaction manner of synthesized compounds with the receptor. The molecular docking evaluation revealed that the examined compounds may possess potential antibacterial activity.

Copper(ii) complexes with tridentate halogen-substituted Schiff base ligands: synthesis, crystal structures and investigating the effect of halogenation, leaving groups and ligand flexibility on antiproliferative activities

To investigate the effect of different halogen substituents and leaving groups and the flexibility of ligands on the anticancer activity of copper complexes, sixteen copper(ii) complexes with eight different tridentate Schiff-base ligands containing pyridine and 3,5-halogen-substituted phenol moieties were synthesized and characterized by spectroscopic methods. Four of these complexes were also characterized by X-ray crystallography. The cytotoxicity of the complexes was determined in three different tumor cell lines (i.e. the A2780 ovarian, HCT116 colorectal and MCF7 breast cancer cell line) and in a normal primary fibroblast cell line. Complexes were demonstrated to induce a higher loss of cell viability in the ovarian carcinoma cell line (A2780) with respect to the other two tumor cell lines, and therefore the biological mechanisms underlying this loss of viability were further investigated. Complexes with ligand L₁ (containing a 2-pycolylamine-type motif) were more cytotoxic than complexes with L₂ (containing a 2-(2-pyridyl)ethylamine-type motif). The loss of cell viability in A2780 tumor cells was observed in the order Cu(Cl₂-L₁)NO₃ > Cu(Cl₂-L₁)Cl > Cu(Br₂-L₁)Cl > Cu(BrCl-L₁)Cl. All complexes were able to induce reactive oxygen species (ROS) that could be related to the loss of cell viability. Complexes Cu(BrCl-L₁)Cl and Cu(Cl₂-L₁)NO₃ were able to promote A2780 cell apoptosis and autophagy and for complex Cu(BrCl-L₁)Cl the increase in apoptosis was due to the intrinsic pathway. Cu(Cl₂-L₁)Cl and Cu(Br₂-L₁)Cl complexes lead to cellular detachment allowing to correlate with the results of loss of cell viability. Despite the ability of the Cu(BrCl-L₁)Cl complex to induce programmed cell death in A2780 cells, its therapeutic window turned out to be low making the Cu(Cl₂-L₁)NO₃ complex the most promising candidate for additional biological applications.

Cu(I) complexes as new antiproliferative agents against sensitive and doxorubicin resistant colorectal cancer cells: synthesis, characterization, and mechanisms of action

Cancer is one of the worst health issues worldwide, representing the second leading cause of death. Current chemotherapeutic drugs face some challenges like the acquired resistance of the tumoral cells and low specificity leading to unwanted side effects. There is an urgent need to develop new compounds that may target resistant cells. The synthesis and characterization of two Cu(i) complexes of general formula [Cu(PP)(LL)][BF4], where PP is a phosphane ligand (triphenylphosphine or 1,2-bis(diphenylphosphano) ethane) and LL = is a heteroaromatic bidentate ligand (4,4'-dimethyl-2,2'-bipyridine and 6,3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine). The new compounds were fully characterized by spectroscopic techniques (NMR, FTIR and UV-vis.), elemental analysis (C, H, N and S) and two structures were determined by single X-ray diffraction studies. The antiproliferative potential of the new Cu(i) complexes were studied in tumor (breast adenocarcinoma, ovarian carcinoma and in colorectal carcinoma sensitive and resistant to doxorubicin) and normal (fibroblasts) cell lines. Complexes 1-4 did not show any antiproliferative potential. Amongst the complexes 5-8, complex 8 shows high cytotoxic potential against colorectal cancer sensitive and resistant to doxorubicin and low cytotoxicity towards healthy cells. We show that complexes 5-8 can cleave pDNA and, in particular, the in vitro pDNA cleavage is due to an oxidative mechanism. This oxidative mechanism corroborates the induction of reactive oxygen species (ROS), that triggers HCT116 cell death via apoptosis, as proved by the increased expression of BAX protein relative to BCL-2 protein and the depolarization of mitochondrial membrane potential, and via autophagy. Additionally, complex 8 can block the cell cycle in the G1 phase, also exhibiting a cytostatic potential. Proteomic analysis confirmed the apoptotic, autophagic and cytostatic potential of complex 8, as well as its ability to produce ROS and cause DNA damage. The interference of the complex in folding and protein synthesis and its ability to cause post-translational modifications was also verified. Finally, it was observed that the complex causes a reduction in cellular metabolism. The results herein demonstrated the potential of Cu(i) complexes in targeting doxorubicin sensitive and resistant cells which is positive and must be further explored using in vivo animal models.

New copper(I) complexes selective for prostate cancer cells

A new family of eighteen Cu(i) complexes of the general formula [Cu(PP)(LL)][BF4], where PP is a phosphane ligand and LL represents an N,O-heteroaromatic bidentate ligand, has been synthesized and fully characterized by classical analytical and spectroscopic methods. Five complexes of this series were also characterized by single crystal X-ray diffraction studies. The cytotoxicity of all compounds was evaluated in breast (MCF7) and prostate (LNCap) human cancer cells and in a normal prostate cell line (RWPE). In general, all compounds showed higher cytotoxicity for the prostate cancer cells than for the breast cells, with IC50 values in the range 0.2-2 μM after 24 h of treatment. The most cytotoxic compound, [Cu(dppe)(2-ap)][BF4] (16), where dppe = 1,2-bis(diphenylphosphano) ethane and 2-ap = 2-acetylpyridine, showed a high level of cellular internalization, generation of intracellular ROS and activation of the cell death mechanism via apoptosis/necrosis. Owing to its high cytotoxic activity for LNCap cells, being 70-fold higher than that for normal prostate cells (RWPE), complex (16) was found to be the most promising for further research in prostate cancer models.

Equilibria in Aqueous Cobalt(II)-Reduced Schiff Base N-(2-hydroxybenzyl)alanine System: Chemical Characterization, Kinetic Analysis, Antimicrobial and Cytotoxic Properties

The present study describes the coordination properties of a reduced Schiff base, N-(2-hydroxybenzyl)alanine, towards cobalt(II) using potentiometric as well as spectroscopic (UV-Vis and ESI-MS) methods. The results indicate the formation of six mononuclear complexes showing high stability in aqueous solution. Coordination occurs in the {O⁻_phenolic,N,O⁻_carboxyl} and {N,O⁻_carboxyl} chelation modes, depending on the degree of ligand deprotonation. Examination of the complexation equilibria at pH ca 7, which is important from a biological point of view, allowed to identify two species: [CoL] and [CoL₂H]⁻. The kinetic analysis showed a structural change of those cobalt(II) complexes from octahedral to tetrahedral in accordance with a first-order time relationship. The antimicrobial properties of N-(2-hydroxybenzyl)alanine, cobalt(II) nitrate and of the Co(II) – ligand complexes were determined against Gram-positive bacteria (Enterococcus faecalis, Staphylococcus aureus, Staphylococcus epidermidis), Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli, Helicobacter pylori) and a fungal strain (Candida). The results indicate that the complexes are more active for more strains than the ligand alone. Nevertheless, the complexes induce a higher decrease in the metabolic activity of cells but without damage to nuclei. Tetrahedral structures show stronger anti-cellular toxicity than octahedral complexes, which is most likely due to the higher accessibility of the cobalt(II) center.

In vitro antiproliferative effect of vanadium complexes bearing 8-hydroxyquinoline-based ligands – the substituent effect

This is the first comprehensive study demonstrating the antiproliferative effect of vanadium complexes bearing 8-hydroxyquinoline (quinH) ligands, including the parent and –CH₃ (Me), –NO₂, –Cl and –I substituted ligands, on HCT116 and A2780 cancer cell lines.