The chemistry and biology of vanadium compounds in cancer therapeutics

Vanadium(V) complexes derived from triphenylphosphonium and hydrazides: cytotoxicity evaluation and interaction with biomolecules

The development of coordination compounds with antineoplastic therapeutic properties is currently focused on non-covalent interactions with deoxyribonucleic acid (DNA). Additionally, the interaction profiles of these compounds with globular plasma proteins, particularly serum albumin, warrant thorough evaluation. In this study, we report on the interactions between biomolecules and complexes featuring hydrazone-type imine ligands coordinated with vanadium. The potential to enhance the therapeutic efficiency of these compounds through mitochondrial targeting is explored. This targeting is facilitated by the derivatization of ligands with triphenylphosphonium groups. Thus, this work presents the synthesis, characterization, interactions, and cytotoxicity of dioxidovanadium(V) complexes (C1-C5) with a triphenylphosphonium moiety. These VV-species are coordinated to hydrazone-type iminic ligands derived from (3-formyl-4-hydroxybenzyl)triphenylphosphonium chloride ([AH]Cl) and aromatic hydrazides ([H2L1]Cl-[H2L5]Cl). The structures of the five complexes were elucidated through single-crystal X-ray diffraction and vibrational spectroscopies, confirming the presence of dioxidovanadium(V) species in various geometries with degrees of distortion (τ = 0.03-0.50) and highlighting their zwitterionic characteristics. The molecular structural stability of C1-C5 in solution was ascertained using 1H, 19F, 31P, and 51V-nuclear magnetic resonance. Moreover, their interactions with biomolecules were evaluated using diverse spectroscopic methodologies and molecular docking, indicating moderate interactions (Kb ≈ 104 M-1) with calf thymus DNA in the minor groove and with human serum albumin, predominantly in the superficial IB subdomain. Lastly, the cytotoxic potentials of these complexes were assessed in keratinocytes of the HaCaT lineage, revealing that C1-C5 induce a reduction in metabolic activity and cell viability through apoptotic pathways.

A Functional "Key" Amplified Piezoelectric Effect Modulates ROS Storm with an Open Source for Multimodal Synergistic Cancer Therapy

Chemodynamic therapy (CDT) is a non-invasive strategy for generating reactive oxygen species (ROS) and is promising for cancer treatment. However, increasing ROS in tumor therapy remains challenging. Therefore, exogenous excitation and inhibition of electron-hole pair recombination are attractive for modulating ROS storms in tumors. Herein, a Ce-doped BiFeO3 (CBFO) piezoelectric sonosensitizer to modulate ROS generation and realize a synergistic mechanism of CDT/sonodynamic therapy and piezodynamic therapy (PzDT) is proposed. The mixed Fe2+ and Ce3+ can implement a circular Fenton/Fenton-like reaction in the tumor microenvironment. Abundant ·OH can be generated by ultrasound (US) stimulation to enhance CDT efficacy. As a typical piezoelectric sonosensitizer, CBFO can produce O2 - owing to the enhanced polarization by the US, resulting in the motion of charge carriers. In addition, CBFO can produce a piezoresponse irradiated upon US, which accelerates the migration rate of electrons/holes in opposite directions and results in energy band bending, further achieving toxic ROS production and realizing PzDT. Density functional theory calculations confirmed that Ce doping shortens the diffusion of electrons and improves the conductivity and catalytic activity of CBFO. This distinct US-enhanced strategy emphasizes the effects of doping engineering and piezoelectric-optimized therapy and shows great potential for the treatment of malignant tumors.

Oxidovanadium(V) Schiff Base Complexes Derived from Chiral 3-amino-1,2-propanediol Enantiomers: Synthesis, Spectroscopic Studies, Catalytic and Biological Activity

Oxidovanadium(V) complexes, [(+)VOL1-5] and [(-)VOL1-5], with chiral tetradentate Schiff bases, which are products of monocondensation of S(‒)-3-amino-1,2-propanediol or R(+)-3-amino-1,2-propanediol with salicylaldehyde derivatives, have been synthesized. Different spectroscopic methods, viz. 1H and 51V NMR, IR, UV-Vis, and circular dichroism, as well as elemental analysis, have been used for their detailed characterization. Furthermore, the epoxidation of styrene, cyclohexene, and two monoterpenes, S(‒)-limonene and (‒)-α-pinene, using two oxidants, aqueous 30% H2O2 or tert-butyl hydroperoxide (TBHP) in decane, has been studied with catalytic amounts of all complexes. Finally, biological cytotoxicity studies have also been performed with these oxidovanadium(V) compounds for comparison with cis-dioxidomolybdenum(VI) Schiff base complexes with the same chiral ligands, as well as to determine the cytoprotection against the oxidative damage caused by 30% H2O2 in the HT-22 hippocampal neuronal cells in the range of their 10-100 μM concentration.

Multifaceted antineoplastic curative potency of novel water-soluble methylimidazole-based oxidovanadium (IV) complex against triple negative mammary carcinoma

A bunch of complexes harboring vanadium as metal centers have been reported to exhibit a wide array of antineoplastic properties that come under non‑platinum metallodrug series and emerge to offer alternative therapeutic strategies from the mechanistic behaviors of platinum-drugs. Though antineoplastic activities of vanado-complexes have been documented against several animal and xenografted human cancers, the definite mechanism of action is yet to unveil. In present study, a novel water soluble 1-methylimidazole substituted mononuclear dipicolinic acid based oxidovanadium (IV) complex (OVMI) has been evaluated for its antineoplastic properties in breast carcinoma both in vitro and in vivo. OVMI has been reported to generate cytotoxicity in human triple negative breast carcinoma cells, MDA-MB-231 as well as in mouse 4T1 cells by priming them for apoptosis. ROS-mediated, mitochondria-dependent as well as ER-stress-evoked apoptotic death seemed to be main operational hub guiding the cytotoxicity of OVMI in vitro. Moreover, OVMI has been noticed to elicit antimetastatic effect in vitro. Therapeutic application of OVMI has been extended on 4T1-based mammary tumor of female Balb/c mice, where it has been found to reduce tumor size, volume and restore general tissue architecture successfully to a great extent. Apart from that, OVMI has been documented to limit 4T1-based secondary pulmonary metastasis along with being non-toxic and biocompatible in vivo.

Synthesis, Spectroscopic Characterization, Catalytic and Biological Activity of Oxidovanadium(V) Complexes with Chiral Tetradentate Schiff Bases

New oxidovanadium(V) complexes, VOL1-VOL10, with chiral tetradentate Schiff bases obtained by monocondensation reaction of salicylaldehyde derivatives with 1S,2S-(+)-2-amino-1-(4-nitrophenyl)-1,3-propanediol. All complexes have been characterized using different spectroscopic methods, viz. IR, UV-Vis, circular dichroism, one- (1H, 51V) and two-dimensional (COSY, NOESY) NMR spectroscopy, and elemental analysis. Furthermore, the catalytic ability of all compounds in the epoxidation of styrene, cyclohexene, and its naturally occurring monoterpene derivatives, i.e., S(-)-limonene and (-)-α-pinene has also been studied, using two different oxidants, i.e., aqueous 30% H2O2 or tert-butyl hydroperoxide (TBHP). In addition, the biological properties of these chiral oxidovanadium(V) compounds, but also cis-dioxidomolybdenum(VI) complexes with the same chiral Schiff bases, were studied. Their cytotoxic and cytoprotective activity studies with the HT-22 hippocampal neuronal cells revealed a concentration-dependent effect in the range of 10-100 μM. Moreover, vanadium(V) complexes, in contrast to cis-dioxidomolybdenum(VI) compounds, demonstrated higher cytotoxicity and lack of cytoprotective ability against H2O2-induced cytotoxicity.

Bioreactivity of divalent bimetallic vanadyl and zinc complexes bis-oxalyldihydrazone ligand against microbial and human cancer series. ctDNA interaction mode

Two novel divalent bimetallic complexes were constructed from the complexation of O=V4+ and Zn2+ ions (VOL and ZnL), respectively, with diisatin oxalyldihydrazone ligand (H2L). Various spectroscopic tools were used to confirm their chemical structures (FT-IR, NMR, EI-Mass, and electronic spectra), besides, elemental analyses and conductivity features. To estimate the role of divalent metal ions in their coordination compound for developing their bio-reactivity, the free ligand H2Lox, and its complexes (VOL and ZnL) were employed spectroscopic investigations against the growth of some microbial series (fungi and bacteria) and also against three human cancer/normal cells. Furthermore, their interaction behavior against calf thymus DNA (ctDNA) was studied through viscometric and spectrophotometric studies to discover the role of O=V4+ and Zn2+ ions to determine the mode of binding with ctDNA. The inhibiting effect of H2L, VOL, and ZnL versus the titled microbial (bacterial and fungal) was built upon their inhibited zone areas in mm and the MIC concentrations in μM. Their action against the three human cancer cells' growth was evaluated by IC50 values in μM and the selectivity index in percentage. Both VOL and ZnL complexes exhibited an amazing series with three human cancer cell growth (according to the zone values in mm of inhibition, MIC in μM, and IC50 values in μM) compared to those of their uncoordinated H2L ligand. VOL demonstrated a distinguished interacting behavior with ctDNA more than that interaction of ZnL depending on the variation of the central metal ion chemical features. Within the covalent and non-covalent interaction modes, the interaction binding between H2L, VOL, and ZnL with ctDNA was discussed based on the electronic spectroscopic observation.

Interaction of Vanadium Complexes with Proteins: Revisiting the Reported Structures in the Protein Data Bank (PDB) since 2015

The structural determination and characterization of molecules, namely proteins and enzymes, is crucial to gaining a better understanding of their role in different chemical and biological processes. The continuous technical developments in the experimental and computational resources of X-ray diffraction (XRD) and, more recently, cryogenic Electron Microscopy (cryo-EM) led to an enormous growth in the number of structures deposited in the Protein Data Bank (PDB). Bioinorganic chemistry arose as a relevant discipline in biology and therapeutics, with a massive number of studies reporting the effects of metal complexes on biological systems, with vanadium complexes being one of the relevant systems addressed. In this review, we focus on the interactions of vanadium compounds (VCs) with proteins. Several types of binding are established between VCs and proteins/enzymes. Considering that the V-species that bind may differ from those initially added, the mentioned structural techniques are pivotal to clarifying the nature and variety of interactions of VCs with proteins and to proposing the mechanisms involved either in enzymatic inhibition or catalysis. As such, we provide an account of the available structural information of VCs bound to proteins obtained by both XRD and/or cryo-EM, mainly exploring the more recent structures, particularly those containing organic-based vanadium complexes.

In Vitro, Oral Acute, and Repeated 28-Day Oral Dose Toxicity of a Mixed-Valence Polyoxovanadate Cluster

Polyoxovanadates (POV) are a subgroup of polyoxometalates (POM), which are nanosized clusters with reported biological activities. This manuscript describes the first toxicity evaluation of a mixed-valence polyoxovanadate, pentadecavanadate, (Me4N)6[V15O36Cl], abbreviated as V15. Cytotoxicity experiments using peripheral blood mononuclear cells (PBMC), larvae of Artemia salina Leach, and in vivo oral acute and repeated 28-day doses in mice was carried out. The LC50 values in PBMC cells and A. salina were 17.5 ± 5.8 μmol L-1, and 17.9 µg L-1, respectively, which indicates high cytotoxic activity. The toxicity in mice was not observed upon acute exposure in a single dose, however, the V15 repeated 28-day oral administration demonstrated high toxicity using 25 mg/kg, 50 mg/kg and, 300 mg/kg doses. The biochemical and hematological analyses during the 28-day administration of V15 showed significant alteration of the metabolic parameters related to the kidney and liver, suggesting moderate toxicity. The V15 toxicity was attributed to the oxidative stress and lipid peroxidation, once thiobarbituric acid (TBAR) levels significantly increased in both males and females treated with high doses of the POV and also in males treated with a lower dose of the POV. This is the first study reporting a treatment-related mortality in animals acutely administrated with a mixed-valence POV, contrasting with the well-known, less toxic decavanadate. These results document the toxicity of this mixed-valence POV, which may not be suitable for biomedical applications.

Theoretical, antioxidant, antidiabetic and in silico molecular docking and pharmacokinetics studies of heteroleptic oxovanadium(IV) complexes of thiosemicarbazone-based ligands and diclofenac

A series of new heteroleptic oxovanadium(IV) complexes with the general formula [VOL1-6(Dcf)] (1-6), where L1-6 = thiosemicarbazone (TSC)-based ligands and Dcf = diclofenac have been synthesized and characterized. The spectral studies along with the density functional theory calculations evidenced the distorted square-pyramidal geometry around oxovanadium(IV) ion through imine nitrogen and thione sulfur atoms of TSC moiety, and two asymmetric carboxylate oxygen atoms of diclofenac drug. The complexes were evaluated for in vitro antioxidant activity using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,2'-diphenyl-1-picrylhydrazyl (DPPH), hydrogen peroxide (H2O2) and superoxide radical scavenging assays with respect to the standard antioxidant drugs butylated hydroxyanisole (BHA) and rutin. The in vitro antidiabetic activity of the complexes was tested with enzymes such as α-amylase, α-glucosidase and glucose-6-phosphatase. The complexes containing methyl substituent showed higher activity than that containing the nitro substituent due to the electron-donating effect of methyl group. The in silico molecular docking studies of the oxovanadium(IV) complexes with α-amylase and α-glucosidase enzymes showed strong interaction via hydrogen bonding and hydrophobic interactions. The dynamic behavior of the proposed complexes was analyzed by molecular dynamics (MDs) simulations, which revealed the stability of docked structures with α-amylase and α-glucosidase enzymes. The in silico physicochemical and pharmacokinetics parameters, such as Lipinski's 'rule of five', Veber's rule and absorption, distribution, metabolism and excretion (ADME) properties predicted non-toxic, non-carcinogenic and safe oral administration of the synthesized complexes.Communicated by Ramaswamy H. Sarma.

Medicinal applications of vanadium complexes with Schiff bases

Many transition metal complexes have been explored for their therapeutic properties after the discovery of cisplatin. Schiff bases have an efficient complexation tendency with the transition metals and several medicinal properties have been reported. However, fewer studies have reported the medicinal utility of vanadium and its Schiff base complexes. This paper provides a comprehensive overview of vanadium complexes with Schiff bases along with their mechanistic insight. Vanadium complexes in + 4 and + 5 oxidation states have exhibited well-defined geometry and found to be thermodynamically stable. The studies have reported the G0/G1 phase cell cycle arrest and decreased delta psi m, inducing mitochondrial membrane depolarization in cancer cell lines along with the alterations in the metabolism of the cancer cells upon dosing with the vanadium complexes. Cancer cell invasion and growth are also found to be markedly reduced by peroxo complexes of vanadium. The studies included in the review paper have been taken from leading indexing databases and focus was laid on recent reports in literature. The biological potential of vanadium complexes of Schiff bases opens new horizons for future interdisciplinary studies and investigation focussed on understanding the biochemistry of these complexes, along with designing new complexes which have better bioavailability, solubility and low or non-toxicity.

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.

A Series of Non-Oxido VIV Complexes of Dibasic ONS Donor Ligands: Solution Stability, Chemical Transformations, Protein Interactions, and Antiproliferative Activity

A series of mononuclear non-oxido vanadium(IV) complexes, [V^IV(L^1-4)₂] (1-4), featuring tridentate bi-negative ONS chelating S-alkyl/aryl-substituted dithiocarbazate ligands H₂L^1-4, are reported. All the synthesized non-oxido V^IV compounds are characterized by elemental analysis, spectroscopy (IR, UV-vis, and EPR), ESI-MS, as well as electrochemical techniques (cyclic voltammetry). Single-crystal X-ray diffraction studies of 1-3 reveal that the mononuclear non-oxido V^IV complexes show distorted octahedral (1 and 2) or trigonal prismatic (3) arrangement around the non-oxido V^IV center. EPR and DFT data indicate the coexistence of mer and fac isomers in solution, and ESI-MS results suggest a partial oxidation of [V^IV(L^1-4)₂] to [V^V(L^1-4)₂]⁺ and [V^VO₂(L^1-4)]^-; therefore, all these three complexes are plausible active species. Complexes 1-4 interact with bovine serum albumin (BSA) with a moderate binding affinity, and docking calculations reveal non-covalent interactions with different regions of BSA, particularly with Tyr, Lys, Arg, and Thr residues. In vitro cytotoxic activity of all complexes is assayed against the HT-29 (colon cancer) and HeLa (cervical cancer) cells and compared with the NIH-3T3 (mouse embryonic fibroblast) normal cell line by MTT assay and DAPI staining. The results suggest that complexes 1-4 are cytotoxic in nature and induce cell death in the cancer cell lines by apoptosis and that a mixture of V^IV, V^V, and V^VO₂ species could be responsible for the biological activity.

A Vanadium(V) complexes derived from pyridoxal/salicylaldehyde. Interaction with CT-DNA/HSA, and molecular docking assessments

With the increasing development of metallopharmaceuticals, coordination compounds become viable alternatives for therapeutic uses. Despite the importance of platinum derivatives in this area, first-row transition metals complexes are welcome due to their characteristics. Vanadium is a promising metal in this context, as it has a range of compounds with different biological applications, including anticancer therapeutic effects. In this effort, the study of interactions between coordination compounds with deoxyribonucleic acid and with human serum albumin is fundamental. In this way, ten iminic ligands were synthesized by condensing p-substituted aromatic benzohydrazides (OH, CH₃, H, NO₂, and NH₂) with salicylaldehyde (L1As-L5As) or pyridoxal hydrochloride (L1P-L5P). These ligands have characteristics that allow the tridentate coordination of vanadium cations, leading to the formation of ten vanadium(V) complexes (C1As-C5As and C1P-C5P) with different structural features, all characterized by single-crystal X-ray diffraction, UV-Vis and infrared spectroscopies, and cyclic voltammetry. In addition, the complexes were tested for their interactions with calf thymus deoxyribonucleic acid and human serum albumin by spectroscopic assays and molecular docking calculations. These new results can contribute to further research and provide different ways to design new vanadium complexes with biological applications.

Applications of Vanadium, Niobium, and Tantalum Complexes in Organic and Inorganic Synthesis

Organometallic catalysis is a powerful strategy in chemical synthesis, especially with the cheap and low toxic metals based on green chemistry principle. Thus, the selection of the metal is particularly important to plan relevant and applicable processes. The group VB metals have been the subject of exciting and significant advances in both organic and inorganic synthesis. In this Review, we have summarized some reports from recent decades, which are about the development of group VB metals utilized in various types of reactions, such as oxidation, reduction, alkylation, dealkylation, polymerization, aromatization, protein synthesis, and practical water splitting.

Interaction with bioligands and in vitro cytotoxicity of a new dinuclear dioxido vanadium(V) complex

One centrosymmetric bis(μ-oxido)-bridged vanadium(V) dimer with molecular formula [(V^VO₂)₂(pedf)₂] (1) has been synthesized from the reaction of VOSO₄·5H₂O with a Schiff base ligand (abbreviated with pedf^-) obtained from 2-acetylpyridine and 2-furoic hydrazide in methanol. Complex 1 was characterized by elemental analysis, UV-visible (UV-Vis), Fourier-transform infrared spectra (FT-IR), cyclic voltammetry (CV), electron paramagnetic resonance spectroscopy (EPR) and electrospray ionization-mass spectrometry (ESI-MS) techniques along with single crystal X-ray diffraction (SCXRD). The FT-IR spectral data of 1 indicated the involvement of oxygen and azomethine nitrogen in coordination to the central metal ion. The crystallographic studies revealed a dinuclear oxovanadium(V) complex with the Schiff base coordinated via the ONN donor set with formation of two five-membered chelate rings resulting in a distorted octahedral geometry. The interaction of 1 with calf thymus DNA (CT-DNA) was investigated by spectroscopic measurements and results suggested that the complex binds to CT-DNA via moderate intercalative mode with a binding constant (K_b) around 10³ M^-1. In addition, the in vitro protein binding behavior was studied by fluorescence spectrophotometric method using both bovine serum albumin (BSA) and human serum albumin (HSA) and a static quenching mechanism was observed for the interaction of the complex with both albumins that occurs with a K_b in the range (5-6) × 10³ M^-1. In vitro cytotoxicity of complex 1 on lung cancer cells (A549) and human skin carcinoma cell line (A431) demonstrated that the complex had a broad-spectrum of anti-proliferative activity with IC₅₀ value of 64.2 μM and 56.2 μM.

Systemic Essential Metal and Metalloid Levels in Patients with Benign Breast Disease and Breast Cancer

The objective of the present study is evaluation of serum and hair levels of essential metals and metalloids in women with benign breast disease and breast cancer in order to define similar and distinct patterns that may mediate the link between these pathologies. A total of 310 adult women aged 20-80 years old were enrolled in the present study. Of those, 103 patients had benign (fibrocystic) breast disease, 107 patients had breast cancer (stage II), and 100 women were healthy and with absence of breast pathology. Trace metal and metalloid levels in hair and serum were evaluated by inductively coupled argon plasma mass-spectrometry (ICP-MS). The data demonstrate that breast cancer patients were characterized by significantly higher hair Cr and V levels, as well as reduced Cu and Mn content as compared to both benign breast disease patients and controls. In contrast, serum Cu levels in women with breast cancer exceeded those in the controls and benign breast disease cases. Patients with both benign and malignant breast tumors were characterized by lower serum Mn levels as compared to the control values. Serum Cu/Zn and especially Cu/Mn were found to be significantly increased in cancer patients. Significantly reduced hair and serum Se levels were noted only in women with fibrocystic disease. Based on the analysis of two biosamples, it is proposed that malignant breast tumor development is associated with the reduction of systemic Mn and Zn levels, and a concomitant elevation of Cu concentrations.

Vanadyl sulfate-enhanced oncolytic virus immunotherapy mediates the antitumor immune response by upregulating the secretion of pro-inflammatory cytokines and chemokines

Oncolytic viruses (OVs) are promising anticancer treatments that specifically replicate in and kill cancer cells and have profound immunostimulatory effects. We previously reported the potential of vanadium-based compounds such as vanadyl sulfate (VS) as immunostimulatory enhancers of OV immunotherapy. These compounds, in conjunction with RNA-based OVs such as oncolytic vesicular stomatitis virus (VSVΔ51), improve viral spread and oncolysis, leading to long-term antitumor immunity and prolonged survival in resistant tumor models. This effect is associated with a virus-induced antiviral type I IFN response shifting towards a type II IFN response in the presence of vanadium. Here, we investigated the systemic impact of VS+VSVΔ51 combination therapy to understand the immunological mechanism of action leading to improved antitumor responses. VS+VSVΔ51 combination therapy significantly increased the levels of IFN-γ and IL-6, and improved tumor antigen-specific T-cell responses. Supported by immunological profiling and as a proof of concept for the design of more effective therapeutic regimens, we found that local delivery of IL-12 using VSVΔ51 in combination with VS further improved therapeutic outcomes in a syngeneic CT26WT colon cancer model.

Ionic Dioxidovanadium(V) Complexes with Schiff-Base Ligands as Potential Insulin-Mimetic Agents-Substituent Effect on Structure and Stability

Four dioxidovanadium(V) complexes with Schiff-base ligands based on 2-hydroxybenzhydrazide with four different substituted salicylaldehydes (5-chlorosalicylaldehyde, 3,5-dichlorosalicylaldehyde, 5-nitrosalicylaldehyde, 3-bromo-5-chlorosalicylaldehyde) were synthesized and described, by using V₂O₅ and triethylamine. The single crystal X-ray structure measurements as well as elemental analyses and IR spectra confirmed the formulas of the ionic complexes with a protonated triethylamine acting as counterion, HTEA[VO₂(L)] (HL = Schiff-base ligand). The kinetic stability of the complexes at pH = 2 and 7 was discussed with respect to the neutral vanadium(V) complexes previously studied as potential insulin-mimetic agents. A correlation between the substituents in an aromatic ring of the Schiff-base ligands with crystal packing, and also with the stability of the compounds, was presented.

Toxicity of Nanocomplexes Containing Gadolinium Orthovanadate Nanoparticles and Cholesterol

Previous studies have shown the ability of nanocomplexes (NCs), which consist of nanoparticles (NPs) of orthovanadates of rare earth metals (GdYVO₄:Eu³⁺) and cholesterol, to inhibit the growth of Ehrlich's ascites carcinoma (EAC). However, the biosafety of these NCs remains unclear. Our objective was to investigate the acute and subchronic toxicity of NCs. NCs were administered to BALB/c mice in NPs concentration of 5.9; 29.5; 59.1; and 118.2 mg/kg. Acute toxicity was induced by a single administration of NCs, subchronic-by repeated daily administration of NCs for 14 days. On day 15 and on day 31 for acute and subchronic toxicity, respectively, the percentage of animal survival, body weight, condition of visceral organs, and activities of γ-glutamyl transferase (GGT) and glucose-6-phosphate dehydrogenase (G-6-PDH) were determined. It was found that administration of NCs in the concentration of 5.9 mg/kg and 29.5 mg/kg of NPs did not influence on survival of animals or have a negative impact on their performance status, morphological and quantitative characteristics of visceral organs, and activities of the GGT and G-6-PDH in the liver. For acute toxicity, the semi-lethal dose (LD₅₀) of nanocomplexes was determined (118.2 mg/kg of NPs). As to subchronic toxicity, it was found that repeated (for 14 days) administration of NCs containing 59.1 mg/kg of NPs decrease survival of animals to 50%. The coefficient of accumulation (C_acum = 7) indicates the low accumulative ability of NCs upon long-term use. Thus, from the LD₅₀ and accumulation coefficient, NCs can be referred to as low-toxic substances and used in conditionally therapeutic doses in oncological practice to develop nanostructured formulations of drugs.

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.

Relationship between structure and cytotoxicity of vanadium and molybdenum complexes with pyridoxal derived ligands

In this work four vanadium complexes (compounds 1, 2, 3 and 4) and one molybdenum complex (compound 5) with hydrazone ligands derived from pyridoxal were synthesized and characterized. All compounds are mononuclear species, two of them (compounds 3 and 5) are dioxide complexes and the other three (compounds 1, 2 and 4) monoxide complexes. The vanadium atom of the compound 3 is five-coordinated and all the other compounds have a six coordinated environment polyhedron. The poses for the potential intercalation of the compounds 2 and 3 with DNA were obtained by using AutoDock software. Optimizations were also performed at PM6-D3H4 semi-empirical level whereas the study of the nature of the interaction was carried out by means of the Energy Decomposition Analysis and the Non-Covalent Interaction index by using in both cases Density Functional Theory computations. The cytotoxicity in lung cancer cells (A549 cell line) of all the compounds was also evaluated. After 24 h of treatment, vanadium complexes showed high values of IC₅₀, between 419.93 ± 22.58 and 685.88 ± 46.55 μM. After 48 h, the results showed that the compound 3 had the lowest IC₅₀ value, 65.32 ± 9.95 μM, and the compound 2 the highest value, 375.28 ± 32.09 μM. The molybdenum complex showed the lowest IC₅₀ value at 48 h (11.22 ± 1.34 μM). The toxicity of the compounds 3, 4 and 5 was tested in vivo, using zebrafish model, and the molybdenum complex showed higher toxic effects than the studied vanadium complexes.

Binding of VIV O2+ , VIV OL, VIV OL2 and VV O2 L Moieties to Proteins: X-ray/Theoretical Characterization and Biological Implications

Vanadium compounds have frequently been proposed as therapeutics, but their application has been hampered by the lack of information on the different V-containing species that may form and how these interact with blood and cell proteins, and with enzymes. Herein, we report several resolved crystal structures of lysozyme with bound V^IV O²⁺ and V^IV OL²⁺ , where L=2,2'-bipyridine or 1,10-phenanthroline (phen), and of trypsin with V^IV O(picolinato)₂ and V^V O₂ (phen)⁺ moieties. Computational studies complete the refinement and shed light on the relevant role of hydrophobic interactions, hydrogen bonds, and microsolvation in stabilizating the structure. Noteworthy is that the trypsin-V^V O₂ (phen) and trypsin-V^IV O(OH)(phen) adducts correspond to similar energies, thus suggesting a possible interconversion under physiological/biological conditions. The obtained data support the relevance of hydrolysis of V^IV and V^V complexes in the several types of binding established with proteins and the formation of different adducts that might contribute to their pharmacological action, and significantly widen our knowledge of vanadium-protein interactions.

Successive constructions of regular tetra-, hexa- and octanuclear microporous polyoxovanadates(III) for gas adsorption

Pyrazole-assisted tetranuclear microporous polyoxovanadates(III) (POVs) (NH₄)₂K₂[V₄(μ₂-OH)₄(ox)₄(pz)₄]·9H₂O (1, ox = oxalate and pz = pyrazole) and (NH₄)₂Na₂[V₄(μ₂-OH)₄(ox)₄(4-mpz)₄]·7H₂O (2, 4-mpz = 4-methylpyrazole) have been constructed in reduced media, along with their triazole neutral hexa- and octanuclear products K₂[V₆(μ₂-OH)₆(ox)₆(Hdatrz)₆]Cl₂·29.5H₂O (3) and [V₈(μ₂-OH)₈(SO₃)₈(Hdatrz)₈]·38H₂O (4, Hdatrz = 1H-1,2,4-triazole-3,5-diamine) successively. Both polyanionic structures of 1 and 2 share similar inorganic building blocks that consist of regular {V₄(μ₂-OH)₄} skeletons with an inner diameter of 2.8 Å, while a paddle wheel-shaped cluster 3 contains a {V₆(μ₂-OH)₆} skeleton with two chlorides encapsulated around the center of the ring, occupying a hole of 3.7 Å. An interesting isolated intrinsic polyoxometalate-based metal-organic framework (POMOF) 4 exists as an octanuclear petaloid-like skeleton {V₈(μ₂-OH)₈(SO₃)₈} with an inner diameter of 5.2 Å. Bond valence sum calculations manifest that all V ions have severely reduced +3 oxidation states in 1-4, which are supported by charge balance, structural and magnetic data. Moreover, gas adsorptions indicate that 1, 2 and 4 can adsorb CO₂ and O₂ more favorably than N₂, CH₄ and H₂ gases. Compared with 1 and 2, due to the functionalization of microchannels with Lewis base amino and hydroxy groups and uncoordinated azolate N-donors inside POMOF 4, it should have notable affinities toward CO₂ adsorption.

Insights into the transformation of VO2+ motif to VO3+, V2O34+ and VO2+ motifs and their interconversion along with a detailed mechanistic study of their anti-cancer activity in SiHa cervical cancer cells

The basic criteria for the formation of complexes with VO³⁺, V₂O₃⁴⁺ and VO₂⁺ motifs from the VO²⁺ motif and their interconversion were explored utilizing two multidentate O,N-donor hydrazone ligands namely, E-2-Hydroxy-N'-(4-oxopentan-2-ylidine)benzohydrazide (H₃L¹) and E-2-Hydroxy-N'-(4-oxo-4-phenylbutan-2-ylidine)benzohydrazide (H₃L²), derived from the condensation of 2-hydroxybenzoylhydrazide with acetylacetone and benzoylacetone respectively. Under aerobic condition, the possibility of forming complexes with different motifs in different solvents with varying pH was examined theoretically by computational methods with results that were verified experimentally. This study reveals that under aerobic condition, complexes with VO³⁺ (1,2) and V₂O₃⁴⁺ (3, 4) motifs were formed in protic CH₃OH and neutral CHCl₃ solvent respectively while the formation of complexes (5-14) with VO₂⁺ motif required protic CH₃OH solvent and higher pH (≥ 7). Interconversion of VO³⁺, V₂O₃⁴⁺ and VO₂⁺ motifs are associated with specific acid-base equilibria, substantiated by ⁵¹V NMR titrations. Complexes containing these three motifs exhibited promising in vitro anticancer activity in SiHa cervical cancer cells without affecting healthy cells; among them complexes (5-14) with VO₂⁺ motif are more potent. A detailed systematic mechanistic study was carried out, utilizing the two most potent complexes 5 and 6 (IC₅₀ = 13, 6 μM respectively), which indicates that cytotoxicity and anti-proliferative activity of these complexes are manifested through oxidative stress induced apoptotic pathways (caspase mediated).

Biological Properties of Transition Metal Complexes with Metformin and Its Analogues

Metformin is a widely prescribed medication for the treatment and management of type 2 diabetes. It belongs to a class of biguanides, which are characterized by a wide range of diverse biological properties, including anticancer, antimicrobial, antimalarial, cardioprotective and other activities. It is known that biguanides serve as excellent N-donor bidentate ligands and readily form complexes with virtually all transition metals. Recent evidence suggests that the mechanism of action of metformin and its analogues is linked to their metal-binding properties. These findings prompted us to summarize the existing data on the synthetic strategies and biological properties of various metal complexes with metformin and its analogues. We demonstrated that coordination of biologically active biguanides to various metal centers often resulted in an improved pharmacological profile, including reduced drug resistance as well as a wider spectrum of activity. In addition, coordination to the redox-active metal centers, such as Au(III), allowed for various activatable strategies, leading to the selective activation of the prodrugs and reduced off-target toxicity.

Advantageous Reactivity of Unstable Metal Complexes: Potential Applications of Metal-Based Anticancer Drugs for Intratumoral Injections

Injections of highly cytotoxic or immunomodulating drugs directly into the inoperable tumor is a procedure that is increasingly applied in the clinic and uses established Pt-based drugs. It is advantageous for less stable anticancer metal complexes that fail administration by the standard intravenous route. Such hydrophobic metal-containing complexes are rapidly taken up into cancer cells and cause cell death, while the release of their relatively non-toxic decomposition products into the blood has low systemic toxicity and, in some cases, may even be beneficial. This concept was recently proposed for V(V) complexes with hydrophobic organic ligands, but it can potentially be applied to other metal complexes, such as Ti(IV), Ga(III) and Ru(III) complexes, some of which were previously unsuccessful in human clinical trials when administered via intravenous injections. The potential beneficial effects include antidiabetic, neuroprotective and tissue-regenerating activities for V(V/IV); antimicrobial activities for Ga(III); and antimetastatic and potentially immunogenic activities for Ru(III). Utilizing organic ligands with limited stability under biological conditions, such as Schiff bases, further enhances the tuning of the reactivities of the metal complexes under the conditions of intratumoral injections. However, nanocarrier formulations are likely to be required for the delivery of unstable metal complexes into the tumor.

An Overview of Vanadium and Cell Signaling in Potential Cancer Treatments

Vanadium is an ultratrace element present in higher plants, animals, algae, and bacteria. In recent years, vanadium complexes have been studied to be considered as a representative of a new class of nonplatinum metal anticancer drugs. Nevertheless, the study of cell signaling pathways related to vanadium compounds has scarcely been reported on and reviewed thus far; this information is highly critical for identifying novel targets that play a key role in the anticancer activity of these compounds. Here, we perform a review of the activity of vanadium compounds over cell signaling pathways on cancer cells and of the underlying mechanisms, thereby providing insight into the role of these proteins as potential new molecular targets of vanadium complexes.

Tris(2-Pyridylmethylamine)V(O)2 Complexes as Counter Ions of Diprotonated Decavanadate Anion: Potential Antineoplastic Activity

The synthesis and theoretical-experimental characterization of a novel diprotanated decavanadate is presented here due to our search for novel anticancer metallodrugs. Tris(2-pyridylmethyl)amine (TPMA), which is also known to have anticancer activity in osteosarcoma cell lines, was introduced as a possible cationic species that could act as a counterpart for the decavanadate anion. However, the isolated compound contains the previously reported vanadium (V) dioxido-tpma moieties, and the decavanadate anion appears to be diprotonated. The structural characterization of the compound was performed by infrared spectroscopy and single-crystal X-ray diffraction. In addition, DFT calculations were used to analyze the reactive sites involved in the donor-acceptor interactions from the molecular electrostatic potential maps. The level of theory mPW1PW91/6–31G(d)-LANL2DZ and ECP = LANL2DZ for the V atom was used. These insights about the compounds’ main interactions were supported by analyzing the noncovalent interactions utilizing the AIM and Hirshfeld surfaces approach. Molecular docking studies with small RNA fragments were used to assess the hypothesis that decavanadate’s anticancer activity could be attributed to its interaction with lncRNA molecules. Thus, a combination of three potentially beneficial components could be evaluated in various cancer cell lines.

Polyoxovanadates as new P-glycoprotein inhibitors: insights into the mechanism of inhibition

A promising strategy to overcome multidrug resistance is the use of inhibitors of ABC drug transporters. For this reason, we evaluated the polyoxovanadates (POVs) [V₁₀ O₂₈ ]^6- (V₁₀ ), [H₆ V₁₄ O₃₈ (PO₄ )]^5- (V₁₄ ), [V₁₅ O₃₆ Cl]^6- (V₁₅ ) and [V₁₈ O₄₂ I]^7- (V₁₈ ) as inhibitors of three major multidrug resistance-linked ABC transporters: P-glycoprotein (P-gp), ABCG2 and MRP1. All of the POVs selectively inhibited P-gp. V₁₀ and V₁₈ were the two most promising compounds, with IC₅₀ values of transport inhibition of 25.4 and 22.7 µm, respectively. Both compounds inhibited P-gp ATPase activity, with the same IC₅₀ value of 1.26 µm. V₁₀ and V₁₈ triggered different conformational changes in the P-gp protein with time-dependent inhibition, which was confirmed using the synthesized salt of V₁₀ with rhodamine B, RhoB-V₁₀ . The hydrophilic nature of POVs supports the hypothesis that these compounds target an unusual ligand-binding site, opening new possibilities in the development of potent modulators of ABC transporters.

Nanomedicines in the treatment of colon cancer: a focus on metallodrugs

Worldwide, colon cancer (CC) represents the fourth most common type of cancer and the fifth major cause of cancer-associated deaths. Surgical resection is considered the standard therapeutic choice for CC in early stages. However, in latter stages of the disease, adjuvant chemotherapy is essential for an appropriate management of this pathology. Metal-based complexes displaying cytotoxic properties towards tumor cells emerge as potential chemotherapeutic options. One metallodrug, oxaliplatin, was already approved for clinical use, playing an important role in the treatment of CC patients. Unfortunately, most of the newly designed metal-based complexes exhibit lack of selectivity against cancer cells, low solubility and permeability, high dose-limiting toxicity, and emergence of resistances. Nanodelivery systems enable the incorporation of metallodrugs at adequate payloads, solving the above-referred drawbacks. Moreover, drug delivery systems, depending on their physicochemical properties, are able to release the incorporated material preferentially at affected tissues/organs, enhancing the therapeutic activity in vivo, with concomitant fewer side effects. In this review, the general features and therapeutic management of CC will be addressed, with a special focus on preclinical or clinical studies using metal-based compounds. Furthermore, the use of different nanodelivery systems will also be described as tools to potentiate the therapeutic index of metallodrugs for the management of CC.

Exploring Anticancer Activities and Structure-Activity Relationships of Binuclear Oxidovanadium(IV) Complexes

Dimeric mixed-ligand oxidovanadium complexes [V₂O₂(1,3-pdta)(bpy)₂]·9H₂O (1) and [V₂O₂(1,3-pdta)(phen)₂]·6H₂O (2) feature a symmetric binuclear structure bridged by 1,3-pdta, which is different from our previous reported asymmetric binuclear complex [V₂O₂(edta)(phen)₂]·11H₂O (3).In this study, a wide range of analytical techniques were carried out to fully characterize the complexes 1 and 2 and further investigate their structural stabilities. Density functional theory calculations of 1 and 2 also suggest that they might have good reactivity with biomolecules as anticancer agents. To assess and screen the antitumor activities of compounds 1-3 together with their four corresponding monomeric complexes [VO(ida)(phen)], [VO(ida)(bpy)], [VO(OH)(phen)₂]Cl, and [VO(Hedta)]^-, we have performed in vitro experiments with hepatocellular carcinoma HepG2 and SMMC-7721 cell lines by MTT analyses. Complex 2 was found to have the highest inhibitory potency against the growth of HepG2 and SMMC-7721 cells (IC₅₀ = 2.07 ± 0.72 μM for HepG2; 13.00 ± 3.06 μM for SMMC-7721) compared to other compounds. The structure-activity relationship studies showed that the antitumor effect of compound 2 is higher than that of other compounds. After studying the monomeric compounds of 1-3, their effects were also ranked. Moreover, complex 2 displayed stronger binding affinity toward calf thymus DNA (K_b = 5.71 × 10⁴ M^-1) and cleavage activities than the other complexes (K_b = 1.34 × 10⁴ M^-1 for 1 and 5.22 × 10⁴ M^-1 for 3, respectively). We further extended the cellular mechanisms of drug action and found that 2 could block DNA synthesis and cell division of HepG2 and 7721 cells and further induce apoptosis by flow cytometry assays. In short, these results indicate that binuclear oxidovanadium compounds could have potential as simple, effective, and safe antitumor agents.

Spectroscopic/Computational Characterization and the X-ray Structure of the Adduct of the VIVO-Picolinato Complex with RNase A

The structure, stability, and enzymatic activity of the adduct formed upon the reaction of the V-picolinato (pic) complex [VIVO(pic)2(H2O)], with an octahedral geometry and the water ligand in cis to the V═O group, with the bovine pancreatic ribonuclease (RNase A) were studied. While electrospray ionization-mass spectrometry, circular dichroism, and ultraviolet-visible absorption spectroscopy substantiate the interaction between the metal moiety and RNase A, electron paramagnetic resonance (EPR) allows us to determine that a carboxylate group, stemming from Asp or Glu residues, and imidazole nitrogen from His residues are involved in the V binding at acidic and physiological pH, respectively. Crystallographic data demonstrate that the VIVO(pic)2 moiety coordinates the side chain of Glu111 of RNase A, by substituting the equatorial water molecule at acidic pH. Computational methods confirm that Glu111 is the most affine residue and interacts favorably with the OC-6-23-Δ enantiomer establishing an extended network of hydrogen bonds and van der Waals stabilizations. By increasing the pH around neutrality, with the deprotonation of histidine side chains, the binding of the V complex to His105 and His119 could occur, with that to His105 which should be preferred when compared to that to the catalytically important His119. The binding of the V compound affects the enzymatic activity of RNase A, but it does not alter its overall structure and stability.

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).

Water-Soluble Dioxidovanadium(V) Complexes of Aroylhydrazones: DNA/BSA Interactions, Hydrophobicity, and Cell-Selective Anticancer Potential

Five new anionic aqueous dioxidovanadium(V) complexes, [{VO₂L^1,2}A(H₂O)_n]_α (1-5), with the aroylhydrazone ligands pyridine-4-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)hydrazide (H₂L¹) and furan-2-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)hydrazide (H₂L²) incorporating different alkali metals (A = Na⁺, K⁺, Cs⁺) as countercation were synthesized and characterized by various physicochemical techniques. The solution-phase stabilities of 1-5 were determined by time-dependent NMR and UV-vis, and also the octanol/water partition coefficients were obtained by spectroscopic techniques. X-ray crystallography of 2-4 confirmed the presence of vanadium(V) centers coordinated by two cis-oxido-O atoms and the O, N, and O atoms of a dianionic tridentate ligand. To evaluate the biological behavior, all complexes were screened for their DNA/protein binding propensity through spectroscopic experiments. Finally, a cytotoxicity study of 1-5 was performed against colon (HT-29), breast (MCF-7), and cervical (HeLa) cancer cell lines and a noncancerous NIH-3T3 cell line. The cytotoxicity was cell-selective, being more active against HT-29 than against other cells. In addition, the role of hydrophobicity in the cytotoxicity was explained in that an optimal hydrophobicity is essential for high cytotoxicity. Moreover, the results of wound-healing assays indicated antimigration in case of HT-29 cells. Remarkably, 1 with an IC₅₀ value of 5.42 ± 0.15 μM showed greater activity in comparison to cisplatin against the HT-29 cell line.

Thermodynamic Study of Oxidovanadium(IV) with Kojic Acid Derivatives: A Multi-Technique Approach

The good chelating properties of hydroxypyrone (HPO) derivatives towards oxidovanadium(IV) cation, VIVO2+, constitute the precondition for the development of new insulin-mimetic and anticancer compounds. In the present work, we examined the VIVO2+ complex formation equilibria of two kojic acid (KA) derivatives, L4 and L9, structurally constituted by two kojic acid units linked in position 6 through methylene diamine and diethyl-ethylenediamine, respectively. These chemical systems have been characterized in solution by the combined use of various complementary techniques, as UV-vis spectrophotometry, potentiometry, NMR and EPR spectroscopy, ESI-MS spectrometry, and DFT calculations. The thermodynamic approach allowed proposing a chemical coordination model and the calculation of the complex formation constants. Both ligands L4 and L9 form 1:1 binuclear complexes at acidic and physiological pHs, with various protonation degrees in which two KA units coordinate each VIVO2+ ion. The joined use of different techniques allowed reaching a coherent vision of the complexation models of the two ligands toward oxidovanadium(IV) ion in aqueous solution. The high stability of the formed species and the binuclear structure may favor their biological action, and represent a good starting point toward the design of new pharmacologically active vanadium species.

Vanadium(V) Complexes with Siderophore Vitamin E-Hydroxylamino-Triazine Ligands

Novel vitamin E chelate siderophore derivatives and their VV and FeIII complexes have been synthesised and the chemical and biological properties have been evaluated. In particular, the α- and δ-tocopherol derivatives with bis-methyldroxylamino triazine (α-tocTHMA) and (δ-tocDPA) as well their VV complexes, [V2VO3(α-tocTHMA)2] and [V2IVO3(δ-tocTHMA)2], have been synthesised and characterised by infrared (IR), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) and ultra violet-visible (UV-Vis) spectroscopies. The dimeric vanadium complexes in solution are in equilibrium with their respefrctive monomers, H2O + [V2VO2(μ-O)]4+ = 2 [VVO(OH)]2+. The two amphiphilic vanadium complexes exhibit enhanced hydrolytic stability. EPR shows that the complexes in lipophilic matrix are mild radical initiators. Evaluation of their biological activity shows that the compounds do not exhibit any significant cytotoxicity to cells.

Ternary Copper Complex of L-Glutamine and Phenanthroline as Counterions of Cyclo-Tetravanadate Anion: Experimental–Theoretical Characterization and Potential Antineoplastic Activity

Over the last decade, therapeutic metallodrugs have become substantially effective in the treatment of cancer. Thus, developing new effective anticancer drugs is a significant research area against the continuing increase in cancers worldwide. In the search for heterobimetallic prodrugs containing V/Cu, a new cyclo-tetravanadate was synthesized and characterized by UV-visible and FTIR spectroscopies and single-crystal X-ray diffraction. L-Glutamine and 1,10-phenanthroline allow the crystallization of [Cu(L-Gln)(phen)(H2O)]4[V4O12]∙8(H2O) (1), in which the cyclo-tetravanadate acts as a free anion. Density functional theory (DFT) calculations were carried out to characterize the frontier molecular orbitals and molecular electrostatic potential. Global reactivity indexes were calculated and analyzed to give insight into the cyclo-tetravanadate anion and complex counterions interactions. Also, using Bader’s theory of atoms in molecules (AIM), non-covalent interactions were analyzed. Docking analysis with the Casiopeina-like complex resulting from the hydrolysis of compound 1 provided insights into these complex potential anticancer activities by interacting with DNA/tRNA via H-bonds and hydrophobic interactions. The release of both components could act together or separately, acting as prodrugs with potential dual antineoplastic activities.

Vanadyl nanocomplexes enhance photothermia-induced cancer immunotherapy to inhibit tumor metastasis and recurrence

Conventional photothermal therapy (PTT) is insufficient to induce a strong and potent anti-tumor immune response. Herein, we present a vanadyl nanocomplex, which simultaneously serves as a photothermal agent (PTA) and an immunogenic cell death (ICD) inducer to enhance the anti-tumor immunity of PTT. The vanadyl nanocomplex (STVN) is constructed via facile one-step coordination assembly under ambient conditions. STVN not only has a strong and stable photothermal effect under near-infrared (NIR) irradiation, but also can cause severe endoplasmic reticulum (ER) stress by itself, leading to ICD and activating the systemic immune responses. In the absence of any adjuvants, NIR-irradiated STVN almost completely ablates primary tumors and simultaneously inhibits distant tumors in mice bearing bilateral melanoma. Meanwhile, the intratumorally injected STVN combined with NIR effectively suppressed melanoma lung metastasis as well as tumor recurrence, displaying that local STVN-mediated PTT could trigger a systemic anti-tumor immunity. Therefore, STVN, as a novel immunogenicity-enhanced PTA, affords a "one stone two birds" strategy for improved photothermia-induced cancer immunotherapy.

Vanadium-Flavonoid Complexes: A Promising Class of Molecules for Therapeutic Applications

Several reports have revealed the superior biological activity of metal ion-flavonoid complexes when compared with the parent flavonoid. Among the different metal ions explored, vanadium and its compounds are in the forefront because of their anticancer and antidiabetic properties. However, the toxicity of vanadium-based ions and their inorganic derivatives limits their therapeutic applications. Complexation of vanadium with flavonoids not only reduces its adverse effects but also augments its biological activity. This Review discusses the nature of coordination in vanadium-flavonoid complexes, their structure-activity correlations, with special emphasis on their therapeutic activities. Several investigations suggest that the superior biological activity of vanadium complexes arise because of their ability to regulate metabolic pathways distinct from those acted upon by vanadium alone. These studies serve to decipher the underlying molecular mechanism of vanadium-flavonoid complexes that can be explored further for generating a series of novel compounds with improved pharmacological and therapeutic performance.