Suppression of cell proliferation, induction of apoptosis and cell cycle arrest: chemopreventive activity of vanadium in vivo and in vitro

Harnessing the Sulfur-for-Oxygen Shift: A Magic Bullet for Dynamic Photophysical and Anticancer Activities of Indole-Barbituric Acid Construct

The development of small molecule-based drugs emerged as a cornerstone of modern drug discovery. Structural activity relationship (SAR) studies in medicinal chemistry are crucial for lead optimization, where a subtle change in the substituent can significantly alter its binding affinity with the biological target. Herein, a highly efficient single-atom substitution (SAS) approach has been developed, where sulfur for oxygen strategy is utilized as a powerful molecular editing technique to identify N-vinyl Indole-thiobarbituric acid (6 a) as a novel small molecule-based scaffold with tunable photophysical and antiproliferative activities. A series of NIR-emitting indole-barbituric/thiobarbituric acid conjugates exhibiting aggregation-induced emission (AIE) were prepared, where the replacement of oxygen for sulfur strategy emerged as a magic bullet. On the evaluation of photophysical properties and chemopreventive efficacies, a significant improvement in the absorption and emission profile, cellular uptake, and antiproliferative activity was noted for sulfur counterparts. From the pool of the molecules, the lead molecule 6 a unveils a 55 nm emission shift, 142-fold increased anticancer profile, and ~4-fold elevated cellular uptake. Furthermore, the colocalization experiment unravels the nuclear localization of 6 a, where it causes severe DNA damage, arrests the cell cycle in the G2/M phase, and leads to the activation of p53-mediated apoptosis. Our experimental findings represent 6 a as a potential lead molecule possessing excellent anticancer potency in the HCT 116 cell line and HCT 116-derived 3D spheroid model.

Temozolomide alleviates breast carcinoma via the inhibition of EGFR/ERK/ MMP-1 pathway with induction of apoptotic events

PURPOSE

To evaluate the chemotherapeutic activity of temozolomide counter to mammary carcinoma.

METHODS

In-vitro anticancer activity has been conducted on MCF7 cells, and mammary carcinoma has been induced in Wistar rats by introduction of 7, 12-Dimethylbenz(a)anthracene (DMBA), which was sustained for 24 weeks. Histopathology, immunohistochemistry, cell proliferation study and apoptosis assay via TUNEL method was conducted to evaluate an antineoplastic activity of temozolomide in rat breast tissue.

RESULTS

IC50 value of temozolomide in MCF7 cell has been obtained as 103 μM, which demonstrated an initiation of apoptosis. The temozolomide treatment facilitated cell cycle arrest in G2/M and S phase dose dependently. The treatment with temozolomide suggested decrease of the hyperplastic abrasions and renovation of the typical histological features of mammary tissue. Moreover, temozolomide therapy caused the downregulation of epidermal growth factor receptor, extracellular signal-regulated kinase, and metalloproteinase-1 expression and upstream of p53 and caspase-3 proliferation to indicate an initiation of apoptotic events.

CONCLUSIONS

The occurrence of mammary carcinoma has been significantly decreased by activation of apoptotic pathway and abrogation of cellular propagation that allowable for developing a suitable mechanistic pathway of temozolomide in order to facilitate chemotherapeutic approach.

Metal exposure and breast cancer among Northern Mexican women: assessment of genetic susceptibility

This study aims to assess breast cancer (BC) association with metals and whether polymorphisms in CYP1A1, CYP1B1, GSTM1 and GSTT1 act as confounders or as modifiers of those relationships. We performed a secondary analysis of 499 histologically confirmed BC cases and the same number of age-matched population controls. We measured urinary concentrations of 18 metals with mass spectrometry. We determined the genetic variants of interest by allelic discrimination and multiplex PCR. After adjusting for covariates, we found BC negatively associated with arsenic, barium, cobalt, copper, magnesium, molybdenum and vanadium concentrations and positively with those of caesium, manganese, tin and thallium. Most associations remained after stratifying by the genetic variants. We identified that polymorphisms in CYP1B1, CYP1A1 and GSTM1 genes interacted with some metals on BC: interaction p-values CYP1B1 G119T × antimony= 0.036, CYP1B1 G119T × cobalt <0.001, CYP1B1 G119T × tin= 0.032, CYP1A1 A4889G × aluminium= 0.018, CYP1A1 A4889G × arsenic= 0.031, CYP1A1 A4889G × nickel= 0.036, CYP1A1 A4889G × vanadium= 0.031 and GSTM1 deletion × barium= 0.035. Exposure to various individual metals, along with genetic characteristics may contribute to BC development. Further studies are warranted to confirm our results.

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.

Reproductive Hormones Imbalance, Germ Cell Apoptosis, Abnormal Sperm Morphophenotypes and Ultrastructural Changes in Testis of African Giant Rats (Cricetomys gambianus) Exposed to Sodium Metavanadate Intoxication

Environmental exposure to vanadium has been on the increase in recent time. This metal is a known toxicant. The current study was conducted to investigate the reproductive toxicity of sodium metavanadate (SMV) in male African giant rats. Administration of SMV was done intraperitoneally daily for 14 consecutive days at a dosage of 3 mg/kg body weight. Sterile water was administered to the control group. Serum reproductive hormones, sperm reserve and quality as well as testicular ultrastructural changes following SMV treatment were analysed. Results showed SMV-exposed AGR group had statistically decreased concentrations of testosterone (4.7 ng/ml), FSH (3.4 IU/L) and LH (3.8 IU/L). Also, SMV-treated group had statistically decreased sperm motility and mass activity with increased percentage of abnormal morphophenotypes of spermatozoa and upregulation of P53 immunopositive cells. Ultrastructural study revealed vacuolation of germ and Sertoli cells cytoplasm and nucleus, and mitochondrial swelling and vacuolations were also observed. There was severe disintegration of the seminiferous tubules, atrophy and degeneration of myeloid cells and apoptosis of the Leydig, Sertoli and germ cells. In conclusion, intraperitoneal SMV exposure exerts severe adverse effects on some serum reproductive hormones, reduction in the sperm reserve and quality, apoptosis and degenerative changes of the Leydig, Sertoli and germ cells which can lead to infertility.

Silymarin inhibits the progression of Ehrlich solid tumor via targeting molecular pathways of cell death, proliferation, angiogenesis, and metastasis in female mice

BACKGROUND

Plant-derived phytochemicals have been reported to exert anticancer activity. This study investigated the antitumor role of silymarin (Silybum marianum) (SMN) and its molecular targets in Ehrlich solid tumor xenografts in vivo.

METHODS AND RESULTS

Female Swiss albino mice were divided into three groups (of five animals each) that were engrafted with Ehrlich tumor (ET) cells with or without SMN treatment. The 3rd groups treated with DMSO only vehicle control group. A significant reduction in animal body mass and tumor volume/weight were observed in xenografted mice treated with SMN. SMN modulated oxidative stress in tumors while enhancing the antioxidant levels in mouse serum. SMN activated both mitochondrial and death receptor-related apoptosis pathways and induced cell cycle arrest, marked by a significant downregulation of cyclin D1 in SMN-treated tumors. Significant decreases in RNA content and protein expression levels of Ki-67 and proliferating cell nuclear antigen were observed in ET cells. Additionally, SMN downregulated vascular endothelial growth factor and nuclear factor-kappa B levels indicating anti-angiogenesis activity of this agent. SMN upregulated the expression of E-cadherin in tumor tissue suggesting, that SMN has potential ability to inhibit metastasis. Tumor tissue from SMN-treated animals showed a remarkable degeneration and reduction in the neoplastic cell density.

CONCLUSIONS

The anticancer effect was associated with apparent apoptosis in neoplastic cells with abundance of multifocal necrotic areas. SMN was found to inhibit ET growth via enhancing apoptosis, inhibition of cell division and reduction in angiogenesis in vivo. Hypothetical scheme of SMN antitumor effects (mechanism of signaling) in solid ET in vivo. SMN anticancer effect may be mediated by molecular mediators that affect proliferation, cell cycle activity, apoptotic pathways, angiogenesis, and metastasis.

Alternariol alleviates breast carcinoma by inhibiting cellular proliferation correlated with increased apoptotic events in rats

The breast cancer is most frequently diagnosed cancer in the women worldwide. Our study investigated the anticancer effect of alternariol, a secondary metabolite originated from endophytic fungi, against DMBA induced breast carcinoma on Wistar rats. The toxicity study investigated the LD50 and the subsequent doses of alternariol for the carcinogenic study. The breast cancer was developed in rats via induction of DMBA (5 mg/kg, i.v.) and the carcinogenic study was continued for 24 weeks. The induction of breast cancer and the chemotherapeutic effect of alternariol were assessed through histopathological analysis of rat mammary tissue, followed by immunohistochemical analysis, cell proliferation assay and apoptosis assay by TUNEL method. The result showed that alternariol therapy decreased the hyperplastic lesions of mammary tissue and restored the normal histopathological characteristics of breast tissue. Furthermore, alternariol treatment downregulated the expression of carcinogenic markers such as PI3K and Akt increased the expression of apoptotic markers including p53, caspase-3 and Bax. Alternariol therapy also decreased the cellular proliferation and enhanced the apoptotic events. In conclusion, the breast cancer progression was significantly reduced via induction of apoptotic events and inhibition of cell propagation which allowed constructing of suitable mechanism for alternariol mediated chemotherapeutic approach.

Apple polyphenol phloretin complexed with ruthenium is capable of reprogramming the breast cancer microenvironment through modulation of PI3K/Akt/mTOR/VEGF pathways

Our recent investigation directed to synthesize a novel ruthenium-phloretin complex accompanied by the study of antioxidant in addition to DNA binding capabilities, to determine the chemotherapeutic activity against breast carcinoma in vitro and in vivo. Ruthenium-phloretin complex was synthesized and characterized by different spectroscopic methods. The complex was further investigated to determine its efficacy in both MCF-7 and MDA-MB-231 human carcinoma cell lines and finally in an in vivo model of mammary carcinogenesis induced by DMBA in rats. Our studies confirm that the chelation of the metal and ligand was materialize by the 3-OH and 9-OH functional groups of the ligand and the complex is found crystalline and was capable of intercalating with CT-DNA. The complex was capable of reducing cellular propagation and initiate apoptotic events in MCF-7 and MDA-MB-231 breast carcinoma cell lines. Ruthenium-phloretin complex could modulate p53 intervene apoptosis in the breast carcinoma, initiated by the trail of intrinsic apoptosis facilitated through Bcl2 and Bax and at the same time down regulating the PI3K/Akt/mTOR pathway coupled with MMP9 regulated tumor invasive pathways. Ruthenium-phloretin chemotherapy could interrupt, revoke or suspend the succession of breast carcinoma by altering intrinsic apoptosis along with the anti-angiogenic pathway.

Vanadium oxides modify the expression levels of the p21, p53, and Cdc25C proteins in human lymphocytes treated in vitro

In vitro assays have demonstrated that vanadium compounds interact with biological molecules similar to protein kinases and phosphatases and have also shown that vanadium oxides decrease the proliferation of cells, including human lymphocytes; however, the mechanism, the phase in which the cell cycle is delayed and the proteins involved in this process are unknown. Therefore, we evaluated the effects of vanadium oxides (V₂ O₃ , V₂ O₄ and V₂ O₅ ) in human lymphocyte cultures (concentrations of 2, 4, 8, or 16 μg/ml) on cellular proliferation and the levels of the p53, p21 and Cdc25C proteins. After 24 h of treatment with the different concentrations of vanadium oxides, the cell cycle phases were determined by evaluating the DNA content using flow cytometry, and the levels of the p21, p53 and Cdc25C proteins were assessed by Western blot analysis. The results revealed that the DNA content remained unchanged in every phase of the cell cycle; however, only at high concentrations did protein levels increase. Although, according to previous reports, vanadium oxides induce a delay in proliferation, DNA analysis did not show this occurring in a specific cell cycle phase. Nevertheless, the increases in p53 protein levels may cause this delay.

Effects of co-administration of arsenic trioxide and Schiff base oxovanadium complex on the induction of apoptosis in acute promyelocytic leukemia cells

Acute promyelocytic leukaemia (APL) is commonly treated with arsenic trioxide (As2O3) that has many side effects. Given the increasing trend of studies on beneficial therapeutic properties of synthetic compounds containing vanadium, the present study sought to use Schiff base oxovanadium complex to reduce the needed concentration of arsenic trioxide. The HL-60 cell line, which is a model of APL, was selected and the effects of arsenic trioxide and Schiff base oxovanadium complex were individually and simultaneously evaluated on the cell viability by the MTT assay. Flow cytometry and Real-time RT-PCR were also performed to investigate the rate of apoptosis and the expression of P53 and P21 genes, respectively. The IC50 of arsenic trioxide and Schiff base oxovanadium complex on Hl-60 cells was 8.37 ± 0.36 µM and 34.12 ± 1.52 µg/ml, respectively. At the simultaneous administration of both compounds, the maximum decrease in the cell viability was seen in co-administration of 40 µg/ml of Schiff base oxovanadium complex and 0.001 µM of arsenic trioxide. Real-time RT-PCR indicated that the co-administration of Schiff base oxovanadium complex 40 µg/ml and arsenic trioxide 0.001 µM could increase the expression of P53 and P21 genes by 3.76 ± 0.19 and 6.57 ± 1.29 fold change, respectively to the control sample. The flow cytometry studies also indicated that this co-administration could induce apoptosis up to 67% ± 0.9% significantly higher than the control sample. The use of Schiff base oxovanadium complex could significantly reduce the required dose of arsenic trioxide to induce apoptosis in HL-60 cells.

A Novel Ruthenium-Fluvastatin Complex Downregulates SNCG Expression to Modulate Breast Carcinoma Cell Proliferation and Apoptosis via Activating the PI3K/Akt/mTOR/VEGF/MMP9 Pathway

Breast cancer is the most common cause of malignancy and cancer-related morbidity and death worldwide that requests effective and safe chemotherapy. Evaluation of metallodrug-based anticancer agents and statins as chemotherapeutics with fewer side effects is a largely unexplored research field. Synthesis and characterization of the ruthenium-fluvastatin complex were achieved using multiple spectroscopic techniques and thus further examined to evaluate its chemotherapeutic prospects in both MDA-MB-231 and MCF-7 cancer lines and eventually in vivo models of DMBA-induced mammary carcinogenesis in rodents. Our studies indicate that the metal and ligand chelation was materialized by the ligand's functional groups of carbonyl (=O) oxygen and hydroxyl (-OH), and the complex has been observed to be crystalline and able to chelate with CT-DNA. The complex was able to reduce cell proliferation and activate apoptotic events in breast carcinoma cell lines MCF-7 and MDA-MB-231. In addition, the complex was able to modify p53 expressions to interfere with apoptosis in the carcinoma of the breast, stimulated by the intrinsic apoptotic path assisted by Bcl2 and Bax in vivo, yet at the same point, controlling the PI3K/Akt/mTOR/VEGF pathway, as obtained from western blotting, correlates with the MMP9-regulated tumor mechanisms. Our research reveals that ruthenium-fluvastatin chemotherapy may disrupt, rescind, or interrupt breast carcinoma progression by modifying intrinsic apoptosis as well as the antiangiogenic cascade, thereby taking the role of a potential candidate in cancer therapy for the immediate future.

Bavachinin mitigates DMH induced colon cancer in rats by altering p53/Bcl2/BAX signaling associated with apoptosis

Bavachinin is a flavanone obtained from the Chinese herb, Fructus Psoraleae. Flavonoids and flavanones are recognized as cancer preventive agents. We investigated the anticancer properties of bavachinin using a model of dimethylhydrazine (DMH and dextran sodium sulfate (DSS) induced rat colon cancer. We investigated aberrant crypt foci (ACF), hyperplastic lesions, catalase (CAT), superoxide dismutase (SOD) and glutathione (GST) levels in Wistar rats. Expression of cancer biomarkers including IL-6, p53, Bcl2 and BAX was investigated. We found that bavachinin administered to rats re-established the colonic crypts that were damaged by DMH and prevented progression of the cancer.

Anticancer effect of sodium metavanadate on murine breast cancer both in vitro and in vivo

Sodium metavanadate (NaVO₃) exhibits important physiological effects including insulin-like, chemoprevention and anticancer activity. However, the effects of NaVO₃ on breast cancer and underlying mechanisms are still unclear. In this study, our results revealed that NaVO₃ was able to inhibit proliferation of murine breast cancer cells 4T1 with IC₅₀ value of 8.19 μM and 1.92 μM at 24 h and 48 h, respectively. The mechanisms underlying the inhibition activity were that NaVO₃ could increase reactive oxygen species (ROS) level in a concentration-dependent way, arrest cells at G2/M phase, diminish the mitochondrial membrane potential (MMP), finally promote the progress of apoptosis. Furthermore, NaVO₃ also exhibited a dose-dependent anticancer activity in breast cancer-bearing mice that led to the shrinkage of tumor volume (about 50%), lower microvessel density, less propagating cells and more apoptotic cells in vivo, as compared to the saline group. Therefore, NaVO₃ may act as a potential chemotherapeutic agent in breast cancer treatment.

Decrypting the Molecular Mechanistic Pathways Delineating the Chemotherapeutic Potential of Ruthenium-Phloretin Complex in Colon Carcinoma Correlated with the Oxidative Status and Increased Apoptotic Events

To explore fresh strategies in colorectal cancer (CRC) chemotherapy, we evaluated the capability of the ruthenium-phloretin complex in exterminating colon cancer by effectively addressing multiple apoptotic mechanisms on HT-29 cancer cells together with an animal model of colorectal cancer activated by 1,2-dimethylhydrazine and dextran sulfate sodium. Our current approach offers tangible evidence of the application of the ruthenium-phloretin complex in future chemotherapy. The complex triggers intrinsic apoptosis triggered by p53 and modulates the Akt/mTOR pathway along with other inflammatory biomarkers. The ruthenium-phloretin complex has been synthesized and successfully characterized by numerous spectroscopic methodologies accompanied by DPPH, FRAP, and ABTS assays assessing its antioxidant potential. Studies conducted in human cell lines revealed that the complex improved levels of p53 and caspase-3 while diminishing the activities of VEGF and mTOR, triggers apoptosis, and induces fragmentation of DNA in the HT-29 cells. Toxicity studies were conducted to identify the therapeutic doses of the novel complex in animal models. The outcomes of the in vivo report suggest that the complex was beneficial in repressing multiplicity of aberrant crypt foci as well as hyperplastic lesions and also promoted increased levels of CAT, SOD, and glutathione. In addition, the ruthenium-phloretin complex was able to control cell proliferation and boosted apoptotic outbursts in cancer cells associated with the increase in cellular response towards Bax while diminishing responses towards Bcl-2, NF-κB, and MMP-9. Our observations from the experiments deliver testament that the ruthenium-phloretin complex has the potential to act as a promising chemotherapeutic agent in colorectal cancer because it can affect the growth of ACF and hyperplastic abrasions in the colon tissues by evoking cell death.

Novel NMDA-receptor antagonists ameliorate vanadium neurotoxicity

Various NMDA-receptor antagonists have been investigated for their therapeutic potential in Alzheimer's disease with memantine shown to be safe and with relative efficacy. There is, however, need to develop novel drugs to counter tolerance and with better efficacy in ameliorating neurodegeneration. We have shown neurodegeneration in different models of vanadium-exposed mice. This study was designed to evaluate and ascertain the potency of three novel NMDA-receptor antagonists (Compounds A, B and C) to ameliorate neurodegeneration in vanadium-exposed mice. One-month-old mice (n = 6) received sterile water (control) and another group (n = 6) was treated with vanadium (3 mg/kg sodium metavanadate) intraperitoneally for 1 month. Three other groups (n = 6) received vanadium and compounds A, B and C (4.35 mg/kg, 30 mg/kg and 100 mg/kg, respectively) simultaneously for the same period. Assessment of pathologies and neurodegeneration in different brain regions was done to test the ameliorative effects of the 3 antagonists using different immunohistochemical markers. Vanadium exposure resulted in reduced calbindin expression and pyknosis of Purkinje cells, cell loss and destruction of apical dendrites with greater percentage of cytoplasmic vacuolations, morphological alterations characterized by cell clustering and multiple layering patterns in the Purkinje cell layer. In addition, the observed degeneration included demyelination, increased GFAP-immunoreactive cells and microgliosis. Simultaneous administration of the compounds to vanadium-exposed mice resulted in the preservation of cellular integrity in the same anatomical regions and restoration of the cells' vitality with reduced astroglial and microglial activation.

Mini review-vanadium-induced neurotoxicity and possible targets

Vanadium, a transition metal, ubiquitous in nature is known to have therapeutic effect as well as toxic effect. It is known to possess antidiabetic, antitumor and antiparasitic activity. However, on long term exposure, it produces neurotoxicity which may result in memory impairment. The possible mechanism known to cause neurotoxicity suggested is oxidative stress and inflammation of neuronal cells. The present review has focused on discussing the role of protein P38 mitogen-activated protein kinase and oxidative stress as possible targets to treat vanadium-induced neurotoxicity.

Sodium orthovanadate inhibits growth and triggers apoptosis of human anaplastic thyroid carcinoma cells in vitro and in vivo

Vanadium and its compounds exhibit concentration- and time-dependent anticancer effects on various types of tumor; however, the effects of sodium orthovanadate (SOV) on anaplastic thyroid carcinoma (ATC) have not yet been reported. In the present study, the anticancer effects of SOV on ATC were evaluated. In vitro experiments, including cell viability assays, plate colony formation assays, cell cycle analysis and apoptosis analysis were used to study the role of SOV in ATC. Using in vivo experiments, the effects of SOV on the growth and apoptosis of an ATC-xenograft tumor were studied by comparing the SOV-treatment with the control group. The results revealed that treatment of the human ATC cell line 8505C with SOV inhibited cell viability, induced G2/M phase cell cycle arrest, stimulated apoptosis and reduced mitochondrial membrane potential in a concentration-dependent manner. These findings were confirmed in vivo in a nude mouse ATC xenograft model. In conclusion, the present study demonstrated that SOV inhibited human ATC by regulating proliferation, cell cycle progression and apoptosis, thus suggesting that SOV may be considered a novel option for the treatment of ATC.

Vanadium Compounds as Enzyme Inhibitors with a Focus on Anticancer Effects

Vanadium salts and coordination compounds have desirable cellular anticancer effects, and although they have been investigated in detail as a potential treatment for diabetes, less attention has been given to the anticancer effects. The inhibition of some signal transduction enzymes is known, and studies of the metabolism and activation pathways both in vitro and in vivo are important for future investigations and development of vanadium's role as a new potential drug. In addition, a new approach has demonstrated that the enhancement of oncolytic viruses using vanadium salts and coordination complexes for immunotherapy is very promising. Some differences exist between this approach and current antidiabetic and anticancer studies because vanadium(iv) complexes have been found to be most potent in the latter approach, but the few compounds investigated with oncolytic viruses show that vanadium(v) systems are more effective. We conclude that recent studies demonstrate effects on signal transduction enzymes and anticancer pathways, thus suggesting potential applications of vanadium as anticancer agents in the future both as standalone treatments as well as combination therapies.

Construing the Biochemical and Molecular Mechanism Underlying the In Vivo and In Vitro Chemotherapeutic Efficacy of Ruthenium-Baicalein Complex in Colon Cancer

In pursuit of a novel approach in colon cancer therapy, we explored the ability of ruthenium baicalein complex to eradicate colon cancer by efficiently targeting various apoptotic pathways on human colon cancer cell line and on a DMH and DSS induced murine model of colorectal cancer. In this study, we provide direct proof of the chemotherapeutic potential of the ruthenium baicalein complex by activating p-53 dependent intrinsic apoptosis and modulating the AKT/mTOR and WNT/β- catenin pathways. The ruthenium baicalein complex was synthesized and its characterizations were accomplished through various spectroscopic techniques followed by assessment of antioxidant potential by DPPH, FRAP, and ABTS methods. In vitro study established that the complex increased p53 and caspase-3 expressions while down regulating VEGF and mTOR expression, induced apoptosis, and DNA fragmentation in the HT-29 cells. Acute and sub-acute toxicity study was also considered and results from in vivo study revealed that complex was effective in suppressing ACF multiplicity and hyperplastic lesions and also raised the CAT, SOD, and glutathione levels. Furthermore, the complex decreased cell proliferation and increased apoptotic events in tumor cells correlated with the upregulation of Bax and downregulation of Bcl2, WNT and β- catenin expressions. Our findings from the in vitro and in vivo study provide robust confirmation that ruthenium baicalein complex possesses a potential chemotherapeutic activity against colon cancer and is competent in reducing ACF multiplicity, hyperplastic lesions in the colon tissues of rats by inducing apoptosis.

Potentiating apoptosis and modulation of p53, Bcl2, and Bax by a novel chrysin ruthenium complex for effective chemotherapeutic efficacy against breast cancer

Breast cancer is the most frequent cause of cancer in women. In the current study, transition metal ruthenium was complexed with flavonoid chrysin to evaluate the chemotherapeutic potential of this compound in Michigan Cancer Foundation-7 (MCF-7) human mammary cancer cell line and 7,12-dimethylbenz(α)anthracene-induced mammary cancer in female Sprague-Dawley rats. The characterizations of the complex were accomplished through UV-visible, NMR, IR, Mass spectra, and XRD techniques and antioxidant activity was assessed by DPPH, FRAP, and ABTS methods. In vitro studies included cell viability, cell cycle analysis, DNA fragmentation, and marker analysis by western blot analysis and found that complex treatment suppressed cell growth-induced cell cycle arrest and enhanced the induction of apoptosis in cancer cells. Moreover, complex treatment modulated signaling pathways including mTOR, VEGF, and p53 in the MCF-7 cells. Acute and subacute toxicity was performed in rats to determine the therapeutic doses. Breast cancer in rats was initiated by the administration of 7,12-dimethylbenz(α)anthracene (0.5 mg/100 g body weight) via single tail vein injection. The histopathological analysis after 24 weeks of carcinogenesis study depicted substantial repair of hyperplastic lesions. Immunohistochemical analysis revealed upregulation of Bax and p53 and downregulation of Bcl2 proteins and TUNEL assay showed an increase in apoptotic index in ruthenium-chrysin-treated groups as compared to the carcinogen control. Our findings from the in vitro and in vivo study support the continued investigation of ruthenium-chrysin complex possesses a potential chemotherapeutic activity against breast cancer and was efficient in reducing hyperplastic lesions in the mammary tissues of rats by inducing apoptosis.

Vanadium: History, chemistry, interactions with α-amino acids and potential therapeutic applications

In the last 30 years, since the discovery that vanadium is a cofactor found in certain enzymes of tunicates and possibly in mammals, different vanadium-based drugs have been developed targeting to treat different pathologies. So far, the in vitro studies of the insulin mimetic, antitumor and antiparasitic activity of certain compounds of vanadium have resulted in a great boom of its inorganic and bioinorganic chemistry. Chemical speciation studies of vanadium with amino acids under controlled conditions or, even in blood plasma, are essential for the understanding of the biotransformation of e.g. vanadium antidiabetic complexes at the physiological level, providing clues of their mechanism of action. The present article carries out a bibliographical research emphaticizing the chemical speciation of the vanadium with different amino acids and reviewing also some other important aspects such as its chemistry and therapeutical applications of several vanadium complexes.

Vanadium quercetin complex attenuates mammary cancer by regulating the P53, Akt/mTOR pathway and downregulates cellular proliferation correlated with increased apoptotic events

Flavonoid metal ion complexes have been deliberated in recent years and are considered as a new class of medicinal agents with enhanced therapeutic activity and low toxicity. Our study deals with chemotherapeutic effects of vanadium, when coordinated with the flavonoid quercetin on a defined model of chemically induced rat mammary carcinogenesis in vivo and on human breast cancer cell line MCF-7 in vitro. The characterization of the complex was achieved through UV-Visible, IR, and Mass spectra and antioxidant activity was assessed by DPPH, FRAP and ABTS methods. In vitro studies established that the complex upregulated the expressions of p53, Caspase 3 and 9, whereas down regulating Akt, mTOR and VEGF expressions and also induced apoptosis and DNA fragmentation in a dose dependent manner. Acute and Sub-acute toxicity was performed to determine safe doses. 7,12-Dimethylbenz(α)anthracene (0.5 mg/100 g body weight) was used for induction of breast cancer in female Sprague-Dawley rats via single tail vein injection. The histopathological analysis after 24 weeks of carcinogenesis study depicted substantial repair of hyperplastic lesions. TUNEL assay showed an increase in apoptotic index (0.14 ± 0.03; 0.15 ± 0.01) in vanadium-quercetin treated groups as compared to the carcinogen control (0.02 ± 0.01) along with upregulation of Bcl-2 and downregulation of Bax and p53. Immunohistochemical analysis also exhibited decrease in cell proliferation in the vanadium-quercetin treated groups (11.3 ± 0.12; 11.8 ± 0.10). Thus, results from both in vivo and in vitro studies revealed that vanadium-quercetin complex could be a potential candidate for development of approved drug for breast cancer in the near future.

Trends in vanadium neurotoxicity

Vanadium, atomic number 23, is a transition metal widely distributed in nature. It is a major contaminant of fossil fuels and is widely used in industry as catalysts, in welding, and making steel alloys. Over the years, vanadium compounds have been generating interests due to their use as therapeutic agents in the control of diabetes, tuberculosis, and some neoplasms. However, the toxicity of vanadium compounds is well documented in literature with occupational exposure of workers in vanadium allied industries, environmental pollution from combustion of fossil fuels and industrial exhausts receiving concerns as major sources of toxicity and a likely predisposing factor in the aetiopathogenesis of neurodegenerative diseases. A lot has been done to understand the neurotoxic effects of vanadium, its mechanisms of action and possible antidotes. Sequel to our review of the subject in 2011, this present review is to detail the recent insights gained in vanadium neurotoxicity.

Deciphering the biochemical and molecular mechanism underlying the in vitro and in vivo chemotherapeutic efficacy of ruthenium quercetin complex in colon cancer

Flavonoids are the most investigated phytochemicals due to their pharmacological and therapeutic activities. Their ability to chelate with metal ions has resulted in the emergence of a new category of molecules with a broader spectrum of pharmacological activities. In this study, the ruthenium quercetin complex has been synthesized and anticancer activity has been evaluated on a well-defined model of DMH followed by DSS induced rat colon cancer and on human colon cancer cell line HT-29. The characterizations accomplished through UV-visible, NMR, IR, Mass spectra and XRD techniques, and antioxidant activity was assessed by DPPH, FRAP, and ABTS methods. In vitro study confirmed that the complex increased p53 expression, reduced VEGF and mTOR expression, apoptosis induction, and DNA fragmentation in the HT-29 cells. Acute and subacute toxicity study was also assessed and results from in vivo study revealed that complex was efficient to suppress ACF multiplicity and hyperplastic lesions and elevated the CAT, SOD, and glutathione levels. Furthermore, the complex was found to decrease cell proliferation and increased apoptotic events in tumor cells correlates upregulation of p53 and Bax and downregulation of Bcl2 expression. Our findings from the in vitro and in vivo study support the continued investigation of ruthenium quercetin complex possesses a potential chemotherapeutic activity against colon cancer and was efficient in reducing ACF multiplicity, hyperplastic lesions in the colon tissues of rats by inducing apoptosis.

Vanadium Compounds as PTP Inhibitors

Phosphotyrosine signaling is regulated by the opposing actions of protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs). Here we discuss the potential of vanadium derivatives as PTP enzyme inhibitors and metallotherapeutics. We describe how vanadate in the V oxidized state is thought to inhibit PTPs, thus acting as a pan-inhibitor of this enzyme superfamily. We discuss recent developments in the biological and biochemical actions of more complex vanadium derivatives, including decavanadate and in particular the growing number of oxidovanadium compounds with organic ligands. Pre-clinical studies involving these compounds are discussed in the anti-diabetic and anti-cancer contexts. Although in many cases PTP inhibition has been implicated, it is also clear that many such compounds have further biochemical effects in cells. There also remain concerns surrounding off-target toxicities and long-term use of vanadium compounds in vivo in humans, hindering their progress through clinical trials. Despite these current misgivings, interest in these chemicals continues and many believe they could still have therapeutic potential. If so, we argue that this field would benefit from greater focus on improving the delivery and tissue targeting of vanadium compounds in order to minimize off-target toxicities. This may then harness their full therapeutic potential.

Selective cytotoxicity of vanadium complexes on human pancreatic ductal adenocarcinoma cell line by inducing necroptosis, apoptosis and mitotic catastrophe process

The pancreatic cancer is the fourth leading cause of cancer-related death and characterized by one of the lowest five-year survival rate. The current therapeutic options are demonstrating minimal effectiveness, therefore studies on new potential anticancer compounds, with non-significant side effects are highly desirable. Recently, it was demonstrated that vanadium compounds, in particular organic derivatives, exhibit anticancer properties against different type of tumor as well as favorable biodistribution from a pancreatic cancer treatment perspective. In this research, we showed selective cytotoxic effect of vanadium complexes, containing phenanthroline and quinoline as an organic ligands, against human pancreatic ductal adenocarcinoma cell line (PANC-1), compared to non-tumor human immortalized pancreas duct epithelial cells (hTERT-HPNE). Results exhibited that vanadium complexes inhibited autophagy process in selective cytotoxic concentration as well as caused the cell cycle arrest in G2/M phase associated with mitotic catastrophe and increased level of reactive oxygen species (ROS). Moreover, in higher concentration, vanadium derivatives induced a mix type of cell death in PANC-1 cells, including apoptotic and necroptotic process. Our investigation emphasizes the anticancer potential of vanadium complexes by indicating their selective cytotoxic activity, through different process posed by alternative type of cell deaths to apoptosis-resistant cancer cells. Further studies supporting the therapeutic potential of vanadium in pancreatic cancer treatment is highly recommended.

Growth arrest of lung carcinoma cells (A549) by polyacrylate-anchored peroxovanadate by activating Rac1-NADPH oxidase signalling axis

Hydrogen peroxide is often required in sublethal, millimolar concentrations to show its oxidant effects on cells in culture as it is easily destroyed by cellular catalase. Previously, we had shown that diperoxovanadate, a physiologically stable peroxovanadium compound, can substitute H2O2 effectively in peroxidation reactions. We report here that peroxovanadate when anchored to polyacrylic acid (PAPV) becomes a highly potent inhibitor of growth of lung carcinoma cells (A549). The early events associated with PAPV treatment included cytoskeletal modifications, increase in GTPase activity of Rac1, accumulation of the reactive oxygen species, and also increase in phosphorylation of H2AX (γH2AX), a marker of DNA damage. These effects persisted even at 24 h after removal of the compound and culminated in increased levels of p53 and p21 together with growth arrest. The PAPV-mediated growth arrest was significantly abrogated in cells pre-treated with the N-acetylcysteine, Rac1 knocked down by siRNA and DPI an inhibitor of NADPH oxidase. In conclusion, our results show that polyacrylate derivative of peroxovanadate efficiently arrests growth of A549 cancerous cells by activating the axis of Rac1-NADPH oxidase leading to oxidative stress and DNA damage.

Regional Myelin and Axon Damage and Neuroinflammation in the Adult Mouse Brain After Long-Term Postnatal Vanadium Exposure

Environmental exposure to vanadium occurs in areas of persistent burning of fossil fuels; this metal is known to induce oxidative stress and oligodendrocyte damage. Here, we determined whether vanadium exposure (3 mg/kg) in mice during the first 3 postnatal months leads to a sustained neuroinflammatory response. Body weight monitoring, and muscle strength and open field tests showed reduction of body weight gain and locomotor impairment in vanadium-exposed mice. Myelin histochemistry and immunohistochemistry for astrocytes, microglia, and nonphosphorylated neurofilaments revealed striking regional heterogeneity. Myelin damage involved the midline corpus callosum and fibers in cortical gray matter, hippocampus, and diencephalon that were associated with axonal damage. Astrocyte and microglial activation was identified in the same regions and in the internal capsule; however, no overt myelin and axon damage was observed in the latter. Double immunofluorescence revealed induction of high tumor necrosis factor (TNF) immunoreactivity in reactive astrocytes. Western blotting analysis showed significant induction of TNF and interleukin-1β expression. Together these findings show that chronic postnatal vanadium exposure leads to functional deficit and region-dependent myelin damage that does not spare axons. This injury is associated with glial cell activation and proinflammatory cytokine induction, which may reflect both neurotoxic and neuroprotective responses.

Stimulation of apoptotic pathways in liver cancer cells: An alternative perspective on the biocompatibility and the utility of biomedical glasses

A host of research opportunities with innumerable clinical applications are open to biomedical glasses if one considers their potential as therapeutic inorganic ion delivery systems. Generally, applications have been limited to repair and regeneration of hard tissues while compositions are largely constrained to the original bioactive glass developed in the 1960s. However, in oncology applications the therapeutic paradigm shifts from repair to targeted destruction. With this in mind, the composition–structure–property–function relationships of vanadium-containing zinc-silicate glasses (0.51SiO2–0.29Na2O–(0.20- X)ZnO– XV2O5, 0 ≤  X ≤ 0.09) were characterized in order to determine their potential as therapeutic inorganic ion delivery systems. Increased V2O5 mole fraction resulted in a linear decrease in density and glass transition temperature (Tg). 29Si MAS NMR peak maxima shifted upfield while 51V MAS NMR peak maxima were independent of V2O5 content and overlapped well with the spectra NaVO3. Increased V2O5 mole fraction caused ion release to increase. When human liver cancer cells, HepG2, were exposed to these ions they demonstrated a concentration-dependent cytotoxic response, mediated by apoptosis. This work demonstrates that the zinc-silicate system studied herein is capable of delivering therapeutic inorganic ions at concentrations that induce apoptotic cell death and provide a simple means to control therapeutic inorganic ion delivery.

Water soluble heterometallic potassium-dioxidovanadium(V) complexes as potential antiproliferative agents

Two water soluble heterometallic potassium–dioxidovanadium polymers, [KVO2(L1)]n (1) and [KVO2(L2)(H2O)]n (2) [H2L1= (2,3-dihydroxybenzylidene)-2-hydroxybenzohydrazide and H2L2=(2,3-dihydroxybenzylidene)benzohydrazide], have been synthesized and characterized by IR, NMR, elemental analysis and single crystal X-ray diffraction. The antiproliferative potentials of 1 and 2 were examined towards human colorectal carcinoma (HCT116), and lung (A549) and breast (MCF7) adenocarcinoma cell lines. 1 exhibits a high cytotoxic activity against colorectal carcinoma cells (HCT116), with IC50 lower than those for cisplatin.

Vanadium compounds in medicine

Vanadium is a transition metal that, being ubiquitously distributed in soil, crude oil, water and air, also found roles in biological systems and is an essential element in most living beings. There are also several groups of organisms which accumulate vanadium, employing it in their biological processes. Vanadium being a biological relevant element, it is not surprising that many vanadium based therapeutic drugs have been proposed for the treatment of several types of diseases. Namely, vanadium compounds, in particular organic derivatives, have been proposed for the treatment of diabetes, of cancer and of diseases caused by parasites. In this work we review the medicinal applications proposed for vanadium compounds with particular emphasis on the more recent publications. In cells, partly due to the similarity of vanadate and phosphate, vanadium compounds activate numerous signaling pathways and transcription factors; this by itself potentiates application of vanadium-based therapeutics. Nevertheless, this non-specific bio-activity may also introduce several deleterious side effects as in addition, due to Fenton's type reactions or of the reaction with atmospheric O2, VCs may also generate reactive oxygen species, thereby introducing oxidative stress with consequences presently not well evaluated, particularly for long-term administration of vanadium to humans. Notwithstanding, the potential of vanadium compounds to treat type 2 diabetes is still an open question and therapies using vanadium compounds for e.g. antitumor and anti-parasitic related diseases remain promising.

New oxovanadium(iv) complexes with pincer ligand obtained in situ: experimental and theoretical studies on the structure, spectroscopic properties and antitumour activity

Experimental and theoretical studies on the structure and spectroscopic properties of two complexes: [VOL¹(NCS)₂] (1) and [VOL¹(NCS)₂]·C₆H₅CH₃ (2) where L¹-N,N-bis(3,5-dimethylpyrazol-1-ylmethyl)amine have been reported.

The molecular response of vanadium complexes of nicotinoyl hydrazone in cervical cancers--a possible interference with HPV oncogenic markers

AIMS

Hydrazones belonging to the class of NNO donor Schiff bases are reported to have extensive anti-viral activity and anti-neoplastic activity against certain cancers such as colon cancer, hepatocellular carcinoma and testicular cancer. Here we aim to study the possible effects of two novel nicotinoyl hydrazones on Human papillomavirus (HPV) infected cervical cancers.

MAIN METHODS

The effect of vanadium complexes on the proliferation of SiHa and HeLa cells was analyzed using MTT assay. The apoptotic potentials of the complexes were assessed by their ability to induce DNA condensation as well as loss of mitochondrial membrane potential. Caspase activity assay and DNA content analysis were performed to understand the mechanism of apoptotic induction. RT-PCR analysis of cell cycle genes, GADD45, p53, p21 and HPV specific oncogenes, E6 and E7 were used to elucidate the molecular mechanism of the complexes.

KEY FINDINGS

OVK 49 exhibits an increased apoptosis inducing potential when compared to OVK 89 in HPV16 positive SiHa cells compared to HPV18 positive HeLa. A down regulation for E6 and E7 mRNA transcripts along with the induction of p53 protein in SiHa cells were observed when treated with OVK 49 indicating that OVK 49 might have promising anti-cancer activity against HPV16 positive cervical cancers.

SIGNIFICANCE

This is the first study demonstrating that vanadium complexes could induce a p53 dependent apoptotic mechanism in high risk HPV16-positive cervical cancers.

Neurobehavioral and cytotoxic effects of vanadium during oligodendrocyte maturation: a protective role for erythropoietin

Vanadium exposure has been known to lead to lipid peroxidation, demyelination and oligodendrocytes depletion. We investigated behaviour and glial reactions in juvenile mice after early neonatal exposure to vanadium, and examined the direct effects of vanadium in oligodendrocyte progenitor cultures from embryonic mice. Neonatal pups exposed to vanadium via lactation for 15 and 22 days all had lower body weights. Behavioural tests showed in most instances a reduction in locomotor activity and negative geotaxis. Brain analyses revealed astrocytic activation and demyelination in the vanadium exposed groups compared to the controls. In cell culture, exposure of oligodendrocytes to 300 μM sodium metavanadate significantly increased cell death. Expression of the oligodendrocyte specific proteins, 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) and oligodendrocyte specific protein (OSP/Claudin) were reduced upon vanadium treatment while simultaneous administration of erythropoietin (EPO; 4-12 U/ml) counteracted vanadium-toxicity. The data suggest that oligodendrocyte damage may explain the increased vulnerability of the juvenile brain to vanadium and support a potential for erythropoietin as a protective agent against vanadium-toxicity during perinatal brain development and maturation.

Biochemical profiling and chemopreventive activity of phloretin on 7,12-Dimethylbenz (a) anthracene induced oral carcinogenesis in male golden Syrian hamsters

OBJECTIVES

The present study was designed to examine the chemopreventive effects of phloretin against 7, 12-dimethylbenz (a) anthracene (DMBA) induced buccal pouch carcinogenesis in male golden Syrian hamsters in order to discover resources to improve the traditional medicine.

MATERIALS AND METHODS

Hamsters were divided into four groups of 10 animals each. Group I was served as an untreated control. Group II hamsters were painted with 0.5% DMBA in liquid paraffin on the left buccal pouches three times a week for 14 weeks. Group III hamsters were orally administrated with phloretin at a dose of 40 mg/kg body Weight (b.wt) on days alternate to DMBA application. Group IV hamsters were orally administrated with phloretin alone and served as the drug control. The experiment was terminated at the end of fourteenth week. The experimental animal's tumors were subjected into morphological examination and subsequently screened the pathological changes and estimate the activities of bi-products of lipid peroxidation, antioxidants enzymes and phase I and II detoxification enzyme status.

RESULTS

In DMBA alone treated hamster showed increased levels of lipid peroxidation by products, leads to decreased levels of enzymatic and non-enzymatic antioxidants status, activities of phase I and II detoxification enzyme status were altered. Normalized the neoplastic changes, decreased the levels of lipid by products, retain the antioxidants and restored the phase I and II enzymes were observed in phloretin administrated animals during DMBA induced oral carcinogenesis.

CONCLUSION

Phloretin has possible chemopreventive role in which modulating the antioxidant and detoxification enzyme status, thereby retarding DMBA induced buccal pouch carcinogenesis.

Promising antioxidant and anticancer (human breast cancer) oxidovanadium(IV) complex of chlorogenic acid. Synthesis, characterization and spectroscopic examination on the transport mechanism with bovine serum albumin

A new chlorogenate oxidovanadium complex (Na[VO(chlorog)(H2O)3].4H2O) was synthesized by using Schlenk methodology in the course of a reaction at inert atmosphere in which deprotonated chlorogenic acid ligand binds to oxidovanadium(IV) in a reaction experiment controlled via EPR technique and based in a species distribution diagram. The compound was characterized by FTIR, EPR, UV-visible and diffuse reflectance spectroscopies and thermogravimetric, differential thermal and elemental analyses. The ligand and the complex were tested for their antioxidant effects on DPPH (1,1-diphenyl-2-picrylhydrazyl radical), ABTS(+) (radical cation of 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt), O2(-), OH and ROO radicals and their cytotoxic activity on different cancer cell lines (SKBR3, T47D and MDAMB231) and primary human mammary epithelial cells. The complex behaved as good antioxidant agent with strongest inhibitory effects on O2(-), OH and ROO radicals and exhibited selective cytotoxicity against SKBR3 cancer cell line. Albumin interaction experiments denoted high affinity toward the complex and its calculated binding constant was indicative of a strong binding to the protein. Based on this study, it is hypothesized that Na[VO(chlorog)(H2O)3].4H2O would be a promising candidate for further evaluation as an antioxidant and anticancer agent.

Therapeutic potential of a pyridoxal-based vanadium(IV) complex showing selective cytotoxicity for cancer versus healthy cells

Vanadium compounds can exert anticancer effects, partly due to inhibition of tyrosine phosphatases. Here, we report the effect of N,N'-ethylenebis (pyridoxylideneiminato) vanadium (IV) complex (Pyr2 enV(IV)), that induced 93% and 57% of cell mortality in A375 (human melanoma) and A549 (human lung carcinoma) cells, respectively; the mortality was <24% in other cancer cell lines and in human normal epidermal keratinocytes, lung cells and peripheral blood mononuclear cells. The mechanism of Pyr2 enV(IV) effect relied on apoptosis induction; this was triggered by ROS increase, followed by mitochondrial membrane depolarization. Indeed, the addition of N-acetyl cysteine to cell cultures abated Pyr2 enV(IV)-induced apoptosis. These results disclose the pro-apoptotic activity of Pyr2 enV(IV) and its mechanism, relying on intracellular ROS increase.

Novel ternary vanadium-betaine-peroxido species suppresses H-ras and matrix metalloproteinase-2 expression by increasing reactive oxygen species-mediated apoptosis in cancer cells

Vanadium is known for its antitumorigenicity. Poised to investigate the impact of well-defined forms of vanadium on processes and specific biomolecules (oncogenes-proteins) involved in cancer cell physiology, a novel ternary V(V)-peroxido-betaine compound was employed in experiments targeting cell viability, apoptosis, reactive oxygen species (ROS) production, H-ras signaling, and matrix metalloproteinase-2 (MMP-2) expression in human breast cancer epithelial and lung adenocarcinoma cells. The results reveal that vanadium imparts a significant decrease in cancer cell viability, reducing H-ras and MMP-2 expression by increasing ROS-mediated apoptosis, distinctly emphasizing the nature, structure and properties of ternary ligands on vanadium anti-tumor activity and its future potential as a metallodrug.