New vanadium-based magnetic resonance imaging probes: clinical potential for early detection of cancer

Efficient Synthesis and HPLC-Based Characterization for Developing Vanadium-48-Labeled Vanadyl Acetylacetonate as a Novel Cancer Radiotracer for PET Imaging

Bis(acetylacetonato)oxidovanadium(IV) [(VO(acac)2], generally known as vanadyl acetylacetonate, has been shown to be preferentially sequestered in malignant tissue. Vanadium-48 (48V) generated with a compact medical cyclotron has been used to label VO(acac)2 as a potential radiotracer in positron emission tomography (PET) imaging for the detection of cancer, but requires lengthy synthesis. Current literature protocols for the characterization of VO(acac)2 require macroscale quantities of reactants and solvents to identify products by color and to enable crystallization that are not readily adaptable to the needs of radiotracer synthesis. We present an improved method to produce vanadium-48-labeled VO(acac)2, [48V]VO(acac)2, and characterize it using high-performance liquid chromatography (HPLC) with radiation detection in combination with UV detection. The approach is suitable for radiotracer-level quantities of material. These methods are readily applicable for production of [48V]VO(acac)2. Preliminary results of preclinical, small-animal PET studies are presented.

MD Simulations to Calculate NMR Relaxation Parameters of Vanadium(IV) Complexes: A Promising Diagnostic Tool for Cancer and Alzheimer's Disease

Early phase diagnosis of human diseases has still been a challenge in the medicinal field, and one of the efficient non-invasive techniques that is vastly used for this purpose is magnetic resonance imaging (MRI). MRI is able to detect a wide range of diseases and conditions, including nervous system disorders and cancer, and uses the principles of NMR relaxation to generate detailed internal images of the body. For such investigation, different metal complexes have been studied as potential MRI contrast agents. With this in mind, this work aims to investigate two systems containing the vanadium complexes [VO(metf)2]·H2O (VC1) and [VO(bpy)2Cl]+ (VC2), being metformin and bipyridine ligands of the respective complexes, with the biological targets AMPK and ULK1. These biomolecules are involved in the progression of Alzheimer's disease and triple-negative breast cancer, respectively, and may act as promising spectroscopic probes for detection of these diseases. To initially evaluate the behavior of the studied ligands within the aforementioned protein active sites and aqueous environment, four classical molecular dynamics (MD) simulations including VC1 + H2O (1), VC2 + H2O (2), VC1 + AMPK + H2O (3), and VC2 + ULK1 + H2O (4) were performed. From this, it was obtained that for both systems containing VCs and water only, the theoretical calculations implied a higher efficiency when compared with DOTAREM, a famous commercially available contrast agent for MRI. This result is maintained when evaluating the system containing VC1 + AMPK + H2O. Nevertheless, for the system VC2 + ULK1 + H2O, there was observed a decrease in the vanadium complex efficiency due to the presence of a relevant steric hindrance. Despite that, due to the nature of the interaction between VC2 and ULK1, and the nature of its ligands, the study gives an insight that some modifications on VC2 structure might improve its efficiency as an MRI probe.

Modelling cyclotron-based production of radioisotopes via TOPAS

Objective. In this work, the irradiation of natural titanium foils in the beam-stop of a compact medical cyclotron, an IBA CYCLONE 18/9, is simulated to assess the efficacy of using a beam-stop as a target holder, and using two different target geometries, in the production of vanadium-48, a positron-emitting radioisotope with potential utility as a cancer imaging agent in positron emission tomography.Approach. TOPAS, the TOol for PArticle Simulation, a Geant4-based Monte Carlo program, was used to model the cyclotron beam parameters, choose an appropriate physics list, and simulate the irradiation of targets made from foils of 12 or 12.5μm thickness. These simulation yields were compared to theoretical yields calculated using cross section data from the literature, as well as assayed yields from experimental irradiations.Main results.We found that most physics lists in TOPAS overestimate the cross section in the desired energy range (16-20 MeV) by at least 136%, with the exception of those using the Bertini Cascade Model. Compared to assayed yields, TOPAS provided a minimum of 0.4% error for cup-shaped targets and at least a 12% overestimation for sphere-shaped targets.Significance.These simulations provide a tool to help explain irregularities in radioisotope production yield and motivate modifications to increase target yield.

Bioinspired Theranostic Coordination Polymer Nanoparticles for Intranasal Dopamine Replacement in Parkinson's Disease

Dopamine (DA) is one of the main neurotransmitters found in the central nervous system and has a vital role in the function of dopaminergic (DArgic) neurons. A progressive loss of this specific subset of cells is one of the hallmarks of age-related neurodegenerative disorders such as Parkinson's disease (PD). Symptomatic therapy for PD has been centered in the precursor l-DOPA administration, an amino acid precursor of DA that crosses the blood-brain barrier (BBB) while DA does not, although this approach presents medium- to long-term side effects. To overcome this limitation, DA-nanoencapsulation therapies are actively being searched as an alternative for DA replacement. However, overcoming the low yield of encapsulation and/or poor biodistribution/bioavailability of DA is still a current challenge. Herein, we report the synthesis of a family of neuromelanin bioinspired polymeric nanoparticles. Our system is based on the encapsulation of DA within nanoparticles through its reversible coordination complexation to iron metal nodes polymerized with a bis-imidazol ligand. Our methodology, in addition to being simple and inexpensive, results in DA loading efficiencies of up to 60%. In vitro, DA nanoscale coordination polymers (DA-NCPs) exhibited lower toxicity, degradation kinetics, and enhanced uptake by BE(2)-M17 DArgic cells compared to free DA. Direct infusion of the particles in the ventricle of rats in vivo showed a rapid distribution within the brain of healthy rats, leading to an increase in striatal DA levels. More importantly, after 4 days of nasal administrations with DA-NCPs equivalent to 200 μg of the free drug per day, the number and duration of apomorphine-induced rotations was significantly lower from that in either vehicle or DA-treated rats performed for comparison purposes. Overall, this study demonstrates the advantages of using nanostructured DA for DA-replacement therapy.

The Transition from Metal-Based to Metal-Free Contrast Agents for T1 Magnetic Resonance Imaging Enhancement

Magnetic resonance imaging (MRI) has received significant attention as the noninvasive diagnostic technique for complex diseases. Image-guided therapeutic strategy for diseases such as cancer has also been at the front line of biomedical research, thanks to the innovative MRI, enhanced by the prior delivery of contrast agents (CAs) into patients' bodies through injection. These CAs have contributed a great deal to the clinical utility of MRI but have been based on metal-containing compounds such as gadolinium, manganese, and iron oxide. Some of these CAs have led to cytotoxicities such as the incurable Nephrogenic Systemic Fibrosis (NSF), resulting in their removal from the market. On the other hand, CAs based on organic nitroxide radicals, by virtue of their structural composition, are metal free and without the aforementioned drawbacks. They also have improved biocompatibility, ease of functionalization, and long blood circulation times, and have been proven to offer tissue contrast enhancement with longitudinal relaxivities comparable with those for the metal-containing CAs. Thus, this Review highlights the recent progress in metal-based CAs and their shortcomings. In addition, the remarkable goals achieved by the organic nitroxide radical CAs in the enhancement of MR images have also been discussed extensively. The focal point of this Review is to emphasize or demonstrate the crucial need for transition into the use of organic nitroxide radicals-metal-free CAs-as against the metal-containing CAs, with the aim of achieving safer application of MRI for early disease diagnosis and image-guided therapy.

Dual T1/ T2 Nanoscale Coordination Polymers as Novel Contrast Agents for MRI: A Preclinical Study for Brain Tumor

In the last years, extensive attention has been paid on designing and developing functional imaging contrast agents for providing accurate noninvasive evaluation of pathology in vivo. However, the issue of false-positives or ambiguous imaging and the lack of a robust strategy for simultaneous dual-mode imaging remain to be fully addressed. One effective strategy for improving it is to rationally design magnetic resonance imaging (MRI) contrast agents (CAs) with intrinsic T₁/ T₂ dual-mode imaging features. In this work, the development and characterization of one-pot synthesized nanostructured coordination polymers (NCPs) which exhibit dual mode T₁/ T₂ MRI contrast behavior is described. The resulting material comprises the combination of different paramagnetic ions (Fe³⁺, Gd³⁺, Mn²⁺) with selected organic ligands able to induce the polymerization process and nanostructure stabilization. Among them, the Fe-based NCPs showed the best features in terms of colloidal stability, low toxicity, and dual T₁/ T₂ MRI contrast performance overcoming the main drawbacks of reported CAs. The dual-mode CA capability was evaluated by different means: in vitro phantoms, ex vivo and in vivo MRI, using a preclinical model of murine glioblastoma. Interestingly, the in vivo MRI of Fe-NCPs show T₁ and T₂ high contrast potential, allowing simultaneous recording of positive and negative contrast images in a very short period of time while being safer for the mouse. Moreover, the biodistribution assays reveals the persistence of the nanoparticles in the tumor and subsequent gradual clearance denoting their biodegradability. After a comparative study with commercial CAs, the results suggest these nanoplatforms as promising candidates for the development of dual-mode MRI CAs with clear advantages.

Vanadium in Biosphere and Its Role in Biological Processes

Ultra-trace elements or occasionally beneficial elements (OBE) are the new categories of minerals including vanadium (V). The importance of V is attributed due to its multifaceted biological roles, i.e., glucose and lipid metabolism as an insulin-mimetic, antilipemic and a potent stress alleviating agent in diabetes when vanadium is administered at lower doses. It competes with iron for transferrin (binding site for transportation) and with lactoferrin as it is secreted in milk also. The intracellular enzyme protein tyrosine phosphatase, causing the dephosphorylation at beta subunit of the insulin receptor, is inhibited by vanadium, thus facilitating the uptake of glucose inside the cell but only in the presence of insulin. Vanadium could be useful as a potential immune-stimulating agent and also as an antiinflammatory therapeutic metallodrug targeting various diseases. Physiological state and dose of vanadium compounds hold importance in causing toxicity also. Research has been carried out mostly on laboratory animals but evidence for vanadium importance as a therapeutic agent are available in humans and large animals also. This review examines the potential biochemical and molecular role, possible kinetics and distribution, essentiality, immunity, and toxicity-related study of vanadium in a biological system.

Kinetic characterization of the inhibition of protein tyrosine phosphatase-1B by Vanadyl (VO2+) chelates

Protein tyrosine phosphatases (PTPases) are a prominent focus of drug design studies because of their roles in homeostasis and disorders of metabolism. These studies have met with little success because (1) virtually all inhibitors hitherto exhibit only competitive behavior and (2) a consensus sequence H/V-C-X5-R-S/T characterizes the active sites of PTPases, leading to low specificity of active site directed inhibitors. With protein tyrosine phosphatase-1B (PTP1B) identifed as the target enzyme of the vanadyl (VO2+) chelate bis(acetylacetonato)oxidovanadium(IV) [VO(acac)2] in 3T3-L1 adipocytes [Ou et al. J Biol Inorg Chem 10: 874-886, 2005], we compared the inhibition of PTP1B by VO(acac)2 with other VO2+-chelates, namely, bis(2-ethyl-maltolato)oxidovanadium(IV) [VO(Et-malto)2] and bis(3-hydroxy-2-methyl-4(1H)pyridinonato)oxidovanadium(IV) [VO(mpp)2] under steady-state conditions, using the soluble portion of the recombinant human enzyme (residues 1-321). Our results differed from those of previous investigations because we compared inhibition in the presence of the nonspecific substrate p-nitrophenylphosphate and the phosphotyrosine-containing undecapeptide DADEpYLIPQQG mimicking residues 988-998 of the epidermal growth factor receptor, a relevant, natural substrate. While VO(Et-malto)2 acts only as a noncompetitive inhibitor in the presence of either subtrate, VO(acac)2 exhibits classical uncompetitive inhibition in the presence of DADEpYLIPQQG but only apparent competitive inhibition with p-nitrophenylphosphate as substrate. Because uncompetitive inhibitors are more potent pharmacologically than competitive inhibitors, structural characterization of the site of uncompetitive binding of VO(acac)2 may provide a new direction for design of inhibitors for therapeutic purposes. Our results suggest also that the true behavior of other inhibitors may have been masked when assayed with only p-nitrophenylphosphate as substrate.

Interaction of [VIV O(acac)2 ] with Human Serum Transferrin and Albumin

[VO(acac)₂ ] is a remarkable vanadium compound and has potential as a therapeutic drug. It is important to clarify how it is transported in blood, but the reports addressing its binding to serum proteins have been contradictory. We use several spectroscopic and mass spectrometric techniques (ESI and MALDI-TOF), small-angle X-ray scattering and size exclusion chromatography (SEC) to characterize solutions containing [VO(acac)₂ ] and either human serum apotransferrin (apoHTF) or albumin (HSA). DFT and modeling protein calculations are carried out to disclose the type of binding to apoHTF. The measured circular dichroism spectra, SEC and MALDI-TOF data clearly prove that at least two VO-acac moieties may bind to apoHTF, most probably forming [V^IV O(acac)(apoHTF)] complexes with residues of the HTF binding sites. No indication of binding of [VO(acac)₂ ] to HSA is obtained. We conclude that V^IV O-acac species may be transported in blood by transferrin. At very low complex concentrations speciation calculations suggest that [(VO)(apoHTF)] species form.

Bis(acetylacetonato)-oxidovanadium(IV) and sodium metavanadate inhibit cell proliferation via ROS-induced sustained MAPK/ERK activation but with elevated AKT activity in human pancreatic cancer AsPC-1 cells

In this study, the antiproliferative effect of bis(acetylacetonato)-oxidovanadium(IV) and sodium metavanadate and the underlying mechanisms were investigated in human pancreatic cancer cell line AsPC-1. The results showed that both exhibited an antiproliferative effect through inducing G2/M cell cycle arrest and can also cause elevation of reactive oxygen species (ROS) levels in cells. Moreover, the two vanadium compounds induced the activation of both PI3K/AKT and MAPK/ERK signaling pathways dose- and time-dependently, which could be counteracted with the antioxidant N-acetylcysteine. In the presence of MEK-1 inhibitor, the degradation of Cdc25C, inactivation of Cdc2 and accumulation of p21 were relieved. However, the treatment of AKT inhibitor did not cause any significant effect. Therefore, it demonstrated that the ROS-induced sustained MAPK/ERK activation rather than AKT contributed to vanadium compounds-induced G2/M cell cycle arrest. The current results also exhibited that the two vanadium compounds did not induce a sustained increase of ROS generation, but the level of ROS reached a plateau instead. The results revealed that an intracellular feedback loop may be against the elevated ROS level induced by vanadate or VO(acac)₂, evidenced by the increased GSH content, the unchanged level at the expression of antioxidant enzymes. Therefore, vanadium compounds can be regarded as a novel type of anticancer drugs through the prolonged activation of MAPK/ERK pathway but retained AKT activity. The present results provided a proof-of-concept evidence that vanadium-based compounds may have the potential as both antidiabetic and antipancreatic cancer agents to prevent or treat patients suffering from both diseases.

X-ray fluorescence microscopy demonstrates preferential accumulation of a vanadium-based magnetic resonance imaging contrast agent in murine colonic tumors

Contrast agents that specifically enhance cancers on magnetic resonance imaging (MRI) will allow earlier detection. Vanadium-based chelates (VCs) selectively enhance rodent cancers on MRI, suggesting selective uptake of VCs by cancers. Here we report x-ray fluorescence microscopy (XFM) of VC uptake by murine colon cancer. Colonic tumors in mice treated with azoxymethane/dextran sulfate sodium were identified by MRI. Then a gadolinium-based contrast agent and a VC were injected intravenously; mice were sacrificed and colons sectioned. VC distribution was sampled at 120 minutes after injection to evaluate the long-term accumulation. Gadolinium distribution was sampled at 10 minutes after injection due to its rapid washout. XFM was performed on 72 regions of normal and cancerous colon from five normal mice and four cancer-bearing mice. XFM showed that all gadolinium was extracellular, with similar concentrations in colon cancers and normal colon. In contrast, the average VC concentration was twofold higher in cancers versus normal tissue (p < .002). Cancers also contained numerous "hot spots" with intracellular VC concentrations sixfold higher than the concentration in normal colon (p < .0001). No hot spots were detected in normal colon. This is the first direct demonstration that VCs selectively accumulate in cancer cells and thus may improve cancer detection.

IV Administered Gadodiamide Enters the Lumen of the Prostatic Glands: X-Ray Fluorescence Microscopy Examination of a Mouse Model

OBJECTIVE

Dynamic contrast-enhanced MRI (DCE-MRI) has become a standard component of multiparametric protocols for MRI examination of the prostate, and its use is incorporated into current guidelines for prostate MRI examination. Analysis of DCE-MRI data for the prostate is usually based on the distribution of gadolinium-based agents, such as gadodiamide, into two well-mixed compartments, and it assumes that gadodiamide does not enter into the glandular lumen. However, this assumption has not been directly tested. The purpose of this study was to use x-ray fluorescence microscopy (XFM) imaging in situ to measure the concentration of gadodiamide in the epithelia and lumens of the prostate of healthy mice after IV injection of the contrast agent.

MATERIALS AND METHODS

Six C57Bl6 male mice (age, 28 weeks) were sacrificed 10 minutes after IV injection of gadodiamide (0.13 mmol/kg), and three mice were sacrificed after saline injection. Prostate tissue samples obtained from each mouse were harvested and frozen; 7-μm-thick slices were sectioned for XFM imaging, and adjacent 5-μm-thick slices were sectioned for H and E staining. Elemental concentrations were determined from XFM images.

RESULTS

A mean (± SD) baseline concentration of gadolinium of 0.01 ± 0.01 mM was determined from XFM measurements of prostatic tissue samples when no gadodiamide was administered, and it was used to determine the measurement error. When gadodiamide was added, the mean concentrations of gadolinium in the epithelia and lumens in 32 prostatic glands from six mice were 1.00 ± 0.13 and 0.36 ± 0.09 mM, respectively.

CONCLUSION

Our data suggest that IV administration of gadodiamide results in uptake of contrast agent by the glandular lumens of the mouse prostate. We were able to quantitatively determine gadodiamide distributions in mouse prostatic epithelia and lumens.

A Spectroscopy Approach for the Study of the Interaction of Oxovanadium(IV)-Salen Complexes with Proteins

Oxovanadium(IV)-salen complexes bind with bovine serum albumin (BSA) and ovalbumin (OVA) strongly with binding constant in the range 10(4)-10(7) M(-1) at physiological pH (7.4) confirmed using UV-visible absorption, fluorescence spectral and circular dichroism (CD) study. CD results show that the binding of oxovanadium(IV) complexes induces the conformational change with the loss of α-helicity in the proteins. Docking studies indicate that mode of binding of oxovanadium(IV)-salen complexes with proteins is hydrophobic in nature.

The Structural Basis of Action of Vanadyl (VO2+) Chelates in Cells

Much emphasis has been given to vanadium compounds as potential therapeutic reagents for the treatment of diabetes mellitus. Thus far, no vanadium compound has proven efficacious for long-term treatment of this disease in humans. Therefore, in review of the research literature, our goal has been to identify properties of vanadium compounds that are likely to favor physiological and biochemical compatibility for further development as therapeutic reagents. We have, therefore, limited our review to those vanadium compounds that have been used in both in vivo experiments with small, laboratory animals and in in vitro studies with primary or cultured cell systems and for which pharmacokinetic and pharmacodynamics results have been reported, including vanadium tissue content, vanadium and ligand lifetime in the bloodstream, structure in solution, and interaction with serum transport proteins. Only vanadyl (VO²⁺) chelates fulfill these requirements despite the large variety of vanadium compounds of different oxidation states, ligand structure, and coordination geometry synthesized as potential therapeutic agents. Extensive review of research results obtained with use of organic VO²⁺-chelates shows that the vanadyl chelate bis(acetylacetonato)oxidovanadium(IV) [hereafter abbreviated as VO(acac)₂], exhibits the greatest capacity to enhance insulin receptor kinase activity in cells compared to other organic VO²⁺-chelates, is associated with a dose-dependent capacity to lower plasma glucose in diabetic laboratory animals, and exhibits a sufficiently long lifetime in the blood stream to allow correlation of its dose-dependent action with blood vanadium content. The properties underlying this behavior appear to be its high stability and capacity to remain intact upon binding to serum albumin. We relate the capacity to remain intact upon binding to serum albumin to the requirement to undergo transcytosis through the vascular endothelium to gain access to target tissues in the extravascular space. Serum albumin, as the most abundant transport protein in the blood stream, serves commonly as the carrier protein for small molecules, and transcytosis of albumin through capillary endothelium is regulated by a Src protein tyrosine kinase system. In this respect it is of interest to note that inorganic VO²⁺ has the capacity to enhance insulin receptor kinase activity of intact 3T3-L1 adipocytes in the presence of albumin, albeit weak; however, in the presence of transferrin no activation is observed. In addition to facilitating glucose uptake, the capacity of VO²⁺- chelates for insulin-like, antilipolytic action in primary adipocytes has also been reviewed. We conclude that measurement of inhibition of release of only free fatty acids from adipocytes stimulated by epinephrine is not a sufficient basis to ascribe the observations to purely insulin-mimetic, antilipolytic action. Adipocytes are known to contain both phosphodiesterase-3 and phosphodiesterase-4 (PDE3 and PDE4) isozymes, of which insulin antagonizes lipolysis only through PDE3B. It is not known whether the other isozyme in adipocytes is influenced directly by VO²⁺- chelates. In efforts to promote improved development of VO²⁺- chelates for therapeutic purposes, we propose synergism of a reagent with insulin as a criterion for evaluating physiological and biochemical specificity of action. We highlight two organic compounds that exhibit synergism with insulin in cellular assays. Interestingly, the only VO²⁺- chelate for which this property has been demonstrated, thus far, is VO(acac)₂.

A new ex vivo method to evaluate the performance of candidate MRI contrast agents: a proof-of-concept study

BACKGROUND

Magnetic resonance imaging (MRI) plays an important role in tumor detection/diagnosis. The use of exogenous contrast agents (CAs) helps to improve the discrimination between lesion and neighbouring tissue, but most of the currently available CAs are non-specific. Assessing the performance of new, selective CAs requires exhaustive assays and large amounts of material. Accordingly, in a preliminary screening of new CAs, it is important to choose candidate compounds with good potential for in vivo efficiency. This screening method should reproduce as close as possible the in vivo environment. In this sense, a fast and reliable method to select the best candidate CAs for in vivo studies would minimize time and investment cost, and would benefit the development of better CAs.

RESULTS

The post-mortem ex vivo relative contrast enhancement (RCE) was evaluated as a method to screen different types of CAs, including paramagnetic and superparamagnetic agents. In detail, sugar/gadolinium-loaded gold nanoparticles (Gd-GNPs) and iron nanoparticles (SPIONs) were tested. Our results indicate that the post-mortem ex vivo RCE of evaluated CAs, did not correlate well with their respective in vitro relaxivities. The results obtained with different Gd-GNPs suggest that the linker length of the sugar conjugate could modulate the interactions with cellular receptors and therefore the relaxivity value. A paramagnetic CA (GNP (E_2)), which performed best among a series of Gd-GNPs, was evaluated both ex vivo and in vivo. The ex vivo RCE was slightly worst than gadoterate meglumine (201.9 ± 9.3% versus 237 ± 14%, respectively), while the in vivo RCE, measured at the time-to-maximum enhancement for both compounds, pointed to GNP E_2 being a better CA in vivo than gadoterate meglumine. This is suggested to be related to the nanoparticule characteristics of the evaluated GNP.

CONCLUSION

We have developed a simple, cost-effective relatively high-throughput method for selecting CAs for in vivo experiments. This method requires approximately 800 times less quantity of material than the amount used for in vivo administrations.

The vanadyl chelate bis(acetylacetonato)oxovanadium(IV) increases the fractional uptake of 2-(fluorine-18)-2-deoxy-D-glucose by cultured human breast carcinoma cells

Detection of breast cancer by positron emission tomography (PET) imaging with 2-(fluorine-18)-2-deoxy-D-glucose (FDG) as the tracer molecule is limited in part by both tumor dimension and metabolic activity. While some types of aggressive breast cancers are associated with a high capacity for FDG uptake, more indolent breast cancers are characterized by low FDG uptake. Moreover, detection of malignant lesions in most clinical settings requires tumor dimensions ≥10 mm. Development of a method to increase the fractional uptake of FDG by cancer tissue would provide a means to detect smaller tumors. However, there is no clinically available pharmacologic reagent known to enhance the preferential uptake of FDG by cancer tissue. Because the vanadyl (VO(2+)) chelate bis(acetylacetonato)oxovanadium(IV) [VO(acac)2] is known to enhance cellular uptake of glucose, we have investigated whether VO(acac)2 facilitates enhanced uptake of FDG by cultured human breast carcinoma cells. We observed that the fractional uptake of FDG by cultured human MDA-MB-231 carcinoma cells is increased in the presence of VO(acac)2 in a dose dependent manner. Preliminary results with xenograft tumors generated in severely compromised, immunodeficient (SCID) female mice showed that VO(acac)2 treatment of mice 3-4 h prior to FDG injection enhanced FDG uptake by the malignant tissue by a factor >2.0 compared with that by normal surrounding tissue.

Vanadium in the detection, prevention and treatment of cancer: the in vivo evidence

Vanadium, a dietary micronutrient, is yet to be established as an essential part of the human diet. Over the past century, several biological effects of vanadium, such as insulin-mimetic action as well as amelioration of hyperlipidemia and hypertension, have been discovered. This transition element is known to influence a battery of enzymatic systems, namely phosphatases, ATPases, peroxidases, ribonucleases, protein kinases and oxidoreductases. Multiple biochemical and molecular actions of vanadium have been implicated in its inhibitory effects on various tumor cells of human origin. Successful in vitro studies over the past few decades have advanced the anticancer research on vanadium into the preclinical stage. Vanadium in several animal cancer models provides protection against all stages of carcinogenesis--initiation, promotion, and progression. This review focuses on the current advances in cancer prevention and treatment as well as early detection by vanadium compounds in preclinical animal models while pointing to possible mechanisms of such diverse beneficial effects. Clinical pharmacokinetic and potential toxicity studies on vanadium are also highlighted in this review. Supporting and challenging evidence as well as future directions of vanadium research exploring the possibility of using this dietary agent for detection, prevention and treatment of human cancers are critically discussed.