Copper and carcinogenesis

Role of hepatocyte nuclear factor 4α in controlling copper-responsive transcription

Previous global transcriptome and interactome analyses of copper-treated HepG2 cells identified hepatocyte nuclear factor 4α (HNF4α) as a potential master regulator of copper-responsive transcription. Copper exposure caused a decrease in the expression of HNF4α at both mRNA and protein levels, which was accompanied by a decrease in the level of HNF4α binding to its consensus DNA binding sequence. qRT-PCR and RNAi studies demonstrated that changes in HNF4α expression ultimately affected the expressions of its down-stream target genes. Analysis of upstream regulators of HNF4α expression, including p53 and ATF3, showed that copper caused an increase in the steady-state levels of these proteins. These results support a model for copper-responsive transcription in which the metal affects ATF3 expression and stabilizes p53 resulting in the down-regulation of HNF4α expression. In addition, copper may directly affect p53 protein levels. The suppression of HNF4α activity may contribute to the molecular mechanisms underlying the physiological and toxicological consequences of copper toxicity in hepatic-derived cells.

Bioinorganic aspects of angiogenesis

Angiogenesis is a physiologic process characterized by the sprouting of a new blood vessel from a pre-existing one. In mammalians the angiogenesis process is dormant, except for few physiological conditions such as wound healing and ovulation. In healthy individuals angiogenesis is finely tuned by pro- and anti-angiogenic factors. The shift from this equilibrium, under pathological conditions (pathological angiogenesis) is associated with several human diseases of high social impact. An efficient angiogenesis also requires that angiogenic factors cooperate with microenvironment derived co-factors, including metals. In this Perspective we describe the bioinorganic aspects of angiogenesis which contribute to a better understanding of the molecular mechanisms and regulation of angiogenesis. In particular, the role of metals, especially copper, metalloproteinases, and the current status on the imaging of angiogenesis targeting VEGF or VEGF receptors will be discussed.

Interaction of copper with iron, iodine, and thyroid hormone status in goitrous patients

In many developing countries, men and women are at high risk of goiter and iron deficiency. The aim of the recent study is to assess the interaction of (Cu), with iron (Fe), iodine/iodide (I), and thyroid hormones in goitrous patients. Sixty goitrous male (GMPs) and 72 female patients (GFPs) were evaluated for the Cu, Fe, I, and thyroid hormones status in biological samples (serum and urine), and compared to non-goitrous subjects of both genders (M = 106, F = 120). The biological samples were analyzed for Cu and Fe concentration using atomic absorption spectrometer, while I was measured by the potentiometric method, prior to microwave-assisted acid digestion (MD). Quality control for the method was established with certified samples. Significantly higher mean values of Cu in serum, and urine samples of GMPs and GFPs, while lower value of Fe and I were observed as compared to control subjects (p < 0.015), respectively. The mean values of free triiodothyronine (FT3) and free thyroxin (FT4) were found to be lower in goitrous patients of both genders than in the age-matched healthy controls (p < 0.006 and 0.002), respectively, in contrast high mean values of thyroid-stimulating hormone (TSH) were detected in patients (p < 0.009), as compared to non-goitrous subjects. It was observed that the deficiencies of Fe, I, and thyroid hormone in goitrous patients could be influenced by efficiency of Cu.

Synchrotron X-ray imaging reveals a correlation of tumor copper speciation with Clioquinol's anticancer activity

Tumor development and metastasis depend on angiogenesis that requires certain growth factors, proteases, and the trace element copper (Cu). Recent studies suggest that Cu could be used as a novel target for cancer therapies. Clioquinol (CQ), an antibiotic that is able to form stable complexes with Cu or zinc (Zn), has shown proteasome-inhibitory, androgen receptor-suppressing, apoptosis-inducing, and antitumor activities in human cancer cells and xenografts. The mechanisms underlying the interaction of CQ with cellular Cu, the alteration of the Cu/Zn ratio and the antitumor role of CQ in vivo have not been fully elucidated. We report here that Cu accumulates in tumor tissue and that the Cu/Zn balances in tumor, but not normal, tissue change significantly after the treatment with CQ. Cu speciation analysis showed that the Cu(I) species is predominant in both normal and tumor tissues and that Cu(II) content was significantly increased in tumor, but not normal tissue after CQ treatment. Our findings indicate that CQ can interact with cellular Cu in vivo, dysregulates the Cu/Zn balance and is able to convert Cu(I) to Cu(II) in tumor tissue. This conversion of Cu(I) to Cu(II) may be associated with CQ-induced proteasome inhibition and growth suppression in the human prostate tumor xenografts.

Adsorption of copper-citrate complexes on chitosan: equilibrium modeling

The effects of complexes on the adsorption of copper from citrate solutions using chitosan were investigated. Various copper to citrate ratios and solution pHs were used to determine the copper adsorption capacity on the chitosan and a mathematical model was developed to simulate the copper adsorption process. According to the model, the three parameters influencing the copper adsorption capacity are the fraction of protonated amine groups (RNH(3)(+)), the fraction of anionic copper-citrate complexes (CuL(-) and CuL(2)(4-)), and the fraction of anionic citrate complexes (HL(2-), H(2)L(-), and L(3-)). The copper adsorption capacities onto chitosan at varying copper-citrate ratios and solution pHs can be predicted by the mathematical model. With such a model to facilitate understand the copper adsorption mechanisms at varying copper-citrate ratios and solution pHs, the copper adsorption efficiency can be increased by the adjustment of the copper-citrate ratio and solution pH.

Mechanism of oxidative DNA damage induced by capsaicin, a principal ingredient of hot chili pepper

Although capsaicin exhibits antitumor activity, carcinogenic potential has also been reported. To clarify the mechanism for expression of potential carcinogenicity of capsaicin, we examined DNA damage induced by capsaicin in the presence of metal ion and various kinds of cytochrome P450 (CYP) using 32P-5'-end-labeled DNA fragments. Capsaicin induced Cu(II)-mediated DNA damage efficiently in the presence of CYP1A2 and partially in the presence of 2D6. CYP1A2-treated capsaicin caused double-base lesions at 5'-TG-3', 5'-GC-3' and CG of the 5'-ACG-3' sequence complementary to codon 273, a hotspot of p53 gene. DNA damage was inhibited by catalase and bathocuproine, a Cu(I) chelator, suggesting that reactive species derived from the reaction of H2O2 with Cu(I) participate in DNA damage. Formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine was significantly increased by CYP1A2-treated capsaicin in the presence of Cu(II). Therefore, we conclude that Cu(II)-mediated oxidative DNA damage by CYP-treated capsaicin seems to be relevant for the expression of its carcinogenicity.

Photo-irradiated Titanium Dioxide Catalyzes Site Specific DNA Damage via Generation of Hydrogen Peroxide

Titanium dioxide (TiO2) is a potential photosensitizer for photodynamic therapy. In this study, the mechanism of DNA damage catalyzed by photo-irradiated TiO2 was examined using [32P]-5'-end-labeled DNA fragments obtained from human genes. Photo-irradiated TiO2 (anatase and rutile) caused DNA cleavage frequently at the guanine residue in the presence of Cu(II) after E. coli formamidopyrimidine-DNA glycosylase treatment, and the thymine residue was also cleaved after piperidine treatment. Catalase, SOD and bathocuproine, a chelator of Cu(I), inhibited the DNA damage, suggesting the involvement of hydrogen peroxide, superoxide and Cu(I). The photocatalytic generation of Cu(I) from Cu(II) was decreased by the addition of SOD. These findings suggest that the inhibitory effect of SOD on DNA damage is due to the inhibition of the reduction of Cu(II) by superoxide. We also measured the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine, an indicator of oxidative DNA damage, and showed that anatase is more active than rutile. On the other hand, high concentration of anatase caused DNA damage in the absence of Cu(II). Typical free hydroxyl radical scavengers, such as ethanol, mannnitol, sodium formate and DMSO, inhibited the copper-independent DNA photodamage by anatase. In conclusion, photo-irradiated TiO2 particles catalyze the copper-mediated site-specific DNA damage via the formation of hydrogen peroxide rather than that of a free hydroxyl radical. This DNA-damaging mechanism may participate in the phototoxicity of TiO2.

Oxidative DNA adducts after Cu(2+)-mediated activation of dihydroxy PCBs: role of reactive oxygen species

Polychlorinated biphenyls (PCBs) are toxic industrial chemicals, complete carcinogens, and efficacious tumor promoters. However, the mechanism(s) of PCB-mediated carcinogenicity remains largely undefined. One likely pathway by which these agents may play a role in carcinogenesis is the generation of oxidative DNA damage by redox cycling of dihydroxylated PCB metabolites. We have now employed a new (32)P-postlabeling system to examine novel oxidative DNA lesions induced by Cu(2+)-mediated activation of PCB metabolites. (32)P postlabeling of DNA incubated with various PCB metabolites resulted in over a dozen novel polar oxidative DNA adducts that were chromatographically similar for all active agents. The most potent metabolites tested were the hydroquinones (hydroxyl groups arranged para to each other), yielding polar oxidative adduct levels ranging from 55 to 142 adducts/10(6) nucleotides. PCB catechols, or ortho-dihydroxy metabolites, were up to 40% less active than their corresponding hydroquinone congeners, whereas monohydroxylated and quinone metabolites did not produce detectable oxidative damage over that of vehicle. With the exception of 2,4,5-Cl-2',5'-dihydroxybiphenyl, this oxidative DNA damage seemed to be inversely related to chlorine content: no chlorine approximately mono->di->trichlorinated metabolites. Importantly, copper, but not iron, was essential for activation of the PCB metabolites to these polar oxidative DNA adducts, because in its absence or in the presence of the Cu(+)-specific scavenger bathocuproine, no adducts were detected. Intervention studies with known reactive oxygen species (ROS) modifiers suggested that H(2)O(2), singlet oxygen, hydroxyl radical, and superoxide may also be involved in this PCB-mediated oxidative DNA damage. These data indicate a mechanistic role for several ROS, in addition to copper, in PCB-induced DNA damage and provide further support for oxidative DNA damage in PCB-mediated carcinogenesis.

Copper intoxication; antioxidant defenses and oxidative damage in rat brain

Copper (Cu) is an integral part of many important enzymes involved in a number of vital biological processes. Even though Cu is essential to life, it can become toxic to cells, at elevated tissue concentrations. Oxidative damage due to Cu has been reported in recent studies in various tissues. In this study, we aimed to determine the effect of excess Cu on oxidative and anti-oxidative substances in brain tissue in a rat model. Sixteen male Wistar albino rats were divided into two groups: the control group, which was given normal tap water, and the experimental group, which received water containing Cu in a dose of 1 g/l. All rats were sacrificed at the end of 4 wk, under ether anesthesia. Cu concentration in the liver and in plasma alanine aminotransferase (ALT) and aspartate transaminase (AST) activities were determined. There were multiparameter changes with significant ALT and AST activity elevation and increased liver Cu concentration. In brain tissue, Cu concentration, superoxide dismutase (SOD) activities, malondialdehyde (MDA) levels and glutathione (GSH) concentrations were determined. Brain Cu concentration was significantly higher in rats receiving excess Cu, compared with control rats (p < 0.05). Our results showed that SOD activities and GSH levels in brain tissue of the Cu-intoxicated animals were significantly lower than in the control group (p < 0.01 and p < 0,001, respectively). The brain MDA levels were found to be significantly higher in the experimental group than in the control group (p < 0.001). The present results indicate that excessive Cu accumulation in the brain depressed SOD activities and GSH levels and resulted in high MDA levels in brain homogenate due to the lipid peroxidation induced by the Cu overload.

Clioquinol targets zinc to lysosomes in human cancer cells

We have previously demonstrated that clioquinol (5-chloro-7-iodo-8-hydroxyquinoline) acts as a zinc ionophore and induces apoptosis of human cancer cells; however, the mechanisms of clioquinol/zinc-induced apoptotic cell death remain to be elucidated further. Using fluorescence-labelled probes, the present study has examined intracellular zinc distribution after clioquinol treatment in human cancer cells in order to identify cellular targets for zinc ionophores. DU 145, a human prostate cancer line, was chosen as a model system for the present study, and results were confirmed in other human cancer cell lines. Although treatment of cancer cells with 50 μM ZnCl2 for 3 days had no effect on cell viability, addition of clioquinol dramatically enhanced the cytotoxicity, confirming our previous observations. The ionophore activity of clioquinol was confirmed using fluorescence microscopy. Intracellular free zinc was found to be concentrated in lysosomes, indicating that lysosomes are the primary target of zinc ionophores. Furthermore, lysosomal integrity was disrupted after addition of clioquinol and zinc to the cells, as shown by redistribution of both Acridine Orange and cathepsin D. Clioquinol plus zinc resulted in a cleavage of Bid (BH3-interacting domain death agonist), a hallmark of lysosome-mediated apoptotic cell death. Thus the present study demonstrates for the first time that clioquinol generates free zinc in lysosomes, leading to their disruption and apoptotic cell death.

Damage to cellular and isolated DNA induced by a metabolite of aspirin

Aspirin has been proposed as a possible chemopreventive agent. On the other hand, a recent cohort study showed that aspirin may increase the risk for pancreatic cancer. To clarify whether aspirin is potentially carcinogenic, we investigated the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), which is correlated with the incidence of cancer, in cultured cells treated with 2,3-dihydroxybenzoic acid (2,3-DHBA), a metabolite of aspirin. 2,3-DHBA induced 8-oxodG formation in the PANC-1 human pancreatic cancer cell line. 2,3-DHBA-induced DNA single-strand breaks were also revealed by comet assay using PANC-1 cells. Flow cytometric analyses showed that 2,3-DHBA increased the levels of intracellular reactive oxygen species (ROS) in PANC-1 cells. The 8-oxodG formation and ROS generation were also observed in the HL-60 leukemia cell line, but not in the hydrogen peroxide (H(2)O(2))-resistant clone HP100 cells, suggesting the involvement of H(2)O(2). In addition, an hprt mutation assay supported the mutagenicity of 2,3-DHBA. We investigated the mechanism underlying the 2,3-DHBA-induced DNA damage using (32)P-labeled DNA fragments of human tumor suppressor genes. 2,3-DHBA induced DNA damage in the presence of Cu(II) and NADH. DNA damage induced by 2,3-DHBA was enhanced by the addition of histone peptide-6 [AKRHRK]. Interestingly, 2,3-DHBA and histone peptide-6 caused base damage in the 5'-ACG-3' and 5'-CCG-3' sequences, hotspots of the p53 gene. Bathocuproine, a Cu(I) chelator, and catalase inhibited the DNA damage. Typical hydroxyl radical scavengers did not inhibit the DNA damage. These results suggest that ROS derived from the reaction of H(2)O(2) with Cu(I) participate in the DNA damage. In conclusion, 2,3-DHBA induces oxidative DNA damage and mutations, which may result in carcinogenesis.

Solid-phase extraction and preconcentration of copper in mineral waters with 4-(2-pyridyl-azo) resorcinol-loaded amberlite XAD-7 and flame atomic absorption spectrometry

A simple, sensitive, accurate, and selective method for determination of ultratrace levels of copper is modified. The method is based on preconcentration of copper on the 4-(2-pyridyl-azo) resorcinol-loaded amberlite XAD-7 (non-ionic copoly[styrene-acrylic compound]) at pH 5.0 to 6.5 for contact time as low as 45 minutes. The adsorbed copper was eluted with concentrated nitric acid and measured by flame atomic absorption spectrometry. Recoveries of up to 90% were achieved. The optimized preconcentration method was applied to copper determination in various water samples. The detection limit was found to be 0.09 ng mL(-1). The relative standard deviation was found to be 9% using 300 mL of 5.0 ng mL(-1) for 10 replicate preconcentration procedures. Copper concentrations in the studied water samples were found to be in the ranges of 0.4 to 18.0 ng mL(-1).

Heavy metal adsorbents prepared from the modification of cellulose: a review

A number of industries currently produce varying concentrations of heavy metal laden waste streams with significant consequences for any receiving environmental compartment. In recent years, increasing emphasis has been placed on environmental impact minimisation and resulting from this the range and capability of natural and prepared materials capable of heavy metal removal has seen steady development. In particular considerable work has been carried out on the use of both natural materials and their modifications. These natural materials, in many instances are relatively cheap, abundant in supply and have significant potential for modification and ultimately enhancement of their adsorption capabilities. This review paper reviews the current state of research on the use of the naturally occurring material cellulose, its modified forms and their efficacy as adsorbents for the removal of heavy metals from waste streams. Adsorbents based on direct modification of cellulose are evaluated initially and subsequently modifications resulting from the grafting of selected monomers to the cellulose backbone with subsequent functionalisation are assessed. The heavy metal adsorption capacities for these modified cellulose materials were found to be significant and levels of uptake were comparable, in many instances, to both other naturally occurring adsorbent materials and commercial ion exchange type resins. Many of the modified cellulose adsorbents proved regenerable and re-usable over a number of adsorption/desorption cycles allowing recovery of the adsorbed heavy metal in a more concentrated form.

New uses for old copper-binding drugs: converting the pro-angiogenic copper to a specific cancer cell death inducer

BACKGROUND

The conventional approach toward anticancer drug development is a time-consuming and expensive procedure.

OBJECTIVE/METHODS

One approach to expedite this process and achieve more affordable means is to discover new applications of existing drugs, since their pharmacokinetics and pharmacological profiles are well known.

RESULTS

Our encouraging findings in recent studies reveal anticancer activities of several copper-binding ligands including disulfiram (an antialcoholism drug), clioquinol (used to treat Alzheimer's and Huntington's diseases) and diethyldithiocarbamate (an agent for HIV-1 infection treatment).

CONCLUSION

These in vitro and in vivo studies have demonstrated that these archaic drugs can target and react with tumor cellular copper, forming complexes that act as potent proteasome inhibitors and apoptosis inducers.

Copper-adenine complex, a compound, with multi-biochemical targets and potential anti-cancer effect

A series of adenine-copper complexes (1-6) with various ligands (Cl(-), SCN(-), BF(4)(-) and acac [acetylacetonate ion]) have been synthesized and characterized by elemental analysis, infrared spectroscopy and thermal analysis. Among the six complexes only complex (1), Cu(2)(adenine)(4)Cl(4).2EtOH (abbreviated as Cu-Ad), demonstrated some toxic effect on different cell lines. In vitro investigations of the biological effect of Cu-Ad complex have shown that it: (1) binds genomic DNA; (2) decreases significantly, the viability of cells in culture in a concentration (15-125 microM)-dependant manner; an estimated IC(50) of: 45 microM with HepG2; 73 microM with C2C12; 103 microM with NIH3T3; and 108 microM with MCF7. Cu-Ad had no effect on A549 cells; (3) inhibits Taq polymerase-catalyzed reaction; (4) inhibits the binding of the transcription factor GATA-5 to labeled DNA probes; (5) inhibits mitochondrial NADH-UQ-reductase with an estimated IC(50) of 2.8 nmol, but had no effect on succinate dehydrogenase activity; (6) increases reactive oxygen species (60%) at 45 microM Cu-Ad; and (7) decreases ATP (80%) at 50 microM Cu-Ad. The new compound Cu(2)(adenine)(4)Cl(4).2EtOH (Cu-Ad), belongs to a class of copper-adenylate complexes that target many biochemical sites and with potential anti-cancer activity.

Effect of Cu(II) on the complex between kanamycin A and the bacterial ribosomal A site

The solution structure of kanamycin A interacting with a ribosomal A-site fragment was solved by transferred-NOE techniques and found to agree with the structure of the complex observed in the crystal. Despite the fast exchange conditions found for the interaction, the bound form was identified by NOESY spectroscopy. At 600 MHz, NOE effects are only observed for the RNA-associated antibiotic. Dissociation constants were measured by NMR spectroscopy for two sites of interaction (K(d1)=150+/-40 microM; K(d2)=360+/-50 microM). Furthermore, the effects of the Cu(II) ion on the antibiotic, on the RNA fragment that mimics the bacterial ribosomal A site, and on the complex formed between these two entities were analyzed. The study led to the proposal of a model that localizes the copper ion within the kanamycin-RNA complex.

Characterization of copper(II) interactions with sinefungin, a nucleoside antibiotic: combined potentiometric, spectroscopic and DFT studies

Interactions between sinefungin and copper(II) ions were investigated. Stoichiometry and stability constants of the metal-free system and two mononuclear complexes present in solution were determined on the basis of potentiometric data analysis. The results were compared to the Cu(II)-ornithine system due to structural similarities between both molecules. Combined spectroscopic and theoretical studies allowed for determination of coordination pattern for the Cu(II)-sinefungin complexes. At acidic pH, copper is bound in “glycine-like” coordination mode, identical with that of ornithine. This involves α-amino group and the carboxyl oxygen. At higher pH, a “bis-complex” is formed by two sinefungin molecules. The second ligand binds in equatorial position displacing two water molecules, what results in the stable {2N,2O} coordination. Both axial positions are supposed to be occupied by N1 nitrogen donors of adenine moiety, what is confirmed by DFT calculations. They interact indirectly with copper(II) through water molecules as the result of dominant syn conformation of purine.

A study on metals content in patients with colorectal polyps

Data on metals involvement in colorectal polyps are scarce and fragmentary. The aim of this study was to examine whether the level of metals could be associated with risk of colorectal polyp development. The concentration of 15 chemical elements (Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg Mg, Mn, Pb, Se, Sr, and Zn) in 17 colorectal biopsies of healthy individuals, in 15 polypotic and corresponding nonpolypotic biopsies taken from the same individual, was evaluated. Concentration in polyps of metals such as Al, Ca, Mg, Mn, Pb, Sr, and Zn was unchanged both in unpaired and paired samples; elements such as Ba, Cd, and Hg were significantly lower and Fe was significantly higher both in individual and paired tissues. Cobalt, Cr, and Cu were significantly different only between polyps and the adjacent normal tissue area; Se showed a significant accumulation comparing polyps versus healthy tissues. The difference found in some elements between polyps and a control tissue provides an indication about the role of essential and nonessential elements in the early stage (polyps) in the colon carcinogenic process and encourages further studies to confirm the involvement of such elements in neoplastic processes.

Clioquinol promotes cancer cell toxicity through tumor necrosis factor alpha release from macrophages

Copper has an important role in cancer growth, angiogenesis, and metastasis. Previous studies have shown that cell-permeable metal ligands, including clioquinol (CQ) and pyrrolidine dithiocarbamate, inhibit cancer cell growth in cell culture and in vivo. The mechanism of action has not been fully determined but may involve metal-mediated inhibition of cancer cell proteasome activity. However, these studies do not fully account for the ability of cell-permeable metal ligands to inhibit cancer cell growth without affecting normal cells. In this study, we examined the effect of CQ on macrophage-mediated inhibition of HeLa cancer cell growth in vitro. When CQ was added to RAW 264.7 macrophage-HeLa cell cocultures, a substantial increase in HeLa cell toxicity was observed compared with CQ treatment of HeLa cells cultured alone. Transfer of conditioned medium from CQ-treated macrophages to HeLa cells also induced HeLa cell toxicity, demonstrating the role of secreted factors in the macrophage-mediated effect. Further investigation revealed that CQ induced copper-dependent activation of macrophages and release of tumor necrosis factor (TNF) alpha. In studies with recombinant TNFalpha, we showed that the level of TNFalpha released by CQ-treated macrophages was sufficient to induce HeLa cell toxicity. Moreover, the toxic effect of conditioned medium from CQ-treated macrophages could be prevented by addition of neutralizing antibodies to TNFalpha. These studies demonstrate that CQ can induce cancer cell toxicity through metal-dependent release of TNFalpha from macrophages. Our results may help to explain the targeted inhibition of tumor growth in vivo by CQ.

Opposite effect of Cu(II) and Se(IV) ions on the antibacterial-toxic action of mycotoxins

The effect of Se(IV) and Cu(II) ions on the antibacterial activity of aflatoxins and ochratoxin A (mycotoxins) was studied in BioArena as a complex bioautographic system. In the presence of 0.23 and 0.46 mg/100 mL Se(IV) the inhibition zones of mycotoxins were decreased, however, lower concentration (0.046 mg/100 mL) increased the antibacterial effect of aflatoxin B1. Cu(II) (1.53 mg/100 mL) enhanced the toxicity of mycotoxins. The results supported the possible role of formaldehyde and its reaction products (e.g. 1O2, O3) in the antibacterial-toxic action of mycotoxins. Cu(II) can probably generate and mobilise the formaldehyde molecules and so it could increase the toxicity with its potential reaction products. It is possible that the enzymatic or spontaneous methylation of Se(IV) takes place through formaldehyde, which may cause partial formaldehyde depletion in the system. The enhanced antibacterial effect at low concentration Se(IV) is overlapping with the often experienced prooxidant effect in cases of natural antioxidants.

On the interaction of bare and hydrated aluminum ion with nucleic acid bases (U, T, C, A, G) and monophosphate nucleotides (UMP, dTMP, dCMP, dAMP, dGMP)

The B3LYP/6-311+G(2df,2p) density functional approach was used to study the interaction that aluminum trication, in the bare and hydrated forms, establishes with the nucleic acid bases and the corresponding monophosphate nucleotides. In this investigation, we determine equilibrium geometry of all possible complexes resulting from the attachment of the ion on the different binding sites selected on each ligand. The relative energies of complexes and metal ion affinities are also given. The most meaningful aspect was found to lie in the energetics of this interaction that underlines a very high affinity of aluminum ion for the examined biological systems.

Metal Cu(II) and Zn(II) bipyridyls as inhibitors of lactate dehydrogenase

Metal complex-protein interaction is an evolving concept for determining cellular targets of metallodrugs. Lacatate dehydrogenase (LDH) is critically implicated in tumor growth and therefore, considered to be an important target protein for anti-tumor metal complexes. Due to efficient biocompatibility of copper (Cu(2+)) and zinc (Zn(2+)), we synthesized CubpyAc(2) . H(2)O (Cu-bpy) and ZnbpyAc(2) . H(2)O (Zn-bpy; where bpy = 2,2' bipyridine, Ac = CH(3)COO(-)) complexes and evaluated their interaction with and modulation of LDH in mouse tissues. The increasing concentration of both the complexes showed a significant shift in UV-Vis spectra of LDH. The binding constant data (Kc = 1 x 10(3) M(-1) for Cu-bpy and 7 x 10(6) M(-1) for Zn-bpy) suggested that Zn-bpy-LDH interaction is stronger than that of Cu-bpy-LDH. LDH modulating potential of the complexes were monitored by perfusing the mice tissues with non-toxic doses of Cu-bpy and Zn-bpy followed by activity measurement and analysis of LDH isozymes on non-denaturing polyacrylamide gel electrophoresis (PAGE). As compared to the control sets, Cu-bpy caused a significant decline (P < 0.05-0.001) in the activity of LDH in all the tissues studied. However, Zn-bpy showed inhibition of LDH only in liver (P < 0.01), kidney (P < 0.001) and heart (P < 0.01), but with no effect in spleen, brain and skeletal muscle tissues. PAGE analysis suggested that all the five LDH isozymes are equally sensitive to both the complexes in the respective tissues. The results suggest that Cu- and Zn-bpy are able to interact with and inhibit LDH, a tumor growth supportive target protein at tissue level.

Apoptotic rate and metallothionein levels in the tissues of cadmium- and copper-exposed rats

It is well known that cadmium (Cd) has toxic and carcinogenic effects in rodents and humans, but the effects of Cd on apoptosis are still not clear. Although some studies have shown that Cd has apoptotic potential, other studies have shown that Cd can be antiapoptotic. Parameters such as sensitivity of the exposed organism or cells and the exposure conditions should be important in delineating the effect of Cd on apoptosis. In the present study, we aimed to determine the apoptotic index (AI) of Sprague-Dawley rat tissues that are loaded at a lower Cd concentration than the critical concentration (50 microg/g) for its toxic effects. Metallothionein (MT) levels of tissues were also determined and the experiments repeated with copper (Cu)-exposed rats. We detected decreases in the apoptotic index in liver and lung tissues of Cd-exposed groups accompanied with an increase in MT levels. Also, decreases of AI were detected in the liver tissues of Cu-exposed groups. These findings indicate that Cd can suppress apoptosis in vivo. The possible role of MT expression on the suppression of apoptosis and the importance of free-Cd ion concentration on switching antiapoptotic effects to proapoptotic effects are also discussed.

Clioquinol, a therapeutic agent for Alzheimer's disease, has proteasome-inhibitory, androgen receptor-suppressing, apoptosis-inducing, and antitumor activities in human prostate cancer cells and xenografts

Tumor growth and metastasis depend on angiogenesis that requires the cofactor copper. Consistently, high levels of copper have been found in many types of human cancers, including prostate, breast, colon, and lung. Recent studies suggest that copper could be used as a novel selective target for cancer therapies. Clioquinol is capable of forming stable complexes with copper and currently used in clinics for treatment of Alzheimer's disease. Most recently, it has been reported that clioquinol possesses antitumor effects. However, the underlying molecular mechanism is unclear. We report here that after binding to copper, clioquinol can inhibit the proteasomal chymotrypsin-like activity, repress androgen receptor (AR) protein expression, and induce apoptotic cell death in human prostate cancer LNCaP and C4-2B cells. In addition, clioquinol alone exhibits similar effects in prostate cancer cell lines with elevated copper at concentrations similar to those found in patients. Addition of dihydrotestosterone did not affect clioquinol-mediated proteasome inhibition in both prostate cancer cell lines. However, dihydrotestosterone partially inhibited clioquinol-induced AR suppression and apoptosis only in androgen-dependent LNCaP cells. Animal studies show that clioquinol treatment significantly inhibits the growth of human prostate tumor C4-2B xenografts (by 66%), associated with in vivo proteasome inhibition, AR protein repression, angiogenesis suppression, and apoptosis induction. Our study provides strong evidence that clioquinol is able to target tumor proteasome in vivo in a copper-dependent manner, resulting in formation of an active AR inhibitor and apoptosis inducer that is responsible for its observed antiprostate tumor effect.

Comparison of trace element concentrations in cancerous and noncancerous human endometrial and ovary tissues

Question of whether trace metal concentrations in tissues are increased or decreased in cancerous patients in comparison with noncancerous patients has not been answered yet, due to the fact that the data known in this field are rare and have contradictory results. Although Zn and Cu concentrations in serum and tissues of cancerous patients have extensively been studied, the precise role of these metals in carcinogenesis is not clearly understood. There are few studies on the concentrations of essential and toxic trace/minor metals in human tissue samples in comparison with serum and plasma samples. Trace metal concentrations including Cd, Cu, Zn, Fe, Mg, Ca, and Ni in both cancerous and noncancerous endometrial, ovary, and cervix uteri tissues were determined by atomic absorption spectrometry. The tissue samples were digested by using microwave energy. Slotted tube atom trap was used to improve the sensitivity of copper and cadmium in flame atomic absorption spectrometry determination. The concentrations of iron in cancerous endometrial tissues were found to be significantly higher than those in noncancerous samples (P < 0.01). On the contrary Fe, Zn concentration in cancerous endometrial tissue was found to be lower significantly than those in noncancerous samples (P= 0.005), whereas the other studied metals were not observed different. Furthermore, Cu and Ca concentrations in cancerous ovary samples were observed to be higher than those in noncancerous ovary tissues (P < 0.01 for Cu and P= 0.1 for Ca), whereas Mg, Fe, and Zn levels in cancerous ovary samples were not found to be different than those in noncancerous tissues.

Distribution of trace metal concentrations in paired cancerous and non-cancerous human stomach tissues

AIM

To assess whether trace metal concentrations (which influence metabolism as both essential and non-essential elements) are increased or decreased in cancerous tissues and to understand the precise role of these metals in carcinogenesis.

METHODS

Concentrations of trace metals including Cd, Ni, Cu, Zn, Fe, Mg and Ca in both cancerous and non-cancerous stomach tissue samples were determined by atomic absorption spectrometry (AAS). Tissue samples were digested using microwave energy. Slotted tube atom trap was used to improve the sensitivity of copper and cadmium in flame AAS determinations.

RESULTS

From the obtained data in this study, the concentrations of nickel, copper and iron in the cancerous human stomach were found to be significantly higher than those in the non-cancerous tissues, by using t-test for the paired samples. Furthermore, the average calcium concentrations in the cancerous stomach tissue samples were found to be significantly lower than those in the non-cancerous stomach tissue samples by using t-test. Exceedingly high Zn concentrations (207-826 mg/kg) were found in two paired stomach tissue samples from both cancerous and non-cancerous parts.

CONCLUSION

In contrast to the literature data for Cu and Fe, the concentrations of copper, iron and nickel in cancerous tissue samples are higher than those in the non-cancerous samples. Furthermore, the Ca levels are lower in cancerous tissue samples than in non-cancerous tissue samples.

Metal Ion Interaction with Phosphorylated Tyrosine Analogue Monolayers on Gold

Phosphorylated tyrosine analogue molecules (pTyr-PT) were assembled onto gold substrates, and the resulting monolayers were used for metal ion interaction studies. The monolayers were characterized by X-ray photoelectron spectroscopy (XPS), infrared reflection-absorption spectroscopy (IRAS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), both prior to and after exposure to metal ions. XPS verified the elemental composition of the molecular adsorbate and the presence of metal ions coordinated to the phosphate groups. Both the angle-dependent XPS and IRAS results were consistent with the change in the structural orientation of the pTyr-PT monolayer upon exposure to metal ions. The differential capacitance of the monolayers upon coordination of the metal ions was evaluated using EIS. These metal ions were found to significantly change the capacitance of the pTyr-PT monolayers in contrast to the nonphosphorylated tyrosine analogue (TPT). CV results showed reduced electrochemical blocking capabilities of the phosphorylated analogue monolayer when exposed to metal ions, supporting the change in the structure of the monolayer observed by XPS and IRAS. The largest change in the structure and interfacial capacitance was observed for aluminum ions, compared to calcium, magnesium, and chromium ions. This type of monolayer shows an excellent capability to coordinate metal ions and has a high potential for use as sensing layers in biochip applications to monitor the presence of metal ions.

Mechanism for manganese enhancement of dopamine-induced oxidative DNA damage and neuronal cell death

Although the cause of dopaminergic cell death in Parkinson's disease is still poorly understood, there is accumulating evidence suggesting that metal ions can be involved in the processes. We investigated the effect of manganese on cell death and DNA damage in PC12 cells treated with dopamine. Mn(II) enhanced cell death induced by dopamine. Mn(II) also increased the 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) contents of DNA in PC12 cells treated with dopamine. To clarify the mechanism of cellular DNA damage, we investigated DNA damage induced by dopamine and Mn(II) using (32)P-labeled DNA fragments. Mn(II) enhanced Cu(II)-dependent DNA damage by dopamine. The Mn(II)-enhanced DNA damage was greatly increased by NADH. Piperidine and formamidopyrimidine-DNA glycosylase treatment induced cleavage sites mainly at T and G of the 5'-TG-3' sequence, respectively. Bathocuproine, a Cu(I) chelator, and catalase inhibited the DNA damage. Oxygen consumption and UV-visible spectroscopic measurements showed that Mn(II) enhanced autoxidation of dopamine with H(2)O(2) formation. These results suggest that reactive species derived from the reaction of H(2)O(2) with Cu(I) participates in Mn(II)-enhanced DNA damage by dopamine plus Cu(II). Therefore, it is concluded that oxidative DNA damage induced by dopamine in the presence of Mn(II), NADH, and Cu(II) is possibly linked to the degeneration of dopaminergic neurons.

Differences in tumor-associated protein levels among middle-age Flemish women in association with area of residence and exposure to pollutants

We measured tumor-associated proteins (TAPs) and pollutants in blood, serum, and urine of 200 nonsmoking women 50-65 years of age, residing in the rural municipality of Peer or in Hoboken or Wilrijk, industrial suburbs of Antwerp, Belgium. Persons with occupational exposures or commuting to other towns were excluded. Residents from Hoboken had significantly higher levels of blood lead and serum zinc and polychlorinated biphenyls. Surprisingly, residents of Peer had significantly higher levels of serum cadmium, dioxin-like activity in blood fat, and urinary 1-hydroxypyrene. For 5 of the 12 TAPs assessed in this study, we observed significant differences in serum levels among residents of the three municipalities after adjusting for personal or lifestyle parameters. Although we found levels of internal exposure to pollutants to be quite homogeneous in Flanders, we found significantly higher levels of TAPs only in the industrial suburbs. In multiple regression with all 29 available personal, lifestyle, and internal exposure parameters, blood lead levels showed a positive association with serum levels of anti-p53, carcino-embryonic antigen (CEA), and tissue polypeptide-specific antigen (TPS) and with an index for mean TAP level (I(tap)); dioxin-like activity in serum and serum copper showed a positive association with serum CA 125 (cancer antigen 125); and serum zinc showed a positive association with serum levels of c-erbB-2 ectodomain and TPS. An index of internal exposure showed a positive association with serum levels of both CEA and anti-p53 and with I(tap). This study provides some evidence that levels of internal exposure such as those present in Flanders, in particular concerning lead, are indeed associated with biologic effects.

Copper-1,10-Phenanthroline-Induced Apoptosis in Liver Carcinoma Bel-7402 Cells Associates with Copper Overload, Reactive Oxygen Species Production, Glutathione Depletion and Oxidative DNA Damage

The mechanism of cytotoxicity on liver carcinoma Bel-7402 cells induced by copper-1,10-phenanthroline, Cu(OP)2, has been studied. Cell viability and apoptotic rate were examined in cells treated with Cu(OP)2 or Cu2+ alone. It was found that the apoptosis induced by Cu(OP)2 could not be induced by Cu2+ or OP alone in our experimental conditions. Total copper content in cells was measured by atomic absorption spectrophotometry, and the abnormal elevation of intracellular copper transported by lipophilic OP ligand may play the role of initial factor in the apoptosis, which caused subsequent redox state changes in cells. Intracellular levels of reactive oxygen species (ROS) were detected by fluorescent probe 2',7'-dichlorofluorescein diacetate (DCFH-DA). Reduced (GSH) and total glutathione (GSSG + GSH) were determined by High-performance liquid chromatography (HPLC) after derivatization, and the ratios of GSH/GSSG were subsequently calculated. The overproduction of ROS and the decreased GSH/GSSG ratio were observed in cells which represented the occurrence of oxidative stress in the apoptosis. Oxidative DNA damage was also found in cells treated with Cu(OP)2 in the early stage of the apoptosis, and it suggests that the activation of DNA repair system may be involved in the pathway of the apoptosis induced by Cu(OP)2.

Comparison of the concentration of trace metals (Ni, Zn, Co, Cu and Se), Fe, vitamins A, C and E, and lipid peroxidation in patients with prostate cancer

The anticarcinogenic and antioxidant properties of vitamins A, C, E and pro- or antioxidant properties of trace metals have recently attracted increased attention. We examined the levels of antioxidant vitamins (A, C and E), selenium and malondialdehyde (MDA), and trace metals (Fe, Ni, Zn, Co and Cu) in patients with prostate cancer. In total, 41 subjects (21 controls and 20 prostate cancer patients) were included in the study. The levels of trace elements and Fe in whole blood were determined by atomic absorption spectrophotometry. Serum levels of Se were determined using a fluorimetric method, while a HPLC method was used for serum levels of vitamins and MDA. The levels of vitamins A and E were significantly lower and MDA levels were significantly higher (p<0.001) in patients with prostate cancer compared to controls. Serum vitamin C was significantly lower in patients with prostate cancer when compared to controls (p<0.01). Moreover, Se and Zn levels were also significantly lower, and levels of Ni, Co, and Cu were higher (p<0.001) in patients with prostate cancer than in controls. Fe levels were not significantly different in patients compared to controls (p>0.05). Our findings, together with the results of previous animal studies, suggest that the administration of vitamins A, C, and E, and Se and Zn may be beneficial in the prevention and treatment of human prostate cancer.

Hypericin-photodynamic therapy (PDT) using an alternative treatment regime suitable for multi-fraction PDT

Photodynamic therapy (PDT) outcome depends on the conditions under which it is carried out. Maintaining the tumour tissue oxygen level is important for PDT efficacy and using a low fluence rate can improve outcome. In this work we studied the response of human nasopharyngeal carcinoma tumours in murine models to hypericin-PDT carried out under low fluence and fluence rate. A drug-light interval (DLI) of 1h or 6h was used for 1h-PDT and 6h-PDT, respectively. Evan's blue test was used to assess necrosis and TUNEL staining for apoptosis. Nuclear microscopy was used to quantify elemental concentrations in tumours. Serum vascular endothelial growth factor (VEGF) levels were also determined. TUNEL results showed that 6h-PDT induced significantly more apoptosis compared to 1h-PDT (p<0.01). This was supported by nuclear microscopy showing an increase in calcium and a decrease in zinc levels (both known triggers of apoptosis) in 6h-PDT tumours compared to non-PDT tumours (p<0.05). These results further imply a zinc-mediated pathway in hypericin-PDT induced apoptosis. 6h-PDT also resulted in a significant increase in copper concentrations compared to non-PDT tumours (p<0.05). Serum VEGF levels measured after 6h-PDT were lower than those obtained after 1h-PDT. Overall tumour response to hypericin-PDT under low fluence and fluence rate and using a 6h DLI showed increased apoptosis and lower serum VEGF levels. This treatment regime is suitable for the alternative approach of multi-fraction PDT in which the tumour can be exposed to multiple PDT fractions for complete tumour response. This alternative approach might yield improved outcome.

Metal ions and carcinogenesis

Metals are essential for the normal functioning of living organisms. Their uses in biological systems are varied, but are frequently associated with sites of critical protein function, such as zinc finger motifs and electron or oxygen carriers. These functions only require essential metals in minute amounts, hence they are termed trace metals. Other metals are, however, less beneficial, owing to their ability to promote a wide variety of deleterious health effects, including cancer. Metals such as arsenic, for example, can produce a variety of diseases ranging from keratosis of the palms and feet to cancers in multiple target organs. The nature and type of metal-induced pathologies appear to be dependent on the concentration, speciation, and length of exposure. Unfortunately, human contact with metals is an inescapable consequence of human life, with exposures occurring from both occupational and environmental sources. A uniform mechanism of action for all harmful metals is unlikely, if not implausible, given the diverse chemical properties of each metal. In this chapter we will review the mechanisms of carcinogenesis of arsenic, cadmium, chromium, and nickel, the four known carcinogenic metals that are best understood. The key areas of speciation, bioavailability, and mechanisms of action are discussed with particular reference to the role of metals in alteration of gene expression and maintenance of genomic integrity.

Formation of M1G-dR from endogenous and exogenous ROS-inducing chemicals

The present study provides fundamental information regarding the production of M1G-dR by ROS. To investigate the production of M1G-dR from deoxyribose damage as caused by ROS, calf thymus DNA (CT-DNA) was incubated with NAD(P)H, CuCl2, and various concentrations of hydrogen peroxide (H2O2). The incubation of CT-DNA with H2O2 resulted in concentration-dependent increases in the number of M1G-dR adducts. In subsequent experiments, 1,4-tetrachlorobenzoquinone or catechol estrogens were evaluated for their effects on M1G-dR formation. In addition, the role of lipid peroxidation in the formation of M1G-dR was verified using an in vitro lipid peroxidation model which consisted of methyl esters of either fish oil or purified fatty acids found in cellular membranes. This experiment confirmed that M1G-dR is a major DNA adduct produced by lipid peroxidation. Furthermore, the number of double bonds in polyunsaturated fatty acids was found to be the key factor in the formation of M1G-dR. The findings obtained from this study provide important information regarding the molecular pathways for M1G-dR formation by ROS, which is an essential element in understanding and evaluating the genotoxicity of a variety of ROS-inducing chemicals.

Procyanidin B2 has anti- and pro-oxidant effects on metal-mediated DNA damage

Procyanidin B2 (epicatechin-(4beta-8)-epicatechin), which is present in grape seeds, apples, and cacao beans, has antioxidant properties. We investigated the mechanism of preventive action of procyanidin B2 against oxidative DNA damage in human cultured cells and isolated DNA. Procyanidin B2 inhibited the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in the human leukemia cell line HL-60 treated with an H2O2-generating system. In contrast, a high concentration of procyanidin B2 increased the formation of 8-oxodG in HL-60 cells. Experiments with calf thymus DNA also revealed that procyanidin B2 decreased 8-oxodG formation by Fe(II)/H2O2, whereas procyanidin B2 induced DNA damage in the presence of Cu(II), and H2O2 extensively enhanced it. An electron spin resonance spin trapping study utilizing 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M4PO) demonstrated that procyanidin B2 decreased the signal of M4PO-OH from H2O2 and Fe(II), whereas procyanidin B2 enhanced the signal from H2O2 and Cu(II). As an antioxidant mechanism, UV-visible spectroscopy showed that procyanidin B2 chelated Fe(II) at equivalent concentrations. As a pro-oxidant property, we examined DNA damage induced by procyanidin B2, using 32P-labeled DNA fragments obtained from genes relevant to human cancer. Our results raise the possibility that procyanidin B2 exerts both antioxidant and pro-oxidant properties by interacting with H2O2 and metal ions.

Clioquinol and pyrrolidine dithiocarbamate complex with copper to form proteasome inhibitors and apoptosis inducers in human breast cancer cells

INTRODUCTION

A physiological feature of many tumor tissues and cells is the tendency to accumulate high concentrations of copper. While the precise role of copper in tumors is cryptic, copper, but not other trace metals, is required for angiogenesis. We have recently reported that organic copper-containing compounds, including 8-hydroxyquinoline-copper(II) and 5,7-dichloro-8-hydroxyquinoline-copper(II), comprise a novel class of proteasome inhibitors and tumor cell apoptosis inducers. In the current study, we investigate whether clioquinol (CQ), an analog of 8-hydroxyquinoline and an Alzheimer's disease drug, and pyrrolidine dithiocarbamate (PDTC), a known copper-binding compound and antioxidant, can interact with copper to form cancer-specific proteasome inhibitors and apoptosis inducers in human breast cancer cells. Tetrathiomolybdate (TM), a strong copper chelator currently being tested in clinical trials, is used as a comparison.

METHODS

Breast cell lines, normal, immortalized MCF-10A, premalignant MCF10AT1K.cl2, and malignant MCF10DCIS.com and MDA-MB-231, were treated with CQ or PDTC with or without prior interaction with copper, followed by measurement of proteasome inhibition and cell death. Inhibition of the proteasome was determined by levels of the proteasomal chymotrypsin-like activity and ubiquitinated proteins in protein extracts of the treated cells. Apoptotic cell death was measured by morphological changes, Hoechst staining, and poly(ADP-ribose) polymerase cleavage.

RESULTS

When in complex with copper, both CQ and PDTC, but not TM, can inhibit the proteasome chymotrypsin-like activity, block proliferation, and induce apoptotic cell death preferentially in breast cancer cells, less in premalignant breast cells, but are non-toxic to normal/non-transformed breast cells at the concentrations tested. In contrast, CQ, PDTC, TM or copper alone had no effects on any of the cells. Breast premalignant or cancer cells that contain copper at concentrations similar to those found in patients, when treated with just CQ or PDTC alone, but not TM, undergo proteasome inhibition and apoptosis.

CONCLUSION

The feature of breast cancer cells and tissues to accumulate copper can be used as a targeting method for anticancer therapy through treatment with novel compounds such as CQ and PDTC that become active proteasome inhibitors and breast cancer cell killers in the presence of copper.

Sensitivity enhancement in flame atomic absorption spectrometry for determination of copper in human thyroid tissues

Various designs of quartz tube in a slotted tube atom trap were examined for improving the sensitivity of flame AAS. A 3.5-fold enhancement in the sensitivity was obtained by using the optimized method. The method was applied to the determination of Cu in cancerous and non-cancerous human thyroid tissues. The Cu concentrations of the cancerous samples tended to increase compared with the non-cancerous samples. Zn concentrations of the same tissues were also determined.

Anticancer activity of the antibiotic clioquinol

Clioquinol, a metal chelator, has been used for many years as an antimicrobial agent and more recently as a potential treatment for Alzheimer's disease. Because it binds copper and zinc, metals essential for the activity of the enzyme superoxide dismutase-1 (SOD1), a potential target for anticancer drug development, we investigated its effects on human cancer cells. Treatment with clioquinol reduced the viability of eight different human cancer cell lines in a concentration-dependent manner, with IC(50) values in the low micromolar range. Biochemical analysis revealed that clioquinol induced cancer cell death through apoptotic pathways that require caspase activity. Although clioquinol induced modest inhibition of SOD1 activity in treated cells, comparable inhibition by a known SOD1 inhibitor, diethyldithiocarbamate, did not result in cytotoxicity. The addition of copper, iron, or zinc did not rescue cells from cliquinol-induced cytotoxicity but enhanced its killing, arguing against metal chelation as its major mechanism of action. To test if clioquinol might act as an ionophore, a fluorescent probe was used to monitor intracellular zinc concentrations. The addition of clioquinol resulted in elevated levels of intracellular zinc, indicating that clioquinol acts as a zinc ionophore. In an in vivo xenografts mouse model, clioquinol inhibited tumor growth of xenografts over a 6-week period, without inducing visible toxicity. Our results show that clioquinol has anticancer effects both in vitro and in vivo. Transition metal ionophores may be a subclass of metal chelators with anticancer activity deserving of further development.