The therapeutic potential of iron chelators

Iron Chelation Therapy Elicits Innate Immune Control of Metastatic Ovarian Cancer

Iron accumulation in tumors contributes to disease progression and chemoresistance. Although targeting this process can influence various hallmarks of cancer, the immunomodulatory effects of iron chelation in the tumor microenvironment are unknown. Here, we report that treatment with deferiprone, an FDA-approved iron chelator, unleashes innate immune responses that restrain ovarian cancer. Deferiprone reprogrammed ovarian cancer cells toward an immunostimulatory state characterized by the production of type-I IFN and overexpression of molecules that activate NK cells. Mechanistically, these effects were driven by innate sensing of mitochondrial DNA in the cytosol and concomitant activation of nuclear DNA damage responses triggered upon iron chelation. Deferiprone synergized with chemotherapy and prolonged the survival of mice with ovarian cancer by bolstering type-I IFN responses that drove NK cell-dependent control of metastatic disease. Hence, iron chelation may represent an alternative immunotherapeutic strategy for malignancies that are refractory to current T-cell-centric modalities. Significance: This study uncovers that targeting dysregulated iron accumulation in ovarian tumors represents a major therapeutic opportunity. Iron chelation therapy using an FDA-approved agent causes immunogenic stress responses in ovarian cancer cells that delay metastatic disease progression and enhance the effects of first-line chemotherapy. See related commentary by Bell and Zou, p. 1771.

An Indian Desert Shrub 'Hiran Chabba', Farsetia hamiltonii Royle, Exhibits Potent Antioxidant and Hepatoprotective Effect Against Iron- Overload Induced Liver Toxicity in Swiss Albino Mice

BACKGROUND

Farsetia hamiltonii Royle, also known as Hiran Chabba grows in desert regions. It is widely used as folk medicine to treat joint pains, diarrhea and diabetes. However, its antioxidant and iron chelation abilities both in vitro and in vivo have not yet been investigated.

METHODS

The 70% methanolic extract of F. hamiltonii (FHME) was investigated for its free radical scavenging and iron chelation potential, in vitro. An iron-overload situation was established by intraperitoneal injection of iron-dextran in Swiss albino mice, followed by oral administration of FHME. Liver damage and serum parameters due to iron-overload were measured biochemically and histopathologically to test iron-overload remediation and hepatoprotective potential of FHME. Phytochemical analyses were performed to determine its probable bioactive components.

RESULTS

FHME showed promising antioxidant activity, scavenged various reactive oxygen and nitrogen species and chelated iron in vitro. FHME reduced liver iron, serum ferritin, normalized serum parameters, reduced oxidative stress in liver, serum and improved liver antioxidant status in ironoverloaded mice. It also alleviated liver damage and fibrosis as evident from biochemical parameters and morphological analysis of liver sections. The phytochemical analyses of FHME reflected the presence of alkaloids, phenols, flavonoids and tannins. HPLC analysis indicated presence of tannic acid, quercetin, methyl gallate, catechin, reserpine, ascorbic acid and gallic acid.

CONCLUSION

Based on the experimental outcome, FHME, an ethnologically important plant can be envisaged as excellent antioxidant and iron chelator drug capable of remediating iron-overload induced hepatotoxicity and the bioactive compounds present in FHME might be responsible for its efficacy.

Thiosemicarbazones as Potent Anticancer Agents and their Modes of Action

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Thiosemicarbazones (TSCs) are a class of Schiff bases usually obtained by the condensation of thiosemicarbazide with a suitable aldehyde or ketone. TSCs have been the focus of chemists and biologists due to their wide range of pharmacological effects. One of the promising areas in which these excellent metal chelators are being developed is their use against cancer. TSCs have a wide clinical antitumor spectrum with efficacy in various tumor types such as leukemia, pancreatic cancer, breast cancer, non-small cell lung cancer, cervical cancer, prostate cancer and bladder cancer. To obtain better activity, different series of TSCs have been developed by modifying the heteroaromatic system in their molecules. These compounds possessed significant antineoplastic activity when the carbonyl attachment of the side chain was located at a position α to the ring nitrogen atom, whereas attachment of the side chain β or γ to the heterocyclic N atom resulted in inactive antitumor agents. In addition, replacement of the heterocyclic ring N with C also resulted in a biologically inactive compound suggesting that a conjugated N,N,S-tridentate donor set is essential for the biological activities of thiosemicarbazones. Several possible mechanisms have been implemented for the anticancer activity of thiosemicarbazones.

The Role of the Antioxidant Response in Mitochondrial Dysfunction in Degenerative Diseases: Cross-Talk between Antioxidant Defense, Autophagy, and Apoptosis

The mitochondrion is an essential organelle important for the generation of ATP for cellular function. This is especially critical for cells with high energy demands, such as neurons for signal transmission and cardiomyocytes for the continuous mechanical work of the heart. However, deleterious reactive oxygen species are generated as a result of mitochondrial electron transport, requiring a rigorous activation of antioxidative defense in order to maintain homeostatic mitochondrial function. Indeed, recent studies have demonstrated that the dysregulation of antioxidant response leads to mitochondrial dysfunction in human degenerative diseases affecting the nervous system and the heart. In this review, we outline and discuss the mitochondrial and oxidative stress factors causing degenerative diseases, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, and Friedreich's ataxia. In particular, the pathological involvement of mitochondrial dysfunction in relation to oxidative stress, energy metabolism, mitochondrial dynamics, and cell death will be explored. Understanding the pathology and the development of these diseases has highlighted novel regulators in the homeostatic maintenance of mitochondria. Importantly, this offers potential therapeutic targets in the development of future treatments for these degenerative diseases.

A natural antioxidant, tannic acid mitigates iron-overload induced hepatotoxicity in Swiss albino mice through ROS regulation

Tannic acid (TA), a water soluble natural polyphenol with 8 gallic acids groups, is abundantly present in various medicinal plants. Previously TA has been investigated for its antimicrobial and antifungal properties. Being a large polyphenol, TA chelates more than 1 metal. Hence TA has been explored for potent antioxidant activities against reactive oxygen species (ROS), reactive nitrogen species (RNS) and as iron chelator in vitro thereby mitigating iron-overload induced hepatotoxicity in vivo. Iron dextran was injected intraperitoneally in Swiss albino mice to induce iron-overload triggered hepatotoxicity, followed by oral administration of TA for remediation. After treatment, liver, spleen, and blood samples were processed from sacrificed animals. The liver iron, serum ferritin, serum markers, ROS, liver antioxidant status, and liver damage parameters were assessed, followed by histopathology and protein expression studies. Our results show that TA is a prominent ROS and RNS scavenger as well as iron chelator in vitro. It also reversed the ROS levels in vivo and restricted the liver damage parameters as compared to the standard drug, desirox. Moreover, this natural polyphenol exclusively ameliorates the histopathological and fibrotic changes in liver sections reducing the iron-overload, along with chelation of liver iron and normalization of serum ferritin. The protective role of TA against iron-overload induced apoptosis in liver was further supported by changed levels of caspase 3, PARP as well as Bax/BCl-2 ratio. Thus, TA can be envisaged as a better orally administrable iron chelator to reduce iron-overload induced hepatotoxicity through ROS regulation.

Curcumin Attenuates Iron Accumulation and Oxidative Stress in the Liver and Spleen of Chronic Iron-Overloaded Rats

OBJECTIVES

Iron overload is now recognized as a health problem in industrialized countries, as excessive iron is highly toxic for liver and spleen. The potential use of curcumin as an iron chelator has not been clearly identified experimentally in iron overload condition. Here, we evaluate the efficacy of curcumin to alleviate iron overload-induced hepatic and splenic abnormalities and to gain insight into the underlying mechanisms.

DESIGN AND METHODS

Three groups of male adult rats were treated as follows: control rats, rats treated with iron in a drinking water for 2 months followed by either vehicle or curcumin treatment for 2 more months. Thereafter, we studied the effects of curcumin on iron overload-induced lipid peroxidation and anti-oxidant depletion.

RESULTS

Treatment of iron-overloaded rats with curcumin resulted in marked decreases in iron accumulation within liver and spleen. Iron-overloaded rats had significant increases in malonyldialdehyde (MDA), a marker of lipid peroxidation and nitric oxide (NO) in liver and spleen when compared to control group. The effects of iron overload on lipid peroxidation and NO levels were significantly reduced by the intervention treatment with curcumin (P<0.05). Furthermore, the endogenous anti-oxidant activities/levels in liver and spleen were also significantly decreased in chronic iron overload and administration of curcumin restored the decrease in the hepatic and splenic antioxidant activities/levels.

CONCLUSION

Our study suggests that curcumin may represent a new horizon in managing iron overload-induced toxicity as well as in pathological diseases characterized by hepatic iron accumulation such as thalassemia, sickle cell anemia, and myelodysplastic syndromes possibly via iron chelation, reduced oxidative stress derived lipid peroxidation and improving the body endogenous antioxidant defense mechanism.

An Antioxidant Extract of the Insectivorous Plant Drosera burmannii Vahl. Alleviates Iron-Induced Oxidative Stress and Hepatic Injury in Mice

Free iron typically leads to the formation of excess free radicals, and additional iron deposition in the liver contributes to the oxidative pathologic processes of liver disease. Many pharmacological properties of the insectivorous plant Drosera burmannii Vahl. have been reported in previous studies; however, there is no evidence of its antioxidant or hepatoprotective potential against iron overload. The antioxidant activity of 70% methanolic extract of D. burmannii (DBME) was evaluated. DBME showed excellent DPPH, hydroxyl, hypochlorous, superoxide, singlet oxygen, nitric oxide, peroxynitrite radical and hydrogen peroxide scavenging activity. A substantial iron chelation (IC₅₀ = 40.90 ± 0.31 μg/ml) and supercoiled DNA protection ([P]₅₀ = 50.41 ± 0.55 μg) were observed. DBME also displayed excellent in vivo hepatoprotective activity in iron-overloaded Swiss albino mice compared to the standard desirox treatment. Administration of DBME significantly normalized serum enzyme levels and restored liver antioxidant enzymes levels. DBME lowered the raised levels of liver damage parameters, also reflected from the morphological analysis of the liver sections. DBME also reduced liver iron content by 115.90% which is also seen by Perls’ staining. A phytochemical analysis of DBME confirms the presence of various phytoconstituents, including phenols, flavonoids, carbohydrates, tannins, alkaloids and ascorbic acid. Alkaloids, phenols and flavonoids were abundantly found in DBME. An HPLC analysis of DBME revealed the presence of purpurin, catechin, tannic acid, reserpine, methyl gallate and rutin. Purpurin, tannic acid, methyl gallate and rutin displayed excellent iron chelation but exhibited cytotoxicity toward normal (WI-38) cells; while DBME found to be non-toxic to the normal cells. These findings suggest that the constituents present in DBME contributed to its iron chelation activity. Additional studies are needed to determine if DBME can be used as a treatment for iron overload diseases.

Investigation of the biological properties of (hetero)aromatic thiosemicarbazones

Two series of thiosemicarbazone-based iron chelators (twenty-seven compounds) were designed and synthesized using a microwave-assisted approach. Quinoline and halogenated phenyl were selected as parent scaffolds on the basis of a similarity search. The lipophilicity of the synthesized compounds was measured using HPLC and then calculated. Primary in vitro screening of the synthesized compounds was performed against eight pathogenic fungal strains. Only a few compounds showed moderate activity against fungi, and (E)-2-(quinolin-2-ylvinyl)-N,N-dimethylhydrazine-carbothioamide appeared to be more effective than fluconazole against most of the fungal strains tested. Antiproliferative activity was measured using a human colon cancer cell line (HCT-116). Several of the tested compounds showed submicromolar antiproliferative activity. Compounds were also tested for their activity related to the inhibition of photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. The structure-activity relationships are discussed for all of the compounds.

Synthesis and biological evaluation of 1,4-naphthoquinones and quinoline-5,8-diones as antimalarial and schistosomicidal agents

Improving the solubility of polysubstituted 1,4-naphthoquinone derivatives was achieved by introducing nitrogen in two different positions of the naphthoquinone core, at C-5 and at C-8 of menadione through a two-step, straightforward synthesis based on the regioselective hetero-Diels-Alder reaction. The antimalarial and the antischistosomal activities of these polysubstituted aza-1,4-naphthoquinone derivatives were evaluated and led to the selection of distinct compounds for antimalarial versus antischistosomal action. The Ag(II)-assisted oxidative radical decarboxylation of the phenyl acetic acids using AgNO(3) and ammonium peroxodisulfate was modified to generate the 3-picolinyl-menadione with improved pharmacokinetic parameters, high antimalarial effects and capacity to inhibit the formation of β-hematin.

Hepatoprotective Potential of Caesalpinia crista against Iron-Overload-Induced Liver Toxicity in Mice

The present study was carried out to evaluate the ameliorating effect of Caesalpinia crista Linn. (CCME) extract on iron-overload-induced liver injury. Iron overload was induced by intraperitoneal administration of iron dextran into mice. CCME attenuated the percentage increase in liver iron and serum ferritin levels when compared to control group. CCME also showed a dose-dependent inhibition of lipid peroxidation, protein oxidation, and liver fibrosis. The serum enzyme markers were found to be less, whereas enhanced levels of liver antioxidant enzymes were detected in CCME-treated group. In presence of CCME, the reductive release of ferritin iron was increased significantly. Furthermore, CCME exhibited DPPH radical scavenging and protection against Fe(2+)-mediated oxidative DNA damage. The current study confirmed the hepatoprotective effect of CCME against the model hepatotoxicant iron overload and the activity is likely related to its potent antioxidant and iron-chelating property.

Nanoparticle and iron chelators as a potential novel Alzheimer therapy

Current therapies for Alzheimer disease (AD) such as the acetylcholinesterase inhibitors and the latest NMDA receptor inhibitor, Namenda, provide moderate symptomatic delay at various stages of the disease, but do not arrest the disease progression or bring in meaningful remission. New approaches to the disease management are urgently needed. Although the etiology of AD is largely unknown, oxidative damage mediated by metals is likely a significant contributor since metals such as iron, aluminum, zinc, and copper are dysregulated and/or increased in AD brain tissue and create a pro-oxidative environment. This role of metal ion-induced free radical formation in AD makes chelation therapy an attractive means of dampening the oxidative stress burden in neurons. The chelator desferrioxamine, FDA approved for iron overload, has shown some benefit in AD, but like many chelators, it has a host of adverse effects and substantial obstacles for tissue-specific targeting. Other chelators are under development and have shown various strengths and weaknesses. Here, we propose a novel system of chelation therapy through the use of nanoparticles. Nanoparticles conjugated to chelators show unique ability to cross the blood-brain barrier (BBB), chelate metals, and exit through the BBB with their corresponding complexed metal ions. This method may provide a safer and more effective means of reducing the metal load in neural tissue, thus attenuating the harmful effects of oxidative damage and its sequelae. Experimental procedures are presented in this chapter.

Metal chelators coupled with nanoparticles as potential therapeutic agents for Alzheimer's disease

Alzheimer's disease (AD) is a devastating neuro-degenerative disorder characterized by the progressive and irreversible loss of memory followed by complete dementia. Despite the disease's high prevalence and great economic and social burden, an explicative etiology or viable cure is not available. Great effort has been made to better understand the disease's pathogenesis, and to develop more effective therapeutic agents. However, success is greatly hampered by the presence of the blood-brain barrier that limits a large number of potential therapeutics from entering the brain. Nanoparticle-mediated drug delivery is one of the few valuable tools for overcoming this impediment and its application as a potential AD treatment shows promise. In this review, the current studies on nanoparticle delivery of chelation agents as possible therapeutics for AD are discussed because several metals are found excessive in the AD brain and may play a role in the disease development. Specifically, a novel approach involving transport of iron chelation agents into and out of the brain by nanoparticles is highlighted. This approach may provide a safer and more effective means of simultaneously reducing several toxic metals in the AD brain. It may also provide insights into the mechanisms of AD pathophysiology, and prove useful in treating other iron-associated neurodegenerative diseases such as Friedreich's ataxia, Parkinson's disease, Huntington's disease and Hallervorden-Spatz Syndrome. It is important to note that the use of nanoparticle-mediated transport to facilitate toxicant excretion from diseased sites in the body may advance nanoparticle technology, which is currently focused on targeted drug delivery for disease prevention and treatment. The application of nanoparticle-mediated drug transport in the treatment of AD is at its very early stages of development and, therefore, more studies are warranted.

Iron(III) Complexes with a Biologically Relevant Aroylhydrazone: Crystallographic Evidence for Coordination Versatility

Complexation of iron(III) with the heterodonor chelating agent 3,5-di-tert-butylsalicylidene benzoylhydrazine, H2(3,5-tBu2)salbh, in the absence or presence of a base affords the complex cation [Fe{H(3,5-tBu2)salbh}2]+ or the neutral compound [Fe{H(3,5-tBu2)salbh}{(3,5-tBu2)salbh}], respectively, as revealed by single-crystal X-ray analyses. Such a synthetic and crystallographic demonstration of the coordination versatility of an aroylhydrazone toward iron is uncommon. The oxidation and spin states of the iron have been verified with magnetic and spectroscopic measurements.

Dipyridyl thiosemicarbazone chelators with potent and selective antitumor activity form iron complexes with redox activity

There has been much interest in the development of iron (Fe) chelators for the treatment of cancer. We developed a series of di-2-pyridyl ketone thiosemicarbazone (HDpT) ligands which show marked and selective antitumor activity in vitro and in vivo. In this study, we assessed chemical and biological properties of these ligands and their Fe complexes in order to understand their marked activity. This included examination of their solution chemistry, electrochemistry, ability to mediate redox reactions, and antiproliferative activity against tumor cells. The higher antiproliferative efficacy of the HDpT series of chelators relative to the related di-2-pyridyl ketone isonicotinoyl hydrazone (HPKIH) analogues can be ascribed, in part, to the redox potentials of their Fe complexes which lead to the generation of reactive oxygen species. The most effective HDpT ligands as antiproliferative agents possess considerable lipophilicity and were shown to be charge neutral at physiological pH, allowing access to intracellular Fe pools.

Nanoparticle iron chelators: a new therapeutic approach in Alzheimer disease and other neurologic disorders associated with trace metal imbalance

Accumulating evidence suggests that oxidative stress may be a major etiologic factor in initiating and promoting neurodegeneration in Alzheimer disease. Contributing to this, there is a dyshomeostasis of metal ions in Alzheimer disease with abnormally high levels of redox-active metals, particularly iron, in affected areas of the brain. Although it is unclear whether metal excesses are the sole cause of oxidative stress and neurodegeneration or a by-product of neuronal loss, the finding that metal chelators can partially solubilize amyloid-beta deposits in Alzheimer disease suggests a promising therapeutic role for chelating agents. However, the blood-brain barrier and toxicity of known chelators limit their utility. In this study, we suggest that covalent conjugation of iron chelators with nanoparticles may help overcome the limitations in blood-brain barrier permeability of existing chelation therapy. Using in vitro studies, we have shown that a chelator-nanoparticle system and the chelator-nanoparticle system complexed with iron, when incubated with human plasma, preferentially adsorb apolipoprotein E and apolipoprotein A-I, that would facilitate transport into and out of the brain via mechanisms used for transporting low-density lipoprotein. Our studies suggest a unique approach, utilizing nanoparticles, to transport chelators and chelator-metal complexes in both directions across the blood-brain barrier, thus providing safer and more effective chelation treatment in Alzheimer disease and other neurodegenerative diseases.

Dietary supplementation of baicalin and quercetin attenuates iron overload induced mouse liver injury

The introduction of new iron chelating drugs may ultimately improve iron-chelation therapy for patients with iron overload diseases such as thalassaemia and other disorders. In this paper, the in vivo effects of baicalin and quercetin on iron overload induced liver injury were studied on mice. It was found that when iron-dextran induced iron overload mice were fed baicalin or quercetin containing diet (1% w/w) for 45 days, both flavonoids significantly inhibited iron overload induced lipid peroxidation and protein oxidation of liver, decreased hepatic iron and hepatic collagen content, increased the serum non-heme iron level but not serum ferritin level. Flavonoids supplementation also increased the excretion of iron through feces. In vitro study demonstrated that both flavonoids could release iron from ferritin. These results indicate that besides acting as antioxidants, both flavonoids can also release iron from liver and finally excrete it through feces. The present study provides further support for flavonoids to be medicines for iron overload diseases.

Design, synthesis and in vitro antimalarial activity of an acylhydrazone library

A library of acylhydrazone iron chelators was synthesized and tested for its ability to inhibit the growth of a chloroquine-resistant strain of Plasmodium falciparum. Some of these new compounds are significantly more active than desferrioxamine DFO, the iron chelator in widespread clinical use and also than the most effective chelators.

Nanoparticle and other metal chelation therapeutics in Alzheimer disease

Current therapies for Alzheimer disease (AD) such as the anticholinesterase inhibitors and the latest NMDA receptor inhibitor, Namenda, provide moderate symptomatic delay at various stages of disease, but do not arrest disease progression or supply meaningful remission. As such, new approaches to disease management are urgently needed. Although the etiology of AD is largely unknown, oxidative damage mediated by metals is likely a significant contributor since metals such as iron, aluminum, zinc, and copper are dysregulated and/or increased in AD brain tissue and create a pro-oxidative environment. This role of metal ion-induced free radical formation in AD makes chelation therapy an attractive means of dampening the oxidative stress burden in neurons. The chelator desferioxamine, FDA approved for iron overload, has shown some benefit in AD, but like many chelators, it has a host of adverse effects and substantial obstacles for tissue-specific targeting. Other chelators are under development and have shown various strengths and weaknesses. In this review, we propose a novel system of chelation therapy through the use of nanoparticles. Nanoparticles conjugated to chelators show a unique ability to cross the blood-brain barrier (BBB), chelate metals, and exit through the BBB with their corresponding complexed metal ions. This method may prove to be a safe and effective means of reducing the metal load in neural tissue thus staving off the harmful effects of oxidative damage and its sequelae.

Effects of dietary baicalin supplementation on iron overload-induced mouse liver oxidative injury

Iron overload is one of the most common metal related toxicity. Under this circumstance, excessive iron deposition in liver will lead to further injury such as hepatocellular necrosis, inflammation, fibrosis, and in some cases even to carcinoma. In this paper, the effect of a nature flavonoid, baicalin, on iron overload-induced mouse liver oxidative injury has been studied. It was found that when iron-dextran-induced iron overload, mice were fed baicalin-containing diet (0.25% and 1%) for 50 days, hepatic iron, liver-to-body weight ratio, and hepatic lipid peroxidation were dose-dependently decreased; while catalase activity, total antioxidant status, and serum iron content were dose dependently increased. The protective effect of baicalin on liver of iron overload mouse may due to both the antioxidant and iron chelation activities of baicalin. These data provide preliminary experimental support for baicalin as medicine for iron overload diseases.

Potent antitumor activity of novel iron chelators derived from di-2-pyridylketone isonicotinoyl hydrazone involves fenton-derived free radical generation

PURPOSE

The development of novel and potent iron chelators as clinically useful antitumor agents is an area of active interest. Antiproliferative activity of chelators often relates to iron deprivation or stimulation of iron-dependent free radical damage. Recently, we showed that novel iron chelators of the di-2-pyridylketone isonicotinoyl hydrazone (PKIH) class have potent and selective antineoplastic activity (E. Becker, et al., Br. J. Pharmacol., 138: 819-30, 2003). In this study, we assessed the effects of the PKIH analogues on the redox activity of iron in terms of understanding their antitumor activity.

EXPERIMENTAL DESIGN

We tested the PKIH analogues for their ability to promote iron-mediated ascorbate oxidation, benzoate hydroxylation, and plasmid degradation. Subsequent experiments assessed their ability to bind DNA, inhibit topoisomerase I, and cause DNA damage. To measure intracellular reactive oxygen species, we used the redox-sensitive probe, 2',7'-dichloro-fluorescein-diacetate, to measure intracellular PKIH-dependent redox activity.

RESULTS

The PKIH analogues had relatively little effect on ascorbate oxidation in the presence of Fe(III) but stimulated benzoate hydroxylation and plasmid DNA degradation in the presence of Fe(II) and H2O2. These ligands could not inhibit DNA topoisomerase I or cause DNA damage in intact cells. PKIH markedly increased the intracellular generation of reactive oxygen species, and this was inhibited by catalase. This enzyme also decreased the antiproliferative effect of PKIH, indicating H2O2 played a role in its cytotoxic activity.

CONCLUSIONS

Our results suggest that the antiproliferative effects of these chelators relates to intracellular iron chelation, followed by the stimulation of iron-mediated free radical generation via the so-formed iron complex.

Novel aroylhydrazone and thiosemicarbazone iron chelators with anti-malarial activity against chloroquine-resistant and -sensitive parasites

Iron (Fe) is crucial for cellular proliferation, and Fe chelators have shown activity at preventing the growth of the malarial parasite in cell culture and in animal and human studies. We investigated the anti-malarial activity of novel aroylhydrazone and thiosemicarbazone Fe chelators that show high activity at inhibiting the growth of tumour cells in cell culture [Blood 100 (2002) 666]. Experiments with the chelators were performed using the chloroquine-sensitive, 3D7, and chloroquine-resistant, 7G8, strains of Plasmodium falciparum in vitro. The new ligands were significantly more active in both strains than the Fe chelator in widespread clinical use, desferrioxamine (DFO). The most effective chelators examined were 2-hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone and 2-hydroxy-1-naphthylaldehyde-4-phenyl-3-thiosemicarbazone. The anti-malarial activity correlates with anti-proliferative activity against neoplastic cells demonstrated in a previous study. Our studies suggest that this class of lipophilic chelators may have potential as useful agents for the treatment of malaria.

Iron chelators for the treatment of iron overload disease: relationship between structure, redox activity, and toxicity

The success of the iron (Fe) chelator desferrioxamine (DFO) in the treatment of beta-thalassemia is limited by its lack of bioavailability. The design and characterization of synthetic alternatives to DFO has attracted much scientific interest and has led to the discovery of orally active chelators that can remove pathological Fe deposits. However, chelators that access intracellular Fe pools can be toxic by either inhibiting Fe-containing enzymes or promoting Fe-mediated free radical damage. Interestingly, toxicity does not necessarily correlate with Fe-binding affinity or with chelation efficacy, suggesting that other factors may promote the cytopathic effects of chelators. In this review, we discuss the interactions of chelators and their Fe complexes with biomolecules that can lead to toxicity and tissue damage.

Beta-thalassaemia: emergence of new and improved iron chelators for treatment

Beta-thalassaemia is an inherited blood disorder which through repeated blood transfusions and enhanced iron uptake from the gastrointestinal tract, results in marked iron overload. Untreated, the iron accumulation results in the dysfunction of vital organs such as the heart and liver. At present, the most effective treatment for beta-thalassaemia is the use of the iron chelator, desferrioxamine, which is expensive, orally inactive and requires long subcutaneous infusions. In this concise review, we will focus on novel chelators which show therapeutic potential to replace desferrioxamine. Furthermore, we will discuss the potential of combined iron chelation therapy and the principle that, in the future, the use of more than just one chelator may be beneficial in tailoring individual iron chelation regimens.

Interactions of the pyridine-2-carboxaldehyde isonicotinoyl hydrazone class of chelators with iron and DNA: implications for toxicity in the treatment of iron overload disease

Iron chelation therapy for the management of iron-overload disease is dominated by desferrioxamine (DFO). However, treatment using DFO is very arduous. Recently, novel Fe chelators of the pyridine-2-carboxaldehyde isonicotinoyl hydrazone (PCIH) class have shown high chelation efficacy and the potential to replace DFO. A critical consideration in the design of alternatives to DFO is that the chelator forms a redox-inert Fe complex. In the present study, the participation of Fe complexes in redox reactions has been investigated. Ascorbate oxidation in the presence of Fe(III) or benzoate hydroxylation in the presence of Fe(II) was not enhanced by the PCIH analogues. However, redox-induced DNA strand breaks were observed with these ligands under highly oxidizing conditions in the presence of Fe(II) and hydrogen peroxide. Experiments then examined the interactions of the PCIH analogues with DNA, and this was found to be weak. Considering this, we suggest that under extreme conditions seen in the DNA-strand break assay, weak DNA-binding may potentiate the redox activity of the PCIH analogues. However, importantly, in contrast to naked plasmid DNA, DNA damage by these chelators using intact human cells was not significant. Collectively, our results support the potential of the PCIH analogues for the treatment of Fe overload.

The influence of deferiprone (L1) and deferoxamine on iron and essential element tissue level and parameters of oxidative status in dietary iron-loaded mice

The seven week feeding of a diet enriched with 0.5% TMH-ferrocene to male mice was used in this study to produce an iron-overload model in experimental animals for evaluating the effect of deferoxamine (DFO) and deferiprone (L1) on tissue-stored iron, induced lipid peroxidation (LP) and parameters of oxidative status. The iron concentration in the liver reached 600% of the level in control animals. The administration of seven doses of deferoxamine (DFO) i.p. and deferiprone (L1) p.o. (0.72 mmol/kg b.w., every 48 h) during 9th and 10th week significantly decreased the liver, kidneys and heart iron level in both iron-loaded and control mice. The DFO and L1 treatment also equally attenuated lipid peroxidation and increased the GSH level in the liver of iron loaded mice. The glutathione peroxidase (GSH-Px) activity and catalase activity were not affected by iron loading, however, both DFO and L1 caused a decrease of GSH-Px activity.

Advances in experimental treatment of beta-thalassaemia

Beta-thalassaemia is highly prevalent and world wide in its distribution. The gene to modify the clinical course of patients with transfusion-dependent thalassaemia (thalassaemia major), the gamma-globin gene, is already present in these patients but silenced in the course of development. During erythropoiesis, progenitors are believed to go through a phase where the milieu favours gamma-globin production. One pharmacological strategy to increase gamma-globin production is directed at recruiting such early progenitors through the use of cytotoxic agents (+/- erythropoietin) that presumably deplete more mature progenitors. Another promising strategy is to use chromatin-modifying agents that prevent the silencing of the gamma-globin gene that occurs during development. These agents, the methyl-transferase inhibitors and histone deacetylase inhibitors, either alone or in combination, may be able to produce the robust increase in gamma-globin and hence fetal haemoglobin and total haemoglobin, needed to successfully treat thalassaemia major. Studies of these agents, which are already available for clinical trials, should be encouraged.

The controversial role of deferiprone in the treatment of thalassemia

The role of the orally active iron (Fe) chelator deferiprone in the treatment of beta-thalassemia remains a controversial subject. Despite initial studies showing high Fe chelation efficacy in vitro and also in animals and human subjects, several latter studies have not been so successful. In fact, it has been reported in several clinical trials that deferiprone after long-term treatment had either little effect or actually increased hepatic Fe loading. In addition, an increase in liver fibrosis was noted in one study. However, more recently, results by other investigators have suggested that the drug may be used under some circumstances without marked toxicity. In particular, it has been demonstrated that the combination of deferoxamine (DFO) and deferiprone results in more Fe excretion than when either chelator is used alone. Moreover, a combination of both drugs led to a decrease in deferiprone-mediated toxicity. Other studies performed in patients for up to 10 years showed no progressive fibrosis after deferiprone therapy, while a possible trend toward increasing fibrosis was noted in another investigation. Additional studies using larger numbers of deferiprone-treated patients are essential to determine the efficacy and safety of this drug, particularly in relation to the development of fibrosis. The present review discusses the possible role of deferiprone in the treatment of Fe overload.

Genotoxicity of iron chelators in L5178Y mouse lymphoma cells

To further study the mechanism of observed iron mutagenicity and cellular toxicity, a number of different iron chelators were evaluated to select a compound that was not mutagenic and had limited toxicity to mouse lymphoma cells. A series of iron chelators including those used clinically, those under development for clinical applications, and those used in nonclinical applications were evaluated. The mutagenic activity of the iron chelators was assessed in L5178Y mouse lymphoma cells. Eight of the 12 iron chelators that were tested induced mutagenic responses both with and without the addition of S9. Among those chelators used clinically or developed for clinical use, the only compound that did not induce a mutagenic response was the starch deferoxamine conjugate. In contrast, deferoxamine mesylate showed the highest toxicity in this group of chemicals and the concentrations leading to toxicity and mutagenicity between the activated and nonactivated assays were not significantly different. The other three chelators that were not mutagenic were Na2EDTA, phytic acid, and ferrozine.

Frataxin: its role in iron metabolism and the pathogenesis of Friedreich's ataxia

Friedreich's ataxia (FA) is a severe neurodegenerative condition with an incidence of 1:50000 in the European population. In 97% of patients this disease is due to an intronic GAA triplet repeat expansion in the FRDA gene resulting in a marked decrease in its expression. The protein encoded by this gene is known as frataxin which is found within the mitochondrion. Upon deletion of the homologous gene (YFH1) in the yeast, there was an accumulation of iron (Fe) within the mitochondrion. When the YFH1 gene was reintroduced back into the yeast cell Fe was exported out of the mitochondrion and into the cytosol. Evidence that human frataxin is also involved in mitochondrial Fe-overload comes from studies in FA patients that have shown an accumulation of Fe within the heart. While the precise role of human frataxin remains to be determined, the molecule appears to be involved indirectly in regulating the export and/or import of mitochondrial Fe. The finding of mitochondrial Fe-overload suggests that the use of specific Fe chelators which can permeate the mitochondrion may have potential in the treatment of this disease.