Iron chelators in medicine

Ferroptosis in Ischemic Stroke and Related Traditional Chinese Medicines

Stroke is a severe neurological disorder resulting from the rupture or blockage of blood vessels, leading to significant mortality and disability worldwide. Among the different types of stroke, ischemic stroke (IS) is the most prevalent, accounting for 70-80% of cases. Cell death following IS occurs through various mechanisms, including apoptosis, necrosis, and ferroptosis. Ferroptosis, a recently identified form of regulated cell death characterized by iron overload and lipid peroxidation, was first described by Dixon in 2012. Currently, the only approved pharmacological treatment for IS is recombinant tissue plasminogen activator (rt-PA), which is limited by a narrow therapeutic window and often results in suboptimal outcomes. Recent research has identified several traditional Chinese medicines (TCMs) that can inhibit ferroptosis, thereby mitigating the damage caused by IS. This review provides an overview of stroke, the role of ferroptosis in IS, and the potential of certain TCMs to inhibit ferroptosis and contribute to stroke treatment.

New Deferric Amine Compounds Efficiently Chelate Excess Iron to Treat Iron Overload Disorders and to Prevent Ferroptosis

Excess iron accumulation occurs in organs of patients with certain genetic disorders or after repeated transfusions. No physiological mechanism is available to excrete excess iron and iron overload to promote lipid peroxidation to induce ferroptosis, thus iron chelation becomes critical for preventing ion toxicity in these patients. To date, several iron chelators have been approved for iron chelation therapy, such as deferiprone and deferoxamine, but the current iron chelators suffer from significant limitations. In this context, new agents are continuously sought. Here, a library of new deferric amine compounds (DFAs) with adjustable skeleton and flexibility is synthesized by adopting the beneficial properties of conventional chelators. After careful evaluations, compound DFA1 is found to have greater efficacy in binding iron through two molecular oxygens in the phenolic hydroxyl group and the nitrogen atom in the amine with a 2:1 stoichiometry. This compound remarkably ameliorates iron overload in diverse murine models through both oral and intravenous administration, including hemochromatosis, high iron diet-induced, and iron dextran-stimulated iron accumulation. Strikingly, this compound is found to suppress iron-induced ferroptosis by modulating the intracellular signaling that drives lipid peroxidation. This study opens a new approach for the development of iron chelators to treat iron overload.

Renal clearable nanochelators for iron overload therapy

Iron chelators have been widely used to remove excess toxic iron from patients with secondary iron overload. However, small molecule-based iron chelators can cause adverse side effects such as infection, gastrointestinal bleeding, kidney failure, and liver fibrosis. Here we report renal clearable nanochelators for iron overload disorders. First, after a singledose intravenous injection, the nanochelator shows favorable pharmacokinetic properties, such as kidney-specific biodistribution and rapid renal excretion (>80% injected dose in 4 h), compared to native deferoxamine (DFO). Second, subcutaneous (SC) administration of nanochelators improves pharmacodynamics, as evidenced by a 7-fold increase in efficiency of urinary iron excretion compared to intravenous injection. Third, daily SC injections of the nanochelator for 5 days to iron overload mice and rats decrease iron levels in serum and liver. Furthermore, the nanochelator significantly reduces kidney damage caused by iron overload without demonstrating DFO's own nephrotoxicity. This renal clearable nanochelator provides enhanced efficacy and safety.

Toward Cochlear Therapies

Sensorineural hearing impairment is the most common sensory disorder and a major health and socio-economic issue in industrialized countries. It is primarily due to the degeneration of mechanosensory hair cells and spiral ganglion neurons in the cochlea via complex pathophysiological mechanisms. These occur following acute and/or chronic exposure to harmful extrinsic (e.g., ototoxic drugs, noise...) and intrinsic (e.g., aging, genetic) causative factors. No clinical therapies currently exist to rescue the dying sensorineural cells or regenerate these cells once lost. Recent studies have, however, provided renewed hope, with insights into the therapeutic targets allowing the prevention and treatment of ototoxic drug- and noise-induced, age-related hearing loss as well as cochlear cell degeneration. Moreover, genetic routes involving the replacement or corrective editing of mutant sequences or defected genes are showing promise, as are cell-replacement therapies to repair damaged cells for the future restoration of hearing in deaf people. This review begins by recapitulating our current understanding of the molecular pathways that underlie cochlear sensorineural damage, as well as the survival signaling pathways that can provide endogenous protection and tissue rescue. It then guides the reader through to the recent discoveries in pharmacological, gene and cell therapy research towards hearing protection and restoration as well as their potential clinical application.

Iron: effect of overload and deficiency

Iron is a redox active metal which is abundant in the Earth's crust. It has played a key role in the evolution of living systems and as such is an essential element in a wide range of biological phenomena, being critical for the function of an enormous array of enzymes, energy transduction mechanisms, and oxygen carriers. The redox nature of iron renders the metal toxic in excess and consequently all biological organisms carefully control iron levels. In this overview the mechanisms adopted by man to control body iron levels are described.Low body iron levels are related to anemia which can be treated by various forms of iron fortification and supplementation. Elevated iron levels can occur systemically or locally, each giving rise to specific symptoms. Systemic iron overload results from either the hyperabsorption of iron or regular blood transfusion and can be treated by the use of a selection of iron chelating molecules. The symptoms of many forms of neurodegeneration are associated with elevated levels of iron in certain regions of the brain and iron chelation therapy is beginning to find an application in the treatment of such diseases. Iron chelators have also been widely investigated for the treatment of cancer, tuberculosis, and malaria. In these latter studies, selective removal of iron from key enzymes or iron binding proteins is sought. Sufficient selectivity between the invading organism and the host has yet to be established for such chelators to find application in the clinic.Iron chelation for systemic iron overload and iron supplementation therapy for the treatment of various forms of anemia are now established procedures in clinical medicine. Chelation therapy may find an important role in the treatment of various neurodegenerative diseases in the near future.

X-ray crystallographic structures of the Escherichia coli periplasmic protein FhuD bound to hydroxamate-type siderophores and the antibiotic albomycin

Siderophore-binding proteins play an essential role in the uptake of iron in many Gram-positive and Gram-negative bacteria. FhuD is an ATP-binding cassette-type (ABC-type) binding protein involved in the uptake of hydroxamate-type siderophores in Escherichia coli. Structures of FhuD complexed with the antibiotic albomycin, the fungal siderophore coprogen and the drug Desferal have been determined at high resolution by x-ray crystallography. FhuD has an unusual bilobal structure for a periplasmic ligand binding protein, with two mixed beta/alpha domains connected by a long alpha-helix. The binding site for hydroxamate-type ligands is composed of a shallow pocket that lies between these two domains. Recognition of siderophores primarily occurs through interactions between the iron-hydroxamate centers of each siderophore and the side chains of several key residues in the binding pocket. Rearrangements of side chains within the binding pocket accommodate the unique structural features of each siderophore. The backbones of the siderophores are not involved in any direct interactions with the protein, demonstrating how siderophores with considerable chemical and structural diversity can be bound by FhuD. For albomycin, which consists of an antibiotic group attached to a hydroxamate siderophore, electron density for the antibiotic portion was not observed. Therefore, this study provides a basis for the rational design of novel bacteriostatic agents, in the form of siderophore-antibiotic conjugates that can act as "Trojan horses," using the hydroxamate-type siderophore uptake system to actively deliver antibiotics directly into targeted pathogens.

Cisplatin ototoxicity: involvement of iron and enhanced formation of superoxide anion radicals

Since there are indications that iron influences cisplatin nephrotoxicity, we studied the role of iron in cisplatin ototoxicity in an in vitro model of the neurosensory epithelium of the guinea pig cochlea. Viability tests showed that Deiters and Hensen cells were not damaged and inner hair cells were only slightly damaged by cisplatin (50 microM). The outer hair cells were most sensitive to cisplatin toxicity. The iron chelator 2,2'-dipyridyl provided partial protection against cisplatin-induced cell death. In addition, we studied the influence of the iron chelators 2,2'-dipyridyl and deferoxamine on the chelatable iron pool in the various cells of the neurosensory epithelium using the fluorescent iron indicator Phen Green SK. Both chelators decreased the chelatable iron accessible to Phen Green SK, although the effect of deferoxamine was weaker because it entered the cells more slowly. The cellular concentration of the chelatable iron was measured using Phen Green SK and quantitative laser scanning microscopy. The concentration of chelatable iron in the inner ear cells ranged from 1.3 +/- 0.4 microM iron in inner hair cells to 3.7 +/- 1.7 microM iron in Hensen cells and did not correlate with the various cell types' susceptibility to cisplatin. Furthermore, cisplatin did not raise the intracellular chelatable iron concentration but enhanced the production of superoxide anions inside the neurosensory epithelium, especially inside the hair cells, as detected by the nitrotetrazolium blue reduction assay. Our conclusion is that cisplatin ototoxicity is partially mediated by an iron-dependent pathway and is associated with an enhanced formation of superoxide anions.

Chelator-induced iron excretion in iron-overloaded marmosets

In order to test new orally active iron chelators in a predictive way, a primate model has been developed. This model makes use of the marmoset monkey (Callithrix jacchus) and its overall design is similar to a previously reported monkey model. However, this new model enables a higher compound throughput and requires lower amounts of test compound because the animals are much easier to handle and have much lower body weights. The marmosets were iron-overloaded by three intraperitoneal injections of iron (III) hydroxide polyisomaltose. For the iron-balance studies, the animals were kept in metabolic cages and were maintained on a low-iron diet in order to reduce faecal background. After compound administration, the excretion of iron in urine and faeces was followed for 2 d. A series of well-known chelators was tested for validation of the model. In particular, comparison of the iron-clearing properties of DFO, L1, CP94 and HBED in marmosets and humans demonstrated the predictive value of the model and justify our expectation that if iron chelators such as CGP65015, ICL670A and CGP75254A are active in marmosets, they will be active in humans as well.

Surface oxidase and oxidative stress propagation in aging

This report summarizes new evidence for a plasma-membrane-associated hydroquinone oxidase designated as CNOX (constitutive plasma membrane NADH oxidase) that functions as a terminal oxidase for a plasma membrane oxidoreductase (PMOR) electron transport chain to link the accumulation of lesions in mitochondrial DNA to cell-surface accumulations of reactive oxygen species. Previous considerations of plasma membrane redox changes during aging have lacked evidence for a specific terminal oxidase to catalyze a flow of electrons from cytosolic NADH to molecular oxygen (or to protein disulfides). Cells with functionally deficient mitochondria become characterized by an anaerobic metabolism. As a result, NADH accumulates from the glycolytic production of ATP. Elevated PMOR activity has been shown to be necessary to maintain the NAD(+)/NADH homeostasis essential for survival. Our findings demonstrate that the hyperactivity of the PMOR system results in an NADH oxidase (NOX) activity capable of generating reactive oxygen species at the cell surface. This would serve to propagate the aging cascade both to adjacent cells and to circulating blood components. The generation of superoxide by NOX forms associated with aging is inhibited by coenzyme Q and provides a rational basis for the anti-aging activity of circulating coenzyme Q.

Absorption and biodistribution of 111indium-labelled desferrioxamine (111In-DFO) after subcutaneous injection of 111In-DFO liposomes

In the present study the kinetics of the release of desferrioxamine (DFO) from liposomes (fluid and rigid liposome type) at the subcutaneous (s.c.) injection site was studied. DFO was labelled with 111indium (111In-DFO) and the fate of s.c. administered liposomal 111In-DFO was monitored with a gamma camera. Free 111In-DFO rapidly disappeared from the s.c. injection site [90% of the injected dose (%ID) within 2 h]. After s.c. injection of the fluid liposome type, 20 %ID was released within 4 h and 50 %ID within 24 h. Approximately 25 %ID remained at the injection site 6 days after injection. With the rigid liposome type, no initial release (within 4 h) was observed. The rate of DFO release was similar to the fluid liposome type. Free drug was rapidly cleared from the bloodstream (within 2 h), while low, but detectable blood levels of 111In-DFO were maintained for 6 days after s.c. injection of liposomal drug. This resulted in higher peak levels of 111In-DFO in liver and kidney (4-6 %ID/g) compared with free drug (2-4 %ID/g), which were reached later in time. The present data point to sustained release of DFO from s.c. administered DFO-liposomes as the mechanism behind their enhanced therapeutic effect in murine malaria.

Attenuation of cochlear damage from noise trauma by an iron chelator, a free radical scavenger and glial cell line-derived neurotrophic factor in vivo

Tissue injury by reactive oxygen species (ROS) may play a role in noise-induced hearing loss (NIHL). Since iron is involved in ROS generation, we studied if an iron chelator, deferoxamine mesylate (DFO), alone or in combination with mannitol, a hydroxyl scavenger and weak iron chelator, attenuates NIHL. Further, we investigated if glial cell line-derived neurotrophic factor (GDNF) provides additive or synergistic protection of the cochlea from acoustic trauma when given together with DFO and mannitol. Pigmented female guinea pigs were exposed to noise (4 kHz octave band, 115 dB SPL, 5 h). One hour before, immediately after, and 5 h after noise exposure, subjects received an injection of 5 ml saline/kg (control, group I), 100 mg DFO/kg (group II), 15 mg mannitol/kg (group III), or both DFO and mannitol (group IV and V). Animals in group V underwent implantation of an osmotic pump filled with GDNF (100 ng/ml) in the left ear 4 days before noise. Each treatment afforded some protection from noise damage. Group I showed significantly greater outer hair cell loss and threshold shifts at two or more frequencies compared to groups II through V. GDNF provided an additive functional, but not morphological, protection with DFO and mannitol. These findings indicate that iron chelators can attenuate NIHL, as do ROS scavengers, supporting the notion that ROS generation plays a role in NIHL. Additional functional protection provided with GDNF suggests that GDNF may attenuate noise-induced cochlear damage through a mechanism that is additive with antioxidants.

Synthesis, physicochemical properties, and evaluation of N-substituted-2-alkyl-3-hydroxy-4(1H)-pyridinones

The synthesis of a range of 3-hydroxy-4(1H)-pyridinones with potential for the chelation of iron(III) is described. The pKa values of respective ligands and the stability constants of their iron(III) complexes are presented. The distribution coefficient values of a range of 48 hydroxypyridinones and their corresponding iron(III) complexes between 1-octanol and MOPS buffer (pH 7.4) are reported. The range of log Dcomplex values covers 7 orders of magnitude. The results suggest the existence of a biphasic relationship between the distribution coefficient values of the chelator and the corresponding iron(III) complexes. For ligands with a log Dligand = -1, a linear relationship exists with a value of the slope 2.53, whereas with ligands with a log Dligand < -1, a linear relationship exists with a slope of 0.49. The reduced slope for the more hydrophilic molecules of the series offers some advantage for this type of hydroxypyridinone as the distribution coefficients for such complexes do not change so rapidly with increasing ligand hydrophilicity. The ability of selected 3-hydroxypyridinones to facilitate the excretion of iron in bile was investigated in non-iron-overloaded, bile duct-cannulated rats and in a [59Fe]ferritin-loaded rat model. Both systems compare the ability of chelators to remove iron from the liver, the prime target organ in thalassemia. The N-(hydroxyalkyl)-3-hydroxypyridin-4-ones are demonstrated to be orally active under the in vivo conditions adopted. Thus both 1-(hydroxyalkyl)- and 1-(carboxyalkyl)pyridinones are able to remove iron from the liver. Although 1-(carboxyalkyl)hydroxypyridinones are active, they do not demonstrate any clear advantage over Deferiprone (1,2-dimethyl-3-hydroxypyridin-4-one). Indeed 1-(hydroxyalkyl)hydroxypyridinones which are known to be rapidly converted to 1-(carboxyalkyl)hydroxypyridinones are also marginally superior to Deferiprone. In contrast, 2-ethyl-1-(2'-hydroxyethyl)-3-hydroxypyridin-4-one, which is not metabolized to the corresponding (carboxyalkyl)hydroxypyridinone, was found to be superior to Deferiprone and therefore deserves further consideration as an orally active iron chelator with potential for the treatment of iron overload associated with transfusion-dependent thalassemia.

Role of mitochondria in oxidative stress and ageing

Mitochondria are deeply involved in the production of reactive oxygen species through one-electron carriers in the respiratory chain; mitochondrial structures are also very susceptible to oxidative stress as evidenced by massive information on lipid peroxidation, protein oxidation, and mitochondrial DNA (mtDNA) mutations. Oxidative stress can induce apoptotic death, and mitochondria have a central role in this and other types of apoptosis, since cytochrome c release in the cytoplasm and opening of the permeability transition pore are important events in the apoptotic cascade. The discovery that mtDNA mutations are at the basis of a number of human pathologies has profound implications: maternal inheritance of mtDNA is the basis of hereditary mitochondrial cytopathies; accumulation of somatic mutations of mtDNA with age has represented the basis of the mitochondrial theory of ageing, by which a vicious circle is established of mtDNA damage, altered oxidative phosphorylation and overproduction of reactive oxygen species. Experimental evidence of respiratory chain defects and of accumulation of multiple mtDNA deletions with ageing is in accordance with the mitochondrial theory, although some other experimental findings are not directly ascribable to its postulates.

Aminoglycoside ototoxicity: prevention in sight?

Despite the development of new antibiotics, the aminoglycosides are still indispensable in the treatment of life-threatening diseases. Worldwide they are the most commonly used antibiotics, and their use is expected to increase in the wake of the rising incidence of tuberculosis. The most prominent side effects of aminoglycoside treatment--cochlear, vestibular, and renal impairment--are a limiting factor in the utility of these drugs. A novel mechanism of gentamicin ototoxicity is based on observations of iron chelation and free radical formation. Predictions from this mechanism have led to successful therapeutic prevention of ototoxicity by use of iron chelators and radical scavengers in guinea pigs. The drugs used for this interventive treatment affect neither serum levels of gentamicin nor its antibacterial efficacy. Because these drugs are in clinical use, the suggested protective treatment should lend itself to clinical trials.

New chelate-forming polymer microspheres carrying dyes as chelators for iron overload

Dye-incorporated [poly(EGDMA-HEMA)] microspheres were investigated as a new chelate-forming polymer for iron overload. Poly(EGDMA-HEMA) microspheres, in the size range of 150-200 microm, were produced by a modified suspension polymerization of EGDMA and HEMA. The reactive dye-ligands (i.e. Cibacron Blue F3GA, Alkali Blue 6B and Congo Red) were covalently incorporated to the microspheres. The maximum dye incorporations were 16.5 micromol Cibacron Blue F3GA g(-1), 23.7 micromol Alkali Blue 6B g(-1), and 14.5 micromol Congo Red g(-1). The maximum Fe(III) adsorptions on the dye-incorporated microspheres from aqueous solutions containing different amounts of Fe(III) ions were 51.0, 37.3, and 25.1 mg g(-1) for the Cibacron Blue F3GA, Alkali Blue 6B, and Congo Red carrying microspheres, respectively. The maximum Fe(III) adsorptions were observed at pH 4.0 in all cases. Fe(III) removal from human plasma was also investigated. The maximum adsorption capacities of Fe(III) ions from human plasma for Cibacron Blue F3GA, Alkali Blue 6B, and Congo Red, were of 12.0, 7.5, and 3.8 mg g(-1) polymer, respectively. It was observed that Fe(III) could be repeatedly adsorbed and desorbed without significant loss in adsorption capacity.

IRC011, a New Synthetic Chelator With Selective Interaction With Catabolic Red Blood Cell Iron: Evaluation in Hypertransfused Rats With Hepatocellular and Reticuloendothelial Radioiron Probes and in Iron-Loaded Rat Heart Cells in Culture

A major consideration in the selection of new and improved iron chelators for clinical use is preferential interaction with the most toxic iron compartment. We describe the biologic properties of a new synthetic hexadentate iron chelator (IRC011) that is a substituted polyaza compound. Unlike deferoxamine (DF ), the polyaza structure of IRC011 does not contain any readily hydrolyzable covalent bonds and is anticipated to resist in vivo biotransformation. In the present studies, the ability of IRC011 to remove radioiron from iron-loaded heart cells in vitro was similar to DF, with a decrease to 20.0 ± 0.4% and 19.7 ± 0.5% of initial values after 24 hours of incubation with 0.3 mmol/L of DF or IRC011, respectively. The in vivo interaction of IRC011 with specific iron stores was studied in hypertransfused rats using selective labeling of reticuloendothelial (RE) iron stores with 59Fe-heat-denatured red blood cells (DRBCs) and of hepatocellular stores with 59Fe-ferritin. The pattern of radioiron excretion with IRC011 was quite different from that with DF. Although with both compounds, hepatocellular iron excretion was through the bile, whereas RE iron excretion was mainly in the urine, the magnitude of these effects was quite different. After the administration of a single parenteral dose of 200 mg/kg representing a 53% higher iron-binding capacity for IRC011 compared with DF, 48-hour urinary excretion of RE iron with IRC011 was 22.8% ± 1.1% (% of total body 59Fe), but only 6.0% ± 3.6% with DF. By contrast, the corresponding biliary excretion of hepatocellular radioiron was 14.2% ± 3.2% with DF, but only 0.7% ± 0.3% with IRC011. Thus, the new iron chelator IRC011 is distinguished from DF by the following features: (1) a higher affinity to Fe(III), (2) anticipated resistance to in vivo catabolism, (3) preferential interaction with RE iron derived from RBC breakdown, and (4) selective renal excretion. Because RBC breakdown is the most likely source of the toxic nontranferrin plasma iron, IRC011 may be a useful iron chelator for protecting vital organs from peroxidative damage.

Oxidative stress in malaria; implications for prevention and therapy

Malaria affects world-wide more than 200 million people, of which 1-2 million die every year. New drugs and treatment strategies are needed to face the rapidly increasing problems of drug resistance. During a malaria infection, both host and parasite are under oxidative stress. Increased production levels of reactive oxygen species (ROS, e.g superoxide anion and the hydroxyl radical) are produced by activated neutrophils in the host and during degradation of haemoglobin in the parasite. The effects of ROS in malaria can be both beneficial and pathological, depending on the amount and place of production. Enhanced ROS production after the administration of pro-oxidants, which is directed against the intra-erythrocytic parasite, inhibits the infection both in vitro and in vivo. However, ROS are also involved in pathological changes in host tissue like damage of the vascular endothelial lining during a malaria infection (cerebral malaria). Pro-oxidants support the host defense against the parasite when working in or near the infected cell but potentially cause vascular damage when working on or near the vascular lining. Examples of pro-oxidants are found among xenobiotics and food components. Important new drugs belonging to the class of pro-oxidants are artemisinin and its derivatives. Anti-oxidants potentially counteract these agents. Treatment with anti-oxidants or chelators of metals to prevent their catalytic function in the generation of ROS may prevent vascular pathology. In addition, the iron chelator desferrioxamine, exhibits an antiparasitic activity, because iron is also essential for the proliferation of the parasite. Cytokines play an important role in ROS-related pathology of malaria, though their mechanism of action is not completely elucidated. This field might bring up new treatment concepts and drugs. Drugs which prevent host pathology, such as the cerebral complications might be life saving.

Variable efficacy of radical scavengers and iron chelators to attenuate gentamicin ototoxicity in guinea pig in vivo

Recent studies from our laboratory have suggested that the ototoxic side effects of gentamicin are caused by a metabolized or 'activated' from the drug. Furthermore, we have postulated that the activation proceeds via the formation of an iron-gentamicin complex and that this complex produces free radicals. The present study assessed the protection effects of free radical scavengers and iron chelators on gentamicin-induced ototoxicity in guinea pigs in vivo. Gentamicin (120 mg/kg per day for 19 days) caused progressive threshold shifts reaching 50-65 dB at 18 kHz. Co-therapy with different radical scavengers yielded results ranging from no protection (with allopurinol, dimethyl sulfoxide, benzoate, lazaroid U74389G) to a moderate attenuation of hearing loss (with mannitol, 4-methylthiobenzoate, WR-2721). This finding agrees well with previous reports of inconsistent effects of scavengers on aminoglycoside-induced ototoxicity although it should be cautioned that only a single dose and route of application was tested. Two iron chelators, deferoxamine and 2,3-dihydroxybenzoate, significantly reduced the gentamicin-induced threshold shifts to about 10 dB or less. Iron chelators markedly decreased total serum iron levels while gentamicin treatment alone had no influence. There were no differences in serum gentamicin levels among all treated groups. This study confirms that iron plays a critical role in gentamicin ototoxicity and suggests that iron chelators, which are well-established drugs in clinical therapy, may be promising therapeutic agents to reduce aminoglycoside ototoxicity.

Deferoxamine-induced cytotoxicity in human neuronal cell lines: protection by free radical scavengers

Deferoxamine (DFO) caused decreased viability of human neuronal tumor cells (SK-N-MC neuroblastoma and U-373 MG astrocytoma) in a dose-dependent manner. The addition of stoichiometric amounts of ferric ions did not decrease the cytotoxic effect of DFO on the neuroblastoma cells. However, the cotreatments with various antioxidants, hydroxyl radical scavengers or intracellular Ca2+ release blockers significantly protected against the effects of DFO. These results suggest that DFO-induced cytoxicity may be not due to chelating iron, but due to the production of hydroxyl radicals and that intracellular Ca2+ may play a role in the cytotoxic effects of DFO.

Control of disease by selective iron depletion: a novel therapeutic strategy utilizing iron chelators

Recognition of the central role of iron in the generation of toxic, oxygen-derived species through the Haber-Weiss reaction, the ability of desferrioxamine (DFX) to prevent the damage associated with free radical generation in reperfusion injury, and its inhibitory effect on cell proliferation by inactivation of the iron dependent enzyme ribonucleotide reductase, resulted in an increasing number of studies exploring the novel therapeutic applications of iron chelating drugs: (a) Animal models of reperfusion injury have shown that DFX is able to decrease post-anoxic damage to the brain and heart as manifested in decreased infarct size and improved functional recovery. Iron chelators may be particularly useful in improving the preservation of organs intended for transplantation such as the heart, lung or kidney. (b) Anthracycline cardiotoxicity is aggravated by iron and inhibited by iron chelators. Because the mechanism of its antineoplastic effect differs from its cardiotoxic effect, it is possible to inhibit anthracycline cardiotoxicity without interfering with therapeutic efficacy. In vivo and in vitro animal studies have yielded encouraging results but much additional experimental work is still required before iron chelating therapy may be advocated for use in patients on anthracycline therapy. (c) Cell proliferation can be inhibited by iron chelators through the reversible inhibition of ribonucleotide reductase, a rate-limiting enzyme in DNA synthesis. This may be exploited for the treatment of malignant disease, and preliminary studies have already shown that DFX in combination with multidrug chemotherapy is effective in controlling neuroblastoma and other tumours. However, the contribution of DF to the overall clinical effect is unclear. Prospective controlled clinical studies are required in order to establish whether the antiproliferative, or cell synchronizing properties of DFX may be of practical usefulness in the control of malignant disease. (d) Control of protozoal infection: Experimental in vivo and in vitro models have shown that malarial infection may be inhibited by iron chelating therapy. This useful effect of DFX and other iron chelators is most probably related to ribonucleotide reductase inhibition. Clinical studies of asymptomatic P. falciparum malaria and of cerebral malaria have shown both an accelerated rate of parasite clearance and earlier recovery from coma. These observations lend new meaning to the term 'nutritional immunity' and open new channels for exploring the possibility of controlling infection by means of selective intracellular iron deprivation. Experimental models for studying the effect of iron chelators on other intracellular pathogens such as Toxoplasma gondii, Chlamydia psittaci, or Mycobacterium tuberculosis should be established.(ABSTRACT TRUNCATED AT 400 WORDS)

Oral iron-chelating therapy: the L1 experience

L1 is the most widely studied oral iron-chelating drug and at present the only one shown to be effective at causing negative iron balance in long-term clinical trials for thalassemia major and other transfusion-dependent refractory anaemias. Because of side-effects, both in experimental animals and in humans, its development as a widely available pharmaceutical agent has been delayed. However, for the large numbers of transfusion-dependent, iron-overloaded patients who do not use DFX because of poor compliance, adverse effects or unavailability of the drug, L1 may be a suitable alternative for iron chelation. However, its use should be restricted to Ethical Committee approved clinical trials. Patients who are capable of using DFX effectively should be encouraged to continue doing so until an oral iron chelator has been fully established for clinical use. It is hoped that 3-hydroxypyrid-4-one analogues of L1 as well as compounds related to pyridoxal isonicotinyl hydrazone, HBED or hydroxamic acid can be found both orally effective and safe for long-term administration. Current and future trials of L1 could address some of the following issues, beside extending present studies on the efficacy and adverse effects of L1: 1. The effect of administering a reduced dose of L1 (< 75 mg/kg per day) on the incidence of adverse effects and on long-term efficacy. 2. The efficacy and adverse effects of L1 at a low dose in patients with non-transfusional iron overload such as thalassaemia intermedia, primary haemochromatosis and congenital haemolytic anaemias. 3. The effect of combining oral L1 with intravenous or subcutaneous DFX on the incidence of adverse effects and efficacy. 4. Elucidation of the mechanisms involved in agranulocytosis and joint toxicity and finding methods to predict for individual susceptibility to these adverse effects and ways of preventing them.

Iron chelators as therapeutic agents against Pneumocystis carinii

Iron plays a critical role in host-parasite interactions, and iron chelators have been demonstrated to serve as effective adjunct therapeutic agents against malaria. The effects of the parenteral iron chelator deferoxamine (DFO) on the growth of rat-derived Pneumocystis carinii were studied in a human fibroblast cell culture model and in two in vivo models of experimental infection. In addition, the effects of the investigational oral iron chelator CP20 and its 3-hydroxypyridin-4-one analogs CP51, CP94, and CP96 on the growth of P. carinii in vitro were assessed. DFO suppressed the growth of P. carinii in vitro in a dose-dependent manner, and daily injections of DFO markedly reduced the intensity of P. carinii infection in both mice and rats. Cell cultures treated with iron chelators that are administered orally to humans also showed substantial P. carinii growth inhibition. Reduction of P. carinii numbers after iron chelator therapy correlated with alterations in P. carinii morphology, as viewed by transmission electron microscopy. Since the use of current anti-P. carinii drugs is limited by toxicity or incomplete efficacy, or both, the role of iron chelation as adjunctive anti-P. carinii chemotherapy merits additional investigation.

DNA cleavage by Cu(II)-desferal: identification of C1'-hydroxylation as the initial event for DNA damage

Desferal, a siderophore of microbial origin is the only drug currently used for clinical treatment of a genetic disorder, thalassemia. By using a combination of HPLC and 31P-NMR, it is demonstrated that the Cu complex of desferal cleaves DNA, the primary site of hydroxyl radical attack being the sugar C1' in the minor groove, which leads to production of 5-methylene furanone. While no C5'-oxidation was observed, a minor process involving C4'-attack accompanies the above cleavage path. The oxidative cleavage of DNA observed with CuDFO may have implications in the emerging applications of desferal as a drug delivery agent and an antimalarial.

The action of nine chelators on iron-dependent radical damage

Nine iron chelators were tested in five systems for their effects on radical-generation and conversion at chelator: iron molar ratios from 0.1 to 10. Stimulatory actions might distinguish toxic from safer chelators. Radical-generating reactions which represent different aspects of iron (ferrous and ferric) availability were studied: a) the reaction with hydrogen peroxide to hydroxylate benzoate; b) the oxidation of ascorbate; c) the reaction with hydrogen peroxide to fragment proteins; d) the reaction with hydrogen peroxide to permit amplified chemiluminescence; and e) the induction of peroxidation of mitochondrial membrane lipids. The compounds used were HBED, CP130, Desferal, EDTA, pyridine-hydrazone (CGP 43'902B), Ferrozine, CP94 (CGP 46'700), L1 (CGP 37,391) and rhodotorulic acid (CGP 45 274). Only the hexadentate compounds HBED, CP130 and Desferal were uniformly inhibitory ("protective"). The protective compounds were also apparently more stable during radical fluxes than the other chelators.

Results from a phase I clinical trial of HBED

In summary, it has been shown that orally administered HBED causes enhanced excretion of iron in all of the thalassemia major patients studied and that both urinary and stool iron are increased in the process. Increasing the dose from 40 to 80 mg/kg divided t.i.d. caused iron balance to increase from 38% to 50%. While this is significantly less than that expected based on our preclinical studies in animals, the potential usefulness of this chelator has been demonstrated. Efforts to increase its oral bioavailability are now in progress. Lending further support to the effort is the fact that no evidence of toxicity has been observed in the studies performed to date and that negative iron balance was achieved in the one thalassemia intermedia patient studied. The results also reinforce the conclusion that DFO causes the excretion of substantially more iron than would be predicted by an assessment of serum ferritin levels or past compliance with chelation therapy. In patients with thalassemia major, serum ferritin levels relate more to tissue damage than to body iron load. Effective chelation therapy can diminish the former much faster than it can remove storage iron. Hence, in cases of iron overload, aggressive chelation therapy should not be tapered off until a significant reduction in iron excretion can be demonstrated. Routine measurements of urinary iron excretion should now be considered essential in the management of beta-thalassemia. Finally, two more patients with thalassemia intermedia will be studied in an effort to substantiate that net negative iron balance can be achieved in this subgroup of patients. We also plan to study several transfused patients in whom the dose of HBED will be increased to 120 mg/kg divided t.i.d. While the chances of achieving net negative iron balance in these patients seems remote, we hope to further demonstrate the safety of this drug with an eye toward the development of an effective prodrug.