Toxicity of oral iron chelator L1

Deferiprone and Iron-Maltol: Forty Years since Their Discovery and Insights into Their Drug Design, Development, Clinical Use and Future Prospects

The historical insights and background of the discovery, development and clinical use of deferiprone (L1) and the maltol-iron complex, which were discovered over 40 years ago, highlight the difficulties, complexities and efforts in general orphan drug development programs originating from academic centers. Deferiprone is widely used for the removal of excess iron in the treatment of iron overload diseases, but also in many other diseases associated with iron toxicity, as well as the modulation of iron metabolism pathways. The maltol-iron complex is a recently approved drug used for increasing iron intake in the treatment of iron deficiency anemia, a condition affecting one-third to one-quarter of the world's population. Detailed insights into different aspects of drug development associated with L1 and the maltol-iron complex are revealed, including theoretical concepts of invention; drug discovery; new chemical synthesis; in vitro, in vivo and clinical screening; toxicology; pharmacology; and the optimization of dose protocols. The prospects of the application of these two drugs in many other diseases are discussed under the light of competing drugs from other academic and commercial centers and also different regulatory authorities. The underlying scientific and other strategies, as well as the many limitations in the present global scene of pharmaceuticals, are also highlighted, with an emphasis on the priorities for orphan drug and emergency medicine development, including the roles of the academic scientific community, pharmaceutical companies and patient organizations.

Iron chelation alleviates multiple pathophysiological pathways in a rat model of cardiac pressure overload

Iron dysmetabolism affects a great proportion of heart failure patients, while chronic hypertension is one of the most common risk factors for heart failure and death in industrialized countries. Serum data from reduced ejection fraction heart failure patients show a relative or absolute iron deficiency, whereas cellular myocardial analyses field equivocal data. An observed increase in organellar iron deposits was incriminated to cause reactive oxygen species formation, lipid peroxidation, and cell death. Therefore, we studied the effects of iron chelation on a rat model of cardiac hypertrophy. Suprarenal abdominal aortic constriction was achieved surgically, with a period of nine weeks to accommodate the development of chronic pressure overload. Next, deferiprone (100 mg/kg/day), a lipid-permeable iron chelator, was administered for two weeks. Pressure overload resulted in increased inflammation, fibrotic remodeling, lipid peroxidation, left ventricular hypertrophy and mitochondrial iron derangements. Deferiprone reduced cardiac inflammation, lipid peroxidation, mitochondrial iron levels, and hypertrophy, without affecting circulating iron levels or ejection fraction. In conclusion, metallic molecules may pose ambivalent effects within the cardiovascular system, with beneficial effects of iron redistribution, chiefly in the mitochondria.

Recommendations for Pregnancy in Rare Inherited Anemias

Rare inherited anemias are a subset of anemias caused by a genetic defect along one of the several stages of erythropoiesis or in different cellular components that affect red blood cell integrity, and thus its lifespan. Due to their low prevalence, several complications on growth and development, and multi-organ system damage are not yet well defined. Moreover, during the last decade there has been a lack of proper understanding of the impact of rare anemias on maternal and fetal outcomes. In addition, there are no clear-cut guidelines outlining the pathophysiological trends and management options unique to this special population. Here, we present on behalf of the European Hematology Association, evidence- and consensus-based guidelines, established by an international group of experts in different fields, including hematologists, gynecologists, general practitioners, medical geneticists, and experts in rare inherited anemias from various European countries for standardized and appropriate choice of therapeutic interventions for the management of pregnancy in rare inherited anemias, including Diamond-Blackfan Anemia, Congenital Dyserythropoietic Anemias, Thalassemia, Sickle Cell Disease, Enzyme deficiency and Red cell membrane disorders.

Reproductive health issues in female patients with beta-thalassaemia major: a narrative literature review

β-thalassaemia major (BTM) has a high prevalence worldwide and is associated with considerable morbidity and mortality. The aim of this review is to provide an illustrative overview of the reproductive health and pregnancy related issues in females with β-thalassaemia. A literature search was performed in four international databases (1980-2018) to identify the potentially relevant articles. Common reproductive health disorders are hypo-gonadotrophic hypogonadism, infertility, delayed or absent sexual development, diabetes, hypothyroidism, hypoparathyroidism, osteopenia, preeclampsia, gestational hypertension, polyhydramnios, oligohydramnios, thrombosis, renal failure, peripheral vascular resistance, placenta previa, pleural effusion and pulmonary hypertension. Many of those aspects are related to iron overload and to ineffective erythropoiesis. Foetal complications include neural tube defects, abnormalities in different organs, spontaneous abortion, foetal loss, preterm birth, foetal growth restriction and low birth weight. Antenatal screening and accurate genetic prenatal examinations are effective measures to early diagnosis of thalassaemia and a detailed plan for management of pregnancies in BTM is important for favourable maternal and foetal outcome.

Pregnancy in Thalassemia

Therapeutic advances, including the availability of oral iron chelators and new non-invasive methods for early detection and treatment of iron overload, have significantly improved the life expectancy and quality of thalassemia patients, with a consequent increase in their reproductive potential and desire to have children. Hundreds of pregnancies have been reported so far, highlighting that women carefully managed in the preconception phase usually carry out a successful gestation and labor, both in case of spontaneous conception and assisted reproductive techniques. A multidisciplinary team including a cardiologist, an endocrinologist, and a gynecologist, under the supervision of an expert in beta-thalassemia, should be involved.

During pregnancy, a close follow-up of maternal disorders and of the baby’s status is recommended. Hemoglobin should be maintained over 10 g/dL to allow normal fetal growth. Chelators are not recommended; nevertheless, it may be reasonable to consider restarting chelation therapy with desferrioxamine towards the end of the second trimester when the potential benefits outweigh the potential fetal risk.

Women with non-transfusion-dependent thalassemia who have never previously been transfused or who have received only minimal transfusion therapy are at risk of severe alloimmune anemia if blood transfusions are required during pregnancy. Since pregnancy increases the risk of thrombosis three-fold to four-fold and thalassemia is also a hypercoagulable state, the recommendation is to keep women who are at higher risk -such as those who are not regularly transfused and those splenectomised- on prophylaxis during pregnancy and the postpartum period.

Effect of Systemic Iron Overload and a Chelation Therapy in a Mouse Model of the Neurodegenerative Disease Hereditary Ferritinopathy

Mutations in the ferritin light chain (FTL) gene cause the neurodegenerative disease neuroferritinopathy or hereditary ferritinopathy (HF). HF is characterized by a severe movement disorder and by the presence of nuclear and cytoplasmic iron-containing ferritin inclusion bodies (IBs) in glia and neurons throughout the central nervous system (CNS) and in tissues of multiple organ systems. Herein, using primary mouse embryonic fibroblasts from a mouse model of HF, we show significant intracellular accumulation of ferritin and an increase in susceptibility to oxidative damage when cells are exposed to iron. Treatment of the cells with the iron chelator deferiprone (DFP) led to a significant improvement in cell viability and a decrease in iron content. In vivo, iron overload and DFP treatment of the mouse model had remarkable effects on systemic iron homeostasis and ferritin deposition, without significantly affecting CNS pathology. Our study highlights the role of iron in modulating ferritin aggregation in vivo in the disease HF. It also puts emphasis on the potential usefulness of a therapy based on chelators that can target the CNS to remove and redistribute iron and to resolubilize or prevent ferritin aggregation while maintaining normal systemic iron stores.

Antibiotic activity of iron-sequestering polymers

Increasing antibiotic resistance has compelled the development of novel antibiotics and adjuvant therapies that enhance the efficacy of existing antibiotics. Iron plays a critical role in bacterial infections, yet the use of iron chelators as adjuvant therapy with antibiotics has yielded highly variable outcomes. Multivalent polymeric materials offer an alternative approach to bind and sequester iron via high avidity interactions. Here, a biomimetic iron-sequestering polymer (PAI-DHBA) was synthesized by modifying side chains of cross-linked polyallylamine (cPAI) with 2,3-dihydroxybenzoic acid (DHBA). PAI-DHBA polymer gels with various DHBA contents showed high iron affinity indices and high selectivity for iron. The polymers showed mild antibiotic properties when used to treat established bacterial cultures. Pretreating culture media with PAI-DHBA polymer, however, removed all detectable iron from media and effectively inhibited the growth of Pseudomonas aeruginosa. In addition, bacterial growth was more susceptible to antibiotics combined with PAI-DHBA. Multivalent polymers that bind and sequester iron, such as PAI-DHBA, offer a promising early intervention or adjuvant to antibiotics.

Clinically approved iron chelators influence zebrafish mortality, hatching morphology and cardiac function

Iron chelation therapy using iron (III) specific chelators such as desferrioxamine (DFO, Desferal), deferasirox (Exjade or ICL-670), and deferiprone (Ferriprox or L1) are the current standard of care for the treatment of iron overload. Although each chelator is capable of promoting some degree of iron excretion, these chelators are also associated with a wide range of well documented toxicities. However, there is currently very limited data available on their effects in developing embryos. In this study, we took advantage of the rapid development and transparency of the zebrafish embryo, Danio rerio to assess and compare the toxicity of iron chelators. All three iron chelators described above were delivered to zebrafish embryos by direct soaking and their effects on mortality, hatching and developmental morphology were monitored for 96 hpf. To determine whether toxicity was specific to embryos, we examined the effects of chelator exposure via intra peritoneal injection on the cardiac function and gene expression in adult zebrafish. Chelators varied significantly in their effects on embryo mortality, hatching and morphology. While none of the embryos or adults exposed to DFO were negatively affected, ICL -treated embryos and adults differed significantly from controls, and L1 exerted toxic effects in embryos alone. ICL-670 significantly increased the mortality of embryos treated with doses of 0.25 mM or higher and also affected embryo morphology, causing curvature of larvae treated with concentrations above 0.5 mM. ICL-670 exposure (10 µL of 0.1 mM injection) also significantly increased the heart rate and cardiac output of adult zebrafish. While L1 exposure did not cause toxicity in adults, it did cause morphological defects in embryos at 0.5 mM. This study provides first evidence on iron chelator toxicity in early development and will help to guide our approach on better understanding the mechanism of iron chelator toxicity.

Distal ulnar changes in children with thalassemia and deferiprone related arthropathy

BACKGROUND

Regular blood transfusion and iron chelation are the standard of care for children with thalassemia. Deferiprone is an effective oral iron chelator but is known to cause significant arthropathy. Though clinical and radiographic features of deferiprone related arthropathy have been described, the long-term effects are not known.

PROCEDURE

Routine radiographs of left wrist and hand done for bone age estimation in 40 children with thalassemia were evaluated and revealed unique radiographic changes in 13 children (10 males: 3 females) with previous or current deferiprone related arthropathy. Subsequently, these children underwent radiographs of both the knee joints.

RESULTS

The changes on wrist X-ray included lucency and thinning of the ulnar metaphysis, small ulnar epiphysis, deformation and impaired growth of the physeal cartilage leading to reduced distance between the epiphysis and metaphysis. The knee radiograph showed subchondral flattening of femoral and tibial condyles with irregular articular margins.

CONCLUSIONS

Bony dysplasia, deformation and impaired growth of ulnar epiphyses, metaphyses and physes may be an expression of deferiprone related arthropathy in children with thalassemia major.

Immune and neural status of thalassemic patients receiving deferiprone or combined deferiprone and deferoxamine chelation treatment

Deferiprone (L1), has previously been reported to be associated with immunological abnormalities in iron loaded thalassemia patients. However, other factors may also have similar effects such as the level of iron overload, chronic immuno-stimulation due to transfusions, splenectomy and deferoxamine (DFO). During chelation therapy with DFO, several complications have been reported, which were due to pharmacological activity and high dose toxicity with regard to both acoustic and visual effects, as well as peripheral nerve disorders that were measured by nerve conduction velocities. The immune and neural status of 44 beta-thalassemic patients, aged 10-30 years (mean 19.4 +/- 4.9), receiving L1 as a monotherapy (n = 21), or in combination with DFO (n = 23), has been followed for 2 years by monitoring the level of immunoglobulins (IgG, IgM, IgA), the level of T and B lymphocytes (CD4/CD8), the auto antibodies: anti nuclear (ANA), anti-double-stranded (anti-ds DNA), anti reticulin (anti-R1), anti-extra nuclear (anti-ENA), anti histone (anti-AHA), anti liver-kidney-muscle (anti-LKM), anti-smooth muscle (anti-SMA), anti-thyroid (anti-ATA), anti-mitochondrial (anti-AMA) antibodies and the C-reactive protein. The percentage of patients with disorders of the immune and nervous system concerned very few cases. None of our patients with pathological findings in their immunological or neurophysiological examinations presented any signs or symptoms of involvement of the immune or nervous system. Further advantages have been identified for the oral use of L1 and its combination with DFO, including synergistic efficacy and lower dosing with limited toxicity.

Chelation of bismuth by combining desferrioxamine and deferiprone in rats

Consumption and production of bismuth compounds are increasing, however, a little information on the toxic effect and also the effective method in removal of bismuth compounds are available. The present research aimed to characterize the potential efficiency of two chelators after bismuth administration for 55 days following two dose levels of 20 and 40 mg/kg body weight daily to male rats. However, we found abnormalities after bismuth administration in clinical signs, such as body weight, kidneys and liver damages, a black line on gums and skin reactions. Furthermore, the hypothesis that the two chelators might be more efficient as combined therapy than as single therapy in removing bismuth from the body was considered. Along this line, two known chelators deferiprone (1, 2-dimethy1-3-hydroxypyride-4-one, L1) and desferrioxamine (DFO) were chosen and tested in the acute rat model. Chelators were given orally (L1) or intraperitoneally (DFO) as a single or combined therapy for the period of a week. Doses of L1 and DFO were 110 mg/kg body weight in experiments. Bismuth and iron concentrations in various tissues were determined by graphite furnace and flame atomic absorption spectrometry, respectively. The combined chelation therapy results show that DFO and L1 are able to remove bismuth ions from the body, whereas iron concentration returned to the normal level and symptoms are also decreased. DFO was more effective than L1 in reducing bismuth concentration in tissues. The efficiency of DFO + L1 is more than DFO or L1 in removing bismuth from organs. Our results are indicative that the design procedure might be useful for preliminary in-vivo testing of the efficiency of chelating agents. Results of combined chelators’ treatment should be confirmed in a different experimental model before extrapolation to other systems. This testing procedure of course does not provide all the relevant answers for efficiency of chelating agents in bismuth toxicity.

Coordination chemistry and biology of chelators for the treatment of iron overload disorders

Treatment of the medical condition generally referred to as iron overload through the delivery of chelators has recently received a major boost. In 2005 Novartis gained FDA approval for the drug deferasirox, which may be taken orally. Until this time most patients with Fe overload have had to endure long periods of subcutaneous infusions of the orally ineffective drug desferrioxamine (desferal) which has led to major problems with patient compliance. An effective Fe chelator must possess a number of properties for it to be able to complex Fe in vivo and be excreted intact. This Perspective will provide an overview of the current state of chelators for Fe overload; both those currently approved and those undergoing preclinical development.

Deferasirox and deferiprone remove cardiac iron in the iron-overloaded gerbil

INTRODUCTION

Deferasirox effectively controls liver iron concentration; however, little is known regarding its ability to remove stored cardiac iron. Deferiprone seems to have increased cardiac efficacy compared with traditional deferoxamine therapy. Therefore, the relative efficacy of deferasirox and deferiprone were compared in removing cardiac iron from iron-loaded gerbils.

METHODS

Twenty-nine 8- to 10-week-old female gerbils underwent 10 weekly iron dextran injections of 200 mg/kg/week. Prechelation iron levels were assessed in 5 animals, and the remainder received deferasirox 100 mg/kg/D po QD (n = 8), deferiprone 375 mg/kg/D po divided TID (n = 8), or sham chelation (n = 8), 5 days/week for 12 weeks.

RESULTS

Deferasirox reduced cardiac iron content 20.5%. No changes occurred in cardiac weight, myocyte hypertrophy, fibrosis, or weight-to-dry weight ratio. Deferasirox treatment reduced liver iron content 51%. Deferiprone produced comparable reductions in cardiac iron content (18.6% reduction). Deferiprone-treated hearts had greater mass (16.5% increase) and increased myocyte hypertrophy. Deferiprone decreased liver iron content 24.9% but was associated with an increase in liver weight and water content.

CONCLUSION

Deferasirox and deferiprone were equally effective in removing stored cardiac iron in a gerbil animal model, but deferasirox removed more hepatic iron for a given cardiac iron burden.

Removal of thallium by combining desferrioxamine and deferiprone chelators in rats

The hypothesis that two known chelators deferiprone (1,2-dimethy1-3-hydroxypyrid-4-one, L1) and desferrioxamine (DFO) might be more efficient as combined treatment than as monotherapies in removing thallium from the body was tested in rats. Six-week-old male Wistar rats received chelators: L1 (p.o.), DFO (i.p.) or L1 + DFO as 110 or 220 mg/kg dose half an hour after a single i.p. administration of 8 mg Tl/kg body weight in the form of chloride. Serum thallium concentration, urinary thallium and iron excretions were determined by graphite furnace atomic absorption spectrometry. Both chelators were effective only at the higher dose level, while DFO was more effective than L1 in enhancing urinary thallium excretion, L1 was more effective than DFO in enhancing urinary iron excretion. In the combined treatment group, L1 did not increase the DFO effect on thallium and DFO did not increase the effect of L1 on iron elimination. Our results support the usefulness of this animal model for preliminary in vivo testing of thallium chelators. Urinary values were more useful because of the high variability of serum results. Result of combined chelators treatment should be confirmed in a different experimental model before extrapolation to other systems.

Safety of oral iron chelator deferiprone in young thalassaemics

Deferiprone is now widely used for iron chelation in patients with thalassaemia. Studies on its efficacy and safety have largely included older children and adults.

OBJECTIVE

To assess the safety of deferiprone in children <6 yr of age.

METHODS

The study is based on scrutiny of follow-up data of 44 patients of age <6 yr receiving deferiprone for a variable period of time. Occurrence of various side effects including gastrointestinal, osteoarticular were noticed and complete blood counts were performed every 2-4 wk.

RESULTS

Nausea and vomiting were noticed in 12 (27.2%), joint symptoms were reported by four (9.1%) and neutropenia was observed in only two patients (4.5%). None of the patient had agranulocytosis. Thrombocytopenia was observed in 20 patients (45.45%), which occurred 3 months to 1 yr after deferiprone therapy. Interruption of deferiprone for 2-4 wk led to reversal of symptoms in all but two patients.

CONCLUSION

Thrombocytopenia is one of the major side effects in young thalassaemics and necessitates frequent close monitoring of blood counts but its resolution after discontinuation and absence of clinical evidence of bleeding does not preclude its use.

Benefits and risks of deferiprone in iron overload in Thalassaemia and other conditions: comparison of epidemiological and therapeutic aspects with deferoxamine

Deferiprone is the only orally active iron-chelating drug to be used therapeutically in conditions of transfusional iron overload. It is an orphan drug designed and developed primarily by academic initiatives for the treatment of iron overload in thalassaemia, which is endemic in the Mediterranean, Middle East and South East Asia and is considered an orphan disease in the European Union and North America. Deferiprone has been used in several other iron or other metal imbalance conditions and has prospects of wider clinical applications. Deferiprone has high affinity for iron and interacts with almost all the iron pools at the molecular, cellular, tissue and organ levels. Doses of 50-120 mg/kg/day appear to be effective in bringing patients to negative iron balance. It increases urinary iron excretion, which mainly depends on the iron load of patients and the dose of the drug. It decreases serum ferritin levels and reduces the liver and heart iron content in the majority of chronically transfused iron loaded patients at doses >80 mg/kg/day. It is metabolised to a glucuronide conjugate and cleared through the urine in the metabolised and a non-metabolised form, usually of a 3 deferiprone: 1 iron complex, which gives the characteristic red colour urine. Peak serum levels of deferiprone are observed within 1 hour of its oral administration and clearance from blood is within 6 hours. There is variation among patients in iron excretion, the metabolism and pharmacokinetics of deferiprone. Deferiprone has been used in more than 7500 patients aged from 2-85 years in >50 countries, in some cases daily for >14 years. All the adverse effects of deferiprone are considered reversible, controllable and manageable. These include agranulocytosis with frequency of about 0.6%, neutropenia 6%, musculoskeletal and joint pains 15%, gastrointestinal complains 6% and zinc deficiency 1%. Discontinuation of the drug is recommended for patients developing agranulocytosis. Deferiprone is of similar therapeutic index to subcutaneous deferoxamine but is more effective in iron removal from the heart, which is the target organ of iron toxicity and mortality in iron-loaded thalassaemia patients. Deferiprone is much less expensive to produce than deferoxamine. Combination therapy of deferoxamine and deferiprone has been used in patients not complying with subcutaneous deferoxamine or experiencing toxicity or not excreting sufficient amounts of iron with use of either drug alone. New oral iron-chelating drugs are being developed, but even if successful these are likely to be more expensive than deferiprone and are not likely to become available in the next 5-8 years. About 25% of treated thalassaemia patients in Europe and more than 50% in India are using deferiprone. For most thalassaemia patients worldwide who are not at present receiving any form of chelation therapy the choice is between deferiprone and fatal iron toxicity.

Iron chelators and iron toxicity

Iron chelation may offer new approaches to the treatment and prevention of alcoholic liver disease. With chronic excess, either iron or alcohol alone may individually injure the liver and other organs. In combination, each exaggerates the adverse effects of the other. In alcoholic liver disease, both iron and alcohol contribute to the production of hepatic fibrosis through their effects on damaged hepatocytes, hepatic macrophages, hepatic stellate cells, and the extracellular matrix. The pivotal role of iron in these processes suggests that chelating iron may offer a new approach to arresting or ameliorating liver injury. For the past four decades, deferoxamine B mesylate has been the only iron-chelating agent generally available for clinical use. Clinical experience with deferoxamine has demonstrated the safety and effectiveness of iron chelation for the prevention and treatment of iron overload. Determined efforts to develop alternative agents have at last resulted in the development of a variety of candidate iron chelators that are now in or near clinical trial, including (a) the hexadentate phenolic aminocarboxylate HBED [N,N'-bis(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid], (b) the tridentate desferrithiocin derivative 4'-OH-dadmDFT [4'-hydroxy-(S)-desazadesmethyl-desferrithiocin; (S)-4,5-dihydro-2-(2,4-dihydroxyphenyl)-4-thiazolecarboxylic acid], (c) the tridentate triazole ICL670A [CGP72 670A; 4-[3,5-bis-(hydroxyphenyl)-1,2,4-triazol-1-yl]-benzoic acid], and (d) the bidentate hydroxypyridin-4-one deferiprone [L1, CP20; 1,2-dimethyl-3-hydroxypyridin-4-one]. These agents may provide new pharmacological means of averting or ameliorating liver damage in alcoholic liver disease by binding, inactivating, and eliminating the reactive forms of iron that contribute to oxidative injury of cellular components, are involved in signal transduction, or both.

Hydrolysis of pyridoxal isonicotinoyl hydrazone and its analogs

An orally available iron chelator is desirable for the treatment of secondary iron overload. Pyridoxal isonicotinoyl hydrazone (PIH) and its analogs effectively mobilize iron in vivo and in vitro, and are therefore promising candidates for this purpose. PIH analogs undergo significant amino acid-catalyzed hydrolysis in cell culture medium and in serum, achieving equilibrium with their corresponding aldehydes and hydrazides with half-times of 1-8 h. The extent of hydrolysis in RPMI is significant, even in experiments of a few hours' duration, although the half-life of PIH in phosphate-buffered saline (PBS) is approximately 24 h. Therefore, the biological effects (e.g., 59Fe mobilization, toxicity) of these iron chelators have been underestimated in previous studies. Measurement of the affinity of PIH analogs for Fe(3+) under conditions in which hydrolysis is minimal resulted in conditional affinity constants of 10(26) to 10(27) M, which are much lower than predicted by the overall formation constants determined under conditions that likely allowed extensive hydrolysis. These data indicate the importance of hydrolysis of PIH analogs in the interpretation of previous studies, and the importance of designing clinically useful analogs whose efficacies are not limited by hydrolysis.

Cellular zinc content is a major determinant of iron chelator-induced apoptosis of thymocytes

Desferrioxamine (DFO) and the hydroxypiridinone (HPO) deferiprone (CP20) chelate iron as well as other metals. These chelators are used clinically to treat iron overload, but they induce apoptosis in thymocytes. Thymocyte apoptosis is potentiated by zinc deficiency, suggesting that these iron chelators may induce apoptosis by depleting stores of zinc. Exposure of murine thymocytes to either DFO or deferiprone resulted in significant reductions in the labile intracellular zinc pool. Moreover, increasing intracellular zinc levels, by chronic zinc dietary supplementation to mice or in vitro loading with zinc, abrogated deferiprone-induced murine thymocyte apoptosis. Bidentate hydroxypyridinones such as deferiprone interact with intracellular zinc pools in a manner distinct from that of DFO, which is a hexadentate iron chelator. Whereas deferiprone acts synergistically with the zinc chelator NNNN-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) to induce apoptosis, DFO does not. This difference is most likely due to the ability of HPOs but not DFO to "shuttle" zinc onto acceptors such as metallothioneins. By nature of its structure, DFO is larger than deferiprone and is thus less able to access some intracellular zinc pools. Additionally, metal complexes of DFO are more stable than those of HPOs and thus are less likely to donate zinc to other acceptors. The ability of deferiprone to preferentially access zinc pools was also demonstrated by inhibition of a zinc-containing enzyme phospholipase C, particularly when combined with TPEN. These findings suggest that bidentate iron chelators access intracellular zinc pools not available to DFO and that zinc chelation is a mechanism of apoptotic induction by such chelators in thymocytes.

Secondary iron overload

Transfusion therapy for inherited anemias and acquired refractory anemias both improves the quality of life and prolongs survival. A consequence of chronic transfusion therapy is secondary iron overload, which adversely affects the function of the heart, the liver and other organs. This session will review the use of iron chelating agents in the management of transfusion-induced secondary iron overload. In Section I Dr. John Porter describes techniques for the administration of deferoxamine that exploit the pharmacokinetic properties of the drug and minimize potential toxic side effects. The experience with chelation therapy in patients with thalassemia and sickle cell disease will be reviewed and guidelines will be suggested for chelation therapy of chronically transfused adults with refractory anemias. In Section II Dr. Nancy Olivieri examines the clinical consequences of transfusion-induced secondary iron overload and suggests criteria useful in determining the optimal timing of the initiation of chelation therapy. Finally, Dr. Olivieri discusses the clinical trials evaluating orally administered iron chelators.

Chelation of aluminium by combining DFO and L1 in rats

The hypothesis that two known chelators 1, 2-dimethyl-3-hydroxypyrid-4-one (L1) and desferrioxamine (DFO) might be more efficient as combined treatment than as monotherapies in removing aluminium from the body was tested in a new acute rat model. Five-week old female rats received chelators: L1 (p.o.), DFO (i.p.) or L1+DFO as 100 or 200 mg/kg dose half an hour after a single i.p. administration of 6 mg Al/kg body weight in the form of chloride. Serum aluminium concentration and urinary aluminium and iron excretions were determined by electrothermal or flame atomic absorption spectrometry. Both chelators were effective only at the higher dose level. While DFO was more effective than L1 in enhancing urinary aluminium excretion, L1 was more effective than DFO in enhancing urinary iron excretion. In the combined treatment group L1 did not increase the DFO effect on aluminium and DFO did not increase the effect of L1 on iron elimination. However, in this group a simultaneous increase in both aluminium and iron elimination was observed. Our results support the usefulness of this animal model for preliminary in vivo testing of aluminium chelators. Urinary values were more useful because of the high variability of serum results. Result of combined chelators treatment should be confirmed in a different experimental model before extrapolation to other systems. This testing procedure of course does not provide all the relevant answers for evaluating the efficiency of chelating agents in aluminium toxicity.

The hexadentate hydroxypyridinonate TREN-(Me-3,2-HOPO) is a more orally active iron chelator than its bidentate analogue

Bidentate hydroxypyridinone chelators effectively complex and facilitate excretion of trivalent iron. To test the hypothesis that hexadentate chelators are more effective than bidentate chelators at low concentrations, urinary and biliary Fe excretions were determined in Fe-loaded rats before and after administration of a bidentate chelator, Pr-(Me-3,2-HOPO), or its hexadentate analogue, TREN-(Me-3,2-HOPO). The bidentate chelator slightly increased biliary Fe excretion in Fe-loaded rats after IV (90 micromol/kg) and PO (90 or 270 micromol/kg) administration, but chelation efficiency did not exceed 1%. The hexadentate chelator markedly increased biliary Fe excretion, achieving overall chelation efficiencies of 14% after IV administration of 30 micromol/kg and 8 or 3% after PO (30 or 90 micromol/kg) administration. The hexadentate chelator was significantly more effective than the bidentate chelator after IV injection and oral dosing. In chelator-treated Fe-loaded or saline-injected rats, >90% of the excreted Fe was in the bile. Oral TREN-(Me-3,2-HOPO), given to non-Fe-loaded rats, did not appreciably change Fe output, indicating that there was little Fe depletion in the absence of Fe overload. These results support the hypothesis that greater Fe chelation efficiency can be achieved with hexadentate than with bidentate chelators at lower, and presumably safer, concentrations. The results also demonstrate that TREN-(Me-3, 2-HOPO) is a promising, orally effective, Fe chelator.

Safety profile of the oral iron chelator deferiprone: a multicentre study

In previous trials, the orally active iron chelator deferiprone (L1) has been associated with sporadic agranulocytosis, milder forms of neutropenia and other side-effects. To determine the incidence of these events, we performed a multicentre prospective study of the chelator. Blood counts were performed weekly, and confirmed neutropenia mandated discontinuation of therapy. Among 187 patients with thalassaemia major, the incidence of agranulocytosis (neutrophils < 0.5 x 109/l) was 0.6/100 patient-years, and the incidence of milder forms of neutropenia (neutrophils 0.5-1.5 x 109/l) was 5.4/100 patient-years. All cases of neutropenia resolved after interruption of therapy. Neutropenia occurred predominantly in non-splenectomized patients. Nausea and/or vomiting occurred early in therapy, was usually transient and caused discontinuation of deferiprone in three patients. Mild to moderate joint pain and/or swelling did not require permanent cessation of deferiprone and occurred more commonly in patients with higher ferritin levels. Mean alanine transaminase (ALT) levels rose during therapy. Increased ALT levels were generally transient and occurred more commonly in patients with hepatitis C. Persistent changes in immunological studies were infrequent, although sporadic abnormalities occurred commonly. Mean zinc levels decreased during therapy. Ferritin levels did not change in the overall group but decreased in those patients with baseline levels > 2500 microgram/l. This study characterized the safety profile of deferiprone, and, under the specific conditions of monitoring, demonstrated that agranulocytosis is less common than previously predicted.

Iron chelating agents for treating malaria

BACKGROUND

Mortality from Plasmodium falciparum malaria remains high; death and sequelae occur in even in patients treated with antimalarial drugs. Researchers are exploring the effects of adding treatments to the main antimalarial regimens in an attempt to reduce mortality. Iron chelation is one potential chemotherapeutic adjuvant treatment. Before advocating adjunctive therapy, the effects of iron chelators in improving patient outcomes needs to be examined.

OBJECTIVES

To assess the effects of iron-chelating agents combined with antimalarial drugs, or iron chelators alone, for treating Plasmodium falciparum malaria in adults and children, in relation to mortality, coma recovery time, parasite clearance, and adverse effects.

SEARCH STRATEGY

Electronic searches of the Cochrane Library, MEDLINE, and EMBASE, using the standard Cochrane search strategy. Bibliographies of retrieved studies were scrutinized in order to identify further relevant trials. Organisations, experts and other individuals in malaria research were contacted for unpublished studies.

SELECTION CRITERIA

All randomised controlled trials of adults or children with P.falciparum malaria.

DATA COLLECTION AND ANALYSIS

Trials were identified and extracted by a single reviewer (HS) and checked by a second (MM). Inclusion criteria were applied, and data were extracted independently by both reviewers. Authors were contacted for missing and additional data. Meta-analysis used Relative Risk (RR) and 95% Confidence Intervals.

MAIN RESULTS

No evidence of benefit or harm were shown in relation to mortality, but studies were small, and one trial was tending towards more deaths with the intervention when it was stopped. The risk of experiencing persistent seizures was significantly lower with desferrioxamine compared to placebo treatment (RR 0.80, 95% CI 0.67 to 0.95). Many adverse effects were more common in participants treated with desferrioxamine.

REVIEWER'S CONCLUSIONS

Trends suggestive of both harm (death) and potential benefit (fewer seizures) are demonstrated in this review. It is not possible to comment on time to event outcomes that include coma recovery or parasitaemia as we are clarifying data with the trialists. Whether to conduct further trials will depend on a judgement about potential benefit.

Deferiprone: a review of its clinical potential in iron overload in beta-thalassaemia major and other transfusion-dependent diseases

Patients with beta-thalassaemia and other transfusion-dependent diseases develop iron overload from chronic blood transfusions and require regular iron chelation to prevent potentially fatal iron-related complications. The only iron chelator currently widely available is deferoxamine, which is expensive and requires prolonged subcutaneous infusion 3 to 7 times per week or daily intramuscular injections. Moreover, some patients are unable to tolerate deferoxamine and compliance with the drug is poor in many patients. Deferiprone is the most extensively studied oral iron chelator to date. Non-comparative clinical studies mostly in patients with beta-thalassaemia have demonstrated that deferiprone 75 to 100 mg/kg/day can reduce iron burden in regularly transfused iron-overloaded patients. Serum ferritin levels are generally reduced in patients with very high pretreatment levels and are frequently maintained within an acceptable range in those who are already adequately chelated. Deferiprone is not effective in all patients (some of whom show increases in serum ferritin and/or liver iron content, particularly during long term therapy). This may reflect factors such as suboptimal dosage and/or severe degree of iron overload at baseline in some instances. Although few long term comparative data are available, deferiprone at the recommended dosage of 75 mg/kg/day appears to be less effective than deferoxamine; however, compliance is superior with deferiprone, which may partly compensate for this. Deferiprone has additive, or possibly synergistic, effects on iron excretion when combined with deferoxamine. The optimum dosage and long term efficacy of deferiprone, and its effects on survival and progression of iron-related organ damage, remain to be established. The most important adverse effects in deferiprone-treated patients are arthropathy and neutropenia/agranulocytosis. Other adverse events include gastrointestinal disturbances, ALT elevation, development of antinuclear antibodies and zinc deficiency. With deferiprone, adverse effects occur mostly in heavily iron-loaded patients, whereas with deferoxamine adverse effects occur predominantly when body iron burden is lower.

CONCLUSION

Deferiprone is the most promising oral iron chelator under development at present. Further studies are required to determine the best way to use this new drug. Although it appears to be less effective than deferoxamine at the recommended dosage and there are concerns regarding its tolerability, it may nevertheless offer a therapeutic alternative in the management of patients unable or unwilling to receive the latter drug. Deferipone also shows promise as an adjunct to deferoxamine therapy in patients with insufficient response and may prove useful as a maintenance treatment to interpose between treatments.

Drug-induced heart failure

Heart failure is a clinical syndrome that is predominantly caused by cardiovascular disorders such as coronary heart disease and hypertension. However, several classes of drugs may induce heart failure in patients without concurrent cardiovascular disease or may precipitate the occurrence of heart failure in patients with preexisting left ventricular impairment. We reviewed the literature on drug-induced heart failure, using the MEDLINE database and lateral references. Successively, we discuss the potential role in the occurrence of heart failure of cytostatics, immunomodulating drugs, antidepressants, calcium channel blocking agents, nonsteroidal anti-inflammatory drugs, antiarrhythmics, beta-adrenoceptor blocking agents, anesthetics and some miscellaneous agents. Drug-induced heart failure may play a role in only a minority of the patients presenting with heart failure. Nevertheless, drug-induced heart failure should be regarded as a potentially preventable cause of heart failure, although sometimes other priorities do not offer therapeutic alternatives (e.g., anthracycline-induced cardiomyopathy). The awareness of clinicians of potential adverse effects on cardiac performance by several classes of drugs, particularly in patients with preexisting ventricular dysfunction, may contribute to timely diagnosis and prevention of drug-induced heart failure.

In vitro and in situ permeability of a 'second generation' hydroxypyridinone oral iron chelator: correlation with physico-chemical properties and oral activity

PURPOSE

The in vitro and in situ transport of CGP 65015 ((+)-3-hydroxy-1-(2-hydroxyethyl)-2-hydroxyphenyl-methyl-1H-pyridin-4-on e), a novel oral iron chelator, is described. The predictive power of these data in assessing intestinal absorption in man is described.

METHODS

Caco-2 epithelial monolayer and in situ rat jejunum perfusion intestinal permeability models were utilized. In vivo iron excretion and preliminary animal pharmacokinetic experiments were described. Ionization constants and octanol/aqueous partition coefficients were measured potentiometrically. Solubilities and intrinsic dissolution rates were determined using standard procedures.

RESULTS

Caco-2 cell (Papp approximately 0.25 x 10(-6) cm x s(-1)) and rat jejunum (Pw approximately 0.4) permeabilities of CGP 65015 were determined. The log D(pH 7.4) of CGP 65015 was 0.58 and its aqueous solubility was < 0.5 mg x ml(-1) (pH 3-9). The intrinsic dissolution rate of CGP 65015 in USP simulated intestinal fluid was 0.012 mg x min(-1) x cm(-2). CGP 65015 promotes iron excretion effectively and dose dependently in animals.

CONCLUSIONS

Caco-2 and rat intestinal permeabilities predict incomplete oral absorption of CGP 65015 in man. Preliminary rat pharmacokinetics support this. Physico-chemical data are, also, in line and suggest that CGP 65015 may, in addition, be solubility/dissolution rate limited in vivo. Nevertheless, early animal pharmacological data demonstrate that CGP 65015 is a viable oral iron chelator candidate.

Bis(5-hydroxy-2-hydroxymethyl-pyran-4-one-6-yl)methane: a novel ligand for the intracellular mobilisation of ferritin-bound iron

The efficacy of a novel tetradentate iron(III) ligand for the in vitro mobilisation of ferritin-bound iron is measured in direct comparison to the clinically approved agents, 1,2-dimethyl-3-hydroxypyridin-4-one and desferrioxamine.

Systemic administration of the iron chelator deferiprone attenuates subarachnoid hemorrhage-induced cerebral vasospasm in the rabbit

OBJECTIVE

Iron catalyzed generation of injurious free radicals has been implicated in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage (SAH). The present study assessed the effects of the iron chelator deferiprone on cerebral vasospasm in an in vivo rabbit model of SAH.

METHODS

Twenty-four rabbits were assigned to three groups as follows: SAH plus placebo (n = 8), SAH plus deferiprone (n = 8), or control plus placebo (n = 8). Deferiprone was administered to an additional group of three rabbits that were not subjected to SAH. Drug administration was initiated 8 hours after SAH was induced and was repeated at 8-hour intervals. The animals were killed using perfusion-fixation 48 hours after SAH. Cross-sectional areas of basilar artery histological sections were measured by an investigator blinded to the treatment groups.

RESULTS

In placebo-treated animals, the average luminal cross-sectional area of the basilar artery was reduced by 54% after SAH compared to controls (i.e., from 0.272 to 0.125 mm2). The vasospastic response after SAH was attenuated significantly in animals treated with deferiprone (0.208 mm2, representing a 24% reduction).

CONCLUSION

Previous experimental studies suggested that iron chelation can be effective in attenuating cerebral vasospasm after SAH. Deferiprone is a recently developed iron chelator that has been extensively evaluated for the treatment of patients requiring chronic blood transfusions. The present study demonstrates that deferiprone is effective in attenuating experimental cerebral vasospasm. Because of its stability, lipophilicity, and ability to penetrate the blood-brain barrier, deferiprone represents an attractive candidate for the treatment of cerebral vasospasm.

Blood transfusion in beta thalassaemia major

Conventional treatment of beta thalassaemia major is based on regular blood transfusion from early childhood. Maximum effectiveness of transfusion therapy depends on the following. (1) Availability of safe blood. Donation programmes should aim at retaining repeat donors, who carry decreased risk of transmitting blood-borne infections. Donors should be screened with laboratory tests performed to the highest possible standard of quality. Selection of safe donors can be improved by the adoption of questionnaires containing direct questions on risk factors for transfusion transmissible infections. (2) Use of good quality red blood cells, which should be leucodepleted, preferably by filtration, that can be carried out at the bedside. (3) Regular evaluation of blood transfusion indices, including mean level of haemoglobin maintained, annual blood requirement, daily haemoglobin fall, mean transfusion interval, transfusion reaction rate. This can be assisted by the use of a computerized patient record. (4) Maintenance of a permanent record of the patient's blood group genotype (including at least Rh, Kell, Kidd and Duffy systems) and any red cell antibodies that develop. This is mandatory to ensure optimal survival of transfused red cells. (5) Continuous monitoring of transfusion transmissible infections. (6) Vaccination against hepatitis B of all suitable patients. (7) Intensive iron chelation. This should be done by regular subcutaneous administration of desferrioxamine B. Oral chelators, which are currently under laboratory and clinical evaluation, are not yet available for general use.

Results of long-term deferiprone (L1) therapy: a report by the International Study Group on Oral Iron Chelators

This report updates the combined experience of four centres involved in the long-term treatment of transfusional iron overload in 84 patients with the oral iron chelator deferiprone (L1) over 167 patient-years. The source of L1 was variable, including two university research laboratories and three pharmaceutical firms. Compliance was rated as excellent in 48%, intermediate in 36%, and poor in 16% of patients. On a mean L1 dose of 73-81 mg/kg/d, urinary iron excretion was stable, at around 0.5 mg/kg/d, with no indication of a diminishing response with time. Serum ferritin showed a very steady decrease with time from an initial mean +/- 1 SD of 4207 +/- 3118 to 1779 +/- 1154 micrograms/l after 48 months (P < 0.001). 17 patients abandoned L1 therapy. Major complications of L1 requiring permanent discontinuation of treatment included agranulocytosis (three), severe nausea (four), arthritis (two) and persistent liver dysfunction (one). The remaining patients abandoned treatment because of low compliance (three) and conditions unrelated to L1 toxicity (four). Lesser complications permitting continued L1 treatment included transient mild neutropenia (four), zinc deficiency (12), transient increase in liver enzymes (37), moderate nausea (three) and arthropathy (17). There was no treatment-related mortality. Although the complications associated with L1 treatment are significant and require close monitoring, they do not preclude effective long-term therapy in the vast majority of patients. Further well-controlled prospective studies of L1 are required in order to enable proper judgement of its suitability for general long-term clinical use.

Synthesis and iron(III) binding properties of 3-hydroxypyrid-4-ones derived from kojic acid

In an attempt to reduce the toxicity of the 3-hydroxypyrid-4-ones, the more hydrophilic derivatives of kojic acid were explored and compared to the standard, 1,2-dimethyl-3-hydroxypyrid-4-one, L1. The synthesis and iron(III) binding properties of these chelators are described. Neither these compounds nor the clinically effective 1,2-dimethyl-3-hydroxypyrid-4 one is able to completely remove all of the iron(III) from the Fe(III)EDTA complex in sodium acetate buffered solutions, when the 3-hydroxypyrid-4-one: Fe(III) ratio is 6:1. The ability of these compounds to enhance the urinary excretion of iron in rats indicates that the behavior of the 3-hydroxypyrid-4-ones derived from kojic acid is comparable to the analogous derivatives of maltol and ethyl maltol. The structure of the iron(III) complex of 3-hydroxy-6-hydroxymethyl-1-methylpyrid-4-one was determined by x-ray diffraction and found to be similar to the previously reported structure of the iron(III) complex of L1.

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.

Aluminum chelation: chemistry, clinical, and experimental studies and the search for alternatives to desferrioxamine

This review focuses on aluminum (Al) chelation, its chemistry and biology. The toxicology and biology of Al in mammalian organisms are briefly reviewed to introduce the problems associated with excessive Al exposure and accumulation and the challenges facing an effective Al chelator. The basics of Al chelation chemistry are considered to help the reader understand the Al chelation chemical literature. The chemical properties of Al enable prediction of effective functional groups for Al chelation. A compilation of distribution coefficients between octanol and aqueous phases (Do/a) for chelators and their complexes with Al shows the effect of complexation on lipophilicity. A compilation of stability constants for Al.chelator complexes illustrates the role of oxygen in ligands that form stable complexes. The history of clinical Al chelation therapy is reviewed, with emphasis on desferrioxamine (DFO), which has been extensively used since 1980. The beneficial and adverse effects and limitations of DFO use in end-stage renal-diseased patients, in patients with neurodegenerative disorders, including Alzheimer's disease, and in animal models of Al intoxication are presented. The methods to evaluate potential Al chelators in vitro, in vivo, and using computer modeling are discussed. The Al chelation literature is reviewed by the chemical class of chelators, including fluoride, carboxylic acids, amino acids, catechols, polyamino carboxylic acids, phenyl carboxylic acids, the hydroxypyridinones, and hydroxamic acids.

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.