Deferasirox-current knowledge and future challenges

Iron; Benefits or threatens (with emphasis on mechanism and treatment of its poisoning)

Iron is a necessary biological element and one of the richest in the human body, but it can cause changes in cell function and activity control. Iron is involved in a wide range of oxidation - reduction activities. Whenever iron exceeds the cellular metabolic needs, its excess causes changes in the products of cellular respiration, such as superoxide, hydrogen peroxide and hydroxyl. The formation of these compounds causes cellular toxicity. Lack of control over reactive oxygen species causes damages to DNA, proteins, and lipids. Conversely, superoxide, hydrogen peroxide and hydroxyl are reactive oxygen species, using antioxidants, restoring DNA function, and controlling iron stores lead to natural conditions. Iron poisoning causes clinical manifestations in the gastrointestinal tract, liver, heart, kidneys, and hematopoietic system. When serum iron is elevated, serum iron concentrations, total iron-binding capacity (TIBC) and ferritin will also increase. Supportive care is provided by whole bowel irrigation (WBI), esophagogastroduodenoscopy is required to evaluate mucosal injury and remove undissolved iron tablets. The use of chelator agents such as deferoxamine mesylate, deferasirox, deferiprone, deferitrin are very effective in removing excess iron. Of course, the combined treatment of these chelators plays an important role in increasing iron excretion, and reducing side effects.

Involvement of cytosolic and mitochondrial iron in iron overload cardiomyopathy: an update

Iron overload cardiomyopathy (IOC) is a major cause of death in patients with diseases associated with chronic anemia such as thalassemia or sickle cell disease after chronic blood transfusions. Associated with iron overload conditions, there is excess free iron that enters cardiomyocytes through both L- and T-type calcium channels thereby resulting in increased reactive oxygen species being generated via Haber-Weiss and Fenton reactions. It is thought that an increase in reactive oxygen species contributes to high morbidity and mortality rates. Recent studies have, however, suggested that it is iron overload in mitochondria that contributes to cellular oxidative stress, mitochondrial damage, cardiac arrhythmias, as well as the development of cardiomyopathy. Iron chelators, antioxidants, and/or calcium channel blockers have been demonstrated to prevent and ameliorate cardiac dysfunction in animal models as well as in patients suffering from cardiac iron overload. Hence, either a mono-therapy or combination therapies with any of the aforementioned agents may serve as a novel treatment in iron-overload patients in the near future. In the present article, we review the mechanisms of cytosolic and/or mitochondrial iron load in the heart which may contribute synergistically or independently to the development of iron-associated cardiomyopathy. We also review available as well as potential future novel treatments.

Safety and tolerability of deferasirox in pediatric hematopoietic stem cell transplant recipients: one facility's five years' experience of chelation treatment

42 pediatric patients with iron overload, who underwent liver biopsy and DFX treatment after hematopoietic stem cell transplantation were included in the study group. The patients were divided into two groups diversified according to deferasirox trough plasma concentrations (DFX C_trough) with cut-off equal to10 mcg/mL. The average dose of DFX was 25.9 mg/kg in the DFX C_trough < 10 mcg/mL group versus 19.2 mg/kg in the DFX C_trough > 10 mcg/mL group (p=0,0003). The mean duration of DFX treatment was 135.7 days in the DFX C_trough < 10 mcg/mL group versus 41.8 days in the DFX C_trough > 10 mcg/mL group (p<0.0001). The mean tissue iron concentration in the DFX C_trough < 10 mcg/mL group was 261.9 μmol/g versus 133.4 μmol/g in the DFX C_trough > 10 mcg/mL group (p < 0.0001). 21 patients (100%) in the DFX C_trough > 10 mcg/mL group had ductopenia which was complete in 47.6% of them and severe in 52.4%. All patients with particularly high C_trough (> 25 mcg/mL) were found to have total ductopenia. 90.5% of all deferasirox-related adverse events and 100% of major adverse events occurred in the DFX C_trough > 10 mcg/mL group. In the DFX C_trough < 10 mcg/mL group only one patient interrupted chelation therapy versus 16 (84.2%) patients in the DFX C_trough > 10 mcg/mL group. We would recommend a close monitoring in pediatric hematopoietic transplant recipients subjected to deferasirox-based therapy because we have observed a high incidence of adverse events and discontinuation of chelation treatment.

Combined Iron Chelator and Antioxidant Exerted Greater Efficacy on Cardioprotection Than Monotherapy in Iron-Overloaded Rats

Background

Iron chelators are used to treat iron overload cardiomyopathy patients. However, a direct comparison of the benefits of three common iron chelators (deferoxamine (DFO), deferiprone (DFP) and deferasirox (DFX)) or an antioxidant (N-acetyl cysteine (NAC)) with a combined DFP and NAC treatments on left ventricular (LV) function with iron overload has not been investigated.

Methods and Findings

Male Wistar rats were fed with either a normal diet or a high iron diet (HFe group) for 4 months. After 2 months, the HFe-fed rats were divided into 6 groups to receive either: a vehicle, DFO (25 mg/kg/day), DFP (75 mg/kg/day), DFX (20 mg/kg/day), NAC (100 mg/kg/day) or the combined DFP and NAC for 2 months. Our results demonstrated that HFe rats had increased plasma non-transferrin bound iron (NTBI), malondialdehyde (MDA), cardiac iron and MDA levels and cardiac mitochondrial dysfunction, leading to LV dysfunction. Although DFO, DFP, DFX or NAC improved these parameters, leading to improved LV function, the combined DFP and NAC therapy caused greater improvement, leading to more extensively improved LV function.

Conclusions

The combined DFP and NAC treatment had greater efficacy than monotherapy in cardioprotection through the reduction of cardiac iron deposition and improved cardiac mitochondrial function in iron-overloaded rats.

Thalassaemia

Thalassaemia is one of the most common genetic diseases worldwide, with at least 60,000 severely affected individuals born every year. Individuals originating from tropical and subtropical regions are most at risk. Disorders of haemoglobin synthesis (thalassaemia) and structure (eg, sickle-cell disease) were among the first molecular diseases to be identified, and have been investigated and characterised in detail over the past 40 years. Nevertheless, treatment of thalassaemia is still largely dependent on supportive care with blood transfusion and iron chelation. Since 1978, scientists and clinicians in this specialty have met regularly in an international effort to improve the management of thalassaemia, with the aim of increasing the expression of unaffected fetal genes to improve the deficiency in adult β-globin synthesis. In this Seminar we discuss important advances in the understanding of the molecular and cellular basis of normal and abnormal expression of globin genes. We will summarise new approaches to the development of tailored pharmacological agents to alter regulation of globin genes, the first trial of gene therapy for thalassaemia, and future prospects of cell therapy.

Recent advances in β-thalassemias

β-thalassemias are heterogeneous hereditary anemias characterized by a reduced output of β-globin chains. The disease is most frequent in the temperate regions of the world, where it represents an important health problem. In the last decades, several programs, aimed at controlling the birth rate of thalassemia newborns by screening and prenatal diagnosis of populations with high risk of β-thalassemia, have been successful accomplished. Bone marrow transplantation has offered a definitive cure for the fraction of patients with available donors. In the same time, steady improvements were made in the traditional clinical management of β-thalassemia patients. The introduction of the oral iron chelators deferiprone that preferentially chelates hearth iron and the development of novel NMR diagnostic methods has led to reduced morbility, increased survival and improved quality of life. More recently, major advances have being made in the discovery of critical modifier genes, such as Myb and especially BCL11A (B cell lymphoma 11A), a master regulator of HbF (fetal hemoglobin) and hemoglobin switching. Polimorphysms of BCL11A, Myb and γ-globin genes account for most of the variability in the clinical phenotypes in β-thalassemia and sickle cell anemia patients. Finally, the year 2010 has brought in the first successful experiment of gene therapy in a β-thalassemia patient, opening up the perspective of a generalized cure for all β- thalassemia patients.

Update on iron chelators in thalassemia

Over the past four decades, there have been dramatic improvements in survival for patients with thalassemia major due in large measure to improved iron chelators. Two chelators are approved for use in the United States and Canada, parenteral deferoxamine and oral deferasirox. Three are available in much of the rest of the world, where oral deferiprone is also approved (in the United States, deferiprone is only available in studies, for emergency use, or on a "compassionate-use" basis). Many trials and worldwide clinical experience demonstrate that each of the three drugs can chelate and remove iron, and thereby prevent or improve transfusional hemosiderosis in thalassemia patients. However, the chelators differ strikingly in side-effect profile, cost, tolerability and ease of adherence, and (to some degree) efficacy for any specific patient. The entire field of chelator clinical trials suffers from the fact that each drug (as monotherapy or in combination) has not been tested directly against all of the other possibilities. Acknowledging the challenges of assessing chelators with diverse properties and imperfect comparative data, the purpose of this review is to summarize the last 4 years of studies that have improved our understanding of the applications and limitations of iron chelators in various settings for thalassemia patients, and to point out areas for much-needed future research.

Advances in iron chelation: an update

INTRODUCTION

Oxidative stress (caused by excess iron) can result in tissue damage, organ failure and finally death, unless treated by iron chelators. The causative factor in the etiology of a variety of disease states is the presence of iron-generated reactive oxygen species (ROS), which can result in cell damage or which can affect the signaling pathways involved in cell necrosis-apoptosis or organ fibrosis, cancer, neurodegeneration and cardiovascular, hepatic or renal dysfunctions. Iron chelators can reduce oxidative stress by the removal of iron from target tissues. Equally as important, removal of iron from the active site of enzymes that play key roles in various diseases can be of considerable benefit to the patients.

AREAS COVERED

This review focuses on iron chelators used as therapeutic agents. The importance of iron in oxidative damage is discussed, along with the three clinically approved iron chelators.

EXPERT OPINION

A number of iron chelators are used as approved therapeutic agents in the treatment of thalassemia major, asthma, fungal infections and cancer. However, as our knowledge about the biochemistry of iron and its role in etiologies of seemingly unrelated diseases increases, new applications of the approved iron chelators, as well as the development of new iron chelators, present challenging opportunities in the areas of drug discovery and development.