Current status of iron overload and chelation with deferasirox

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  • Indian Journal of Pediatrics, Volume 74August, 2007 759

    Special Article

    Correspondence and Reprint requests : Dr. V.P. Choudhry, DirectorSunflag Pahuja Centre for Blood Disorders Sunflag Hospital, Sector16A Faridabad, Haryana-121002, Ph: 01294075184, 9811073904

    [Received October 26, 2006; Accepted March 12, 2007]

    Current Status of Iron Overload and Chelation withDeferasiroxV.P. Choudhry and Rahul Naithani

    Department of Hematology, All India Institute of Medical Sciences, New Delhi.

    ABSTRACTA large number of complications in thalassemia major are due mainly to iron overload. Deferoxamine in iron-overloaded patientshas established that chelation therapy, when given at an adequate dose, reduces iron-related complications. Parenteraladministration and the daily nuisance of an infusion pump hinder the optimal compliance. Deferiprone is moderately effectiveoral iron chelator. Arthralgia and cytopenias constitute the main side effects. Deferasirox is a new orally effective iron chelatorwhich has been shown to be non-inferior to deferoxamine in clinical trials. Further clinical trials especially in Indian children willtell if it stands the test of time. [Indian J Pediatr 2007; 74 (8) : 759-764] E-mail : vedpchoudhry@yahoo.co.inKey words : Thalassemia; Iron overload; Deferasirox

    Patients with chronic anemias such as thalassemia, sicklecell disease, congenital rare anemias and myelodysplasticsyndromes who require regular blood transfusions fortheir survival and/or to improve the quality of life. Thereis no system to eliminate the iron released from thebreakdown of transfused red blood cells.1,2 The excessiron in the body gets deposited in various tissues of thebody, particularly the liver, heart, and endocrine organs.3

    Once the bodys storage capacity is exceeded, free ironcatalyzes the formation of highly reactive hydroxylradicals, which leads to membrane damage anddenaturation of proteins. This process leads to tissuedamage and ultimately to significant morbidity andmortality.4 chronic iron overload progresses to multipleorgan failure and is a major cause of death in patientswho receive blood transfusions regularly withoutappropriate chelation therapy.5

    In children with thalassemia major, within 2 to 3 yr ofinitiation of regular blood transfusions, evidence of ironoverload is manifest as elevated liver iron concentration(LIC) and elevated serum ferritin levels. An increased riskof iron-induced cardiac disease is observed in thalassemiapatients with LIC values above 15 mg of iron per gram ofdry weight of liver (15 mg Fe/g/dw), and in patientswith serum ferritin values above 2500 g/L.6 Patientswith a number of other congenital and acquired anemias

    who may receive frequent blood transfusions are alsosusceptible to the adverse effects of iron loading.7

    LIC values greater than 7 mg Fe/g dw have beenreported in the literature to be associated with anincreased morbidity and mortality. Maintenance orreduction of LIC values to less than 7 mg Fe/g dw isdesirable as an endpoint.

    Measurement of iron overload

    Limitations of serum ferritin as a marker of iron overloadare well known but is important measurement inresource poor settings. Liver biopsy has been the goldstandard for iron balance studies, but the technique isinvasive, expensive, and subject to variability within andbetween research subjects.8

    To avoid the need for invasive liver biopsy, liver ironconcentration (LIC) has been measured non-invasively bybiomagnetic susceptometry using a low criticaltemperature (low-TC) superconducting quantuminterference device (SQUID) biomagnetometer, whichallows the measurement of the paramagneticsusceptibility of the iron stored in the liver ashemosiderin and ferritin.1 In patients with iron overload,the results of biomagnetic susceptometry measurementsof hepatic non-heme iron have been reported to bestrongly correlated with those obtained by conventionalanalysis of liver biopsy.9 LIC values derived frommagnetic susceptometry as milligrams of iron per gram ofliver tissue (wet weight) were multiplied by a factor of3.33 to provide values per gram of liver tissue dry weight(mg Fe/g dw; the conventional units used for LIC).10

  • V.P. Choudhry and R. Naithani

    760 Indian Journal of Pediatrics, Volume 74August, 2007

    Another technique used is a T2* imaging of heart. LowT2* values {< 8 ms compared with normal (> 20 ms)} arerelated to risk of heart failure and death in iron-overloaded thalassemia patients.11 T2* reports initiallyraised concerns about whether it is a good surrogate forcardiac iron concentration for technical reasons as well asthe paradox that liver iron correlated poorly with cardiacT2*. The poor correlation of T2* with hepatic iron is nowunderstood on a kinetic basis. The liver can be readilyunloaded by aggressive chelation much more rapidlythan can the heart, giving rise to patients with low T2*values (heart still iron loaded) while the liver has beenunloaded to values previously thought of as safe.12

    Iron chelators

    More than 40 yr of clinical experience with deferoxamine(Desferal, DFO) in iron-overloaded patients hasestablished that chelation therapy, when given at anadequate dose, reduces iron-related complications andthereby improves quality of life and overall survival.6Ahexadentate chelator, it binds iron tightly, and the iron-DFO complex is excreted in both urine and stool. Thestandard regimen to remove excess iron is bysubcutaneous (sc) infusion of DFO over 8-12 hours, on 3to 7 days each week because the plasma half-life is short(minutes).13 The DFO-iron chelate is charged and does notreadily enter and leave cells.8 Parenteral administrationand the daily nuisance of an infusion pump hinder theoptimal compliance.

    Deferiprone is a bidentate chelator (3 moleculessurround one iron ion). An advantage of this compoundis that the iron (III) chelate of deferiprone carries no netcharge and therefore, can penetrate membranes easily,allowing removal of potentially toxic iron from tissues.6

    Deferiprone often causes gastrointestinal symptoms,idiosyncratic side effects that are potentially severe

    include erosive arthritis (5% to > 20%) and neutropenia(up to 5% of patients), including severe agranulocytosis(up to 0.5% of patients). Therefore close monitoring isrequired.

    An expert group of the International Conference onOral Chelators (ICOC) committee have recommended theICOC combination protocol, which involves the use ofdeferiprone during the day (80-110 mg/Kg/day) anddeferoxamine (40-60 mg/Kg) of a minimum of threenights per week for rapid, safe and effective depletion ofexcess body iron. Following the depletion of excesscardiac and liver iron load deferiprone monotherapy atdoses exceeding 80 mg/Kg/day has also been suggestedfor preventing the reaccumulation of excess iron in theheart and other organs.14

    Deferasirox (Exjade, ICL670) is an N-substituted bis-hydroxyphenyl-triazole 1 that was selected from morethan 700 compounds as part of a rational drugdevelopment program. It represents a new class oftridentate iron chelators with a high specificity for iron.15

    With a plasma half-life of 8 to 16 hours, it is practical toadminister the drug once a day and to maintain effectiveplasma level of the drug. It is able to scavenge nontransferrin-bound labile plasma iron, the chemicalspecies responsible for tissue damage in iron-overloadedsubjects, by means of toxic oxygen intermediaries.16

    Over the years it is now clear what should be theproperties of an ideal chelator. Unfortunately, in spite ofcontinuous work over four decades an ideal iron chelatorhas not been developed, possibly as it is required only bylimited number of patients and many researchlaboratories or pharmaceuticals are not inclined in thisarea. Essential characteristics of an ideal chelator alongwith those of DFO, deferiprone and deferasirox are

    TABLE 1. Comparision of the Three Iron Chelators

    Ideal chelator Deferoxamine Deferiprone Deferasirox

    Molar iron chelating efficiency; High High (hexadentate Low (bidentate) Moderate (tridentate)Iron binding (drug: iron) 1:1 1:1 3:1 2:1Charge of iron (III) complex Uncharged Charged Uncharged UnchargedRoute of administration Oral Iv or subcutaneous Oral OralPlasma half-life Long enough to give Short (minutes) Moderate (< 2 hours) Long, 8-16 hours;

    constant protection from remains in plasma atlabile plasma iron 24 h

    Dosing schedule Once a day Continuous infusion Thrice a day Once a dayTherapeutic index High High Idiosyncratic side Probably high

    effects are mostimportant

    Important side effects None or only in iron- Local skin reactions at Abdominal discom- Abdominal discomfort;depleted subjects infusion sites; Auditory fort; erosive arthritis; rash or mild diarrhea

    and retinal toxicity; Rare but severe upon initiation ofeffects on bones and agranulocytosis; therapy; mildgrowth; all at high doses; mild neutropenia increased creatinine

    levelAbility to chelate intracellular High Probably lower than High in clinical Insufficient clinicalcardiac and other tissue deferiprone and and in vitro studies datairon in humans deferasirox

  • Current Status of Iron overload and Chelation with Deferasirox

    Indian Journal of Pediatrics, Volume 74August, 2007 761

    summarized in Table 1 (adapted from Neufeld J).17

    Mechanism of action

    Deferasirox mobilize tissue iron by forming soluble,stable complexes that are then excreted in the feces.1 It isa tridentate iron chelator requiring 2 molecules of thedrug (as ferric iron has 6 coordination sites) to form thestable complex. Iron is chelated, both from the reticulo-endothelial cells (RE cells) as well as various parenchymaltissues. The chelated iron is cleared by the liver andexcreted through the bile. It also has the ability to preventmyocardial cell iron uptake, remove iron directly frommyocardial cells. In fact, ICL 670 readily yields iron toDFO.18 In animal models, on molar basis, it has beenshown to be 5 times more potent than DFO (hexadentate)and 10 times more potent than deferiprone (bidentate).19

    Iron removal also depends on plasma concentration, hostfactors, degree of loading, and rate of accessibility ofstored iron to chelator.

    Pharmacokinetics

    Drug is orally effective with bioavailability being close to70%.20 The median time to reach the maximalconcentrations of deferasirox ranged from 1 to 2 hours inboth the 10 and 20 mg/Kg/day dose groups and levelspersisted at detectable amounts for at least 24 hours (h)after one dose. Mean elimination half-life of ICL670 inplasma was between 12 and 16 h after multiple doseadministration. Pharmacokinetic steady state wasreached after 3 days of treatment based on trough plasmaconcentrations gathered over the study. It accords withthe expected time to steady state on the basis of half life ofthe drug in plasma.1,20 The fact that UIBC showedsustained increase after one oral dose of ICL670 suggeststhat the drug might eliminate or reduce serum non-transferrin bound iron thought to be a particularlycardiotoxic moiety of the expanded iron pool ofchronically transfused patients with thalassemia.20

    The continuous presence of significant plasma levelseven 24 hours after oral intake of DSX over the timecourse of 360 days is one of the most promisingproperties found for this drug. This may narrow thepathway for iron from sequestered red blood cells inmacrophages into organs and glands susceptible to ironcatalyzed toxicity effects such as the heart, pituitarygland, or pancreas.21

    Iron excretion occurs almost entirely in the feces and is

    dose-dependent, averaging 0.13, 0.34 and 0.56 mg/kg/day at deferasirox doses of 10, 20 and 40 mg/Kg/day,respectively.16 ICL670 produced a linear dose-dependentrise in net iron excretion, with wide variation seen at 40-mg/Kg/day. At the mid-dose range (20 mg Kg1 day1)variation was much less.16 It is highly selective for ironand does not induce the excretion of zinc or copper.19

    Clinical Trials

    Deferasirox (ICL670, Exjade) belongs to a new class oforal tridentate chelator, N-substituted bis-hydroxyphenyltriazoles. Deferasirox underwent extensivesafety testing and clinical trials including preclinicalstudies.22 Initial phase 1 and iron balance studies,16 phase2 efficacy studies in adult23 and pediatric24 thalassemiapatients, patients with a variety of anemias or unable/noncompliant with DFO,25 and the phase 3 clinical trialhave been conducted.8

    The largest clinical trial8 showed that patientsreceiving 5 mg/Kg deferasirox and the majority ofpatients receiving 10 mg/Kg deferasirox (those withbaseline LIC values 7 mg Fe/g dw), all 3 parameters i.e.LIC, serum ferritin and net body iron balance indicated anincrease in iron burden. In patients receiving 20 mg/Kgdeferasirox (those with baseline LIC values LIC between7 and 14 mg Fe/g dw), the iron burden was essentiallyunchanged; while the patients recieving 30 mg/Kg(corresponding to an LIC > 14 mg Fe/g dw), the ironburden was reduced. In frequently transfused patients,defined as individuals receiving 2 to 4 units per month (or7-14 mL/Kg/mo) of packed RBCs, oral deferasirox at aonce-daily dose of 20 mg/Kg led to maintenance of LIC,neutral iron balance, and stable serum ferritin levels. Theresults obtained are consistent with a previouslypublished short-term study examining the ability ofdeferasirox to remove iron from the body.16

    Another large phase 2 study1, patients wererandomized to receive once-daily deferasirox (10 or 20mg/Kg; n=24 in both groups) or DFO (40 mg/Kg, 5days/week; n=23) for 48 weeks. Decreases in liver ironconcentration (LIC) were comparable in the deferasirox20 mg/Kg/day and DFO groups; baseline values of 8.5and 7.9 mg Fe/g dw fell to 6.6 and 5.9 mg Fe/g dw,respectively, by week 48.

    Nisbet et al concluded that ICL 670 given once daily at20 mg/kg seems to be an effective orally active ironchelator and is reasonably well tolerated.16

    TABLE 2. Clinical Studies of Deferasirox

    Reference Phase Number of patients Dose (mg/kg) Outcome

    Nisbet-Brown E (2003)11 II 24 10,20,40 Safe, Effective at 20 and 40 mg/kg/dayGalanello R* (2006)26 II 40 20 Safe, not effectivePiga (2006)1 II 48 10 and 20 Effective and safeCappellini MD (2006)18 III 296 5,10,20,30 Safe, Effective at 20 and 30 mg/kg/day

    *Pediatric study

  • V.P. Choudhry and R. Naithani

    762 Indian Journal of Pediatrics, Volume 74August, 2007

    The one pediatric study published so far has howeverfailed to document clinical efficacy in 40 children at 20mg/kg/day doses used. The drug however was welltolerated and safe.26 Table 2 summarizes the clinicalstudies done.

    In initial pharmacokinetics it was suggested thatdeferasirox can lead to iron deposition in myocardiumbecause of its lipophilicity and long half-life.27 However,in small clinical studies, it has improved cardiac function.Porter et al showed improved myocardial T2* from 18 msto 23.1 milliseconds in a cohort of 23 patients treated withdesferasirox though there was no difference in leftventricular ejection fraction.28 This observation needs tobe confirmed on large multicentric studies.

    Adverse reactions

    Th...

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