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rch Cardiol Mex. 2014;84(3):218---223

www.elsevier.com.mx

EVIEW ARTICLE

nthracycline-mediated cardiomyopathy: Basicolecular knowledge for the cardiologist

oel Salazar-Mendiguchía ∗, José González-Costello, Josep Roca,lbert Ariza-Solé, Nicolás Manito, Ángel Cequier

nidad de Miocardiopatías, Insuficiencia Cardíaca y Trasplante, Área de Enfermedades del Corazón, Hospital Universitarie Bellvitge, Barcelona, Spain

eceived 25 April 2013; accepted 20 August 2013

KEYWORDSAnthracyclinecardiotoxicity;Chemotherapycardiomyopathy;Doxorubicincardiomyopathy;Spain

Abstract Anthracyclines are cytostatic antibiotics discovered almost half a century agoexerting their action through inhibition of topoisomerase II. The two most representativedrugs are doxorubicin and daunorubicin and they have been proven as useful antineoplasticsand are widely prescribed in daily oncology practice; unfortunately, cardiotoxicity has been alimiting factor when it comes to their use.

Diverse mechanisms have been involved in anthracycline cardiotoxicity, none of which arecapable of causing the whole clinical picture by itself. Traditionally, reactive oxygen species(ROS) have received more attention, although recently basic research has proven other factorsto be as important as ROS. These factors mainly involve sarcomeric structure disruption, toxicaccumulation of metabolites, iron metabolism, energetic alterations and inflammation.

The role of genetics has been studied by some groups, although a clear genotype-responserelationship is yet to be elucidated.

With the improved survival from different oncologic diseases we are witnessing more casesof chemotherapy-induced cardiotoxicity and the advent of new anticancer drugs poses severalchallenges for the cardiologist, highlighting the importance of a deep knowledge of the mainmechanisms inducing this toxicity.© 2013 Instituto Nacional de Cardiología Ignacio Chávez. Published by Masson Doyma MéxicoS.A. All rights reserved.

PALABRAS CLAVECardiotoxicidadde antraciclinas;

Miocardiopatía inducida por antraciclinas: conocimientos moleculares básicos para elcardiólogo

Resumen Hace casi medio siglo se descubrieron las antraciclinas; estas son antibióticoscitostáticos inhibidores de la topoisomerasa ii. Los 2 fármacos más representativos de este grupo

∗ Corresponding author at: Área de Enfermedades del Corazón, Hospital Universitari de Bellvitge, Av Feixa Llarga s/n, L’Hospitalet delobregat, 08904 Barcelona, Spain.

E-mail address: jsalazar@bellvitgehospital.cat (J. Salazar-Mendiguchía).

ttp://dx.doi.org/10.1016/j.acmx.2013.08.006405-9940/© 2013 Instituto Nacional de Cardiología Ignacio Chávez. Published by Masson Doyma México S.A. All rights reserved.

Anthracycline-mediated cardiomyopathy 219

Miocardiopatíapor quimioterapia;Miocardiopatíapor doxorrubicina;Espana

son la doxorrubicina y la daunorrubicina. Estos fármacos han demostrado ser eficaces antineo-plásicos y han sido ampliamente utilizados en la práctica oncológica. Desafortunadamente, lacardiotoxicidad sigue siendo un elemento limitante para su uso.

Los mecanismos mediante los cuales estos fármacos ocasionan cardiotoxicidad son múltiplespero ninguno de ellos de forma individual es capaz de explicar el cuadro clínico por com-pleto. Casi siempre se ha considerado que la formación de especies reactivas de oxígeno eraresponsable de gran parte de la toxicidad, sin embargo la experimentación básica reciente hademostrado que hay otros factores, entre los que destacan las alteraciones en la estructura sar-comérica, la acumulación de metabolitos tóxicos, las alteraciones del metabolismo del hierroo de los mecanismos energéticos, y la liberación de mediadores de inflamación.

Por otra parte, diversos grupos han investigado la intervención que la genética podría teneren el desarrollo de esta enfermedad, si bien no se puede definir aún una clara correlacióngenotipo-respuesta.

Con el aumento de la supervivencia por el tratamiento de diversas enfermedades oncoló-gicas, se están detectando más casos de cardiotoxicidad mediada por quimioterapia; y con laaparición de nuevos fármacos quimioterápicos se anaden nuevos retos, con lo que se demuestrala importancia del estudio profundo de los mecanismos causales.© 2013 Instituto Nacional de Cardiología Ignacio Chávez. Publicado por Masson Doyma MéxicoS.A. Todos los derechos reservados.

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Introduction

Anthracyclines are cytostatic antibiotics discovered almosthalf a century ago that exert their action through inhibitionof topoisomerase II.1,2 The two most representative drugs ofthis group are doxorubicin (active against some hematologiccancers and solid tumors)3 and daunorubicin (used mainly inacute hematologic cancer),4 although other drugs have beendeveloped within this family (e.g. epirubicin, idarubicin andmitoxantrone).

These drugs have been proven as useful antineo-plastics and are amongst the most widely prescribedoncologic medication. Unfortunately, cardiotoxicity sec-ondary to anthracyclines still remains a limiting factorwhen used,5 being generally related to dose---response(although there are several reports of cardiotoxicity asso-ciated with lower doses, probably secondary to individualsusceptibility)6,7and manifesting mainly as heart failure usu-ally within a year after completion of treatment, althoughit is widely accepted that it can manifest itself several yearsafter treatment.

Recently, groups have been created in Europe and theUnited States for the study of this toxicity, highlighting itsimportance.8,9

Scope of the problem

Chemotherapy-induced cardiotoxicity is usually classified intwo groups according to the cellular damage induced bythese drugs. Type I cardiotoxicity implies cellular death(either via necrosis or apoptosis) and thus, is not reversible,whereas type II cardiotoxicity is caused by cellular dys-

function (not death) and is usually described as reversible.Type I is characteristic of anthracycline damage, while typeII is more frequent with monoclonal antibodies (namely,trastuzumab).8

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Gianni et al.5 reported some of the several limita-ions that have emerged in terms of describing the currentituation of anthracycline-mediated cardiotoxicity; theseroblems come from a lack of uniformity in reporting oretecting events in these patients and the different forms ofresentation (acute vs. delayed, reversible vs. irreversible).t the same time, the wide difference in the treated popula-ions (adults vs. children) makes it difficult to unify criteria.evertheless, recent statistics regarding survival of onco-

ogic patients give us an overview of the problem.At the moment, in the US there are more than

00,000 survivors of childhood cancer, of whom 50% couldotentially have been treated with anthracyclines,10 andhe probability of accumulated death due to cardiac causeincluding sudden death likely to be cardiac in origin) isreater than the observed in control groups.11,12

Likewise, survival of breast cancer (one of the clinicalcenarios where these drugs have been used extensively)as increased dramatically in the last decades, translatingnto approximately two million women in the US with highikelihood of previous anthracycline exposure.13

Despite several efforts to diminish this adverseffect (mainly by reducing the cumulative dose under00---450 mg/m2 for doxorubicin) and considering the pre-iously mentioned caveats, studies estimate heart failureates between 5 and 10%5,8 with the modern regimensf treatment, depending on age, cumulative dose, indi-idual susceptibility or even past medical history (e.g.ypertension, coronary heart disease, etc.), among otheractors.

echanisms of cardiotoxicity

ith all the aforementioned, it is not surprising thatonsiderable controversy has risen with respect to theechanisms involved in this toxicity. Anthracycline-induced

220

Accumulationof toxic

metabolites

Ironmetabolism Disruption of

energeticmechanisms

Anthracyclinecardiotoxicity

Sarcomericstructure

alterations

Inflammatorymediators

Oxidativestress

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igure 1 Causative mechanisms of anthracycline cardiomy-pathy.

ardiotoxicity seems to be a multi-step condition, with sev-ral pathways involved. Many research groups have tried tolucidate the processes associated; of these, we will focusn this review on those that have been most extensivelytudied.

It is important to acknowledge the fact that these path-ays are not necessarily independent from each other orxclusive, as each of them may play a role in causing car-iotoxicity via different mechanisms, by themselves or inooperation with other pathways. Fig. 1 depicts some of theechanisms generating cardiotoxicity.We will not review in the present work the rare, but

xistent, acute presentation of anthracycline toxicity or thenvolvement of the pericardium.

xidative stress

xidative stress is the most widely studied mechanism and itnvolves a highly complex pathophysiology, which is a matterf permanent debate.

The myocardium is extremely prone to oxidative damagend this is, at least in part, due to its lower levels of catalasectivity and superoxide dismutase (an enzyme that cataly-es the dismutation of superoxide, one of the main reactivexygen species [ROS])14 compared with other tissues.

The metabolism of anthracyclines involves the reductionf the quinone fraction of its formula to semiquinone, whichan rapidly transfer its unpaired electron to an electroncceptor (usually molecular oxygen), returning to its origi-al quinone form, therefore completing the redox cycle andeading to the formation of more ROS.

Other mechanisms involved include the formation of DNAdducts by semiquinone or the generation of superoxidenions by anthracycline metabolism, with subsequent cellu-ar damage by degradation of the sarcomere, mitochondrialysfunction and DNA damage.15,16

A recent paper by Octavia et al.17elegantly describes

he different pathways by which anthracyclines causeOS, including mitochondrial, nitric oxide synthase (NOS),nd nicotinamide adenine dinucleotide phosphate (NADPH)athways.

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Even though the evidence for myocardial damage inducedy ROS is vast, oxidative stress as the sole cause of car-iotoxicity is increasingly questioned and more researchs dedicated to alternative pathways. Part of the reasonor this came from earlier studies that failed to prove therotective role of certain antioxidants in the long term,5

specially when interventions that resembled the ones usedn clinical practice were tested.15 It is noteworthy thatome of the drugs that might have a protective role (e.g.exrazoxane and carvedilol) probably exert their defensiveechanism through alternative molecular routes, besides

heir antioxidant activity. Fig. 2 shows the relationshipsetween DOX, doxorubicinol and ROS in cardiotoxicity.

ccumulation of toxic metabolites

nthracyclines metabolism generates toxic molecules at theyocardium level through a reduction of their carbonyl

roup (producing doxorubicinol in case of doxorubicin, beingp to 50 times more potent than the original compound,r daunorubinicol and idarubicinol in case of daunorubicinnd idarubicin, respectively),17 capable of inhibiting the ionxchange pumps of calcium and sodium, even at the mito-hondrial level, causing an imbalance in the energetics ofhe myocardium and a diminished systolic function.18 More-ver, these secondary alcohol metabolites are more difficulto eliminate from the cardiomyocyte than the parent drug,ccumulating inside them.19

All the anthracyclines have shown to have similar mech-nisms of bioactivation, making them toxic from the cardiactandpoint,2 but the role of toxic metabolites has been chal-enged by the fact that both daunorubicin and idarubicinenerate higher plasma levels of alcohol metabolites com-ared with doxorubicin15 and they tend to generate lessardiotoxicity.

A more detailed description of the molecular damagenduced by each drug is beyond the scope of this paper.

ron metabolism

ron has a major role in cell metabolism and is under controly several regulatory systems.20 Its functions go far beyondhe oxygen transport complex, being part of different pro-esses like bioenergetics, enzymatic coordination or evenmmune system physiology.

Traditionally, it has been considered that anthracyclinesre capable of altering iron homeostasis through the cre-tion of Fe---anthracycline complexes and the posteriorroduction of ROS,21 even in the absence of a reductionystem (through intramolecular redox reactions) and someesearchers have suggested that the toxicity of the combi-ation of iron and some anthracyclines (doxorubicin) is not

simple additive effect.22

At the same time, iron is capable of catalyzing diverseolecular reactions that create ROS, independently of

he abovementioned Fe---anthracycline complex, generatingydroxyl radicals, and it is well known that this reaction is

ccelerated under the influence of iron itself in the cellularnvironment.23

Iron regulatory proteins or IRPs (also known asron responsive element binding proteins) are important

Anthracycline-mediated cardiomyopathy 221

ROS

Doxorubicinol

Toxicaccumulation Semiquinone

DOX

• Mitochondrial damage• DNA adducts• Inhibition of ion exchange pumps• Degradation of sarcomere

Fe+++

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elements in regulating iron metabolism and the interactionsbetween doxorubicin and the human iron regulatory systemhave been studied by some researchers. Studies have foundthat the conversion of IRP1 to a null protein via doxorubi-cin metabolites yields a metabolic cellular impairment thatmay account to a certain degree for myocardial dysfunc-tion, opening new paths towards a better understanding ofthe role of iron metabolism.24

Likewise, animal models have shown that iron over-load is capable of potentiating doxorubicin cardiotoxicity bymechanisms other than ROS production.25 Recently, humanstudies have confirmed this finding, showing that even cumu-lative doses of doxorubicin in the ‘‘safe’’ range are capableof inducing higher iron levels in cardiac tissue, specially atthe intracellular level, opening the possibility of cardiotox-icity related with iron deposits as a new pathophysiologicmechanism26 and raising the question of whether a real‘‘safe’’ dose exists in terms of preventing long term car-diomyopathy.

Disruption of energetic mechanisms

The integrity of mitochondrial function is of cornerstoneimportance in the physiology of myocardial cells, as ATP pro-duction is highly dependent on this organelle (almost all ofthe ATP used by cardiac cells is produced by the electrontransport chain).27

Several studies have suggested that disruptions in themitochondrial membrane potential and respiratory chain arecapable of inducing loss of architectural integrity, loss ofenergy production capability and difficulties in maintainingmetabolic demands.28,29

Recently, cadiolipin, a phospholipid of utmost importance

in energy metabolism and a component of the inner mito-chondrial membrane, has been suggested as having a majorrole in anthracycline-mediated cardiomyopathy.30 Doxorubi-cin, by its ability to bind cardiolipin would modify membrane

tocs

ol and ROS in cardiomyopathy.

roperties, environment and function, leading to disruptionf several energetic mechanisms.

As mentioned before, no pathway by itself justifieshe complete clinical picture, and the disruption of mito-hondrial functions mediated by cardiolipin-doxorubicinnteractions are also mediated by oxidative stress,15 in fact,he disturbance in mitochondrial permeability has beenelated to a direct opening of the permeability transitionore by substances formed during de redox cycling of somenthracyclines and its dysfunction could be an early indica-or of doxorubicin-induced apoptosis.

arcomeric structure alterations

ardiotoxicity is characterized at the sarcomere level byisarray and loss of myofilaments and studies have demon-trated that anthracyclines are capable of disrupting theontractile apparatus by direct mechanisms, moving furtherway from the cytotoxic effects mediated by ROS.

Titin is a giant protein and integral part of the sarcom-re structure, extending from the M-line to the Z-disk andas diverse functions, structural as well as dynamic andegulatory.31 The loss of integrity or function of titin hasecently been shown to play an important role in theathophysiology of dilated cardiomyopathy.32,33 Exposureo anthracyclines induces an accelerated degradation ofitin through proteolytic pathways, leading to energeticompromise. In vitro studies have shown that such effects also related with loss of structural integrity and disarrayr even myocyte necrosis in a calpain-dependent way.34,35

Recently, a very interesting work by Chen et al.36 studiedhe role of cardiac ankyrin repeat protein (CARP or ANKRD1,

transcriptional regulatory protein that may act as a nuclear

ranscription factor negatively regulating the expressionf cardiac genes) in the pathophysiology of anthracyclineardiomyopathy. His group found that CARP is extremelyensible to doxorubicin, leading to depletion of CARP

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rotein levels (by inhibition of CARP transcription) andausing marked sarcomeric disarray. In their same study,oxorubicin induced cardiac transcription factor GATA4GATA Binding Protein 4, thought to regulate genes involvedn myocardial differentiation and function, including CARP)epletion, suggesting a co-dependent role for both proteinsn maintaining sarcomere structure.

nflammatory mediators

nthracyclines are capable of promoting proinflammatoryytokines release, which has been related to severalanifestations ranging from cardiotoxicity to asthenia expe-

ienced by these patients.37

Doxorubicin stimulates macrophages and monocytes withhe subsequent histamine and tumoral necrosis factor alphaelease; these substances have been related with archi-ectural alterations and dilated cardiomyopathy throughyocardial receptors binding.15

Wong et al.38 tested the effects of doxorubicin on theitogen-activated protein kinase (MAPK) pathway, which

s essential in translating signals from the cellular surfacethrough cellular membrane receptors) to the nucleus and,mong other functions, regulates inflammatory cytokines.y using clinically relevant doses of doxorubicin, theyound an increased expression of inflammatory genes inacrophages as well as increased levels of IL-1� and IL-6

n treated cells, without changes in the expression ofumoral necrosis factor (TNF). The expression of theseytokines has been shown to have a relevant role in car-iotoxicity induced by anthracyclines, mainly by modulatingpoptosis through TNF receptors, whose function is affectedy doxorubicin.39

enetics and cardiotoxicity

he study and approach of several cardiovascular dis-ases has changed dramatically with the advent of genomicedicine, and anthracycline-induced cardiotoxicity is not

lien to these advances. Previous evidence exists in terms ofhe usefulness of the study of genetic polymorphisms relatedo certain drug toxicities2,5 and some groups have inves-igated the possible relationship between polymorphismse.g. V244M on the CBR3-carbonyl reductase 3 gene) andeart failure related to these drugs.40 At the same time,ertain genotypes might be associated with intracellularron accumulation26 in patients treated with anthracyclineegimens, possibly favouring cellular damage via the mech-nisms above mentioned.

Wojnowski et al.41 also reported that some genetic vari-nts in doxorubicin transport and in free radical generatingnzymes might be involved in the predisposition to presentoxorubicin-induced cardiotoxicity, at least in certain lym-homas.

While these observations are promising and provide newnsights into different aspects of doxorubicin cardiotoxic-

ty, with the current data, we are not able to define alear genotype-response correlation and further investiga-ion should try to clarify this and provide more informationbout the clinical usefulness of genotyping.

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J. Salazar-Mendiguchía et al.

onclusions

ith the improvements in early diagnosis and anti-tumoralreatments, we are witnessing an increased survival in onco-ogic patients. In this context, cardiologists are faced withew tasks, like how to manage the toxic effects caused byhemotherapy agents.

Anthracycline toxicity seems to be a multistep and mul-ifactorial condition, with complex pathophysiology andequiring a multidisciplinary approach. A deep understand-ng of this toxicity and its mechanisms will possibly allow uso reduce its incidence, identify early markers of suscepti-ility or find more specific therapeutic targets. As we haveeviewed in the present paper, no mechanism seems capabley itself of causing the whole clinical picture.

Development of new anticancer therapies will surelyring further challenges to cardiologists in the next decade,s the advent of novel therapies in oncology will also changehe current landscape of these toxicities. It seems obviouso us that the ‘‘specialty’’ of cardiooncology is much neededn the current context.

unding

here was no funding for this research.

onflict of interest

uthors do not have any conflict of interests regarding thisork.

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