Current views on anthracycline cardiotoxicity

Anthracyclines are well established and effective anticancer agents used to treat a variety of adult and pediatric cancers. Unfortunately, these drugs are also among the commonest chemotherapeutic agents that have been recognized to cause cardiotoxicity. In the last years, several experimental and clinical investigations provided new information and perspectives on anthracycline-related cardiotoxicity. In particular, molecular mechanisms of cardiotoxicity have been better elucidated, early diagnosis has improved through the use of advanced noninvasive cardiac imaging techniques, and emerging data indicate a genetic predisposition to develop anthracycline-related cardiotoxicity. In this article, we review established and new knowledge about anthracycline cardiotoxicity, with special focus on recent advances in cardiotoxicity diagnosis and genetic profiling.

Pathophysiology of anthracycline cardiotoxicity

Anthracyclines (ANTs) are powerful drugs that have reduced the mortality of cancer patients. However, their use is limited by the development of cardiotoxicity (CTX), which is dose dependent and may lead to left ventricular dysfunction and heart failure. Although various strategies have been suggested to reduce the negative effects of ANTs, CTX is still an important unresolved clinical issue. This may be due at least partly to the incomplete characterization of the molecular and cellular mechanisms of ANT-induced CTX. In addition, although various forms of cardiac damage have been demonstrated with the use of these drugs in experimental studies, it is not yet clear how these translate to the clinical setting. Appropriate characterization of potential candidates for ANT-based therapies is essential to decide whether to administer these drugs. Hopefully, new information from genetic profiling will help to identify patients who are at high risk of developing CTX.

Current Views on Anthracycline Cardiotoxicity in Childhood Cancer Survivors

Owing to their high efficacy, anthracycline antibiotics are included in numerous chemotherapeutic regimens used-often in combination with radiation therapy and/or surgery-in treatment of solid tumours and blood malignancies, both in children and adults. However, the efficacy of modern cancer treatments, owing to which the population of cancer survivors has been on the rise in recent years, may be limited by the risk of serious complications involving multiple organs and systems, including the cardiovascular system. Being an important side effect of anthracyclines, cardiotoxicity may limit the efficacy of cancer therapies in the acute phase (i.e. during the treatment) and induce the long-term sequelae, observed years after treatment completion in childhood cancer survivors. It is very important to understand the cardiotoxicity-associated mechanisms and to determine its risk factors in order to develop and/or improve the effective countermeasures. Based on published data, the paper provides an outline of current views on anthracycline cardiotoxicity and discusses such aspects as molecular mechanisms of cardiotoxicity and its clinical manifestations as well as the new preventive strategies and diagnostic techniques used for the assessment of cardiovascular abnormalities. The widespread awareness of cancer treatment-related cardiotoxicity among the healthcare professionals may significantly improve the quality of life of the childhood cancer survivors.

The flavonoid quercetin: possible solution for anthracycline-induced cardiotoxicity and multidrug resistance

Anthracycline chemotherapy is often used in the treatment of various malignancies. Its application, however, encounters several limitations due to development of serious side effects, mainly cardiotoxicity and may be ineffective due to multidrug resistance (MDR). Many different compounds have been evaluated as poorly effective in the protection against anthracycline side effects and in the prevention from MDR. Thus, continuous investigational efforts are necessary to find valuable protectants and the flavonoid quercetin (Q) seems to be a promising candidate. It is present in relatively high amounts in a human diet and the lack of its toxicity, including genotoxicity has been confirmed. The structure of Q favours its high antioxidant activity, the potential to inhibit the activity of oxidative enzymes and to interact with membrane transporter proteins responsible for development of MDR, e.g. P-glycoprotein. Furthermore, Q can influence cellular signalling and gene expression, and thus, alter response to exogenous genotoxicants and oxidative stress in normal cells. It accounts for its chemopreventive and anticancer properties. Overall, these properties might indicate the possibility of application of Q as cardioprotectant during anthracycline chemotherapy. Moreover, numerous biological properties displayed by Q might possibly result in the reversal of MDR in tumour cells and improve the efficacy of chemotherapy. However, these beneficial effects towards anthracycline-induced complications of chemotherapy have to be further explored and confirmed both in animal and clinical studies. Concurrently, investigations aimed at improvement of the bioavailability of Q and further elucidation of its metabolism after application in combination with anthracyclines are needed.

Exercise mitigates cardiac doxorubicin accumulation and preserves function in the rat

PURPOSE

Doxorubicin (DOX) is an effective antineoplastic agent with well-characterized cardiotoxic effects. Although exercise has been shown to protect against DOX cardiotoxicity, a clear and concise mechanism to explain its cardioprotective effects is lacking. The purpose of this study was to determine if exercise training reduces cardiac DOX accumulation, thereby providing a possible mechanism to explain the cardioprotective effects of exercise against DOX toxicity.

METHODS

Sprague-Dawley rats were randomly assigned to 1 of 3 primary experimental groups: sedentary (n = 77), wheel running (n = 65), or treadmill (n = 65). Animals in wheel running and treadmill groups completed 10 weeks of exercise before DOX treatment. DOX was administered 24 hours after the last training session as a bolus intraperitoneal injection at 10 mg/kg. Subgroups of rats from each primary group were killed at 1, 3, 5, 7, and 9 days after DOX exposure to assess cardiac function and DOX accumulation.

RESULTS

Ten weeks of exercise preconditioning reduced myocardial DOX accumulation, and this reduction in accumulation was associated with preserved cardiac function.

CONCLUSIONS

These data suggest that the cardioprotective effects of exercise against DOX-induced injury may be due, in part, to a reduction in myocardial DOX accumulation.

Pixantrone: merging safety with efficacy

Pixantrone is a novel anthracycline derivative, manufactured by Cell Therapeutics Incorporated, WA, USA. It was developed with the aim to retain the efficacy of anthracyclines and be less cardiotoxic. Initial safety trials and single-arm, Phase II trials have shown preliminary evidence of anticancer activity and manageable toxicity. These results were validated in multicenter, randomized clinical trials where pixantrone was used as single agent or in combination with other cytotoxics. Following the results of PIX301, it is now approved by the EMA for use as monotherapy in pretreated patients with refractory non-Hodgkin lymphomas. Ongoing trials are assessing the use of pixantrone in combination with other drugs.

NC-6300, an epirubicin-incorporating micelle, extends the antitumor effect and reduces the cardiotoxicity of epirubicin

Epirubicin is widely used to treat various human tumors. However, it is difficult to achieve a sufficient antitumor effect because of dosage limitation to prevent cardiotoxicity. We hypothesized that epirubicin-incorporating micelle would reduce cardiotoxicity and improve the antitumor effect. NC-6300 comprises epirubicin covalently bound to PEG polyaspartate block copolymer through an acid-labile hydrazone bond. The conjugate forms a micellar structure of 40-80 nm in diameter in an aqueous milieu. NC-6300 (10, 15 mg/kg) and epirubicin (10 mg/kg) were given i.v. three times to mice bearing s.c. or liver xenograft of human hepatocellular carcinoma Hep3B cells. Cardiotoxicity was evaluated by echocardiography in C57BL/6 mice that were given NC-6300 (10 mg/kg) or epirubicin (10 mg/kg) in nine doses over 12 weeks. NC-6300 showed a significantly potent antitumor effect against Hep3B s.c. tumors compared with epirubicin. Moreover, NC-6300 also produced a significantly longer survival rate than epirubicin against the liver orthotopic tumor of Hep3B. With respect to cardiotoxicity, epirubicin-treated mice showed significant deteriorations in fractional shortening and ejection fraction. In contrast, cardiac functions of NC-6300 treated mice were no less well maintained than in control mice. This study warrants a clinical evaluation of NC-6300 in patients with hepatocellular carcinoma or other cancers.

Understanding the binding of daunorubicin and doxorubicin to NADPH-dependent cytosolic reductases by computational methods

The anthracycline anticancer agents daunorubicin (DAUN) and doxorubicin (DOX) are reduced by different NADPH-dependent cytosolic reductases into their corresponding alcohol metabolites daunorubicinol (DAUNol) and doxorubicinol (DOXol), which have been implicated in the development of chronic cardiomyopathy. To better understand the individual importance of each enzyme in the reduction and to provide deeper insight into the binding at atomic level we performed molecular docking and dynamics simulations of DAUN and DOX into the active sites of human carbonyl reductase 1 (CBR1) and human aldehyde reductase (AKR1A1). Such simulations evidenced a different behavior between the reductases with respect to DAUN and DOX suggesting major contribution of CBR1 in the reduction. The results are in agreement with available experimental data and for each enzyme and anthracycline pair provided the identification of key residues involved in the interactions. The structural models that we have derived could serve as a useful tool for structure-guided drug design studies.

Pharmacokinetic characterization of amrubicin cardiac safety in an ex vivo human myocardial strip model. II. Amrubicin shows metabolic advantages over doxorubicin and epirubicin

Anthracycline-related cardiotoxicity correlates with cardiac anthracycline accumulation and bioactivation to secondary alcohol metabolites or reactive oxygen species (ROS), such as superoxide anion (O₂·⁻) and hydrogen peroxide H₂O₂). We reported that in an ex vivo human myocardial strip model, 3 or 10 μM amrubicin [(7S,9S)-9-acetyl-9-amino-7-[(2-deoxy-β-D-erythro-pentopyranosyl)oxy]-7,8,9,10-tetrahydro-6,11-dihydroxy-5,12-napthacenedione hydrochloride] accumulated to a lower level compared with equimolar doxorubicin or epirubicin (J Pharmacol Exp Ther 341:464-473, 2012). We have characterized how amrubicin converted to ROS or secondary alcohol metabolite in comparison with doxorubicin (that formed both toxic species) or epirubicin (that lacked ROS formation and showed an impaired conversion to alcohol metabolite). Amrubicin and doxorubicin partitioned to mitochondria and caused similar elevations of H₂O₂, but the mechanisms of H₂O₂ formation were different. Amrubicin produced H₂O₂ by enzymatic reduction-oxidation of its quinone moiety, whereas doxorubicin acted by inducing mitochondrial uncoupling. Moreover, mitochondrial aconitase assays showed that 3 μM amrubicin caused an O₂·⁻-dependent reversible inactivation, whereas doxorubicin always caused an irreversible inactivation. Low concentrations of amrubicin therefore proved similar to epirubicin in sparing mitochondrial aconitase from irreversible inactivation. The soluble fraction of human myocardial strips converted doxorubicin and epirubicin to secondary alcohol metabolites that irreversibly inactivated cytoplasmic aconitase; in contrast, strips exposed to amrubicin failed to generate its secondary alcohol metabolite, amrubicinol, and only occasionally exhibited an irreversible inactivation of cytoplasmic aconitase. This was caused by competing pathways that favored formation and complete or near-to-complete elimination of 9-deaminoamrubicinol. These results characterize amrubicin metabolic advantages over doxorubicin and epirubicin, which may correlate with amrubicin cardiac safety in preclinical or clinical settings.

Anthracycline cardiotoxicity

INTRODUCTION

Anthracyclines are widely prescribed anticancer agents that cause a dose-related cardiotoxicity, often aggravated by nonanthracycline chemotherapeutics or new generation targeted drugs. Anthracycline cardiotoxicity may occur anytime in the life of cancer survivors. Understanding the molecular mechanisms and clinical correlates of cardiotoxicity is necessary to improve the therapeutic index of anthracyclines or to identify active, but less cardiotoxic analogs.

AREAS COVERED

The authors review the pharmacokinetic, pharmacodynamic and biochemical mechanisms of anthracycline cardiotoxicity and correlate them to clinical phenotypes of cardiac dysfunction. Attention is paid to bioactivation mechanisms that converted anthracyclines to reactive oxygen species (ROS) or long-lived secondary alcohol metabolites. Preclinical aspects and clinical implications of the "oxidative stress" or "secondary alcohol metabolite" hypotheses are discussed on the basis of literature that cuts across bench and evidence-based medicine. Interactions of anthracyclines with comorbidities or unfavorable lifestyle choices were identified as important cofactors of the lifetime risk of cardiotoxicity and as possible targets of preventative strategies.

EXPERT OPINION

Anthracycline cardiotoxicity is a multifactorial process that needs to be incorporated in a translational framework, where individual genetic background, comorbidities, lifestyles and other drugs play an equally important role. Fears for cardiotoxicity should not discourage from using anthracyclines in many oncologic settings. Cardioprotective strategies are available and should be used more pragmatically in routine clinical practice.

Pharmacological foundations of cardio-oncology

Anthracyclines and many other antitumor drugs induce cardiotoxicity that occurs "on treatment" or long after completing chemotherapy. Dose reductions limit the incidence of early cardiac events but not that of delayed sequelae, possibly indicating that any dose level of antitumor drugs would prime the heart to damage from sequential stressors. Drugs targeted at tumor-specific moieties raised hope for improving the cardiovascular safety of antitumor therapies; unfortunately, however, many such drugs proved unable to spare the heart, aggravated cardiotoxicity induced by anthracyclines, or were safe in selected patients of clinical trials but not in the general population. Cardio-oncology is the discipline aimed at monitoring the cardiovascular safety of antitumor therapies. Although popularly perceived as a clinical discipline that brings oncologists and cardiologists working together, cardio-oncology is in fact a pharmacology-oriented translational discipline. The cardiovascular performance of survivors of cancer will only improve if clinicians joined pharmacologists in the search for new predictive models of cardiotoxicity or mechanistic approaches to explain how a given drug might switch from causing systolic failure to inducing ischemia. The lifetime risk of cardiotoxicity from antitumor drugs needs to be reconciled with the identification of long-lasting pharmacological signatures that overlap with comorbidities. Research on targeted drugs should be reshaped to appreciate that the terminal ballistics of new "magic bullets" might involve cardiomyocytes as innocent bystanders. Finally, the concepts of prevention and treatment need to be tailored to the notion that late-onset cardiotoxicity builds on early asymptomatic cardiotoxicity. The heart of cardio-oncology rests with such pharmacological foundations.

Cardiomyocyte death in doxorubicin-induced cardiotoxicity

Doxorubicin (DOX) is one of the most widely used and successful antitumor drugs, but its cumulative and dose-dependent cardiac toxicity has been a major concern of oncologists in cancer therapeutic practice for decades. With the increasing population of cancer survivors, there is a growing need to develop preventive strategies and effective therapies against DOX-induced cardiotoxicity, in particular late-onset cardiomyopathy. Although intensive investigations on DOX-induced cardiotoxicity have continued for decades, the underlying mechanisms responsible for DOX-induced cardiotoxicity have not been completely elucidated. A rapidly expanding body of evidence supports the notion that cardiomyocyte death by apoptosis and necrosis is a primary mechanism of DOX-induced cardiomyopathy and that other types of cell death, such as autophagy and senescence/aging, may participate in this process. This review focuses on the current understanding of the molecular mechanisms underlying DOX-induced cardiomyocyte death, including the major primary mechanism of excess production of reactive oxygen species (ROS) and other recently discovered ROS-independent mechanisms. The different sensitivities to DOX-induced cell death signals between adult and young cardiomyocytes will also be discussed.