Inhibition of Anthracycline Alcohol Metabolite Formation in Human Heart Cytosol: A Potential Role for Several Promising Drugs.

The clinical efficacy of anthracyclines (e.g., doxorubicin and daunorubicin) in cancer therapy is limited by their severe cardiotoxicity, the etiology of which is still not fully understood. The development of anthracycline-induced cardiomyopathy has been found to correlate with myocardial formation and accumulation of anthracycline secondary alcohol metabolites (e.g., doxorubicinol and daunorubicinol) that are produced by distinct cytosolic NADPH-dependent reductases. The aim of the current study is to identify chemical compounds capable of inhibiting myocardial reductases implied in anthracycline reductive metabolism in an attempt to decrease the production of cardiotoxic C-13 alcohol metabolites. Among the variety of tested compounds (metal chelators, radical scavengers, antioxidants, ß-blockers, nitrone spin traps, and lipid-lowering drugs), ebselen, cyclopentenone prostaglandins, nitric oxide donors, and short-chain coenzyme Q analogs resulted in being effective inhibitors of both doxorubicinol and daunorubicinol formation. In particular, ebselen (as well as ebselen diselenide, its storage form in the cells) was the most potent inhibitor of cardiotoxic anthracycline alcohol metabolites with 50% inhibition of doxorubicinol formation at 0.2 mol Eq of ebselen with respect to doxorubicin concentration. The high efficacy, together with its favorable pharmacological profile (low toxicity, lack of adverse effects, and metabolic stability) portends ebselen as a promising cardioprotective agent against anthracycline-induced cardiotoxicity.

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.

Topoisomerase 2ß: a promising molecular target for primary prevention of anthracycline-induced cardiotoxicity.

Anthracyclines are powerful chemotherapy agents that are still widely used today. However, their clinical use is limited by the development of dose-dependent cardiotoxicity. Recently, we showed that topoisomerase 2ß (Top2ß) is required for anthracycline to induce DNA double-strand breaks and changes in the transcriptome, leading to mitochondrial dysfunction and generation of reactive oxygen species. Furthermore, deleting Top2ß from cardiomyocytes prevented the development of anthracycline-induced cardiotoxicity in mice. On the basis of this molecular insight, new strategies should be developed to prevent anthracycline-induced cardiotoxicity. First, Top2α-specific anthracyclines should be tested to determine whether they will spare the heart. Second, Top2ß should be studied as a potential biomarker to predict risk of developing cardiotoxicity before anthracycline treatment. Third, inhibiting and deleting Top2ß in the heart should also be tested as primary prevention strategies. We propose that Top2ß is a promising molecular target that can be used to design interventions to prevent anthracycline-induced cardiotoxicity.

Can anthracycline therapy for pediatric malignancies be less cardiotoxic?

Anthracyclines have a central role in the treatment of cancer in pediatric patients but confer an increased risk of cardiac dysfunction. Several strategies have been employed to help reduce anthracycline-induced cardiotoxicity, including pretreating the patient with the iron chelator dexrazoxane and infusing the dose of anthracycline over a longer period. Much focus has also been placed on the development of methods that decrease the toxicity of parent compounds, specifically through the use of drug carriers such as liposomes, and on the development of new, potentially less toxic anthracycline derivatives, such as amrubicin and pixantrone. We provide a review of these strategies, focusing on studies in pediatric patients when available, and support the idea that anthracycline therapy can be less cardiotoxic in pediatric patients.

Dexrazoxane-afforded protection against chronic anthracycline cardiotoxicity in vivo: effective rescue of cardiomyocytes from apoptotic cell death.

BACKGROUND: Dexrazoxane (DEX, ICRF-187) is the only clinically approved cardioprotectant against anthracycline cardiotoxicity. It has been traditionally postulated to undergo hydrolysis to iron-chelating agent ADR-925 and to prevent anthracycline-induced oxidative stress, progressive cardiomyocyte degeneration and subsequent non-programmed cell death. However, the additional capability of DEX to protect cardiomyocytes from apoptosis has remained unsubstantiated under clinically relevant in vivo conditions. METHODS: Chronic anthracycline cardiotoxicity was induced in rabbits by repeated daunorubicin (DAU) administrations (3 mg kg(-1) weekly for 10 weeks). Cardiomyocyte apoptosis was evaluated using TUNEL (terminal deoxynucleotidyl transferase biotin-dUTP nick end labelling) assay and activities of caspases 3/7, 8, 9 and 12. Lipoperoxidation was assayed using HPLC determination of myocardial malondialdehyde and 4-hydroxynonenal immunodetection. RESULTS: Dexrazoxane (60 mg kg(-1)) co-treatment was capable of overcoming DAU-induced mortality, left ventricular dysfunction, profound structural damage of the myocardium and release of cardiac troponin T and I to circulation. Moreover, for the first time, it has been shown that DEX affords significant and nearly complete cardioprotection against anthracycline-induced apoptosis in vivo and effectively suppresses the complex apoptotic signalling triggered by DAU. In individual animals, the severity of apoptotic parameters significantly correlated with cardiac function. However, this effective cardioprotection occurred without a significant decrease in anthracycline-induced lipoperoxidation. CONCLUSION: This study identifies inhibition of apoptosis as an important target for effective cardioprotection against chronic anthracycline cardiotoxicity and suggests that lipoperoxidation-independent mechanisms are involved in the cardioprotective action of DEX.

Deferiprone does not protect against chronic anthracycline cardiotoxicity in vivo.

Anthracycline cardiotoxicity ranks among the most severe complications of cancer chemotherapy. Although its pathogenesis is only incompletely understood, "reactive oxygen species (ROS) and iron" hypothesis has gained the widest acceptance. Besides dexrazoxane, novel oral iron chelator deferiprone has been recently reported to afford significant cardioprotection in both in vitro and ex vivo conditions. Therefore, the aim of this study was to assess whether deferiprone 1) has any effect on the anticancer action of daunorubicin and 2) whether it can overcome or significantly reduce the chronic anthracycline cardiotoxicity in the in vivo rabbit model (daunorubicin, 3 mg/kg i.v., weekly for 10 weeks). First, using the leukemic cell line, deferiprone (1-300 microM) was shown not to blunt the antiproliferative effect of daunorubicin. Instead, in clinically relevant concentrations (>10 microM), deferiprone augmented the antiproliferative action of daunorubicin. However, deferiprone (10 or 50 mg/kg administered p.o. before each daunorubicin dose) failed to afford significant protection against daunorubicin-induced mortality, left ventricular lipoperoxidation, cardiac dysfunction, and morphological cardiac deteriorations, as well as an increase in plasma cardiac troponin T. Hence, this first in vivo study changes the current view on deferiprone as a potential cardioprotectant against anthracycline cardiotoxicity. In addition, these results, together with our previous findings, further suggest that the role of iron and its chelation in anthracycline cardiotoxicity is not as trivial as originally believed and/or other mechanisms unrelated to iron-catalyzed ROS production are involved.

Schisandrin B prevents doxorubicin-induced cardiotoxicity via enhancing glutathione redox cycling.

PURPOSE: The dose-cumulative cardiotoxicities and the emerging cancerous apoptotic/drug resistance are two major obstacles limiting the efficacy of anthracycline antibiotics, notably doxorubicin. We attempted to prove if schisandrin B (Sch B), a dual inhibitor of P-glycoprotein and multidrug resistance-associated protein 1, could protect against doxorubicin-induced cardiotoxicity, on the premise that Sch B is an enhancer of glutathione redox cycling that may attenuate doxorubicin-induced oxidative stress in the cardiomyocytes. EXPERIMENTAL DESIGN: Mice or rat were dosed with a single injection of doxorubicin (25 mg/kg, i.p.) with or without pretreatment of Sch B. The protective roles of Sch B against doxorubicin-induced cardiac damage were evaluated on the aspects of the release of cardiac enzymes into serum, the formation of malondialdehyde, the activation of matrix metalloproteinase, the structural damage in the left ventricles, the mortality rates, and the cardiac functions. RESULTS: Pretreatment of Sch B significantly attenuated doxorubicin-induced cardiotoxicities on all the aspects listed above. The underlying mechanism was associated with the effect of Sch B on maintaining the cardiomyocytic glutathione and the activities of superoxide dismutase, and the key enzymes (glutathione peroxidase, glutathione reductase, and glutathione transferase) responsible for glutathione redox cycling, which neutralized doxorubicin-induced oxidative stress. CONCLUSION: To the best of our knowledge, Sch B is the only molecule ever proved to function as a cardioprotective agent as well as a dual inhibitor of P-glycoprotein and multidrug resistance-associated protein 1, which is potentially applicable to treat cancers, especially the multidrug-resistant cancers involving doxorubicin or its kin.

Antioxidant defense against anthracycline cardiotoxicity by metallothionein.

Anthracycline cardiotoxicity is related to oxidative stress generated from the metabolism of anthracyclines in the heart. Studies using transgenic mice with high levels of antioxidants such as catalase or metallothionein (MT) specifically in the heart have demonstrated that elevation of cardiac antioxidant defense leads to intervention of anthracycline cardiotoxicity. MT protection against anthracycline-induced cardiac toxicity is related to its anti-apoptotic effect by inhibiting both p38-MAPK-mediated and mitochondrial cytochrome c-release-mediated apoptotic signaling. The anti-apoptotic effect of MT is closely related to its antioxidant action, which involves regulation of zinc homeostasis by the MT redox cycle. MT interferes with oxidant-mediated detrimental process through at least in part zinc release and zinc transfers directly from MT to acceptor proteins. In addition, MT posttranslationally modulates critical proteins involved in mitochondrial respiration and energy metabolism. All of these processes constitute the mechanisms by which MT protects from anthracycline cardiotoxicity.

Other uses of dexrazoxane: Savene, the first proven antidote against anthracycline extravasation injuries.

Dexrazoxane has been in clinical use for more than 25 years for prevention of cardiotoxicity in anthracycline based anticancer therapy. However, we discovered another property of the compound, i.e. the ability to prevent the devastating tissue necrosis after accidental extravasation of anthracyclines. The preclinical and clinical studies leading to the clinical implementation of Savene (dexrazoxane) as the first and only proven antidote in anthracycline extravasation are described in short.

Protection by flavonoids against anthracycline cardiotoxicity: from chemistry to clinical trials.

Cardiotoxic side-effects of doxorubicin limit the clinical use of this anti-cancer agent. Iron chelators have been studied as protectors against doxorubicin-induced cardiotoxicity. These iron chelators do not provide optimal protection and have certain drawbacks. We therefore looked for new protectors and decided that these new compounds should combine iron chelating and antioxidant activity. Flavonoids appeared to possess those combined iron chelating and antioxidant properties. Quantum chemical evaluation of radical stabilization and determination of physico-chemical properties of a series of flavonoids brought our attention to the semi-synthetic flavonoid 7-monohydroxyetylrutoside (monoHER). Both in vitro (using an electrically paced mouse left atrium model) and in vivo (using a mouse ECG telemetry model) experiments corroborated the protective effect of monoHER. MonoHER also showed anti-inflammatory properties. A subsequent clinical phase I study showed that an i.v. dose of 1,500mg/m2 is a feasible and safe dose to be evaluated in a phase II study to investigate the protective properties of monoHER against doxorubicin-induced cardiotoxicity in cancer patients.

Novel antioxidants in anthracycline cardiotoxicity.

It has been suggested nitroxides and their amine precursors prevent incidence of damage caused by superoxide and hydroxyl radicals formed during the oxidative metabolism of doxorubicin (DOX) and daunorubicin (DAU). Both doxorubicin and daunorubicin have been associated with cardiac toxicity in both adults and children. The authors herein suggest that cardioprotective molecules modified by nitroxides and their secondary amine precursors can prevent or diminish the anthracycline-induced cardiomyopathy by accumulating in cardiomiocytes.

Alpha-tocopherol suppresses mammary tumor sensitivity to anthracyclines in fish oil-fed rats.

Polyunsaturated fatty acids (PUFAs) have been reported to enhance the efficacy of chemotherapeutic agents that produce reactive oxygen species such as anthracyclines. We previously reported in a human breast cancer cell line that the increased cytotoxic activity of anthracyclines by several PUFAs was abolished by antioxidants and enhanced by pro-oxidants, suggesting that lipid peroxidation was involved in this effect. To determine the relevance of this observation in vivo, we examined the effect of the oxidative status of the diet on the activity of epirubicin against N-methylnitrosourea-induced mammary tumors in Sprague-Dawley rats. Three groups of rats were fed a basal diet enriched with dietary n-3 PUFA (sardine oil, 15%) alone (control group), with addition of an antioxidant (alpha-tocopherol, 100 UI/kg diet), or with addition of an oxidant system (dehydroascorbate/naphthoquinone). When the first mammary tumor reached 1 cm2, epirubicin was administrated weekly for 3 wk, and subsequent change in tumor size was documented over time. Two weeks after the end of epirubicin injections, tumor size was increased by 34% in the control group. In the pro-oxidant group, tumor size was decreased by 50%. In contrast, tumor size was increased by 188% in the antioxidant group. Thus, addition of pro-oxidants in a fish oil-enriched diet increased the sensitization of mammary tumors to chemotherapy, whereas addition of alpha-tocopherol suppressed tumor response in vivo, indicating that interaction between components of the diet has to be carefully controlled during chemotherapy.

Characterization of the enzymes involved in the in vitro metabolism of amrubicin hydrochloride.

The in vitro metabolism of amrubicin by rat and human liver microsomes and cytosol was examined. The main metabolic routes in both species were reductive deglycosylation and carbonyl group reduction in the side-chain. In vitro metabolism of amrubicinol by rat and human liver microsomes and cytosol was also examined and the main metabolic route of this active metabolite was reductive deglycosylation. Metabolism of amrubicin in human liver microsomes was inhibited by TlCl(3) and that in human liver cytosol was inhibited by dicumarol and quercetin. Generation of amrubicinol was inhibited only by quercetin. The results indicate that metabolism of amrubicin is mediated by NADPH-cytochrome P450 reductase, NADPH:quinone oxidoreductase and carbonyl reductase. In addition, generation of amrubicinol is mediated by carbonyl reductase. Metabolism of amrubicinol in human liver microsomes was inhibited by TlCl(3) and that in human liver cytosol was inhibited by dicumarol. The results indicate that metabolism of amrubicinol is mediated by NADPH-cytochrome P450 reductase and NADPH:quinone oxidoreductase. To investigate the influence of cisplatin on the metabolism of amrubicin and amrubicinol, human liver microsomes and cytosol were pre-incubated with cisplatin. This did not change the rates of amrubicin and amrubicinol metabolism in either human liver microsomes or cytosol.

The role of nitric oxide in anthracycline toxicity and prospects for pharmacologic prevention of cardiac damage.

Anthracycline antibiotics are potent antitumor agents whose activity is severely limited by a cumulative dose-dependent chronic cardiotoxicity that results from the summation of multiple biochemical pathways of cellular damage, which ultimately yields to disruption of myocardiocyte integrity and loss of cardiac function. Nitric oxide (NO) is a key molecule involved in the pathophysiology of heart; dysregulation of activity of NO synthases (NOSs) and of NO metabolism seems to be a common feature in various cardiac diseases. The contribution of NO to anthracycline cardiac damage is suggested by evidence demonstrating anthracycline-mediated induction of NOS expression and NO release in heart and the ability of NOSs to promote anthracycline redox cycling to produce reactive oxygen species (ROS), including O2-* and H2O2. Overproduction of ROS and NO yields to reactive nitrogen species, particularly the powerful oxidant molecule peroxynitrite (ONOO-), which may produce the marked reduction of cardiac contractility. This review focuses on the anthracycline-mediated deregulation of NO network and presents an unifying viewpoint of the main molecular mechanisms involved in the pathogenesis of anthracycline cardiotoxicity, including iron, free radicals, and novel mechanistic notions on cardiac ceramide signaling and apoptosis. The data presented in the literature encourage the development of strategies of pharmacological manipulation of NO metabolism to be used as a novel approach to the prevention of cardiotoxicity induced by anthracyclines.

The nitroxides pirolin and pirolid protect the plasma membranes of rat cardiomyocytes against damage induced by anthracyclines.

This study was performed to evaluate the protective effects of pyrroline and pyrrolidine nitroxides Pirolin, PL, and Pirolid, PD, on the plasma membranes of rat cardiomyocytes treated in vitro with anthracycline drugs aclarubicin (ACL) and doxorubicin (DOX). The influence of two concentrations of drugs (10 and 20 microM) and nitroxides (0.1 and 1 mM) as well as their combinations (a drug and a nitroxide) on membrane fluidity was investigated. The plasma membranes of cardiomyocytes were labelled with a hydrophobic fluorescence probe 12-AS and membrane fluidity was estimated on the basis of the fluorescence anisotropy of the probe. We found that aclarubicin and doxorubicin induced a significant dose-dependent decrease in membrane fluidity, whereas the nitroxides (PL and PD) caused its increase. Preincubation of cardiomyocytes with Pirolin entirely protected plasma membranes of these cells against damage caused by DOX. In the same conditions no protective effect of Pirolid was observed. What is more, Pirolid in combination with DOX caused fluidisation of the plasma membranes of cardiomyocytes. Both nitroxides at low concentration (0.1 mM) protected plasma membranes against rigidification induced by aclarubicin, while high concentration (1 mM) was ineffective and caused fluidisation of the plasma membranes of cardiomyocytes.