Glutathione peroxidase 1-deficient mice are more susceptible to doxorubicin-induced cardiotoxicity

Selenium protection from DNA damage and regulation of apoptosis signaling following cyclophosphamide induced cardiotoxicity in rats

We investigated the mechanism of the cardioprotective effect of selenium (Se) against cyclophosphamide (CPA) induced cardiotoxicity in rats. We divided 24 female Wistar albino rats into four groups. The control group was injected intraperitoneally (i.p.) with normal saline. The CPA group was injected i.p. with 200 mg/kg CPA. The Se group was injected i.p. with 1 mg/kg Se. The CPA + Se group was injected i.p. with 200 mg/kg CPA and 1 mg/kg Se. Rats were euthanized 24 h after injection and heart tissues were harvested. Histopathological examination revealed reduced severity of myocardial lesions in the CPA + Se group compared to CPA induced cardiotoxicity of the CPA group; this finding was confirmed by increased immunoreactivity of cardiac troponin-I (cTn-I) in the CPA + Se group compared to decreased cTn-I immunoreactivity in the CPA group. Administration of CPA increased the immunoreactivity of phosphorylated histone-2AX (γH2AX). Se reduced the CPA induced increase in γH2AX immunoreactivity. Se administration reversed the CPA induced increase of Bax and decrease of Bcl2 gene expressions. Our findings suggest that Se is cardioprotective by reducing DNA damage and regulating the genes responsible for apoptosis caused by CPA in rats.

Cell death regulation in myocardial toxicity induced by antineoplastic drugs

Homeostatic regulation of cardiomyocytes plays a critical role in maintaining normal physiological activity of cardiac tissue. Severe cardiotoxicity can lead to heart disease, including but not limited to arrhythmias, myocardial infarction and cardiac hypertrophy. In recent years, significant progress has been made in developing new therapies for cancer that have dramatically changed the treatment of several malignancies and continue to improve patient survival, but can also lead to serious cardiac adverse effects. Mitochondria are key organelles that maintain homeostasis in myocardial tissue and have been extensively involved in various cardiovascular disease episodes, including ischemic cardiomyopathy, heart failure and stroke. Several studies support that mitochondrial targeting is a major determinant of the cardiotoxic effects triggered by chemotherapeutic agents increasingly used in solid and hematologic tumors. This antineoplastic therapy-induced mitochondrial toxicity is due to different mechanisms, usually altering the mitochondrial respiratory chain, energy production and mitochondrial kinetics, or inducing mitochondrial oxidative/nitrosative stress, ultimately leading to cell death. This review focuses on recent advances in forms of cardiac cell death and related mechanisms of antineoplastic drug-induced cardiotoxicity, including autophagy, ferroptosis, apoptosis, pyroptosis, and necroptosis, explores and evaluates key proteins involved in cardiac cell death signaling, and presents recent advances in cardioprotective strategies for this disease. It aims to provide theoretical basis and targets for the prevention and treatment of pharmacological cardiotoxicity in clinical settings.

An Magnetic-Targeting Nano-Diagnosis and Treatment Platform for TNBC

Purpose

In this experiment, we constructed a magnetic targeting nano-diagnosis and treatment platform of doxorubicin (DOX) combined with iron nanoparticles, and explored their application value and mechanism in the treatment of Triple Negative Breast Cancer (TNBC), as well as its new diagnosis and treatment mode in Magnetic Resonance Imaging (MRI).

Patients and Methods

Hollow mesoporous nanoparticles (HFON) were synthesized by solvothermal method, and loaded the drug DOX (DOX@HFON) to treat TNBC. The experiments in vivo and in vitro were carried out according to the characteristics of the materials. In vitro experiments, the killing effect of the drug on cells was verified by cell viability CCK8, ROS generation level, LPO evaluation and flow cytometry; the MRI effect and targeted anti-tumor therapy effect were studied by in vivo experiments; then the tumor tissue sections were detected by Ki-67, CD31, ROS, LPO and TUNEL immunofluorescence detection; H&E staining and blood biochemical tests were used to evaluate the biosafety of the materials.

Results

Through a series of characterization tests, it is confirmed that the nano-materials prepared in this experiment have positive drug loading properties. MDA-MB-231 cells had great phagocytic ability to DOX@HFON under Confocal Laser Scanning Microscope (CLSM). Experiments in vitro confirmed that DOX and Fe were released and concentrated in cells, and a large number of ROS production and induction of LPO were detected by DCFH-DA and C11-BODIPY probes in cells. Apoptosis experiments further confirmed that DOX@HFON induced apoptosis, autophagy and ferroptosis. In the vivo experiment, the anti-tumor therapy effect of MAGNET@DOX@HFON group was the most significant, and in MRI also proved that the drug had great tendency and imaging ability in tumor tissue.

Conclusion

The new magnetic targeting nano-diagnosis and treatment platform prepared in this experiment is expected to become a new treatment model for TNBC.

A reactive oxygen species-replenishing coordination polymer nanomedicine disrupts redox homeostasis and induces concurrent apoptosis-ferroptosis for combinational cancer therapy

Reactive oxygen species (ROS) are important signal molecules and imbalanced ROS level could lead to cell death. Elevated ROS levels in tumor tissues offer an opportunity to design ROS-responsive drug delivery systems (DDSs) or ROS-based cancer therapy such as chemodynamic therapy. However, their anticancer efficacies are hampered by the ROS-consuming nature of these DDSs as well as the high concentration of reductive agents like glutathione (GSH). Here we developed a doxorubicin (DOX)-incorporated iron coordination polymer nanoparticle (PCFD) for efficient chemo-chemodynamic cancer therapy by using a cinnamaldehyde (CA)-based ROS-replenishing organic ligand (TCA). TCA can ROS-responsively release CA to supplement intracellular ROS and deplete GSH by a thiol-Michael addition reaction, which together with DOX-triggered ROS upregulation and Fe³⁺-enabled GSH depletion facilitated efficient DOX release and enhanced Fenton reaction, thereby inducing redox dyshomeostasis and cancer cell death in a concurrent apoptosis-ferroptosis way. Both in vitro and in vivo study revealed that ROS-replenishing PCFD exhibited much better anticancer effect than ROS-consuming control nanoparticle PAFD. The ingenious ROS-replenishing strategy could be expanded to construct versatile ROS-responsive DDSs and ROS-based nanomedicines with potentiated anticancer activity. STATEMENT OF SIGNIFICANCE: We develop a doxorubicin (DOX)-incorporated iron coordination polymer nanoparticle (PCFD) for efficient chemo-chemodynamic cancer therapy by using a cinnamaldehyde-based reactive oxygen species (ROS)-replenishing organic ligand. This functional ligand can ROS-responsively release cinnamaldehyde to supplement intracellular H₂O₂ and deplete glutathione (GSH) by a thiol-Michael addition reaction, which together with DOX-triggered ROS upregulation and Fe³⁺-enabled GSH depletion facilitates efficient DOX release and enhanced Fenton reaction, thereby inducing redox dyshomeostasis and cancer cell death in a concurrent apoptosis-ferroptosis way. Both in vitro and in vivo study reveal that ROS-replenishing PCFD exhibit much better anticancer effect than ROS consuming counterpart. This study provides a facile and straightforward strategy to design ROS amplifying nanoplatforms for cancer treatment.

The role of glutathione peroxidase-1 in health and disease

Glutathione peroxidase 1 (GPx1) is an important cellular antioxidant enzyme that is found in the cytoplasm and mitochondria of mammalian cells. Like most selenoenzymes, it has a single redox-sensitive selenocysteine amino acid that is important for the enzymatic reduction of hydrogen peroxide and soluble lipid hydroperoxides. Glutathione provides the source of reducing equivalents for its function. As an antioxidant enzyme, GPx1 modulates the balance between necessary and harmful levels of reactive oxygen species. In this review, we discuss how selenium availability and modifiers of selenocysteine incorporation alter GPx1 expression to promote disease states. We review the role of GPx1 in cardiovascular and metabolic health, provide examples of how GPx1 modulates stroke and provides neuroprotection, and consider how GPx1 may contribute to cancer risk. Overall, GPx1 is protective against the development and progression of many chronic diseases; however, there are some situations in which increased expression of GPx1 may promote cellular dysfunction and disease owing to its removal of essential reactive oxygen species.

T-2 toxin and its cardiotoxicity: New insights on the molecular mechanisms and therapeutic implications

T-2 toxin is one of the most toxic and common trichothecene mycotoxins, and can cause various cardiovascular diseases. In this review, we summarized the current knowledge-base and challenges as it relates to T-2 toxin related cardiotoxicity. The molecular mechanisms and potential treatment approaches were also discussed. Pathologically, T-2 toxin-induced cardiac toxicity is characterized by cell injury and death in cardiomyocyte, increased capillary permeability, necrosis of cardiomyocyte, hemorrhage, and the infiltration of inflammatory cells in the heart. T-2 toxin exposure can cause cardiac fibrosis and finally lead to cardiac dysfunction. Mechanistically, T-2 toxin exposure-induced cardiac damage involves the production of ROS, mitochondrial dysfunction, peroxisome proliferator-activated receptor-gamma (PPAR-γ) signaling pathway, endoplasmic reticulum (ER stress), transforming growth factor beta 1 (TGF-β1)/smad family member 2/3 (Smad2/3) signaling pathway, and autophagy and inflammatory responses. Antioxidant supplementation (e.g., catalase, vitamin C, and selenium), induction of autophagy (e.g., rapamycin), blockade of inflammatory signaling (e.g., methylprednisolone) or treatment with PPAR-γ agonists (e.g., pioglitazone) may provide protective effects against these detrimental cardiac effects caused by T-2 toxin. We believe that our review provides new insights in understanding T-2 toxin exposure-induced cardiotoxicity and fuels effective prevention and treatment strategies against this important food-borne toxin-induced health problems.

Mitochondrial-Targeted Therapy for Doxorubicin-Induced Cardiotoxicity

Anthracyclines, such as doxorubicin, are effective chemotherapeutic agents for the treatment of cancer, but their clinical use is associated with severe and potentially life-threatening cardiotoxicity. Despite decades of research, treatment options remain limited. The mitochondria is commonly considered to be the main target of doxorubicin and mitochondrial dysfunction is the hallmark of doxorubicin-induced cardiotoxicity. Here, we review the pathogenic mechanisms of doxorubicin-induced cardiotoxicity and present an update on cardioprotective strategies for this disorder. Specifically, we focus on strategies that can protect the mitochondria and cover different therapeutic modalities encompassing small molecules, post-transcriptional regulators, and mitochondrial transfer. We also discuss the shortcomings of existing models of doxorubicin-induced cardiotoxicity and explore advances in the use of human pluripotent stem cell derived cardiomyocytes as a platform to facilitate the identification of novel treatments against this disorder.

Therapeutic Targets for DOX-Induced Cardiomyopathy: Role of Apoptosis vs. Ferroptosis

Doxorubicin (DOX) is the most widely used anthracycline anticancer agent; however, its cardiotoxicity limits its clinical efficacy. Numerous studies have elucidated the mechanisms underlying DOX-induced cardiotoxicity, wherein apoptosis has been reported as the most common final step leading to cardiomyocyte death. However, in the past two years, the involvement of ferroptosis, a novel programmed cell death, has been proposed. The purpose of this review is to summarize the historical background that led to each form of cell death, focusing on DOX-induced cardiotoxicity and the molecular mechanisms that trigger each form of cell death. Furthermore, based on this understanding, possible therapeutic strategies to prevent DOX cardiotoxicity are outlined. DNA damage, oxidative stress, intracellular signaling, transcription factors, epigenetic regulators, autophagy, and metabolic inflammation are important factors in the molecular mechanisms of DOX-induced cardiomyocyte apoptosis. Conversely, the accumulation of lipid peroxides, iron ion accumulation, and decreased expression of glutathione and glutathione peroxidase 4 are important in ferroptosis. In both cascades, the mitochondria are an important site of DOX cardiotoxicity. The last part of this review focuses on the significance of the disruption of mitochondrial homeostasis in DOX cardiotoxicity.

Myricetin-Based Self-Assembled Nanoparticles for Tumor Synergistic Therapy by Antioxidation Pathway

Nanoplatforms are nano-scale systems that can transport different small molecular anticancer drugs or chemosensitization motif to accumulate in tumor cells without obvious side-effect in normal cells and achieve a synergistic therapy. In this paper the new self-assembled nanoparticles (NPs) merging doxorubicin (DOX) and myricetin (MYR) with ferric ions (Fe³⁺) and polyphenol was employed for forming the DOX@MYR-Fe³⁺ NP (FDMP NP). The FDMP NPs could reduce the DOX-induced toxicity in blood; and they could not cause damage to the heart and kidney tissues by the reasons that the MYR could enhance the anti-oxidation capability in normal cells, which resulted in preventing ROS-induced damage. Additionally, the FDMP NPs were characteristic of small size (37.70 ± 6.30 nm), high DOX loading efficiency (46.67 ± 1.58%), pH-controlled release and excellent stable pharmacokinetics, that inducing drug release and enhancing drug accumulation in the tumor. Moreover, the FDMP NPs could inhibit the expression of the hypoxia-inducible factor-1 α(HIF-1α) and the key angiogenesis mediator vascular endothelial growth factor (VEGF) both in vitro and in vivo, which succeed in preventing the generation of new blood vessel networks; that is the mechanism of the synergistic effect against tumors induced by FDMP NPs.

Selenium, a Micronutrient That Modulates Cardiovascular Health via Redox Enzymology

Selenium (Se) is a trace nutrient that promotes human health through its incorporation into selenoproteins in the form of the redox-active amino acid selenocysteine (Sec). There are 25 selenoproteins in humans, and many of them play essential roles in the protection against oxidative stress. Selenoproteins, such as glutathione peroxidase and thioredoxin reductase, play an important role in the reduction of hydrogen and lipid hydroperoxides, and regulate the redox status of Cys in proteins. Emerging evidence suggests a role for endoplasmic reticulum selenoproteins, such as selenoproteins K, S, and T, in mediating redox homeostasis, protein modifications, and endoplasmic reticulum stress. Selenoprotein P, which functions as a carrier of Se to tissues, also participates in regulating cellular reactive oxygen species. Cellular reactive oxygen species are essential for regulating cell growth and proliferation, protein folding, and normal mitochondrial function, but their excess causes cell damage and mitochondrial dysfunction, and promotes inflammatory responses. Experimental evidence indicates a role for individual selenoproteins in cardiovascular diseases, primarily by modulating the damaging effects of reactive oxygen species. This review examines the roles that selenoproteins play in regulating vascular and cardiac function in health and disease, highlighting their antioxidant and redox actions in these processes.

The role of iron in doxorubicin-induced cardiotoxicity: recent advances and implication for drug delivery

As an anthracycline antibiotic, doxorubicin (DOX) is one of the most potent and widely used chemotherapeutic agents for treating various types of tumors. Unfortunately, the clinical application of this drug results in severe side effects, particularly dose-dependent cardiotoxicity. There are multiple mechanisms involved with the cardiotoxicity caused by DOX, among which intracellular iron homeostasis plays an essential role based on a recent discovery. In this mini-review, we summarize the clinical features and symptoms of DOX-dependent cardiotoxicity, discuss the correlation between iron and cardiotoxicity, and highlight the involvement of iron-dependent ferroptotic cell death therein. Recent advances in this topic will aid the development of novel DOX delivery systems with reduced adverse effects, and expand the clinical application of anthracycline.

HSP27 role in cardioprotection by modulating chemotherapeutic doxorubicin-induced cell death

The common phenomenon expected from any anti-cancer drug in use is to kill the cancer cells without any side effects to non-malignant cells. Doxorubicin is an anthracycline derivative anti-cancer drug active over different types of cancers with anti-cancer activity but attributed to unintended cytotoxicity and genotoxicity triggering mitogenic signals inducing apoptosis. Administration of doxorubicin tends to both acute and chronic toxicity resulting in cardiomyopathy (left ventricular dysfunction) and congestive heart failure (CHF). Cardiotoxicity is prevented through administration of different cardioprotectants along with the drug. This review elaborates on mechanism of drug-mediated cardiotoxicity and attenuation principle by different cardioprotectants, with a focus on Hsp27 as cardioprotectant by prevention of drug-induced oxidative stress, cell survival pathways with suppression of intrinsic cell death. In conclusion, Hsp27 may offer an exciting/alternating cardioprotectant, with a wider study being need of the hour, specifically on primary cell line and animal models in conforming its cardioprotectant behaviour.

Effect of Anticancer Quinones on Reactive Oxygen Production by Adult Rat Heart Myocytes

This study investigated the effect of anthracycline antibiotics, mitomycin C, and menadione on oxygen consumption and hydrogen peroxide production by intact, beating, rat heart myocytes. Doxorubicin produced a dose-dependent increase in the rate of cyanide-resistant respiration by beating myocytes. The anthracycline analogs 4-demethoxydaunorubicin, 4′-epidoxorubicin, 4′-deoxydoxorubicin, and menogaril, as well as the anticancer quinones mitomycin C and menadione, also significantly increased oxygen consumption by cardiac myocytes. However, 5-iminodaunorubicin (which has a substituted quinone group) and mitoxantrone (which is not easily reduced by flavin dehydrogenases) had no effect on cardiac respiration. Both catalase (43%) and acetylated cytochrome c (19%) significantly decreased oxygen consumption that had been stimulated by doxorubicin; furthermore, extracellular hydrogen peroxide production was increased from undetectable control levels to 1.30 ± 0.02 nmol/min/10⁷ myocytes (n = 4, P < 0.01) in the presence of 400 μM doxorubicin. These experiments suggest that the anthracycline antibiotics and other anticancer quinones stimulate cardiac oxygen radical production in intact heart myocytes; such a free radical cascade could contribute to the cardiac toxicity of these drugs.

Heparanase-driven sequential released nanoparticles for ferroptosis and tumor microenvironment modulations synergism in breast cancer therapy

The normal chemotherapy only induces the intracellular apoptosis pathway to promote primary tumor cells death, while not inhibit tumor metastasis. Herein, we proposed a kind of heparanase (HPSE)-driven sequential released nanoparticles, which modified with β-cyclodextrin (β-CD) grafted heparin (NLC/H(D + F + S) NPs) co-loading with doxorubicin (DOX), ferrocene (Fc), and TGF-β receptor inhibitor (SB431542). NLC/H(D + F + S) NPs successfully inhibited breast cancer metastasis by intracellular and extracellular hybrid mechanism. DOX and Fc loaded in NLC/H(D + F + S) NPs effectively enhanced intracellular ROS level to activate ferroptosis pathway, the enhanced ROS also induced the apoptosis pathway and decreased MMP-9 expression to synergize with ferroptosis for tumor therapy. In extracellular site, SB431542 was sequentially released by HPSE-driven, which blocked tumor metastasis by modulating tumor microenvironment, decreasing TAFs activation, and reducing the secretion of TGF-β. In addition, anti-tumor immune response induced by ferroptosis further strengthened the effect of tumor therapy. Finally, under the help of intracellular and extracellular mechanisms launched by NLC/H(D + F + S) NPs, the satisfactory anti-tumor metastasis effect was obtained in the in vivo anti-tumor assays. Therefore, NLC/H(D + F + S) NPs was a novel dosage regimen for breast cancer therapy through intracellular and extracellular mechanisms, in which ferroptosis induced by ROS played an important role.

Prevention of Doxorubicin-Induced Autophagy Attenuates Oxidative Stress and Skeletal Muscle Dysfunction

Clinical use of the chemotherapeutic doxorubicin (DOX) promotes skeletal muscle atrophy and weakness, adversely affecting patient mobility and strength. Although the mechanisms responsible for DOX-induced skeletal muscle dysfunction remain unclear, studies implicate the significant production of reactive oxygen species (ROS) in this pathology. Supraphysiological ROS levels can enhance protein degradation via autophagy, and it is established that DOX upregulates autophagic signaling in skeletal muscle. To determine the precise contribution of accelerated autophagy to DOX-induced skeletal muscle dysfunction, we inhibited autophagy in the soleus via transduction of a dominant negative mutation of the autophagy related 5 (ATG5) protein. Targeted inhibition of autophagy prevented soleus muscle atrophy and contractile dysfunction acutely following DOX administration, which was associated with a reduction in mitochondrial ROS and maintenance of mitochondrial respiratory capacity. These beneficial modifications were potentially the result of enhanced transcription of antioxidant response element-related genes and increased antioxidant capacity. Specifically, our results showed significant upregulation of peroxisome proliferator-activated receptor gamma co-activator 1-alpha, nuclear respiratory factor-1, nuclear factor erythroid-2-related factor-2, nicotinamide-adenine dinucleotide phosphate quinone dehydrogenase-1, and catalase in the soleus with DOX treatment when autophagy was inhibited. These findings establish a significant role of autophagy in the development of oxidative stress and skeletal muscle weakness following DOX administration.

Mechanisms of Anthracycline-Enhanced Reactive Oxygen Metabolism in Tumor Cells

In this investigation, we examined the effect of anthracycline antibiotics on oxygen radical metabolism in Ehrlich tumor cells. In tumor microsomes and nuclei, doxorubicin increased superoxide anion production in a dose-dependent fashion that appeared to follow saturation kinetics; the apparent K _m and V _max for superoxide formation by these organelles was 124.9 μM and 22.6 nmol/min/mg, and 103.4 μM and 4.8 nmol/min/mg, respectively. In both tumor microsomes and nuclei, superoxide formation required NADPH as a cofactor, was accompanied by the formation of hydrogen peroxide, and resulted from the transfer of electrons from NADPH to the doxorubicin quinone by NADPH:cytochrome P-450 reductase (NADPH:ferricytochrome oxidoreductase, EC 1.6.2.4). Anthracycline antibiotics also significantly enhanced superoxide anion production by tumor mitochondria with an apparent K _m and V _max for doxorubicin of 123.2 μM and 14.7 nmol/min/mg. However, drug-stimulated superoxide production by mitochondria required NADH and was increased by rotenone, suggesting that the proximal portion of the electron transport chain in tumor cells was responsible for reduction of the doxorubicin quinone at this site. The net rate of drug-related oxygen radical production was also determined for intact Ehrlich tumor cells; in this system, treatment with doxorubicin produced a dose-related increase in cyanide-resistant respiration that was enhanced by changes in intracellular reducing equivalents. Finally, we found that in the presence of iron, treatment with doxorubicin significantly increased the production of formaldehyde from dimethyl sulfoxide, an indication that the hydroxyl radical could be produced by intact tumor cells following anthracycline exposure. These experiments suggest that the anthracycline antibiotics are capable of significantly enhancing oxygen radical metabolism in Ehrlich tumor cells at multiple intracellular sites by reactions that could contribute to the cytotoxicity of this class of drugs.

Control of doxorubicin-induced, reactive oxygen-related apoptosis by glutathione peroxidase 1 in cardiac fibroblasts

Reactive oxygen formation plays a mechanistic role in the cardiotoxicity of doxorubicin, a chemotherapeutic agent that remains an important component of treatment programs for breast cancer and hematopoietic malignancies. To examine the role of doxorubicin-induced reactive oxygen species (ROS) in drug-related cardiac apoptosis, murine embryonic fibroblast cell lines were derived from the hearts of glutathione peroxidase 1 (Gpx-1) knockout mice. Cells from homozygous Gpx-1 knockout mice and parental animals were propagated with (Se+) and without (Se-) 100 nM sodium selenite. Activity levels of the peroxide detoxifying selenoprotein glutathione peroxidase (GSHPx) were marginally detectable (<1.6 nmol/min/mg) in fibroblasts from homozygous knockout animals whether or not cells were supplemented with selenium. GSHPx activity in Se- cells from parental murine fibroblasts was also <1.6 nmol/min/mg, whereas GSHPx levels in Se+ parental murine fibroblasts were 12.9 ± 2.7 nmol/min/mg (mean ± SE; P < 0.05). Catalase, superoxide dismutase, glutathione reductase, glutathione S-transferase, glucose 6-phosphate dehydrogenase, and reduced glutathione activities did not differ amongst the four cell lines. Reactive oxygen production increased from 908 ± 122 (arbitrary units) for untreated control cells to 1668 ± 54 following exposure to 1 μM doxorubicin for 24 h in parental fibroblasts not supplemented with selenium (P < 0.03); reactive oxygen formation in doxorubicin-treated parental fibroblasts propagated in selenium was 996 ± 69 (P = not significant compared to untreated control cells). Reactive oxygen levels in homozygous Gpx-1 knockout fibroblasts, irrespective of selenium supplementation status, were increased and equivalent to that in selenium deficient wild type fibroblasts. When cardiac fibroblasts were exposed to doxorubicin (0.05 μM) for 96 h and examined for cell cycle alterations by flow cytometry, and apoptosis by TUNEL assay, marked G2 arrest and TUNEL positivity were observed in knockout fibroblasts in the presence or absence of supplemental selenium, and in parental fibroblasts propagated without selenium. Parental fibroblasts propagated with selenium and exposed to the same concentration of doxorubicin demonstrated modest TUNEL positivity and substantially diminished amounts of low molecular weight DNA. These results were replicated in cardiac fibroblasts exposed to doxorubicin (1–2 μM) for 2 h (to mimic clinical drug dosing schedules) and examined 96 h following initiation of drug exposure. Doxorubicin uptake in cardiac fibroblasts was similar irrespective of the mRNA expression level or activity of GSHPx. These experiments suggest that the intracellular levels of doxorubicin-induced reactive oxygen species (ROS) are modulated by GSHPx and play an important role in doxorubicin-related apoptosis and altered cell cycle progression in murine cardiac fibroblasts.

Fenton-reaction-stimulative nanoparticles decorated with a reactive-oxygen-species (ROS)-responsive molecular switch for ROS amplification and triple negative breast cancer therapy

P@P/H NPs were rapidly disintegrated in response to ROS, and this further enhanced ROS level in tumor cells via the Fenton reaction.

Prosurvival long noncoding RNA PINCR regulates a subset of p53 targets in human colorectal cancer cells by binding to Matrin 3

Thousands of long noncoding RNAs (lncRNAs) have been discovered, yet the function of the vast majority remains unclear. Here, we show that a p53-regulated lncRNA which we named PINCR (p53-induced noncoding RNA), is induced ~100-fold after DNA damage and exerts a prosurvival function in human colorectal cancer cells (CRC) in vitro and tumor growth in vivo. Targeted deletion of PINCR in CRC cells significantly impaired G1 arrest and induced hypersensitivity to chemotherapeutic drugs. PINCR regulates the induction of a subset of p53 targets involved in G1 arrest and apoptosis, including BTG2, RRM2B and GPX1. Using a novel RNA pulldown approach that utilized endogenous S1-tagged PINCR, we show that PINCR associates with the enhancer region of these genes by binding to RNA-binding protein Matrin 3 that, in turn, associates with p53. Our findings uncover a critical prosurvival function of a p53/PINCR/Matrin 3 axis in response to DNA damage in CRC cells.

DOI:http://dx.doi.org/10.7554/eLife.23244.001

Though DNA contains the information needed to build the proteins that keep cells alive, only 2% of the DNA in a human cell codes for proteins. The remaining 98% is referred to as non-coding DNA. The information in some of these non-coding regions can still be copied into molecules of RNA, including long molecules called lncRNAs. Little is known about what lncRNAs actually do, but growing evidence suggests that these molecules are important for a number of vital processes including cell growth and survival.

When the DNA in an animal cell gets damaged, the cell needs to decide whether to pause growth and repair the damage, or to kill itself if the harm is too great. One of the best-studied proteins guiding this decision is the p53 protein, which increases the number of protein-coding genes needed to carry out either option in this decision. That is to say that, p53 regulates the genes needed to kill the cell and the genes needed to temporarily pause its growth and repair the damage, which instead keeps the cell alive. So, how does the p53 protein guide the decision, and are lncRNA molecules involved?

Using human colon cancer cells, Chaudhary et al. now report that when DNA is damaged, the levels of a specific lncRNA increase 100-fold. Further experiments showed that this lncRNA – named PINCR, which refers to p53-induced noncoding RNA – promotes the survival of cells. Chaudhary et al. showed that PINCR molecules do this by recruiting a protein called Matrin 3 to a certain region in the DNA called an enhancer and then links it to promoter region in the DNA of specific genes that temporarily pause cell growth but keep the cell alive. This in turn activates these ‘pro-survival genes’. In further experiments, when the PINCR molecules were essentially deleted, p53 was not able to fully activate these genes and as a result more of the cells died.

Together these findings increase our knowledge of how lncRNAs can work, especially in the context of DNA damage in cancer cells. A next important step will be to uncover other roles for the PINCR molecule in both cancer and healthy cells.

DOI:http://dx.doi.org/10.7554/eLife.23244.002

Anthracycline-Induced Cardiomyopathy in Adults

Anthracyclines are one of the most commonly used antineoplastic agent classes, and a core part of the treatment in breast cancers, hematological malignancies, and sarcomas. Their benefit is decreased by their well-recognized cardiotoxicity. The purpose of this review is to outline the presentation, mechanisms, diagnosis, and treatment of anthracyclines-induced cardiotoxicity. Symptomatic heart failure occurs in 2% to 5% of patients treated with anthrayclines and may be higher in older patients or patients with cardiovascular risk factors. The mechanisms involved in anthracycline-induced cardiotoxicity involve myocyte loss by apoptosis in the presence of a limited regenerative capacity. Once symptomatic, anthracycline-induced cardiotoxicity is associated with markedly decreased survival. Left ventricular ejection fraction (LVEF), mostly determined using echocardiography, is used to monitor patients treated with anthracyclines. As more than 1/3 of patients treated with anthracyclines do not recover their baseline LVEF once it is decreased, more sensitive echocardiographic indices of LV function such as myocardial deformation or biomarkers have been studied in patients monitoring. Cardioprotective treatments such as angiotensin-converting enzyme inhibitors, beta-blockers, iron chelators, statins, and metformin are also the topic of research efforts.

Paradoxical Roles of Antioxidant Enzymes: Basic Mechanisms and Health Implications

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated from aerobic metabolism, as a result of accidental electron leakage as well as regulated enzymatic processes. Because ROS/RNS can induce oxidative injury and act in redox signaling, enzymes metabolizing them will inherently promote either health or disease, depending on the physiological context. It is thus misleading to consider conventionally called antioxidant enzymes to be largely, if not exclusively, health protective. Because such a notion is nonetheless common, we herein attempt to rationalize why this simplistic view should be avoided. First we give an updated summary of physiological phenotypes triggered in mouse models of overexpression or knockout of major antioxidant enzymes. Subsequently, we focus on a series of striking cases that demonstrate "paradoxical" outcomes, i.e., increased fitness upon deletion of antioxidant enzymes or disease triggered by their overexpression. We elaborate mechanisms by which these phenotypes are mediated via chemical, biological, and metabolic interactions of the antioxidant enzymes with their substrates, downstream events, and cellular context. Furthermore, we propose that novel treatments of antioxidant enzyme-related human diseases may be enabled by deliberate targeting of dual roles of the pertaining enzymes. We also discuss the potential of "antioxidant" nutrients and phytochemicals, via regulating the expression or function of antioxidant enzymes, in preventing, treating, or aggravating chronic diseases. We conclude that "paradoxical" roles of antioxidant enzymes in physiology, health, and disease derive from sophisticated molecular mechanisms of redox biology and metabolic homeostasis. Simply viewing antioxidant enzymes as always being beneficial is not only conceptually misleading but also clinically hazardous if such notions underpin medical treatment protocols based on modulation of redox pathways.

Genetic variants in SLC22A17 and SLC22A7 are associated with anthracycline-induced cardiotoxicity in children

AIM

To identify novel variants associated with anthracycline-induced cardiotoxicity and to assess these in a genotype-guided risk prediction model.

PATIENTS & METHODS

Two cohorts treated for childhood cancer (n = 344 and 218, respectively) were genotyped for 4578 SNPs in drug ADME and toxicity genes.

RESULTS

Significant associations were identified in SLC22A17 (rs4982753; p = 0.0078) and SLC22A7 (rs4149178; p = 0.0034), with replication in the second cohort (p = 0.0071 and 0.047, respectively). Additional evidence was found for SULT2B1 and several genes related to oxidative stress. Adding the SLC22 variants to the prediction model improved its discriminative ability (AUC 0.78 vs 0.75 [p = 0.029]).

CONCLUSION

Two novel variants in SLC22A17 and SLC22A7 were significantly associated with anthracycline-induced cardiotoxicity and improved a genotype-guided risk prediction model, which could improve patient risk stratification.

Selenoproteins and cardiovascular stress

Dietary selenium (Se) is an essential micronutrient that exerts its biological effects through its incorporation into selenoproteins. This family of proteins contains several antioxidant enzymes such as the glutathione peroxidases, redox-regulating enzymes such as thioredoxin reductases, a methionine sulfoxide reductase, and others. In this review, we summarise the current understanding of the roles these selenoproteins play in protecting the cardiovascular system from different types of stress including ischaemia-reperfusion, homocysteine dysregulation, myocardial hypertrophy, doxirubicin toxicity, Keshan disease, and others.

Oxidative stress, redox signaling, and metal chelation in anthracycline cardiotoxicity and pharmacological cardioprotection

SIGNIFICANCE

Anthracyclines (doxorubicin, daunorubicin, or epirubicin) rank among the most effective anticancer drugs, but their clinical usefulness is hampered by the risk of cardiotoxicity. The most feared are the chronic forms of cardiotoxicity, characterized by irreversible cardiac damage and congestive heart failure. Although the pathogenesis of anthracycline cardiotoxicity seems to be complex, the pivotal role has been traditionally attributed to the iron-mediated formation of reactive oxygen species (ROS). In clinics, the bisdioxopiperazine agent dexrazoxane (ICRF-187) reduces the risk of anthracycline cardiotoxicity without a significant effect on response to chemotherapy. The prevailing concept describes dexrazoxane as a prodrug undergoing bioactivation to an iron-chelating agent ADR-925, which may inhibit anthracycline-induced ROS formation and oxidative damage to cardiomyocytes.

RECENT ADVANCES

A considerable body of evidence points to mitochondria as the key targets for anthracycline cardiotoxicity, and therefore it could be also crucial for effective cardioprotection. Numerous antioxidants and several iron chelators have been tested in vitro and in vivo with variable outcomes. None of these compounds have matched or even surpassed the effectiveness of dexrazoxane in chronic anthracycline cardiotoxicity settings, despite being stronger chelators and/or antioxidants.

CRITICAL ISSUES

The interpretation of many findings is complicated by the heterogeneity of experimental models and frequent employment of acute high-dose treatments with limited translatability to clinical practice.

FUTURE DIRECTIONS

Dexrazoxane may be the key to the enigma of anthracycline cardiotoxicity, and therefore it warrants further investigation, including the search for alternative/complementary modes of cardioprotective action beyond simple iron chelation.

Dexrazoxane for the prevention of cardiac toxicity and treatment of extravasation injury from the anthracycline antibiotics

The cumulative cardiac toxicity of the anthracycline antibiotics and their propensity to produce severe tissue injury following extravasation from a peripheral vein during intravenous administration remain significant problems in clinical oncologic practice. Understanding of the free radical metabolism of these drugs and their interactions with iron proteins led to the development of dexrazoxane, an analogue of EDTA with intrinsic antineoplastic activity as well as strong iron binding properties, as both a prospective cardioprotective therapy for patients receiving anthracyclines and as an effective treatment for anthracycline extravasations. In this review, the molecular mechanisms by which the anthracyclines generate reactive oxygen species and interact with intracellular iron are examined to understand the cardioprotective mechanism of action of dexrazoxane and its ability to protect the subcutaneous tissues from anthracycline-induced tissue necrosis.

Regulation of cell survival and death by pyridine nucleotides

Pyridine nucleotides (PNs), such as NAD(H) and NADP(H), mediate electron transfer in many catabolic and anabolic processes. In general, NAD(+) and NADP(+) receive electrons to become NADH and NADPH by coupling with catabolic processes. These electrons are utilized for biologically essential reactions such as ATP production, anabolism and cellular oxidation-reduction (redox) regulation. Thus, in addition to ATP, NADH and NADPH could be defined as high-energy intermediates and "molecular units of currency" in energy transfer. We discuss the significance of PNs as energy/electron transporters and signal transducers, in regulating cell death and/or survival processes. In the first part of this review, we describe the role of NADH and NADPH as electron donors for NADPH oxidases (Noxs), glutathione (GSH), and thioredoxin (Trx) systems in cellular redox regulation. Noxs produce superoxide/hydrogen peroxide yielding oxidative environment, whereas GSH and Trx systems protect against oxidative stress. We then describe the role of NAD(+) and NADH as signal transducers through NAD(+)-dependent enzymes such as PARP-1 and Sirt1. PARP-1 is activated by damaged DNA in order to repair the DNA, which attenuates energy production through NAD(+) consumption; Sirt1 is activated by an increased NAD(+)/NADH ratio to facilitate signal transduction for metabolic adaption as well as stress responses. We conclude that PNs serve as an important interface for distinct cellular responses, including stress response, energy metabolism, and cell survival/death.

Impact of dietary selenium intake on cardiac health: experimental approaches and human studies

Selenium, a dietary trace mineral, essential for humans and animals, exerts its effects mainly through its incorporation into selenoproteins. Adequate selenium intake is needed to maximize the activity of selenoproteins, among which glutathione peroxidases have been shown to play a major role in cellular defense against oxidative stress initiated by excess reactive oxygen species. In humans, a low selenium status has been linked to increased risk of various diseases, including heart disease. The main objective of this review is to present current knowledge on the role of selenium in cardiac health. Experimental studies have shown that selenium may exert protective effects on cardiac tissue in animal models involving oxidative stress. Because of the narrow safety margin of this mineral, most interventional studies in humans have reported inconsistent findings. Major determinants of selenium status in humans are not well understood and several nondietary factors might be associated with reduced selenium status. In this review, we discuss recent studies regarding the role of selenoproteins in the cardiovascular system, the effect of dietary intake on selenium status, the impact of selenium status on cardiac health, and the cellular mechanisms that can be involved in the physiological and toxic effects of selenium.

Transcriptional regulation of the GPX1 gene by TFAP2C and aberrant CpG methylation in human breast cancer

The complexity of gene regulation has created obstacles to defining mechanisms that establish the patterns of gene expression characteristic of the different clinical phenotypes of breast cancer. TFAP2C is a transcription factor that has a critical role in the regulation of both estrogen receptor-alpha (ERα) and c-ErbB2/HER2 (Her2). Herein, we performed chromatin immunoprecipitation and direct sequencing (ChIP-seq) for TFAP2C in four breast cancer cell lines. Comparing the genomic binding sites for TFAP2C, we identified that glutathione peroxidase (GPX1) is regulated by TFAP2C through an AP-2 regulatory region in the promoter of the GPX1 gene. Knockdown of TFAP2C, but not the related factor TFAP2A, resulted in an abrogation of GPX1 expression. Selenium-dependent GPX activity correlated with endogenous GPX1 expression and overexpression of exogenous GPX1 induced GPX activity and significantly increased resistance to tert-butyl hydroperoxide. Methylation of the CpG island encompassing the AP-2 regulatory region was identified in cell lines where TFAP2C failed to bind the GPX1 promoter and GPX1 expression was unresponsive to TFAP2C. Furthermore, in cell lines where GPX1 promoter methylation was associated with gene silencing, treatment with 5'-aza-2-deoxycytidine (5'-aza-dC) (an inhibitor of DNA methylation) allowed TFAP2C to bind to the GPX1 promoter resulting in the activation of GPX1 RNA and protein expression. Methylation of the GPX1 promoter was identified in ∼20% of primary breast cancers and a highly significant correlation between the TFAP2C and GPX1 expression was confirmed when considering only those tumors with an unmethylated promoter, whereas the related factor, TFAP2A, failed to demonstrate a correlation. The results demonstrate that TFAP2C regulates the expression of GPX1, which influences the redox state and sensitivity to oxidative stress induced by peroxides. Given the established role of GPX1 in breast cancer, the results provide an important mechanism for TFAP2C to further influence oncogenesis and progression of breast carcinoma cells.

Mouse Models of Oxidative Stress Indicate a Role for Modulating Healthy Aging

Aging is a complex process that affects every major system at the molecular, cellular and organ levels. Although the exact cause of aging is unknown, there is significant evidence that oxidative stress plays a major role in the aging process. The basis of the oxidative stress hypothesis is that aging occurs as a result of an imbalance between oxidants and antioxidants, which leads to the accrual of damaged proteins, lipids and DNA macromolecules with age. Age-dependent increases in protein oxidation and aggregates, lipofuscin, and DNA mutations contribute to age-related pathologies. Many transgenic/knockout mouse models over expressing or deficient in key antioxidant enzymes have been generated to examine the effect of oxidative stress on aging and age-related diseases. Based on currently reported lifespan studies using mice with altered antioxidant defense, there is little evidence that oxidative stress plays a role in determining lifespan. However, mice deficient in antioxidant enzymes are often more susceptible to age-related disease while mice overexpressing antioxidant enzymes often have an increase in the amount of time spent without disease, i.e., healthspan. Thus, by understanding the mechanisms that affect healthy aging, we may discover potential therapeutic targets to extend human healthspan.

p21(WAF1/Cip1/Sdi1) knockout mice respond to doxorubicin with reduced cardiotoxicity

Doxorubicin (Dox) is an antineoplastic agent that can cause cardiomyopathy in humans and experimental animals. As an inducer of reactive oxygen species and a DNA damaging agent, Dox causes elevated expression of p21(WAF1/Cip1/Sdi1) (p21) gene. Elevated levels of p21 mRNA and p21 protein have been detected in the myocardium of mice following Dox treatment. With chronic treatment of Dox, wild type (WT) animals develop cardiomyopathy evidenced by elongated nuclei, mitochondrial swelling, myofilamental disarray, reduced cardiac output, reduced ejection fraction, reduced left ventricular contractility, and elevated expression of ANF gene. In contrast, p21 knockout (p21KO) mice did not show significant changes in the same parameters in response to Dox treatment. In an effort to understand the mechanism of the resistance against Dox induced cardiomyopathy, we measured levels of antioxidant enzymes and found that p21KO mice did not contain elevated basal or inducible levels of glutathione peroxidase and catalase. Measurements of 6 circulating cytokines indicated elevation of IL-6, IL-12, IFNγ and TNFα in Dox treated WT mice but not p21KO mice. Dox induced elevation of IL-6 mRNA was detected in the myocardium of WT mice but not p21KO mice. While the mechanism of the resistance against Dox induced cardiomyopathy remains unclear, lack of inflammatory response may contribute to the observed cardiac protection in p21KO mice.

In vivo and in vitro assessment of the role of glutathione antioxidant system in anthracycline-induced cardiotoxicity

The clinical usefulness of anthracycline antineoplastic drugs is limited by their cardiotoxicity. Its mechanisms have not been fully understood, although the induction of oxidative stress is widely believed to play the principal role. Glutathione is the dominant cellular antioxidant, while glutathione peroxidase (GPx) together with glutathione reductase (GR) constitutes the major enzymatic system protecting the cardiac cells from oxidative damage. Therefore, this study aimed to assess their roles in anthracycline cardiotoxicity. Ten-week intravenous administration of daunorubicin (DAU, 3 mg/kg weekly) to rabbits induced heart failure, which was evident from decreased left ventricular ejection fraction and release of cardiac troponins to circulation. However, no significant changes in either total or oxidized glutathione contents or GR activity were detected in left ventricular tissue of DAU-treated rabbits when compared with control animals. GPx activity in the cardiac tissue significantly increased. In H9c2 rat cardiac cells, 24-h DAU exposure (0.1-10 μM) induced significant dose-dependent toxicity. Cellular content of reduced glutathione was insignificantly decreased, oxidized glutathione and GR activity were unaffected, and GPx activity was significantly increased. Neither buthionine sulfoximine (BSO, glutathione biosynthesis inhibitor) nor 2-oxo-4-thiazolidine-carboxylic acid (OTC, glutathione biosynthetic precursor) had significant effects on DAU cytotoxicity. This contrasted with model oxidative injury induced by hydrogen peroxide, which cytotoxicity was increased by BSO and decreased by OTC. In conclusion, our results suggest that the dysfunction of glutathione antioxidant system does not play a causative role in anthracycline cardiotoxicity.

Compilation of a comprehensive gene panel for systematic assessment of genes that govern an individual’s drug responses

Aims: Polymorphisms of genes involved in the pharmacokinetic and pharmacodynamic processes underlie the divergent drug responses among individuals. Despite some successes in identifying these polymorphisms, the candidate gene approach suffers from insufficient gene coverage whereas the genome-wide association approach is limited by less than ideal coverage of SNPs in some important genes. To expand the potential of the candidate approach, we aim to delineate a comprehensive network of drug-response genes for in-depth genetic studies. Materials & methods: Pharmacologically important genes were extracted from various sources including literatures and web resources. These genes, along with their homologs and regulatory miRNAs, were organized based on their pharmacological functions and weighted by literature evidence and confidence levels. Their coverage was evaluated by analyzing three commercial SNP chips commonly used for genome-wide association studies: Affymetrix SNP array 6.0, Illumina HumanHap1M and Illumina Omni. Results: A panel of drug-response genes was constructed, which contains 923 pharmacokinetic genes, 703 pharmacodynamic genes and 720 miRNAs. There are only 16.7% of these genes whose all known SNPs can be directly or indirectly (r2 > 0.8) captured by the SNP chips with coverage of more than 80%. This is possibly because these SNPs chips have notably poor performance over rare SNPs and miRNA genes. Conclusion: We have compiled a panel of candidate genes that may be pharmacologically important. Using this knowledgebase, we are able to systematically evaluate genes and their variants that govern an individual’s response to a given pharmaceutical therapy. This approach can serve as a necessary complement to genome-wide associations.

Unveiling the molecular mechanisms behind selenium-related diseases through knockout mouse studies

Selenium (Se), in the form of the 21st amino acid selenocysteine, is an integral part of selenoproteins and essential for mammals. While a large number of health claims for Se has been proposed in a diverse set of diseases, little is known about the precise molecular mechanisms and the physiological roles of selenoproteins. With the recent and rigorous application of reverse genetics in the mouse, great strides have been made to address this on a more molecular level. In this review, we focus on results obtained from the application of mouse molecular genetics in mouse physiology and discuss these insights into the physiological actions of selenoproteins in light of evidence from human genetics.

Mouse models targeting selenocysteine tRNA expression for elucidating the role of selenoproteins in health and development

Selenium (Se) deficiency has been known for many years to be associated with disease, impaired growth and a variety of other metabolic disorders in mammals. Only recently has the major role that Se-containing proteins, designated selenoproteins, play in many aspects of health and development begun to emerge. Se is incorporated into protein by way of the Se-containing amino acid, selenocysteine (Sec). The synthesis of selenoproteins is dependent on Sec tRNA for insertion of Sec, the 21^st amino acid in the genetic code, into protein. We have taken advantage of this dependency to modulate the expression of Sec tRNA that in turn modulates the expression of selenoproteins by generating transgenic, conditional knockout, transgenic/standard knockout and transgenic/conditional knockout mouse models, all of which involve the Sec tRNA gene, to elucidate the intracellular roles of this protein class.

Phyllaemblicin B inhibits Coxsackie virus B3 induced apoptosis and myocarditis

Coxsackie virus B3 (CVB3) is believed to be a major contributor to viral myocarditis since virus-associated apoptosis plays a role in the pathogenesis of experimental myocarditis. In this study, we investigated the in vitro and in vivo antiviral activities of Phyllaemblicin B, the main ellagitannin compound isolated from Phyllanthus emblica, a Chinese herb medicine, against CVB3. Herein we report that Phyllaemblicin B inhibited CVB3-mediated cytopathic effects on HeLa cells with an IC(50) value of 7.75+/-0.15microg/mL. In an in vivo assay, treatment with 12mgkg(-1)d(-1) Phyllaemblicin B reduced cardiac CVB3 titers, decreased the activities of LDH and CK in murine serum, and alleviated pathological damages of cardiac muscle in myocarditic mice. Moreover, Phyllaemblicin B clearly inhibited CVB3-associated apoptosis effects both in vitro and in vivo. These results show that Phyllaemblicin B exerts significant antiviral activities against CVB3. Therefore, Phyllaemblicin B may represent a potential therapeutic agent for viral myocarditis.

Anthracycline-induced cardiotoxicity: overview of studies examining the roles of oxidative stress and free cellular iron

The risk of cardiotoxicity is the most serious drawback to the clinical usefulness of anthracycline antineoplastic antibiotics, which include doxorubicin (adriamycin), daunorubicin or epirubicin. Nevertheless, these compounds remain among the most widely used anticancer drugs. The molecular pathogenesis of anthracycline cardiotoxicity remains highly controversial, although the oxidative stress-based hypothesis involving intramyocardial production of reactive oxygen species (ROS) has gained the widest acceptance. Anthracyclines may promote the formation of ROS through redox cycling of their aglycones as well as their anthracycline-iron complexes. This proposed mechanism has become particularly popular in light of the high cardioprotective efficacy of dexrazoxane (ICRF-187). The mechanism of action of this drug has been attributed to its hydrolytic transformation into the iron-chelating metabolite ADR-925, which may act by displacing iron from anthracycline-iron complexes or by chelating free or loosely bound cellular iron, thus preventing site-specific iron-catalyzed ROS damage. However, during the last decade, calls for the critical reassessment of this "ROS and iron" hypothesis have emerged. Numerous antioxidants, although efficient in cellular or acute animal experiments, have failed to alleviate anthracycline cardiotoxicity in clinically relevant chronic animal models or clinical trials. In addition, studies with chelators that are stronger and more selective for iron than ADR-925 have also yielded negative or, at best, mixed outcomes. Hence, several lines of evidence suggest that mechanisms other than the traditionally emphasized "ROS and iron" hypothesis are involved in anthracycline-induced cardiotoxicity and that these alternative mechanisms may be better bases for designing approaches to achieve efficient and safe cardioprotection.