Redox cycling of anthracyclines by cardiac mitochondria. I. Anthracycline radical formation by NADH dehydrogenase

Subclinical Cardiac Dysfunction in Childhood Cancer Survivors on 10-Years Follow-Up Correlates With Cumulative Anthracycline Dose and Is Best Detected by Cardiopulmonary Exercise Testing, Circulating Serum Biomarker, Speckle Tracking Echocardiography, and Tissue Doppler Imaging

Background: Survivors of childhood cancer are at risk for anthracycline- and/or radiotherapy-induced cardiotoxicity. Aims: The aim of this study was to assess clinical, laboratory, and imaging parameters of subclinical cardiovascular disease in childhood cancer survivors. Methods: Patients underwent cardiopulmonary exercise test (CPET), laboratory testing, transthoracic echocardiography (TTE) with tissue doppler imaging (TDI) and speckle tracking. A subset of patients also underwent cardiovascular magnetic resonance imaging (CMR). Findings were correlated to cumulative anthracycline and exposure to mediastinal irradiation during cancer treatment. In a subgroup analysis, TTE and CMR findings were compared to data from 40 gender- and age-matched patients with childhood onset hypertrophic cardiomyopathy (HCM). Results: Cardiac evaluation was performed in 79 patients (43 males) at 11.2 ± 4.5 years after cancer treatment. Oncologic diagnosis at a median age of 12.0 years was Hodgkin lymphoma in 20, sarcoma in 17, acute leukemia in 24, relapse leukemia in 10, and others in 8 patients. Cumulative anthracycline dose exceeded 300 mg/m² in 28 patients. Twenty six patients also received mediastinal irradiation. Decreased peak respiratory oxygen uptake in % predicted on CPET, increased levels of N-terminal pro-brain natriuretic peptide (NTproBNP), increased global longitudinal strain on TTE speckle tracking, and diastolic dysfunction on TDI were the most prominent findings on detailed cardiology follow-up. In contrast to HCM patients, childhood cancer survivors did not show left ventricular hypertrophy (LVPWd z-score median 0.9 vs. 2.8, p < 0.001), hyperdynamic systolic function on TTE (Ejection fraction 62 ± 7 vs. 72 ± 12%, p = 0.001), or fibrotic myocardial changes on CMR (Late gadolinium positive 0/13 vs. 13/36, p = 0.001; extracellular volume fraction 22 ± 2 vs. 28 ± 3, p < 0.001) at time of follow-up. There was no correlation between chest radiation exposure and abnormal cardiac findings. Cumulative anthracycline dose was the only significant independent predictor on multivariate analysis for any cardiovascular abnormality on follow-up (p = 0.036). Conclusion: Increasing cumulative anthracycline dose during cancer treatment correlates with subclinical cardiac dysfunction in childhood cancer survivors best detected by elevated cardiac serum biomarkers, decreased exercise capacity on CPET, and abnormalities on echocardiographic speckle tracking and TDI.

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.

Teaching the basics of the mechanism of doxorubicin-induced cardiotoxicity: Have we been barking up the wrong tree?

Doxorubicin (DOX), or Adriamycin, an anthracycline antibiotic discovered serendipitously as a chemotherapeutic drug several decades ago, is still one of the most effective drugs for treating various adult and pediatric cancers (breast cancer, Hodgkin's disease, lymphoblastic leukemia). However, one of the major side effects of the continuous use of DOX is dose-dependent, long-term, and potentially lethal cardiovascular toxicity (congestive heart failure and cardiomyopathy) in cancer survivors many years after cessation of chemotherapy. In addition, predisposition to cardiotoxicity varied considerably among individuals. The long-held notion that DOX cardiotoxicity is caused by reactive oxygen species formed from the redox-cycling of DOX semiquinone lacks rigorous proof in a chronic animal model, and administration of reactive oxygen species detoxifying agents failed to reverse DOX-induced cardiac problems. In this review, I discuss the pros and cons of the reactive oxygen species pathway as a primary or secondary mechanism of DOX cardiotoxicity, the role of topoisomerases, and the potential use of mitochondrial-biogenesis-enhancing compounds in reversing DOX-induced cardiomyopathy. New approaches for well-designed clinical trials that repurpose FDA-approved drugs and naturally occurring polyphenolic compounds prophylactically to prevent or mitigate cardiovascular complications in both pediatric and adult cancer survivors are needed. Essentially, the focus should be on enhancing mitochondrial biogenesis to prevent or mitigate DOX-induced cardiotoxicity.

Doxorubicin-induced cardiomyocyte death is mediated by unchecked mitochondrial fission and mitophagy

Doxorubicin (Dox) is a widely used antineoplastic agent that can cause heart failure. Dox cardiotoxicity is closely associated with mitochondrial damage. Mitochondrial fission and mitophagy are quality control mechanisms that normally help maintain a pool of healthy mitochondria. However, unchecked mitochondrial fission and mitophagy may compromise the viability of cardiomyocytes, predisposing them to cell death. Here, we tested this possibility by using Dox-treated H9c2 cardiac myoblast cells expressing either the mitochondria-targeted fluorescent protein MitoDsRed or the novel dual-fluorescent mitophagy reporter mt-Rosella. Dox induced mitochondrial fragmentation as shown by reduced form factor, aspect ratio, and mean mitochondrial size. This effect was abolished by short interference RNA-mediated knockdown of dynamin-related protein 1 (DRP1), a major regulator of fission. Importantly, DRP1 knockdown decreased cell death as indicated by the reduced number of propidium iodide-positive cells and the cleavage of caspase-3 and poly (ADP-ribose) polymerase. Moreover, DRP1-deficient mice were protected from Dox-induced cardiac damage, strongly supporting a role for DRP1-dependent mitochondrial fragmentation in Dox cardiotoxicity. In addition, Dox accelerated mitophagy flux, which was attenuated by DRP1 knockdown, as assessed by the mitophagy reporter mt-Rosella, suggesting the necessity of mitochondrial fragmentation in Dox-induced mitophagy. Knockdown of parkin, a positive regulator of mitophagy, dramatically diminished Dox-induced cell death, whereas overexpression of parkin had the opposite effect. Together, these results suggested that Dox cardiotoxicity was mediated, at least in part, by the increased mitochondrial fragmentation and accelerated mitochondrial degradation by the lysosome. Strategies that limit mitochondrial fission and mitophagy in the physiologic range may help reduce Dox cardiotoxicity.-Catanzaro, M. P., Weiner, A., Kaminaris, A., Li, C., Cai, F., Zhao, F., Kobayashi, S., Kobayashi, T., Huang, Y., Sesaki, H., Liang, Q. Doxorubicin-induced cardiomyocyte death is mediated by unchecked mitochondrial fission and mitophagy.

The anti-cancer drug doxorubicin induces substantial epigenetic changes in cultured cardiomyocytes

The anthracycline doxorubicin (DOX) is widely used in cancer therapy with the limitation of cardiotoxicity leading to the development of congestive heart failure. DOX-induced oxidative stress and changes of the phosphoproteome as well as epigenome were described but the exact mechanisms of the adverse long-term effects are still elusive. Here, we tested the impact of DOX treatment on cell death, oxidative stress parameters and expression profiles of proteins involved in epigenetic pathways in a cardiomyocyte cell culture model. Markers of oxidative stress, apoptosis and expression of proteins involved in epigenetic processes were assessed by immunoblotting in cultured rat myoblasts (H9c2) upon treatment with DOX (1 or 5 μM for 24 or 48 h) in adherent viable and detached apoptotic cells. The apoptosis markers cleaved caspase-3 and fractin as well as oxidative stress markers 3-nitrotyrosine and malondialdehyde were dose-dependently increased by DOX treatment. Histone deacetylases (SIRT1 and HDAC2), histone lysine demethylases (KDM3A and LSD1) and histone lysine methyltransferases (SET7 and SMYD1) were significantly regulated by DOX treatment with generation of cleaved protein fragments and posttranslational modifications. Overall, we found significant decrease in histone 3 acetylation in DOX-treated cells. DOX treatment of cultured cardiomyocyte precursor cells causes severe cell death by apoptosis associated with cellular oxidative stress. In addition, significant regulation of proteins involved in epigenetic processes and changes in global histone 3 acetylation were observed. However, the significance and clinical impact of these changes remain elusive.

Doxorubicin-Induced Cardiomyopathy in Children

Doxorubicin-induced cardiotoxicity in childhood cancer survivors is a growing problem. The population of patients at risk for cardiovascular disease is steadily increasing, as five-year survival rates for all types of childhood cancers continue to improve. Doxorubicin affects the developing heart differently from the adult heart and in a subset of exposed patients, childhood exposure leads to late, irreversible cardiomyopathy. Notably, the prevalence of late-onset toxicity is increasing in parallel with improved survival. By the year 2020, it is estimated that there will be 500,000 childhood cancer survivors and over 50,000 of them will suffer from doxorubicin-induced cardiotoxicity. The majority of the research to-date, concentrated on childhood cancer survivors, has focused mostly on clinical outcomes through well-designed epidemiological and retrospective cohort studies. Preclinical studies have elucidated many of the cellular mechanisms that elicit acute toxicity in cardiomyocytes. However, more research is needed in the areas of early- and late-onset cardiotoxicity and more importantly improving the scientific understanding of how other cells present in the cardiac milieu are impacted by doxorubicin exposure. The overall goal of this review is to succinctly summarize the major clinical and preclinical studies focused on doxorubicin-induced cardiotoxicity. As the prevalence of patients affected by doxorubicin exposure continues to increase, it is imperative that the major gaps in existing research are identified and subsequently utilized to develop appropriate research priorities for the coming years. Well-designed preclinical research models will enhance our understanding of the pathophysiology of doxorubicin-induced cardiotoxicity and directly lead to better diagnosis, treatment, and prevention. © 2019 American Physiological Society. Compr Physiol 9:905-931, 2019.

Punicalagin protects H9c2 cardiomyocytes from doxorubicin-induced toxicity through activation of Nrf2/HO-1 signaling

Doxorubicin (DOX) is a wide-spectrum antitumor agent, but its clinical application is largely limited by its cardiotoxicity. Therefore, identification of effective agents against DOX-induced cardiotoxicity is of critical importance. The present study aimed to determine the beneficial role of punicalagin (PUN), a polyphenol isolated from pomegranate, in DOX-induced cardiotoxicity in vitro and explored the underlying mechanisms. H9c2 cardiomyocytes were pretreated with different concentrations (50, 100 and 200 μM) of PUN prior to DOX exposure. The results showed that PUN pretreatment significantly increased cell viability, inhibited lactate dehydrogenase (LDH) release and suppressed cell apoptosis induced by DOX. Additionally, PUN pretreatment attenuated the loss of mitochondrial membrane potential and cytochrome c release. Besides, PUN further enhanced the expression of nuclear Nrf2 and HO-1 in DOX-treated H9c2 cells, and the aforementioned beneficial effects of PUN were partially abolished by small interfering RNA (siRNA)-mediated Nrf2 knockdown. Hence, our findings clearly revealed that PUN might be a promising agent for alleviating the cardiotoxicity of DOX, and Nrf2/HO-1 signaling might serve a critical role during this process.

68Ga-Galmydar: A PET imaging tracer for noninvasive detection of Doxorubicin-induced cardiotoxicity

Background

Cancer patients undergoing Doxorubicin (DOX) treatment are susceptible to acute and chronic cardiac anomalies, including aberrant arrhythmias, ventricular dysfunction, and heart failure. To stratify patients at high risk for DOX -related heart failure (CHF), diagnostic techniques have been sought. While echocardiography is used for monitoring LVEF and LV volumes due to its wide-availability and cost-efficiency, it may not identify early stages of the initiation of DOX-induced systolic heart failure. To address these limitations, PET tracers could also provide noninvasive assessment of early and reversible metabolic changes of the myocardium.

Objective

Herein, we report a preliminary investigation of ⁶⁸Ga-Galmydar potential to monitor Dox-induced cardiomyopathy in vivo, ex vivo, and in cellulo employing both nuclear- and optical imaging.

Methods and results

To assess ⁶⁸Ga-Galmydar ability for monitoring DOX-induced cardiomyopathy, microPET imaging was performed 5 d post treatment of rats either with a single dose of DOX (15 mg/kg) or vehicle as a control (saline) and images were co-registered for anatomical reference using CT. Following tail-vein injection of the radiotracer in rats at 60 min, micro-PET/CT static scan (10 min acquisition), ⁶⁸Ga-Galmydar demonstrated 1.91-fold lower uptake in hearts of DOX-treated (standard uptake value; SUV: 0.92, n = 3) rats compared with their vehicle treated (SUV: 1.76, n = 3) control counterparts. For correlation of PET imaging data, post-imaging quantitative biodistribution studies were also performed, wherein excised organs were counted for γ activity, and normalized to injected dose. The post imaging pharmacokinetic data also demonstrated heart uptake values of 2.0 fold lower for DOX treated rats(%ID/g; DOX: 0.44 ± 0.1, n = 3) compared to their vehicle-treated controls (%ID/g; Control: 0.89 ± 0.03, n = 3, p = 0.04). Employing the fluorescent traits of Galmydar, live cell fluorescence imaging indicated a gradual decrease in uptake and retention of Galmydar within mitochondria of H9c2 cells following DOX-treatment, while indicating dose-dependent and time-dependent uptake profiles. Following depolarization of electronegative transmembrane gradients at the mitochondrial membrane, the uptake of the probe was decreased in H9c2 cells, and the uptake profiles were found to be identical, using both fluorescence and radiotracer bioassays. Finally, the decreased uptake of the metalloprobe in H9c2 cells also correlated with caspase-3 expression resulting from DOX-induced cardiotoxicity and cell death.

Conclusions

⁶⁸Ga-Galmydar could provide a noninvasive assessment of DOX-related and likely reversible metabolic changes at earliest stages. Further studies with other chemotherapeutics (potentially capable of inducing cardiomyopathy) are underway.

Doxorubicin-induced cardiotoxicity is maturation dependent due to the shift from topoisomerase IIα to IIβ in human stem cell derived cardiomyocytes

Doxorubicin (DOX) is widely used to treat various cancers affecting adults and children; however, its clinical application is limited by its cardiotoxicity. Previous studies have shown that children are more susceptible to the cardiotoxic effects of DOX than adults, which may be related to different maturity levels of cardiomyocyte, but the underlying mechanisms are not fully understood. Moreover, researchers investigating DOX‐induced cardiotoxicity caused by human‐induced pluripotent stem cell‐derived cardiomyocytes (hiPSC‐CMs) have shown that dexrazoxane, the recognized cardioprotective drug for treating DOX‐induced cardiotoxicity, does not alleviate the toxicity of DOX on hiPSC‐CMs cultured for 30 days. We have suggested that this may be ascribed to the immaturity of the 30 days hiPSC‐CMs. In this study, we investigated the mechanisms of DOX induced cardiotoxicity in cardiomyocytes of different maturity. We selected 30‐day‐old and 60‐day‐old hiPSC‐CMs (day 30 and day 60 groups), which we term ‘immature’ and ‘relatively mature’ hiPSC‐CMs, respectively. The day 30 CMs were found to be more susceptible to DOX than the day 60 CMs. DOX leads to more ROS (reactive oxygen species) production in the day 60 CMs than in the relatively immature group due to increased mitochondria number. Moreover, the day 60 CMs mainly expressed topoisomerase IIβ presented less severe DNA damage, whereas the day 30 CMs dominantly expressed topoisomerase IIα exhibited much more severe DNA damage. These results suggest that immature cardiomyocytes are more sensitive to DOX as a result of a higher concentration of topoisomerase IIα, which leads to more DNA damage.

Is the combinational administration of doxorubicin and glutathione a reasonable proposal?

The combinational administration of antioxidants and chemotherapeutic agents during conventional cancer treatment is among one of the most controversial areas in oncology. Although the data on the combinational usage of doxorubicin (DOX) and glutathione (GSH) agents have been explored for over 20 years, the duration, administration route, and authentic rationality have not yet been fully understood yet. In the current study, we systematically investigated the pharmacokinetics (PK) and pharmacodynamics (PD) with both in vivo and in vitro models to elucidate the influence of GSH on the toxicity and efficacy of DOX. We first studied the cardioprotective and hepatoprotective effects of GSH in Balb/c mice, H9c2, and HL7702 cells. We showed that coadministration of exogenous GSH (5, 50, and 500 mg/kg per day, intragastric) significantly attenuated DOX-induced cardiotoxicity and hepatotoxicity by increasing intracellular GSH levels, whereas the elevated GSH concentrations did not affect the exposure of DOX in mouse heart and liver. From PK and PD perspectives, then the influences of GSH on the chemotherapeutic efficacy of DOX were investigated in xenografted nude mice and cancer cell models, including MCF-7, HepG2, and Caco-2 cells, which revealed that administration of exogenous GSH dose-dependently attenuated the anticancer efficacy of DOX in vivo and in vitro, although the elevated GSH levels neither influenced the concentration of DOX in tumors in vivo, nor the uptake of DOX in MCF-7 tumor cells in vitro. Based on the results we suggest that the combined administration of GSH and DOX should be contraindicated during chemotherapy unless DOX has caused serious hepatotoxicity and cardiotoxicity.

A phase II clinical study of 13-deoxy, 5-iminodoxorubicin (GPX-150) with metastatic and unresectable soft tissue sarcoma

BACKGROUND

13-Deoxy, 5-iminodoxorubicin (GPX-150) is a doxorubicin (DOX) analog synthesized to reduce the formation of reactive oxygen species and the cardiotoxic metabolite, doxorubiciniol, the two pathways that are linked to the irreversible, cumulative dose-dependent cardiotoxicity of DOX. In a preclinical chronic models and a phase I clinical study of GPX-150, no irreversible, cumulative dose-dependent cardiotoxicity was demonstrated. Recent studies suggest that DOX cardiotoxicity may be mediated, at least in part, by the poisoning of topoisomerase IIβ.

PATIENTS AND METHODS

An open-label, single-arm phase II clinical study in metastatic and unresectable soft tissue sarcoma (STS) patients was initiated to further evaluate the efficacy and safety of GPX-150, including cardiac function, specifically left ventricular ejection fraction (LVEF).

RESULTS

GPX-150 was administered at 265 mg/m² every 3 weeks for up to 16 doses with prophylactic G-CSF until progression, death, or patient withdrawal from the study. GPX-150 exhibited efficacy assessed as progression-free survival (PFS) rates of 38% and 12% at 6 and 12 months and an overall survival rate of 74% and 45% at 6 and 12 months. GPX-150-treated patients did not develop any evidence of irreversible, cumulative dose-dependent chronic cardiotoxicity. Toxicities included grade 3 anemia, neutropenia, and one grade 4 leukopenia. Correlative analysis demonstrated that GPX-150 was more selective than DOX for the inhibition of topoisomerase IIα over IIβ in vitro.

CONCLUSION

These results suggest future studies are warranted to further evaluate the clinical efficacy of GPX-150 in STS, perhaps at doses higher than 265 mg/m² .

Modelling changes in glutathione homeostasis as a function of quinone redox metabolism

Redox cycling is an understated mechanism of toxicity associated with a plethora of xenobiotics, responsible for preventing the effective treatment of serious conditions such as malaria and cardiomyopathy. Quinone compounds are notorious redox cyclers, present in drugs such as doxorubicin, which is used to treat a host of human cancers. However, the therapeutic index of doxorubicin is undermined by dose-dependent cardiotoxicity, which may be a function of futile redox cycling. In this study, a doxorubicin-specific in silico quinone redox metabolism model is described. Doxorubicin-GSH adduct formation kinetics are thermodynamically estimated from its reduction potential, while the remainder of the model is parameterised using oxygen consumption rate data, indicative of hydroquinone auto-oxidation. The model is then combined with a comprehensive glutathione metabolism model, facilitating the simulation of quinone redox cycling, and adduct-induced GSH depletion. Simulations suggest that glutathione pools are most sensitive to exposure duration at pharmacologically and supra-pharmacologically relevant doxorubicin concentrations. The model provides an alternative method of investigating and quantifying redox cycling induced oxidative stress, circumventing the experimental difficulties of measuring and tracking radical species. This in silico framework provides a platform from which GSH depletion can be explored as a function of a compound’s physicochemical properties.

The Role of Mitochondria in Reactive Oxygen Species Generation and Its Implications for Neurodegenerative Diseases

Mitochondria are dynamic cellular organelles that consistently migrate, fuse, and divide to modulate their number, size, and shape. In addition, they produce ATP, reactive oxygen species, and also have a biological role in antioxidant activities and Ca²⁺ buffering. Mitochondria are thought to play a crucial biological role in most neurodegenerative disorders. Neurons, being high-energy-demanding cells, are closely related to the maintenance, dynamics, and functions of mitochondria. Thus, impairment of mitochondrial activities is associated with neurodegenerative diseases, pointing to the significance of mitochondrial functions in normal cell physiology. In recent years, considerable progress has been made in our knowledge of mitochondrial functions, which has raised interest in defining the involvement of mitochondrial dysfunction in neurodegenerative diseases. Here, we summarize the existing knowledge of the mitochondrial function in reactive oxygen species generation and its involvement in the development of neurodegenerative diseases.

Cardio-oncology: Understanding cardiotoxicity to guide patient focused imaging

Current cancer therapy has led to tremendous improvements in outcomes. These therapies rely both on established therapies, such as anthracyclines and radiation, and molecularly-targeted therapies, such as tyrosine kinase inhibitors and immune modulators. Integrative care for patients with cancer must consider the potential effects of these therapies on a variety of organ systems, including the cardiovascular system. As a result, specialties such as cardio-oncology have developed to identify these effects, determine how to best monitor for these effects, and how to treat and ultimately prevent these effects while allowing the patient to receive the therapy they require for their cancer. This review provides a basis for understanding the cardiovascular effects of cancer therapies so that the most appropriate imaging modality may be selected to prevent and treat these effects.

Hematopoietic Stem Cells: Normal Versus Malignant

SIGNIFICANCE

The long-term hematopoietic stem cell (LT-HSC) demonstrates characteristics of self-renewal and the ability to manage expansion of the hematopoietic compartment while maintaining the capacity for differentiation into hematopoietic stem/progenitor cell (HSPC) and terminal subpopulations. Deregulation of the HSPC redox environment results in loss of signaling that normally controls HSPC fate, leading to a loss of HSPC function and exhaustion. The characteristics of HSPC exhaustion via redox stress closely mirror phenotypic traits of hematopoietic malignancies and the leukemic stem cell (LSC). These facets elucidate the HSC/LSC redox environment as a druggable target and a growing area of cancer research. Recent Advances: Although myelosuppression and exhaustion of the hematopoietic niche are detrimental side effects of classical chemotherapies, new agents that modify the HSPC/LSC redox environment have demonstrated the potential for protection of normal HSPC function while inducing cytotoxicity within malignant populations.

CRITICAL ISSUES

New therapies must preserve, or only slightly disturb normal HSPC redox balance and function, while simultaneously altering the malignant cellular redox state. The cascade nature of redox damage makes this a critical and delicate line for the development of a redox-based therapeutic index.

FUTURE DIRECTIONS

Recent evidence demonstrates the potential for redox-based therapies to impact metabolic and epigenetic factors that could contribute to initial LSC transformation. This is balanced by the development of therapies that protect HSPC function. This pushes toward therapies that may alter the HSC/LSC redox state but lead to initiation cell fate signaling lost in malignant transformation while protecting normal HSPC function. Antioxid. Redox Signal.

Endurance exercise protects skeletal muscle against both doxorubicin-induced and inactivity-induced muscle wasting

Repeated bouts of endurance exercise promotes numerous biochemical adaptations in skeletal muscle fibers resulting in a muscle phenotype that is protected against a variety of homeostatic challenges; these exercise-induced changes in muscle phenotype are often referred to as "exercise preconditioning." Importantly, exercise preconditioning provides protection against several threats to skeletal muscle health including cancer chemotherapy (e.g., doxorubicin) and prolonged muscle inactivity. This review summarizes our current understanding of the mechanisms responsible for exercise-induced protection of skeletal muscle fibers against both doxorubicin-induced muscle wasting and a unique form of inactivity-induced muscle atrophy (i.e., ventilator-induced diaphragm atrophy). Specifically, the first section of this article will highlight the potential mechanisms responsible for exercise-induced protection of skeletal muscle fibers against doxorubicin-induced fiber atrophy. The second segment will discuss the biochemical changes that are responsible for endurance exercise-mediated protection of diaphragm muscle against ventilator-induced diaphragm wasting. In each section, we highlight gaps in our knowledge in hopes of stimulating future research in this evolving field of investigation.

Doxorubicin induces an extensive transcriptional and metabolic rewiring in yeast cells

Doxorubicin is one of the most effective chemotherapy drugs used against solid tumors in the treatment of several cancer types. Two different mechanisms, (i) intercalation of doxorubicin into DNA and inhibition of topoisomerase II leading to changes in chromatin structure, (ii) generation of free radicals and oxidative damage to biomolecules, have been proposed to explain the mode of action of this drug in cancer cells. A genome-wide integrative systems biology approach used in the present study to investigate the long-term effect of doxorubicin in Saccharomyces cerevisiae cells indicated the up-regulation of genes involved in response to oxidative stress as well as in Rad53 checkpoint sensing and signaling pathway. Modular analysis of the active sub-network has also revealed the induction of the genes significantly associated with nucleosome assembly/disassembly and DNA repair in response to doxorubicin. Furthermore, an extensive re-wiring of the metabolism was observed. In addition to glycolysis, and sulfate assimilation, several pathways related to ribosome biogenesis/translation, amino acid biosynthesis, nucleotide biosynthesis, de novo IMP biosynthesis and one-carbon metabolism were significantly repressed. Pentose phosphate pathway, MAPK signaling pathway biological processes associated with meiosis and sporulation were found to be induced in response to long-term exposure to doxorubicin in yeast cells.

Dexrazoxane Significantly Reduces Anthracycline-induced Cardiotoxicity in Pediatric Solid Tumor Patients: A Systematic Review

Cardiotoxicity is a dose-limiting and potentially lethal complication of anthracycline administration. Previous studies failed to determine definitive toxic doses or cardioprotective factors. Current dosing strategies may utilize unnecessarily high anthracycline doses, such that survival benefit may not outweigh increased toxicity rates. A systematic review of randomized controlled trials and prospective/retrospective studies investigating anthracycline treatment in pediatric solid tumors was performed from PubMed/MEDLINE and Cochrane databases. Generalized linear models mapping survival, cardiotoxicity, and cardiotoxicity-free survival adjusted for male-to-female ratio, follow-up time, and concomitant chemotherapeutic drugs or cardioprotective agents (dexrazoxane) were generated using R. Survival rose linearly with increasing cumulative anthracycline dose whereas cardiotoxicity demonstrated exponential increases both without (dose, >200 mg/m) and with (dose, >400 mg/m) dexrazoxane. Maximum cardiotoxicity-free survival was 268.2 mg/m without and 431.8 mg/m with dexrazoxane. Despite increasing cardiotoxicity-free dose by >150 mg/m, dexrazoxane minimally improved projected survival (71.9% vs. 75.4%). Cardiotoxicity increased linearly as a function of follow-up time with rates doubling from 5 to 20 years, without evidence of plateau. On the basis of our model, current dosing regimens-doxorubicin doses >375 mg/m without dexrazoxane-overvalue increased anthracycline administration and may contribute to devastating cardiotoxicity. The linear increase of cardiotoxicity without evidence of plateau confirms the necessity for lifelong cardiac monitoring.

Definition of hidden drug cardiotoxicity: paradigm change in cardiac safety testing and its clinical implications

Unexpected cardiac adverse effects are the leading causes of discontinuation of clinical trials and withdrawal of drugs from the market. Since the original observations in the mid-90s, it has been well established that cardiovascular risk factors and comorbidities (such as ageing, hyperlipidaemia, and diabetes) and their medications (e.g. nitrate tolerance, adenosine triphosphate-dependent potassium inhibitor antidiabetic drugs, statins, etc.) may interfere with cardiac ischaemic tolerance and endogenous cardioprotective signalling pathways. Indeed drugs may exert unwanted effects on the diseased and treated heart that is hidden in the healthy myocardium. Hidden cardiotoxic effects may be due to (i) drug-induced enhancement of deleterious signalling due to ischaemia/reperfusion injury and/or the presence of risk factors and/or (ii) inhibition of cardioprotective survival signalling pathways, both of which may lead to ischaemia-related cell death and/or pro-arrhythmic effects. This led to a novel concept of ‘hidden cardiotoxicity’, defined as cardiotoxity of a drug that manifests only in the diseased heart with e.g. ischaemia/reperfusion injury and/or in the presence of its major comorbidities. Little is known on the mechanism of hidden cardiotoxocity, moreover, hidden cardiotoxicity cannot be revealed by the routinely used non-clinical cardiac safety testing methods on healthy animals or tissues. Therefore, here, we emphasize the need for development of novel cardiac safety testing platform involving combined experimental models of cardiac diseases (especially myocardial ischaemia/reperfusion and ischaemic conditioning) in the presence and absence of major cardiovascular comorbidities and/or cotreatments.

Influence of PARP-1 inhibition in the cardiotoxicity of the topoisomerase 2 inhibitors doxorubicin and mitoxantrone

Doxorubicin (DOX) and Mitoxantrone (MTX) are very effective drugs for a range of tumors despite being highly cardiotoxic. DNA topoisomerase 2 beta (Top2ß) was revealed as key mediator of DOX-induced cardiotoxicity, although ROS generation is also an important mechanism. Oxidative stress is also an important issue in MTX-induced cardiotoxicity that is manifested by mitochondrial dysfunction. Studies have demonstrated the relationship between PARP-1 overactivation and cell viability in DOX-treated cardiomyocytes. In reference of MTX, data regarding PARP-1 overactivation as the mechanism responsible for cardiotoxicity is difficult to find. The aim of this study was to evaluate the influence of PARP-1 inhibitor DPQ on DOX- and MTX-mediated cardiotoxicity. Cells were exposed for 24 h to DOX or MTX in the presence or absence of DPQ. Viability, apoptosis, and genotoxicity assays were carried out. Immunofluorescence of phosphorylated histone H2AX was analyzed in H9c2 cells and cardiomyocytes from neonatal rats. Results demonstrated that DPQ co-treatment increases DOX-induced apoptosis in H9c2 cells. DPQ also prevents DOX and MTX-ROS generation in part by increasing SOD and CAT activities. Furthermore, DPQ co-treatment increased the generation of DNA strand breaks by DOX and MTX whilst also inducing phosphorylation of H2AX, MRE11, and ATM in H9c2 cells. Our results demonstrated that as well as increasing DNA damage and inducing apoptotic cell death, DPQ enhances DOX- and MTX-mediated cytotoxicity in H9c2.

Doxorubicin triggers bioenergetic failure and p53 activation in mouse stem cell-derived cardiomyocytes

Doxorubicin (DOX) is a widely used anticancer drug that could be even more effective if its clinical dosage was not limited because of delayed cardiotoxicity. Beating stem cell-derived cardiomyocytes are a preferred in vitro model to further uncover the mechanisms of DOX-induced cardiotoxicity. Our objective was to use cultured induced-pluripotent stem cell(iPSC)-derived mouse cardiomyocytes (Cor.At) to investigate the effects of DOX on cell and mitochondrial metabolism, as well as on stress responses. Non-proliferating and beating Cor.At cells were treated with 0.5 or 1 μM DOX for 24 h, and morphological, functional and biochemical changes associated with mitochondrial bioenergetics, DNA-damage response and apoptosis were measured. Both DOX concentrations decreased ATP levels and SOD2 protein levels and induced p53-dependent caspase activation. However, differential effects were observed for the two DOX concentrations. The highest concentration induced a high degree of apoptosis, with increased nuclear apoptotic morphology, PARP-1 cleavage and decrease of some OXPHOS protein subunits. At the lowest concentration, DOX increased the expression of p53 target transcripts associated with mitochondria-dependent apoptosis and decreased transcripts related with DNA-damage response and glycolysis. Interestingly, cells treated with 0.5 μM DOX presented an increase in PDK4 transcript levels, accompanied by an increase in phospho-PDH and decreased PDH activity. This was accompanied by an apparent decrease in basal and maximal oxygen consumption rates (OCR) and in basal extracellular acidification rate (ECAR). Cells pre-treated with the PDK inhibitor dichloroacetate (DCA), with the aim of restoring PDH activity, partially recovered OCR and ECAR. The results suggest that the higher DOX concentration mainly induces p53-dependent apoptosis, whereas for the lower DOX concentration the cardiotoxic effects involve bioenergetic failure, unveiling PDH as a possible therapeutic target to decrease DOX cardiotoxicity.

Chemotherapeutic Drugs and Mitochondrial Dysfunction: Focus on Doxorubicin, Trastuzumab, and Sunitinib

Many cancer therapies produce toxic side effects whose molecular mechanisms await full elucidation. The most feared and studied side effect of chemotherapeutic drugs is cardiotoxicity. Also, skeletal muscle physiology impairment has been recorded after many chemotherapeutical treatments. However, only doxorubicin has been extensively studied for its side effects on skeletal muscle. Chemotherapeutic-induced adverse side effects are, in many cases, mediated by mitochondrial damage. In particular, trastuzumab and sunitinib toxicity is mainly associated with mitochondria impairment and is mostly reversible. Vice versa, doxorubicin-induced toxicity not only includes mitochondria damage but can also lead to a more robust and extensive cell injury which is often irreversible and lethal. Drugs interfering with mitochondrial functionality determine the depletion of ATP reservoirs and lead to subsequent reversible contractile dysfunction. Mitochondrial damage includes the impairment of the respiratory chain and the loss of mitochondrial membrane potential with subsequent disruption of cellular energetic. In a context of increased stress, AMPK has a key role in maintaining energy homeostasis, and inhibition of the AMPK pathway is one of the proposed mechanisms possibly mediating mitochondrial toxicity due to chemotherapeutics. Therapies targeting and protecting cell metabolism and energy management might be useful tools in protecting muscular tissues against the toxicity induced by chemotherapeutic drugs.

The beneficial role of exercise in mitigating doxorubicin-induced Mitochondrionopathy

Doxorubicin (DOX) is a widely used antineoplastic agent for a wide range of cancers, including hematological malignancies, soft tissue sarcomas and solid tumors. However, DOX exhibits a dose-related toxicity that results in life-threatening cardiomyopathy. In addition to the heart, there is evidence that DOX toxicity extends to other organs. This general toxicity seems to be related to mitochondrial network structural, molecular and functional impairments. Several countermeasures for these negative effects have been proposed, being physical exercise, not only one of the most effective non-pharmacologic strategy but also widely recommended as booster against cancer-related fatigue. It is widely accepted that mitochondria are critical sensors of tissue functionality, both modulated by DOX and exercise. Therefore, this review focuses on the current understanding of the mitochondrial-mediated mechanisms underlying the protective effect of exercise against DOX-induced toxicity, not only limited to the cardiac tissue, but also in other tissues such as skeletal muscle, liver and brain. We here analyze recent developments regarding the beneficial effects of exercise targeting mitochondrial responsive phenotypes against redox changes, mitochondrial bioenergetics, apoptotic, dynamics and quality control signalling affected by DOX treatment.

Mechanism of doxorubicin cardiotoxicity evaluated by integrating multiple molecular effects into a biophysical model

BACKGROUND AND PURPOSE

Doxorubicin (DOX) is an effective cancer therapeutic agent but causes therapy-limiting cardiotoxicity. The effects of DOX and its metabolite doxorubicinol (DOXL) on individual channels have been well characterized in isolation. However, it is unknown how the action and interaction of affected channels combine to generate the phenotypic cardiotoxic outcome. We sought to develop an in silico model that links drug effects on channels to action potential duration (APD) and intracellular Ca²⁺ concentration in order to address this gap in knowledge.

EXPERIMENTAL APPROACH

We first propose two methods to obtain, from published values, consensus drug effects on the currents of individual channels, transporters and pumps. Separately, we obtained equivalent values for APD and Ca²⁺ concentration (the readouts used as surrogates for cardiotoxicity). Once derived, the consensus effects on the currents were incorporated into established biophysical models of the cardiac myocyte and were refined adjusting the sarcoplasmic reticulum Ca²⁺ leak current (I_Leak ) until the consensus effects on APD and Ca²⁺ dynamics were replicated. Using factorial analysis, we then quantified the relative contribution of each channel to DOX and DOXL cardiotoxicity.

KEY RESULTS

The factorial analysis identified the rapid delayed rectifying K⁺ current, the L-type Ca²⁺ current and the sarcoplasmic reticulum I_Leak as the targets primarily responsible for the cardiotoxic effects on APD and Ca²⁺ dynamics.

CONCLUSIONS AND IMPLICATIONS

This study provides insight into the mechanisms of DOX-induced cardiotoxicity and a framework for the development of future diagnostic and therapeutic strategies.

Topoisomerases as anticancer targets

Many cancer type-specific anticancer agents have been developed and significant advances have been made toward precision medicine in cancer treatment. However, traditional or nonspecific anticancer drugs are still important for the treatment of many cancer patients whose cancers either do not respond to or have developed resistance to cancer-specific anticancer agents. DNA topoisomerases, especially type IIA topoisomerases, are proved therapeutic targets of anticancer and antibacterial drugs. Clinically successful topoisomerase-targeting anticancer drugs act through topoisomerase poisoning, which leads to replication fork arrest and double-strand break formation. Unfortunately, this unique mode of action is associated with the development of secondary cancers and cardiotoxicity. Structures of topoisomerase-drug-DNA ternary complexes have revealed the exact binding sites and mechanisms of topoisomerase poisons. Recent advances in the field have suggested a possibility of designing isoform-specific human topoisomerase II poisons, which may be developed as safer anticancer drugs. It may also be possible to design catalytic inhibitors of topoisomerases by targeting certain inactive conformations of these enzymes. Furthermore, identification of various new bacterial topoisomerase inhibitors and regulatory proteins may inspire the discovery of novel human topoisomerase inhibitors. Thus, topoisomerases remain as important therapeutic targets of anticancer agents.

Chemotherapeutic agents induce mitochondrial superoxide production and toxicity but do not alter respiration in skeletal muscle in vitro

Chemotherapeutic agents (CAs) can independently promote skeletal muscle dysfunction, fatigue and wasting with mitochondrial toxicity implicated as a possible mechanism. Thus, we aimed to characterise the effects of various CAs on mitochondrial function, viability and oxidant production in C2C12 myoblasts and myotubes. All CAs significantly reduced the viable mitochondrial pool but did not affect mitochondrial functional parameters. Doxorubicin and oxaliplatin increased oxidant production in myotubes while all CAs, except for irinotecan, increased oxidant production in myoblasts and reduced myotube diameter. Our data demonstrate CAs mito-toxic effects, highlighting the potential for mitochondria-protective therapeutics to address chemotherapy-induced skeletal muscle damage.

Molecular mechanism of doxorubicin-induced cardiomyopathy - An update

Doxorubicin is utilized for anti-neoplastic treatment for several decades. The utility of this drug is limited due to its side effects. Generally, doxorubicin toxicity is originated from the myocardium and then other organs are also ruined. The mechanism of doxorubicin is intercalated with the DNA and inhibits topoisomerase 2. There are various signalling mechanisms involved in doxorubicin cardiotoxicity. First and foremost, the doxorubicin-induced cardiotoxicity is due to oxidative stress. Cardiac mitochondrial damage is supposed after few hours following the revelation of doxorubicin. This has led important new uses for the mechanism of doxorubicin-induced cardiotoxicity and novel avenues of investigation to determine better pharmacotherapies and interventions for the impediment of cardiotoxicity. The idea of this review is to bring up to date the recent findings of the mechanism of doxorubicin cardiomyopathies such as calcium dysregulation, endoplasmic reticulum stress, impairment of progenitor cells, activation of immune, ubiquitous system and some other parameters.

Chemotherapy-Induced Tissue Injury: An Insight into the Role of Extracellular Vesicles-Mediated Oxidative Stress Responses

The short- and long-term side effects of chemotherapy limit the maximum therapeutic dose and impair quality of life of survivors. Injury to normal tissues, especially chemotherapy-induced cardiomyopathy, is an unintended outcome that presents devastating health impacts. Approximately half of the drugs approved by the Food and Drug Administration for cancer treatment are associated with the generation of reactive oxygen species, and Doxorubicin (Dox) is one of them. Dox undergoes redox cycling by involving its quinone structure in the production of superoxide free radicals, which are thought to be instrumental to the role it plays in cardiomyopathy. Dox-induced protein oxidation changes protein function, translocation, and aggregation that are toxic to cells. To maintain cellular homeostasis, oxidized proteins can be degraded intracellularly by ubiquitin-proteasome pathway or by autophagy, depending on the redox status of the cell. Alternatively, the cell can remove oxidized proteins by releasing extracellular vesicles (EVs), which can be transferred to neighboring or distant cells, thereby instigating an intercellular oxidative stress response. In this article, we discuss the role of EVs in oxidative stress response, the potential of EVs as sensitive biomarkers of oxidative stress, and the role of superoxide dismutase in attenuating EV-associated oxidative stress response resulting from chemotherapy.

BGP-15 Protects against Oxaliplatin-Induced Skeletal Myopathy and Mitochondrial Reactive Oxygen Species Production in Mice

Chemotherapy is a leading intervention against cancer. Albeit highly effective, chemotherapy has a multitude of deleterious side-effects including skeletal muscle wasting and fatigue, which considerably reduces patient quality of life and survivability. As such, a defense against chemotherapy-induced skeletal muscle dysfunction is required. Here we investigate the effects of oxaliplatin (OXA) treatment in mice on the skeletal muscle and mitochondria, and the capacity for the Poly ADP-ribose polymerase (PARP) inhibitor, BGP-15, to ameliorate any pathological side-effects induced by OXA. To do so, we investigated the effects of 2 weeks of OXA (3 mg/kg) treatment with and without BGP-15 (15 mg/kg). OXA induced a 15% (p < 0.05) reduction in lean tissue mass without significant changes in food consumption or energy expenditure. OXA treatment also altered the muscle architecture, increasing collagen deposition, neutral lipid and Ca²⁺ accumulation; all of which were ameliorated with BGP-15 adjunct therapy. Here, we are the first to show that OXA penetrates the mitochondria, and, as a possible consequence of this, increases mtROS production. These data correspond with reduced diameter of isolated FDB fibers and shift in the fiber size distribution frequency of TA to the left. There was a tendency for reduction in intramuscular protein content, albeit apparently not via Murf1 (atrophy)- or p62 (autophagy)- dependent pathways. BGP-15 adjunct therapy protected against increased ROS production and improved mitochondrial viability 4-fold and preserved fiber diameter and number. Our study highlights BGP-15 as a potential adjunct therapy to address chemotherapy-induced skeletal muscle and mitochondrial pathology.

Anthracycline Chemotherapy and Cardiotoxicity

Anthracycline chemotherapy maintains a prominent role in treating many forms of cancer. Cardiotoxic side effects limit their dosing and improved cancer outcomes expose the cancer survivor to increased cardiovascular morbidity and mortality. The basic mechanisms of cardiotoxicity may involve direct pathways for reactive oxygen species generation and topoisomerase 2 as well as other indirect pathways. Cardioprotective treatments are few and those that have been examined include renin angiotensin system blockade, beta blockers, or the iron chelator dexrazoxane. New treatments exploiting the ErbB or other novel pro-survival pathways, such as conditioning, are on the cardioprotection horizon. Even in the forthcoming era of targeted cancer therapies, the substantial proportion of today's anthracycline-treated cancer patients may become tomorrow's cardiac patient.

Doxorubicin caused severe hyperglycaemia and insulin resistance, mediated by inhibition in AMPk signalling in skeletal muscle

BACKGROUND

Cancer is considered the second leading cause of death in the world, and for the treatment of this disease, pharmacological intervention strategies are frequently based on chemotherapy. Doxorubicin (DOX) is one of the most widely used chemotherapeutic agents in clinical practice for treating a number of solid tumours. The treatment with DOX mimics some effects of cancer cachexia, such as anorexia, asthenia, decreases in fat and skeletal muscle mass and fatigue. We observed that treatment with DOX increased the systemic insulin resistance and caused a massive increase in glucose levels in serum. Skeletal muscle is a major tissue responsible for glucose uptake, and the positive role of AMPk protein (AMP-activated protein kinase) in GLUT-4 (Glucose Transporter type 4) translocation, is well established. With this, our aim was to assess the insulin sensitivity after treatment with DOX and involvement of AMPk signalling in skeletal muscle in this process.

METHODS

We used Wistar rats which received a single dose of doxorubicin (DOX group) or saline (CT group) intraperitoneally at a dose of 15 mg/kg b.w. The expression of proteins involved in insulin sensitivity, glucose uptake, inflammation, and activity of electron transport chain was assessed in extensor digitorum longus muscle, as well as the histological evaluation. In vitro assays were performed in L6 myocytes to assess glucose uptake after treatment with DOX. Agonist of AMPk [5-aminoimidazole-4-carboxamide (AICAR)] and the antioxidant n-acetyl cysteine were used in L6 cells to evaluate its effect on glucose uptake and cell viability.

RESULTS

The animals showed a significant insulin resistance, hyperglycaemia, and hyperinsulinemia. A decrease in the expression of AMKP and GLUT-4 was observed in the extensor digitorum longus muscle. Also in L6 cells, DOX leads to a decrease in glucose uptake, which is reversed with AICAR.

CONCLUSIONS

DOX leads to conditions similar to cachexia, with severe glucose intolerance both in vivo and in vitro. The decrease of AMPk activity of the protein is modulated negatively with DOX, and treatment with agonist of AMPk (AICAR) has proved to be a possible therapeutic target, which is able to recover glucose sensitivity in skeletal muscle.

A Biophysical Systems Approach to Identifying the Pathways of Acute and Chronic Doxorubicin Mitochondrial Cardiotoxicity

The clinical use of the anthracycline doxorubicin is limited by its cardiotoxicity which is associated with mitochondrial dysfunction. Redox cycling, mitochondrial DNA damage and electron transport chain inhibition have been identified as potential mechanisms of toxicity. However, the relative roles of each of these proposed mechanisms are still not fully understood. The purpose of this study is to identify which of these pathways independently or in combination are responsible for doxorubicin toxicity. A state of the art mathematical model of the mitochondria including the citric acid cycle, electron transport chain and ROS production and scavenging systems was extended by incorporating a novel representation for mitochondrial DNA damage and repair. In silico experiments were performed to quantify the contributions of each of the toxicity mechanisms to mitochondrial dysfunction during the acute and chronic stages of toxicity. Simulations predict that redox cycling has a minor role in doxorubicin cardiotoxicity. Electron transport chain inhibition is the main pathway for acute toxicity for supratherapeutic doses, being lethal at mitochondrial concentrations higher than 200μM. Direct mitochondrial DNA damage is the principal pathway of chronic cardiotoxicity for therapeutic doses, leading to a progressive and irreversible long term mitochondrial dysfunction.

Sex-related differential susceptibility to doxorubicin-induced cardiotoxicity in B6C3F1 mice

Sex is a risk factor for development of cardiotoxicity, induced by the anti-cancer drug, doxorubicin (DOX), in humans. To explore potential mechanisms underlying differential susceptibility to DOX between sexes, 8-week old male and female B6C3F₁ mice were dosed with 3mg/kg body weight DOX or an equivalent volume of saline via tail vein once a week for 6, 7, 8, and 9 consecutive weeks, resulting in 18, 21, 24, and 27mg/kg cumulative DOX doses, respectively. At necropsy, one week after each consecutive final dose, the extent of myocardial injury was greater in male mice compared to females as indicated by higher plasma concentrations of cardiac troponin T at all cumulative DOX doses with statistically significant differences between sexes at the 21 and 24mg/kg cumulative doses. A greater susceptibility to DOX in male mice was further confirmed by the presence of cytoplasmic vacuolization in cardiomyocytes, with left atrium being more vulnerable to DOX cardiotoxicity. The number of TUNEL-positive cardiomyocytes was mostly higher in DOX-treated male mice compared to female counterparts, showing a statistically significant sex-related difference only in left atrium at 21mg/kg cumulative dose. DOX-treated male mice also had an increased number of γ-H2A.X-positive (measure of DNA double-strand breaks) cardiomyocytes compared to female counterparts with a significant sex effect in the ventricle at 27mg/kg cumulative dose and right atrium at 21 and 27mg/kg cumulative doses. This newly established mouse model provides a means to identify biomarkers and access potential mechanisms underlying sex-related differences in DOX-induced cardiotoxicity.

Coenzyme Q10 for Prevention of Anthracycline-Induced Cardiotoxicity

Preclinical and clinical studies suggest that anthracycline-induced cardiotoxicity can be prevented by administering coenzyme Q10 during cancer chemotherapy that includes drugs such as doxorubicin and daunorubicin. Studies further suggest that coenzyme Q10 does not interfere with the antineoplastic action of anthracyclines and might even enhance their anticancer effects. Preventing cardiotoxicity might allow for escalation of the anthracycline dose, which would further enhance the anticancer effects. Based on clinical investigation, although limited, a cumulative dose of doxorubicin of up to 900 mg/m2, and possibly higher, can be administered safely during chemotherapy as long as coenzyme Q10 is administered concurrently. The etiology of the dose-limiting cardiomyopathy that is induced by anthracyclines can be explained by irreversible damage to heart cell mitochondria, which differ from mitochondria of other cells in that they possess a unique enzyme on the inner mitochondrial membrane. This enzyme reduces anthracyclines to their semiquinones, resulting in severe oxidative stress, disruption of mitochondrial energetics, and irreversible damage to mitochondrial DNA. Damage to mitochondrial DNA blocks the regenerative capability of the organelle and ultimately leads to apoptosis or necrosis of myocytes. Coenzyme Q10, an essential component of the electron transport system and a potent intracellular antioxidant, appears to prevent damage to the mitochondria of the heart, thus preventing the development of anthracycline-induced cardiomyopathy.

Cardiac cytochrome c and cardiolipin depletion during anthracycline-induced chronic depression of mitochondrial function

AIMS

It is still unclear why anthracycline treatment results in a cardiac-specific myopathy. We investigated whether selective doxorubicin (DOX) cardiotoxicity involving mitochondrial degeneration is explained by different respiratory complexes reserves between tissues by comparing and contrasting treatment effects in heart vs liver and kidney. Alternatively, we have also explored if the degeneration is due to alterations of mitochondrial thresholds to incompatible states.

METHODS AND RESULTS

Heart, liver and kidney mitochondria were isolated from male Wistar rats weekly injected with DOX during 7weeks. Global flux and isolated step curves were obtained for Complex I, III, IV, as well as for the adenine nucleotide translocator. We show treatment-related alterations in global flux curve for Complex III in all analyzed tissues and in Complex IV activity curve solely in heart. However, all mitochondrial threshold curves remained unchanged after treatment in the analyzed tissues. No treatment-related differences were detected on transcript or protein analysis of selected respiratory complexes subunits. However, a specific loss of cytochrome c and cardiolipin was measured in heart, but not in other organs, mitochondria from DOX-treated animals.

CONCLUSIONS

Contrary to our hypothesis, impaired mitochondrial respiration could not be explained by intrinsic differences in respiratory complexes reserves among tissues or, by alterations in mitochondrial thresholds after treatment. Instead, we propose that loss of cytochrome c and cardiolipin are responsible for the depressed mitochondrial respiration observed after chronic DOX treatment. Moreover, cardiac cytochrome c and cardiolipin depletion decreases metabolic network buffering, hindering cardiac ability to respond to increased workload, accelerating cardiac aging.

Review : Amifostine and other chemoprotective agents in cancer chemotherapy: A brief review

Objective. Cytotoxic chemotherapy is a frequently, and increasingly, used treatment for malignant disease and is associated with substantial toxicity. A number of drugs have been developed in recent years for the prevention and treatment of chemotherapy-induced toxicity. Most are specific to one group of drugs, eg, mesna and the oxazophosphorines, or one type of toxicity, eg, the 5-HT3 antagonist antiemetics. The first multiorgan cytoprotective, amifostine, recently was launched, and another, glutathione, is under development. The purpose of this review is to con sider the agents currently available for the manage ment of cytotoxic drug-induced toxicity and their place in treatment. Special attention is directed to amifostine and drugs in development, including glu tathione, Ossirene (Baker Norton), ORG-2766, and dexrazoxane and less to agents in routine clinical use.

Data sources. A variety of sources were used, including manual and on-line (Medline) literature searching. Approved and other drug names were used as the primary search terms, linked with cytotoxic chemotherapy where limitation was required. Medi cal information departments of drug companies also were used where appropriate.

Study selection. Particular attention was directed to randomized clinical trials, but nonrandomised and animal studies were considered where appropriate.

Conclusions. Over the past decade significant advances have been made in the control of chemo therapy-induced toxicity and new agents promise even greater control. This is important, not only because they may improve the quality of life of conventionally treated cancer patients, but also be cause they should allow the dose-response relation ship for cytotoxic drug treatment to be fully explored. Unfortunately, the data available at present are insuf ficient to determine the extent to which this promise will be fulfilled.

Phosphodiesterase 5 Inhibition Limits Doxorubicin-induced Heart Failure by Attenuating Protein Kinase G Iα Oxidation

Phosphodiesterase 5 (PDE5) inhibitors limit myocardial injury caused by stresses, including doxorubicin chemotherapy. cGMP binding to PKG Iα attenuates oxidant-induced disulfide formation. Because PDE5 inhibition elevates cGMP and protects from doxorubicin-induced injury, we reasoned that this may be because it limits PKG Iα disulfide formation. To investigate the role of PKG Iα disulfide dimerization in the development of apoptosis, doxorubicin-induced cardiomyopathy was compared in male wild type (WT) or disulfide-resistant C42S PKG Iα knock-in (KI) mice. Echocardiography showed that doxorubicin treatment caused loss of myocardial tissue and depressed left ventricular function in WT mice. Doxorubicin also reduced pro-survival signaling and increased apoptosis in WT hearts. In contrast, KI mice were markedly resistant to the dysfunction induced by doxorubicin in WTs. In follow-on experiments the influence of the PDE5 inhibitor tadalafil on the development of doxorubicin-induced cardiomyopathy in WT and KI mice was investigated. In WT mice, co-administration of tadalafil with doxorubicin reduced PKG Iα oxidation caused by doxorubicin and also protected against cardiac injury and loss of function. KI mice were again innately resistant to doxorubicin-induced cardiotoxicity, and therefore tadalafil afforded no additional protection. Doxorubicin decreased phosphorylation of RhoA (Ser-188), stimulating its GTPase activity to activate Rho-associated protein kinase (ROCK) in WTs. These pro-apoptotic events were absent in KI mice and were attenuated in WTs co-administered tadalafil. PKG Iα disulfide formation triggers cardiac injury, and this initiation of maladaptive signaling can be blocked by pharmacological therapies that elevate cGMP, which binds kinase to limit its oxidation.

Mitochondrial Function, Biology, and Role in Disease: A Scientific Statement From the American Heart Association

Cardiovascular disease is a major leading cause of morbidity and mortality in the United States and elsewhere. Alterations in mitochondrial function are increasingly being recognized as a contributing factor in myocardial infarction and in patients presenting with cardiomyopathy. Recent understanding of the complex interaction of the mitochondria in regulating metabolism and cell death can provide novel insight and therapeutic targets. The purpose of this statement is to better define the potential role of mitochondria in the genesis of cardiovascular disease such as ischemia and heart failure. To accomplish this, we will define the key mitochondrial processes that play a role in cardiovascular disease that are potential targets for novel therapeutic interventions. This is an exciting time in mitochondrial research. The past decade has provided novel insight into the role of mitochondria function and their importance in complex diseases. This statement will define the key roles that mitochondria play in cardiovascular physiology and disease and provide insight into how mitochondrial defects can contribute to cardiovascular disease; it will also discuss potential biomarkers of mitochondrial disease and suggest potential novel therapeutic approaches.

Mechanisms of Doxorubicin Toxicity in Pancreatic β-Cells

Exposure to chemotherapeutic agents has been linked to an increased risk of type 2 diabetes (T2D), a disease characterized by both the peripheral insulin resistance and impaired glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells. Using the rat β-cell line INS-1 832/13 and isolated mouse pancreatic islets, we investigated the effect of the chemotherapeutic drug doxorubicin (Adriamycin) on pancreatic β-cell survival and function. Exposure of INS-1 832/13 cells to doxorubicin caused impairment of GSIS, cellular viability, an increase in cellular toxicity, as soon as 6 h post-exposure. Doxorubicin impaired plasma membrane electron transport (PMET), a pathway dependent on reduced equivalents NADH and NADPH, but failed to redox cycle in INS-1 832/13 cells and with their lysates. Although NADPH/NADP(+ )content was unaffected, NADH/NAD(+ )content decreased at 4 h post-exposure to doxorubicin, and was followed by a reduction in ATP content. Previous studies have demonstrated that doxorubicin functions as a topoisomerase II inhibitor via induction of DNA cross-linking, resulting in apoptosis. Doxorubicin induced the expression of mRNA for mdm2, cyclin G1, and fas whereas downregulating p53, and increased the melting temperature of genomic DNA, consistent with DNA damage and induction of apoptosis. Doxorubicin also induced caspase-3 and -7 activity in INS-1 832/13 cells and mouse islets; co-treatment with the pan-caspase inhibitor Z-VAD-FMK temporarily attenuated the doxorubicin-mediated loss of viability in INS-1 832/13 cells. Together, these data suggest that DNA damage, not H2O2 produced via redox cycling, is a major mechanism of doxorubicin toxicity in pancreatic β-cells.

Mitochondria: Inadvertent targets in chemotherapy-induced skeletal muscle toxicity and wasting?

Chemotherapy has been associated with increased mitochondrial reactive oxygen species production, mitochondrial dysfunction and skeletal muscle atrophy leading to severe patient clinical complications including skeletal muscle fatigue, insulin resistance and wasting. The exact mechanisms behind this skeletal muscle toxicity are largely unknown, and as such co-therapies to attenuate chemotherapy-induced side effects are lacking. Here, we review the current literature describing the clinical manifestations and molecular origins of chemotherapy-induced myopathy with a focus on the mitochondria as the target organelle via which chemotherapeutic agents establish toxicity. We explore the likely mechanisms through which myopathy is induced, using the anthracycline doxorubicin, and the platinum-based alkylating agent oxaliplatin, as examples. Finally, we recommend directions for future research and outline the potential significance of these proposed directions.

Oxidative Stress Induced Ventricular Arrhythmia and Impairment of Cardiac Function in Nos1ap Deleted Mice

Genome-wide association study has identified that the genetic variations at NOS1AP (neuronal nitric oxide synthase-1 adaptor protein) were associated with QT interval and sudden cardiac death (SCD). However, the mechanism linking a genetic variant of NOS1AP and SCD is poorly understood. We used Nos1ap knockout mice (Nos1ap(-/-)) to determine the involvement of Nos1ap in SCD, paying special attention to oxidative stress.At baseline, a surface electrocardiogram (ECG) and ultrasound echocardiography (UCG) showed no difference between Nos1ap(-/-) and wild-type (WT) mice. Oxidative stress was induced by a single injection of doxorubicin (Dox, 25 mg/kg). After Dox injection, Nos1ap(-/-) showed significantly higher mortality than WT (93.3 versus 16.0% at day 14, P < 0.01). ECG showed significantly longer QTc in Nos1ap(-/-) than WT, and UCG revealed significant reduction of fractional shortening (%FS) only in Nos1ap(-/-) after Dox injection. Spontaneous ventricular tachyarrhythmias were documented by telemetry recording after Dox injection only in Nos1ap(-/-). Ex vivo optical mapping revealed that the action potential duration (APD)90 was prolonged at baseline in Nos1ap(-/-), and administration of Dox lengthened APD90 more in Nos1ap(-/-) than in WT. The expression of Bnp and the H2O2 level were higher in Nos1ap(-/-) after Dox injection. Nos1ap(-/-) showed a reduced amplitude of calcium transient in isolated cardiomyocytes after Dox injection. Administration of the antioxidant N-acetyl-L-cysteine significantly reduced mortality of Nos1ap(-/-) by Dox injection, accompanied by prevention of QT prolongation and a reduction in %FS.Although Nos1ap(-/-) mice have apparently normal hearts, oxidative stress evokes ventricular tachyarrhythmia and heart failure, which may cause sudden cardiac death.

Characterization of Fluorescein-Based Monoboronate Probe and Its Application to the Detection of Peroxynitrite in Endothelial Cells Treated with Doxorubicin

Boronate probes have emerged recently as a versatile tool for the detection of reactive oxygen and nitrogen species. Here, we present the characterization of a fluorescein-based monoboronate probe, a 4-(pinacol boronate)benzyl derivative of fluorescein methyl ester (FBBE), that proved to be useful to detect peroxynitrite in cell culture experiments. The reactivity of FBBE toward peroxynitrite as well hypochlorite, hydrogen peroxide, and tyrosyl hydroperoxide was determined. Second-order rate constants of the reactions of FBBE with peroxynitrite, HOCl, and H2O2 at pH 7.4 were equal to (2.8 ± 0.2) × 10(5) M(-1) s(-1), (8.6 ± 0.5) × 10(3) M(-1) s(-1), and (0.96 ± 0.03) M(-1) s(-1), respectively. The presence of glutathione completely blocked the oxidation of the probe by HOCl and significantly inhibited its oxidation by H2O2 and tyrosyl hydroperoxide but not by peroxynitrite. The oxidative conversion of the probe was also studied in the systems generating singlet oxygen, superoxide radical anion, and nitric oxide in the presence and absence of glutathione. Spectroscopic characterization of FBBE and its oxidation product has been also performed. The differences in the reactivity pattern were supported by DFT quantum mechanical calculations. Finally, the FBBE probe was used to study the oxidative stress in endothelial cells (Ea.hy926) incubated with doxorubicin, a quinone anthracycline antibiotic. In endothelial cells pretreated with doxorubicin, FBBE was oxidized, and this effect was reversed by PEG-SOD and L-NAME but not by catalase.