Model systems for cardiotoxic effects of anthracyclines

Modeling Doxorubicin-Induced Cardiomyopathy With Fibrotic Myocardial Damage in Wistar Rats

Background

Cardiovascular complications, arising after anthracycline chemotherapy, cause a significant deterioration in the life quality and expectancy of those patients who were previously successfully treated for malignant neoplasms. A number of clinical studies have demonstrated that patients with cardiotoxicity manifested during anthracyclines therapy also have extensive fibrotic changes in the cardiac muscle in the long term. Given the lack of an unambiguous understanding of the mechanisms of fibrotic changes formation under doxorubicin treatment in the myocardium, there is the obvious necessity to create a relevant experimental model of chronic doxorubicin-induced cardiomyopathy with fibrotic myocardial lesions and delayed development of diastolic dysfunction.

Methods

The study was divided into two stages: first stage (creation of acute doxorubicin cardiomyopathy) - 35 male Wistar rats; second stage (creation of chronic doxorubicin cardiomyopathy) - 40 male Wistar rats. The animals were split into eight groups (two control ones and six experimental ones), which determined the doxorubicin dose (first stage: 25, 20.4, 15 mg/kg; second stage: 5, 10, 15 mg/kg, intraperitoneally) and the frequency of injection. Echocardiographic, hematological, histological, and molecular methods were used to confirm the successful modeling of acute and chronic doxorubicin-induced cardiomyopathy with fibrotic lesions.

Results

A model of administration six times every other day with a cumulative dose of doxorubicin 20 mg/kg is suitable for evaluation of acute cardiotoxicity. The 15 mg/kg doxorubicin dose is highly cardiotoxic; what's more, it correlates with progressive deterioration of the clinical condition of the animals after 2 months. The optimal cumulative dose of doxorubicin leads to clinical manifestations confirmed by echocardiographic, histological, molecular changes associated with the development of chronic doxorubicin-induced cardiomyopathy with fibrotic lesions of the left ventricular of the cardiac muscle and ensure long-term survival of animals is 10 mg/kg doxorubicin. A dose of 5 mg/kg of the doxorubicin does not ensure the development of fibrous changes formation.

Conclusion

We assume that cumulative dose of 10 mg/kg with a frequency of administration of six times in 2 days can be used to study the mechanisms of anthracycline cardiomyopathy development.

Analysis of Models of Doxorubicin-Induced Cardiomyopathy in Rats and Mice. A Modern View From the Perspective of the Pathophysiologist and the Clinician

Today the pharmacological possibilities of treating cancer are expanding and as a result, life expectancy is increasing against the background of chemotherapy and supportive treatment. In the conditions of successful antitumor treatment, complications associated with its toxic effect on healthy tissues and organs began to come to the fore. Anthracycline cardiomyopathy was the first serious cardiovascular complication to draw the attention of oncologists and cardiologists around the world. Anthracycline drugs such as doxorubicin, epirubicin, idarubicin are still widely used in oncological practice to treat a wide range of solid and hematological malignancies. Doxorubicin-induced cardiomyopathy is closely associated with an increase in oxidative stress, as evidenced by reactive oxygen species (ROS) nduced damage such as lipid peroxidation, and decreased levels of antioxidants. Myofibrillar destruction and dysregulation of intracellular calcium are also important mechanisms, usually associated with doxorubicin-induced cardiotoxicity. Despite the abundance of data on various mechanisms involved in the implementation of doxorubicin-induced cardiotoxicity, a final understanding of the mechanism of the development of doxorubicin cardiomyopathy has not yet been formed. It poses the most significant challenges to the development of new methods of prevention and treatment, as well as to the unambiguous choice of a specific treatment regimen using the existing pharmacological tools. In order to resolve these issues new models that could reflect the development of the chemotherapy drugs effects are needed. In this review we have summarized and analyzed information on the main existing models of doxorubicin cardiomyopathy using small laboratory animals. In addition, this paper discusses further areas of research devoted to the development and validation of new improved models of doxorubicin cardiomyopathy suitable both for studying the mechanisms of its implementation and for the preclinical drugs effectiveness assessment.

Improving the preclinical models for the study of chemotherapy-induced cardiotoxicity: a Position Paper of the Italian Working Group on Drug Cardiotoxicity and Cardioprotection

Although treatment for heart failure induced by cancer therapy has improved in recent years, the prevalence of cardiomyopathy due to antineoplastic therapy remains significant worldwide. In addition to traditional mediators of myocardial damage, such as reactive oxygen species, new pathways and target cells should be considered responsible for the impairment of cardiac function during anticancer treatment. Accordingly, there is a need to develop novel therapeutic strategies to protect the heart from pharmacologic injury, and improve clinical outcomes in cancer patients. The development of novel protective therapies requires testing putative therapeutic strategies in appropriate animal models of chemotherapy-induced cardiomyopathy. This Position Paper of the Working Group on Drug Cardiotoxicity and Cardioprotection of the Italian Society of Cardiology aims to: (1) define the distinctive etiopatogenetic features of cardiac toxicity induced by cancer therapy in humans, which include new aspects of mitochondrial function and oxidative stress, neuregulin-1 modulation through the ErbB receptor family, angiogenesis inhibition, and cardiac stem cell depletion and/or dysfunction; (2) review the new, more promising therapeutic strategies for cardioprotection, aimed to increase the survival of patients with severe antineoplastic-induced cardiotoxicity; (3) recommend the distinctive pathological features of cardiotoxicity induced by cancer therapy in humans that should be present in animal models used to identify or to test new cardioprotective therapies.

Autophagy in cardiovascular biology

Cardiovascular disease is the leading cause of death worldwide. As such, there is great interest in identifying novel mechanisms that govern the cardiovascular response to disease-related stress. First described in failing hearts, autophagy within the cardiovascular system has been widely characterized in cardiomyocytes, cardiac fibroblasts, endothelial cells, vascular smooth muscle cells, and macrophages. In all cases, a window of optimal autophagic activity appears to be critical to the maintenance of cardiovascular homeostasis and function; excessive or insufficient levels of autophagic flux can each contribute to heart disease pathogenesis. In this Review, we discuss the potential for targeting autophagy therapeutically and our vision for where this exciting biology may lead in the future.

Tuning flux: autophagy as a target of heart disease therapy

PURPOSE OF REVIEW

Despite maximum medical and mechanical support therapy, heart failure remains a relentlessly progressive disorder with substantial morbidity and mortality. Autophagy, an evolutionarily conserved process of cellular cannibalization, has been implicated in virtually all forms of cardiovascular disease. Indeed, its role is context dependent, antagonizing or promoting disease depending on the circumstance. Here, we review current understanding of the role of autophagy in the pathogenesis of heart failure and explore this pathway as a target of therapeutic intervention.

RECENT FINDINGS

In preclinical models of heart disease, cardiomyocyte autophagic flux is activated; indeed, its role in disease pathogenesis is the subject of intense investigation to define mechanism. Similarly, in failing human heart of a variety of etiologies, cardiomyocyte autophagic activity is upregulated, and therapy, such as with mechanical support systems, elicits declines in autophagy activity. However, when suppression of autophagy is complete, rapid and catastrophic cell death occurs, consistent with a model in which basal autophagic flux is required for proteostasis. Thus, a narrow zone of 'optimal' autophagy seems to exist. The challenge moving forward is to tune the stress-triggered autophagic response within that 'sweet spot' range for therapeutic benefit.

SUMMARY

Whereas we have known for some years of the participation of lysosomal mechanisms in heart disease, it is only recently that upstream mechanisms (autophagy) are being explored. The challenge for the future is to dissect the underlying circuitry and titrate the response into an optimal, proteostasis-promoting range in hopes of mitigating the ever-expanding epidemic of heart failure.

Electrochemical Reduction of Quinones in Different Media: A Review

The electron transfer reactions involving quinones, hydroquinones, and catechols are very important in many areas of chemistry, especially in biological systems. The therapeutic efficiency as well as toxicity of anthracycline anticancer drugs, a class of anthraquinones, is governed by their electrochemical properties. Other quinones serve as important functional moiety in various biological systems like electron-proton carriers in the respiratory chain and their involvement in photosynthetic electron flow systems. The present paper summarizes literatures on the reduction of quinones in different solvents under various conditions using different electrochemical methods. The influence of different reaction conditions including pH of the media, nature of supporting electrolytes, nature of other additives, intramolecular or intermolecular hydrogen bonding, ion pair formation, polarity of the solvents, stabilization of the semiquinone and quinone dianion, catalytic property, and adsorption at the electrode surface, are discussed and relationships between reaction conditions and products formed have been presented.

Preclinical cardiac safety assessment of drugs

The heart is a frequent site of toxicity of pharmaceutical compounds in humans, and when developing a new drug it is critical to conduct a thorough preclinical evaluation of its possible adverse effects on cardiac structure and function. Changes in cardiac morphology such as myocardial necrosis, hypertrophy or valvulopathy are assessed in regulatory toxicity studies in laboratory animals, although specific models may be needed for a more accurate detection of the risk. The potential proarrhythmic risk of new drugs is a major subject of concern and needs to be fully addressed before treatment of volunteers or patients takes place. In vitro assays are conducted to determine the effects on cardiac ion channels, in particular I(Kr) potassium channel antagonism. Prolongation of the QT interval is assessed in vivo, generally in telemetered dogs. Together, these two tests are considered to detect most arrhythmic drugs. The results of this core battery can be refined by additional studies, in particular assays on isolated cardiac tissues determining changes in cardiac action potential duration, shape and variability over time. Triggering of arrhythmia is assessed in hypokalaemic dogs with artificially created bradycardia, or in vitro in isolated whole hearts. The proarrhythmic risk of the new compound is then evaluated by integrating the results of these different tests. Drug adverse effects on cardiac electrophysiological function, in particular impulse formation and conduction, are evaluated through changes in ECG, generally recorded in dogs, pigs or monkeys. Changes in cardiac contractility occurring either as a primary effect of the drug on cardiac function or as a consequence of cardiac lesions should also be carefully assessed. In telemetered or anaesthetised animals, cardiac contractility is evaluated by measurement of left ventricular pressure and its first derivative over time. Echocardiography allows non-invasive measurement of drug-induced changes in ventricular wall movements and cardiac haemodynamics indicative of effects on contractility. In conclusion, a reliable and accurate evaluation of the cardiac safety of a new pharmaceutical agent is based on the results of in vitro tests, with overall moderate to high throughput, and in vivo experiments assessing the effects of the drug on the heart in its physiological environment. The specific sensitivities of the animals used in these assays to cardiac adverse effects should also be considered. The final evaluation of the cardiac risk is therefore based on an integrated analysis of the results from a battery of tests.

Fas-mediated apoptosis in adriamycin-induced cardiomyopathy in rats: In vivo study

BACKGROUND

The precise molecular mechanism of Adriamycin-induced cardiomyopathy (ADR-CM) is still unknown. We address the demonstration of apoptotic myocardial cell death and the apoptosis-inducing molecules in ADR-CM induced in rats.

METHODS AND RESULTS

Until 8 weeks after the first administration of ADR, there was no increase in the number of labeled cells by terminal deoxynucleotidyl transferase assay (TUNEL method). Apoptotic indices increased significantly at weeks 9 and 10 in hearts of the ADR-treated group but not in those of the control group (0.42+/-0.12% versus 0.10+/-0.02% and 0.86+/-0.11% versus 0.09+/-0.04% at weeks 9 and 10, respectively). DNA ladder formation was also observed in the myocardial tissues during the late stages of the ADR-CM of rats. There was no significant difference in expression of p53 gene between the ADR group and the control group at either the message or the protein level. An overexpression of Fas antigen was shown in myocardial cells of ADR-treated hearts at weeks 9 and 10 by both Western blotting and immunofluorescent staining. Furthermore, we confirmed that neutralization of anti-Fas ligand antibody inhibited ADR-induced apoptosis.

CONCLUSIONS

Apoptotic cell death was observed in the hearts of ADR-CM rats, and the number of apoptotic myocardial cells increased with the deterioration of morphological findings and cardiac function, indicating that apoptosis may be an important mechanism of loss of myocardial cells and cardiac dysfunction in ADR-CM. Apoptosis in ADR-CM rats is not p53-dependent but rather is executed through a Fas-mediated pathway.

Adriamycin-induced heart failure: mechanism and modulation

Adriamycin (doxorubicin) is one of the most effective chemotherapeutic agents against a variety of cancers, but its usefulness is seriously curtailed by the risk of developing heart failure. Available laboratory evidence suggests that an increase in oxidative stress, brought about by increased free radical production and decreased myocardial endogenous antioxidants, plays an important role in the pathogenesis of heart failure. Adriamycin-induced apoptosis and hyperlipidemia may also be involved in the process. Probucol, a lipid-lowering drug and an antioxidant, completely prevents the occurrence of heart failure by reducing oxidative stress as well as by the modulation of apoptosis and high lipid concentrations. Thus, combined therapy with adriamycin and probucol has a high potential for optimizing the treatment of cancer patients.

Sex dependent electrocardiogram (ECG) changes in anthracycline-treated mice

Single administration of 2 mg/kg Violamycin B I induces a cardiomyopathy in mice associated with prolongation of the QRS- and S alpha T-segment in the electrocardiogram (ECG). The changes of the QRS-segment were independent of sex (males: control 6.10 ms +/- 0.41, 8 days after Violamycin B I application 9.13 ms +/- 1.16; females: control 6.41 ms +/- 0.46, 8 days after Violamycin B I application 8.78 ms +/- 0.83), the prolongation of the S alpha T-segment in males (control 3.52 ms +/- 0.21, 8 days after Violamycin B I application 11.18 ms +/- 2.25) was significantly stronger than in females (control 3.46 ms +/- 0.20, 8 days after Violamycin B I application 8.22 ms +/- 1.04). A reduction of the acetylcholine effect in the heart tissue could be responsible for the sex dependent prolongation of the S alpha T segment, because acetylcholine accelerates the repolarization which is part of the S alpha T segment, and the heart of females seems to have a greater amount of acetylcholine storage.

Evaluation of 4'-iodo-4'-deoxydoxorubicin-induced cardiotoxicity in two experimental rat models

In the present study, 1 single-dose and 1 multiple-dose models were applied in studying 4'-iodo-4'-deoxydoxorubicin (I-DX) cardiotoxicity. Anthracycline cardiotoxicity has been reproduced in several animals including mice, rats, hamsters, rabbits, dogs, and monkeys. Of these species the rat can be considered the most suitable species for the study of anthracycline-induced cardiomyopathy. The cardiotoxicity induced by I-DX in male Sprague-Dawley rats was compared to that of doxorubicin (DX), used as standard positive control. Groups of 36-42 rats were observed for up to 35 wk to follow the progression of the lesions. Cardiomyopathy was evaluated through well-established qualitative/quantitative morphological grading. The new DX derivative proved to be clearly less cardiotoxic than DX with both treatment schedules. Although both models can be considered useful for evaluating and comparing the cardiotoxicity of new anthracycline derivatives and mimicking the transvenous endomyocardial biopsies in humans, the chronic test seems to be more suitable for compounds like I-DX, which possess a low cardiotoxic potential and which could go undetected in the single-dose test.

Survival, body weight, and spontaneous neoplasms in ad Libitum-fed and food-restricted Fischer-344 rats

Ad libitum-fed (AL) and food-restricted (FR) Fischer-344 male and female rats were monitored for survival, body weight, and spontaneous neoplasms. Mean and maximal lifespans for each group were inversely related to mean body weights. AL males were the shortest lived (mean lifespan 101 wk) followed by AL females (118 wk), FR males (125 wk), and FR females (132 wk). Gross and microscopic examinations were performed on 851 rats from cross-sectional and longevity components of the study. In FR groups, the incidence of mammary gland fibroadenomas, testicular interstitial cell tumors, and pituitary neoplasms was decreased while the latency of these neoplasms was increased. In longevity components, most FR groups had a higher incidence of leukemia than AL cohorts, but all FR groups had a higher mean age at death for the rats with leukemia. Higher leukemia rate in the FR groups was thought to be a result of their extended mean lifespan.

In-vivo and in-vitro mitochondrial membrane damages induced in mice by adriamycin and derivatives

A major limitation to a prolonged use of adriamycin (ADM) during a clinical treatment is its dose-dependent cardiotoxicity. This toxicity has been related to a general disturbance of the inner mitochondrial membrane structure and its essential biological functions, associated to the production of free radicals by the anthracyclines. 4'-Epiadriamycin (4'-epiADM), 4'-deoxyadriamycin (4'-deoxyADM), 4'-deoxy-4'-iodoadriamycin (4'-deoxy-4'-iodoADM) and 4'-demethoxydaunorubicin (4-demethoxyDNR) are ADM and daunorubicin (DNR) derivatives differing from their parent compounds by minor structural modifications. They are nevertheless documented as less cardiotoxic. Our purpose was to establish whether mitochondrial membrane damages induced in vivo in mice heart by those compounds are correlated with the free radical formation. Heart mitochondria of treated mice were isolated 48 h after a single drug injection in order to measure the acute mitochondrial toxicity. Enzymatic activities of complex I-III and complex IV of the mitochondrial respiratory chain, mitochondrial membrane fluidity and lipid peroxidation were measured. None of the ADM and DNR derivatives displayed a significant acute mitochondrial toxicity. A mitochondrial toxicity was however detected for 4-deoxyADM and 4-demethoxyDNR when drugs were given chronically, but it was strongly reduced as compared with ADM and DNR. Electron transfer between NADH and cytochrome c, formation of superoxide radicals and lipid peroxidation were measured in vitro for the various drugs. Comparison of the in-vivo and in-vitro results provides evidence that free radical production explains only partly the in-vivo toxicities.

Prevention of doxorubicin-induced myocardial and haematological toxicities in rats by the iron chelator desferrioxamine

Biochemical and histopathological evaluations of the protective effects of the iron-chelator desferrioxamine against the cardiac and haematological toxicities of doxorubicin in normal rats were carried out. A single dose of doxorubicin (15 mg/kg, i.v.) caused myocardial damage that manifested biochemically as an elevation of serum cardiac enzyme [glutamic oxaloacetic transaminase (GOT), lactic dehydrogenase (LDH) and creatine phosphokinase (CPK)] and cardiac isoenzyme levels and histopathologically as a swelling and separation of cardiac muscle fibers. Doxorubicin caused severe leucopenia and decreases in red blood cell counts and haemoglobin concentrations at 72 h after its administration. Desferrioxamine treatment (250 mg/kg, i.p.) carried out 30 min before doxorubicin administration protected the heart and blood elements from the toxic effects of doxorubicin as indicated by the recovery of levels of cardiac enzymes and isoenzymes and of red blood cell counts to normal values and by the absence of significant myocardial lesions. The findings of this study suggest that desferrioxamine can potentially be used clinically to prevent doxorubicin-induced cardiac and haematological toxicities.

Scintigraphic evaluation of myocardial uptake of thallium 201 and technetium 99m pyrophosphate utilizing a rat model of chronic doxorubicin cardiotoxicity

To evaluate the usefulness of myocardial scintigraphy as a monitoring tool for chronic doxorubicin (DXR) cardiotoxicity, a rat model was used to investigate the relationship between the myocardial uptake of thallium 201 (Tl) or rechnetium 99m pyrophosphate (99mTc-PPi) and histological changes of the heart. Although there was no significant difference in myocardial Tl uptake between control and DXR-treated rats at an early phase after Tl injection, late-phase Tl uptake was significantly higher in the DXR-treated rats than in the control rats, indicating a slow wash-out of Tl from the myocardium. The wash-out rate calculated from scintigraphic examination of DXR-treated rats was significantly decreased with increasing degree of cardiomyopathy. Since the Tl wash-out rate was sharply decreased even in animals with minimal histological changes, it may be a possible monitoring tool for the early detection of chronic DXR cardiotoxicity. On the other hand, myocardial 99mTc-PPi images could be obtained only in rats with severe myocardial changes and hence would not useful for early detection.

Fluorinated anthracyclines: interactions with DNA

Four fluorine containing derivatives of anthracyclines (daunomycin and adriamycin) were synthesised, and comprised C-13, 1,1,1-trifluoroethyl-hydrazones of each anthracycline, and C-14 4-F and 4-CF3-benzoate esters of adriamycin. All four derivatives intercalated into DNA in a manner similar to their parent anthracycline. The ester derivatives exhibited 3-4-fold higher binding affinity to DNA, and slower DNA dissociation kinetics than adriamycin. This stabilisation derives from additional contacts of the C-14 side chain to the DNA minor groove. The hydrazone derivatives showed lower binding affinity to DNA, and dissociated from DNA 3-4 times faster than the parent compound. The 19F resonance of the bound drug was broadened to 120 Hz and shifted 60 Hz downfield (0.32 ppm) relative to the sharp (7.5 Hz) peak of the free drug. These values imply a rapid exchange between the free and DNA bound forms (DNA lifetime greater than 5 ms), with the fluorine group residing in a hydrophobic region in close contact with the DNA minor groove. The 4-8 fold lesser specific potency of the ester derivatives supports the concept that DNA binding is an important factor, but not sole determinant of biological activity of these analogues.

Effects of recombinant human alpha-interferon in a rodent cardiotoxicity model

Recombinant human alpha-interferon infused intravenously into rats at doses of 10(6) (1st infusion) and 10(5) IU (2nd and 3rd infusion) produced marginal evidence of liver damage but no serious toxicity. During the 2nd and 3rd infusions an increased incidence of cardiac arrhythmias of various types was observed. In 2 rats electrocardiographic evidence of myocardial ischemia was noted. No changes in myocardial structure were demonstrated by light and electron microscopy. With the high dose the decrease in body temperature resulting from anesthesia was significantly reduced. Antibodies to interferon were demonstrated in the majority of the animals.

Laser time-resolved fluorescence study of the interaction between anthracyclines and cardiolipin

The molecular interaction between cardiolipin vesicles and two representative anthracyclines, daunomycin and 5-iminodaunomycin, has been studied at pH 7.1 by laser time-resolved fluorescence, for a cardiolipin-to-anthracycline ratio r ranging from 0.02 to 5. The fluorescence lifetime of daunomycin is 1.03 ns. For r = 0.3 - 5 a longer-lived transient (1.91 - 1.49 ns) is present and originates from the excitation of daunomycin bound on a single phosphate group of cardiolipin. At r = 0.3 two lifetimes are observed, the second one being due, partially, to free daunomycin and bound drug molecules embedded in the lipid bilayer. The fastest-decaying species is present for r = 0.5 - 2.0 and identified as two adjacent, stacked-up daunomycin molecules bound onto the two phosphate groups of the cardiolipin. In the case of 5-iminodaunomycin, a less cardiotoxic analogue, three-exponential decay is never observed and a fast-decaying component, pi approximately 0.2 ns, is already present at low r and vanishes for r greater than 0.5. The constancy of the lifetimes of the longer-lived species may originate from the reorientation of the bound drug from the hydrophilic to the lipid domain.

Enzymatic oxidative activation of 5-iminodaunorubicin. Spectrophotometric and electron paramagnetic resonance studies

Horseradish peroxidase catalyzed oxidation of the antitumor agent 5-iminodaunorubicin by hydrogen peroxide was studied with both spectrophotometric and electron paramagnetic resonance methods. Kinetics of oxidation of the drug at pH 3, 6 and 8 were determined. Rapid formation of a nitrogen-centered free radical metabolite was demonstrated with electron paramagnetic resonance employing the 15N-labeled drug and by deuterium exchange techniques. This enzymatic oxidative activation of 5-iminodaunorubicin suggests an alternative mode of metabolism and mechanism of action of this less cardiotoxic anticancer agent. By contrast, the parent compound, daunorubicin, did not undergo oxidation by the horseradish peroxidase-hydrogen peroxide system.

Free radical formation by antitumor quinones

Quinones are among the most frequently used drugs to treat human cancer. All of the antitumor quinones can undergo reversible enzymatic reduction and oxidation, and form semiquinone and oxygen radicals. For several antitumor quinones enzymatic reduction also leads to formation of alkylating species but whether this involves reduction to the semiquinone or the hydroquinone is not always clear. The antitumor activity of quinones is frequently linked to DNA damage caused by alkylating species or oxygen radicals. Some other effects of the antitumor quinones, such as cardiotoxicity and skin toxicity, may also be related to oxygen radical formation. The evidence for a relationship between radical formation and the biological activity of the antitumor quinones is evaluated.

Time- and dose-related modifications in cardiac function in rats after single intravenous doses of epirubicin

Time-related changes in cardiac output have been studied in rats after the intravenous administration of a range of single doses of epirubicin. There was an initial decline in cardiac function in the first 4-12 weeks after drug treatment at a rate that appeared to be dose-related. After 12 weeks, an average cardiac output of approximately 70%, relative to control values, was maintained in animals that survived until the end of the study. This effect was independent of the drug dose, reflecting the death of animals in the higher dose groups. The incidence of drug-induced cardiotoxic deaths, the majority of which (approximately 62%) occurred within the first 12 weeks, was dose-related, and suggested a LD50 for cardiac-related mortality of 5.48 +/- 0.39 mg/kg. There appeared to be a relationship between the reduction in cardiac output at 12 weeks and the probability of a further deterioration in function. Animals showing a greater than 40% reduction in cardiac output at 12 weeks accounted for greater than 90% of all the additional deaths between 12 and 20 weeks. Rats showing a less than 40% reduction in cardiac output at 12 weeks had a very high probability of surviving without clinical signs, although with a persistently depressed cardiac function. These findings are similar to the trends demonstrated in the sparse clinical data and this supports the view that the present simple animal model is suitable for the investigation of cardiotoxicity after the administration of cardiotoxic cytotoxic drugs.

Effects of three new anthracyclines and doxorubicin on the rat isolated heart

The acute cardiac toxicity of three second-generation anthracycline analogues and doxorubicin was compared in a model of the rat isolated Langendorff perfused heart. The drugs, doxorubicin (DX), 4-epi-doxorubicin (4'EDX), 4-demethoxy-daunorubicin (4DMDR) and 4'-deoxy-doxorubicin (4'dxDX) were infused for 40 min at a concentration of 26 microM into the isolated hearts. All four compounds significantly reduced cardiac work and its first derivative. The time to 50% decrease in work (TW50) was respectively 36, 23, 9 and 7 min for DX, 4'EDX, 4'dxDX and 4DMDR. The three anthracycline derivatives, but not DX, significantly increased coronary resistance. Heart rate was reduced by all compounds compared with baseline, but not compared with controls. Rhythm disturbances were seen with all five hearts perfused with 4DMDR, which stopped beating before 40 min; 2/5 hearts in the 4'EDX group and 1/5 hearts in the 4'dxDX group also stopped before the end of perfusion. All the compounds reached concentrations in the myocardium 8 to 50 times higher than in the perfusing medium. The more cardiotoxic the compound, the higher was its myocardial concentration; a significant correlation was found for all four agents. Noradrenaline was never measurable in the perfusate of control and DX hearts; perfusion with the three anthracycline derivatives caused some release, but the pattern was not clearcut and the maximum concentrations attained in the perfusate were relatively low (less than or equal to 1.6 X 10(-9) M). In conclusion, in the rat isolated perfused heart, the early cardiotoxicity induced by equimolar concentrations of the three anthracycline compounds was greater than that induced by DX and was directly related to drug accumulation in the myocardium. Catecholamines do not seem to have a major role in the development of toxicity in this model.

Effects of the anti-cancer drug adriamycin on the energy metabolism of rat heart as measured by in vivo 31P-NMR and implications for adriamycin-induced cardiotoxicity

In vivo 31P-NMR was used to measure the effects of the anti-tumor drug adriamycin on the energy metabolism of rat heart. The exclusive acquisition of NMR signal from cardiac muscle was assured by positioning a solenoidal radio-frequency NMR coil around the heart. Appropriate control experiments verified that 31P-NMR spectra solely originated from this organ. Acute effects occurring shortly after adriamycin administration are expressed in 31P spectra as a dose-dependent decline in the cardiac levels of phosphocreatine, after which stabilization at a new steady-state level occurs. These acute effects of a single dose are complete in 30-60 min and no significant further changes take place within 150 min after drug introduction. Longer-term effects of single high doses and of multiple lower doses were measured up to a week after the initiation of treatment. It seemed that at a total dose of 20 mg/kg, drug-induced interference with cardiac energy metabolism was more pronounced than at the same dose in the acute phase. These 31P-NMR data demonstrate that adriamycin treatment is accompanied by a decrease of the cardiac phosphocreatine/ATP ratio which might be an expression of the well-established cardiotoxicity of the drug.

The influence of inosine on adriamycin-induced cardiomyopathy in rats

The effect of inosine on adriamycin-induced cardiomyopathy was studied. Total adriamycin (ADR) dose of 25 mg/kg i.p. injected in 15 equal partial doses 3 times a week for five following weeks evoked fully developed cardiomyopathy in rats. Inosine 200 mg/kg i.p. injected 5 times a week parallel to ADR diminished ADR cardiotoxicity evaluated by electrocardiographic recordings and histopathological examination. Moreover lower cytostatic toxicity was observed as judged by less-expressed leucopenia and lower SGOT activities in inosine treated animals.

Structural requirements for inducing cardiotoxicity by anthracycline antibiotics: studies with neonatal rat cardiac myocytes in culture

Neonatal rat cardiac myocytes maintained in tissue culture were utilized to screen cardiotoxicity induced by a number of adriamycin and daunomycin analogs. Cell toxicity was assessed by leakage of cytoplasmic enzymes and was confirmed by electron microscopy. A number of modifications of structure of adriamycin and daunomycin markedly altered the incidence of toxicity caused by these drugs. Even though some of these structural alterations markedly altered lipid solubility or reactivity of quinone function, these changes did not always account for the differences in the toxicity induced by anthracycline analogs. The cardiomyocyte culture system used in this simple screening technique should be useful in the development of active anthracycline analog with least cardiotoxic potential.

One- and two-electron reduction of hydroxy-1,4-naphthoquinones and hydroxy-9,10-anthraquinones. The role of internal hydrogen bonding and its bearing on the redox chemistry of the anthracycline antitumour quinones

First and second half-wave reduction potentials of 11 1,4-naphthoquinones and 42 9,10-anthraquinones have been measured for solutions in dimethylformamide. The presence of hydroxy groups at the 5- and 8-positions of the 1,4-naphthoquinone nucleus, and at the 1-, 4-, 5- and 8-positions of the 9,10-anthraquinone (the alpha-positions) markedly raises both reduction potentials. Measurements on the corresponding methoxy- and acetoxyquinones indicate that internal hydrogen bonding in the alpha-hydroxyquinones makes a major contribution to stabilisation of the semiquinone, probably as a result of increased delocalisation due to exchange of the hydroxy hydrogen between the two neighbouring oxygen atoms. The bearing of this phenomenon on the mechanism of action of anthracycline antitumour quinones is discussed, and the stabilising effect on the semiquinone of hydroxy groups at the 1- and 5-positions of the 9,10-anthraquinone nucleus is highlighted.

Metabolism of 4'-modified analogs of doxorubicin. unique glucuronidation pathway for 4'-epidoxorubicin

The metabolism of doxorubicin (A), 4'-epidoxorubicin (E) and 4'-deoxydoxorubicin (D) was studied in vitro by incubating the analogs with rat liver subcellular fractions and in vivo by chromatographic analysis of human urine. Metabolites were identified by high-pressure liquid chromatography, fluorescence spectroscopy and enzymatic conversion. Human urine contained unchanged drug as well as the corresponding alcohol metabolites in all cases; however, urine of patients who received E also contained two glucuronides which could not be detected in the urine of patients who received A or D. We have identified these glucuronides as 4'-epidoxorubicin glucuronide (E-Glu) and 4'-epidoxorubicinol glucuronide (Eol-Glu). It was concluded that the glucuronide moiety is linked to the daunosamine sugar at the C4'-OH position. A hypothesis is proposed that this glucuronidation pathway may explain the differences in pharmacokinetics and toxicity between E and A. Rat liver microsomes were found to convert all three drugs to the 7-deoxyaglycones at the same rate. Rat liver 100,000 g supernatant was found to be capable of converting these drugs to their respective alcohol metabolites, doxorubicinol (Aol) being formed somewhat slower than 4'-epidoxorubicinol (Eol) and 4'-deoxydoxorubicinol (Dol).

Acute anthracycline cardiotoxicity. Comparative morphologic study of three analogues

Chemotherapeutic use of anthracycline antibiotics is limited by their cardiotoxic effects. A potential solution to this problem is the development of anthracycline analogues retaining antitumor efficacy but without cardiac toxicity. An isolated perfused rabbit heart model was used to compare the nature and extent of early ultrastructural effects on the myocyte of three anthracycline analogues purported to have lesser cardiotoxicity than Adriamycin (doxorubicin). Seventeen rabbit hearts were perfused with oxygenated Krebs-Ringer bicarbonate buffer at 39 degrees C containing either Adriamycin (4 mg/L), daunomycin (10.6 mg/L), aclacinomycin (8 mg/L), or rubidazone (17.6 mg/L). For comparison, three hearts each were exposed to phosphoramide mustard (14.7 mg or 25 mg/L) or 4-hydroperoxy cyclophosphamide (24 mg or 17 mg/L), two active congeners of cyclophosphamide, an agent interacting with DNA differently than the anthracyclines and which is known to be cardiotoxic in high dose. Two hearts were exposed to dactinomycin (0.1 mg or 0.2 mg/L) which intercalates with DNA in a manner similar to the anthracyclines but which is not cardiotoxic. Ten control hearts were perfused with oxygenated buffer solution only. Light microscopic study disclosed no differences between treated and control hearts. Electron microscopic examination showed a striking and distinctive clumping of nuclear chromatin with clearing of chromatin from the nuclear membrane in all anthracycline treated hearts but in no hearts treated with 4-hydroperoxy cyclophosphamide, phosphoramide Mustard, dactinomycin, or control hearts. The nuclear effects of the four anthracycline analogues were indistinguishable. Thus, all anthracycline analogues studied produced acute nuclear alterations which were distinctive from the changes produced by other DNA interactive chemotherapeutic agents. The relationship of the distinctive anthracycline nuclear changes to the late cardiomyopathy requires further definition.

Current trends in safety testing and toxicological research

The paper reviews current concepts of toxicological evaluation of new drugs and other chemicals. Instead of completing a predetermined check-list toxicologists now consider the potential adverse effects of the substances under actual conditions of use. They then design experimental models which have a high probability to predict the toxic effects. Moreover, the enhanced susceptibilities of special risk populations is more and more taken into consideration.

Comparison of cardiotoxicity of two anthracenediones and doxorubicin in rats

Two new anthracenediones with antineoplastic activities resembling those of the anthracycline antibiotics were studied in a rat cardiotoxicity model system. NCS-196473 was approx. 10-fold less toxic than doxorubicin and caused only minor electrocardiogram (ECG) changes. Its dihydroxyanalog NSC-279836 was somewhat more toxic than doxorubicin, caused marked leukopenia and induced ECG changes and moderate elevation of serum GOT, LDH and creatine phosphokinase (CK). Both anthracenediones induced marked alterations of mitochondrial structure in the heart but no dilatation of the sarcoplasmic reticulum and distortion of the contractile elements. It is concluded that the cardiotoxic effects of the anthracenediones are of a less specific nature than those caused by doxorubicin.

Further studies on the generation of reactive oxygen species from activated anthracyclines and the relationship to cytotoxic action and cardiotoxic effects

The relative ease of generation of reactive oxygen species from a series of reductively activated aglycone and sugar modified anthracyclines was compared by the extents of single strand scission in supercoiled PM2-covalently closed circular (CCC)-DNA. The electrochemical properties of these agents were used as a quantitative measure of the ease of reduction and subsequent reoxidation of the reduced species. The relationship of these processes to various biological properties of the anthracyclines, in particular to the measured cardiotoxicity of the drugs, was examined. An attempt was made to identify those structural changes which ameliorate the cardiotoxic effects measured in other test systems while permitting the expression of antitumor properties.

Newer diagnostic procedures in chronic toxicity studies in rats

A large number of diagnostic procedures which are either adapted from clinical laboratory tests or are based on pharmacological and biochemical concepts are available for introduction into routine animal toxicology. In order to illustrate the variety of possible experimental approaches several examples are given, ranging from simple determinations of bleeding time and fibrinolysis to cardiovascular function studies including serial electrocardiography, measurement of the cardiac output and the catecholamine-arrhythmia threshold. Moreover, the use of serial fine needle aspiration biopsy for early diagnosis of various liver lesions is described. It is stressed that these diagnostic procedures should not be included indiscriminately into the classical toxicological programs, but should be used judiciously to test a clearly stated scientific hypothesis.