Doxorubicin-induced cardiac toxicity

Secondary alcohol metabolites mediate iron delocalization in cytosolic fractions of myocardial biopsies exposed to anticancer anthracyclines. Novel linkage between anthracycline metabolism and iron-induced cardiotoxicity

The cardiotoxicity of doxorubicin (DOX) and other quinone-containing antitumor anthracyclines has been tentatively attributed to the formation of drug semiquinones which generate superoxide anion and reduce ferritin-bound Fe(III), favoring the release of Fe(II) and its subsequent involvement in free radical reactions. In the present study NADPH- and DOX-supplemented cytosolic fractions from human myocardial biopsies are shown to support a two-step reaction favoring an alternative mechanism of Fe(II) mobilization. The first step is an enzymatic two-electron reduction of the C-13 carbonyl group in the side chain of DOX, yielding a secondary alcohol metabolite which is called doxorubicinol (3.9 +/- 0.4 nmoles/mg protein per 4 h, mean +/- SEM). The second step is a nonenzymatic and superoxide anion-independent redox coupling of a large fraction of doxorubicinol (3.2 +/- 0.4 nmol/mg protein per 4 h) with Fe(III)-binding proteins distinct from ferritin, regenerating stoichiometric amounts of DOX, and mobilizing a twofold excess of Fe(II) ions (6.1 +/- 0.7 nmol/mg protein per 4 h). The formation of secondary alcohol metabolites decreases significantly (Pi < 0.01) when DOX is replaced by less cardiotoxic anthracyclines such as daunorubicin, 4'-epi DOX, and 4-demethoxy daunorubicin (2.1 +/- 0.1, 1.2 +/- 0.2, and 0.6 +/- 0.2 nmol/mg protein per 4 h, respectively). Therefore, daunorubicin, 4'-epi DOX, and 4-demethoxy daunorubicin are significantly (P < 0.01) less effective than DOX in mobilizing Fe(II) (3.5 +/- 0.1, 1.8 +/- 0.2, and 0.9 +/- 0.3 nmol/mg protein per 4 h, respectively). These results highlight the formation of secondary alcohol metabolites and the availability of nonferritin sources of Fe(III) as novel and critical determinants of Fe(II) delocalization and cardiac damage by structurally distinct anthracyclines, thus providing alternative routes to the design of cardioprotectants for anthracycline-treated patients.

Effects of doxorubicin on excitation-contraction coupling in guinea pig ventricular myocardium

Doxorubicin, an anticancer drug, was recently shown to release Ca2+ from cardiac sarcoplasmic reticulum (SR) by increasing the open probability of Ca2+ release channels. In the present study, we investigated the effects of doxorubicin on excitation-contraction coupling of guinea pig heart preparations. In papillary muscles contracting at 0.5 Hz, 100 mumol/L doxorubicin produced within 3 hours the following effects: it increased the force of contraction by 269.3 +/- 19.8% (n = 6) and prolonged the time to peak force by 75.1 +/- 8.7% (n = 6), relaxation time by 54.7 +/- 8.7% (n = 6), and action potential duration (APD) at 90% repolarization (APD90) by 38.6 +/- 2.9% (n = 3). Despite its positive inotropic effect, doxorubicin depressed the early contraction component by increasing the latency between stimulus and the onset of force development. In single myocytes, 100 mumol/L doxorubicin prolonged APD90 by 62.1% (n = 18) and blocked time-dependent delayed rectifier K+ current (IK) by 44% (n = 9). Ca2+ inward current and inward rectifier K+ current were not affected by doxorubicin. Ca2+ transients elicited in myocytes loaded with the fluorescent Ca2+ indicator fura 2 were strongly suppressed by doxorubicin in their initial rising phase. There-after, doxorubicin produced a delayed rise in intracellular Ca2+, which reached a late peak exceeding that of the control peak by 52 +/- 8% (n = 5). The results suggest that doxorubicin decreases Ca(2+)-induced Ca2+ release from cardiac SR, probably by increasing the SR Ca2+ leak. On the other hand, prolongation of APD due to inhibition of IK allows more Ca2+ to enter the cell. After being only temporarily buffered by the SR, Ca2+ may accumulate in the cytosol as long as depolarization is maintained and lead to a more complete activation of contractile proteins.

Doxorubicin-induced cardiomyopathy

Doxorubicin (Adriamycin; Adria Laboratories, Columbus, OH) is one of the most effective chemotherapeutic agents used in the management of pediatric neoplastic disorders during the past 20 years. However, its use has been limited by well-characterized, dose-related cardiac toxicity. Recently, cardiac dysfunction has been noted in pediatric patients who had received doxorubicin years before. This article summarizes current information regarding the pathophysiology and risk factors associated with cardiotoxicity and reviews detection methods and treatments of this condition.

Flow cytometric detection of hydrogen peroxide production induced by doxorubicin in cancer cells

2',7'-Dichlorofluorescin diacetate (DCFH-DA) has been previously used to study the oxidative burst of neutrophils induced by different stimuli. The method is based on the fact that DCFH-DA diffuses through the cell membrane and it is hydrolyzed by intracellular esterases to DCFH, which remains trapped within the cells. DCFH, a nonfluorescent compound, is able to react with free radical products, particularly with hydrogen peroxide, and to generate the fluorescent 2',7'-dichlorofluorescein (DCF). By flow cytometric detection of DCF fluorescence, an indirect measure of reactive oxygen species production in single cells may be obtained. Using a modified procedure to load cells of the human colon adenocarcinoma cell line LoVo with DCFH-DA, a significant fluorescence increase above the basal fluorescence level has been detected after treatment with doxorubicin doses as low as 0.4 microM. This increase is not detectable when the cells are preloaded with catalase, using a scraping method, and it is not due to doxorubicin own fluorescence. These experiments prove that the increase of DCF fluorescence intensity observed during doxorubicin treatment is not due to technical artifacts but it is attributable to free radicals produced in the cells by the drug.

Cellular Ca2+ loading and inotropic effects of doxorubicin in atrial muscle preparations isolated from rat or guinea-pig hearts

The inotropic effects of doxorubicin were examined under conditions that alter the Ca2+ loading of myocardial cells. Atrial muscle preparations isolated from rat or guinea-pig hearts were used. Cellular Ca2+ loading was altered by changing the temperature, extracellular Ca2+ concentrations or the frequency of electrical stimulation. In guinea-pig heart muscle preparations stimulated at 2 Hz at 30 degrees C in the presence of 1.2 mM CaCl2, 30 microM doxorubicin caused biphasic (early and late phase) positive inotropic effects. A higher concentration (200 microM) of doxorubicin caused a transient positive inotropic effect followed by a gradual decrease in developed tension. An increase in CaCl2 concentration from 1.2 to 2.4 mM decreased the positive inotropic effect of 30 microM doxorubicin and changed the inotropic effect of 200 microM doxorubicin from positive to negative after a transient increase in developed tension. At 0.5-Hz stimulation or 36 degrees C incubation, 30 or 200 microM doxorubicin produced remarkable late phase positive inotropic effects. In rat heart muscle preparations, the patterns of the inotropic effects of doxorubicin were similar to those observed with guinea-pig hearts; however, the negative inotropic effect observed at 200 microM doxorubicin was greater. These results indicate that the early and the late phase positive inotropic effects of doxorubicin have different mechanisms. The pattern of inotropic effects of doxorubicin is affected by conditions that alter cellular Ca2+ loading or the concentration of doxorubicin.

Management of lithium in patients with cancer

This article reviews the management of lithium in patients who require optimum management of cancer and simultaneous prevention of mania or depression in lithium-sensitive affective illness. Two cases are described. Discussion focuses on whether lithium should be continued during chemotherapy and radiation treatment, the complications that would lead to lithium toxicity in an otherwise stable patient, the likely settings for hypothyroidism, and the role of lithium to stabilize steroid-induced affective changes. The authors conclude that lithium may be withheld 1 or 2 days before cytotoxic chemotherapy and restarted when the patient is able to drink. It may be given as usual through routine radiation treatment, but it should be discontinued during cranial radiation. Calcium, renal, cardiac, and thyroid functions should be monitored.

The hydrolysis product of ICRF-187 promotes iron-catalysed hydroxyl radical production via the Fenton reaction

d-1,2-Bis(3,5-dioxopiperazine-1-yl)propane (ICRF-187) (ADR-529) is a drug that ameliorates the cardiotoxicity of Adriamycin. The drug enters cells where hydrolysis leads to its diacid diamide product, dl-N,N'-dicarboxamidomethyl-N,N'-dicarboxymethyl-1,2-diamino propane (ICRF-198) (ADR-925), which is structurally similar to ethylenediaminetetraacetic acid (EDTA). The protective mechanism of ICRF-187 is unknown, but a plausible explanation is that ICRF-198 chelates iron intracellularly to prevent iron-dependent free radical reactions such as hydroxyl radical (.OH) production. We have compared Fe(ICRF-198) with Fe(EDTA) in its ability to promote .OH formation in several Fenton reaction systems. The Fenton reaction was studied with H2O2 and Fe2+ chelates or catalytic amounts of the iron chelates in the presence of Adriamycin radicals, paraquat radicals, superoxide anion radicals (O2-), and ascorbate as reducing species. .OH was detected with deoxyribose and dimethyl sulfoxide. The two methods gave comparable results. Fe(ICRF-198) was 80-100% as effective as Fe(EDTA) at promoting .OH production in the presence of the organic radicals and ascorbate, 30-70% in the presence of O2-, and 150% with non-cycling Fe2+. Fe(EDTA) is a more efficient catalyst of .OH production than physiological chelates such as ADP, ATP and citrate. Therefore, by comparing previous work which examined physiological chelates and Fe(EDTA) with the present work, Fe(ICRF-198) appears to be a better .OH catalyst than the physiological chelates. These results suggest that ICRF-198 generated in vivo from ICRF-187 would not protect against intracellular .OH production. They also imply that .OH production may not be as important in Adriamycin cardiotoxicity as other radical reactions, such as lipid peroxidation and thiol oxidation, that are inhibited by ICRF-198.

Cancer in the elderly

This article reviews geriatric oncology and assesses options for treatment and care of the elderly patient with cancer. The size of the population over 65 years old is defined, with particular reference to the continuing growth of this subsection of the community. The high incidence of many cancers and their associated mortality rates in the elderly are identified and the epidemiology of such diseases in the geriatric population is addressed. Given the discrepancies in incidence and survival rates between patients younger and older than 65 years, the association between tumorigenesis and the aging process is explored. Specific aspects of tumor growth in the elderly are considered. General considerations of therapy for elderly patients with cancer are discussed, including the pharmacokinetics and pharmacodynamics of chemotherapy in those over 65 years old, surgical options, the use of radiotherapy, and overall patient assessment. Next, treatment options for individual cancer states are reviewed, with particular emphasis on newer treatment options designed specifically for the elderly. Sections on cancer screening and supportive care are also included, the latter dealing with aspects of symptom control, quality of life assessment, and the physical and psychologic rehabilitation of the elderly patient with cancer who is undergoing treatment. Conclusions are then drawn as to the extent of the oncological process in those over 65 years old, with particular emphasis on the underdiagnosis and undertreatment of many malignancies in the past. The challenge created by the growing elderly population is underscored and necessary plans of action for oncologists in the future are defined. Such proposals are necessary if inroads are to be made into the unacceptable morbidity and mortality rates borne by our elderly patients with cancer.

Comparison of cardiac actions of doxorubicin, pirarubicin and aclarubicin in isolated guinea-pig heart

The cardiac actions of doxorubicin were compared with those of pirarubicin and aclarubicin to understand the mechanisms responsible for differences in cardiotoxic effects of anthracycline agents. In left atrial muscle preparations obtained from guinea-pig heart and stimulated at 2 Hz, anthracyclines produced positive inotropic effects. The magnitude of the effect was pirarubicin > doxorubicin > aclarubicin. The order for depression of potentiated postrest contraction and prolongation of the time to peak twitch tension was doxorubicin > pirarubicin > aclarubicin. Drug washout following a 2-h incubation with 100 microM doxorubicin prevented a further increase in the time to peak twitch tension, caused a marked recovery of depressed potentiated postrest contractions, and augmented the positive inotropic effect. Pirarubicin and doxorubicin, but not aclarubicin, caused a parallel rightward shift of the dose-response curve for the negative inotropic effect of acetylcholine. The potency of inhibition of [3H]quinuclidinyl benzilate binding was pirarubicin > doxorubicin > aclarubicin. These results indicate that three anthracycline anticancer agents share similar effects on cardiac muscle contractility and on muscarinic acetylcholine receptors. The actions of aclarubicin were weak compared to those of doxorubicin or pirarubicin. Increases in the time to peak twitch tension and the depression of potentiated postrest contraction are apparently mediated by mechanisms different from those responsible for the positive inotropic effects or antagonism at muscarinic acetylcholine receptors.

The role of reactive oxygen species, antioxidants and phytopharmaceuticals in human immunodeficiency virus activity

Currently, several prominent researchers are investigating the role of reactive oxygen and free radicals in the activation of latent HIV in infected individuals. Early clinical applications of free radical scavengers and plant-based antioxidant systems have shown promise of efficacy in altering this process. This manuscript demonstrates a premise for the existence of 'oxidative stress' as an important element in HIV progression and a basis for the use of these phytopharmaceutical substances.

Oxidative stress in mouse heart by antitumoral drugs: a comparative study of doxorubicin and mitoxantrone

Doxorubicin and mitoxantrone were given to mice in a single dose of 15 mg/kg body wt (i.p.). 'In situ' heart spontaneous chemiluminescence, hydroperoxide-initiated chemiluminescence and TBARS were measured in heart homogenates of treated and control animals at 2-5 days after injection. Heart spontaneous emission (control value: 45 +/- 5 cps/cm2) was increased by 10-fold in doxorubicin-treated mice 4 days after administration, whereas mitoxantrone did not produce any significant change. Administration of doxorubicin produced increases of 50% in hydroperoxide-initiated chemiluminescence and of 80% in TBARS levels 4 days after injection. Mitoxantrone did not induce significant changes in these parameters as compared with the controls. Cardiac reduced glutathione levels were not affected by mitoxantrone but were decreased (about 30%) by doxorubicin (control value: 0.98 +/- 0.08 mumol/g organ). Our data indicate that mitoxantrone does not induce an increase in the endogenous lipoperoxidation rate in heart tissue as doxorubicin does; this could contribute to the lower cardiotoxicity of mitoxantrone as compared with doxorubicin.

Low dose continuous infusion doxorubicin in children and young adults

Ten patients (age range 3.2-26.3 yrs) with relapsed or resistant malignancies received a total of 20 courses of low dose continuous infusion doxorubicin (3 mg/m2/day for 28 days) delivered by portable Graseby infusion pumps via central venous catheters. Each patient received a median dose of 144 mg/m2 (range 87-261). Four patients responded to treatment (1 complete response (CR) and 3 partial response (PR)) and performance status improved in seven patients. Overall toxicity was minimal: WHO Grade 4 anaemia in 2/18 courses, Grade 4 neutropenia in 1/18, Grade 3-4 thrombocytopenia in 3/18, nausea and vomiting of Grades 2 and 4 in 4/20 and 1/20 respectively, and mucositis of Grades 2 and 4 in 2/20 courses each. Cardiac toxicity was assessed using echocardiography, and fractional shortening remained within normal limits in all patients. Low dose continuous infusion doxorubicin is a feasible, well tolerated, ambulatory therapy in children and may be an effective way of delivering doxorubicin with less toxicity, thus enabling the development of more dose intensive regimens.

3'-Deamino-3'-(2-methoxy-4-morpholinyl)-doxorubicin (FCE 23762): a new anthracycline derivative with enhanced cytotoxicity and reduced cardiotoxicity

The purpose of this study was to examine the cytotoxicity and cardiotoxicity of the new doxorubicin derivative, 3'-deamino-3'-(2-methoxy-4-morpholinyl)-doxorubicin (FEC 23762). The concentration of FCE 23762 that resulted in a 50% reduction in colony formation of DU 145, COLO 320DM, A549 and A2780 human cancer cell lines ranged from 1.1 and 3.2 nmol/l and was 3-9 times as low as doxorubicin. In the isolated perfused rat hearts, doxorubicin 10(-5) mol/l induced a significant prolongation of S alpha T segment and Q-Fmax interval, and reduction in dF/dtmax and coronary flow while only FCE 23762 10(-5) mol/l induced a widening of QRS complex. Anaesthetised rats given a single intravenous (i.v.) dose of doxorubicin 10 mg/kg showed significant changes in both ECG (S alpha T segment and QRS complex enlargement) and haemodynamic parameters (increase in mean arterial blood pressure and reduction in systemic arterial dP/dtmax), while animals given FCE 23762 (0.1 and 0.3 mg/kg) had a significant increase in QRS complex duration after the highest dose. In the chronic cardiotoxicity study animals receiving FCE 23762 (0.03 mg/kg i.v. once a week for 3 weeks) did not show any significant alteration of ECG and minor changes of cardiac histological picture; by contrast doxorubicin (3 mg/kg i.v. once a week for 3 weeks) induced a severe cardiomyopathy, characterised by progressive widening of S alpha T segment, increase in T wave and histological damage consisting of vacuolations and loss of myofibrils. These results indicate that FCE 23762 is more active in vitro than doxorubicin and markedly less cardiotoxic in vivo at the doses used in the present study.

Doxorubicin: an antagonist of muscarinic receptors in guinea pig heart

While studying the mechanisms of doxorubicin-induced cardiotoxicity, we observed that doxorubicin inhibited the negative inotropic effect of acetylcholine in isolated heart muscle preparations. We therefore examined the effects of doxorubicin on muscarinic acetylcholine receptors. In left atrial muscle preparations isolated from guinea pig heart and stimulated at 2 Hz at 30 degrees C, doxorubicin caused a parallel right-ward shift of the dose-response curves for the negative inotropic effects of acetylcholine. The inhibitory action was reversed by an additional incubation in the absence of doxorubicin. Doxorubicin reversed the carbachol-induced inhibition of developed tension: a high concentration of doxorubicin brought the force back to its original strength. Doxorubicin inhibited specific [3H]quinuclidinyl benzilate (QNB) binding to membrane preparations obtained from ventricular muscle of guinea pig hearts. The pA2 value for doxorubicin obtained in the inotropic study corresponded to the IC50 value for doxorubicin observed in the [3H]QNB binding assay. These results indicate that doxorubicin acts as a weak competitive antagonist on muscarinic acetylcholine receptors.

The role of an endogenous nonheme iron in microsomal redox reactions

Microsomal membranes contain a nonheme iron which serves in vitro for the peroxidation of unsaturated lipids or the oxidation of several other chemicals. These redox reactions are reviewed in light of a recent identification of two or more iron-binding proteins in the microsomal milieu. Indirect evidence that the microsomal iron might serve in vivo for the synthesis of heme iron is also presented and discussed. Consistent with this, the newly identified iron proteins not only participate in redox reactions but also release their bound iron upon incubation with certain intermediates of heme synthesis.

Ventricular late potentials: another expression of cardiotoxicity of cytostatic drugs in children?

With the aim of finding a sensitive method to detect early anthracycline-induced myocardial damage ultimately resulting in cardiomyopathy, we studied the occurrence of ventricular late potentials, using a signal averaged electrocardiogram, in 68 children with cancer during or after chemotherapy. Ten (15%) of the children showed late potentials; in addition, patients treated with cytostatic drugs had significantly lower voltages of the last 40 ms of the QRS complex (RMS40) and a longer duration of low amplitude signals in the terminal QRS (LAS) than control patients. The occurrence of late potentials was not significantly correlated with anthracycline therapy or dosage, nor with the presence of echocardiographic abnormalities; in none of the patients we found late potentials during therapy with anthracyclines. We therefore conclude that late potentials are not helpful for early detection of myocardial injury. The occurrence of late potentials, however, does show another expression of cardiotoxicity not specifically related to anthracycline therapy. The occurrence of these late potentials may have prognostic significance with regard to the risk of ventricular arrhythmias during longer follow-up of these patients.

Roles of iron in neoplasia. Promotion, prevention, and therapy

Research and clinical observations during the past six decades have shown that: 1. Iron promotes cancer cell growth; 2. Hosts attempt to withhold or withdraw iron from cancer cells; and 3. Iron is a factor in prevention and in therapy of neoplastic disease. Although normal and neoplastic cells have similar qualitative requirements for iron, the neoplastic cells have more flexibility in acquisition of the metal. Excessive iron levels in animals and humans are associated with enhanced neoplastic cell growth. In invaded hosts, cytokine-activated macrophages increase intracellular ferritin retention of the metal, scavenge iron in areas of tumor growth, and secrete reactive nitrogen intermediates to effect efflux of nonheme iron from tumor cells. Procedures associated with lowering host intake of excess iron can assist in prevention and in management of neoplastic disease. Chemical methods for prevention of iron assimilation by neoplastic cells are being developed in experimental and clinical protocols. The antineoplastic activity of a considerable variety of chemicals, as well as of radiation, is modulated by iron. The present article focuses on recent findings and suggests directions for further cancer-iron research.

Reduced cardiotoxicity and increased cytotoxicity in a novel anthracycline analogue, 4'-amino-3'-hydroxy-doxorubicin

The acute and chronic cardiotoxicity and cytotoxicity of the novel doxorubicin (DXR) derivative 4'-amino-3'-hydroxy-DXR were compared with those of 4'-deoxy-DXR and DXR. In the acute cardiotoxicity study, the ECG and hemodynamic changes recorded in anesthetized rats that had been treated i.v. with 10 mg/kg 4'-amino-3'-hydroxy-DXR or 8.6 mg/kg 4'-deoxy-DXR were significantly less severe than those caused by 13 mg/kg DXR. In the chronic cardiotoxicity study, rats received 3 weekly i.v. injections of 3 mg/kg DXR, 3 mg/kg 4'-amino-3'-hydroxy-DXR, or 2 mg/kg 4'-deoxy-DXR during the first 14 days of the study and were observed for an additional 35-day period. DXR induced severe cardiomyopathy that was characterized by ECG changes in vivo (S alpha T-segment widening and T-wave flattening) and by impairment of the contractile responses (Fmax, +/- dF/dtmax) to adrenaline of hearts isolated from treated animals. 4'-Deoxy-DXR caused a progressive enlargement of the S alpha T segment in vivo and a significant impairment of the -dF/dtmax value in vitro, which were less severe than those produced by DXR. The least cardiotoxic drug was 4'-amino-3'-hydroxy-DXR, which induced minor ECG changes without causing significant alterations in the contractile responses of isolated hearts to adrenaline. On the basis of the drug concentration required to inhibit 50% of the colony formation (IC50) of cell lines in vitro, 4'-amino-3'-hydroxy-DXR was less active than 4'-deoxy-DXR but at least twice as active as DXR against human cancer and murine transformed cell lines. These data indicate that 4'-amino-3'-hydroxy-DXR is significantly less cardiotoxic and more cytotoxic than DXR.

Atrial natriuretic peptide as a marker for doxorubicin-induced cardiotoxic effects

Doxorubicin is an effective antineoplastic agent, but it frequently causes dose-related cardiotoxic effects. Because the atrial natriuretic peptide (ANP) level is elevated in children with heart defects, the authors measured the ANP levels in children to determine whether ANP might serve as a simple diagnostic indicator of cardiotoxic effects. Sixteen patients, 5 to 19 years of age, who were being treated with doxorubicin (45 mg/m2 body surface area) for various malignancies had ANP levels measured in plasma. There was a group of six children, with a significant peak of plasma ANP (pANP) levels 3 weeks after the administration of the drug. Of these six patients, five had received high cumulative doses of doxorubicin (160 to 370 mg/m2), and two of them went into congestive heart failure without a previous decline in left ventricular ejection fraction, a standard technique for monitoring cardiac function during treatment with doxorubicin. The other ten patients had normal ANP levels throughout the study, and signs of cardiac dysfunction did not develop. None of the patients in the control group who had cancer and were not treated with doxorubicin and none of the healthy volunteers had elevated ANP levels. These preliminary results suggest that pANP may be useful as an early and sensitive indicator for doxorubicin-related myocardial damage.

Cardiotoxicity and cytotoxicity of the anthracycline analog 4'-deoxy-4'-iodo-doxorubicin

The cardiotoxicity and cytotoxicity of the novel doxorubicin (DXR) derivative 4'-deoxy-4'-iodo-DXR were evaluated and compared to DXR. A single dose of DXR 10 mg/kg i.v. in anesthetized rats induced a significant widening of S alpha T segment of the electrocardiogram, an increase in both mean arterial blood pressure and heart rate and a fall in systemic arterial dP/dtmax, while 4'-deoxy-4'-iodo-DXR 4 mg/kg i.v. induced a significant widening of S alpha T segment and an increase in mean arterial blood pressure. A chronic cardiomyopathy was induced over a 6-week period by three injections of DXR 3 mg/kg per week i.v. and was characterized by a progressive enlargement of S alpha T segment, a flattening of T wave, the occurrence of arrhythmias and histological alterations of myocardium. The contractile responses to adrenaline of isolated hearts from DXR-treated animals were significantly reduced compared to controls. 4'-Deoxy-4'-iodo-DXR (1.2 mg/kg per week three times) induced minor ECG alterations and sporadic episodes of arrhythmias. The contractile responses of isolated hearts were not significantly different from those of controls and microscopic examination of hearts revealed only minor changes. Cytotoxicity in vitro was evaluated by the colony formation assay; based on IC50, 4'-deoxy-4'-iodo-DXR was up to six times more cytotoxic than DXR on four human cancer cell lines. These results suggest that 4'-deoxy-4'-iodo-DXR is significantly less cardiotoxic and more cytotoxic than DXR.