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Session III of the Second International Colloquium on Cardio-Oncology focused on the diagnosis, management, and prevention of cardiovascular toxicity of cancer drugs. With a large menu of biomarkers and imaging modalities available to the cardio oncologist, there continues to be no consensus regarding the best use of each modality alone and in combination and whether we can actually prevent early and late cardiotoxicity using these tests to guide a preventive strategy. It has become increasingly clear that early diagnosis and intervention leads to less late cardiotoxicity and fewer cardiac-related events. This can be accomplished by taking a thorough history and performing a goal directed physical examination coupled with use of biomarkers and imaging studies. This session attempted to provide rationale for a current and integrated approach to these issues.

Session IV of the Second International Colloquium on Cardio-Oncology held in Kraków, focused on the cardiovascular risks of using hormone replacement therapy in breast cancer and androgen deprivation therapy in prostate cancer and continued the theme from Session 3 with a discussion of risk reduction strategies. The discussion then moved to an overview of modern radiation therapy and evolving mechanisms of cardioprotection. The risks and late cardiotoxic effects that must be considered in patients treated prior to the “modern era” were enumerated stressing the importance of long term follow-up of this population.

Guidelines for the diagnosis, management, and surveillance of cancer patients have evolved with the single goal of improving patient care based on established data when available, or in the absence of firm data, on the standard practices of those with broad experience in actual hands-on patient care. Two initiatives intended to disseminate information to cardio-oncologists, were discussed in this session: the first, from the American Society of Clinical Oncologywas focused on available data and the confidence level of that data; the second, from The European Society of Cardiologywas a position paper. Interestingly, notwithstanding the somewhat different focus, there is considerable agreement between these two initiatives. Nevertheless, guidelines my not be applicable to all afflicted patients, and may raise questions as to when deviations from published standards should be considered. Such deviations may result in allegations of failure to meet standards of care or legal liability.

Session V of the Colloquium was chaired by Professors Teresa López-Fernández of Spain and Grzegorz Opolski of Poland. The 3 speakers addressed cardio-oncology issues as they relate to both clinical studies and real life situations. Professor Susan Dent discussed cardio-oncology networks for patients, emphasizing the importance of establishing a framework where the expertise of the cardiology consultant can supplement and reinforce the goals of optimal cancer therapy. Professor Thomas Suter moved the discussion further, sharing his insight into cardiac monitoring in clinical trials, emphasizing the lack of uniform criteria and lack of consensus regarding reversibility of cardiac events and long-term implications of modest declines in systolic function frequently found in clinical trials for which long-term follow-up may not be a component of the trial. Professor Giorgio Minotti added important considerations to the discussion of clinical trials. He emphasized that the usual reporting of cardiac systolic function omits important diastolic dysfunction data generated but often ignored during the routine cardiac exams. The inclusion of cardiac biomarker changes would also help to broaden the perspective of cardiac effects and events seen in patients enrolled in clinical trials.

Malignant disease and its treatment carry huge burdens for patients. Some are immediate, in that the disease itself presents as a life threatening event, or the treatment may result in immediate and devastating toxicity. More often the treatment of cancer is associated with more subtle or late events, yet these may impact the quality of life for cancer survivors in a variety of ways. In addition to the physical sequelae of cancer or its treatment, cancer survivors often experience consequences in the form of social or mental incapacity. Session III of this Colloquium on Cardio-Oncology focuses on some of these concerns, both from the perspective of health care providers who strive to minimize the burdens, but also from the viewpoint of the patient him or herself who must deal with the price that must often be paid for increased survival or cure.

The opening session of Second International Colloquium on Cardio-Oncology addressed two areas of vital interest. The first reviewed new thoughts related to established agents. While anthracycline cardiotoxicity has been studied and reviewed extensively, ongoing research attempting to understand why it appears the mechanism(s) of toxicity differs from that of oncologic efficacy continue to evoke comment and intriguing speculation. Better understanding of the role of β-topoisomerase II in toxicity has advanced our understanding of the cascade of events that lead to heart failure. Additionally, the cardioprotective role of dexrazoxane fits well with our new understanding of how β-topoisomerase II works. Beyond the anthracyclines, new insight is providing us insight to better understand the impact on cardiac function seen with other agents including those targeting HER2 and several tyrosine-kinase inhibitors. Unlike the anthracyclines, these agents affect cardiac function in ways that are less direct, and therefore have different characteristics and should be thought of in alternate ways. This new knowledge regarding established agents furthers our understanding of the spectrum of cardiotoxicity and cardiac dysfunction in the cancer patient. The session also addressed cardiovascular toxicities of newer and established agents beyond myocardial dysfunction including effects on the vasculature. These agents cause changes that may be temporary or permanent, and that range from subclinical to life-threatening. The session ended with a discussion of the cardiac effects of immune checkpoint inhibitors. These agents can cause rare and sometimes fatal cardiac inflammation, for which long-term follow up may be required.

Session II of the Second International Colloquium on Cardio-Oncology, chaired by Dr Breccia (Rome, Italy) and Dr Jurczak (Krakòw, Poland), focused on mechanisms and clinical course of cardiovascular toxicity of cancer treatment. Whereas the venerable anthracyclines keep challenging patients and clinicians with risk of left ventricular dysfunction and heart failure, other newer drugs cause substantially different clinical phenotypes of cardiovascular toxicity. In particular, Session II not only focused on arterial thrombosis and venous thromboembolism, but also hypertension or cardiomyopathy or atrial fibrillation induced by many otherwise life-saving drugs. Dr Breccia (Rome, Italy) reviewed incidence, mechanisms, risk factors, and principles for prevention of cardiovascular events induced by tyrosine kinase inhibitors of hematologic interest, such as those used to treat chronic myeloid leukemia. Dr Carver (Philadelphia) reviewed the incidence, predisposing factors, and principles for proactive management of cardiovascular events in patients treated by conventional chemotherapy or new drugs for treatment of multiple myeloma. Dr Szmit (Warsaw, Poland) discussed on how coagulation disorders should be classified according to patient- or drug-related factors and how they should be diagnosed and treated in patients with solid or hematologic tumors. Dr Minotti (Rome. Italy) illustrated some potential pitfalls of accelerated drug development and approval and their possible impact on clinical incidence of cardiovascular events induced by tyrosine kinase inhibitors of hematologic interest. Session II therefore offered a broad perspective of the risk-benefit ratio of new drugs that are plagued with concerns about cardiovascular events.

ABSTRACTIntroduction: In spite of the proven efficacy of the tyrosine kinase inhibitor (TKI), imatinib, in chronic myeloid leukemia (CML), many patients develop intolerance and discontinue therapy in the long-term. Second-generation TKIs (dasatinib, nilotinib, bosutinib) and the third-generation TKI, ponatinib, have added opportunities but also complexity in the settings of CML treatment.Areas covered: Different definitions of intolerance have been used through several clinical trials, making the published data non homogenous. In most cases, only the severity of acute adverse events (AEs), graded by conventional scales such as Common Terminology Criteria for Adverse Events, was reported. Limited attention to long-term events or more in general, to the impact of AEs on patient quality of life (QoL), remains a problem. Ponatinib is active against all BCR-ABL1 mutants, including T315I, and is widely used to treat patients who developed resistance to other TKIs in any CML phase; however, only limited data is available on the possible role of ponatinib for intolerant patients.Expert opinion: We review the different definitions of intolerance used in sponsored trials and in clinical practice, and we discuss how such definitions impact on the management of AEs. We summarize how to evaluate QoL during treatment with TKIs and how to include ponatinib among possible option for intolerant patients.

ABSTRACTIntroduction: All anticancer drugs can cause idiosyncratic liver injury. Therefore, hepatoprotective agents assume particular importance to preserve liver function. Hepatic injury represents 10% of cases of acute hepatitis in adults; drug-related damage is still misjudged because of relative clinical underestimation and difficult differential diagnosis. Chemotherapeutic agents can produce liver toxicity through different pathways, resulting in different categories of liver injuries, but these drugs are not homogeneously hepatotoxic. Frequently, anticancer-induced hepatotoxicity is idiosyncratic and influenced by multiple factors.Areas covered: The aim of this paper is to perform a review of the literature regarding anticancer-induced liver toxicity. We described hepatotoxicity mechanisms of principal anticancer agents and respective dose reductions. Furthermore, we reviewed studies on hepatoprotectors and their optimal use. Tiopronin, magnesium isoglycyrrhizinate and S-Adenosylmethionine (AdoMet) demonstrated, in some small studies, a potential hepatoprotective activity.Expert Opinion: Actually, in the literature only small experiences are reported. Even though hepatoprotective agents seem to be useful in the oncologic setting, the lack of well-designed prospective Phase III randomized controlled trials is a major limit in the introduction of hepatoprotectors in cancer patients and these kind of studies are warranted to support their use and to give further recommendations for the clinical practice.

Cardiotoxicity from the antitumor anthracycline doxorubicin correlates with doxorubicin cardiac levels, redox activation to superoxide anion (O(2)(._)) and hydrogen peroxide (H(2)O(2)), and formation of the long-lived secondary alcohol metabolite doxorubicinol. Cardiotoxicity may first manifest during salvage therapy with other drugs, such as the anthracenedione mitoxantrone. Minimal evidence for cardiotoxicity in anthracycline-pretreated patients with refractory-relapsed non-Hodgkin lymphoma was observed with the novel anthracenedione pixantrone. We characterized whether pixantrone and mitoxantrone caused different effects on doxorubicin levels, redox activation, and doxorubicinol formation. Pixantrone and mitoxantrone were probed in a validated ex vivo human myocardial strip model that was either doxorubicin-naïve or preliminarily subjected to doxorubicin loading and washouts to mimic doxorubicin treatment and elimination in the clinical setting. In doxorubicin-naïve strips, pixantrone showed higher uptake than mitoxantrone; however, neither drug formed O(2)(._) or H(2)O(2). In doxorubicin-pretreated strips, neither pixantrone nor mitoxantrone altered the distribution and clearance of residual doxorubicin. Mitoxantrone showed an unchanged uptake and lacked effects on doxorubicin levels, but synergized with doxorubicin to form more O(2)(._) and H(2)O(2), as evidenced by O(2)(._)-dependent inactivation of mitochondrial aconitase or mitoxantrone oxidation by H(2)O(2)-activated peroxidases. In contrast, pixantrone uptake was reduced by prior doxorubicin exposure; moreover, pixantrone lacked redox synergism with doxorubicin, and formed an N-dealkylated product that inhibited metabolism of residual doxorubicin to doxorubicinol. Redox inactivity and inhibition of doxorubicinol formation correlate with the cardiac safety of pixantrone in doxorubicin-pretreated patients. Redox inactivity in the face of high cardiac uptake suggests that pixantrone might also be safe in doxorubicin-naïve patients.

The pharmacokinetics of pegylated liposomal doxorubicin (PLD) were investigated in 17 women undergoing intraoperative hyperthermic intraperitoneal chemotherapy (HIPEC) for advanced ovarian cancer and peritoneal carcinomatosis. HIPEC was performed immediately after completing debulking surgery, which included a number of peritonectomy procedures. PLD was injected and allowed to equilibrate in peritoneal cavity filled with 4 liters of physiological solution and stabilized at 42°C; next, the outflow line was opened and perfusion proceeded for 1 h. PLD was stable in peritoneal perfusate and plasma. During HIPEC, PLD peritoneal perfusate/plasma gradients averaged ∼600 or ≥1000 for peak concentration or area under the curve. After HIPEC, PLD plasma levels remained stable or decreased. Biopsy samples of residual normal peritoneum or ovarian carcinomatosis were collected at the end of HIPEC and were shown to contain free doxorubicin. Correlating PLD decrements in peritoneal perfusate with plasma exposure to PLD or peritoneal deposition of free doxorubicin showed that the former occurred during preperfusional equilibration of PLD in peritoneal cavity, whereas the latter occurred during 1 h of perfusion. Plasma exposure to PLD correlated negatively with the number of peritonectomy procedures performed during surgery, whereas peritoneal deposition of free doxorubicin correlated positively. Taken together, these results show that PLD administered by intraoperative HIPEC undergoes limited systemic diffusion and releases active free doxorubicin in peritoneum exposed to ovarian carcinomatosis. PLD pharmacokinetics seem to be influenced by peritonectomy procedures.

Anthracycline-related cardiotoxicity correlates with cardiac anthracycline accumulation and bioactivation to secondary alcohol metabolites or reactive oxygen species (ROS), such as superoxide anion (O₂·⁻) and hydrogen peroxide H₂O₂). We reported that in an ex vivo human myocardial strip model, 3 or 10 μM amrubicin [(7S,9S)-9-acetyl-9-amino-7-[(2-deoxy-β-D-erythro-pentopyranosyl)oxy]-7,8,9,10-tetrahydro-6,11-dihydroxy-5,12-napthacenedione hydrochloride] accumulated to a lower level compared with equimolar doxorubicin or epirubicin (J Pharmacol Exp Ther 341:464-473, 2012). We have characterized how amrubicin converted to ROS or secondary alcohol metabolite in comparison with doxorubicin (that formed both toxic species) or epirubicin (that lacked ROS formation and showed an impaired conversion to alcohol metabolite). Amrubicin and doxorubicin partitioned to mitochondria and caused similar elevations of H₂O₂, but the mechanisms of H₂O₂ formation were different. Amrubicin produced H₂O₂ by enzymatic reduction-oxidation of its quinone moiety, whereas doxorubicin acted by inducing mitochondrial uncoupling. Moreover, mitochondrial aconitase assays showed that 3 μM amrubicin caused an O₂·⁻-dependent reversible inactivation, whereas doxorubicin always caused an irreversible inactivation. Low concentrations of amrubicin therefore proved similar to epirubicin in sparing mitochondrial aconitase from irreversible inactivation. The soluble fraction of human myocardial strips converted doxorubicin and epirubicin to secondary alcohol metabolites that irreversibly inactivated cytoplasmic aconitase; in contrast, strips exposed to amrubicin failed to generate its secondary alcohol metabolite, amrubicinol, and only occasionally exhibited an irreversible inactivation of cytoplasmic aconitase. This was caused by competing pathways that favored formation and complete or near-to-complete elimination of 9-deaminoamrubicinol. These results characterize amrubicin metabolic advantages over doxorubicin and epirubicin, which may correlate with amrubicin cardiac safety in preclinical or clinical settings.

Antitumor anthracyclines such as doxorubicin and epirubicin are known to cause cardiotoxicity that correlates with anthracycline accumulation in the heart. The anthracycline amrubicin [(7S,9S)-9-acetyl-9-amino-7-[(2-deoxy-β-d-erythro-pentopyranosyl)oxy]-7,8,9,10-tetrahydro-6,11-dihydroxy-5,12-napthacenedione hydrochloride] has not shown cardiotoxicity in laboratory animals or patients in approved or investigational settings; therefore, we conducted preclinical work to characterize whether amrubicin attained lower levels than doxorubicin or epirubicin in the heart. Anthracyclines were evaluated in ex vivo human myocardial strips incubated in plasma to which anthracycline concentrations of 3 or 10 μM were added. Four-hour incubations were performed to characterize myocardial anthracycline accumulation derived from anthracycline uptake in equilibrium with anthracycline clearance. Short-term incubations followed by multiple washouts were performed to obtain independent measurements of anthracycline uptake or clearance. In comparison with doxorubicin or epirubicin, amrubicin attained very low levels in the soluble and membrane fractions of human myocardial strips. This occurred at both 3 and 10 μM anthracycline concentrations and was caused primarily by a highly favorable clearance of amrubicin. Amrubicin clearance was facilitated by formation and elimination of sizeable levels of 9-deaminoamrubicin and 9-deaminoamrubicinol. Amrubicin clearance was not mediated by P glycoprotein or other drug efflux pumps, as judged from the lack of effect of verapamil on the partitioning of amrubicin and its deaminated metabolites across myocardial strips and plasma. Limited accumulation of amrubicin in an ex vivo human myocardial strip model may therefore correlate with the improved cardiac tolerability observed with the use of amrubicin in preclinical or clinical settings.

Introduction:Anthracyclines are widely prescribed anticancer agents that cause a dose-related cardiotoxicity, often aggravated by nonanthracycline chemotherapeutics or new generation targeted drugs. Anthracycline cardiotoxicity may occur anytime in the life of cancer survivors. Understanding the molecular mechanisms and clinical correlates of cardiotoxicity is necessary to improve the therapeutic index of anthracyclines or to identify active, but less cardiotoxic analogs.Areas covered:The authors review the pharmacokinetic, pharmacodynamic and biochemical mechanisms of anthracycline cardiotoxicity and correlate them to clinical phenotypes of cardiac dysfunction. Attention is paid to bioactivation mechanisms that converted anthracyclines to reactive oxygen species (ROS) or long-lived secondary alcohol metabolites. Preclinical aspects and clinical implications of the “oxidative stress” or “secondary alcohol metabolite” hypotheses are discussed on the basis of literature that cuts across bench and evidence-based medicine. Interactions of anthracyclines with comorbidities or unfavorable lifestyle choices were identified as important cofactors of the lifetime risk of cardiotoxicity and as possible targets of preventative strategies.Expert opinion:Anthracycline cardiotoxicity is a multifactorial process that needs to be incorporated in a translational framework, where individual genetic background, comorbidities, lifestyles and other drugs play an equally important role. Fears for cardiotoxicity should not discourage from using anthracyclines in many oncologic settings. Cardioprotective strategies are available and should be used more pragmatically in routine clinical practice.

Anthracyclines and many other antitumor drugs induce cardiotoxicity that occurs "on treatment" or long after completing chemotherapy. Dose reductions limit the incidence of early cardiac events but not that of delayed sequelae, possibly indicating that any dose level of antitumor drugs would prime the heart to damage from sequential stressors. Drugs targeted at tumor-specific moieties raised hope for improving the cardiovascular safety of antitumor therapies; unfortunately, however, many such drugs proved unable to spare the heart, aggravated cardiotoxicity induced by anthracyclines, or were safe in selected patients of clinical trials but not in the general population. Cardio-oncology is the discipline aimed at monitoring the cardiovascular safety of antitumor therapies. Although popularly perceived as a clinical discipline that brings oncologists and cardiologists working together, cardio-oncology is in fact a pharmacology-oriented translational discipline. The cardiovascular performance of survivors of cancer will only improve if clinicians joined pharmacologists in the search for new predictive models of cardiotoxicity or mechanistic approaches to explain how a given drug might switch from causing systolic failure to inducing ischemia. The lifetime risk of cardiotoxicity from antitumor drugs needs to be reconciled with the identification of long-lasting pharmacological signatures that overlap with comorbidities. Research on targeted drugs should be reshaped to appreciate that the terminal ballistics of new "magic bullets" might involve cardiomyocytes as innocent bystanders. Finally, the concepts of prevention and treatment need to be tailored to the notion that late-onset cardiotoxicity builds on early asymptomatic cardiotoxicity. The heart of cardio-oncology rests with such pharmacological foundations.

Secondary alcohol metabolites and reactive oxygen species mediate cardiomyopathy induced by cumulative doses of antitumor anthracyclines, such as doxorubicin and epirubicin. Epirubicin exhibits a defective conversion to both toxic species, thereby inducing cardiotoxicity at doses higher than equiactive to doxorubicin; however, the gain in cardiac tolerability seems to be marginal compared with the magnitude of the metabolic defects of epirubicin. Cardiomyopathy may occur independent of toxic metabolites if a given anthracycline tends to accumulate in the heart; therefore, we characterized whether epirubicin showed an unusual accumulation in human myocardial strips incubated in plasma. Epirubicin exhibited a higher uptake and reached myocardial levels 2 times higher than those of doxorubicin. Epirubicin also showed a unique metabolization to doxorubicinolone, the product of epirubicin deglycosidation and carbonyl reduction. In diffusing from the strips to plasma, doxorubicinolone caused membrane permeation effects that augmented epirubicin elimination. Experiments with purified doxorubicinolone showed that the efflux of 1 mol doxorubicinolone promoted the concomitant elimination of as many as approximately 40 mol epirubicin. Doxorubicinolone could also diffuse from plasma back to the strips, causing a permeation effect that promoted epirubicin reuptake; however, this reverse process was slower and less potent. On balance, doxorubicinolone efflux diminished the epirubicin to doxorubicin accumulation ratio to approximately 1.5. These results suggest that the cardiac tolerability of epirubicin is limited by its accumulation in the heart and that such accumulation would be even higher in the absence of doxorubicinolone formation and efflux. These results may also serve guidelines for developing noncardiotoxic anthracyclines.

Antitumor therapy with the anthracycline doxorubicin is limited by a severe cardiotoxicity, which seems to correlate with the cardiac levels of doxorubicin and its metabolization to reactive oxygen species. Previous biochemical studies showed that hydrogen peroxide-activated myoglobin caused an oxidative degradation of doxorubicin; however, a pharmacological evaluation of this metabolic pathway was precluded by the lack of safe and specific inhibitors of doxorubicin degradation. We found that tert-butoxycarbonyl-alanine inhibited doxorubicin degradation induced in vitro by hydrogen peroxide-activated oxyferrous myoglobin. When assessed in H9c2 cardiomyocytes, tert-butoxycarbonyl-alanine neither stimulated the cellular uptake of doxorubicin nor diminished its efflux; moreover, tert-butoxycarbonyl-alanine did not cause toxicity per se nor did it augment the toxicity induced by hydrogen peroxide or chemical agents that increased the cellular levels of reactive oxygen species. Nonetheless, tert-butoxycarbonyl-alanine increased the cellular levels of doxorubicin, its conversion to reactive oxygen species, and its concentration-related toxicity. tert-Butoxycarbonyl-alanine also aggravated the toxicity of a degradation-prone anthracycline analog, daunorubicin, but it caused a minor effect on the toxicity of a degradation-resistant analog, aclarubicin. These results suggested that tert-butoxycarbonyl-alanine increased the cellular levels and toxicity of doxorubicin by inhibiting its oxidative degradation to harmless products. Accordingly, doxorubicin samples that had been oxidized in vitro with hydrogen peroxide and oxyferrous myoglobin lacked toxicity to cardiomyocytes. The effects of tert-butoxycarbonyl-alanine were most evident at 0.1 to 1 muM doxorubicin, which may be relevant to clinical conditions. These studies identify an oxidative degradation of doxorubicin as a possible salvage mechanism for diminishing its levels and toxicity in cardiomyocytes.

The antitumor anthracycline doxorubicin induces a dose-related cardiotoxicity that correlates with the myocardial levels of its secondary alcohol metabolite doxorubicinol. Combining doxorubicin with taxanes such as paclitaxel or docetaxel may aggravate cardiotoxicity, presumably because the taxanes cause an allosteric-like stimulation of cytoplasmic aldehyde reductases that convert doxorubicin to doxorubicinol in the heart. A less severe aggravation of cardiotoxicity was observed on combining taxanes with epirubicin, a closely related analog of doxorubicin; therefore, we characterized whether the cardiac tolerability of epirubicin-taxane therapies could be due to a defective taxane stimulation of the conversion of epirubicin to its secondary alcohol metabolite epirubicinol. Comparisons between doxorubicin and epirubicin in isolated human heart cytosol showed that epirubicin exhibited a lower V(max)/K(m) value for reaction with aldehyde reductases and a defective stimulation of epirubicinol formation by paclitaxel or docetaxel. A similar pattern occurred in the soluble fraction of human myocardial strips incubated in plasma with anthracyclines and paclitaxel or docetaxel, formulated in their clinical vehicles Cremophor EL or polysorbate 80. Doxorubicin, but not epirubicin, was also able to generate reactive oxygen species in the membrane fraction of myocardial strips; however, the levels of doxorubicin-derived reactive oxygen species were not further augmented by paclitaxel. These results support the notion that taxanes might aggravate the cardiotoxicity of doxorubicin through a specific stimulation of doxorubicinol formation. The failure of paclitaxel or docetaxel to stimulate epirubicinol formation therefore uncovers an important determinant of the improved cardiac tolerability of epirubicin-taxane combinations.

Antitumor therapy with the anthracycline doxorubicin is limited by a dose-related cardiotoxicity that is aggravated by a concomitant administration of the taxane paclitaxel. Previous limited studies with isolated human heart cytosol showed that paclitaxel was able to stimulate an NADPH-dependent reduction of doxorubicin to its toxic secondary alcohol metabolite doxorubicinol. Here we characterized that 0.25 to 2.5 muM paclitaxel caused allosteric effects that increased doxorubicinol formation in human heart cytosol, whereas 5 to 10 muM paclitaxel decreased doxorubicinol formation. The closely related taxane docetaxel caused similar effects. Basal or taxane-stimulated doxorubicinol formation was blunted by 2,7-difluorospirofluorene-9,5'-imidazolidine-2',4'-dione (AL1576), a specific inhibitor of aldehyde reductases. Doxorubicinol was measured also in the cytosol of human myocardial strips incubated in plasma and exposed to doxorubicin in the absence or presence of paclitaxel or docetaxel and their clinical vehicles Cremophor EL or polysorbate 80. Low concentrations of taxanes stimulated doxorubicinol formation, whereas high concentrations decreased it. Doxorubicinol formation reached its maximum on adding plasma with 6 muM paclitaxel or docetaxel; this corresponded to the partitioning of 1.5 to 2.5 muM taxanes in the cytosol of the strips. Taxane-stimulated doxorubicinol formation was not mediated by vehicles, nor was it caused by increased doxorubicin uptake or de novo protein synthesis; however, doxorubicinol formation was blunted by AL1576. These results show that allosteric interactions with cytoplasmic aldehyde reductases enable paclitaxel or docetaxel to stimulate doxorubicinol formation in human heart. This information serves metabolic insights into the risk of cardiotoxicity induced by doxorubicin-taxane therapies.

The clinical use of doxorubicin and other anticancer anthracyclines is limited by the possible development of a life-threatening form of cardiomyopathy. Here, we briefly review biochemical and pharmacological studies that identify secondary alcohol metabolites as important mediators of cardiotoxicity induced by anthracyclines. The pharmacokinetics and pharmacodynamics of secondary alcohol metabolites suggest that they might cause cardiotoxicity while not mediating or actually diminishing the antitumour potency of anthracyclines. This concept implies that novel anthracyclines forming fewer amounts of their secondary alcohol metabolites might prove to spare the vulnerable cardiomyocytes while also retaining good activity in cancer cells, thus offering advantages over currently available anthracyclines in terms of therapeutic index. MEN 10755 (sabarubicin) is a newly designed disaccharide anthracycline that fits well in this context: it forms less alcohol metabolite than doxorubicin, and consistently induces less cardiac toxicity in laboratory animals in the face of an equal or even improved spectrum of activity in human tumour xenografts. On the basis of these preclinical findings, MEN 10755 has entered clinical trials, which will define its activity and safety and will serve an opportunity to probe the "secondary alcohol metabolite hypothesis" of cardiotoxicity.

The association of doxorubicin (DOX) and paclitaxel (PTX) is very active in breast cancer. Unfortunately, PTX may potentiate the cardiotoxic effects of anthracyclines: it causes nonlinear disposition of DOX and its metabolites, leading to persistant of elevated plasma concentrations of the anthracyclines. However, this pharmacokinetic interference is not sufficient to explain the enhanced cardiotoxicity of the combination. Recent data suggest that PTX stimulates the conversion of DOX to cardiotoxic metabolites (namely doxorubicinol) inside cardiomyocytes. Docetaxel (DTX) does not have a major influence on DOX plasma concentration because it does not interfere with its elimination. Clinical data suggest that DTX may not enhance anthracycline cardiotoxicity, but patients seldom received a total anthracycline dose compatible with increased risk. Furthermore, there are experimental data indicating that DTX can also stimulate the metabolism of DOX to toxic species in human heart.

The anticancer anthracycline doxorubicin (DOX) causes cardiotoxicity. Enzymatic reduction of a side chain carbonyl group converts DOX to a secondary alcohol metabolite that has been implicated in cardiotoxicity. We therefore monitored negative inotropism, assessed as inhibition of post‐rest contractions, in rat right ventricle strips exposed to DOX or to analogues forming fewer amounts of their alcohol metabolites (epirubicin, EPI, and the novel disaccharide anthracycline MEN 10755).Thirty μMEPI exhibited higher uptake than equimolar DOX, but formed comparable amounts of alcohol metabolite due to its resistance to carbonyl reduction. MEN 10755 exhibited also an impaired uptake, and consequently formed the lowest levels of alcohol metabolite. Accordingly, DOX and EPI inhibited post‐rest contractions by ∼40 – 50%, whereas MEN 10755 inhibited by ∼6%.One hundred μMEPI exhibited the same uptake as equimolar DOX, but formed ∼50% less alcohol metabolite. One hundred μMMEN 10755 still exhibited the lowest uptake, forming ∼60% less alcohol metabolite than EPI. Under these conditions DOX inhibited post‐rest contractions by 88%. EPI and MEN 10755 were ∼18% (P<0.05) or ∼80% (P<0.001) less inhibitory than DOX, respectively.The negative inotropism of 30 – 100 μMDOX, EPI, or MEN 10755 correlated with cellular levels of both alcohol metabolites (r=0.88, P<0.0001) and carbonyl anthracyclines (r=0.79, P<0.0001). Nonetheless, multiple comparisons showed that alcohol metabolites were ∼20 – 40 times more effective than carbonyl anthracyclines in inhibiting contractility. The negative inotropism of MEN 10755 was therefore increased by chemical procedures, like side chain valeryl esterification, that facilitated its uptake and conversion to alcohol metabolite but not its retention in a carbonyl form.These results demonstrate that secondary alcohol metabolites are important mediators of cardiotoxicity. A combination of reduced uptake and limited conversion to alcohol metabolite formation might therefore render MEN 10755 more cardiac tolerable than DOX and EPI.

The clinical use of anticancer anthra‐cyclines is limited by the development of a distinctive and life‐threatening form of cardiomyopathy upon chronic treatment. Commonly accepted mechanistic hypotheses have assigned a pivotal role to iron, which would act as a catalyst for free radical reactions and oxidative stress. Although perhaps involved in acute aspects of anthracycline cardiotoxicity, the role of free radical‐based mechanisms in long‐term effects has been challenged on both experimental and clinical grounds, and alternative hypotheses independent of iron and free radicals have flourished. More recently, studies of the role of C‐13 hydroxy metabolites of anthracyclines have provided new perspectives on the role of iron in the cardio‐toxicity of these drugs, showing that such metabolites can impair intracellular iron handling and homeostasis. The present review applies a multisided approach to the critical evaluation of various hypotheses proposed over the last decade for the role of iron in anthracycline‐induced cardiotoxicity. The main goal of the authors is to build a unifying pattern that would both account for hitherto unexplained experimental observations and help design novel and more rational strategies toward a much‐needed improvement in the therapeutic index of anthracyclines.—Minotti, G., Cairo, G., Monti, E. Role of iron in anthracycline cardiotoxicity: new tunes for an old song? FASEB J.13, 199–212 (1999)

Studies were carried out on microsomes isolated from the highly differentiated (slow-growing) Morris hepatoma 9618A, on microsomes and plasma membranes from the poorly differentiated (fast-growing) Morris hepatoma 3924A, and rat liver used as control. The lipid composition (phospho-lipid and cholesterol content, degree of fatty acid unsaturation) and peroxidation of such membranes has been correlated with the order and fluidity of the membrane bilayer. The results indicate that substrate availability is the rate-limiting step in microsomal and plasma membrane lipid peroxidation of hepatoma 3924A. From diphenylhexatriene fluorescence depolarization measurements it appears that the changes in lipid composition cause an increase in the order of the lipid bilayer on going from the control to hepatoma 9618A and 3924A microsomes, while fluidity is virtually unchanged. Conversely, for similar chemical changes, in plasma membranes from hepatoma 3924A the order is nearly the same and there is a decrease in fluidity. The changes in the above parameters of tumor membranes might be partly related to the loss of protective enzymes against oxygen radicals. This is supported by the observation that inhibition of liver superoxide dismutase and glutathione reductase, by treatment of rats with diethyldithiocarbamate and chloroethyl nitrosourea, respectively, renders the microsomal membranes more resistant to lipid peroxidation in vitro.

Microsomal membranes from the slow-growing Morris hepatoma 9618A catalyze, in the presence of t-butyl hydroperoxide, lower rates of lipid peroxidation than rat liver microsomes. The cytochrome P-450 content of hepatoma microsomes is about 40% that of the liver. SKF 525-A, an inhibitor of mixed-function oxidase, produces in hepatoma microsomes a P-450 type I binding spectrum similar to that of hepatic microsomes. The concentration of the inhibitor required for half-maximal spectral change is about 2 μM in both microsome types. SKF 525-A or ethylmorphine inhibit lipid peroxidation of normal and tumor microsomes to the same extent (about 60%). Treatment of the tumor-bearing rats with 3-methylcholanthrene increases the hepatoma cytochrome P-450 to values comparable to those of control membranes, although the hemoprotein has a peak in the CO-reduced difference absorption spectrum at 448 nm. The cytochrome P-448 induction is accompanied by an almost complete restoration of the hydroperoxide-dependent lipid peroxidation.

Cellular iron homeostasis is regulated by the cytoplasmic iron regulatory protein (IRP), which binds to iron‐responsive elements (IRE) of mRNAs, modulating iron uptake and sequestration, respectively. When iron is scarce, IRP binds to IRE and coordinately increases the synthesis of transferrin receptor and decreases that of ferritin, thus providing the cell with readily available free iron. When iron is in excess, IRP does not bind and iron sequestration prevails over iron uptake. We have found that incubation of rat liver lysates with xanthine oxidase (XO), which generates Superoxide (O2−)and hydrogen peroxide (H2O2), caused a remarkable but reversible inhibition of IRP activity, as the formation of IRE‐IRP decreased by 70‐80% but returned to baseline values upon exposure to a reducing agent like 2‐mercaptoethanol. IRP inhibition was prevented by separate or simultaneous addition of Superoxide dismutase and catalase, showing that both O2−and H2O2 were involved. By contrast, iron chelators and hydroxyl radical scavengers did not impede the inhibition of IRP, suggesting that O2−and H2O2acted independently of free iron sources. Ferritin enhanced IRP inhibition, but this process involved tightly bound iron centers that shunted reducing equivalents from XO and returned them to oxygen, thus increasing the formation of O2−. In agreement with the exclusive role of O2−and H2O2, XO also inhibited recombinant human IRP in the absence of iron. These results demonstrate that O2−and H2O2can directly but reversibly down‐regulate the RNA‐binding activity of IRP, causing transient decrease of free iron that otherwise would convert them into more potent oxidants such as hydroxyl radicals or equally aggressive iron‐peroxo complexes. This establishes a novel protective stratagem against oxidative injury under pathophysiologic conditions characterized by the excessive generation of O2−and H2O2.—Cairo, G., Castrusini, E., Minotti, G., Bernelli‐Zazzera, A. Superoxide and hydrogen peroxide‐dependent inhibition of iron regulatory protein activity: a protective stratagem against oxidative injury. FASEB J.10, 1326‐1335 (1996)

Anticancer therapy with doxorubicin (DOX) is limited by severe cardiotoxicity, presumably reflecting the intramyocardial formation of drug metabolites that alter cell constituents and functions. In a previous study, we showed that NADPH-supplemented cytosolic fractions from human myocardial samples can enzymatically reduce a carbonyl group in the side chain of DOX, yielding a secondary alcohol metabolite called doxorubicinol (DOXol). Here we demonstrate that DOXol delocalizes low molecular weight Fe(II) from the [4Fe-4S] cluster of cytoplasmic aconitase. Iron delocalization proceeds through the reoxidation of DOXol to DOX and liberates DOX-Fe(II) complexes as ultimate by-products. Under physiologic conditions, cluster disassembly abolishes aconitase activity and forms an apoprotein that binds to mRNAs, coordinately increasing the synthesis of transferrin receptor but decreasing that of ferritin. Aconitase is thus converted into an iron regulatory protein-1 (IRP-1) that causes iron uptake to prevail over sequestration, forming a pool of free iron that is used for metabolic functions. Conversely, cluster reassembly converts IRP-1 back to aconitase, providing a regulatory mechanism to decrease free iron when it exceeds metabolic requirements. In contrast to these physiologic mechanisms, DOXol-dependent iron release and cluster disassembly not only abolish aconitase activity, but also affect irreversibly the ability of the apoprotein to function as IRP-1 or to reincorporate iron within new Fe-S motifs. This damage is mediated by DOX-Fe(II) complexes and reflects oxidative modifications of ?SH residues having the dual role to coordinate cluster assembly and facilitate interactions of IRP-1 with mRNAs. Collectively, these findings describe a novel mechanism of cardiotoxicity, suggesting that intramyocardial formation of DOXol may perturb the homeostatic processes associated with cluster assembly or disassembly and the reversible switch between aconitase and IRP-1. These results may also provide a guideline to design new drugs that mitigate the cardiotoxicity of DOX.

Microsomal membranes from the slow‐growing Morris hepatoma 9618A catalyze, in the presence of t‐butyl hydroperoxide, lower rates of lipid peroxidation than rat liver microsomes. The cytochrome P‐450 content of hepatoma microsomes is about 40% that of the liver. SKF 525‐A, an inhibitor of mixed‐function oxidase, produces in hepatoma microsomes a P‐450 type I binding spectrum similar to that of hepatic microsomes. The concentration of the inhibitor required for half‐maximal spectral change is about 2 μM in both microsome types. SKF 525‐A or ethylmorphine inhibit lipid peroxidation of normal and tumor microsomes to the same extent (about 60%). Treatment of the tumor‐bearing rats with 3‐methylcholanthrene increases the hepatoma cytochrome P‐450 to values comparable to those of control membranes, although the hemoprotein has a peak in the CO‐reduced difference absorption spectrum at 448 nm. The cytochrome P‐448 induction is accompanied by an almost complete restoration of the hydroperoxide‐dependent lipid peroxidation.

Heme oxygenase (HO)-catalyzed degradation of cellular heme moieties generates biliverdin and equimolar amounts of carbon monoxide (CO), which has been implicated as a possible modulator of neural function. Technical difficulties preclude direct measurements of CO within intact nervous tissues; hence, alternative procedures are needed to monitor the formation and possible biologic functions of this gas. In the present study rat hypothalamic explants were found to generate 114 ± 5 or 127 ± 11 pmol biliverdin/hypothalamus/1 h (n = 3) upon incubation with 1 or 10 μM hemin, respectively. Ten micromolar zinc-protoporphyrin IX (Zn-PP-IX), a known inhibitor of HO, significantly decreased the degradation of 10 μM hemin from 127 ± 11 to 26 ± 11 pmol biliverdin/hypothalamus/1 h (n = 3; P < 0.01). Biliverdin was the principal product of HO-dependent heme degradation, as its possible conversion into bilirubin was precluded by hemin-dependent inhibition of biliverdin reductase. Basal or hemin-supplemented hypothalamic incubations were also shown to generate sizable amounts of propentdyopents (PDPs), reflecting HO-independent degradation pathways which do not liberate CO and cannot be inhibited by Zn-PP-IX. Plotting the ratio of biliverdin to PDPs thus provided an index of the efficiency with which hemin was degraded through biochemical pathways involving CO. Under the experimental conditions of our study, the biliverdin/PDPs ratio varied from 0 to 32 or 15%, depending on the absence or presence of 1 or 10 μM hemin respectively: this suggested that the formation of CO was most efficient at 1 μM hemin. Under these defined conditions, 1 μM hemin was also found to inhibit the release of arginine vasopressin (AVP) evoked by depolarizing solutions of KCl. A series of experiments showed that the effect of hemin was counteracted by Zn-PP-IX, and also by tin-mesoporphyrin IX, which is even more selective in inhibiting HO; it was also attenuated in the presence of the gaseous scavenger ferrous hemoglobin. Furthermore, the inhibition of AVP release could be reproduced by omitting hemin and by incubating hypothalami under CO, whereas treatment with biliverdin had no effect. This suggested that the release of AVP was suppressed by HO degradation of hemin, yielding CO as a modulator of hypothalamic function. These observations may be relevant to diseases characterized by inappropriate secretion of AVP and enzymatic disturbances affecting the synthesis of heme and the formation of CO through the HO pathway (e.g., acute intermittent porphyria or lead intoxication).

Heme oxygenase (HO)-catalyzed degradation of cellular heme moieties generates biliverdin and equimolar amounts of carbon monoxide (CO), which has been implicated as a possible modulator of neural function. Technical difficulties preclude direct measurements of CO within intact nervous tissues; hence, alternative procedures are needed to monitor the formation and possible biologic functions of this gas. In the present study rat hypothalamic explants were found to generate 114 ±5 or 127 ±11 pmol biliverdin/hypothalamus/1h (n =3) upon incubation with 1 or 10mM hemin, respectively. Ten micromolar zinc-protoporphyrin IX (Zn-PP-IX), a known inhibitor of HO, significantly decreased the degradation of 10 µM hemin from 127 ±11 to 26 ±11 pmol biliverdin/hypothalamus/1h (n= 3; P <0.01). Biliverdin was the principal product of HO-dependent heme degradation, as its possible conversion into bilirubin was precluded by hemin-dependent inhibition of biliverdin reductase. Basal or hemin-supplemented hypothalamic incubations were also shown to generate sizable amounts of propentdyopents (PDPs), reflecting HO-independent degradation pathways which do not liberate CO and cannot be inhibited by Zn-PP-IX. Plotting the ratio of biliverdin to PDPs thus provided an index of the efficiency with which hemin was degraded through biochemical pathways involving CO. Under the experimental conditions of our study, the biliverdin/PDPs ratio varied from 0 to 32 or 15%, depending on the absence or presence of 1 or 10 µM hemin respectively: this suggested that the formation of CO was most efficient at 1 µM hemin. Under these defined conditions, 1 µM hemin was also found to inhibit the release of arginine vasopressin (AVP) evoked by depolarizing solutions of KCl. A series of experiments showed that the effect of hemin was counteracted by Zn-PP-IX, and also by tin-mesoporphyrin IX, which is even more selective in inhibiting HO; it was also attenuated in the presence of the gaseous scavenger ferrous hemoglobin. Furthermore, the inhibition of AVP release could be reproduced by omitting hemin and by incubating hypothalami under CO, whereas treatment with biliverdin had no effect. This suggested that the release of AVP was suppressed by HO degradation of hemin, yielding CO as a modulator of hypothalamic function. These observations may be relevant to diseases characterized by inappropriate secretion of AVP and enzymatic disturbances affecting the synthesis of heme and the formation of CO through the HO pathway (e.g., acute intermittent porphyria or lead intoxication).

Possible sources of iron for lipid peroxidation are described and discussed. In particular. evidence is presented that microsomes contain ferric nonheme iron which may participate in formation of lipid oxidants. provided reductants are available to favor its mobilization from membrane binding sites. Aging-and tumor-associated changes of this microsomal pool of nonheme iron are also described and discussed from biochemical and biomedical viewpoints.

Iron plays a central role in oxidative injury, reportedly because it catalyzes superoxide- and hydrogen peroxide-dependent reactions yielding a powerful oxidant such as the hydroxyl radical. Iron is also thought to mediate the cardiotoxic and antitumour effects of adriamycin and related compounds. NADPH-supplemented microsomes reduce adriamycin to a semiquinone radical, which in turn re-oxidizes in the presence of oxygen to form superoxide and hence hydrogen peroxide. During this redox cycling membrane-bound nonheme iron undergoes superoxide dismutase- and catalase-insensitive reductive release. Membrane iron mobilization triggers lipid peroxidation, which is markedly enhanced by simultaneous addition of superoxide dismutase and catalase. The results indicate that : i) lipid peroxidation is mediated by the release of iron, yet the two reactions are governed by different mechanisms; and ii) oxygen radicals are not involved in or may actually inhibit adriamycin-induced lipid peroxidation. Microsomal iron delocalization and lipid peroxidation might represent oxyradical-independent mechanisms of adriamycin toxicity.

Doxorubicin (DOX) and related drugs are incompletely cleared from the heart, persist for months to years (Stewart et al Anticancer Res 1993), and slowly transform to longer-lived and more toxic secondary alcohol metabolites (eg, DOXOL) that are associated with an increased lifetime risk of congestive heart failure (Minotti et al J Pharmacol Exp Ther 2010). Anthracycline-related cardiotoxicity can be precipitated by enhanced stress or exposure to drugs that increase DOXOL formation. PIX is a novel aza-anthracenedione that is under development in patients with NHL that relapsed or was refractory after DOX-containing combination therapy. In preclinical models, PIX produced substantially less cardiotoxicity than DOX or MITOX even when animals were pretreated with DOX. Compared to anthracyclines and the anthracenedione analogue, mitoxantrone (MITOX), PIX lacks a hydroquinone moiety that binds iron and facilitates cardiotoxic free radical reactions. To further establish that it is safe in patients with NHL and prior DOX exposure, PIX should also have no effect on or diminish DOXOL formation from the cardiac residues of first-line DOX.To characterize the effects of PIX on DOXOL formation in a translational cardiac model of DOX administration followed by PIX administration. MITOX was used as the comparator.Myocardial samples that were routinely discarded during aorto-coronary bypass grafting were dissected into strips and loaded with 10 μM DOX in plasma. After 30 min the strips were subjected to 2h multiple washouts to simulate post-treatment clearance. The strips were then incubated for 1.5h in fresh anthracycline-free plasma w/wo 1 μM PIX or MITOX. After the experiments, DOX(OL), PIX, and MITOX were extracted from the soluble fractions of the strips and assayed by HPLC. Pharmacometabolic interactions of 10 μM or 50 μM DOX with increasing concentrations of PIX or MITOX were also studied in NADPH-supplemented isolated soluble fractions.After sequential DOX loading/clearance and PIX or MITOX administration, PIX:DOX ratios were significantly higher than MITOX:DOX ratios in soluble fractions of human myocardial strips. This correlated with inhibition of DOXOL formation by both PIX and MITOX, but PIX decreased DOXOL levels in a significant manner when compared to MITOX (Table). In isolated soluble fractions, both PIX and MITOX, in a concentration-dependent manner, inhibited the metabolism of 10 μM DOX to DOXOL; however, PIX caused stronger inhibition (Figure). Increasing DOX to 50 μM abated inhibition by MITOX but not by PIX.PIX inhibited DOXOL formation in a translation model of human heart used to simulate sequential DOX and PIX administration. This finding was obtained under pharmacokinetically relevant conditions that probed DOX and PIX at their clinically documented plasma Cmax values of 10 μM or 1 μM, respectively. Studies with isolated soluble fractions suggest that PIX diminished DOXOL formation by noncompetitive inhibition of NADPH-dependent reductases. MITOX was less effective than PIX at diminishing DOXOL formation, which correlated with the lower MITOX:DOX ratios in treated human myocardial strips and with the competitive mode of action of MITOX. By inhibiting formation of toxic and long-lived DOXOL, PIX potentially is a cardiac tolerable therapeutic agent for patients with NHL that failed or relapsed after DOX treatment.Inhibition of DOXOL formation by PIX and MITOX in isolated soluble fractions of human myocardium incubated with NADPH (0.25 mM) and DOX for 4h. Control DOXOL was 0.15–0.19 nmoles/mg of protein at 10 μM DOX and 0.34–0.84 nmoles/mg of protein at 50 μM DOX. Each inhibition curve is the mean and SE of three experiments.Salvatorelli: Cell Therapeutics, Inc: Research Funding. Gonzalez Paz:Cell Therapeutics, Inc: Research Funding. Singer:Cell Therapeutics, Inc: Employment. Menna:Cell Therapeutics, Inc: Research Funding. Minotti:Cell Therapeutics, Inc: Research Funding.

Abstract 4966