American Journal of Therapeutics 21, 512–522 (2014)

Cardiovascular Safety Monitoring During Oncology Drug Development and Therapy J. Rick Turner, PhD,1* Gopi Krishna Panicker, BHMS, PGDCR,2 Dilip R. Karnad, MD, FACP, FRCP(Glasg),2 Christopher H. Cabell, MD, MHS, FACC,3 Ronald Lieberman, MD,4 and Snehal Kothari, MD, DM, FACC, FESC2

Assessments of cardiac and cardiovascular toxicity are prominent components of drug safety endeavors during drug development and clinical practice. Oncologic drugs bring several challenges to both domains. First, during drug development, it is necessary to adapt the ICH E14 “Thorough QT/QTc Study” because the cytotoxic nature of many oncologics precludes their being administered to healthy individuals. Second, appropriate benefit–risk assessments must be made by regulators: given the benefit these drugs provide in life-threatening illnesses, a greater degree of risk may be acceptable when granting marketing authorization than for drugs for less severe indications. Third, considerable clinical consideration is needed for patients who are receiving and have finished receiving pharmacotherapy. Paradoxically, although such therapy has proved very successful in many cases, with disease states going into remission and patients living for many years after cessation of treatment, cardiotoxicities can manifest themselves relatively soon or up to a decade later. Oncologic drugs have been associated with various off-target cardiovascular responses, including cardiomyopathy leading to heart failure, cardiac dysrhythmias, thromboembolic events, and hypertension. Follow-up attention and care are, therefore, critical. This article reviews the process of benefit–risk estimation, provides an overview of nonclinical and preapproval clinical assessment of cardiovascular safety of oncology drugs, and discusses strategies for monitoring and management of patients receiving drugs with known cardiotoxicity risk. These measures include cardiac function monitoring, limitation of chemotherapy dose, use of anthracycline analogs and cardioprotectants, and early detection of myocardial cell injury using biomarkers. Keywords: cardiac safety, proarrhythmia, oncology, drug development and therapy, QT interval, thorough QT/QTc study

INTRODUCTION Assessments of drug safety during preapproval clinical development programs and the safety of patients receiving all forms of biopharmaceutical therapy are rightly of 1

Quintiles Cardiac Safety Center of Excellence, Durham, NC; Quintiles Cardiac Safety Services, Mumbai, India; 3Quintiles Therapeutic Delivery Unit, Durham, NC; and 4Quintiles Oncology Therapeutic Area, Rockville, MD. The authors have no funding or conflicts of interest to declare. *Address for correspondence: Senior Scientific Director, 4820 Emperor Blvd, Room 846, Durham, NC 27703. E-mail: rick. [email protected] 2

1075–2765 Ó 2014 Lippincott Williams & Wilkins

considerable current interest among multiple stakeholders in many countries. In the United States, these include the US Food and Drug Administration (FDA), Congress, the Supreme Court, prescribing physicians, patients, the Institute of Medicine (IOM), pharmaceutical companies, and patient advocacy groups.1 Assessments of cardiac and cardiovascular toxicity are prominent components of drug safety endeavors,2,3 and associated concerns remain a major reason for attrition of potential drugs. Drug cardiovascular toxicities include cardiac dysrhythmias, hypertension, cardiomyopathy (CMP), valvular heart disease, pericarditis or myocarditis, ischemia and myocardial infarction, and congestive heart failure.4 A study spanning 2 decades of drug www.americantherapeutics.com

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Table 1. Cardiotoxicity parameters listed in package inserts for a sample of oncologic drugs.

Drug (class and indication) Bevacizumab (vascular endothelial growth factor-specific angiogenesis inhibitor: multiple indications including metastatic colorectal cancer, with intravenous 5fluorouracil–based chemotherapy for first- or secondline treatment) Doxorubicin (anthracycline topoisomerase inhibitor: indicated for ovarian cancer after failure of platinum-based chemotherapy; AIDS-related Kaposi Sarcoma after failure of prior systemic chemotherapy or intolerance to such therapy) Lapatinib (kinase inhibitor: indicated in combination with (1) capecitabine, for the treatment of patients with advanced or metastatic breast cancer whose tumors overexpress HER2 and who have received prior therapy including an anthracycline, a taxane, and trastuzumab and (2) letrozole for the treatment of postmenopausal women with hormone receptor positive metastatic breast cancer that overexpresses the HER2 receptor for whom hormonal therapy is indicated) Nilotinib (kinase inhibitor: indicated for newly diagnosed adult patients with Philadelphia chromosome positive chronic myeloid leukemia (Ph+ CML) in chronic phase; chronic phase (CP) and accelerated phase (AP) Ph+ CML in adult patients resistant to or intolerant to prior therapy that included imatinib) Pazopanib (kinase inhibitor: indicated for advanced renal cell carcinoma; patients with advanced soft tissue sarcoma who have received prior chemotherapy) Sorafenib (kinase inhibitor: indicated for unresectable hepatocellular carcinoma; advanced renal cell carcinoma) Sunitinib (kinase inhibitor: indicated for gastrointestinal stromal tumor after disease progression or intolerance to imatinib mesylate; advanced renal cell carcinoma; progressive, well-differentiated pancreatic neuroendocrine tumors (pNET) in patients with unresectable locally advanced or metastatic disease) Vandetanib (kinase inhibitor: indicated for symptomatic or progressive medullary thyroid cancer in patients with unresectable locally advanced or metastatic disease)

development revealed that of all the potential new drug molecules that fail in the nonclinical phase, 27% do so because of cardiovascular toxicity concerns: for phase 1 trials, the respective figure is 9%.5 Of the 47 marketed drugs withdrawn between 1957 and 2007, 45% were withdrawn because of cardiovascular toxicity concerns.5 In the past 5 years, 4 drugs (pergolide, tegaserod, sibutramine, and propoxyphene) have been similarly withdrawn.6 Although attention during development of all categories of drugs focuses on the prospective exclusion of www.americantherapeutics.com

Parameters mentioned in the “highlights of prescribing information” Arterial thromboembolic events, for example, myocardial infarction, cerebral infarction: hypertension7

Acute left ventricular failure; heart failure; cardiomyopathy (Note: information presented in Section 5.1 of the full prescribing information) Boxed warning: cardiotoxicity8 QT prolongation possible in some patients; decreased LVEF9

QT prolongation; sudden deaths in patients with resistant or intolerant Ph+ CML (ventricular repolarization abnormalities may have contributed to their occurrence). Boxed warning for QT prolongation and sudden deaths10

QT prolongation and TdP; congestive heart failure and decreased LVEF; hypertension; fatal hemorrhagic events; arterial thrombotic events11 Hypertension; cardiac ischemia and/or infarction may occur12 QT prolongation and TdP; cardiac toxicity including LVEF declines to below the lower limit of normal and cardiac failure including death; hypertension; hemorrhagic events13

QT prolongation, TdP, and sudden death; heart failure; hemorrhage; hypertension. Boxed warning for QT prolongation, TdP, and sudden death. Risk evaluation mitigation strategy in place14

unacceptable cardiovascular risk associated with each drug, the level of risk that is deemed acceptable differs according to various factors, including the severity of the disease for which a drug would be indicated and the availability or not of other marketed treatments. Given the short-term life-threatening nature of many forms of cancer, cardiovascular risks associated with an oncologic therapy may well be regarded as more acceptable by regulators, physicians, and patients than commensurate risk associated with drugs for less severe indications. Additionally, although postmarketing American Journal of Therapeutics (2014) 21(6)

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surveillance is important for all drugs because unanticipated rare toxicities can arise for any drug used in a large number of patients, close monitoring of oncology patients receiving drugs with cardiotoxic liabilities known at the time of marketing approval is critical. Oncologic drugs are associated with various offtarget cardiovascular responses, including cardiomyopathy leading to heart failure, cardiac dysrhythmias, thromboembolic events, and hypertension. Table 1 provides some examples of oncologic drugs and associated cardiotoxicities: each of these drugs is discussed subsequently. As Cardinale et al15 recently discussed, “Cardiotoxicity due to cancer treatment is of rising concern, for both cardiologists and oncologists, because it may have a significant impact on cancer patient management and outcome.” A major concern is that, while some cardiotoxicities will manifest themselves relatively quickly, others will not: Octavia et al16 observed that approximately 10% of patients treated with doxorubicin or its derivatives will develop cardiac complications up to 10 years after the cessation of chemotherapy. Therefore, “prevention of cardiotoxicity remains the most important strategy.”15 Such a preventative strategy has components in both drug development and clinical practice. First, identification and minimization of the cardiotoxicity of drugs brought to market is important. Second, when a drug with an identified cardiotoxic liability is marketed because regulators consider that, at a public health level, it has a favorable benefit–risk balance in the context of providing treatment for a serious disease(s), appropriate benefit–risk assessments must be made by prescribing physicians on a patient-by-patient basis, and appropriate cardiovascular monitoring was performed. Various measures include cardiac function monitoring, limitation of chemotherapy dose, use of anthracycline analogs

Benefit
risk estimate 5

The safety and efficacy of biopharmaceutical medicines are both of interest. Straightforward statistical analyses reveal whether or not a clinical trial has provided compelling evidence of efficacy, where the term compelling is operationalized by a set of statistical conventions that all interested parties have agreed to honor and which centers on demonstration of attainment of the P , 0.05 level of statistical significance (if this is attained, equally important attention then turns to evaluation of clinical significance, a quite separate assessment). However, defining safety in this context is considerably less straightforward.17 Although use of the word in everyday language might initially predispose one to think that safety is synonymous with the absence of risk, this is not so. Operational definitions of safety are therefore needed, and an authoritative one was provided by the FDA’s Sentinel Initiative18: Using medical products brings benefits and risks. Although marketed medical products are required by federal law to be safe for their intended use, safety does not mean zero risk. A safe product is one that has acceptable risks, given the magnitude of benefit expected in a specific population and within the context of alternatives available. Deciding on whether the risk of harm from a drug is “acceptable,” therefore, requires concurrent consideration of the therapeutic benefit of the drug, the severity of the disease or clinical condition of concern, and the availability or not of alternative therapies. The construct of benefit–risk estimates has become pragmatically useful in this regard. Turner and Durham3 conceptualized this determination as follows:

Estimate ðprobability and degreeÞ of benefit Estimate ðprobability and degreeÞ of harm

and cardioprotectants, and early detection of myocardial cell injury using biomarkers.15 This article reviews the process of benefit–risk estimation, provides an overview of nonclinical and preapproval clinical assessment of cardiovascular safety of oncology drugs, and discusses strategies for monitoring and management of patients receiving drugs with known cardiac toxicity risk. American Journal of Therapeutics (2014) 21(6)

DEFINING “SAFETY” IN BIOPHARMACEUTICAL MEDICINE

In preapproval clinical trials, benefit would be measured by the likelihood and magnitude of the efficacy of a new therapy, and harm by adverse events; in a postmarketing setting, these would be measured by effectiveness and adverse drug reactions, respectively. For a given likelihood of occurrence, a greater magnitude of either benefit or harm will carry more weight in the estimation of the safety profile of a drug (risk-adjusted benefit). www.americantherapeutics.com

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Garattini19 observed that “drug authorization, prescription, and utilization are all based on benefit–risk assessment.” This observation captures well the ubiquity and importance of benefit–risk estimation. However, it is not an easy process. Currently, qualitative assessments of benefit–harm are most commonly performed, although there is considerable interest in further refining this process by incorporation of quantitative approaches.20,21 Both the development of a drug and its therapeutic use require favorable benefit–harm estimations. In the context of cardiovascular safety assessments, this approach translates into methodologies for the prospective exclusion of unacceptable risk during drug development.

DYSRHYTHMIAS, QT INTERVAL PROLONGATION, AND TORSADOGENIC LIABILITY Torsades de Pointes (TdP—discussed in more detail shortly), atrial fibrillation (AF), and bradyarrhythmias such as sinus bradycardia, sinus node dysfunction, and atrioventricular conduction disorders constitute the most frequent drug-induced dysrhythmias. Ascribing causality to drug-associated AF is more difficult than with other drug-induced dysrhythmias such as TdP because it is more likely to occur in patients who are at high risk of developing spontaneous AF because of advanced age, alcohol consumption, family history of AF, hypertension, thyroid dysfunction, sleep apnea, and heart disease. The occurrence of drug-induced TdP has been known since the early 1960s.22 TdP is a polymorphic ventricular tachycardia that is often self-correcting but, in rare cases, can be fatal. It has 3 characteristics:

 It is associated with QT interval prolongation.  The morphology of the QRS complex appears to twist around an imaginary axis [the isoelectric line on the electrocardiogram (ECG)], hence the French name meaning “twisting of the points.”  There are many QRS morphologies seen twisting around the axis, leading to the term polymorphic. The QT interval represents the total time of cardiomyocyte depolarization and repolarization and is defined as the length in the time domain from the onset of the Q-wave to the offset of the T-wave as seen on the ECG, measured in milliseconds. QT interval prolongation is reflective of delayed repolarization. TdP is among the most common dysrhythmias encountered with cardiotoxic medications and the phenomenon of drug-induced QT interval prolongation as its harbinger has been well established.3,23–27 www.americantherapeutics.com

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The association of TdP with QT interval prolongation has led to the use of the latter as a cardiac safety biomarker of torsadogenic liability during drug development. Indeed, since the early 1990s, after the exponential increase in reports of dysrhythmias associated with QT prolongation by new noncardiac drugs (drugs for noncardiac indications), its assessment has dominated the evaluation of cardiac risk. Growing concern over drug-induced QT prolongation among the regulatory authorities resulted in the release in 2005 of 2 International Conference on Harmonisation (ICH) guidelines after almost 8 years of deliberation and debate.27,28 These were the ICH S7B guidance for nonclinical testing of QT prolongation,29 and the ICH E14 guidance addressing the clinical assessment of proarrhythmic potential of a new drug.30,31 ICH E14 describes a dedicated clinical trial, the Thorough QT/QTc (TQT) study, in which any drug-induced QT prolongation can be measured. Nonclinical assessments In almost all reported cases, drugs that prolong the QT interval do so by inhibition of the IKr potassium channel (also known as the hERG channel, encoded by hERG), through which flows the repolarizing IKr current (hERG current). Drug blockade of the channel results in a decrease in function of the channel, less IKr current, and a reduction in net repolarizing influence.3 The S7B guideline describes a core cardiovascular study battery that includes an in vitro test and an in vivo experimental model for experiments on this channel.29 The in vitro model includes patch clamp experiments in Human Embryonic Kidney 293 (HEK293) or Chinese Hamster Ovary cell lines that have been stably transfected with the encoding gene, or in native cardiac cells that express the IKr potassium channel on the cell membrane.32 The ratio of the 50% inhibitory concentration (IC50) for the hERG assay or serum concentration that produces a 10% prolongation of the QT interval in patch clamp studies to the free plasma concentration of drug required for clinical efficacy is used as an index of proarrhythmic potential. Although the S7B guideline does not specify thresholds to stratify proarrhythmic risk based on these studies, a ratio of ,30 is considered to be indicative of likely QT interval prolongation, values between 30 to 100 are borderline, wheras a value .100 is considered to reflect acceptable safety.33 Gintant34 recently reviewed the correlation between results of hERG assay and TQT studies for 39 drugs. Of the 16 drugs found to be safe on hERG assay (IC50 . 100 mM), 3 drugs (alfusozin, sitagliptin, and ambrisentan) produced a mean QTc prolongation of .5 ms in TQT studies. Ten drugs had a ratio of American Journal of Therapeutics (2014) 21(6)

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IC50/mean Cmax of ,30; 8 of these showed mean QTc prolongation of .5 ms in TQT studies. However, so did 1 of 5 drugs with ratios between 30 and 100 and 5 of 19 drugs with ratios .100.34 Gintant concluded that a hERG safety margin ratio of 45 had sensitivity of 64% and specificity of 88% and an area under the receiver operating characteristic curve of 0.72. Thus, an integrated risk assessment approach combining findings of several preclinical assays as suggested by the ICH S7B guideline seems prudent as an individual test may have limitations.29 In vivo cardiovascular studies are conducted by telemetric monitoring of conscious, freely moving nonrodents, with emphasis given to the collection of ECG data and to the morphological analysis of the T-wave. Preapproval clinical assessments The ICH E14 guideline30 and the associated “Questions & Answers” document31 lay out the framework under which all new drugs with systemic bioavailability currently have to undergo a TQT study designed specifically to test whether the new drug, when compared with placebo, causes a QT interval prolongation around 5 ms. Digital 12-lead ECGs are recorded at several time points, which are maximally clustered around the drug’s Tmax, after administration of the proposed therapeutic dose and also a supratherapeutic dose of the drug. The definition of a supratherapeutic dose, which is frequently (but not necessarily) a significant multiple of the proposed therapeutic dose, is one that covers the worst possible scenario, that is, a dose sufficient to equal or exceed the highest concentration achieved by metabolic or excretion blockade, such as hepatic or renal impairment.25 Continuous highquality digital Holter ECG recording is increasingly used in TQT studies. This offers several advantages, including options of extracting more ECGs at time points close to the Tmax and extracting ECGs at any other time points that become of interest, and obtaining 10-second snapshots at stable heart rates, thereby permitting better heart rate correction of the QT interval.23 Moreover, the sensitivity of Holter ECGs to diagnose some transient arrhythmias is several folds higher than with conventional 10-second ECGs.35 ECGs are analyzed in a core ECG laboratory by expert readers. The measured QT interval is corrected for the effect of heart rate (heart rate and QT interval are negatively associated, but imperfectly so) to obtain QTc, the QT interval “corrected” for heart rate. If the 95% 1-sided upper bound of a confidence interval placed around the treatment effect point estimate of the placebo-adjusted QTc prolongation is ,10 ms at all time points at which ECGs are recorded, for both the therapeutic and supratherapeutic doses of a new American Journal of Therapeutics (2014) 21(6)

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drug, subsequent clinical studies will receive less regulatory scrutiny for proarrhythmic risk. If the 10-ms threshold is breached at any time point, additional regulatory scrutiny will be generated. It should be emphasized that, as a result of adopting a benefit–risk approach, drugs falling in this category are not necessarily doomed to fail to achieve final marketing approval, but at a minimum they will require more stringent ECG monitoring during subsequent phase 2 and phase 3 studies, and if approved they may carry certain warnings in their package inserts. Execution of the traditional TQT study just discussed is not suitable for many oncology drugs because their general toxicities make them inappropriate for administration to the healthy adult population involved in TQT studies. This, however, does not excuse these drugs from QT prolongation assessment: the requirement here (similarly to other cases where a drug cannot ethically be given to healthy adult participants) is to do assessments that are as thorough as possible in patients with cancer.36–38 The following alternative study designs for TQT studies have been accepted by the FDA in some specific instances: (1) TQT studies in patients with advanced cancer in phase 1 or in a subset of the target study population in a phase 3 trial which incorporates a placebo control;39 (2) use of the recommended phase 3 dose but no requirement for a positive control (typically moxifloxacin) or use of a supratherapeutic dose;40,41 and (3) testing the statistical hypothesis that the mean maximal QTc prolongation is less than 20 ms.37,42 In addition, the inclusion/exclusion criteria should define certain concomitant medications noted in the section entitled Risk Mitigation Strategies in Clinical Practice that are known to be associated with TdP and/or prolongation of the QT interval. It is important to note that the rationale for each departure from the ICH E14-defined QT risk assessment paradigm should be stated explicitly and the next best alternative analysis plan justified. However, standard design features are usually recommended, including the use of concentration-QTc (CQT) modeling with collection of time-matched QTc intervals between baseline and multiple postdose time points with mean placebo- and baseline-corrected QTc intervals. The postdose CQT modeling data are usually collected after a single dose and, more importantly, after multiple doses at steady state, capturing sufficient drug concentration samples to adequately characterize the exposure-time profile. Current recommendations further recognize that CQT modeling may have particular value in phase 1 first-in-human dose escalation studies in cancer patients when high-quality ECGs www.americantherapeutics.com

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and correlative pharmacokinetic testing can be obtained across multiple treatment centers. Drugs where potential benefits outweigh cardiovascular risks (e.g., vandetanib for the treatment of symptomatic or progressive medullary thyroid cancer in patients with unresectable, locally advanced or metastatic disease43) are developed further despite the QT effect. These drugs may receive regulatory approval for marketing because of their unique features, albeit with the addition of a precautionary statement in the package insert, a black box warning, and/or requirements associated with a risk evaluation mitigation strategy. In these cases, extensive postmarketing surveillance with spontaneous reporting of adverse events by patients and physicians is expected by regulators (although it should be noted that such reporting has been found to significantly underestimate the true incidence of drug-induced TdP44). Risk mitigation strategies in clinical practice Despite their limitations, drugs that prolong the QT interval are commonly used in patients with cancer. Patients should be evaluated thoroughly for other conditions that prolong the QT interval, such as female sex, electrolyte imbalances such as hypokalemia or hypocalcemia, and concomitant medications such as ondansetron, granisetron, metoclopramide, prochlorperazine, diphenhydramine, haloperidol, fluoroquinolones, macrolide antibiotics, and some cardiac medications such as sotalol, flecainide, and mexilitine. The risks of using an anticancer drug with a QT liability must then be weighed against its benefits, and alternative drugs should be considered. If it is decided to administer the drug, reversible conditions and concomitant medicines that may exaggerate the QT effect must be addressed before drug initiation. It would be prudent to record ECGs at a time point close to the Tmax and also just before the next dose. QT prolongation in excess of 500 ms would require delaying the next dose of the drug and close observation for development of TdP.

CARDIOMYOPATHY CMPs include a heterogeneous group of myocardial diseases associated with mechanical and/or electrical dysfunction, which usually exhibit inappropriate ventricular hypertrophy or dilatation, and are further classified according to morphological and functional criteria into dilated, hypertrophic, restrictive, and arrhythmogenic right ventricular cardiomyopathy.45 Several oncologic drugs have been associated with CMP, and it is classically seen with anthracyclines such www.americantherapeutics.com

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as daunorubicin and doxorubicin.46 Anthracyclineinduced cardiotoxicity may be acute (,3 months after treatment), early-onset (3–12 months after treatment), and late-onset (1 year or more after completion of treatment).46 The acute cardiotoxicity is not dose dependent and is seen in 1% of cancer patients. It manifests as acute pericarditis/myocarditis and is characterized by a transient decline in indices of myocardial contractility on echocardiography and alterations in the ST segment and T-wave morphology with prolongation of the QT interval. Early-onset cardiotoxicity is reported in 1.6%– 2.1% of patients and is dose dependent. Late-onset cardiomyopathy is observed in up to 1.6%–5% of patients.46 Suter and Ewer47 recently classified cardiotoxicity for oncologic drugs as irreversible (type 1) and reversible (type 2) dysfunctions. Type 1 cardiotoxicity occurs because of cell loss that induces the progressive myocardial dysfunction classically seen with anthracyclines.48 Other drugs with dose-dependent or concomitant drugbased type 1 toxicity include cyclophosphamide (.1.50 g$m22$d21), ifosfamide (12.5 g$m22), paclitaxel, and docetaxel.46 Type 2 cardiotoxicity results from cellular dysfunction that is usually reversible, not associated with release of markers of myocardial injury, and with normalization of cardiovascular function on completion of therapy. Anti-HER2 (human epidermal growth factor receptor 2) agents typically cause type 2 cardiotoxicity. Trastuzumab, a humanized monoclonal antibody directed against the HER2 receptor, usually produces type 2 toxicity, but may cause type 1 toxicity in patients with preexisting heart disease or prior anthracycline therapy.46 Interferon-a is another agent that may cause type 1 or type 2 cardiotoxicity, probably secondary to myocardial inflammation.48 This classification is of importance in the assessment of the risk of CMP induced by targeted oncology drugs, and type 2 drugs may be considered more favorably in “go/no-go” decisions during drug development.46 Nonclinical assessments The nonclinical assessments of chemotherapeutic drugs for the risk of CMP have been most substantially characterized with anthracyclines as the prototype of Suter and Ewer’s type 1 cardiotoxicity.47,48 Anthracyclines have been shown to cause a concentration-dependent increase of intracellular oxidative stress, increased cytosolic calcium, mitochondrial dysfunction, and myocyte apoptosis or necrosis.49 Other possible mechanisms include accumulation of hydrophilic metabolites of anthracyclines in cardiomyocytes, causing impaired expression of various important cardiac proteins, disruption of cellular and mitochondrial calcium homeostasis, induction of mitochondrial DNA lesions and disruption of mitochondrial bioenergetics, American Journal of Therapeutics (2014) 21(6)

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degradation of myofilamental and cytoskeletal proteins such as titin and dystrophin, and interference with various prosurvival kinases.49,50 Several nonclinical models have been proposed to assess these potential mechanisms. These include cell-free in vitro experiments involving microsomes and simple cellular models using isolated neonatal and adult rat cardiomyocytes.50 Recent cellular model studies have used cardiomyocyte-derived cell lines such as H9c2 rat embryonic cardiomyoblasts.50 Ex vivo studies use isolated atria, papillary muscles, or whole heart Langendorff preparations perfused with the study drug.50 In vivo studies involve repeated administration of anthracyclines in animal models including the mouse, rat, rabbit, pig, and dog, leading to loss of myocardial cells and exhaustion of compensatory mechanisms resulting in chronic cardiotoxicity similar to that seen in clinical practice.49 These studies could also be used to predict the cumulative dose that results in cardiac dysfunction. Newly developed targeted therapies such as trastuzumab, imatinib, and bevacizumab, which specifically inhibit highly selected targets and stop cancer cell proliferation, were thought to have less harmful off-target effects and were not subjected to stringent nonclinical assessment for cardiac toxicity. They were subsequently identified to have type 2 cardiotoxicity.47 It is now known that some of the targets inhibited by these new oncologic drugs are important for the maintenance of cellular homeostasis of normal tissue leading to reversible myocardial cell dysfunction. Because the mechanisms of cardiac toxicity of these drugs are not clearly understood, screening and early detection of cardiac toxicity are still at a nascent stage. Various strategies for screening are being developed including exposure of human cardiac myocytes to the study drug to evaluate its effect on key cardiac metabolic pathways such as the AMP-activated kinase pathway and on intracellular lipid and reactive oxygen species accumulation, mitochondrial changes, and cellular apoptosis.51,52 Although these models have helped in understanding the mechanisms of cardiotoxicity of already-developed anticancer agents, their ability to predict clinical outcomes has not been tested and cutoffs to define toxicity are unclear.53 Risk mitigation strategies in clinical practice Establishing the diagnosis of cardiomyopathy in patients undergoing active cancer treatment is often challenging, as common symptoms and signs such as fatigue, dyspnea, increased jugular venous distension, and lung crepitations may be due to other causes.4 Noninvasive modalities are preferred for evaluation of chemotherapy-induced CMP. These include American Journal of Therapeutics (2014) 21(6)

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echocardiography, radionuclide ventriculography, multiple-gated acquisition (MUGA), CT, and MRI scans.48,53 Echocardiography is commonly used for monitoring cardiac function in cancer patients because it permits quantification of left ventricular size and function, diastolic function, assessment of heart valvular status, and diagnosis of pericardial disease.52 Because drug-induced CMP may be irreversible, the use of biomarkers may help identify myocardial damage before a decline in left ventricular ejection fraction (LVEF).54 Increased serum levels of cardiac troponin can help identify patients who will subsequently develop a reduction in LVEF.55 In clinical practice, patients treated with drugs causing type 1 cardiotoxicity must be evaluated by echocardiography for a 15% decline in LVEF or 10% decline in a value ,50%.46,47 If LVEF is decreased and blood levels of troponin and B-type natriuretic peptide are elevated or LVEF is persistently reduced after 3 weeks, alternative chemotherapy options must be explored. In asymptomatic patients, echocardiography at 6, 12, 24, and 36 months is recommended, followed by 3- to 5-yearly assessments for life.43

HYPERTENSION Epidemiological studies have suggested that an increase of 3 mm Hg in blood pressure (BP) is associated with a 10%–20% increase in congestive heart failure.56 Conversely, a 3–4 mm Hg reduction in BP in hypertensive individuals decreases the risk of myocardial infarction by 22% and of stroke by 33%.57 However, there is no current consensus concerning the clinical significance of a drug-induced increase in BP of these magnitudes in patients where BP remains in the normotensive range. Nonetheless, it is possible that small drug-induced BP increases may have significant impact in patients with enhanced cardiovascular risk because of older age, cardiovascular comorbidities, or other traditional cardiovascular risk factors. Consequently, off-target drug-induced BP elevations have increasingly attracted scientific interest58–60: As Grossman and Messerli58 observed, “A myriad variety of therapeutic agents or chemical substances can induce either a transient or persistent increase in blood pressure.” Presently, there is no regulatory guidance on the assessment of circadian BP changes induced by noncardiovascular drugs. There are inherent difficulties in establishing a standard methodology for establishing an off-target BP signal in clinical trials. Consequently, a strategy of systematic nonclinical assessments for identifying potential off-target effects of drugs which www.americantherapeutics.com

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can translate into more focused studies during clinical and postmarketing evaluation of drugs for cardiovascular risk is warranted. Preapproval clinical assessments Although BP is commonly monitored in clinical trials, the detection of a small drug-induced change is complicated by the fact that it may be influenced by the frequency and type of BP measurement and the length of the trial. A report from the Cardiac Safety Research Consortium (CSRC) on assessment of drug-induced increases in BP during drug development61 lists 7 different methods of BP monitoring: clinical BP measurement using auscultation by observer, clinic BP measurement using noninvasive auscultation devices, clinical oscillometric BP measurement using a digital device, ambulatory BP monitoring, centralized office BP monitoring, self-measured home BP using a digital device, and self-measured home BP measurement using telemonitoring. Each of these methods has strengths and limitations, and, more importantly, the outcomes from these methods vary considerably. The auscultatory methods are subject to observer variability, whereas investigatorrecorded BP readings may result in white-coat hypertension.62–64 Ambulatory BP monitoring has the advantage of virtually eliminating the white-coat effect, providing several BP readings during sleep and during normal day-to-day physical activity, and allowing modeling of diurnal variations.60,65 Possible consequences of drug-induced changes in BP should be interpreted after taking into account factors such as whether the increased BP is sustained or transient, the reversibility or otherwise of the BP effect after stopping the drug, other cardiac effects such as increased heart rate, intended duration of use (shortterm use vs. chronic use), age of the target population, interaction with antihypertensive medications, and effects in special populations such as those with cardiac or renal disorders. Risk mitigation strategies in clinical practice Hypertension has been observed as the most common adverse effect of anti-vascular endothelial growth factor (VEGF) agents that inhibit tyrosine kinases stimulated by VEGF. This group includes bevacizumab, pazopanib, sorafenib, sunitinib, and vandetanib. The cause of elevated BP with these agents is multifactorial, with decreased nitric oxide production, reduction in the density of microvascular beds, loss of antioxidative effect, and activation of the endothelin-1 system being suggested as possible mechanisms. In a study evaluating the safety of bevacizumab plus irinotecan, fluorouracil, and leucovorin for the treatment of www.americantherapeutics.com

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metastatic colorectal cancer, severe hypertension (BP .200/100 mm Hg) was 3 to 5 times higher as compared with the placebo group.66 In another trial (the Bevacizumab Regimens’ Investigation of Treatment Effects study), de novo hypertension was reported in 22% of patients, and 18.7% of patients with preexisting hypertension experienced worsening of the condition.67 Similarly, sorafenib, which is approved for advanced renal cell carcinoma and hepatocellular carcinoma, increased mean systolic BP by 8.2 mm Hg and diastolic BP by 6.5 mm Hg within 24 hours of treatment with 400 mg given twice a day. Hypertension occurred in 23.4% of patients on sorafenib with severe hypertension occurring in 5.7%.68 The respective figures for sunitinib were 21.6% and 6.8%.69

FUTURE DIRECTIONS A Think Tank sponsored by the CSRC,70 the Health and Environmental Sciences Institute,71 and the FDA was held at FDA Headquarters in July 2013, to discuss a potential future paradigm in which appropriately thorough nonclinical assessments of proarrhythmic liability may preclude the need for a dedicated clinical assessment. A White Paper summarizing these discussions in the American Heart Journal,72 and a Synopsis is currently posted on the CSRC’s Web site as of December 2013. Briefly here, discussions centered on the fact that the current cardiac safety paradigm is not actually focused on proarrhythmia, the issue of clinical concern, but on delayed ventricular repolarization as represented by the cardiac safety biomarkers of reduced hERG current and QT interval prolongation. This has several adverse consequences. First, although QT prolongation is a highly sensitive biomarker in the prediction of risk for ventricular proarrhythmia, it is not a very specific one. Second, many sponsors have come to regard reduced hERG current and QT interval prolongation as major limiting influences of obtaining marketing approval or product acceptance. The unfortunate consequence can be premature discontinuation of specific compounds or development programs for drugs with potentially high public health benefits. A new paradigm, the Comprehensive In vitro ProArrhythmia (CIPA) Assay, was therefore put before attendees for discussion. CIPA incorporates investigations of macroscopic ionic currents, computer models of cellular ventricular repolarization, and isolated human cardiomyocytes. An early, rapid, and comprehensive survey of drug effects on multiple cardiac currents (depolarizing Na+ and Ca++ currents as well as repolarizing K+ currents) that influence the human ECG is the first step. In silico American Journal of Therapeutics (2014) 21(6)

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modeling focusing on reconstruction and cellular integration of drug effects on these multiple currents would follow.73 A complementary cell-based arm of CIPA would focus on drug effects on human ventricular myocytes by employing human-induced pluripotent stem cell-derived cardiomyocytes.74 Clinical evaluations would complement the new paradigm, but the TQT study would not be a required component. More focused ECG assessments would be undertaken in early clinical trials to evaluate a drug’s effects on ECG intervals in general, atrioventricular conduction,75 and heart rate. It will be of great interest to many stakeholders in drug development to follow the progression of these discussions in the next several years.

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