Emerging Therapies for Congestive Heart Failure

Transcription

1 Emerging Therapies for Congestive Heart Failure Thomas J. Povsic 1 The treatment of atherosclerotic heart disease has improved remarkably over the last several decades; however, the outlook for patients with symptomatic congestive heart failure with reduced ejection fraction remains bleak. Current drug therapies target the neurohormonal activation that accompanies congestive heart failure, but do not address the fundamental pathology inherent in this condition the loss of contractile capacity. Stem cell therapies offer the possibility of rectifying this deficiency and normalizing left ventricular dimensions and cardiac performance by regenerating novel contractile tissue, thereby reversing the negative remodeling that portends progressive left ventricular dysfunction, worsening symptoms, and ultimately cardiogenic shock. Here we review the promise of stem cell therapies in the treatment of heart failure with reduced ejection fraction, the current state of clinical developments, and briefly comment on the future of the field. Over the last several decades, the development of a variety of novel cardiovascular therapeutics coupled with lifestyle modifications, such as smoking cessation, has resulted in a remarkable 30 35% decline in cardiovascular mortality and up to a 65% reduction in cardiovascular events. 1 Such statistics have led to the perception that cardiovascular disease has been cured however, cardiovascular disease accounts for more than one of every three deaths in the US 2 and ischemic heart disease remains the leading cause of death both worldwide and in the US. This is especially true in the elderly, where cardiovascular disease accounts for over 50% of all deaths in patients over age 75 and over 3-fold more deaths than cancer in patients over age As the treatment of acute myocardial infarction (MI) and chronic ischemic heart disease continues to improve, the burden of heart failure (HF) is accumulating both in terms of incidence and cost, with an estimated 38 million patients with this condition worldwide. 3 Current projections estimate that the prevalence of HF will increase by up to 46% over the next 18 years. By 2023, it is estimated that over 8 million patients in the US alone will have a diagnosis of congestive HF (CHF). 2 CHF remains the most common and expensive diagnosis in the Medicare system, with over 1 million annual hospitalizations for CHF in both the US and Europe. With the aging patient population, this number is expected to grow by over 50% in the next 15 years. 4 In addition, within 60 days of hospitalization for CHF, 30 50% of patients either die or are rehospitalized, with 20 30% mortality at 1 year and 40 50% mortality by 5 years. 5 The majority of medications that have been successful in treating CHF (angiotensin converting enzyme (ACE) inhibitors, angiotensin II receptor blockers (ARBs), beta-blockers, aldosterone antagonists) target chronic neurohormonal aberrations that occur in response to this condition. While this approach was initially extremely effective, further attempts at continued targeting of the neurohormonal axis have been largely disappointing, and only neprilysin inhibition has translated into improvements in clinical outcomes. 6 Meanwhile, the fundamental pathology of HF, the loss of contractile capacity due to loss of cardiomyocytes, remains unaddressed. The lack of therapies targeting the underlying loss of contractility inherent in HF offers an opportunity to fundamentally change the way HF is approached. One method to address this deficiency is the use of regenerative therapies to stimulate either native repair processes or to regenerate and replace injured myocardium de novo. Given the high mortality in high-risk patients with CHF, this seems like an ideal target for regenerative therapies aimed at directly addressing the need for improved cardiac performance. In this article we briefly review the preclinical basis for such an approach, discuss the most advanced clinical development programs aiming to bring this approach to patients, and highlight next-generation technologies. REGENERATION FROM SIMPLE ORGANISMS TO HUMANS Although clinical regeneration in humans does not occur to a clinically meaningful degree, the regenerative capacities of more primitive organisms are not so limited. For instance, zebrafish are able to regenerate significant amounts of myocardium after injury, with the ability to replace up to 25% of resected myocardium with histologically indistinct tissue. 7 1 Duke Clinical Research Institute, Duke University Medical Center, Durham, North Carolina, USA. Correspondence: T.J. Povsic (povsi001@mc.duke.edu) Received 14 August 2017; accepted 6 October 2017; advance online publication 16 October doi: /cpt.913 CLINICAL PHARMACOLOGY & THERAPEUTICS VOLUME 103 NUMBER 1 JANUARY

2 Figure 1 Model of the use of cell therapies for prevention of left ventricular remodeling after myocardial infarction. While human cardiac regeneration does not recapitulate what is observed in more primitive organisms, several lines of evidence point to a low but present level of continuous cardiac turnover mediated by stem cells. First, a series of studies demonstrated that in patients who have received cardiac transplantation, a low level of myocardial tissue and, to an even greater extent, the supporting tissues (e.g., vasculature) are replaced by cells derived from the host, as evidenced by expression of sex chromosomes or other distinguishing markers. 8,9 While the number of host cells in the transplant are low, this was the first demonstration that host cells replace or support the native heart. Second, a series of 14 C detection experiments taking advantage of the large change in atmospheric 14 C secondary to atomic experimentation in the mid-20th century firmly establish the degree of turnover of myocardial tissue in late childhood and early adulthood, suggesting that 50% of the myocardium is replaced by newly generated tissue over the course of a 70-year lifetime. 10 CELL THERAPY FOR CONGESTIVE HEART FAILURE The possibility of effectively harnessing these biological repair processes to address the loss of contractile functionality in the failing heart using stem cell therapy, coupled with intriguing early preclinical data, led to rapid translation of this approach to the clinic. Here we briefly review the use of stem cells to prevent CHF post-mi, and sequentially address the use of unselected, selected, and engineered or specifically cultured stem cells for treatment of systolic dysfunction. PREVENTION OF LEFT VENTRICULAR REMODELING POSTACUTE MYOCARDIAL INFARCTION ST-elevation MI can lead to significant loss of myocardial tissue, the degree of which is directly related to long-term clinical outcomes. In current practice, there are various cardioprotective strategies aimed at minimizing injury associated with reperfusion or apoptosis, but the idea that stem cells could be used to mitigate the amount of injury or stimulate an early reparative response offers a new approach to the treatment of this disease (Figure 1). 11,12 Early proof-of-concept studies 13 rapidly progressed to clinical trials modestly powered to determine the effectiveness of cell therapy on either infarct size or global left ventricular (LV) function as assessed using angiography, magnetic resonance imaging (MRI), or echocardiography The close relationship between the surrogates of infarct size and LV function and subsequent mortality, as determined in very large clinical outcomes studies, serves as a clear basis for the use of such assessments for clinical effectiveness Encouragingly, a series of meta-analyses (Table 1) suggest that bone marrow cell administration in the days post-mi results in a highly statistically significant improvement in ejection fraction (EF), a finding that has been replicated multiple times. 21,22,28,29 Unfortunately, several hurdles remain. Despite the large numbers of patients enrolled in trials to date, no definitive evaluation of the efficacy of cell therapy has been performed. In many ways, this is a reflection of the broader state of clinical research, in which many if not most trials enroll small numbers of patients, resulting in nondefinitive conclusions. 30 Meta-analyses demonstrate that significant effort has been spent to conduct many (up to 50) trials of modest size (mean enrollment reported in the two largest meta-analyses is and patients, with a median enrollment of ) that have largely focused on similar clinical questions. The limitations of combining data from a series of smaller trials is exemplified by the finding that a patient-level analysis of these data failed to replicate the findings from a meta-analysis of trial data, 31 although this analysis also has its own limitations. 32 This illustrates the vital need for adequately powered definitive outcome studies, and there has been gradual but steady progress in the size and definitiveness of planned clinical studies. The currently enrolling BAMI trial (The Effect of Intracoronary Reinfusion of Bone Marrow-derived Mononuclear Cells (BM- MNC) on All-Cause Mortality in Acute Myocardial Infarction (NCT )) is a large, simple trial aimed at determining whether an infusion of bone marrow-derived mononuclear cells results in improvements in mortality among patients with residual LV dysfunction post-mi, a population in which mortality remains significantly elevated. Unfortunately, enrollment in BAMI has been slow and the sample size has been gradually decreased, putting at risk the primary hypothesis being tested and perhaps the development of at least first-generation cell therapy for this indication. Finally, the majority of the research to date has focused on the use of unselected bone marrow cells to improve LV function post-mi, with small studies looking at selected cells, 33 and virtually no studies with more advanced, cultured, reprogrammed, or multipotent stem cell populations capable of true myocardial regeneration. A recent study using autologous CD34 1 cells, an approach that has been extensively explored for other indications and with a significant safety record, 34,35 suggests that in patients with adequate stem cell dosing an effect on cardiovascular clinical endpoints might be observed. 36 This observation is consistent 78 VOLUME 103 NUMBER 1 JANUARY

3 Table 1 Meta-analyses of bone marrow cells post-mi Trials Patients BMC: control DEF BMC-Ctr P-value DInfarct size P-value Hristov (23) : (0.21, 8.22) <0.04 Abdel-Latif (21) : (1.56, 5.73) <0.001 Lipinski (24) : (1.88, 4.04) < Martin-Rendon (25) : (1.26, 4.72) Zimmet (26) 29 1, (1.5, 3.9) <0.001 Delewi (22) 23 1, : (1.0, 3.5) < (24.5, 0.1) 0.07 Jeevanantham (27) 50 2,625 1,460:1, (2.9, 5.0) < (25.5, -2.6) < with what is seen when this approach is used to treat patients with advanced coronary disease, where a statistically significant impact on mortality has been observed (Povsic et al. unpublished data 37 ). TREATMENT OF ADVANCED CONGESTIVE HEART FAILURE The treatment of CHF has evolved over the last decades to include a broad armamentarium of therapeutics, including inhibition of the renin-angiotensin system, the adrenergic system, aldosterone signaling, and most recently natriuretic peptide degradation, as well as the use of a variety of device-based therapies, including resynchronization and ever smaller, more efficient, and less error-prone LV assist devices. This has resulted in a decrease in mortality, which is reflected in the size of clinical trials required to develop add-on therapies. 38,39 Despite these advances, however, pharmacologic therapies fail to directly address the loss of myocardial contractility that is the hallmark of CHF with systolic dysfunction. Given the still high mortality in high-risk patients with CHF, this seems like an ideal target for regenerative therapies aimed at directly addressing the need for improved cardiac performance. A variety of stem cell types have been targeted. Here we summarize those that have undergone the most advanced testing in human trials, as well as future approaches undergoing active development. Myoblasts HF can result from chronic ischemic insults or, not infrequently, from large MI leading to an area of scar and later LV remodeling (Figure 1). The first attempt at cell therapy, pioneered by Doris Taylor, aimed to take advantage of the regenerative capacity found in peripheral muscle with the harvesting of myoblasts. 40 The use of myoblasts is fundamentally different from the majority of other regenerative approaches to the treatment of LV systolic dysfunction, in that it targets patients with nonviable tissue, taking advantage of the tolerance of these cells to ischemia and conditions in chronically scarred, largely nonviable tissue (Figure 2). As such, myoblast therapy, which has not undergone further development in the last several years, represents an approach to a patient population with an unmet medical need that other regenerative approaches have yet to fulfill. While these cells are fundamentally different from the electrically integrated syncytium of involuntary myocardial tissue of the heart, it was hoped that introduction of myoblasts into scarred tissue would lead at minimum to the generation of tissue within scar that would reduce wall stress and prevent further LV remodeling. Preclinical models suggested favorable effects of myoblast administration on LV function and myocardial performance, 41 and suggested that myoblasts might eventually lead to new contractile tissue in areas of scar and possibly stimulation of immature cardiomyocyte formation. 42 Clinical development proceeded from initial first-in-man studies followed by two phase I open-label dose-escalation studies (MYOHEART and CAUSMIC) 43 (Figure 3). A phase II study in Europe represented the first randomized experience with intramyocardial administration of autologous skeletal myoblasts. 44 While this was an open-label study, no change in EF was observed in myoblast-treated subjects (n 5 26) vs. control patients (n 5 26). Notably, all patients treated with cell therapy received prophylactic amiodarone therapy. A significant burden of ventricular tachycardia was consistently observed during the 6- month follow-up period; however, the incidence of arrhythmias appeared similar in both groups. Nonetheless, the time to onset Figure 2 Use of cell therapies for treatment of left ventricular dysfunction. CLINICAL PHARMACOLOGY & THERAPEUTICS VOLUME 103 NUMBER 1 JANUARY

4 Figure 3 Outline of studies of percutaneously delivered myoblasts for treatment of left ventricular scar. of the first serious adverse event appeared to be shorter in the myoblast-treated subjects, although a statistical analysis of this curve was not presented. 44 Two randomized, blinded studies attempted to define the efficacy and safety of myoblast therapy. MAGIC was a blinded placebo-controlled surgical trial that randomized 97 patients to epicardial injection of 800 million myoblasts, 400 million myoblasts, or placebo. 45 Myoblast administration did not appear to affect global or regional LV function, with changes in overall EF of 5.2% ( 4.4, 11.0), 3.4% ( 0.3, 12.4), and 4.4% (0.2, 7.3) in the high-dose, low-dose, and placebo groups. There appeared to be a direct relationship between cell dose and changes in LV enddiastolic and end-systolic volumes, and there were significant differences between patients treated with high-dose myoblast therapy as compared with the other groups. Although the overall incidence of major adverse cardiovascular events was similar among the three arms at 6 months, the incidence of ventricular arrhythmias was higher in the immediate postprocedural period in myoblast-treated patients. Nonetheless, by 24 months the risk of arrhythmia was similar in the three arms, with the placebotreated patients having an intermediate risk between what was observed in the two cell therapy doses. 45 The MARVEL program was designed to rigorously determine the efficacy and safety of intramyocardially delivered myoblasts. Targeting enrollment of 390 patients randomized to doubleblind injection of 800 million, 400 million, or 0 (placebo injections) cells, the MARVEL program was suspended after enrollment of 22 patients due to financial limitations at the sponsor. 46 While small, MARVEL demonstrated that a blinded placebo-controlled trial utilizing placebo injections was feasible. Mean change in 6-min walk distance favored both the high- and low-dose myoblast arms compared with placebo, with improvements of meters and meters compared with meters (placebo). Notably, there was a consistent increase in 6-min walk distance from baseline to 3 and 6 months in cell-treated patients, while patients receiving placebo had a transient increase at 3 months, that then dropped back to baseline levels at 6 months. Mean Minnesota Living with Heart Failure questionnaire (MLHFQ) scores declined in all patients, with no differences among the groups, demonstrating a strong placebo effect consistent with rigorous patient blinding in this study. While the overall rate of serious adverse events was not different among the groups, the risk of sustained ventricular arrhythmias was higher in cell-treated patients, prompting the trial leadership to advocate prophylactic amiodarone administration at the time of intramyocardial injections in the last portion of the trial. MARVEL suggested that amiodarone is highly effective at suppressing arrhythmias due to myoblast integration, as short periods of therapy effectively suppressed arrhythmic events. For instance, 10 patients with no amiodarone therapy, or amiodarone started only at time of implantation, experienced sustained ventricular tachycardia, which was effectively suppressed with amiodarone in five patients. However, of the four patients in whom amiodarone was started at the time of muscle biopsy and continued, no arrhythmic events were detected. No ventricular tachycardia events after discontinuation of amiodarone were reported. These data suggest that short-term amiodarone might be highly effective in suppressing arrhythmogenicity arising from coupling between myoblasts and potentially other myogenic cellular therapies. 46 Bone marrow cells Unselected bone marrow cells represent a readily available and minimally manipulated stem cell source. As an autologous product, concerns about immunogenicity leading to either rejection or sensitization are avoided; however, this represents a largely unpurified product whose true stem cell content is <5%. In addition, these (and other stem cells described below) must be injected into viable tissue to maximize survival and effectiveness, thus targeting patients with at least some degree of viable tissue (Figure 2). Nonetheless, given the ease of acquisition, minimal processing, and the potential for regulation as a minimally manipulated product, this therapy has undergone initial evaluation. The TOPCARE-CHD trial compromised a multiphase program progressing from phase I, to a randomized phase II study, and finally a crossover phase in which patients who had received placebo crossed over to cell therapy, while patients receiving either circulating progenitor cells or bone marrow progenitors were treated with the therapy they had not received on initial randomization. 47 This study demonstrated a modest 2.9% increase in EF in those receiving bone marrow-derived cells, but no change with either placebo or circulating progenitor cell therapy. Consistent findings were observed on regional contractility and these findings were largely confirmed in the crossover phase of the study, where patients treated with bone marrow-derived cells again demonstrated the most consistent benefit. 47 Mirroring what was observed in the application of such regenerative therapies in the post-mi period, the US experience has been less sanguine. The National Institutes of Health (NIH)- sponsored, multicenter, double-blind FOCUS-CCTRN trial randomized 82 patients in a 2:1 fashion to treatment with intramyocardial delivery of an autologous bone marrow cell product. The study failed to demonstrate a statistically significant impact on any of the three 80 VOLUME 103 NUMBER 1 JANUARY

5 prestipulated primary endpoints (peak MVO2, LV volumes, or degree of ischemia), and a large number of secondary endpoints. 48 The investigators reported an improvement in EF (an endpoint that was not listed as a primary or secondary analysis) in younger patients receiving more potent autologous stem cells. While this approach may seem conceptually attractive, given the number of endpoints and subgroups analyzed, the chances of a type I statistical observation must be strongly considered. Further analysis, however, lays the foundation for the development of more potent and efficacious therapies, while concomitantly demonstrating the importance of translational bedside to bench efforts in such clinical programs. Thorough characterization of bone marrow stem cell content and functionality established the variability inherent in autologous stem cell sources and the impact this has on functional outcomes observed in FOCUS-CCTRN. 49 One approach to enhancing the efficacy of unselected bone marrow cells is to improve homing of cells to the area of injury. Taking advantage of the fact that extracorporeal shock wave treatment may increase expression of homing factors in target tissue, investigators randomized 103 patients to either low-dose, high-dose, or placebo shock wave treatment. 50 Twenty-four hours after pretreatment, patients were then randomized to receive intracoronary infusion of autologous bone marrow cells. Patients who received shock wave 1 placebo had a nonsignificant increase in EF of 1.0%, as compared with a 3.2% increase in EF among those treated with shock wave 1 bone marrow cell therapy (P ). Shock wave 1 bone marrow cell therapy was also associated with improved regional wall thickening and, as seen in other studies, a decreased risk of major adverse cardiovascular events (hazard ratio (HR) 0.58, 95% confidence interval (CI) , P ). Thus, it may be that mechanisms to enhance cell homing to the target tissue are required, particularly in the chronic setting in which it is known that the production of stromal cell derived factor-1 is less robust than after acute infarction. 50 Selected bone marrow cells A second-generation cell product may be represented by selection of particular stem cell populations from unpurified sources. Cell types that have been studied in small studies include CD133 1 cells, 51,52 CXCR4 1, 36 and cells selected based on aldehyde dehydrogenase activity. 53 Mesenchymal stem cells (MSCs) are of interest given their inflammatory modulating properties. In addition, MSCs may undergo less functional deterioration in reparative capacity compared with other bone marrow populations, can be readily expanded and formulated into an allogeneic product, and have the capacity in culture for multiorgan expansion. Adipose tissue represents one particularly attractive source of MSCs. Whereas the number of MSCs in the bone marrow drops from 1 in 10,000 cells at birth to 1 in 400,000 cells at age 50 and 1 in 1 million cells at age 80, the numbers of MSCs derived from adipose tissue remains relatively constant over time. 54 Adipose tissue is relatively simple to obtain via fat harvest utilizing a limited liposuction procedure, and automated same-day processing using a self-contained device allows rapid and simple purification of a cell product without requirements of culture, expansion, or complex processing/selection. An initial investigation into this approach demonstrated improvements in peak MVO2, decreases in infarct size, and a 67% reduction in mortality in cell-treated patients. 55 These findings led to the conduct of two parallel trials: the Adipose-derived regenerative cells in the Treatment of patients with chronic ischemic Heart disease Not Amenable to surgical or interventional revascularization I and II (ATHENA I and II) trials. Each trial compared a different dose of adiposederived regenerative cells with treatment with placebo. Ultimately, these trials were terminated prematurely due to protocol-dictated delays, leading to suspension of this program. However, based on observations in the 31 randomized patients, there were greater improvements in both Canadian Cardiovascular Society angina class and New York Heart Association (NYHA) class as well as SF-36 scores in patients treated with cell therapy as compared with those who received placebo. 56 MSCs derived from bone marrow have also undergone clinical development, originally under the purview of OSIRIS Therapeutics, which sponsored a trial in 53 patients in which these cells were infused postacute MI. 57 While the treatment did not show any impact on changes in global EF, the trial showed no safety concerns and intriguingly showed benefit with lower premature ventricular complex burden and improvements in FEV1, a particularly notable finding given that cell trafficking to the lungs was high, as the cells were given intravenously. 57 To compare MSCs with unselected bone marrow cells, Hare et al. randomized 65 patients with ischemic cardiomyopathy to intramyocardial injection of MSCs, bone marrow cells, or placebo. 58 Although the small sample size limits the definitiveness of any conclusions, MSCs appeared to be superior to bone marrow cells in most measures, as improvements in 6-min walk distance, infarct size as assessed by MRI, and regional myocardial function were only statistically significant in the MSC group; both MSCs and bone marrow cells improved the MLHFQ score. Hare et al. have further compared the effects of allogeneic and autologous MSC sources in the POSEIDON trial. 59 In addition, the CCTRN-coordinated Combination of Mesenchymal and C- kit1 Cardiac Stem Cells as Regenerative Therapy for Heart Failure (CONCERT-HF) trial is the first study to explore the possibility of combination therapy with different stem cell types. These trials are addressing for the first time many of the issues that will require further exploration as the field matures, including comparative effectiveness, combination therapy, and establishing the effectiveness of repetitive therapy. However, at a time when the safety and effectiveness of even a straightforward therapeutic approach has not been rigorously established and there are (growing) concerns in the broad cardiology community about the field, 60 there is some thought that resources would be better utilized in a simpler, better-powered approach. More recently, a variety of bone marrow-derived MSCs have been applied to the treatment of refractory angina and ischemic HF by the group of Kastrup et al. in Denmark. The MSC-HF trial was a randomized trial exploring the use of expanded bone marrow MSCs, demonstrating an improvement in LV end- CLINICAL PHARMACOLOGY & THERAPEUTICS VOLUME 103 NUMBER 1 JANUARY

6 systolic volume, the primary endpoint, 61 as well as in EF and stroke volume, all of which were measured by MRI. Intriguingly, however, these effects did not translate into effects on patientcentered outcomes, including improvements in NYHA functional class, 6-min walking test, or quality of life. This group is now leading a multinational trial sponsored by the European Union to investigate the utility of an allogeneic formulation of these cells in the Stem Cell Therapy in IschEmic Non-treatable Cardiac Disease (SCIENCE) trial, which is designed to enroll 138 patients with a primary imaging endpoint (Clinicaltrials.gov identifier NCT ). One other interesting approach to exploring the regenerative mechanisms underlying cell therapy is the treatment of patients undergoing placement of a left ventricular assist device. Early studies suggested some effect of an allogeneic stem cell product in this extremely ill population, 62 but future studies offer the promise of recovery of tissue from treated patients, perhaps offering pathological insight into the mechanisms of cell therapy approaches. Cardiac stem cells A more cardiac-directed approach would take advantage of the fact that cardiac tissue contains resident stem cells, perhaps uniquely suited to cardiac repair. Two approaches to this strategy have undergone clinical testing. In the first approach, resident c-kit 1 cells have been expanded directly from cardiac tissue. These cells are felt to represent multipotent cells with significant potential to improve LV remodeling. 63 The need for significant cardiac tissue to obtain adequate numbers of c-kit 1 cells dictated enrollment of patients undergoing elective coronary artery bypass graft surgery, at which time trial tissue was harvested for c-kit 1 cell expansion and then redelivery via an intracoronary approach at a mean of 113 days after surgery. 64 An interim analysis of 23 out of 81 enrolled patients reported an improvement in EF from 30.3% to 35.9% 1 month after infusion and 38.5% 4 months after infusion. In a small cohort of patients with 1 year of follow-up, there was a suggestion that EF continued to improve up to 1 year. In contrast, in seven control patients no change in EF was observed. 64 Cardiosphere-derived stem cells represent an alternative regenerative product derived from cardiac tissue. 65,66 The phase I CArdiosphere-Derived autologous stem Cells to reverse ventricular dysfunction (CADUCEUS) study assessed the feasibility of culturing adequate numbers of autologous cardiosphere-derived cells from endomyocardial biopsies in 31 patients with recent MI, and analyzed the efficacy and safety of treatment of these patients with intracoronary infusion of these cells months post-mi. 67 Of 23 patients randomized to cardiosphere-derived cell therapy, 17 (74%) underwent treatment. While scar size was unchanged in eight control patients (D EF 0.3% 6 5.4%), the change in scar size was 7.7% in cardiosphere-derived celltreated patients. These results remained at 12 months (D EF 2.2% 6 7.1% (control) vs (cardiosphere-derived cells)). This reduction in LV scar size (both as a percentage of LV mass as well as absolute scar mass) was accompanied by an increase in viable myocardial mass in cardiosphere-derived Figure 4 Paradigm of use of a next-generation cardiopoietic therapy for improvement of cardiovascular outcomes in patients with left ventricular dysfunction. cell-treated patients (D g) but not in controls (D 0.9% g), suggesting that this therapy is capable of scar transformation or at least resorption with the concomitant transformation of new myocardial tissue. 67 Cardiopoietic stem cells While derivation of cardiac stem cells from cardiac tissue is feasible, endomyocardial biopsy is not benign, the yield of tissue is small and may not be reliable, 67 and surgical approaches have clear limitations. 64 A next (third generation) approach to the production of cells with enhanced myocardial reparative capacity is the expansion and differentiation of programmed cells specifically for cardiac regeneration. 68 This approach would both allow use of autologous cell products, avoiding concerns about immune clearance and sensitization associated with allogeneic products, while preserving a uniform, highly active product and minimizing the variation inherent in unmanipulated autologous cell sources. In addition, such an approach offers the possibility of matching the regenerative stem cell product with the organ targeted for repair. Derivation of cardiopoietic stem cells from bone marrow MSC sources, capable of demonstrating hallmark traits of cardiac development, represents one such application of this approach to cardiac stem cell-mediated repair. In guided cardiopoiesis, patient bone marrow cells are expanded in a cardiogenic conditioning medium, thereby directing them towards a cardiac lineage without the need for genetic manipulation (Figure 4). 69 Using this approach, a uniform and characterized autologous cell product with known therapeutic capability can be reliably produced. Preclinical testing demonstrated repair of failing myocardial tissue A first-in-man study randomized 47 patients in a 2:1 fashion to cardiopoietic stem cell therapy or placebo injections. Bone marrow harvest was successful in all patients, with a high rate of success of initial MSC expansion and acceptable yield of the target dose to cells (75%). While this trial was not powered for efficacy, there was a 7% increase in EF in cell-treated 82 VOLUME 103 NUMBER 1 JANUARY

7 Figure 5 Changes in left ventricular end-diastolic volume and left ventricular end-systolic volume at week 52 by number of injections of cardiopoietic stem cells. 78 (Permission to reprint from Teerlink, J.R. et al. Eur. J. Heart Fail. 2017:doi: /ejhf.898.) patients compared with a 0.2% increase in the control group. Consistent results were also seen on other markers of LV remodeling, including LV volumes. 72 These encouraging results led to the CHART-1 trial, the largest regenerative trial in CHF completed to date, which employed several intriguing novel design elements including the use of a much-discussed but infrequently implemented approach to mitigate the large increases in sample size required to demonstrate improvements in major adverse cardiovascular events as mortality decreases The primary efficacy outcome in CHART-1 was a hierarchical composite of mortality, number of worsening HF events, changes in MLHFQ score, 6-min walk distance, change in LV end-systolic volume, and change in LVEF, thus incorporating a mix of clinical, functional, and imaging data. 76 CHART-1 also utilized a blinded design incorporating separate interventional and follow-up clinical teams to maintain full blinding in the study while mitigating risk by not subjecting placebo patients to full intramyocardial injections. 76 CHART-1 ultimately enrolled 348 patients who underwent bone marrow harvest, by far the largest effort in the cardiovascular regenerative field to date. 77 While the overall results of the CHART-1 study failed to demonstrate efficacy on the primary endpoint, there were intriguing signals of efficacy in groups of patients that might be expected to particularly benefit from this therapy. Notably, patients who had an LV end-diastolic diameter above the median and those with baseline LV end-diastolic volumes ml receiving cardiopoietic cell treatment had a better outcome on the composite primary endpoint compared with the sham control group (Mann Whitney estimator 0.61, 95% CI , P ; Mann Whitney odds 1.57, 95% CI ). 77 These patients also experienced consistent improvements in MLHFQ score, and hard cardiac endpoints (mortality, worsening HF events) were directionally consistent in this group. More recently, a further analysis suggested a relationship between the number of cell injections and outcomes, such that patients who had fewer injections (<20) experienced improvements in indices of LV remodeling as well as clinical endpoints (Figure 5). 78 While the exact reason for this observation is unclear, it should be noted that this type of relationship is not unprecedented, as several clinical programs have reported a ceiling effect with cell dose or number of injections. 34,60 NONISCHEMIC CARDIOMYOPATHY Although much of the research to date has focused on ischemic cardiomyopathy, where regenerative capacity may be directed toward both ischemia (via angiogenesis) as well as loss of contractile function (via paracrine stimulation of endogenous regenerative mechanisms), a substantive body of data suggests that cell therapies may also be effective for the growing population of nonischemic cardiomyopathy patients, who now constitute over 60% of HF presentations. Autologous CD34 1 cells have been investigated as a particularly interesting population. CD34 was the first marker used to identify and expand endothelial progenitor cells, cells that can both recapitulate the hematopoietic system as well as give rise to new vasculature. 79,80 In vivo, these cells are capable of angiogenesis and improving blood flow to ischemic tissue, 81,82 and indeed appear more potent when administered as a selected product than when administered in equal numbers as an unpurified bone marrow extract. 83 Recent studies have also demonstrated that circulating CD34 1 cells may be particularly predictive of subsequent cardiovascular outcomes, including mortality. 84 These cells not only associate with functional capacity, 85 but predict both future functional status and change in functional status over time, 86 suggesting that CD34 identifies a cell with a central role in cardiovascular fitness and vascular reparative capacity. When administered to patients with nonischemic cardiomyopathy, but in whom ischemia has been demonstrated, auto- CD34 1 cell administration resulted in a statistically significant improvement in a variety of endpoints, including imaging (EF and LV end-diastolic dimension), functional (6-min walk distance), and biochemical (N-terminal pro b-type natriuretic peptide (NT-proBNP)) parameters. 87 Notably, EF, 6-min walk distance, and NT-proBNP were each statistically significantly different between auto-cd34 1 -treated patients and an open-label untreated control population at yearly intervals between 1 and 5 years. In addition, total mortality in the cell-treated patients (14%) was 60% lower than that observed in controls (35%), a CLINICAL PHARMACOLOGY & THERAPEUTICS VOLUME 103 NUMBER 1 JANUARY

8 finding that was replicated when analyzing patients who died of pump failure. All of these findings are consistent with and mirror observations in the large clinical experience with the use of these cells for advanced ischemic heart disease. 34,35,88 Interestingly, one possible mechanism of this improvement may be by effecting improvement in perfusion, even in those patients without coronary disease. 89 A combination therapy of granulocyte colonystimulating factor (G-CSF) in addition to intracoronary bone marrow cell delivery resulted in improvements in EF of 5%, compared with no improvement in placebo or peripheral bloodinfused patients. 90 Cell therapy was also associated with improvements in brain natriuretic peptide levels, NYHA functional class, and levels of maximal oxygen consumption. ONGOING RESEARCH While interest in regenerative approaches to HF has theoretical and conceptual attractiveness, translation to clinically applicable therapeutics has not been straightforward due to a variety of barriers, including difficulties in standardizing cell therapies and effecting reliable delivery and retention, and the significant hurdles to development of new cardiovascular therapeutics. 91 In response to these issues, the field of cardiovascular regenerative therapies has continued to evolve, and increasing interest is focused in two areas: 1) the completion of larger, more definitive trials to firmly define efficacy and safety of these approaches, and 2) the development of newer regenerative approaches with enhanced potential for myocardial regeneration. Two clinical programs, the BAMI trial and DREAM-HF (Clinicaltrials.gov identifier: NCT ), are under way and are likely to have significant impact at least in the near term on this field, while a third smaller trial (SCIENCE, ClinicalTrials. gov identifier NCT ) represents a broad multinational European Union-sponsored effort. As designed, BAMI (n 5 3,000) and DREAM-HF (n 5 1,730) were to have enrolled many more patients than any previously completed trials. Although the mortality rate expected in the placebo arm of the BAMI trial (25%) and the relative risk reduction (25%) may be ambitious, there is no doubt that these trials, if run to completion, would go much further to define the efficacy of unselected bone marrow cells and allogeneic mesenchymal precursor cells, respectively, to affect clinical outcomes. Unfortunately, there are signals that financial and logistic considerations are significantly impacting the original trial designs. Slow enrollment in BAMI makes achievement of the target enrollment challenging, and the DREAM-HF trial has undergone considerable modification, with a current target enrollment of 600 patients. While this still represents a huge undertaking, the risk with both trials is that they will remain underpowered, and as such not fulfill their goals of bringing cell therapy to the clinic. This would be a significant setback to the field, with the implication that regenerative methods to treat HF may await novel approaches. Other novel approaches are currently in the early stages of development; however, several programs have extremely intriguing preclinical data that suggest that much more powerful strategies may be available in the near future. Genetically modified stem cells may address the lack of viability and short tissue residence of current cell therapies. PIM-1 kinase is an important regulator of cell survival and proliferation. 92 Human c-kit 1 cardiac progenitor cells overexpressing PIM-1 are capable of greater cardioprotection when injected into infarcted mouse hearts due to greater cell proliferation and attenuated apoptosis. 93 These results have recently been replicated in a large animal model, 94 and this type of approach utilizing genetic modification is likely to be more commonly applied clinically in the near future. 95 A paradigm-shifting approach is the use of true pluripotential stem cells, in particular, induced pluripotent stem cells and stem cells derived from embryonic stem cells, which may be capable of replacing the over 1 billion cells that are lost after MI. 95,96 In a primate model of MI, which approximates a human infarction in terms of number of cells lost and need for regeneration, treatment with human embryonic cell-derived cardiomyocytes resulted in regeneration of about 40% of the infarct volume with human cardiac tissue. 97 While this type of research is vital to capturing the full promise of cardiac (and potentially other organ) regeneration, significant issues remain to be addressed. Integration into the primate heart was associated with significant arrhythmias, 97 although these appeared transient. In addition, current work in animal models has relied on significant immunosuppressive regimens to prevent graft rejection; the degree to which such immunosuppression may be required indefinitely remains to be determined. CONCLUSION Despite, and perhaps because of, improvements in the care of chronic ischemic heart disease, HF continues to grow in incidence and expense, and remains the leading cause of death. Current strategies ignore the fundamental loss of myocardial contractile function that underlies CHF with systolic dysfunction. Regenerative approaches offer a mechanism to directly address this deficit. Significant efforts at preventing CHF post- MI with the use of various bone marrow-derived stem cell types has culminated in the currently enrolling BAMI trial exploring the effect of stem cell therapy on mortality after large acute STelevation MI. The regenerative treatment of HF with more advanced modified cell therapeutics has progressed to larger, more definitive studies, such as the recently completed CHART- 1(n 5 240) and the ongoing DREAM-HF (n 5 600) and EU international SCIENCE trials. Global efforts to standardize and unify work in this field are growing and may better establish priorities in the development and study of new approaches. 98 The development of genetically modified and optimized therapies, as well as the use of multipotent stem cells like embryonic-derived stem cells, offers the possibility of direct regeneration of cardiac tissue, eventually replacing the myocardial contractility lost in systolic dysfunction. Finally, noncell-based approaches that recapitulate the effects of cell therapies without the expense of cell acquisition and expansion would fulfill the promise of regenerative approaches in an affordable and scalable manner, which would allow an approach of health maintenance, rather than disease treatment, thereby promoting not only increased lifespan 84 VOLUME 103 NUMBER 1 JANUARY

9 but extending the time of healthy living. 99 While these remain aspirational goals, the remarkable promise remains. CONFLICT OF INTEREST The author declared no conflicts of interest. VC 2017 American Society for Clinical Pharmacology and Therapeutics 1. Mensah, G.A. et al. Decline in cardiovascular mortality: possible causes and implications. Circ. Res. 120, (2017). 2. Mozaffarian, D. et al. Heart disease and stroke statistics 2015 update: a report from the American Heart Association. Circulation 131, e29 e322 (2015). 3. Braunwald, E. The war against heart failure: the Lancet lecture. Lancet 385, (2015). 4. Vigen, R., Maddox, T.M. & Allen, L.A. Aging of the United States population: impact on heart failure. Curr. Heart Fail. Rep. 9, (2012). 5. Chen, J., Normand, S.T., Wang, Y. & Krumholz, H.M. National and regional trends in heart failure hospitalization and mortality rates for Medicare beneficiaries, JAMA 306, (2011). 6. McMurray, J.J.V. et al. Angiotensin-neprilysin inhibition versus enalapril in heart failure. N. Engl. J. Med. 371, (2014). 7. Gemberling, M., Bailey, T.J., Hyde, D.R. & Poss, K.D. The zebrafish as a model for complex tissue regeneration. Trends Genet. 29, (2013). 8. Laflamme, M.A., Myerson, D., Saffitz, J.E. & Murry, C.E. Evidence for cardiomyocyte repopulation by extracardiac progenitors in transplanted human hearts. Circ. Res. 90, (2002). 9. Quaini, F. et al. Chimerism of the transplanted heart. N. Engl. J. Med. 346, 5 15 (2002). 10. Bergmann, O. et al. Evidence for cardiomyocyte renewal in humans. Science 324, (2009). 11. Bainey, K.R. & Armstrong, P.W. Clinical perspectives on reperfusion injury in acute myocardial infarction. Am. Heart J. 167, (2014). 12. Heusch, G. & Rassaf, T. Time to give up on cardioprotection? A critical appraisal of clinical studies on ischemic pre-, post-, and remote conditioning. Circ. Res. 119, (2016). 13. Wollert, K.C. et al. Intracoronary autologous bone-marrow cell transfer after myocardial infarction: the BOOST randomised controlled clinical trial. Lancet 364, (2004). 14. Schachinger, V. et al. Improved clinical outcome after intracoronary administration of bone-marrow-derived progenitor cells in acute myocardial infarction: final 1-year results of the REPAIR-AMI trial. Eur. Heart J. 27, (2006). 15. Lunde, K. et al. Intracoronary injection of mononuclear bone marrow cells in acute myocardial infarction. N. Engl. J. Med. 355, (2006). 16. Traverse, J.H. et al. Effect of intracoronary delivery of autologous bone marrow mononuclear cells 2 to 3 weeks following acute myocardial infarction on left ventricular function: the LATETIME randomized trial. JAMA 306, (2011). 17. Traverse, J.H. et al. Effect of the use and timing of bone marrow mononuclear cell delivery on left ventricular function after acute myocardial infarction: The TIME randomized trial. JAMA 308, (2012). 18. Stone, G.W. et al. Relationship between infarct size and outcomes following primary PCI: patient-level analysis from 10 randomized trials. J. Am. Coll. Cardiol. 67, (2016). 19. Volpi, A. et al. Determinants of 6-month mortality in survivors of myocardial infarction after thrombolysis. Results of the GISSI-2 database. Circulation 88, (1993). 20. Wu, E. et al. Infarct size by contrast enhanced cardiac magnetic resonance is a stronger predictor of outcomes than left ventricular ejection fraction or end-systolic volume index: prospective cohort study. Heart 94, (2008). 21. Abdel-Latif, A. et al. Adult bone marrow-derived cells for cardiac repair: a systematic review and meta-analysis. Arch. Intern. Med. 167, (2007). 22. Delewi, R., Andriessen, A., Tijssen, J.G.P., Zijlstra, F., Piek, J.J. & Hirsch, A. Impact of intracoronary cell therapy on left ventricular function in the setting of acute myocardial infarction: a meta-analysis of randomised controlled clinical trials. Heart 99, (2013). 23. Hristov, M., Heussen, N., Schober, A. & Weber, C. Intracoronary infusion of autologous bone marrow cells and left ventricular function after acute myocardial infarction: a meta-analysis. J. Cell. Mol. Med. 10, (2006). 24. Lipinski, M.J. et al. Impact of intracoronary cell therapy on left ventricular function in the setting of acute myocardial infarction: a collaborative systematic review and meta-analysis of controlled clinical trials. J. Am. Coll. Cardiol. 50, (2007). 25. Martin-Rendon, E., Brunskill, S.J., Hyde, C.J., Stanworth, S.J., Mathur, A. & Watt, S.M. Autologous bone marrow stem cells to treat acute myocardial infarction: a systematic review. Eur. Heart J. 29, (2008). 26. Zimmet, H. et al. Short- and long-term outcomes of intracoronary and endogenously mobilized bone marrow stem cells in the treatment of ST-segment elevation myocardial infarction: a meta-analysis of randomized control trials. Eur. J. Heart Fail. 14, (2012). 27. Jeevanantham, V., Butler, M., Saad, A., Abdel-Latif, A., Zuba-Surma, E.K. & Dawn, B. Adult bone marrow cell therapy improves survival and induces long-term improvement in cardiac parameters: a systematic review and meta-analysis. Circulation 126, (2012). 28. Jeevanantham, V., Butler, M., Saad, A., Dawn, B., Abdel-Latif, A. & Zuba-Surma, E.K. Response to letter regarding article, Adult bone marrow cell therapy improves survival and induces long-term improvement in cardiac parameters: a systematic review and metaanalysis. Circulation 127, e548 (2013). 29. de Jong, R., Houtgraaf, J.H., Samiei, S., Boersma, E. & Duckers, H.J. Intracoronary stem cell infusion after acute myocardial infarction: a meta-analysis and update on clinical trials. Circ. Cardiovasc. Intervent. 7, (2014). 30. Califf, R.M., Zarin, D.A., Kramer, J.M., Sherman, R.E., Aberle, L.H. & Tasneem, A. Characteristics of clinical trials registered in clinicaltrials.gov, JAMA 307, (2012). 31. Fisher, S.A., Doree, C., Mathur, A. & Martin-Rendon, E. Meta-analysis of cell therapy trials for patients with heart failure: novelty and significance. Circ. Res. 116, (2015). 32. Assmus, B., Dimmeler, S. & Zeiher, A.M. Cardiac cell therapy. Lost in meta-analyses. Circ. Res. 116, (2015). 33. Tendera, M. et al. Intracoronary infusion of bone marrow-derived selected CD341CXCR41 cells and non-selected mononuclear cells in patients with acute STEMI and reduced left ventricular ejection fraction: results of randomized, multicentre Myocardial Regeneration by Intracoronary Infusion of Selected Population of Stem Cells in Acute Myocardial Infarction (REGENT) Trial. Eur. Heart J. 30, (2009). 34. Losordo, D.W. et al. Intramyocardial, autologous CD341 cell therapy for refractory angina. Circ. Res. 109, (2011). 35. Povsic, T.J. et al. The RENEW Trial: efficacy and safety of intramyocardial autologous CD341 cell administration in patients with refractory angina. JACC Cardiovasc. Intervent. 9, (2016). 36. Quyyumi, A.A. et al. PreSERVE-AMI: a randomized, double-blind, placebo-controlled clinical trial of intracoronary administration of autologous CD341 cells in patients with left ventricular dysfunction post-stemi. Circ. Res. 120, (2017). 37. Fisher, S., Dorre, C., Brunskill, S.J., Mathur, A. & Martin-Rendon, E. Bone marrow stem cell treatment for ischemic heart disease in patients with no option of revascularization: a systematic review and meta-analysis. PLoS One 9, e64669 (2013). 38. Packer, M. Development and evolution of a hierarchical clinical composite end point for the evaluation of drugs and devices for acute and chronic heart failure. A 20-year perspective. Circulation 134, (2016). 39. Anker, S.D. et al. Traditional and new composite endpoints in heart failure clinical trials: facilitating comprehensive efficacy assessments and improving trial efficiency. Eur. J. Heart Fail. 18, (2016). 40. Taylor, D.A. et al. Generating functional myocardium: improved performance after skeletal myoblast transplantation. Nat. Med. 4, (1998). 41. He, K-L. et al. Autologous skeletal myoblast transplantation improved hemodynamics and left ventricular function in chronic heart failure dogs. J. Heart Lung Transplant. 24, (2005). CLINICAL PHARMACOLOGY & THERAPEUTICS VOLUME 103 NUMBER 1 JANUARY