Clinical Trials Update AHA Congress 2010

Correcting Calcium Dysregulation in Chronic Heart Failure Using SERCA2a Gene Therapy

Chronic heart failure (CHF) is a major contributor to cardiovascular disease and is the leading cause of hospitalization for those over the age of 65, which is estimated to account for close to seventy billion dollars in healthcare costs by 2030 in the US alone. The successful therapies for preventing and reversing CHF progression are urgently required. One strategy under active investigation is to restore dysregulated myocardial calcium (Ca²⁺), a hallmark of CHF. It is well established that intracellular Ca²⁺ concentrations are tightly regulated to control efficient myocardial systolic contraction and diastolic relaxation. Among the many cell surface proteins and intracellular organelles that act as the warp and woof of the regulatory network controlling intracellular Ca²⁺ signals in cardiomyocytes, sarco/endoplasmic reticulum Ca²⁺ ATPase type 2a (SERCA2a) undoubtedly plays a central role. SERCA2a is responsible for sequestrating cytosolic Ca²⁺ back into the sarcoplasmic reticulum during diastole, allowing for efficient uncoupling of actin-myosin and subsequent ventricular relaxation. Accumulating evidence has demonstrated that the expression of SERCA2a is downregulated in CHF, which subsequently contributes to severe systolic and diastolic dysfunction. Therefore, restoring SERCA2a expression and improving cardiomyocyte Ca²⁺ handling provides an excellent alternative to currently used transplantation and mechanical assist devices in the treatment of CHF. Indeed, advancements in safe and effective gene delivery techniques have led to the emergence of SERCA2a gene therapy as a potential therapeutic choice for CHF patients. This mini-review will succinctly detail the progression of SERCA2a gene therapy from its inception in plasmid and animal models, to its clinical trials in CHF patients, highlighting potential avenues for future work along the way.

Phospholamban overexpression in mice causes a centronuclear myopathy-like phenotype

Centronuclear myopathy (CNM) is a congenital myopathy that is histopathologically characterized by centrally located nuclei, central aggregation of oxidative activity, and type I fiber predominance and hypotrophy. Here, we obtained commercially available mice overexpressing phospholamban (Pln^OE), a well-known inhibitor of sarco(endo)plasmic reticulum Ca²⁺-ATPases (SERCAs), in their slow-twitch type I skeletal muscle fibers to determine the effects on SERCA function. As expected with a 6- to 7-fold overexpression of phospholamban, SERCA dysfunction was evident in Pln^OE muscles, with marked reductions in rates of Ca²⁺ uptake, maximal ATPase activity and the apparent affinity of SERCA for Ca²⁺. However, our most significant discovery was that the soleus and gluteus minimus muscles from the Pln^OE mice displayed overt signs of myopathy: they histopathologically resembled human CNM, with centrally located nuclei, central aggregation of oxidative activity, type I fiber predominance and hypotrophy, progressive fibrosis and muscle weakness. This phenotype is associated with significant upregulation of muscle sarcolipin and dynamin 2, increased Ca²⁺-activated proteolysis, oxidative stress and protein nitrosylation. Moreover, in our assessment of muscle biopsies from three human CNM patients, we found a significant 53% reduction in SERCA activity and increases in both total and monomeric PLN content compared with five healthy subjects, thereby justifying future studies with more CNM patients. Altogether, our results suggest that the commercially available Pln^OE mouse phenotypically resembles human CNM and could be used as a model to test potential mechanisms and therapeutic strategies. To date, there is no cure for CNM and our results suggest that targeting SERCA function, which has already been shown to be an effective therapeutic target for murine muscular dystrophy and human cardiomyopathy, might represent a novel therapeutic strategy to combat CNM.

Summary: Phospholamban overexpression in mouse slow-twitch muscle impairs SERCA function and causes histopathological features associated with human centronuclear myopathy.

Mechanisms of altered Ca²⁺ handling in heart failure

Ca²⁺ plays a crucial role in connecting membrane excitability with contraction in myocardium. The hallmark features of heart failure are mechanical dysfunction and arrhythmias; defective intracellular Ca²⁺ homeostasis is a central cause of contractile dysfunction and arrhythmias in failing myocardium. Defective Ca²⁺ homeostasis in heart failure can result from pathological alteration in the expression and activity of an increasingly understood collection of Ca²⁺ homeostatic and structural proteins, ion channels, and enzymes. This review focuses on the molecular mechanisms of defective Ca²⁺ cycling in heart failure and considers how fundamental understanding of these pathways may translate into novel and innovative therapies.

Niacin in cardiovascular disease: recent preclinical and clinical developments

Niacin has been used for more than 50 years in the treatment of cardiovascular disease, although its use has largely been superseded by better-tolerated lipid-modulating interventions. There has been a renewed interest in the HDL-cholesterol raising properties of niacin, with the appreciation that substantial cardiovascular risk remains despite effective treatment of LDL-cholesterol. This coincides with increasing evidence that the complex functional properties of HDL are not well reflected by measurement of HDL-cholesterol alone. In addition to favorable actions on lipoproteins, it is becoming apparent that niacin may also possess lipoprotein independent or pleiotropic effects including the inhibition of inflammatory pathways mediated by its receptor GPR109A, which is expressed by adipocytes and some leukocytes. In this article we consider emerging and prior clinical trial data relating to niacin. We review recent data in respect of mechanisms of action on lipoproteins, which remain complex and incompletely understood. We discuss the recent reports of anti-inflammatory effects of niacin in adipocytes and through bone marrow derived cells and vascular endothelium. These novel observations come at an interesting time, with current imaging and outcome studies leaving outstanding questions on niacin efficacy in statin-treated patients.

A short perspective on gene therapy: Clinical experience on gene therapy of gliomablastoma multiforme

More than two decades have passed since the first gene therapy clinical trial was conducted. During this time, we have gained much knowledge regarding gene therapy in general, but also learned to understand the fear that persists in society. We have experienced drawbacks and successes. More than 1700 clinical trials have been conducted where gene therapy is used as a means for therapy. In the very first trial, patients with advanced melanoma were treated with tumor infiltrating lymphocytes genetically modified ex-vivo to express tumor necrosis factor. Around the same time the first gene therapy trial was conducted, the ethical aspects of performing gene therapy on humans was intensively discussed. What are the risks involved with gene therapy? Can we control the technology? What is ethically acceptable and what are the indications gene therapy can be used for? Initially, gene therapy was thought to be implemented mainly for the treatment of monogenetic diseases, such as adenosine deaminase deficiency. However, other therapeutic areas have become of interest and currently cancer is the most studied therapeutic area for gene therapy based medicines. In this review I will be giving a short introduction into gene therapy and will direct the discussion to where we should go from here. Furthermore, I will focus on the use of the Herpes simplex virus-thymidine kinase for gene therapy of malignant gliomas and highlight the efficacy of gene therapy for the treatment of malignant gliomas, but other strategies will also be mentioned.

Evolving treatment strategies for management of cardiorenal syndrome

OPINION STATEMENT

The treatment of acute decompensated heart failure in the presence of progressive renal dysfunction is a commonly encountered dilemma in clinical practice. Also known as cardiorenal syndrome, this complex disease state has forced researchers and clinicians to develop new treatment strategies to relieve the symptomatic congestion of heart failure while preserving renal function. Loop diuretics remain the standard of pharmacologic treatment of acute heart failure, but their effects on renal function have been called into question. The DOSE trial set out to determine optimal diuretic dosing strategies but no clear regimen was firmly established. Initial studies with vasopressin antagonists showed promise in their ability to increase urine output, provide short-term symptom relief, and correct hyponatremia while maintaining renal function. Unfortunately, the EVEREST trial did not demonstrate any benefit on long-term clinical outcomes. Adenosine antagonists also appeared to be an emerging therapeutic option, but the recently completed PROTECT trial failed to establish their role in the treatment of cardiorenal syndrome. Both nesiritide and low-dose dopamine have endured years of trials with mixed results. Most recently, findings from the ASCEND-HF trial showed that nesiritide was safe with no adverse effects on renal function or mortality and was associated with a modest improvement in dyspnea. The ongoing ROSE study, sponsored by the National Institutes of Health Heart Failure Research Network, will attempt to confirm the safety and efficacy profiles of low-dose nesiritide and dopamine, as well as clarify their roles within acute heart failure management. Despite its inherent complexities, ultrafiltration has demonstrated potential benefit in several clinical outcomes compared to traditional pharmacotherapy. The results of the CARRESS-HF trial will reveal how the use of ultrafiltration specifically applies to patients with cardiorenal syndrome. The most exciting aspects about our evolving understanding of the cardiorenal system are the innovative treatments that have emerged as a result. The creation of chimeric natriuretic peptides, targeted intra-renal pharmacotherapy, the novel use of phosphodiesterase inhibitors, and combination treatment strategies demonstrate that despite our varied success in treating cardiorenal syndrome in the past, there are highly encouraging translational therapies rapidly developing in the pipeline.

Clopidogrel "resistance": where are we now?

Antiplatelet therapy with aspirin and clopidogrel in PCI patients, though effective, is still associated with thrombotic complications. These are multifactorial in origin, but partially attributable to "clopidogrel resistance." However, how best to identify and manage "clopidogrel resistance" remains unclear. Targeting therapeutic changes specifically at those individuals with poor response to clopidogrel is likely to be a solution. A "one size fits all" approach to clopidogrel dosing is probably flawed. This review will explore (1) the definition and mechanisms of clopidogrel resistance, (2) assessment of clopidogrel resistance by (i) platelet function testing and (ii) genetic testing, (3) the management of "clopidogrel resistance," and (4) newer antiplatelet agents, and evolving stent technology. A pubmed literature review was performed using the keywords "clopidogrel", "resistance", "poor response", "adverse events", "platelet function tests", and "genetic tests". In looking at new agents, keywords "prasugrel", "cangrelor", "ticagrelor""Elinogrel", and "P2Y12 receptor antagonists" were used. Third, a search was performed looking at "stent design", "IVUS", "bioabsorbable stents", and "stent apposition". Whilst new P2Y12 receptor antagonists and improved stent technology may reduce thrombotic events in the future, there is still a need for clopidogrel. There is good evidence that poor response to clopidogrel is associated with adverse outcome. Platelet function tests probably provide more clinically useful data than genetic tests, but the question of how best to identify and manage variability in response to clopidogrel demands further research.