Disease-specific efffects of novel, selective NCX1 Inhibitors

Summary of proposed research including key goals for scientifically qualified assessors Severe disturbances in intracellular ion homeostasis are indicated in a number of common, often lethal cardiac diseases (myocardial infarct, arrhythmias, heart failure). In their development an increased activity of the Na+/Ca2+ exchanger (NCX1) is known to play a pivotal role. The fact that until recently no specific NCX1 inhibitors were available, may explain that the usually positive, but often contradicting results of animal studies, obtained by application of less specific compounds, did not facilitate clinical trials to test in humans the putative cardioprotective effects of NCX1 blockade. The highly selective inhibitors (ORM10103, ORM10962) recently developed by ORION Pharma are in the moment only available to our research group, providing a unique opportunity to evaluate in details the effects of selective NCX1 inhibition, in a tight cooperation with our partners in Graz, in the framework of the present proposal. The proposed experimental work is aimed to evaluate the pharmacokinetic parameters and mechanisms of action of the new inhibitors essential for their future application. Furthermore, we also plan to investigate the feasibility and efficacy of the putative protective effects of NCX1 inhibition in a number of species (rat, rabbit, pig), in well established animal models of acute ischemic injury, reperfusion-induced arrhythmias and chronic heart failure. The experimental work is shared between the two institutes based on available facilities and research expertise, and will be performed using up-to-date cellular electrophysiological (standard microelectrode and patch clamp) and fluorescent optical (Ca2+ measurements and epifluorescent mapping) techniques. Research question Significantly enhanced activity of NCX1 is known to play a major role in initiation and progression of a number of cardiac diseases. In spite of this fact, the application of inhibitory drugs is missing from clinical practice. The primary reason is the lack of effective, validated substances. In the proposed project we attempt to experimentally prove our working hypothesis, according to which, when using the new, selective NCX1 inhibitors (ORM10103 and ORM10962) the inhibition exerts substantial protective effect in our experimental animal models, therefore it can be considered a prospective cardioprotective strategy in clinical practice, as well, in human symptoms, analogue to our animal models. Two subtopics are to be investigated in details: I) What is the effect of selective NCX1 blockade on intracellular Ca2+ homeostasis and its adaptive mechanisms? In details: How the efficacy of inhibition is depending on intra- and extracellular ion concentrations? Is the efficacy of inhibition depending on transport direction? What is the role of the subsarcolemmal Ca2+ and Na+ microdomains in development of the inhibition? II) Is there any, and if yes, what is the efficacy of cardioprotection exerted by selective NCX1 inhibition in acute and chronic experimental cardiac disease models, in which disturbed NCX1 activity has a critical role in arrhythmia induction, as well as in elevation (acute ischemic models) or reduction (heart failure phenotypes) of the intracellular Ca2+ levels. Depending on availability, animal experiments will be supplemented with measurements performed on human samples obtained from healthy and diseased hearts during heart surgeries. What is the significance of your research? The results of the experimental work proposed in this project may facilitate a better understanding of pathomechanisms of a number of severe, often lethal, endemic heart diseases, myocardial infarction, arrhythmias and heart failure, and may establish a significant future improvement in their, in the moment by far not satisfactory, clinical pharmacotherapy. Our expected results are in part theoretically important: since until recently no selective NCX1 inhibitors were available, for the first time, there is an opportunity to directly and reliably answer questions related to transport activity of NCX1 and consequences of its inhibition, precluding the artifacts caused by the less specific selectivity of earlier inhibitors. Furthermore, the expected positive experimental results may carry important practical relevance by providing the basis for clinical trials targeted to test the efficacy of selective NCX1 inhibition in severe human syndromes. Consequently, the results of the proposed project in one respect could establish the use of the new, selective NCX1 inhibitors as research tools in scientific projects related to specific and selective modulation of the NCX1, its physiological activity, regulation and functional perturbations. On the other hand, our expected results may establish novel clinical therapeutic strategies, which could significantly contribute to the reduction of tissue injury during acute myocardial infarction and the probability of reperfusion-induced arrhythmias, and may delay the development and progression of chronic heart failure, threatening especially the elderly people, and finally prevent sudden cardiac death most often striking in the early phase of the disease. To accomplish the goals targeted in the project a tight collaboration has been established between well recognized researchers of two internationally acknowledged institutes, Department of Pharmacology and Pharmacotherapy of University of Szeged and Department of Cardiology of Medical University Graz. A lasting and multilateral cooperation between the two institutes may provide significant, mutual benefits, based on their complementary scientific methods, experimental models, research infrastructure and expertise. Summary and aims of the proposed research for the public. Pathologic overactivity of a cellular mechanism, responsible for relaxation of the heart plays a pivotal role in development of some very common and severe often lethal cardiac diseases (myocardial infarction, arrhythmias and chronic heart failure). Nonetheless, medicines inhibiting this overactivity are missing from clinical practice. The primary reason is the lack of agents with established efficacy. Based on a long-lasting cooperation, two highly promising compounds, recently synthesized by ORION Pharma, Finland, were made exclusively available to our workgroup, providing us a unique opportunity to investigate the inhibition in details, at the cellular level. We plan to carry out these investigations in cooperation with our partners in Graz, who has access to several methods and animal models not available in our institute, and also have access to samples obtained from failing human hearts. In case, if as expected we could univocally demonstrate that the new inhibitors exert significant beneficial effects in our heart disease models, their application would provide a promising strategy in clinical practice as well, in symptoms analogue to the animal models used, and could accelerate related clinical trials. In summary, our results may help to establish novel clinical therapies, which could significantly reduce the tissue injury and probability of arrhythmia generation during acute myocardial infarction, delay the progression of chronic heart failure, threatening especially elderly people, and prevent sudden cardiac death of the patients.

Heart failure is a progressive condition in which the heart fails to beat and contract properly. Current managment is inadequate to preventing heart failure progression and minimizing the risk of dying suddenly. Thus there is an urgent clinical need of better medication for treating this syndrome. Two research groups from the university of Szeged and Medical university of Graz initiated an international collaboration to explore a new therapeutic strategy to improving cardiac function and reducing arrhythmia risk in heart failure. New compounds against the sodium/calcium exchanger (NCX) were tested in cell-based and animal studies. The compounds were designed and synthetized by a collaborating pharmaceutical industry partner (Orion Pharma) and distributed exclusively to the partners. RationaleThe NCX is a small protein located in the membrane of cardiac cells. Its main function is to removing calcium from the cell after contraction. Disturbed NCX function typically causes imbalance of calcium handling and electrical instability. In heart failure, overactivity of NCX is considered a major cause of impaired contraction, slow relaxation and irregular beating. Up-to-date, NCX has not been clinically exploited as a target against heart failure and arrhythmias for the important reason that currently available NCX blockers lack specificity. In addition, the regulation of NCX in cardiac cells is highly complex and the efficacy of NCX inhibition is therefore hard to predict, particularly in settings of cardiac disease. The project aims at investigating the efficacy of specific NCX blockers against different types of heart failure and arrhythmia disease. Findings and PerspectivesBasic characterization and pharmacological profiling of the new compounds was performed at the university of Szeged. The partners in Graz tested the specific NCX blockers in two clinically relevant animal models of hypertension and cardiorenal failure. In both models, acute NCX inhibition improved contraction and relaxation of cardiac cells. Chronic treatment of heart failure rats with NCX blockers ameliorated overall cardiac performance and slowed heart failure progression. The findings of this FWF project promote further proof-of-concept studies in preclinical models and patients and may encourage pharma industry to consider NCX inhibitory compounds as novel drugs in the pipeline for heart failure.