Heart failure is a major world-wide public health problem and is the only cardiac disorder that is increasing in incidence. In the United States alone, 5 million patients suffer from heart failure, with a new diagnosis made in 0.5 million patients per year. Despite advances in therapy over the last decade, the annual number of hospitalisations has increased from 550 000 to 900 000 as a primary diagnosis, and from 1.7 to 2.6 million as a primary or secondary diagnosis (J. Am. Pharm. Assoc., vol. 41(5), pp. 672-681, 2001). Unless treated, heart failure may lead to death. Hence, new approaches are warranted to treat or prevent heart failure.
Although the terminology heart failure seems to be the most accepted terminology for describing this cardiac disorder, various further equivalent terminologies can be found in the scientific, patent or medical literature as, for example, cardiac failure, insufficient cardiac output, cardiac insufficiency, cardiac collapse and cardiac syncope.
Furthermore, though heart failure is invariably a chronic cardiac disorder, often with an insidious onset, heart failure may be present acutely or be punctuated by episodes of acute deterioration, so called “decompensated” heart failure. To describe these conditions also related to heart failure, further terminologies will commonly be found in the scientific, patent or medical literature such as, for example, chronic heart failure, acute heart failure, heart decompensation, cardiac decompensation and cardial decompensation.
Lastly, as will be explained in the foregoing, as heart failure can be caused by a dysfunctioning of the heart reflected by various clinical presentations and sometimes subjected to further complications, further terminologies related to heart failure will also commonly be found in the scientific, patent or medical literature such as, for example, myocardial failure, myocardial insufficiency, heart muscle insufficiency, cardiac muscle insufficiency, heart muscle weakness, cardiac muscle weakness, systolic or left ventricular heart failure, diastolic heart failure, left or right sided heart failure, biventricular heart failure and congestive heart failure.
Hence, a distinction can be made between the systolic or diastolic origin of the dysfunctioning. Commonly, heart failure is a consequence of a progressive deterioration of myocardial contractile function, named systolic or left ventricular dysfunction. However, diastolic dysfunction is becoming increasingly recognised as an important cause of heart failure too. This occurs when the heart chambers are unable to expand sufficiently during diastole (period of heart relaxation in which the chambers fill with blood) and hence blood volume in the ventricles is inadequate. Whether systolic and/or diastolic dysfunction is the basis of heart failure, cardiac output is diminished. When additionally there is “damming” back of blood in the venous system, congestion may ensue in the lungs (pulmonary oedema) and/or in the abdomen or peripheries (peripheral oedema). When both occur, the terminology congestive heart failure is often used.
In other respects, the distinction between left and right sided heart failure can be applied to reflect the clinical presentation (i.e. pulmonary oedema indicative of left sided heart failure, whereas the principal symptom of right sided heart failure is fluid retention in the peripheries) or to denote the underlying cause. Right sided heart failure is most commonly a consequence of left sided heart failure, although diseases of the lung (such as chronic obstructive pulmonary disease), the right ventricle (e.g. right ventricular infarction) or the vasculature (primary or secondary pulmonary hypertension, the latter due to conditions such as pulmonary embolism for example), may result in predominate right sided heart failure.
According to the International Classification of Functioning, Disability and Health, lastly published by the World Health Organization on 15 Nov. 2001 (ISBN 91 4 1545429) and accepted by 191 countries during the 54th World Health Assembly (Resolution WHA 54.21), heart failure occurs when the heart function of pumping the blood in adequate or required amounts and pressure throughout the body is impaired.
As cardiac output is normally 5 liters/minute, although this can increase five fold with heavy exercise, in essence, heart failure occurs when the heart is unable to meet this demand.
As heart failure manifests itself in a variety of ways, at the time of this patent application, the treatment or prevention of heart failure comprises a combination of typical medications. These medications are based upon the principles of promoting fluid excretion to lessen oedema and volume overload (e.g. various types of diuretics), vasodilatory drugs to reduce preload (i.e. atrial pressures) and/or afterload (i.e. pressure against which the heart has to beat), and inotropic drugs to increase contractility.
Vasodilatory drugs available at this time include Angiotensin Converting Enzyme (ACE) inhibitors, Angiotensin II Receptor blockers (ARBs) and nitrate venodilators. Inotropic drugs are usually administered only in acute situations Although cardiac glycosides such as digoxin are sometimes prescribed for their inotropic properties, their use is more common in heart failure patients when atrial arrhythmias co-exist.
Recently, beta-blockers, which were once thought to be contra-indicated in heart failure due to their negative inotropic (decreased contractility) property, have been shown to be effective in the treatment of heart failure. Meta-analyses of randomised controlled trials have shown that, in addition to established background therapy of ACE inhibitors and diuretics with or without digoxin, a reduction of all cause mortality and cardiovascular morbidity is conferred by beta-blockers such as carvedilol, metoprolol or bisoprolol (Brophy J. M. et al., Ann. Intern. Med. 2001, Vol. 134, pp. 550-560; Lechat P. et al., Circ. 1998, pp. 1184-1191; Heidenreich P. A. et al., J. Am. Coll. Cardiol., 1997, Vol. 30, pp 27-34).
As heart failure progresses, heart failure treatment is also usually not limited to one single therapy. Hence, add-on therapy use is disclosed for carvedilol, for example, in WO 96/24348, for decreasing the mortality of patients suffering from congestive heart failure. WO 96/40258 discloses a combination therapy comprising an angiotensin II antagonist and spironolactone, an aldosterone receptor antagonist, for the treatment of hypertension, congestive heart disease, cirrhosis and ascites. WO 00/02543 discloses a combination therapy comprising an angiotensin II antagonist (valsartan) and a calcium channel blocker (amlodipine or verapamil) for the treatment of several heart diseases, amongst which acute and chronic congestive heart diseases are cited.
However, as with all therapies, there are constraints to their use. For example, beta-blockers may be contra-indicated in patients with concomitant diseases such as asthma, peripheral vascular disease and decompensated heart failure. Certain drug classes may not be tolerated due to unwanted side effects, e.g. cough with ACE inhibitors, fatigue, dizziness or impotence in association with beta-blockers, and hyponatremia with diuretics. Furthermore, a slow and careful titration period may be required upon drug initiation, as with beta-blockers, where if not performed, the initial negative effects on the heart's pumping action (negative inotropy) may result in drug intolerance and deterioration in heart failure status.
Hence, to echo the statement set out at the beginning of this section, despite the advances made by therapies established at this time, there is still a need to reduce the unacceptable burden of heart failure and new additional approaches to treatment and prevention of disease progression should be sought.
In searching for new therapies for heart failure, the underlying pathophysiology of the failing heart needs to be considered. It has long been observed in the failing heart that heart rate and contractility are initially increased in order to maintain cardiac performance. In the long term, this response is ultimately damaging. It is, for example, acknowledged that increased heart rate is a risk factor for mortality and morbidity with adverse consequences on vascular function, atherogenesis, myocardial ischaemia, myocardial energetics and left ventricular function. Chronic tachyarrhythmias are a cause of reversible cardiomyopathy in humans and rapid atrial pacing is established as an animal model of cardiomyopathy. In chronic heart failure, excess adrenergic stimulation signals adverse biological responses (including increased heart rate) via β1, β2 and α2 receptors in the myocardium.
In the failing heart, maintenance of adequate ventricular contraction is sought, but occurs at the expense of oxygen and energy consumption by the myocardium. Heart rate influences such energy demand, with increased heart rate requiring greater expenditure of energy. Thus, greater energetic efficiency could potentially result if heart rate were lowered in heart failure patients.
It thus follows that drugs which have the ability to reduce heart rate may be of benefit in the treatment or prevention of heart failure. For the treatment of cardiac insufficiency, a term also used to denote heart failure, EP 0 471 388 (and its US counterpart U.S. Pat. No. 5,516,773) suggests the use of a specific group of compounds derived from the benzazepine basic chemical structure, and more specifically the compound named zatebradine [1-(7,8-dimethoxy-1,3,4,5-tetrahydro-2H-3-benzazepin-2-one-3-yl)-3-[N-methyl-N-(2-(3,4-dimethoxy-phenyl)-ethyl)-propane].
These benzazepine derivatives were firstly described in EP 0 065 229, as well as their ability to reduce heart rate (bradycardic effect) by acting directly on the sinoatrial node, and their ability to reduce the oxygen requirement of the heart. Zatebradine is also known from WO 01/78699 for the treatment and induction of the regression of idiopathic hypertrophic cardiomyopathy (HCM), ischemic cardiomyopathy and valvular hypertrophic heart diseases.
The effects of the bradycardic agent zatebradine have been studied in a small number of patients with heart failure, also subject to no therapy or atrial pacing, to induce a tachycardia (Shinke et al., Jpn. Circ. Journal, 1999, Vol. 63, pp. 957-964) or in comparison to the beta-blocker propranolol (Shinke et al. Abstract Circ., 1997, Vol. 96, I-644).
In the former study, it was concluded by the authors that the oxygen saving effect of the bradycardia due to zatebradine treatment could be beneficial for the treatment of heart failure. In the latter study, the comparable heart rate reduction observed with zatebradine and the beta-blocker had favourable effects compared to pre-treatment. However, it should be noted that under beta-blocker treatment overall cardiac efficiency was preserved, since the energy saving benefits of heart rate reduction remedied the observed negative effect on contractility. This, the authors proposed, might account for good beta-blockers tolerance and possible efficacy in heart failure. Zatebradine treatment however improved cardiac efficiency since heart rate reduction occurred, but with no accompanying adverse effect on contractility.
It should be noted that these two studies are small and do not attempt to evaluate the benefits of chronic zatebradine administration on the hemodynamic or clinical manifestations of heart failure. Furthermore, the relationships between heart rate reduction, left ventricular function and prognosis in heart failure are complex. However, there is a scientific rationale that improved cardiac energetics secondary to heart rate reduction is an important concept in the treatment and prevention of the progression of heart failure due to systolic and/or diastolic dysfunction (Laperche et al., Heart 1999, Vol. 81, pp. 336-341).
Another specific group of compounds derived from a basic cyclic amine chemical structure, have been shown to also have valuable pharmacological bradycardic properties. These compounds, the process for their preparation and pharmaceutical compositions containing them are described in EP 0 224 794 and its US counterpart U.S. Pat. No. 5,175,157.
One of these cyclic amine derivatives, 3-[(N-(2-(3,4-dimethoxy-phenyl)-ethyl)-piperidin-3-yl)-methyl]-7,8-dimethoxy-1,3,4,5-tetrahydro-2H-3-benzazepin-2-one, and more particularly its S-(+) enantiomer named cilobradine [(+)-3-[(N-(2-(3,4-dimethoxy-phenyl)-ethyl)-piperidin-3-(S)-yl)-methyl]-7,8-dimethoxy-1,3,4,5-tetrahydro-2H-3-benzazepin-2-one], is also known from WO 01/78699 for the treatment and induction of the regression of idiopathic hypertrophic cardiomyopathy (HCM), ischemic cardiomyopathy and valvular hypertrophic heart diseases.
However, these cyclic amine derivatives, and more specifically cilobradine, have not been suggested for the treatment or prevention of heart failure.
Scientific studies performed with zatebradine and cilobradine in order to determine the mechanism of action of these bradycardic substances have shown that both zatebradine and cilobradine selectively block hyperpolarisation activated, cAMP-modulated cation current channels (HCN) in cardiac conductive tissue, channels responsible for the transmembrane current known as If. It is through blockade of this current that zatebradine and cilobradine are assumed to produce their specific bradycardic effect.
However, HCN channels are widely distributed in the nervous system, and in the eye they mediate the current known as Ih. The effect of zatebradine and cilobradine on the Ih channel has also been investigated (Neuroscience, Vol. 59(2), pp. 363-373, 1994 for zatebradine, and British Journal of Pharmacology, Vol. 125, pp. 741-750, 1998 for cilobradine). The results have suggested that although Ih can also be blocked by these compounds, the interaction with the channels is somewhat different for both tissues. Since Ih has been described in the different neurones of the visual signal processing system, the effect on Ih current has been suggested to be an explanation for the side-effects (visual disturbances) seen by patients treated with If blockers.
Further studies have been performed using electroretinogram (ERG) responses recorded from cat eyes and psychophysical measurements conducted on volunteer human subjects, in normal conditions and after administration of zatebradine (Archives Italiennes de Biologie, vol. 137, pp. 299-309, 1999, and Vision Research, vol. 39, pp. 1767-1774, 1999). The results of these studies have shown that zatebradine reduces the amplitude of the response to stimuli of frequency above 1 Hz, as shown by the ERG recordings. Furthermore, the measurement of the attenuation and phase characteristics of the first harmonic constructed by plotting the response amplitude and the phase as a function of the temporal frequency of the stimulus in control conditions and after intravenous injection or oral administration of zatebradine have shown that the main effect of the Ih blocker zatebradine is to decrease the response amplitude to stimuli in the frequency range of 2 to 15 Hertz, by introducing a cut-off in the band-pass at about 2 Hertz.
To confirm these assumptions, recent studies have been performed using intraretinal and vitreal electroretinogram (ERG) recordings in dark-adapted intact cat retina (Visual Neuroscience, vol. 18(3), pp. 353-363, 2001). These studies compared the changes in the recovery phase following the a- and b-waves induced by an exposure with bright flashes of diffuse white light, after intraretinal injections of substances known to block the responses of bipolar and horizontal cells, or substances known to block Ih. The authors of this study have concluded that blockers of Ih reduce the recovery phase following the a-wave induced by the light exposure.
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