The effects of the novel anti-anginal compound RS 43285 on myocardial conduction in the anaesthetized dog

The inadequacy of the reductionist approach in discovering new therapeutic agents against complex diseases

For more than 20 years, drug discovery has relied on two assumptions, i.e. (i) a therapeutic response can be triggered by modulating the activity of a single gene product, and (ii) a compound uncovered by its activity on a recombinant protein in vitro can perform its activity in vivo. Drug discovery operates accordingly by using the concepts of targets and pipelines. The target, such as a gene product, is the intended point of therapeutic intervention, and compounds that modulate its activity in vitro follow a series of downstream developments. This reductionist approach has developed due to advances in combinatorial chemistry, robotics, molecular biology, and genomics. The expectation of this approach is that the frequency of drug discovery will dramatically increase, while its associated cost would decrease. However, the frequency of new drug discovery has decreased, while the associated costs have surged. We performed a retrospective study that examined how successful development programs have led to marketed drugs for all indications except anti-infective and anti-neoplastic agents. We concluded that the target and pipeline paradigms are limited and are actually causing the drug development industry to collectively fail to meet the critical medical needs. Impact statement The initial scope of this investigation was to build the set of human genes that are presumed to be the therapeutic intervention points of US FDA-approved drugs, in all therapeutics areas but oncology. The prerequisite for this study was the establishment of the non-redundant set of all active pharmaceutical ingredients for these disease areas. Pertaining to complex diseases, the main observation was that there is not a single instance in the history of drug discovery, where a compound, initially selected by means of a biochemical assay, achieved a significant therapeutic response. The whole field of Drug R&D faces an unacceptable lack of new treatments to address unmet medical needs. The conclusion is that complex biological assays have to be designed for the primary selection of candidate therapeutics.

Ranolazine, an Inhibitor of the Late Sodium Channel Current, Reduces Postischemic Myocardial Dysfunction in the Rabbit

Ranolazine is a selective inhibitor of the late sodium current relative to peak sodium channel current, and via this mechanism, it may decrease sodium-dependent intracellular calcium overload during ischemia and reperfusion. Ranolazine reduces the frequency of angina attacks, but there is little information on its effects on myocardial stunning after short-term ischemia. The objective of this study was to test the effects of ranolazine on left ventricular (LV) function and myocardial stunning after ischemia/reperfusion in rabbits. Myocardial stunning was induced in rabbits by 15 minutes of coronary artery occlusion (CAO) followed by 3 hours reperfusion. Ten minutes before CAO, rabbits were randomly assigned to vehicle (n = 15) or ranolazine (2 mg/kg bolus plus 60 μg/kg/min infusion, IV, n = 15). Myocardial stunning was assessed by LV 2-dimensional echocardiography using, as a marker of severity, ischemic free-wall fractional thickening (FWft; systolic wall thickness – diastolic wall thickness/diastolic wall thickness). Regional ejection fraction (EF) was also assessed. During CAO, FWft was depressed in both groups, indicating an ischemic insult (FWft was reduced from 0.62 ± 0.05 at baseline to 0.10 ± 0.04 in vehicle and from 0.73 ± 0.05 to 0.26 ± 0.07 in ranolazine, P < 0.05, ranolazine vs vehicle). After reperfusion, previously ischemic myocardium remained stunned; however, FWft recovered significantly better in ranolazine (0.51 ± 0.05) than in vehicle (0.35 ± 0.04, P = .027). Baseline EF was 0.65 ± 0.02 in the ranolazine and 0.68 ± 0.02 in vehicle ( P = ns). During CAO, EF was reduced by 36% ± 6% in vehicle versus only 20% ± 6% in ranolazine ( P < .05). At the end of reperfusion, EF remained depressed in both groups, but the reduction in the vehicle group (25% ± 5%) was significantly worse than in ranolazine (9% ± 4%, P = .017). Improvement in function was independent of necrosis (negligible) or differences in hemodynamics (no differences between groups). Ranolazine treatment reduced myocardial stunning following brief ischemia/reperfusion suggesting that inhibiting the late sodium channel current may be a novel approach to treating stunning independent of effects on hemodynamics.

Ranolazine: new approach for the treatment of stable angina pectoris

Myocardial ischemia is a metabolic problem involving reduced delivery of oxygen to cardiac mitochondria, resulting in less ATP formation, acceleration of glycolysis and production of lactate and H+ by the cell. Traditional therapies for ischemia aim at restoring the balance between mitochondrial ATP production and breakdown by reducing the need for ATP via suppression of heart rate, blood pressure and cardiac contractility, or by increasing oxygen delivery via increased myocardial blood flow. Despite optimal treatment with traditional hemodynamically oriented drugs (beta-adrenergic receptor antagonist, Ca2+ channel antagonist and nitrates), many patients continue to suffer from angina. Thus, there is a need for anti-anginal drugs that act directly on cardiomyocytes to lessen the metabolic abnormalities induced by ischemia and reduce the symptoms (chest pain and exercise intolerance). Ranolazine has been demonstrated to improve exercise time to angina or 1 mm of ST-segment depression in a manner similar to currently approved drugs, but without any significant effects on heart rate or blood pressure at rest or during exercise. In two Phase III trials, ranolazine improved exercise tolerance and reduced the frequency of angina attacks in chronic severe angina patients when administered either as monotherapy or on a background of atenolol, amlodinine or diltiazem. At present, ranolazine is under review for US Food and Drug Administration approval and, if approved, it will represent the first drug of its class in the USA.

Ranolazine reduces Ca2+ overload and oxidative stress and improves mitochondrial integrity to protect against ischemia reperfusion injury in isolated hearts

Ranolazine is a clinically approved drug for treating cardiac ventricular dysrhythmias and angina. Its mechanism(s) of protection is not clearly understood but evidence points to blocking the late Na+ current that arises during ischemia, blocking mitochondrial complex I activity, or modulating mitochondrial metabolism. Here we tested the effect of ranolazine treatment before ischemia at the mitochondrial level in intact isolated hearts and in mitochondria isolated from hearts at different times of reperfusion. Left ventricular (LV) pressure (LVP), coronary flow (CF), and O2 metabolism were measured in guinea pig isolated hearts perfused with Krebs-Ringer's solution; mitochondrial (m) superoxide (O2·-), Ca2+, NADH/FAD (redox state), and cytosolic (c) Ca2+ were assessed on-line in the LV free wall by fluorescence spectrophotometry. Ranolazine (5 μM), infused for 1 min just before 30 min of global ischemia, itself did not change O2·-, cCa2+, mCa2+ or redox state. During late ischemia and reperfusion (IR) O2·- emission and m[Ca2+] increased less in the ranolazine group vs. the control group. Ranolazine decreased c[Ca2+] only during ischemia while NADH and FAD were not different during IR in the ranolazine vs. control groups. Throughout reperfusion LVP and CF were higher, and ventricular fibrillation was less frequent. Infarct size was smaller in the ranolazine group than in the control group. Mitochondria isolated from ranolazine-treated hearts had mild resistance to permeability transition pore (mPTP) opening and less cytochrome c release than control hearts. Ranolazine may provide functional protection of the heart during IR injury by reducing cCa2+ and mCa2+ loading secondary to its effect to block the late Na+ current. Subsequently it indirectly reduces O2·- emission, preserves bioenergetics, delays mPTP opening, and restricts loss of cytochrome c, thereby reducing necrosis and apoptosis.

Chick embryo partial ischemia model: a new approach to study ischemia ex vivo

BACKGROUND

Ischemia is a pathophysiological condition due to blockade in blood supply to a specific tissue thus damaging the physiological activity of the tissue. Different in vivo models are presently available to study ischemia in heart and other tissues. However, no ex vivo ischemia model has been available to date for routine ischemia research and for faster screening of anti-ischemia drugs. In the present study, we took the opportunity to develop an ex vivo model of partial ischemia using the vascular bed of 4(th) day incubated chick embryo.

METHODOLOGY/PRINCIPAL FINDINGS

Ischemia was created in chick embryo by ligating the right vitelline artery using sterile surgical suture. Hypoxia inducible factor- 1 alpha (HIF-1alpha), creatine phospho kinase-MB and reactive oxygen species in animal tissues and cells were measured to confirm ischemia in chick embryo. Additionally, ranolazine, N-acetyl cysteine and trimetazidine were administered as an anti-ischemic drug to validate the present model. Results from the present study depicted that blocking blood flow elevates HIF-1alpha, lipid peroxidation, peroxynitrite level in ischemic vessels while ranolazine administration partially attenuates ischemia driven HIF-1alpha expression. Endothelial cell incubated on ischemic blood vessels elucidated a higher level of HIF-1alpha expression with time while ranolazine treatment reduced HIF-1alpha in ischemic cells. Incubation of caprine heart strip on chick embryo ischemia model depicted an elevated creatine phospho kinase-MB activity under ischemic condition while histology of the treated heart sections evoked edema and disruption of myofibril structures.

CONCLUSIONS/SIGNIFICANCE

The present study concluded that chick embryo partial ischemia model can be used as a novel ex vivo model of ischemia. Therefore, the present model can be used parallel with the known in vivo ischemia models in understanding the mechanistic insight of ischemia development and in evaluating the activity of anti-ischemic drug.

Ranolazine

Ranolazine (Ranexa), a piperazine derivative, is a new antianginal agent approved for the treatment of chronic stable angina pectoris for use as combination therapy when angina is not adequately controlled with other antianginal agents. While the exact mechanism of action of ranolazine is not known, its antianginal and anti-ischaemic effects do not appear to depend upon changes in blood pressure or heart rate. An extended-release (ER) oral formulation of ranolazine has been developed to facilitate twice-daily administration whilst maintaining therapeutically effective plasma concentrations. In patients with chronic stable angina, ranolazine ER monotherapy was shown to improve exercise duration at trough plasma drug concentration in a dose-dependent manner compared with placebo. The drug was effective as adjunctive therapy in patients with chronic stable angina whose condition was not controlled adequately with conventional antianginal therapy. In randomised clinical trials, ranolazine ER was well tolerated, with no overt effects on cardiovascular haemodynamics or conduction, apart from a modest increase in corrected QT (QTc) interval (but no torsades de pointes). Importantly, the efficacy and tolerability of ranolazine ER were not affected by comorbid conditions, including old age, heart failure (HF) or diabetes mellitus. Comparative trials of ranolazine ER with other antianginal agents and trials examining its effects on long-term morbidity and mortality in patients with ischaemic heart disease are required to determine with greater certainty the place of the drug in current antianginal therapy. Nevertheless, ranolazine ER may well prove to be a useful alternative and adjunct to conventional haemodynamic antianginal therapy in the treatment of chronic stable angina.

Ranolazine: ion-channel-blocking actions and in vivo electrophysiological effects

Ranolazine is a novel anti-ischemic drug that prolongs the QT interval. To evaluate the potential mechanisms and consequences, we studied: (i) Ranolazine's effects on HERG and IsK currents in Xenopus oocytes with two-electrode voltage clamp; (ii) effects of ranolazine, compared to d-sotalol, on effective refractory period (ERP), QT interval and ventricular rhythm in a dog model of acquired long QT syndrome; and (iii) effects on selected native currents in canine atrial myocytes with whole-cell patch-clamp technique. Ranolazine inhibited HERG and IsK currents with different potencies. HERG was inhibited with an IC(50) of 106 micromol l(-1), whereas the IC(50) for IsK was 1.7 mmol l(-1). d-Sotalol caused reverse use-dependent ERP and QT interval prolongation, whereas ranolazine produced modest, nonsignificant increases that plateaued at submaximal doses. Neither drug affected QRS duration. d-Sotalol had clear proarrhythmic effects, with all d-sotalol-treated dogs developing torsades de pointes (TdP) ventricular tachyarrhythmias, of which they ultimately died. In contrast, ranolazine did not generate TdP. Effects on I(Kr) and I(Ks) were similar to those on HERG and IsK. Ranolazine blocked I(Ca) with an IC(50) of approximately 300 micromol l(-1). I(Na) was unaffected. We conclude that ranolazine inhibits I(Kr) by blocking HERG currents, inhibits I(Ca) at slightly larger concentrations, and has modest and self-limited effects on the QT interval. Unlike d-sotalol, ranolazine does not cause TdP in a dog model. The greater safety of ranolazine may be due to its ability to inhibit I(Ca) at concentrations only slightly larger than those that inhibit I(Kr), thus producing offsetting effects on repolarization.

Ranolazine: a potential new treatment for chronic stable angina

Ranolazine is a novel antianginal agent currently under investigation as monotherapy and adjunct therapy for the treatment of chronic stable angina. Although the mechanism of action of ranolazine is not completely understood, it is believed to involve a reduction in fatty acid oxidation, ultimately leading to a shift in myocardial energy production from fatty acid oxidation to glucose oxidation. Because the oxidation of glucose requires less oxygen than the oxidation of fatty acids, ranolazine can help maintain myocardial function in times of ischemia. In addition, ranolazine does not significantly affect blood pressure, heart rate, or cardiac conduction. The clinical data with ranolazine focuses on its use in chronic stable angina, where it has been shown to increase exercise tolerance and decrease angina compared with placebo and in combination with beta-blockers and calcium-channel blockers. The use of ranolazine for other cardiac conditions and the effect of ranolazine on morbidity and mortality remain to be determined.

Protective Effects of Ranolazine on Ventricular Fibrillation Induced by Activation of the ATP-Dependent Potassium Channel in the Rabbit Heart

BACKGROUND: The authors studied the antifibrillatory effects of the adenosine-triphosphate (ATP)-sparing metabolic modulator ranolazine in a rabbit isolated heart model in which ventricular fibrillation occurs under conditions of hypoxia/reoxygenation in the presence of the ATP-dependent potassium channel opener pinacidil. METHODS AND RESULTS: Ten minutes after ranolazine or vehicle administration, addition of pinacidil (1.25 µM) to the buffer was followed by a 12-minute hypoxic period and 40 minutes of reoxygenation. At a reduced concentration of ranolazine (10 µM), ventricular fibrillation occurred in 60% of the hearts, compared to 89% in the control group (P = NS). In contrast, only three of nine hearts (33%) treated with 20 µM ranolazine developed ventricular fibrillation (P <.05 vs vehicle). Hemodynamic parameters including coronary perfusion pressure, left ventricular developed pressure, and +/-dP/dt were not affected by the presence of ranolazine in the perfusion medium. Ranolazine did not prevent or modify the negative inotropic or coronary vasodilator actions of pinacidil, suggesting a mechanism of action independent of potassium channel antagonism. CONCLUSIONS: Ranolazine significantly reduced the incidence of ventricular fibrillation in the hypoxic/reoxygenated heart exposed to the ATP-dependent potassium channel opener, pinacidil. The reported ability of ranolazine to prevent the decrease in cellular ATP during periods of a reduced oxygen supply may account for its observed antifibrillatory action. By maintaining intracellular ATP, ranolazine may modulate or prevent further opening of the ATP-dependent potassium channel in response to hypoxia and/or pinacidil.

Protective effects of calcium antagonists in different organs and tissues

The therapeutic efficacy of calcium antagonists in ischemic disorders of various tissues is attributed to vasodilator and antivasoconstrictor activities. A direct, energy-conserving, antiischemic effect of certain calcium antagonists has been claimed repeatedly by basic scientists. The clinical value of such effects has been doubtful until recently, when the organ-protective activity of certain calcium antagonists was confirmed in a few large-controlled clinical trials. The following evidence has been presented for the protective activity of calcium antagonists: (1) for the heart, beneficial effects of verapamil and diltiazem have been shown on reinfarction and mortality rates, (2) relative to the brain, the beneficial effect of nimodipine has been shown in preventing neurologic deficits after subarachnoidal hemorrhage, and an antimigraine effect of flunarizine has been demonstrated, (3) concerning the blood vessels, israpidine and lacidipine have been demonstrated to have antiatherogenic potency in animal models, and (4) for the kidneys, an antivasoconstrictor effect occurs at the preglomerular level. In addition, verapamil, diltiazem, and nitrendipine may protect against radiocontrast-induced nephrotoxicity, and verapamil counteracts cyclosporine nephrotoxicity.

A comparison of the effects of a series of anti-anginal agents in a novel canine model of transient myocardial ischaemia

1. An anaesthetized canine model of transient myocardial ischemia (TMI) has been developed in which reproducible and reversible electrocardiographic (ECG) and haemodynamic responses are exacerbated by electrical pacing. 2. The model could separate the ECG and haemodynamic effects of compounds with anti-ischaemic properties. 3. Compounds known to possess peripheral or coronary vasodilator properties did not necessarily alleviate the ECG consequences of TMI since glyceryl trinitrate was active whereas dipyridamole was not. The effects of verapamil were complicated by its adverse conduction effects while lidoflazine inhibited the ECG changes only during the ischaemic phase and the 'metabolic modulator' oxfenicine worsened the ECG response. 4. In a model considered to lack coronary reserve, improvements observed in the ischaemic ECG and global ventricular function were considered to result from a direct myocardial effect of the drugs examined rather than by a vascular influence. This was provided to the greatest degree by the Ca2+-entry blockers nifedipine and nicardipine, with flunarizine adopting an intermediate position.