Inhibition of late Na+ current, a novel target to improve diastolic function and electrical abnormalities in Dahl salt-sensitive rats.

Late Na(+) current (INaL) is enhanced in myocytes of animals with chronic heart failure and patients with hypertrophic cardiomyopathy. To define the role of INaL in diastolic heart failure, the effects of GS-458967 (GS-967), a potent INaL inhibitor on mechanical and electrical abnormalities, were determined in an animal model of diastolic dysfunction. Dahl salt-sensitive (DSS) rats fed a high-salt (HS) diet for 8 wk, compared with a normal salt (NS) diet, had increased left ventricular (LV) mass (1,257 ± 96 vs. 891 ± 34 mg) and diastolic dysfunction [isovolumic relaxation time (IVRT): 26.8 ± 0.5 vs. 18.9 ± 0.2 ms; early transmitral flow velocity/early mitral annulus velocity (E/E') ratio: 25.5 ± 1.9 vs. 14.9 ± 0.9]. INaL in LV myocytes from HS rats was significantly increased to 0.41 ± 0.02 from 0.14 ± 0.02 pA/pF in NS rats. The action potential duration (APD) was prolonged to 136 ± 12 from 68 ± 9 ms in NS rats. QTc intervals were longer in HS vs. NS rats (267 ± 8 vs. 212 ± 2 ms). Acute and chronic treatment with GS-967 decreased the enhanced INaL to 0.24 ± 0.01 and 0.17 ± 0.02 pA/pF, respectively, vs. 0.41 ± 0.02 pA/pF in the HS group. Chronic treatment with GS-967 dose-dependently reduced LV mass, the increases in E/E' ratio, and the prolongation of IVRT by 27, 27, and 20%, respectively, at the 1.0 mg·kg(-1)·day(-1) dose without affecting blood pressure or LV systolic function. The prolonged APDs in myocytes and QTc of HS rats were significantly reduced with GS-967 treatment. These results indicate that INaL is a significant contributor to the LV diastolic dysfunction, hypertrophy, and repolarization abnormalities and thus, inhibition of this current is a promising therapeutic target for diastolic heart failure.

Discovery of triazolopyridinone GS-462808, a late sodium current inhibitor (Late INai) of the cardiac Nav1.5 channel with improved efficacy and potency relative to ranolazine.

Previously we disclosed the discovery of potent Late INa current inhibitor 2 (GS-458967, IC50 of 333nM) that has a good separation of late versus peak Nav1.5 current, but did not have a favorable CNS safety window due to high brain penetration (3-fold higher partitioning into brain vs plasma) coupled with potent inhibition of brain sodium channel isoforms (Nav1.1, 1.2, 1.3). We increased the polar surface area from 50 to 84Å(2) by adding a carbonyl to the core and an oxadiazole ring resulting in 3 GS-462808 that had lower brain penetration and serendipitously lower activity at the brain isoforms. Compound 3 has an improved CNS window (>20 rat and dog) relative to 2, and improved anti-ischemic potency relative to ranolazine. The development of 3 was not pursued due to liver lesions in 7day rat toxicology studies.

Discovery of triazolopyridine GS-458967, a late sodium current inhibitor (Late INai) of the cardiac NaV 1.5 channel with improved efficacy and potency relative to ranolazine.

We started with a medium throughput screen of heterocyclic compounds without basic amine groups to avoid hERG and ß-blocker activity and identified [1,2,4]triazolo[4,3-a]pyridine as an early lead. Optimization of substituents for Late INa current inhibition and lack of Peak INa inhibition led to the discovery of 4h (GS-458967) with improved anti-arrhythmic activity relative to ranolazine. Unfortunately, 4h demonstrated use dependent block across the sodium isoforms including the central and peripheral nervous system isoforms that is consistent with its low therapeutic index (approximately 5-fold in rat, 3-fold in dog). Compound 4h represents our initial foray into a 2nd generation Late INa inhibitor program and is an important proof-of-concept compound. We will provide additional reports on addressing the CNS challenge in a follow-up communication.

Ranolazine reduces remodeling of the right ventricle and provoked arrhythmias in rats with pulmonary hypertension.

Pulmonary arterial hypertension (PAH) is a progressive disease that often results in right ventricular (RV) failure and death. During disease progression, structural and electrical remodeling of the right ventricle impairs pump function, creates proarrhythmic substrates, and triggers for arrhythmias. Notably, RV failure and lethal arrhythmias are major contributors to cardiac death in patients with PAH that are not directly addressed by currently available therapies. Ranolazine (RAN) is an antianginal, anti-ischemic drug that has cardioprotective effects in experimental and clinical settings of left-sided heart dysfunction. RAN also has antiarrhythmic effects due to inhibition of the late sodium current in cardiomyocytes. We therefore hypothesized that RAN could reduce the maladaptive structural and electrical remodeling of the right ventricle and could prevent triggered ventricular arrhythmias in the monocrotaline rat model of PAH. Indeed, in both in vivo and ex vivo experimental settings, chronic RAN treatment reduced electrical heterogeneity (right ventricular-left ventricular action potential duration dispersion), shortened heart-rate corrected QT intervals in the right ventricle, and normalized RV dysfunction. Chronic RAN treatment also dose-dependently reduced ventricular hypertrophy, reduced circulating levels of B-type natriuretic peptide, and decreased the expression of fibrotic markers. In addition, the acute administration of RAN prevented isoproterenol-induced ventricular tachycardia/ventricular fibrillation and subsequent cardiovascular death in rats with established PAH. These results support the notion that RAN can improve the electrical and functional properties of the right ventricle, highlighting its potential benefits in the setting of RV impairment.

Selective inhibition of the late sodium current has no adverse effect on electrophysiological or contractile function of the normal heart.

Inhibition of cardiac late Na(+) current (I(Na,L)) decreases sodium-dependent calcium overload in diseased hearts. Because INa,L is small in the absence of disease, its inhibition is not expected to significantly alter function of the normal heart. To test this hypothesis, we determined the effects of GS-458967 (GS967), a novel selective inhibitor of I(Na,L) (IC(50) = 0.13 µM), on cardiac function and hemodynamics. The bradycardic agent ivabradine and the Na(+) channel blocker flecainide were used for comparison. A single per os administration of GS967 (5 mg/kg) had no effect on blood pressure or heart rate (HR) in unanesthetized rats. In anesthetized rats, GS967 (0.6 ± 0.1 µM plasma concentration) had no significant effect on HR, PR or QRS electrocardiogram intervals, or contraction. Flecainide (8 mg/kg) slowed HR by 23% ± 3% (P < 0.001), prolonged the PR and QRS intervals by 42% ± 8% and 64% ± 12% (P < 0.001), and had a significant negative inotropic effect. Ivabradine (3 mg/kg) slowed HR by 36% ± 6% (P < 0.001). In rat and rabbit isolated perfused hearts, GS967 (0.1-3 µM) had no significant effects on HR, QRS interval, or contractile function. The results show that selective inhibition of cardiac I(Na,L) is not associated with chronotropic, dromotropic, inotropic, or hemodynamic changes.

Preference for a Novel Oral Alternative to Parenterally Administered Medications.

Background: Rani Therapeutics is developing a robotic pill (RP), an oral drug delivery platform called RaniPill™ that can deliver a number of biotherapeutics with high bioavailability; eliminating the need for injections. While patients in general prefer oral to injectable therapies, preference for a more frequent oral regimen compared to a less frequent injectable regimen is unknown. Two marketing surveys were conducted to gather data on preference for oral versus injectable therapies. A clinical study gathered data on participant preference for oral pills vs injections before and after swallowing a Mock-RP capsule. Methods: A total of 1689 adults taking injections (mean duration 3-7 years) to treat endocrine or inflammatory conditions were anonymously surveyed online for their preference to administer/prescribe medications orally via the RP. In the clinical study, 150 participants currently taking injections for chronic conditions evaluated the swallowability of a Mock-RP and completed a questionnaire regarding their preferences. Results: Majority of respondents surveyed stated they would be willing to convert to an oral alternative over their current parenteral therapy regardless of drug or disease. In the clinical study, all participants were able to swallow the Mock-RP and 91% indicated their preference for the oral route versus their current parenteral route of drug administration. Survey respondents and those in the clinical study using frequent injections were more willing to select a once-daily capsule compared to those injecting infrequently. Even study participants who inject infrequently (≥monthly: 80%) would prefer a once-daily pill over their injection regimen. Conclusion: Patients taking injections and prescribing physicians strongly prefer oral dosing to parenteral administration of biologics even if dosing frequency with the oral option, such as the RP, is increased.

A novel, potent, and selective inhibitor of cardiac late sodium current suppresses experimental arrhythmias.

Inhibition of cardiac late sodium current (late I(Na)) is a strategy to suppress arrhythmias and sodium-dependent calcium overload associated with myocardial ischemia and heart failure. Current inhibitors of late I(Na) are unselective and can be proarrhythmic. This study introduces GS967 (6-[4-(trifluoromethoxy)phenyl]-3-(trifluoromethyl)-[1,2,4]triazolo[4,3-a]pyridine), a potent and selective inhibitor of late I(Na), and demonstrates its effectiveness to suppress ventricular arrhythmias. The effects of GS967 on rabbit ventricular myocyte ion channel currents and action potentials were determined. Anti-arrhythmic actions of GS967 were characterized in ex vivo and in vivo rabbit models of reduced repolarization reserve and ischemia. GS967 inhibited Anemonia sulcata toxin II (ATX-II)-induced late I(Na) in ventricular myocytes and isolated hearts with IC(50) values of 0.13 and 0.21 µM, respectively. Reduction of peak I(Na) by GS967 was minimal at a holding potential of -120 mV but increased at -80 mV. GS967 did not prolong action potential duration or the QRS interval. GS967 prevented and reversed proarrhythmic effects (afterdepolarizations and torsades de pointes) of the late I(Na) enhancer ATX-II and the I(Kr) inhibitor E-4031 in isolated ventricular myocytes and hearts. GS967 significantly attenuated the proarrhythmic effects of methoxamine+clofilium and suppressed ischemia-induced arrhythmias. GS967 was more potent and effective to reduce late I(Na) and arrhythmias than either flecainide or ranolazine. Results of all studies and assays of binding and activity of GS967 at numerous receptors, transporters, and enzymes indicated that GS967 selectively inhibited late I(Na). In summary, GS967 selectively suppressed late I(Na) and prevented and/or reduced the incidence of experimentally induced arrhythmias in rabbit myocytes and hearts.

A robotic pill for oral delivery of biotherapeutics: safety, tolerability, and performance in healthy subjects.

Biotherapeutics are highly efficacious, but the pain and inconvenience of chronic injections lead to poor patient compliance and compromise effective disease management. Despite innumerable attempts, oral delivery of biotherapeutics remains unsuccessful due to their degradation in the gastrointestinal (GI) environment and poor intestinal absorption. We have developed an orally ingestible robotic pill (RP) for drug delivery, which protects the biotherapeutic drug payload from digestion in the GI tract and auto-injects it into the wall of the small intestine as a safe, pain-free injection since the intestines are insensate to sharp stimuli. The payload is delivered upon inflation of a balloon folded within the RP, which deflates immediately after drug delivery. Here we present results from two clinical studies demonstrating the safety, tolerability and performance of the RP in healthy humans. In the first study, three versions of the RP (A, B and C) were evaluated, which were identical in all respects except for the diameter of the balloon. The RP successfully delivered a biotherapeutic (octreotide) in 3 out of 12 subjects in group A, 10 out of 20 subjects in group B and 16 out of 20 subjects in group C, with a mean bioavailability of 65 ± 9% (based on successful drug deliveries in groups A and B). Thus,  reliability of drug delivery with the RP ranged from 25 to 80%, with success rate directly related to balloon size. In a separate study, the deployment of the RP was unaffected by fed or fasting conditions suggesting that the RP may be taken with or without food. These promising clinical data suggest that biotherapeutics currently administered parenterally may be safely and reliably delivered via this versatile, orally ingestible drug delivery platform.

Ranolazine increases ß-cell survival and improves glucose homeostasis in low-dose streptozotocin-induced diabetes in mice.

In addition to its anti-ischemic and antianginal effects, ranolazine has been shown to lower hemoglobin A(1c) (HbA(1c)) in patients with coronary artery disease and diabetes. The present study was undertaken to test the hypothesis that ranolazine lowers HbA(1c) because of improved glucose homeostasis in an animal model. Diabetes in mice was induced by giving multiple low doses of streptozotocin. Ranolazine was given twice daily via an oral gavage (20 mg/kg) for 8 weeks. Fasting plasma glucose levels were significantly lower in the ranolazine-treated group (187 ± 19 mg/dl) compared with the vehicle group (273 ± 23 mg/dl) at 8 weeks. HbA(1c) was 5.8 ± 0.4% in the vehicle group and 4.5 ± 0.2% in the ranolazine-treated group (p < 0.05). Glucose disposal during the oral glucose tolerance test (OGTT) and insulin tolerance test were not different between the two groups; however, during OGTT, peak insulin levels were significantly (p < 0.05) higher in ranolazine-treated mice. Mice treated with ranolazine had healthier islet morphology and significantly (p < 0.01) higher ß-cell mass (69 ± 2% per islet) than the vehicle group (50 ± 5% per islet) as determined from hematoxylin and eosin staining. The number of apoptotic cells was significantly (p < 0.05) less in the pancreas of the ranolazine-treated group (14 ± 2% per islet) compared with the vehicle group (24 ± 4% per islet). In addition, ranolazine increased glucose-stimulated insulin secretion in rat and human islets in a glucose-dependent manner. These data suggest that ranolazine may be a novel antidiabetic agent that causes ß-cell preservation and enhances insulin secretion in a glucose-dependent manner in diabetic mice.

Ranolazine as a cardioplegia additive improves recovery of diastolic function in isolated rat hearts.

BACKGROUND: Ranolazine (Ran), an antianginal agent, inhibits late Na(+) current. The purpose of this study was to determine whether there was an added benefit of adding Ran to cardioplegia (CP) in a model of global ischemia/reperfusion. METHODS AND RESULTS: Isolated rat hearts were Langendorff-perfused and exposed to 40-minute normothermic, cardioplegic global ischemia and 30 minutes of reperfusion. Before ischemia and during reperfusion, hearts were treated with no drug (control) or with the late Na(+) current inhibitors Ran (5 micromol/L) or tetrodotoxin (1 micromol/L). Ischemic cardioplegic arrest led to an increase of left ventricular end-diastolic pressure (LVEDP) by > or =20 mm Hg (ie, cardiac contracture). Ten out of 11 hearts treated with CP alone developed contracture, whereas 6 out of 11 hearts treated with CP plus Ran developed contracture. Ran added to CP reduced LVEDP at the end of ischemia from 41+/-5 mm Hg in CP alone to 26+/-3 mm Hg in CP plus Ran (P=0.024). Area under the curve for LVEDP during the entire ischemic period was also smaller in CP plus Ran versus CP alone. The percent increase (from baseline) of LVEDP measured at the end of 30-minute reperfusion was smaller for CP plus Ran (66+/-18%) versus CP alone (287+/-90%; P=0.035). The area under the curve for LVEDP during reperfusion was smaller in CP plus Ran versus CP alone. Tetrodotoxin (1 micromol/L) also reduced cardiac contracture during ischemia/reperfusion, compared to CP alone. CONCLUSIONS: Our results suggest that Ran may have therapeutic potential as an adjunct to CP and further support a protective role of Na(+) current inhibition during ischemia/reperfusion.

Ranolazine, an antianginal agent, markedly reduces ventricular arrhythmias induced by ischemia and ischemia-reperfusion.

We tested the effect of the antianginal agent ranolazine on ventricular arrhythmias in an ischemic model using two protocols. In protocol 1, anesthetized rats received either vehicle or ranolazine (10 mg/kg, iv bolus) and were subjected to 5 min of left coronary artery (LCA) occlusion and 5 min of reperfusion with electrocardiogram and blood pressure monitoring. In protocol 2, rats received either vehicle or three doses of ranolazine (iv bolus followed by infusion) and 20 min of LCA occlusion. With protocol 1, ventricular tachycardia (VT) occurred in 9/12 (75%) vehicle-treated rats and 1/11 (9%) ranolazine-treated rats during reperfusion (P = 0.003). Sustained VT occurred in 5/12 (42%) vehicle-treated but 0/11 in ranolazine-treated rats (P = 0.037). The median number of episodes of VT during reperfusion in vehicle and ranolazine groups was 5.5 and 0, respectively (P = 0.0006); median duration of VT was 22.2 and 0 s in vehicle and ranolazine rats, respectively (P = 0.0006). With protocol 2, mortality in the vehicle group was 42 vs. 17% (P = 0.371), 10% (P = 0.162) and 0% (P = 0.0373) with ranolazine at plasma concentrations of 2, 4, and 8 microM, respectively. Ranolazine significantly reduced the incidence of ventricular fibrillation [67% in controls vs. 42% (P = 0.414), 30% (P = 0.198) and 8% (P = 0.0094) in ranolazine at 2, 4, and 8 microM, respectively]. Median number (2.5 vs. 0; P = 0.0431) of sustained VT episodes, incidence of sustained VT (83 vs. 33%, P = 0.0361), and the duration of VT per animal (159 vs. 19 s; P = 0.0410) were also significantly reduced by ranolazine at 8 microM. Ranolazine markedly reduced ischemia-reperfusion induced ventricular arrhythmias. Ranolazine demonstrated promising anti-arrhythmic properties that warrant further investigation.

Partial A1 adenosine receptor agonist regulates cardiac substrate utilization in insulin-resistant rats in vivo.

Reducing the availability and uptake of fatty acids is a plausible pharmaceutical target to ameliorate glucose intolerance and insulin resistance. CVT-3619 [2-{6-[((1R,2R)-2-hydroxycyclopentyl) amino]purin-9-yl(4S,5S,2R,3R)-5-[(2-fluorophenylthio)methyl]oxolane-3,4-diol] is a partial A(1) adenosine receptor agonist with antilipolytic properties. Aims of the present study were to examine the acute effects of CVT-3619 on whole-body and cardiac glucose and fatty acid kinetics in vivo in normal and diet-induced insulin-resistant rats. Male Sprague-Dawley rats were fed either a chow (CH) or high-fat (HF) diet for 4 weeks. Catheters were then chronically implanted in the carotid artery and jugular vein for sampling and infusions, respectively. After 5 days of recovery, fasted animals (10 h) received either saline or CVT-3619 (0.4 mg/kg bolus + 1 mg/kg/h). Indices of glucose and fatty acid utilization were obtained by the administration of 2-deoxy[(14)C]glucose and [9,10-(3)H]-(R)-2-bromopalmitate. HF feeding resulted in elevated, fasting insulin and free fatty acid (FFA) levels compared with CH. CVT-3619 caused a 64 and 86% reduction of FFA and insulin in HF (p < 0.05) but less (N.S.) in CH diet-fed animals. In HF diet-fed rats, CVT-3619 increased whole-body glucose clearance with no change in fatty acid kinetics. Likewise, analysis of cardiac tissue metabolism showed that CVT-3619 caused an increased glucose but not fatty acid clearance in HF-fed animals. Results show that the acute administration of CVT-3619 lowers circulating fatty acid levels, leading to improved whole-body and cardiac glucose clearance in a model of diet-induced insulin resistance. As such, CVT-3619 may be a treatment option for the restoration of substrate balance in the insulin-resistant heart.

Ranolazine as an adjunct to cardioplegia: a potential new therapeutic application.

The purpose of this study was to examine the therapeutic potential of ranolazine, a novel antianginal drug, as an adjunctive therapy to hyperkalemic cardioplegia. Rat hearts were Langendorff-perfused and exposed to 40 minutes of ischemia and 30 minutes of reperfusion without (control) or with cardioplegia or cardioplegia with 50 micromol/L ranolazine. During ischemia, cardioplegia prolonged time to contracture, defined as the time to reach an intraventricular pressure of 20 mm Hg, from 12 +/- 1 minute (control) to 25 +/- 2 minutes (P < .05). Ranolazine supplement further lengthened the time to contracture to 34 +/- 2 minutes (P < .05). Ischemia/reperfusion caused a dramatic elevation in left ventricular end diastolic pressure (LVEDP) during reperfusion. Cardioplegia lessened the LVEDP elevation measured at 30 minutes of reperfusion from 76 +/- 3 mm Hg (control) to 32 +/- 3 mm Hg (P < .05). The increase in LVEDP was reduced even further to 17 +/- 2 mm Hg in hearts receiving cardioplegia plus ranolazine (P < .05). These results suggest that addition of ranolazine during hyperkalemic ischemic cardioplegic arrest is beneficial and provides further protection against contracture.

A1 adenosine receptor: role in diabetes and obesity.

Adenosine mediates its diverse effects via four subtypes (A(1), A(2A), A(2B) and A(3)) of G-protein-coupled receptors. The A(1) adenosine receptor (A(1)AR) subtype is the most extensively studied and is well characterized in various organ systems. The A(1)ARs are highly expressed in adipose tissue, and endogenous adenosine has been shown to tonically activate adipose tissue A(1)ARs. Activation of the A(1)ARs in adipocytes reduces adenylate cyclase and cAMP content and causes inhibition of lipolysis. The role of A(1)ARs in lipolysis has been well characterized by using several selective A(1)AR agonists as well as A(1)AR knockout mice. However, the contribution of A(1)ARs to the regulation of lipolysis in pathological conditions like insulin resistance, diabetes and dyslipidemia, where free fatty acids (FFA) play an important role, has not been well characterized. Pharmacological agents that reduce the release of FFA from adipose tissue and thus the availability of circulating FFA have the potential to be useful for insulin resistance and hyperlipidemia. Toward this goal, several selective and efficacious agonists of the A(1)ARs are now available, and some have entered early-phase clinical trials; however, none have received regulatory approval yet. Here we review the existing knowledge on the role of A(1)ARs in insulin resistance, diabetes and obesity, and the progress made in the development of A(1)AR agonists as antilipolytic agents, including the challenges associated with this approach.

Jejunal wall delivery of insulin via an ingestible capsule in anesthetized swine-A pharmacokinetic and pharmacodynamic study.

Biotherapeutic agents must be administered parenterally to obtain therapeutic blood concentrations, lowering patient compliance and complicating care. An oral delivery platform (ODP) was developed to deliver drugs into the small intestinal wall. This proof-of-concept study was performed in 17 anesthetized, laparotomized swine. In 8 swine weighing 17.4 ± 1.2 kg (mean ± SEM), 20 IU of recombinant human insulin (RHI) were auto-injected into the jejunal wall by placing the ODP inside the jejunum via an enterotomy. In 9 control swine weighing 17.0 ± 0.4 kg, 20 IU of RHI were injected subcutaneously. In both groups, under a 60-80 mg/dL euglycemic glucose clamp, blood glucose was measured with a handheld glucometer and serum insulin was measured using ELISA, at 10-minute intervals between -20 and +420 minutes after RHI delivery. The peak serum concentration of RHI was 517 ± 109 pmol/L in the ODP and 342 ± 50 pmol/L in the subcutaneous group (ns). The areas under the insulin concentration curves (83 ± 18 and 81 ± 10 nmol/L·min) were also similar in both groups. The mean time to peak serum concentration of insulin was 139 ± 42 minutes in the ODP and 227 ± 24 minutes in the subcutaneous group (ns). In conclusion, (a) The bioactivity of RHI was preserved after its delivery into the jejunal wall, (b) the intrajejunal route delivered insulin as rapidly and physiologically as the subcutaneous route, and (c) these pharmacokinetic and pharmacodynamic characteristics of RHI after intrajejunal delivery suggest that drugs currently administered parenterally, such as basal insulin, could be successfully delivered into the proximal intestinal wall via the ingestible capsule.

Antitorsadogenic effects of ({+/-})-N-(2,6-dimethyl-phenyl)-(4[2-hydroxy-3-(2-methoxyphenoxy)propyl]-1-piperazine (ranolazine) in anesthetized rabbits.

Ranolazine [Ranexa; (+/-)-N-(2,6-dimethyl-phenyl)-(4[2-hydroxy-3-(2-methoxyphenoxy)propyl]-1-piperazine] is novel anti-ischemic agent that has been shown to inhibit late I(Na) and I(Kr) and to have antiarrhythmic effects in various preclinical in vitro models. This study was undertaken to investigate the effects of ranolazine on drug-induced Torsade de Pointes (TdP) in vivo. TdP was induced by an I(Kr) blocker, clofilium, in anesthetized, alpha(1)-agonist-sensitized rabbits. Clofilium prolonged QT interval corrected for heart rate (QTc) (52 +/- 9%) and monophasic action potential duration (MAPD)(90) (56 +/- 9%) and caused TdP in eight of eight rabbits. Pretreatment with ranolazine (480 microg/kg/min) or lidocaine (200 microg/kg/min) reduced the clofilium-induced prolongation of QTc (15 +/- 3 and 19 +/- 3%, respectively, p < 0.001 versus vehicle) and MAPD(90) (21 +/- 4 and 20 +/- 2%, respectively, p < 0.001 versus vehicle) and prevented the occurrence of TdP (zero of eight and zero of eight, respectively). Administration of ranolazine after the first episode of TdP terminated TdP and prevented its recurrence (zero of four versus vehicle, four of four). To rule out an alpha(1)-adrenoceptor antagonistic activity of ranolazine, we compared the effects of ranolazine on blood pressure with those of the alpha(1)-antagonist, prazosin. Although prazosin (10 microg/kg/min) markedly shifted the phenylephrine (alpha(1)-agonist) dose-response curve to the right, it did not have any effect on clofilium-induced prolongation of QTc and MAPD(90) (43 +/- 7 and 53 +/- 9%, respectively) or the occurrence of TdP (seven of eight). In contrast, ranolazine completely suppressed TdP but did not cause any shift in the phenylephrine dose-response curve at the highest dose tested (480 microg/kg/min). We conclude that ranolazine antagonizes the ventricular repolarization changes caused by clofilium and suppresses clofilium-induced TdP in rabbits.

Discovery of Dihydrobenzoxazepinone (GS-6615) Late Sodium Current Inhibitor (Late INai), a Phase II Agent with Demonstrated Preclinical Anti-Ischemic and Antiarrhythmic Properties.

Late sodium current (late INa) is enhanced during ischemia by reactive oxygen species (ROS) modifying the Nav 1.5 channel, resulting in incomplete inactivation. Compound 4 (GS-6615, eleclazine) a novel, potent, and selective inhibitor of late INa, is currently in clinical development for treatment of long QT-3 syndrome (LQT-3), hypertrophic cardiomyopathy (HCM), and ventricular tachycardia-ventricular fibrillation (VT-VF). We will describe structure-activity relationship (SAR) leading to the discovery of 4 that is vastly improved from the first generation late INa inhibitor 1 (ranolazine). Compound 4 was 42 times more potent than 1 in reducing ischemic burden in vivo (S-T segment elevation, 15 min left anteriorior descending, LAD, occlusion in rabbits) with EC50 values of 190 and 8000 nM, respectively. Compound 4 represents a new class of potent late INa inhibitors that will be useful in delineating the role of inhibitors of this current in the treatment of patients.

Pharmacology and therapeutic applications of A1 adenosine receptor ligands.

Adenosine's diverse physiological functions are mediated by four subtypes of receptors (A(1), A(2A), A(2B) and A(3)). The A(1) adenosine receptor pharmacology and therapeutic application of ligands for this receptor are the subjects of this review. A(1) receptors are present on the surface of cells in organs throughout the body. Actions mediated by A(1) receptors include slowing of heart rate and AV nodal conduction, reduction of atrial contractility, attenuation of the stimulatory actions of catecholamines on beta-adrenergic receptors, reduction of lipolysis in adipose tissue, reduction of urine formation, and inhibition of neuronal activity. Although adenosine analogs with high efficacy, affinity, and selectivity for the A(1) receptor are available, the ubiquitous distribution and wide range of physiological actions mediated by A(1) receptors are obstacles to development of therapeutic agents that activate these receptors. However, it may be possible to exploit the high A(1) "receptor reserve" for some actions of adenosine by use of weak (partial) agonists to target these actions while avoiding others for which receptor reserve is low. The presence of high receptor reserves for the anti-arrhythmic and anti-lipolytic actions of adenosine suggests that partial A(1) agonists could be used as anti-arrhythmic and anti-lipolytic agents. In addition, allosteric enhancers of the binding of adenosine to A(1) receptors could be used therapeutically to potentiate desirable effects of endogenous adenosine. Antagonists of the A(1) receptor can increase urine formation, and because they do not decrease renal blood flow, are particularly useful to maintain glomerular filtration in patients having edema secondary to reduced cardiac function.

Blockade of Na+ channels in pancreatic α-cells has antidiabetic effects.

Pancreatic α-cells express voltage-gated Na(+) channels (NaChs), which support the generation of electrical activity leading to an increase in intracellular calcium, and cause exocytosis of glucagon. Ranolazine, a NaCh blocker, is approved for treatment of angina. In addition to its antianginal effects, ranolazine has been shown to reduce HbA1c levels in patients with type 2 diabetes mellitus and coronary artery disease; however, the mechanism behind its antidiabetic effect has been unclear. We tested the hypothesis that ranolazine exerts its antidiabetic effects by inhibiting glucagon release via blockade of NaChs in the pancreatic α-cells. Our data show that ranolazine, via blockade of NaChs in pancreatic α-cells, inhibits their electrical activity and reduces glucagon release. We found that glucagon release in human pancreatic islets is mediated by the Nav1.3 isoform. In animal models of diabetes, ranolazine and a more selective NaCh blocker (GS-458967) lowered postprandial and basal glucagon levels, which were associated with a reduction in hyperglycemia, confirming that glucose-lowering effects of ranolazine are due to the blockade of NaChs. This mechanism of action is unique in that no other approved antidiabetic drugs act via this mechanism, and raises the prospect that selective Nav1.3 blockers may constitute a novel approach for the treatment of diabetes.

The beneficial effects of ranolazine on cardiac function after myocardial infarction are greater in diabetic than in nondiabetic rats.

Ranolazine (RAN) is known to exert both anti-ischemic and antidiabetic actions. Thus, this study has explored the hypothesis that RAN would have greater effect on the recovery of cardiac function in diabetic mellitus (DM) rat hearts following myocardial infarction (MI). Myocardial infarction was induced in nondiabetic (MI, n = 14) and diabetic (streptozotocin induced; DM-MI, n = 13) Wistar rats by permanent ligation of the left coronary artery. Cardiac function was evaluated using echocardiography (left ventricular ejection fraction %) and in isolated heart preparations by measuring left ventricular developed pressure (LVDP), and the positive and negative first derivative of LVDP (± dp/dt). Ranolazine (20 mg/kg, ip once a day) was administered 24 hours after surgical procedure for 4 weeks to nondiabetic (MI + RAN, n = 17) and diabetic rats (DM-MI + RAN, n = 15). The RAN improved the recovery of function in both the nondiabetic and the diabetic postinfarcted hearts but this effect was greater and achieved statistical significance only in the diabetic group. The RAN resulted in increased levels of phosphorylated protein kinase B (Akt) and mammalian target of rapamycin (mTOR, a component of Akt signaling) in both nondiabetic and diabetic infarcted hearts without changes in the activation of mitogen-activated protein kinases (MAPKs; p38 MAPK, c-Jun N-terminal kinase, and extracellular signal-regulated kinase). In addition, in diabetic hearts, RAN resulted in a significant increase in the ratio of sarcoplasmic Ca(2+)-ATPase/phospholamban (a target of Akt signaling, 2.0-fold increase) and increased levels of phosphorylated calcium-regulated adenosine monophosphate-activated protein kinase (AMPK; 2.0-fold increase). In diabetic animals, RAN increased insulin and lowered glucose levels in serum. In conclusion, the beneficial effect of RAN on the recovery of cardiac function after MI was greater in DM rats. This response was associated with activation of Akt/mTOR and AMPK. These findings provide a plausible explanation for the results of the Type 2 Diabetes Evaluation of Ranolazine in Subjects With Chronic Stable Angina (TERISA) trial, which showed a greater antianginal effect of RAN in patients with coronary artery disease and diabetes.