Aficamten for Symptomatic Obstructive Hypertrophic Cardiomyopathy.

BACKGROUND: One of the major determinants of exercise intolerance and limiting symptoms among patients with obstructive hypertrophic cardiomyopathy (HCM) is an elevated intracardiac pressure resulting from left ventricular outflow tract obstruction. Aficamten is an oral selective cardiac myosin inhibitor that reduces left ventricular outflow tract gradients by mitigating cardiac hypercontractility. METHODS: In this phase 3, double-blind trial, we randomly assigned adults with symptomatic obstructive HCM to receive aficamten (starting dose, 5 mg; maximum dose, 20 mg) or placebo for 24 weeks, with dose adjustment based on echocardiography results. The primary end point was the change from baseline to week 24 in the peak oxygen uptake as assessed by cardiopulmonary exercise testing. The 10 prespecified secondary end points (tested hierarchically) were change in the Kansas City Cardiomyopathy Questionnaire clinical summary score (KCCQ-CSS), improvement in the New York Heart Association (NYHA) functional class, change in the pressure gradient after the Valsalva maneuver, occurrence of a gradient of less than 30 mm Hg after the Valsalva maneuver, and duration of eligibility for septal reduction therapy (all assessed at week 24); change in the KCCQ-CSS, improvement in the NYHA functional class, change in the pressure gradient after the Valsalva maneuver, and occurrence of a gradient of less than 30 mm Hg after the Valsalva maneuver (all assessed at week 12); and change in the total workload as assessed by cardiopulmonary exercise testing at week 24. RESULTS: A total of 282 patients underwent randomization: 142 to the aficamten group and 140 to the placebo group. The mean age was 59.1 years, 59.2% were men, the baseline mean resting left ventricular outflow tract gradient was 55.1 mm Hg, and the baseline mean left ventricular ejection fraction was 74.8%. At 24 weeks, the mean change in the peak oxygen uptake was 1.8 ml per kilogram per minute (95% confidence interval [CI], 1.2 to 2.3) in the aficamten group and 0.0 ml per kilogram per minute (95% CI, -0.5 to 0.5) in the placebo group (least-squares mean between-group difference, 1.7 ml per kilogram per minute; 95% CI, 1.0 to 2.4; P<0.001). The results for all 10 secondary end points were significantly improved with aficamten as compared with placebo. The incidence of adverse events appeared to be similar in the two groups. CONCLUSIONS: Among patients with symptomatic obstructive HCM, treatment with aficamten resulted in a significantly greater improvement in peak oxygen uptake than placebo. (Funded by Cytokinetics; SEQUOIA-HCM ClinicalTrials.gov number, NCT05186818.).

Cardiac biomarkers and effects of aficamten in obstructive hypertrophic cardiomyopathy: the SEQUOIA-HCM trial.

BACKGROUND AND AIMS: The role of biomarker testing in the management of obstructive hypertrophic cardiomyopathy (oHCM) is not well defined. This pre-specified analysis of SEQUOIA-HCM (NCT05186818) sought to define the associations between clinical characteristics and baseline concentrations of N-terminal pro-B-type natriuretic peptide (NT-proBNP) and high-sensitivity cardiac troponin I (hs-cTnI), and to evaluate effect of treatment with aficamten on biomarker concentrations. METHODS: Cardiac biomarkers were measured at baseline and serially throughout the study. Regression analyses determined predictors of baseline NT-proBNP and hs-cTnI concentrations, and to evaluate whether early changes in these biomarkers relate to later changes in left ventricular outflow tract gradient (LVOT-G), other echocardiographic measures, health status, and functional capacity. RESULTS: Baseline concentration of NT-proBNP was associated with LVOT-G and measures of diastolic function, while hs-cTnI was associated with left ventricular thickness. Within 8 weeks of treatment with aficamten, NT-proBNP was reduced by 79% (95% CI 83%-76%, P < .001) and hs-cTnI by 41% (95% CI 49%-32%, P < .001); both biomarkers reverted to baseline after washout. Reductions in NT-proBNP and hs-cTnI by 24 weeks were strongly associated with a lowering of LVOT-G, improvement in health status, and increased peak oxygen uptake. NT-proBNP reduction strongly correlated with the majority of improvements in exercise capacity. Furthermore, the change in NT-proBNP by Week 2 was associated with the 24-week change in key endpoints. CONCLUSIONS: NT-proBNP and hs-cTnI concentrations are associated with key variables in oHCM. Serial measurement of NT-proBNP and hs-cTnI appears to reflect clinical response to aficamten therapy.

Cardiac Myosin Activation with Omecamtiv Mecarbil in Systolic Heart Failure.

BACKGROUND: The selective cardiac myosin activator omecamtiv mecarbil has been shown to improve cardiac function in patients with heart failure with a reduced ejection fraction. Its effect on cardiovascular outcomes is unknown. METHODS: We randomly assigned 8256 patients (inpatients and outpatients) with symptomatic chronic heart failure and an ejection fraction of 35% or less to receive omecamtiv mecarbil (using pharmacokinetic-guided doses of 25 mg, 37.5 mg, or 50 mg twice daily) or placebo, in addition to standard heart-failure therapy. The primary outcome was a composite of a first heart-failure event (hospitalization or urgent visit for heart failure) or death from cardiovascular causes. RESULTS: During a median of 21.8 months, a primary-outcome event occurred in 1523 of 4120 patients (37.0%) in the omecamtiv mecarbil group and in 1607 of 4112 patients (39.1%) in the placebo group (hazard ratio, 0.92; 95% confidence interval [CI], 0.86 to 0.99; P = 0.03). A total of 808 patients (19.6%) and 798 patients (19.4%), respectively, died from cardiovascular causes (hazard ratio, 1.01; 95% CI, 0.92 to 1.11). There was no significant difference between groups in the change from baseline on the Kansas City Cardiomyopathy Questionnaire total symptom score. At week 24, the change from baseline for the median N-terminal pro-B-type natriuretic peptide level was 10% lower in the omecamtiv mecarbil group than in the placebo group; the median cardiac troponin I level was 4 ng per liter higher. The frequency of cardiac ischemic and ventricular arrhythmia events was similar in the two groups. CONCLUSIONS: Among patients with heart failure and a reduced ejection, those who received omecamtiv mecarbil had a lower incidence of a composite of a heart-failure event or death from cardiovascular causes than those who received placebo. (Funded by Amgen and others; GALACTIC-HF ClinicalTrials.gov number, NCT02929329; EudraCT number, 2016-002299-28.).

Cardiac Troponin and Treatment Effects of Omecamtiv Mecarbil: Results From the GALACTIC-HF Study.

BACKGROUND: Omecamtiv mecarbil improves outcomes in patients with heart failure and reduced ejection fraction (HFrEF). We examined the relationship between baseline troponin levels, change in troponin levels over time and the treatment effect of omecamtiv mecarbil in patients enrolled in the Global Approach to Lowering Adverse Cardiac Outcomes through Improving Contractility in Heart Failure (GALACTIC-HF) trial (NCT02929329). METHODS: GALACTIC-HF was a double-blind, placebo-controlled trial that randomized 8256 patients with symptomatic HFrEF to omecamtiv mecarbil or placebo. High-sensitivity troponin I (cTnI) was measured serially at a core laboratory. We analyzed the relationship between both baseline cTnI and change in cTnI concentrations with clinical outcomes and the treatment effect of omecamtiv mecarbil. RESULTS: Higher baseline cTnI concentrations were associated with a risk of adverse outcomes (hazard ratio for the primary endpoint of time to first HF event or CV death = 1.30; 95% CI 1.28, 1.33; P < 0.001 per doubling of baseline cTnI). Although the incidence of safety outcomes was higher in patients with higher baseline cTnI, there was no difference between treatment groups. Treatment with omecamtiv mecarbil led to a modest increase in cTnI that was related to plasma concentrations of omecamtiv mecarbil, and it peaked at 6 weeks. An increase in troponin from baseline to week 6 was associated with an increased risk of the primary endpoint (P < 0.001), which was similar, regardless of treatment assignment (P value for interaction = 0.2). CONCLUSIONS: In a cohort of patients with HFrEF, baseline cTnI concentrations were strongly associated with adverse clinical outcomes. Although cTnI concentrations were higher in patients treated with omecamtiv mecarbil, we did not find a differential effect of omecamtiv mecarbil on either safety or efficacy based on baseline cTnI status or change in cTnI.

The Effect of Omecamtiv Mecarbil in Hospitalized Patients as Compared With Outpatients With HFrEF: An Analysis of GALACTIC-HF.

BACKGROUND: In the Global Approach to Lowering Adverse Cardiac Outcomes Through Improving Contractility in Heart Failure (GALACTIC-HF) trial, omecamtiv mecarbil, compared with placebo, reduced the risk of worsening heart failure (HF) events, or cardiovascular death in patients with HF and reduced ejection fraction. The primary aim of this prespecified analysis was to evaluate the safety and efficacy of omecamtiv mecarbil by randomization setting, that is, whether participants were enrolled as outpatients or inpatients. METHODS AND RESULTS: Patients were randomized either during a HF hospitalization or as an outpatient, within one year of a worsening HF event (hospitalization or emergency department visit). The primary outcome was a composite of worsening HF event (HF hospitalization or an urgent emergency department or clinic visit) or cardiovascular death. Of the 8232 patients analyzed, 2084 (25%) were hospitalized at randomization. Hospitalized patients had higher N-terminal prohormone of B-type natriuretic peptide concentrations, lower systolic blood pressure, reported more symptoms, and were less frequently treated with a renin-angiotensin system blocker or a beta-blocker than outpatients. The rate (per 100 person-years) of the primary outcome was higher in hospitalized patients (placebo group = 38.3/100 person-years) than in outpatients (23.1/100 person-years); adjusted hazard ratio 1.21 (95% confidence interval 1.12-1.31). The effect of omecamtiv mecarbil versus placebo on the primary outcome was similar in hospitalized patients (hazard ratio 0.89, 95% confidence interval 0.78-1.01) and outpatients (hazard ratio 0.94, 95% confidence interval 0.86-1.02) (interaction P = .51). CONCLUSIONS: Hospitalized patients with HF with reduced ejection fraction had a higher rate of the primary outcome than outpatients. Omecamtiv mecarbil decreased the risk of the primary outcome both when initiated in hospitalized patients and in outpatients.

Efficacy and Safety of Aficamten in Symptomatic Nonobstructive Hypertrophic Cardiomyopathy: Results From the REDWOOD-HCM Trial, Cohort 4.

BACKGROUND: This open-label phase 2 trial evaluated the safety and efficacy of aficamten in patients with nonobstructive hypertrophic cardiomyopathy (nHCM). METHODS: Patients with symptomatic nHCM (left ventricular outflow tract obstruction gradient ≤ 30 mmHg, left ventricular ejection fraction [LVEF] ≥ 60%, N-terminal pro-B-type natriuretic peptide [NT-proBNP] > 300 pg/mL) received aficamten 5-15 mg once daily (doses adjusted according to echocardiographic LVEF) for 10 weeks. RESULTS: We enrolled 41 patients (mean ± SD age 56 ± 16 years; 59% female). At Week 10, 22 (55%) patients experienced an improvement of ≥ 1 New York Heart Association class; 11 (29%) became asymptomatic. Clinically relevant improvements in Kansas City Cardiomyopathy Questionnaire Clinical Summary Scores occurred in 22 (55%) patients. Symptom relief was paralleled by reductions in NT-proBNP levels (56%; P < 0.001) and high-sensitivity cardiac troponin I (22%; P < 0.005). Modest reductions in LVEF (mean ± SD) of -5.4% ± 10 to 64.6% ± 9.1 were observed. Three (8%) patients had asymptomatic reduction in LVEF < 50% (range: 41%-48%), all returning to normal after 2 weeks of washout. One patient with prior history of aborted sudden cardiac death experienced a fatal arrhythmia during the study. CONCLUSIONS: Aficamten administration for symptomatic nHCM was generally safe and was associated with improvements in heart failure symptoms and cardiac biomarkers. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT04219826.

Acute and chronic tirasemtiv treatment improves in vivo and in vitro muscle performance in actin-based nemaline myopathy mice.

Nemaline myopathy, a disease of the actin-based thin filament, is one of the most frequent congenital myopathies. To date, no specific therapy is available to treat muscle weakness in nemaline myopathy. We tested the ability of tirasemtiv, a fast skeletal troponin activator that targets the thin filament, to augment muscle force-both in vivo and in vitro-in a nemaline myopathy mouse model with a mutation (H40Y) in Acta1. In Acta1H40Y mice, treatment with tirasemtiv increased the force response of muscles to submaximal stimulation frequencies. This resulted in a reduced energetic cost of force generation, which increases the force production during a fatigue protocol. The inotropic effects of tirasemtiv were present in locomotor muscles and, albeit to a lesser extent, in respiratory muscles, and they persisted during chronic treatment, an important finding as respiratory failure is the main cause of death in patients with congenital myopathy. Finally, translational studies on permeabilized muscle fibers isolated from a biopsy of a patient with the ACTA1H40Y mutation revealed that at physiological Ca2+ concentrations, tirasemtiv increased force generation to values that were close to those generated in muscle fibers of healthy subjects. These findings indicate the therapeutic potential of fast skeletal muscle troponin activators to improve muscle function in nemaline myopathy due to the ACTA1H40Y mutation, and future studies should assess their merit for other forms of nemaline myopathy and for other congenital myopathies.

Effects of omecamtiv mecarbil in heart failure with reduced ejection fraction according to blood pressure: the GALACTIC-HF trial.

AIM: Patients with heart failure with reduced ejection fraction and low systolic blood pressure (SBP) have high mortality, hospitalizations, and poorly tolerate evidence-based medical treatment. Omecamtiv mecarbil may be particularly helpful in such patients. This study examined its efficacy and tolerability in patients with SBP ≤100 mmHg enrolled in the Global Approach to Lowering Adverse Cardiac outcomes Through Improving Contractility in Heart Failure (GALACTIC-HF). METHODS AND RESULTS: The GALACTIC-HF enrolled patients with baseline SBP ≥85 mmHg with a primary outcome of time to cardiovascular death or first heart failure event. In this analysis, patients were divided according to their baseline SBP (≤100 vs. >100 mmHg). Among the 8232 analysed patients, 1473 (17.9%) had baseline SBP ≤100 mmHg and 6759 (82.1%) had SBP >100 mmHg. The primary outcome occurred in 715 (48.5%) and 2415 (35.7%) patients with SBP ≤100 and >100 mmHg, respectively. Patients with lower SBP were at higher risk of adverse outcomes. Omecamtiv mecarbil, compared with placebo, appeared to be more effective in reducing the primary composite endpoint in patients with SBP ≤100 mmHg [hazard ratio (HR), 0.81; 95% confidence interval (CI), 0.70-0.94] compared with those with SBP >100 mmHg (HR, 0.95; 95% CI, 0.88-1.03; P-value for interaction = 0.051). In both groups, omecamtiv mecarbil did not change SBP values over time and did not increase the risk of adverse events, when compared with placebo. CONCLUSION: In GALACTIC-HF, risk reduction of heart failure outcomes with omecamtiv mecarbil compared with placebo was large and significant in patients with low SBP. Omecamtiv mecarbil did not affect SBP and was well tolerated independent of SBP values.

Influence of atrial fibrillation on efficacy and safety of omecamtiv mecarbil in heart failure: the GALACTIC-HF trial.

AIMS: In GALACTIC-HF, the cardiac myosin activator omecamtiv mecarbil compared with placebo reduced the risk of heart failure events or cardiovascular death in patients with heart failure with reduced ejection fraction. We explored the influence of atrial fibrillation or flutter (AFF) on the effectiveness of omecamtiv mecarbil. METHODS AND RESULTS: GALACTIC-HF enrolled patients with New York Heart Association (NYHA) Class II-IV heart failure, left ventricular ejection fraction ≤35%, and elevated natriuretic peptides. We assessed whether the presence or absence of AFF, a pre-specified subgroup, modified the treatment effect for the primary and secondary outcomes, and additionally explored effect modification in patients who were or were not receiving digoxin. Patients with AFF (n = 2245, 27%) were older, more likely to be randomized as an inpatient, less likely to have a history of ischaemic aetiology or myocardial infarction, had a worse NYHA class, worse quality of life, lower estimated glomerular filtration rate, and higher N-terminal pro-B-type natriuretic peptide. The treatment effect of omecamtiv mecarbil was modified by baseline AFF (interaction P = 0.012), with patients without AFF at baseline deriving greater benefit. The worsening of the treatment effect by baseline AFF was significantly more pronounced in digoxin users than in non-users (interaction P = 0.007); there was minimal evidence of effect modification in those patients not using digoxin (P = 0.47) or in digoxin users not in AFF. CONCLUSION: Patients in AFF at baseline were less likely to benefit from omecamtiv mecarbil than patients without AFF, although the attenuation of the treatment effect was disproportionally concentrated in patients with AFF who were also receiving digoxin.Clinical Trial Registration: NCT02929329.

Pharmacokinetics of a single dose of Aficamten (CK-274) on cardiac contractility in a A31P MYBPC3 hypertrophic cardiomyopathy cat model.

Hypertrophic cardiomyopathy (HCM) is the most prevalent cardiac disease in cats and lacks efficacious preclinical pharmacologic intervention, prompting investigation of novel therapies. Genetic mutations encoding sarcomeric proteins are implicated in the development of HCM and small molecule myosin inhibitors are an emerging class of therapeutics designed to target the interaction of actin and myosin to alleviate the detrimental effects of inappropriate contractile protein interactions. The purpose of this study was to characterize the pharmacodynamic effects of a single oral dose of the novel cardiac myosin inhibitor aficamten (CK-274) on cardiac function in purpose bred cats with naturally occurring A31P MYBPC3 mutation and a clinical diagnosis of HCM with left ventricular outflow tract obstruction (LVOTO). Five purpose bred cats were treated with aficamten (2 mg/kg) or vehicle and echocardiographic evaluations were performed at 0, 6, 24, and 48 h post-dosing. High dose aficamten (2 mg/kg) reduced left ventricular fractional shortening (LVFS%) by increasing the LV systolic internal dimension (LVIDs) and reduced isovolumic relaxation time (IVRT) compared with baseline without significant adverse effects. The marked reduction in systolic function and reduced IVRT coupled with an increased heart rate in treated cats, suggest a lower dose may be optimal. Further studies to determine optimal dosing of aficamten are indicated.

Effect of Omecamtiv Mecarbil on Exercise Capacity in Chronic Heart Failure With Reduced Ejection Fraction: The METEORIC-HF Randomized Clinical Trial.

Importance: Exercise limitation is a cardinal manifestation of heart failure with reduced ejection fraction (HFrEF) but is not consistently improved by any of the current guideline-directed medical therapies. Objective: To determine whether omecamtiv mecarbil, a novel direct myosin activator that improves cardiac performance and reduces the risk for cardiovascular death or first HF event in HFrEF, can improve peak exercise capacity in patients with chronic HFrEF. Design, Setting, and Participants: Phase 3, double-blind, placebo-controlled randomized trial of patients with HFrEF (left ventricular ejection fraction ≤35%), New York Heart Association class II-III symptoms, N-terminal pro-B-type natriuretic peptide level of 200 pg/mL or greater, and baseline peak oxygen uptake (V̇o2) of 75% or less of predicted. Patients were randomized in a 2:1 ratio (omecamtiv mecarbil to placebo) between March 2019 and May 2021 at 63 sites in North America and Europe, with the last patient visit occurring on November 29, 2021. Interventions: Omecamtiv mecarbil (n = 185) or matching placebo (n = 91), given orally twice daily at a dose of 25 mg, 37.5 mg, or 50 mg based on target plasma levels, for 20 weeks. Main Outcomes and Measures: The primary end point was a change in exercise capacity (peak V̇o2) from baseline to week 20. Secondary end points included total workload, ventilatory efficiency, and daily physical activity as determined by accelerometry. Results: Among 276 patients who were randomized (median age, 64 years; IQR, 55-70 years; 42 women [15%]), 249 (90%) completed the trial. The median left ventricular ejection fraction was 28% (IQR, 21-33) and the median baseline peak V̇o2 was 14.2 mL/kg/min (IQR, 11.6-17.4) in the omecamtiv mecarbil group and 15.0 mL/kg/min (IQR, 12.0-17.2) in the placebo group. Mean change in peak V̇o2 did not differ significantly between the omecamtiv mecarbil and placebo groups (mean, -0.24 mL/kg/min vs 0.21 mL/kg/min; least square mean difference, -0.45 mL/kg/min [95% CI, -1.02 to 0.13]; P = .13). Adverse events included dizziness (omecamtiv mecarbil: 4.9%, placebo: 5.5%), fatigue (omecamtiv mecarbil: 4.9%, placebo: 4.4%), heart failure events (omecamtiv mecarbil: 4.9%, placebo: 4.4%), death (omecamtiv mecarbil: 1.6%, placebo: 1.1%), stroke (omecamtiv mecarbil: 0.5%, placebo: 1.1%), and myocardial infarction (omecamtiv mecarbil: 0%, placebo: 1.1%). Conclusions and Relevance: In patients with chronic HFrEF, omecamtiv mecarbil did not significantly improve exercise capacity over 20 weeks compared with placebo. These findings do not support the use of omecamtiv mecarbil for treatment of HFrEF for improvement of exercise capacity. Trial Registration: ClinicalTrials.gov Identifier: NCT03759392.

Fast skeletal muscle troponin activator CK-2066260 increases fatigue resistance by reducing the energetic cost of muscle contraction.

KEY POINTS: Skeletal muscle fatigue limits performance in various physical activities, with exercise intolerance being a key symptom in a broad spectrum of diseases. We investigated whether a small molecule fast skeletal troponin activator (FSTA), CK-2066260, can mitigate muscle fatigue by reducing the cytosolic free [Ca2+ ] required to produce a given submaximal force and hence decreasing the energy requirement. Isolated intact single mouse muscle fibres and rat muscles in-situ treated with CK-2066260 showed improved muscle endurance., which was accompanied by decreased ATP demand and reduced glycogen usage. CK-2066260 treatment improved in-vivo exercise capacity in healthy rats and in a rat model of peripheral artery insufficiency. In conclusion, we show that the FSTA CK-2066260 effectively counteracts muscle fatigue in rodent skeletal muscle in vitro, in situ, and in vivo. This may translate to humans and provide a promising pharmacological treatment to patients suffering from severe muscle weakness and exercise intolerance. ABSTRACT: Skeletal muscle fatigue limits performance during physical exercise and exacerbated muscle fatigue is a prominent symptom among a broad spectrum of diseases. The present study investigated whether skeletal muscle fatigue is affected by the fast skeletal muscle troponin activator (FSTA) CK-2066260, which increases myofibrillar Ca2+ sensitivity and amplifies the submaximal force response. Because more force is produced for a given Ca2+ , we hypothesized that CK-2066260 could mitigate muscle fatigue by reducing the energetic cost of muscle activation. Isolated single mouse muscle fibres were fatigued by 100 repeated 350 ms contractions while measuring force and the cytosolic free [Ca2+ ] or [Mg2+ ] ([Mg2+ ]i ). When starting fatiguing stimulation at matching forces (i.e. lower stimulation frequency with CK-2066260): force was decreased by ∼50% with and by ∼75% without CK-2066260; [Mg2+ ]i was increased by ∼10% with and ∼32% without CK-2066260, reflecting a larger decrease in [ATP] in the latter. The glycogen content in in situ stimulated rat muscles fatigued by repeated contractions at matching forces was about two times higher with than without CK-2066260. Voluntary exercise capacity, assessed by rats performing rotarod exercise and treadmill running, was improved in the presence of CK-2066260. CK-2066260 treatment also increased skeletal muscle fatigue resistance and exercise performance in a rat model of peripheral artery insufficiency. In conclusion, we demonstrate that the FSTA CK-2066260 mitigates skeletal muscle fatigue by reducing the metabolic cost of force generation.

Highly selective inhibition of myosin motors provides the basis of potential therapeutic application.

Direct inhibition of smooth muscle myosin (SMM) is a potential means to treat hypercontractile smooth muscle diseases. The selective inhibitor CK-2018571 prevents strong binding to actin and promotes muscle relaxation in vitro and in vivo. The crystal structure of the SMM/drug complex reveals that CK-2018571 binds to a novel allosteric pocket that opens up during the "recovery stroke" transition necessary to reprime the motor. Trapped in an intermediate of this fast transition, SMM is inhibited with high selectivity compared with skeletal muscle myosin (IC50 = 9 nM and 11,300 nM, respectively), although all of the binding site residues are identical in these motors. This structure provides a starting point from which to design highly specific myosin modulators to treat several human diseases. It further illustrates the potential of targeting transition intermediates of molecular machines to develop exquisitely selective pharmacological agents.

Functional Characterization of the Intact Diaphragm in a Nebulin-Based Nemaline Myopathy (NM) Model-Effects of the Fast Skeletal Muscle Troponin Activator tirasemtiv.

Respiratory failure due to diaphragm dysfunction is considered a main cause of death in nemaline myopathy (NM) and we studied both isometric force and isotonic shortening of diaphragm muscle in a mouse model of nebulin-based NM (Neb cKO). A large contractile deficit was found in nebulin-deficient intact muscle that is frequency dependent, with the largest deficits at low-intermediate stimulation frequencies (e.g., a deficit of 72% at a stimulation frequency of 20 Hz). The effect of the fast skeletal muscle troponin activator (FSTA) tirasemtiv on force was examined. Tirasemtiv had a negligible effect at maximal stimulation frequencies, but greatly reduced the force deficit of the diaphragm at sub-maximal stimulation levels with an effect that was largest in Neb cKO diaphragm. As a result, the force deficit of Neb cKO diaphragm fell (from 72% to 29% at 20 Hz). Similar effects were found in in vivo experiments on the nerve-stimulated gastrocnemius muscle complex. Load-clamp experiments on diaphragm muscle showed that tirasemtiv increased the shortening velocity, and reduced the deficit in mechanical power by 33%. Thus, tirasemtiv significantly improves muscle function in a mouse model of nebulin-based nemaline myopathy.

CK-2127107 amplifies skeletal muscle response to nerve activation in humans.

INTRODUCTION: Three studies evaluated safety, tolerability, pharmacokinetics, and pharmacodynamics of CK-2127107 (CK-107), a next-generation fast skeletal muscle troponin activator (FSTA), in healthy participants. We tested the hypothesis that CK-107 would amplify the force-frequency response of muscle in humans. METHODS: To assess the force-frequency response, participants received single doses of CK-107 and placebo in a randomized, double-blind, 4-period, crossover study. The force-frequency response of foot dorsiflexion following stimulation of the deep fibular nerve to activate the tibialis anterior muscle was assessed. RESULTS: CK-107 significantly increased tibialis anterior muscle response with increasing dose and plasma concentration in a frequency-dependent manner; the largest increase in peak force was ∼60% at 10 Hz. DISCUSSION: CK-107 appears more potent and produced larger increases in force than tirasemtiv-a first-generation FSTA-in a similar pharmacodynamic study, thereby supporting its development for improvement of muscle function of patients. Muscle Nerve 57: 729-734, 2018.

The Ca2+ sensitizer CK-2066260 increases myofibrillar Ca2+ sensitivity and submaximal force selectively in fast skeletal muscle.

KEY POINTS: We report that the small molecule CK-2066260 selectively slows the off-rate of Ca2+ from fast skeletal muscle troponin, leading to increased myofibrillar Ca2+ sensitivity in fast skeletal muscle. Rodents dosed with CK-2066260 show increased hindlimb muscle force and power in response to submaximal rates of nerve stimulation in situ. CK-2066260 has no effect on free cytosolic [Ca2+ ] during contractions of isolated muscle fibres. We conclude that fast skeletal muscle troponin sensitizers constitute a potential therapy to address an unmet need of improving muscle function in conditions of weakness and premature muscle fatigue. ABSTRACT: Skeletal muscle dysfunction occurs in many diseases and can lead to muscle weakness and premature muscle fatigue. Here we show that the fast skeletal troponin activator, CK-2066260, counteracts muscle weakness by increasing troponin Ca2+ affinity, thereby increasing myofibrillar Ca2+ sensitivity. Exposure to CK-2066260 resulted in a concentration-dependent increase in the Ca2+ sensitivity of ATPase activity in isolated myofibrils and reconstituted hybrid sarcomeres containing fast skeletal muscle troponin C. Stopped-flow experiments revealed a ∼2.7-fold decrease in the Ca2+ off-rate of isolated troponin complexes in the presence of CK-2066260 (6 vs. 17 s-1 under control conditions). Isolated mouse flexor digitorum brevis fibres showed a rapidly developing, reversible and concentration-dependent force increase at submaximal stimulation frequencies. This force increase was not accompanied by any changes in the free cytosolic [Ca2+ ] or its kinetics. CK-2066260 induced a slowing of relaxation, which was markedly larger at 26°C than at 31°C and could be linked to the decreased Ca2+ off-rate of troponin C. Rats dosed with CK-2066260 showed increased hindlimb isometric and isokinetic force in response to submaximal rates of nerve stimulation in situ producing significantly higher absolute forces at low isokinetic velocities, whereas there was no difference in force at the highest velocities. Overall muscle power was increased and the findings are consistent with a lack of effect on crossbridge kinetics. In conclusion, CK-2066260 acts as a fast skeletal troponin activator that may be used to increase muscle force and power in conditions of muscle weakness.

Chronic Oral Study of Myosin Activation to Increase Contractility in Heart Failure (COSMIC-HF): a phase 2, pharmacokinetic, randomised, placebo-controlled trial.

BACKGROUND: Impaired contractility is a feature of heart failure with reduced ejection fraction. We assessed the pharmacokinetics and effects on cardiac function and structure of the cardiac myosin activator, omecamtiv mecarbil. METHODS: In this randomised, double-blind study, done at 87 sites in 13 countries, we recruited patients with stable, symptomatic chronic heart failure and left ventricular ejection fraction 40% or lower. Patients were randomly assigned equally, via an interactive web response system, to receive 25 mg oral omecamtiv mecarbil twice daily (fixed-dose group), 25 mg twice daily titrated to 50 mg twice daily guided by pharmacokinetics (pharmacokinetic-titration group), or placebo for 20 weeks. We assessed the maximum concentration of omecamtiv mecarbil in plasma (primary endpoint) and changes in cardiac function and ventricular diameters. This trial is registered with ClinicalTrials.gov, number NCT01786512. FINDINGS: From March 17, 2014, to March 5, 2015, we enrolled 150 patients in the fixed-dose omecamtiv mecarbil group and 149 in the pharmacokinetic-titration and placebo groups. Mean maximum concentration of omecamtiv mecarbil at 12 weeks was 200 (SD 71) ng/mL in the fixed-dose group and 318 (129) ng/mL in the pharmacokinetic-titration group. For the pharmacokinetic-titration group versus placebo group at 20 weeks, least square mean differences were as follows: systolic ejection time 25 ms (95% CI 18-32, p<0·0001), stroke volume 3·6 mL (0·5-6·7, p=0·0217), left ventricular end-systolic diameter -1·8 mm (-2·9 to -0·6, p=0·0027), left ventricular end-diastolic diameter -1·3 mm, (-2·3 to 0·3, p=0·0128), heart rate -3·0 beats per min (-5·1 to -0·8, p=0·0070), and N-terminal pro B-type natriuretic peptide concentration in plasma -970 pg/mL (-1672 to -268, p=0·0069). The frequency of adverse clinical events did not differ between groups. INTERPRETATION: Omecamtiv mecarbil dosing guided by pharmacokinetics achieved plasma concentrations associated with improved cardiac function and decreased ventricular diameter. FUNDING: Amgen.

Navigating the Future of Cardiovascular Drug Development-Leveraging Novel Approaches to Drive Innovation and Drug Discovery: Summary of Findings from the Novel Cardiovascular Therapeutics Conference.

PURPOSE: The need for novel approaches to cardiovascular drug development served as the impetus to convene an open meeting of experts from the pharmaceutical industry and academia to assess the challenges and develop solutions for drug discovery in cardiovascular disease. METHODS: The Novel Cardiovascular Therapeutics Summit first reviewed recent examples of ongoing or recently completed programs translating basic science observations to targeted drug development, highlighting successes (protein convertase sutilisin/kexin type 9 [PCSK9] and neprilysin inhibition) and targets still under evaluation (cholesteryl ester transfer protein [CETP] inhibition), with the hope of gleaning key lessons to successful drug development in the current era. Participants then reviewed the use of innovative approaches being explored to facilitate rapid and more cost-efficient evaluations of drug candidates in a short timeframe. RESULTS: We summarize observations gleaned from this summit and offer insight into future cardiovascular drug development. CONCLUSIONS: The rapid development in genetic and high-throughput drug evaluation technologies, coupled with new approaches to rapidly evaluate potential cardiovascular therapies with in vitro techniques, offer opportunities to identify new drug targets for cardiovascular disease, study new therapies with better efficiency and higher throughput in the preclinical setting, and more rapidly bring the most promising therapies to human testing. However, there must be a critical interface between industry and academia to guide the future of cardiovascular drug development. The shared interest among academic institutions and pharmaceutical companies in developing promising therapies to address unmet clinical needs for patients with cardiovascular disease underlies and guides innovation and discovery platforms that are significantly altering the landscape of cardiovascular drug development.

Reduced force of diaphragm muscle fibers in patients with chronic thromboembolic pulmonary hypertension.

Patients with pulmonary hypertension (PH) suffer from inspiratory muscle weakness. However, the pathophysiology of inspiratory muscle dysfunction in PH is unknown. We hypothesized that weakness of the diaphragm, the main inspiratory muscle, is an important contributor to inspiratory muscle dysfunction in PH patients. Our objective was to combine ex vivo diaphragm muscle fiber contractility measurements with measures of in vivo inspiratory muscle function in chronic thromboembolic pulmonary hypertension (CTEPH) patients. To assess diaphragm muscle contractility, function was studied in vivo by maximum inspiratory pressure (MIP) and ex vivo in diaphragm biopsies of the same CTEPH patients (N = 13) obtained during pulmonary endarterectomy. Patients undergoing elective lung surgery served as controls (N = 15). Muscle fiber cross-sectional area (CSA) was determined in cryosections and contractility in permeabilized muscle fibers. Diaphragm muscle fiber CSA was not significantly different between control and CTEPH patients in both slow-twitch and fast-twitch fibers. Maximal force-generating capacity was significantly lower in slow-twitch muscle fibers of CTEPH patients, whereas no difference was observed in fast-twitch muscle fibers. The maximal force of diaphragm muscle fibers correlated significantly with MIP. The calcium sensitivity of force generation was significantly reduced in fast-twitch muscle fibers of CTEPH patients, resulting in a ∼40% reduction of submaximal force generation. The fast skeletal troponin activator CK-2066260 (5 µM) restored submaximal force generation to levels exceeding those observed in control subjects. In conclusion, diaphragm muscle fiber contractility is hampered in CTEPH patients and contributes to the reduced function of the inspiratory muscles in CTEPH patients.