Omecamtiv mecarbil is a selective, small-molecule activator of cardiac myosin that is being developed as a potential treatment for heart failure with reduced ejection fraction. Here we determine the ...crystal structure of cardiac myosin in the pre-powerstroke state, the most relevant state suggested by kinetic studies, both with (2.45 Å) and without (3.10 Å) omecamtiv mecarbil bound. Omecamtiv mecarbil does not change the motor mechanism nor does it influence myosin structure. Instead, omecamtiv mecarbil binds to an allosteric site that stabilizes the lever arm in a primed position resulting in accumulation of cardiac myosin in the primed state prior to onset of cardiac contraction, thus increasing the number of heads that can bind to the actin filament and undergo a powerstroke once the cardiac cycle starts. The mechanism of action of omecamtiv mecarbil also provides insights into uncovering how force is generated by molecular motors.Omecamtiv mecarbil (OM) is a cardiac myosin activator that is currently in clinical trials for heart failure treatment. Here, the authors give insights into its mode of action and present the crystal structure of OM bound to bovine cardiac myosin, which shows that OM stabilizes the pre-powerstroke state of myosin.
Hypercontractility of the cardiac sarcomere may be essential for the underlying pathological hypertrophy and fibrosis in genetic hypertrophic cardiomyopathies. Aficamten (CK-274) is a novel cardiac ...myosin inhibitor that was discovered from the optimization of indoline compound
. The important advancement of the optimization was discovery of an Indane analogue (
) with a less restrictive structure-activity relationship that allowed for the rapid improvement of drug-like properties. Aficamten was designed to provide a predicted human half-life (
) appropriate for once a day (qd) dosing, to reach steady state within two weeks, to have no substantial cytochrome P450 induction or inhibition, and to have a wide therapeutic window
with a clear pharmacokinetic/pharmacodynamic relationship. In a phase I clinical trial, aficamten demonstrated a human
similar to predictions and was able to reach steady state concentration within the desired two-week window.
In GALACTIC-HF (Global Approach to Lowering Adverse Cardiac outcomes Through Improving Contractility in Heart Failure) (n = 8,256), the cardiac myosin activator, omecamtiv mecarbil, significantly ...reduced the primary composite endpoint (PCE) of time-to-first heart failure event or cardiovascular death in patients with heart failure and reduced ejection fraction (EF) (≤35%).
The purpose of this study was to evaluate the influence of baseline EF on the therapeutic effect of omecamtiv mecarbil.
Outcomes in patients treated with omecamtiv mecarbil were compared with placebo according to EF.
The risk of the PCE in the placebo group was nearly 1.8-fold greater in the lowest EF (≤22%) compared with the highest EF (≥33%) quartile. Amongst the pre-specified subgroups, EF was the strongest modifier of the treatment effect of omecamtiv mecarbil on the PCE (interaction as continuous variable, p = 0.004). Patients receiving omecamtiv mecarbil had a progressively greater relative and absolute treatment effect as baseline EF decreased, with a 17% relative risk reduction for the PCE in patients with baseline EF ≤22% (n = 2,246; hazard ratio: 0.83; 95% confidence interval: 0.73 to 0.95) compared with patients with EF ≥33% (n = 1,750; hazard ratio: 0.99; 95% confidence interval: 0.84 to 1.16; interaction as EF by quartiles, p = 0.013). The absolute reduction in the PCE increased with decreasing EF (EF ≤22%; absolute risk reduction, 7.4 events per 100 patient-years; number needed to treat for 3 years = 11.8), compared with no reduction in the highest EF quartile.
In heart failure patients with reduced EF, omecamtiv mecarbil produced greater therapeutic benefit as baseline EF decreased. These findings are consistent with the drug’s mechanism of selectively improving systolic function and presents an important opportunity to improve the outcomes in a group of patients at greatest risk. (Registrational Study With Omecamtiv Mecarbil/AMG 423 to Treat Chronic Heart Failure With Reduced Ejection Fraction GALACTIC-HF; NCT02929329)
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A central factor in the pathogenesis of heart failure (HF) with reduced ejection fraction is the initial decrease in systolic function. Prior attempts at increasing cardiac contractility with oral ...drugs have uniformly resulted in signals of increased mortality at pharmacologically effective doses. Omecamtiv mecarbil is a novel, selective cardiac myosin activator that has been shown to improve cardiac function and to decrease ventricular volumes, heart rate, and N-terminal pro-B-type natriuretic peptide in patients with chronic HF. The GALACTIC-HF (Global Approach to Lowering Adverse Cardiac outcomes Through Improving Contractility in Heart Failure) trial tests the hypotheses that omecamtiv mecarbil can safely improve symptoms, prevent clinical HF events, and delay CV death in patients with chronic HF. The GALACTIC-HF trial is an international, multicenter, randomized, double-blind, placebo-controlled, event-driven cardiovascular outcomes trial. More than 8,000 patients with chronic symptomatic (New York Heart Association functional class II to IV) HF, left ventricular ejection fraction ≤35%, elevated natriuretic peptides, and either current hospitalization for HF or history of hospitalization or emergency department visit for HF within a year of screening will be randomized to either oral placebo or omecamtiv mecarbil employing a pharmacokinetic-guided dose titration strategy using doses of 25, 37.5, or 50 mg twice daily. The primary efficacy outcome is the time to cardiovascular death or first HF event. The study has 90% power to assess a final hazard ratio of approximately 0.80 in cardiovascular death, the first secondary outcome. The GALACTIC-HF trial is the first trial examining whether selectively increasing cardiac contractility in patients with HF with reduced ejection fraction will result in improved clinical outcomes. (Registrational Study With Omecamtiv Mecarbil/AMG 423 to Treat Chronic Heart Failure With Reduced Ejection Fraction GALACTIC-HF; NCT02929329).
Decreased cardiac contractility is a central feature of systolic heart failure. Existing drugs increase cardiac contractility indirectly through signaling cascades but are limited by their ...mechanism-related adverse effects. To avoid these limitations, we previously developed omecamtiv mecarbil, a small-molecule, direct activator of cardiac myosin. Here, we show that it binds to the myosin catalytic domain and operates by an allosteric mechanism to increase the transition rate of myosin into the strongly actin-bound force-generating state. Paradoxically, it inhibits adenosine 5′-triphosphate turnover in the absence of actin, which suggests that it stabilizes an actin-bound conformation of myosin. In animal models, omecamtiv mecarbil increases cardiac function by increasing the duration of ejection without changing the rates of contraction. Cardiac myosin activation may provide a new therapeutic approach for systolic heart failure.
Left ventricular outflow tract (LVOT) obstruction is a major determinant of heart failure symptoms in obstructive hypertrophic cardiomyopathy (oHCM). Aficamten, a next-in-class cardiac myosin ...inhibitor, may lower gradients and improve symptoms in these patients.
This study aims to evaluate the safety and efficacy of aficamten in patients with oHCM.
Patients with oHCM and LVOT gradients ≥30 mm Hg at rest or ≥50 mm Hg with Valsalva were randomized 2:1 to receive aficamten (n = 28) or placebo (n = 13) in 2 dose-finding cohorts. Doses were titrated based on gradients and ejection fraction (EF). Safety and changes in gradient, EF, New York Heart Association functional class, and cardiac biomarkers were assessed over a 10-week treatment period and after a 2-week washout.
From baseline to 10 weeks, aficamten reduced gradients at rest (mean difference: −40 ± 27 mm Hg, and −43 ± 37 mm Hg in Cohorts 1 and 2, P = 0.0003 and P = 0.0004 vs placebo, respectively) and with Valsalva (−36 ± 27 mm Hg and −53 ± 44 mm Hg, P = 0.001 and <0.0001 vs placebo, respectively). There were modest reductions in EF (−6% ± 7.5% and −12% ± 5.9%, P = 0.007 and P < 0.0001 vs placebo, respectively). Symptomatic improvement in ≥1 New York Heart Association functional class was observed in 31% on placebo, and 43% and 64% on aficamten in Cohorts 1 and 2, respectively (nonsignificant). With aficamten, N-terminal pro–B-type natriuretic peptide was reduced (62% relative to placebo, P = 0.0002). There were no treatment interruptions and adverse events were similar between treatment arms.
Aficamten resulted in substantial reductions in LVOT gradients with most patients experiencing improvement in biomarkers and symptoms. These results highlight the potential of sarcomere-targeted therapy for treatment of oHCM.
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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.
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.
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.
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.
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.
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%).
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.
ClinicalTrials.gov Identifier: NCT03759392.
Summary Background Many patients with heart failure remain symptomatic and have a poor prognosis despite existing treatments. Decreases in myocardial contractility and shortening of ventricular ...systole are characteristic of systolic heart failure and might be improved by a new therapeutic class, cardiac myosin activators. We report the first study of the cardiac myosin activator, omecamtiv mecarbil, in patients with systolic heart failure. Methods We undertook a double-blind, placebo-controlled, crossover, dose-ranging, phase 2 trial investigating the effects of omecamtiv mecarbil (formerly CK-1827452), given intravenously for 2, 24, or 72 h to patients with stable heart failure and left ventricular systolic dysfunction receiving guideline-indicated treatment. Clinical assessment (including vital signs, echocardiograms, and electrocardiographs) and testing of plasma drug concentrations took place during and after completion of each infusion. The primary aim was to assess safety and tolerability of omecamtiv mecarbil. This study is registered at ClinicalTrials.gov , NCT00624442. Findings 45 patients received 151 infusions of active drug or placebo. Placebo-corrected, concentration-dependent increases in left ventricular ejection time (up to an 80 ms increase from baseline) and stroke volume (up to 9·7 mL) were recorded, associated with a small reduction in heart rate (up to 2·7 beats per min; p<0·0001 for all three measures). Higher plasma concentrations were also associated with reductions in end-systolic (decrease of 15 mL at >500 ng/mL, p=0·0026) and end-diastolic volumes (16 mL, p=0·0096) that might have been more pronounced with increased duration of infusion. Cardiac ischaemia emerged at high plasma concentrations (two patients, plasma concentrations roughly 1750 ng/mL and 1350 ng/mL). For patients tolerant of all study drug infusions, no consistent pattern of adverse events with either dose or duration emerged. Interpretation Omecamtiv mecarbil improved cardiac function in patients with heart failure caused by left ventricular dysfunction and could be the first in class of a new therapeutic agent. Funding Cytokinetics Inc.
Summary 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.
Summary Background Decreased systolic function is central to the pathogenesis of heart failure in millions of patients worldwide, but mechanism-related adverse effects restrict existing inotropic ...treatments. This study tested the hypothesis that omecamtiv mecarbil, a selective cardiac myosin activator, will augment cardiac function in human beings. Methods In this dose-escalating, crossover study, 34 healthy men received a 6-h double-blind intravenous infusion of omecamtiv mecarbil or placebo once a week for 4 weeks. Each sequence consisted of three ascending omecamtiv mecarbil doses (ranging from 0·005 to 1·0 mg/kg per h) with a placebo infusion randomised into the sequence. Vital signs, blood samples, electrocardiographs (ECGs), and echocardiograms were obtained before, during, and after each infusion. The primary aim was to establish maximum tolerated dose (the highest infusion rate tolerated by at least eight participants) and plasma concentrations of omecamtiv mecarbil; secondary aims were evaluation of pharmacodynamic and pharmacokinetic characteristics, safety, and tolerability. This study is registered at ClinicalTrials.gov , number NCT01380223. Findings The maximum tolerated dose of omecamtiv mecarbil was 0·5 mg/kg per h. Omecamtiv mecarbil infusion resulted in dose-related and concentration-related increases in systolic ejection time (mean increase from baseline at maximum tolerated dose, 85 SD 5 ms), the most sensitive indicator of drug effect ( r2 =0·99 by dose), associated with increases in stroke volume (15 2 mL), fractional shortening (8% 1), and ejection fraction (7% 1; all p<0·0001). Omecamtiv mecarbil increased atrial contractile function, and there were no clinically relevant changes in diastolic function. There were no clinically significant dose-related adverse effects on vital signs, serum chemistries, ECGs, or adverse events up to a dose of 0·625 mg/kg per h. The dose-limiting toxic effect was myocardial ischaemia due to excessive prolongation of systolic ejection time. Interpretation These first-in-man data show highly dose-dependent augmentation of left ventricular systolic function in response to omecamtiv mecarbil and support potential clinical use of the drug in patients with heart failure. Funding Cytokinetics Inc.
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