Discovery of Nelutroctiv (CK-136), a Selective Cardiac Troponin Activator for the Treatment of Cardiovascular Diseases Associated with Reduced Cardiac Contractility.

Cardiac myosin activation has been shown to be a viable approach for the treatment of heart failure with reduced ejection fraction. Here, we report the discovery of nelutroctiv (CK-136), a selective cardiac troponin activator intended for patients with cardiovascular conditions where cardiac contractility is reduced. Discovery of nelutroctiv began with a high-throughput screen that identified compound 1R, a muscle selective cardiac sarcomere activator devoid of phosphodiesterase-3 activity. Optimization of druglike properties for 1R led to the replacement of the sulfonamide and aniline substituents which resulted in improved pharmacokinetic (PK) profiles and a reduced potential for human drug-drug interactions. In vivo echocardiography assessment of the optimized leads showed concentration dependent increases in fractional shortening and an improved pharmacodynamic window compared to myosin activator CK-138. Overall, nelutroctiv was found to possess the desired selectivity, a favorable pharmacodynamic window relative to myosin activators, and a preclinical PK profile to support clinical development.

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.).

Pathogenic TNNI1 variants disrupt sarcomere contractility resulting in hypo- and hypercontractile muscle disease.

Troponin I (TnI) regulates thin filament activation and muscle contraction. Two isoforms, TnI-fast (TNNI2) and TnI-slow (TNNI1), are predominantly expressed in fast- and slow-twitch myofibers, respectively. TNNI2 variants are a rare cause of arthrogryposis, whereas TNNI1 variants have not been conclusively established to cause skeletal myopathy. We identified recessive loss-of-function TNNI1 variants as well as dominant gain-of-function TNNI1 variants as a cause of muscle disease, each with distinct physiological consequences and disease mechanisms. We identified three families with biallelic TNNI1 variants (F1: p.R14H/c.190-9G>A, F2 and F3: homozygous p.R14C), resulting in loss of function, manifesting with early-onset progressive muscle weakness and rod formation on histology. We also identified two families with a dominantly acting heterozygous TNNI1 variant (F4: p.R174Q and F5: p.K176del), resulting in gain of function, manifesting with muscle cramping, myalgias, and rod formation in F5. In zebrafish, TnI proteins with either of the missense variants (p.R14H; p.R174Q) incorporated into thin filaments. Molecular dynamics simulations suggested that the loss-of-function p.R14H variant decouples TnI from TnC, which was supported by functional studies showing a reduced force response of sarcomeres to submaximal [Ca2+] in patient myofibers. This contractile deficit could be reversed by a slow skeletal muscle troponin activator. In contrast, patient myofibers with the gain-of-function p.R174Q variant showed an increased force to submaximal [Ca2+], which was reversed by the small-molecule drug mavacamten. Our findings demonstrated that TNNI1 variants can cause muscle disease with variant-specific pathomechanisms, manifesting as either a hypo- or a hypercontractile phenotype, suggesting rational therapeutic strategies for each mechanism.

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.

Cardiac Troponin Activator CK-963 Increases Cardiac Contractility in Rats.

Novel cardiac troponin activators were identified using a high throughput cardiac myofibril ATPase assay and confirmed using a series of biochemical and biophysical assays. HTS hit 2 increased rat cardiomyocyte fractional shortening without increasing intracellular calcium concentrations, and the biological target of 1 and 2 was determined to be the cardiac thin filament. Subsequent optimization to increase solubility and remove PDE-3 inhibition led to the discovery of CK-963 and enabled pharmacological evaluation of cardiac troponin activation without the competing effects of PDE-3 inhibition. Rat echocardiography studies using CK-963 demonstrated concentration-dependent increases in cardiac fractional shortening up to 95%. Isothermal calorimetry studies confirmed a direct interaction between CK-963 and a cardiac troponin chimera with a dissociation constant of 11.5 ± 3.2 µM. These results provide evidence that direct activation of cardiac troponin without the confounding effects of PDE-3 inhibition may provide benefit for patients with cardiovascular conditions where contractility is reduced.

Tricuspid Regurgitation and Clinical Outcomes in Heart Failure With Reduced Ejection Fraction.

BACKGROUND: Tricuspid regurgitation (TR) is common and is associated with poor outcomes in patients with heart failure (HF). However, data with adjudicated events from fully characterized patients with heart failure with reduced ejection fraction (HFrEF) are lacking. OBJECTIVES: This study sought to explore the association between mild or moderate/severe TR and clinical outcomes of patients with HFrEF. METHODS: GALACTIC-HF (Global Approach to Lowering Adverse Cardiac Outcomes Through Improving Contractility in Heart Failure) was a double-blind, placebo-controlled randomized trial comparing omecamtiv mecarbil vs placebo in patients with symptomatic HFrEF. RESULTS: Among the 8,232 patients analyzed in the GALACTIC-HF trial, 8,180 (99%) had data regarding baseline TR (none: n = 6,476 [79%], mild: n = 919 [11%], and moderate/severe: n = 785 [10%]). The primary composite outcome of a first HF event or cardiovascular death occurred in 2,368 (36.6%) patients with no TR, 353 (38.4%) patients with mild TR, and 389 (49.6%) patients with moderate/severe TR. Moderate/severe TR was independently associated with a higher relative risk of the primary composite outcome compared with either no TR (adjusted HR: 1.12 [95% CI: 1.01-1.26]; P = 0.046) or no/mild TR (adjusted HR: 1.14 [95% CI: 1.02-1.27]; P = 0.025) driven predominantly by HF events. The association between moderate/severe TR and clinical outcomes was more pronounced in outpatients with worse renal function, higher left ventricular ejection fraction, and lower N-terminal pro-B-type natriuretic peptide and bilirubin levels. The beneficial treatment effect of omecamtiv mecarbil vs placebo on clinical outcomes was not modified by TR. CONCLUSIONS: In symptomatic patients with HFrEF, baseline moderate/severe TR was independently associated with cardiovascular death or HF events driven predominantly by HF events. The beneficial treatment effect of omecamtiv mecarbil on the primary outcome was not modified by TR.

Tirasemtiv enhances submaximal muscle tension in an Acta1:p.Asp286Gly mouse model of nemaline myopathy.

Nemaline myopathies are the most common form of congenital myopathies. Variants in ACTA1 (NEM3) comprise 15-25% of all nemaline myopathy cases. Patients harboring variants in ACTA1 present with a heterogeneous disease course characterized by stable or progressive muscle weakness and, in severe cases, respiratory failure and death. To date, no specific treatments are available. Since NEM3 is an actin-based thin filament disease, we tested the ability of tirasemtiv, a fast skeletal muscle troponin activator, to improve skeletal muscle function in a mouse model of NEM3, harboring the patient-based p.Asp286Gly variant in Acta1. Acute and long-term tirasemtiv treatment significantly increased muscle contractile capacity at submaximal stimulation frequencies in both fast-twitch extensor digitorum longus and gastrocnemius muscle, and intermediate-twitch diaphragm muscle in vitro and in vivo. Additionally, long-term tirasemtiv treatment in NEM3 mice resulted in a decreased respiratory rate with preserved minute volume, suggesting more efficient respiration. Altogether, our data support the therapeutic potential of fast skeletal muscle troponin activators in alleviating skeletal muscle weakness in a mouse model of NEM3 caused by the Acta1:p.Asp286Gly variant.

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.

Relationship between quantitative strength and functional outcomes in the phase 2 FORTITUDE-ALS trial.

OBJECTIVE: To assess the relationship among measurements of strength, function, and quality of life in an amyotrophic lateral sclerosis (ALS) clinical trial. METHODS: In the FORTITUDE-ALS clinical trial (NCT03160898), 456 participants in the full-analysis set were treated with either reldesemtiv or placebo for 12 weeks; this post hoc analysis included all participants regardless of treatment assignments. Assessments included slow vital capacity (SVC), the ALS Functional Rating Scale-Revised (ALSFRS-R), and the 5-item ALS Assessment Questionnaire (ALSAQ-5). Muscle strength was measured quantitatively with hand-held dynamometry, and grip strength with a dedicated dynamometer. The relationship between strength and ALSFRS-R fine and gross motor domain scores, or responses to ALSAQ-5 questions on hand function and walking, was assessed with Spearman's rank correlation. The relationship between mean upper- or lower-extremity muscle strength and specific ALSFRS-R domains was modeled using principal-components analysis. RESULTS: Upper-extremity muscle strength and hand grip were highly correlated with ALSFRS-R fine motor scores and the ALSAQ-5 hand function question. Similarly, lower-extremity strength correlated well with ALSFRS-R gross motor domain and the ALSAQ-5 walking question. For SVC, correlation was poor with the ALSFRS-R respiratory domain, but stronger with the total score, potentially reflecting the insensitivity of the respiratory questions in the scale. Upper- and lower-extremity strength were both strong predictors of ALSFRS-R domain scores. CONCLUSIONS: In this analysis of data from an ALS clinical trial, muscle strength quantified by dynamometry was strongly correlated with functional capacity. These results suggest that muscle strength directly relates to specific functions of importance to people with ALS.

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.

Exercise Capacity in Patients With Obstructive Hypertrophic Cardiomyopathy: SEQUOIA-HCM Baseline Characteristics and Study Design.

Patients with obstructive hypertrophic cardiomyopathy (oHCM) have increased risk of arrhythmia, stroke, heart failure, and sudden death. Contemporary management of oHCM has decreased annual hospitalization and mortality rates, yet patients have worsening health-related quality of life due to impaired exercise capacity and persistent residual symptoms. Here we consider the design of clinical trials evaluating potential oHCM therapies in the context of SEQUOIA-HCM (Safety, Efficacy, and Quantitative Understanding of Obstruction Impact of Aficamten in HCM). This large, phase 3 trial is now fully enrolled (N = 282). Baseline characteristics reflect an ethnically diverse population with characteristics typical of patients encountered clinically with substantial functional and symptom burden. The study will assess the effect of aficamten vs placebo, in addition to standard-of-care medications, on functional capacity and symptoms over 24 weeks. Future clinical trials could model the approach in SEQUOIA-HCM to evaluate the effect of potential therapies on the burden of oHCM. (Safety, Efficacy, and Quantitative Understanding of Obstruction Impact of Aficamten in HCM [SEQUOIA-HCM]; NCT05186818).

Sex Differences in Heart Failure With Reduced Ejection Fraction in the GALACTIC-HF Trial.

BACKGROUND: Women with heart failure with reduced ejection fraction (HFrEF) receive less guideline-recommended therapy and experience worse quality of life than men. OBJECTIVES: The authors sought to assess differences in baseline characteristics, outcomes, efficacy, and safety of omecamtiv mecarbil between men and women enrolled in the GALACTIC-HF (Registrational Study With Omecamtiv Mecarbil [AMG 423] to Treat Chronic Heart Failure With Reduced Ejection Fraction) study. METHODS: In GALACTIC-HF, patients with symptomatic heart failure with EF of 35% or less, recent heart failure event, and elevated natriuretic peptides were randomized to omecamtiv mecarbil or placebo. The current analysis investigated differences in baseline characteristics, clinical outcomes, and efficacy and safety of omecamtiv mecarbil between men and women. RESULTS: Of 8,232 patients analyzed, 21.2% were women. Women more likely self-identified as being Black, had worse symptoms (lower Kansas City Cardiomyopathy Questionnaire Total Symptom Score [KCCQ-TSS]), and were less likely to be treated with angiotensin receptor/neprilysin inhibitor and devices at baseline. Compared with men, women had lower rates of the primary endpoint (adjusted HR: 0.80, 95% CI: 0.73-0.88). Sex did not significantly modify omecamtiv mecarbil's treatment effect (P interaction = 0.68). Women also had 20% less risk of cardiovascular death, heart failure event, and all-cause death. Women participants had lower rates of serious adverse events. CONCLUSIONS: Women participants of the GALACTIC-HF trial had worse quality of life and were less likely to be treated with guideline-based therapies at baseline. Despite KCCQ-TSS being predictive of poor outcomes in this population, women had a 20% lower risk of an HF event or cardiovascular death compared with men. The beneficial effect of omecamtiv mecarbil did not significantly differ by sex. (Registrational Study With Omecamtiv Mecarbil [AMG 423] to Treat Chronic Heart Failure With Reduced Ejection Fraction [GALACTIC-HF]; NCT02929329).

COURAGE-ALS: a randomized, double-blind phase 3 study designed to improve participant experience and increase the probability of success.

Objective: To determine the target population and optimize the study design of the phase 3 clinical trial evaluating reldesemtiv in participants with amyotrophic lateral sclerosis (ALS).Methods: We evaluated the phase 2 study of reldesemtiv, FORTITUDE-ALS, to inform eligibility criteria and design features that would increase trial efficiency and reduce participant burden of the phase 3 trial.Results: In FORTITUDE-ALS, the effect of reldesemtiv was particularly evident among participants in the intermediate- and fast-progressing tertiles for pre-study disease progression. These participants most often had symptom onset ≤24 months and an ALS Functional Rating Scale-Revised (ALSFRS-R) total score ≤44 at baseline. Compared with the overall FORTITUDE-ALS population, the subgroup meeting these criteria declined by fewer ALSFRS-R points at 12 weeks (difference of least-squares mean [SE] versus placebo 1.84 [0.49] and 0.87 [0.35] for the overall population). These inclusion criteria will be used for the phase 3 clinical trial, COURAGE-ALS, in which the primary outcome is the change in ALSFRS-R total score at week 24. We also measure durable medical equipment use and evaluate strength in muscles expected to change rapidly. To reduce participant burden, study visits are often remote, and strength evaluation is simplified to reduce time and effort.Conclusions: In COURAGE-ALS, the phase 3 clinical trial to evaluate reldesemtiv, the sensitivity of detecting a potential treatment effect may be increased by defining eligibility criteria that limit the proportion of participants who have slower disease progression. Implementing remote visits and simplifying strength measurements will reduce both site and participant burden.ClinicalTrials.gov identifiers: NCT03160898 (FORTITUDE-ALS) and NCT04944784 (COURAGE-ALS).

Omecamtiv Mecarbil in Black Patients With Heart Failure and Reduced Ejection Fraction: Insights From GALACTIC-HF.

BACKGROUND: Omecamtiv mecarbil improves cardiovascular outcomes in patients with heart failure (HF) with reduced ejection fraction (EF). Consistency of drug benefit across race is a key public health topic. OBJECTIVES: The purpose of this study was to evaluate the effect of omecamtiv mecarbil among self-identified Black patients. METHODS: In GALACTIC-HF (Global Approach to Lowering Adverse Cardiac Outcomes Through Improving Contractility in Heart Failure) patients with symptomatic HF, elevated natriuretic peptides, and left ventricular ejection fraction (LVEF) ≤35% were randomized to omecamtiv mecarbil or placebo. The primary outcome was a composite of time to first event of HF or cardiovascular death. The authors analyzed treatment effects in Black vs White patients in countries contributing at least 10 Black participants. RESULTS: Black patients accounted for 6.8% (n = 562) of overall enrollment and 29% of U.S. enrollment. Most Black patients enrolled in the United States, South Africa, and Brazil (n = 535, 95%). Compared with White patients enrolled from these countries (n = 1,129), Black patients differed in demographics, comorbid conditions, received higher rates of medical therapy and lower rates of device therapies, and experienced higher overall event rates. The effect of omecamtiv mecarbil was consistent in Black vs White patients, with no difference in the primary endpoint (HR = 0.83 vs 0.88, P-interaction = 0.66), similar improvements in heart rate and N-terminal pro-B-type natriuretic peptide, and no significant safety signals. Among endpoints, the only nominally significant treatment-by-race interaction was the placebo-corrected change in blood pressure from baseline in Black vs White patients (+3.4 vs -0.7 mm Hg, P for interaction = 0.02). CONCLUSIONS: GALACTIC-HF enrolled more Black patients than other recent HF trials. Black patients treated with omecamtiv mecarbil had similar benefit and safety compared with White counterparts.

Phase 2 Study of Aficamten in Patients With Obstructive Hypertrophic Cardiomyopathy.

BACKGROUND: 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. OBJECTIVES: This study aims to evaluate the safety and efficacy of aficamten in patients with oHCM. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Efficacy of omecamtiv mecarbil in heart failure with reduced ejection fraction according to N-terminal pro-B-type natriuretic peptide level: insights from the GALACTIC-HF trial.

AIM: N-terminal pro-B-type natriuretic peptide (NT-proBNP) is predictive of both outcomes and response to treatment in patients with heart failure with reduced ejection fraction (HFrEF). The aim of this study was to examine the effect of the cardiac myosin activator omecamtiv mecarbil according to baseline NT-proBNP level in the Global Approach to Lowering Adverse Cardiac outcomes Through Improving Contractility in Heart Failure trial (GALACTIC-HF). METHODS AND RESULTS: The primary outcome was the composite of a worsening heart failure event (urgent clinic visit, emergency department visit, or hospitalization) or cardiovascular death. We prespecified analysis of the effect of treatment according to baseline NT-proBNP (≤ median, > median), excluding individuals with atrial fibrillation/flutter (AF/AFL). Of the 8232 patients analysed, 8206 had an available baseline NT-proBNP measurement. Among the 5971 patients not in AF/AFL, the median (Q1-Q3) NT-proBNP level was 1675 (812-3579) pg/ml. Hazard ratios (HR) for the effect of omecamtiv mecarbil, compared with placebo, for the primary endpoint in patients without AF/AFL were: ≤ median 0.94 (95% confidence interval [CI] 0.80-1.09), > median 0.81 (0.73-0.90) (p-interaction = 0.095); for the overall population (including patients with AF/AFL) the HRs were ≤ median 1.01 (0.90-1.15) and > median 0.88 (0.80-0.96) (p-interaction = 0.035). There was an interaction between treatment and NT-proBNP, examined as a continuous variable, with greater effect of omecamtiv mecarbil on the primary outcome in patients with a higher baseline NT-proBNP (p-interaction = 0.086). CONCLUSIONS: In GALACTIC-HF, the benefit of omecamtiv mecarbil appeared to be larger in patients with higher baseline NT-proBNP levels, especially in patients without AF/AFL. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov Identifier NCT02929329; EudraCT number, 2016-002299-28.

Effects of Aficamten on cardiac contractility in a feline translational model of hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy (HCM) is the most prevalent inherited cardiac disease in humans and cats and lacks efficacious pharmacologic interventions in the preclinical phase of disease. LV outflow tract obstruction (LVOTO) is commonly observed in HCM-affected patients and is a primary driver of heart failure symptoms and reduced quality of life. Novel small-molecule cardiac myosin inhibitors target actin-myosin interactions to alleviate overactive protein interactions. A prospective, randomized, controlled cross-over study was performed to evaluate pharmacodynamic effects of two doses (0.3 and 1 mg/kg) of a next-in-class cardiac myosin inhibitor, aficamten (CK-3773274, CK-274), on cardiac function in cats with the A31P MYBPC3 mutation and oHCM. Dose-dependent reductions in LV systolic function, LVOT pressure gradient, and isovolumetric relaxation times compared to baseline were observed. Promising beneficial effects of reduced systolic function warrant further studies of this next-in-class therapeutic to evaluate the benefit of long-term administration in this patient population.

Titin-truncating variants in hiPSC cardiomyocytes induce pathogenic proteinopathy and sarcomere defects with preserved core contractile machinery.

Titin-truncating variants (TTNtv) are the single largest genetic cause of dilated cardiomyopathy (DCM). In this study we modeled disease phenotypes of A-band TTNtv-induced DCM in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) using genome editing and tissue engineering technologies. Transcriptomic, cellular, and micro-tissue studies revealed that A-band TTNtv hiPSC-CMs exhibit pathogenic proteinopathy, sarcomere defects, aberrant Na+ channel activities, and contractile dysfunction. These phenotypes establish a dual mechanism of poison peptide effect and haploinsufficiency that collectively contribute to DCM pathogenesis. However, TTNtv cellular defects did not interfere with the function of the core contractile machinery, the actin-myosin-troponin-Ca2+ complex, and preserved the therapeutic mechanism of sarcomere modulators. Treatment of TTNtv cardiac micro-tissues with investigational sarcomere modulators augmented contractility and resulted in sustained transcriptomic changes that promote reversal of DCM disease signatures. Together, our findings elucidate the underlying pathogenic mechanisms of A-band TTNtv-induced DCM and demonstrate the validity of sarcomere modulators as potential therapeutics.

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.