A Phase 1 Dose-Escalation Study of the Cardiac Myosin Inhibitor Aficamten in Healthy Participants

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.).

The Revolution of Cardiac Myosin Inhibitors in Patients With Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiomyopathy worldwide and causes significant morbidity and mortality. For decades, medical treatment options have been limited and untargeted, with frequent need for invasive interventions not readily accessible to many HCM patients. More recently, our understanding of the genetic basis and pathophysiologic mechanism of HCM has grown significantly, leading to the discovery of a new class of medications, cardiac myosin inhibitors (CMIs), that shift myosin into the super-relaxed state to counteract the hypercontractility in HCM. Subsequent clinical trials have proven the mechanism and efficacy of CMIs in humans with obstructive HCM, and additional trials are under way in patients with nonobstructive HCM. With favourable results in the completed clinical trials and ongoing research on the horizon, CMIs represent a bright new era in the targeted management of HCM. This review is focused on the discovery of CMIs, provides a summary of the results of clinical trials to date, provides clinicians with a roadmap for implementing CMIs into practice, and identifies gaps in our current understanding as well as areas of ongoing investigation.

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 Myosin Inhibitors: Expanding the Horizon for Hypertrophic Cardiomyopathy Management

OBJECTIVE

To review the current literature on the efficacy and safety of cardiac myosin inhibitors (CMIs) for the treatment of hypertrophic cardiomyopathy (HCM).

DATA SOURCES

A literature search was conducted on PubMed from origin to April 2023, using the search terms "MYK-461," "mavacamten," "CK-3773274," and "aficamten." Studies were limited to English-based literature, human subjects, and clinical trials resulting in the inclusion of 13 articles. ClinicalTrials.gov was also used with the same search terms for ongoing and completed trials.

STUDY SELECTION AND DATA EXTRACTION

Only phase II and III studies were included in this review except for pharmacokinetic studies that were used to describe drug properties.

DATA SYNTHESIS

CMIs enable cardiac muscle relaxation by decreasing the number of myosin heads that can bind to actin and form cross-bridges. Mavacamten, the first Food and Drug Administration (FDA)-approved drug in this class, has been shown to improve hemodynamic, functional, and quality of life measures in HCM with obstruction. In addition, aficamten is likely to become the next FDA-approved CMI with promising phase II data and an ongoing phase III trial expected to release results in the next year.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE IN COMPARISON WITH EXISTING DRUGS

CMIs provide a novel option for obstructive hypertrophic cardiomyopathy, particularly in those not suitable for septal reduction therapy. Utilization of these agents requires knowledge of drug interactions, dose titration schemes, and monitoring parameters for safety and efficacy.

CONCLUSIONS

CMIs represent a new class of disease-specific drugs for treatment of HCM. Cost-effectiveness studies are needed to delineate the role of these agents in patient therapy.

Differentiating Cardiac Troponin Levels During Cardiac Myosin Inhibition or Cardiac Myosin Activation Treatments: Drug Effect or the Canary in the Coal Mine?

PURPOSE OF REVIEW

Cardiac myosin inhibitors (CMIs) and activators are emerging therapies for hypertrophic cardiomyopathy (HCM) and heart failure with reduced ejection fraction (HFrEF), respectively. However, their effects on cardiac troponin levels, a biomarker of myocardial injury, are incompletely understood.

RECENT FINDINGS

In patients with HCM, CMIs cause substantial reductions in cardiac troponin levels which are reversible after stopping treatment. In patients with HFrEF, cardiac myosin activator (omecamtiv mecarbil) therapy cause modest increases in cardiac troponin levels which are reversible following treatment cessation and not associated with myocardial ischaemia or infarction. Transient changes in cardiac troponin levels might reflect alterations in cardiac contractility and mechanical stress. Such transient changes might not indicate cardiac injury and do not appear to be associated with adverse outcomes in the short to intermediate term. Longitudinal changes in troponin levels vary depending on the population and treatment. Further research is needed to elucidate mechanisms underlying changes in troponin levels.

Mavacamten: a first-in-class myosin inhibitor for obstructive hypertrophic cardiomyopathy

Mavacamten is a first-in-class, targeted, cardiac-specific myosin inhibitor approved by the US Food and Drug Administration for the treatment of adults with symptomatic New York Heart Association Classes II and III obstructive hypertrophic cardiomyopathy (oHCM). Mavacamten was developed to target the hyper-contractile phenotype, which plays a critical role in the pathophysiology of the disease. In Phase 2 and 3 clinical trials, mavacamten was well tolerated, reduced left ventricular outflow tract gradients, improved exercise capacity and symptoms, and was associated with improvements in other clinically relevant parameters, such as patient-reported outcomes and circulating biomarkers. In addition, treatment with mavacamten was associated with evidence of favourable cardiac remodelling in multi-modality imaging studies. Mavacamten substantially reduced guideline eligibility for septal reduction therapy candidates with oHCM and drug-refractory symptoms. In this article, the available efficacy and safety data from completed and ongoing clinical studies of mavacamten in patients with symptomatic oHCM are reviewed. Longer term extension studies may help address questions related to the positioning of mavacamten in current oHCM management algorithms, interactions with background therapy, as well as the potential for disease modification beyond symptomatic relief of left ventricular outflow tract obstruction.

Aficamten-A Second in Class Cardiac Myosin Inhibitor for Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy is an under-recognized disease with a genetic component that results in abnormal and often asymmetric thickening of the left ventricle in addition to decreased compliance and progressive fibrosis of the myocardium. It further poses significant complications related to dynamic left ventricular outflow obstruction over time in a significant majority. The medical management of obstructive hypertrophic cardiomyopathy has evolved over the decades as our understanding has grown. Traditionally, the mainstay in management has included the use of various negative inotropic agents. In contrast, the cardiac myosin inhibitors, aficamten and mavacamten, are novel therapies targeting cardiac contractility at the sarcomere level that have demonstrated improvement in clinical outcomes for patients, and mavacamten (Bristol Myers Squibb, Inc.) has now been approved by the Food and Drug Administration for the treatment of symptomatic obstructive HCM. Aficamten (Cytokinetics, Inc.) is the second in class cardiac myosin inhibitor that is currently being evaluated in ongoing phase III clinical trials, and is the subject of this review.

Aficamten: A Breakthrough Therapy for Symptomatic Obstructive Hypertrophic Cardiomyopathy

Aficamten is a novel cardiac myosin inhibitor that has demonstrated its ability to safely lower left ventricular outflow tract (LVOT) gradients and improve heart failure symptoms in patients with obstructive hypertrophic cardiomyopathy (HCM). Based on the REDWOOD-HCM open label extension (OLE) study, participants receiving aficamten had significantly reduced resting and Valsalva LVOT gradient within 2 weeks after initiating treatment, with ongoing improvements over 24 weeks, and recent evidence suggests effects can sustain up to 48 weeks. While beta-blockers, calcium channel blockers, and disopyramide have shown some benefits in managing HCM, they have limited direct impact on the underlying disease process in patients with obstructive HCM. Aficamten achieves its therapeutic effect by reducing hypercontractility and improving diastolic function in obstructive HCM. Mavacamten was the first cardiac myosin inhibitor approved for symptomatic obstructive HCM. However, aficamten has a shorter human half-life (t1/2) and fewer drug-drug interactions, making it a preferable treatment option. This review evaluates the long-term clinical value and safety of aficamten in patients with obstructive HCM based on available data from completed and ongoing clinical trials. Additionally, the molecular basis of sarcomere-targeted therapy in reducing LVOT gradients is explored, and its potential in managing obstructive HCM is discussed.

Evolution of genetic testing and gene therapy in hypertrophic cardiomyopathy

Studies over the last 30 years have identified hypertrophic cardiomyopathy (HCM) as predominantly an autosomal dominant disorder caused by disease-causing variants in genes encoding the sarcomere proteins critical for contractile function. The two most common disease genes implicated are the MYBPC3 and MYH7 genes, with disease-causing variants in these two genes accounting for 70-80% of all genotype-positive HCM patients. This increased knowledge of the genetic basis of HCM has heralded the era of precision medicine, with genetic testing leading to more improved and precise diagnosis, effective cascade genetic testing in at-risk family members, assistance with reproductive decisions, targeted therapeutics guided by both phenotype and genotype, and providing important insights into risk stratification and prognosis. Most recently, novel insights into genetic mechanisms have been elucidated, spanning non-Mendelian aetiologies, non-familial forms of HCM, and development of polygenic risk scores. These advances have laid the platform for exciting future endeavours such as newer gene therapy approaches in HCM, including gene replacement studies and genome editing approaches to ultimately cure disease. This brief review summarises the current role of genetic testing in HCM patients and families, and introduces some new mechanistic insights leading to the consideration of gene therapy approaches for HCM.

Safety, tolerability, pharmacokinetics, and pharmacodynamics of single and multiple doses of aficamten in healthy Chinese participants: a randomized, double-blind, placebo-controlled, phase 1 study

Objectives: Aficamten is a selective, small-molecule allosteric inhibitor of cardiac sarcomere being developed as a chronic oral treatment for patients with symptomatic obstructive hypertrophic cardiomyopathy. This was the first-in-Chinese study aiming to investigate the safety, tolerability, pharmacokinetics, and pharmacodynamics of aficamten in healthy adults. Methods: This double-blind, randomized, placebo-controlled, phase 1 study was conducted in 28 healthy male and female Chinese participants after single ascending dose (SAD) and multi-dose (MD) administrations of aficamten. In the SAD cohort, 16 participants were randomized to receive a single oral dose of aficamten: 10 mg, 20 mg, or placebo. In the MD cohort, 12 participants were randomized to receive multiple doses of aficamten: 5 mg or placebo once daily for 14 days. Safety was monitored throughout the study with electrocardiograms, echocardiograms, clinical laboratory tests, and reporting of adverse events (AEs). Pharmacokinetic profiles of aficamten and metabolites, as well as CYP2D6 genetic impact, were evaluated. Results: A total of 35 treatment-emergent AEs were reported by 14 (50%) participants with mild severity. There were no serious AEs or adverse decreases in left ventricular ejection fraction below 50% during the study. Aficamten was dose-proportional over the dose range of 5-20 mg and accumulated in the MD cohort. Conclusion: Aficamten was safe and well-tolerated in the healthy Chinese adult participants. The pharmacokinetics of aficamten in the Chinese population was comparable to those previously found in Western participants. These phase 1 data support the progression of aficamten into future clinical studies in Chinese patients. Clinical Trial registration: https://clinicaltrials.gov, identifier: NCT04783766.

Current and emerging pharmacotherapy for the management of hypertrophic cardiomyopathy

INTRODUCTION

Hypertrophic cardiomyopathy (HCM) is one of the most common genetic causes of heart disease. Since the initial description of HCM, there have been minimal strides in management options. Obstructive HCM constitutes a larger subset of patients with increased left ventricular outflow tract gradients causing symptoms. Septal reduction therapy (SRT) has been successful, but it is not the answer for all patients and is not disease modifying.

AREAS COVERED

Current guideline recommendations include beta-blockers, calcium channel blockers, or disopyramides for medical management, but there lacks evidence of much benefit with these drugs. In recent years, there has been the emergence of cardiac myosin inhibitors (CMI) which have demonstrated positive results in patients with both obstructive and non-obstructive HCM. In addition to CMIs, other drugs have been investigated as we have learned more about HCM's pathological mechanisms. Drugs targeting sodium channels and myocardial energetics, as well as repurposed drugs that have demonstrated positive remodeling are being investigated as potential therapeutic targets. Gene therapy is being explored with vast potential for the treatment of HCM.

EXPERT OPINION

The armamentarium of therapeutic options for HCM is continuously increasing with the emergence of CMIs as mainstays of treatment. The future of HCM treatment is promising.

Familial Hypertrophic Cardiomyopathy: Diagnosis and Management

Hypertrophic cardiomyopathy (HCM) is widely recognized as one of the most common inheritable cardiac disorders. Since its initial description over 60 years ago, advances in multimodality imaging and translational genetics have revolutionized our understanding of the disorder. The diagnosis and management of patients with HCM are optimized with a multidisciplinary approach. This, along with increased safety and efficacy of medical, percutaneous, and surgical therapies for HCM, has afforded more personalized care and improved outcomes for this patient population. In this review, we will discuss our modern understanding of the molecular pathophysiology that underlies HCM. We will describe the range of clinical presentations and discuss the role of genetic testing in diagnosis. Finally, we will summarize management strategies for the hemodynamic subtypes of HCM with specific emphasis on the rationale and evidence for the use of implantable cardioverter defibrillators, septal reduction therapy, and cardiac myosin inhibitors.