Mavacamten, a precision medicine for hypertrophic cardiomyopathy: From a motor protein to patients

Effect of Mavacamten on Echocardiographic Features in Chinese Patients with Obstructive Hypertrophic Cardiomyopathy: Results from the EXPLORER-CN Study

INTRODUCTION

Mavacamten, a cardiac myosin inhibitor, has demonstrated positive outcomes in left ventricular outflow tract (LVOT) gradient reduction and improvements of symptoms and function in Chinese patients with symptomatic obstructive hypertrophic cardiomyopathy (HCM) in EXPLORER-CN. This exploratory analysis aimed to evaluate the effect of mavacamten on echocardiographic measures of cardiac structure and function and its relationship with other clinical biomarkers.

METHODS

Key echocardiographic parameters acquired over 30 weeks from 81 patients (n = 54 on mavacamten and n = 27 on placebo) were assessed in a central laboratory.

RESULTS

At 30 weeks, greater improvements in measures of diastolic function were observed with mavacamten versus placebo, including lateral E/e' (least-squares mean [LSM] change from baseline [CFB] - 5.1 vs. 0.6; between-group LSM difference - 5.7; 95% confidence interval [CI] - 7.6 to - 3.7), septal E/e' (LSM CFB - 6.0 vs. - 0.3; between-group LSM difference - 5.7; 95% CI - 7.8 to - 3.7), and left atrial volume index (LAVI) (LSM CFB - 11.7 vs. - 3.5 ml/m2; between-group LSM difference - 8.2; 95% CI - 12.0 to - 4.4) (nominal p < 0.001 for all). Twelve patients (23.1%) treated with mavacamten had complete resolution of mitral valve systolic anterior motion (SAM) versus two patients (7.4%) receiving placebo. Among mavacamten-treated patients, reductions in resting and Valsalva LVOT gradients, left ventricular (LV) mass index, LAVI, and lateral and septal E/e' were associated with reduced N-terminal pro-B-type natriuretic peptide levels (nominal p < 0.0001 for all). In the mavacamten group, reductions in LVOT gradients and LV end-diastolic interventricular septal thickness were associated with improved patient-reported Kansas City Cardiomyopathy Questionnaire Overall Summary Score (nominal p < 0.05 for all).

CONCLUSIONS

Clinically meaningful improvements were evident in Chinese patients treated with mavacamten compared with placebo in several hallmarks of obstructive HCM, including measures of LV diastolic function, SAM, and LVOT gradient. These results add further evidence to support the positive effects of mavacamten in cardiac remodeling.

REGISTRATION

ClinicalTrials.gov identifier: NCT05174416.

Risk-Based Primary Prevention of Heart Failure: A Scientific Statement From the American Heart Association

The growing morbidity, mortality, and health care costs related to heart failure (HF) underscore the urgent need to prioritize its primary prevention. Whereas a risk-based approach for HF prevention remains in its infancy, several key opportunities exist to actualize this paradigm in clinical practice. First, the 2022 American Heart Association/American College of Cardiology/Heart Failure Society of America HF guidelines provided recommendations, for the first time, on the clinical utility of multivariable risk equations to estimate risk of incident HF. Second, the American Heart Association recently developed the PREVENT (Predicting Risk of Cardiovascular Disease Events) equations, which not only enable prediction of incident HF separately, but also include HF in the prediction of total cardiovascular disease. Third, the predominant phenotype of HF risk has emerged as the cardiovascular-kidney-metabolic syndrome. Fourth, the emergence of novel therapies that prevent incident HF (eg, sodium-glucose cotransporter-2 inhibitors) and target multiple cardiovascular-kidney-metabolic axes demonstrate growing potential for risk-based interventions. Whereas the concept of risk-based prevention has been established for decades, it has only been operationalized for atherosclerotic cardiovascular disease prevention to date. Translating these opportunities into a conceptual framework of risk-based primary prevention of HF requires implementation of PREVENT-HF (Predicting Risk of Cardiovascular Disease Events-Heart Failure) equations, targeted use of cardiac biomarkers (eg, natriuretic peptides) and echocardiography for risk reclassification and earlier detection of pre-HF, and definition of therapy-specific risk thresholds that incorporate net benefit and cost-effectiveness. This scientific statement reviews the current evidence for accurate risk prediction, defines strategies for equitable prevention, and proposes potential strategies for the successful implementation of risk-based primary prevention of HF.

Outcomes of a multidisciplinary approach to management of mavacamten in obstructive hypertrophic cardiomyopathy

PURPOSE

Traditional treatments for obstructive hypertrophic cardiomyopathy (oHCM) include β-blockers, calcium channel blockers, and disopyramide. Mavacamten, a novel cardiac myosin inhibitor, is a promising oHCM therapy but has practical challenges limiting its use. This descriptive study aimed to describe a clinic workflow for mavacamten management in a real-world setting, addressing challenges such as cost, drug interactions, and monitoring requirements. The focus was on reducing patient-level costs while ensuring feasibility and efficiency.

SUMMARY

A retrospective analysis was conducted on 34 patients with oHCM for whom mavacamten was considered between May 2022 and May 2023. The clinic workflow involved cardiologist assessment, pharmacist evaluation of drug interactions, enrollment in the mavacamten risk evaluation and mitigation strategy program, cost reduction measures, and initiation of monitoring through scheduled echocardiograms. Of the 34 patients, 21 (62%) were initiated on mavacamten and followed for up to 1 year on therapy. The median time from referral to prior authorization approval and first fill was 5 and 22 days, respectively. Patients demonstrated high adherence (99.1%) as measured by the proportion of days covered. Echocardiogram follow-up showed improvements in left ventricular outflow tract parameters with no patients having a decrease in left ventricular ejection fraction to less than 50%.

CONCLUSION

The described workflow effectively addressed challenges associated with mavacamten management, emphasizing roles for clinic personnel, cost reduction strategies, and structured patient monitoring. While the workflow's specifics may need adaptation in different settings, this report provides valuable insights for clinics implementing structured mavacamten management approaches.

Genotype and arrhythmic risk in patients with apical hypertrophic cardiomyopathy

BACKGROUND

Apical hypertrophic cardiomyopathy (HCM) is a rare variant of HCM, often considered to have a benign prognosis. This study aimed to compare the clinical characteristics and genetic predisposition of apical HCM with non-apical HCM.

METHODS

We included 195 patients with HCM who underwent next-generation sequencing at two tertiary centres in South Korea (2017-2024). The primary outcome was a composite of lethal arrhythmic events (LAE), including death, ventricular arrhythmia, implantable cardioverter defibrillator (ICD) implantation and appropriate ICD shock. Secondary outcomes included major adverse cardiovascular events (MACE), such as new-onset atrial fibrillation, ischaemic stroke, heart failure hospitalisation, septal reduction therapy or heart transplant.

RESULTS

Of the 195 patients, 67 (34.4%) had apical HCM. Patients with apical HCM were older at diagnosis and had lower maximal left ventricular wall thickness compared with non-apical HCM. Disease-causing variants were less frequent in apical HCM (20.9% vs 46.9%, p<0.001). MYBPC3 and MYH7 variants were less common in apical HCM (50.0%) than in non-apical HCM (75.0%). MACE occurred less frequently in apical HCM (HR 0.38, 95% CI 0.19 to 0.75), but no difference was observed in LAE (HR 0.62, 95% CI 0.36 to 1.08). The presence of disease-causing variants was independently associated with LAE (adjusted HR 2.50, 95% CI 1.44 to 4.35).

CONCLUSIONS

Although apical HCM is associated with less hypertrophy and lower genetic yield, it is not entirely benign. The presence of disease-causing variants is an important predictor of arrhythmic risk, underscoring the value of genetic testing in all HCM patients, regardless of phenotype.

Thick-Filament-Based Regulation and the Determinants of Force Generation

Background/Objectives: Thick-filament-based regulation in muscle is generally conceived as processes that modulate the number of myosin heads capable of force generation. It has been generally assumed that biochemical and structural assays of myosin active and inactive states provide equivalent measures of myosin recruitment, but recent studies indicate that this may not always be the case. Here, we studied the steady-state and dynamic mechanical changes in skinned porcine myocardium before and after treatment with omecamtiv mecarbil (OM) or piperine to help decipher how the biochemical and structural states of myosin separately affect contractile force. Methods: Force-Ca2+ relationships were obtained from skinned cardiomyocytes isolated from porcine myocardium before and after exposure to 1 μM OM and 7 μM piperine. Crossbridge kinetics were acquired using a step response stretch activation protocol allowing myosin attachment and detachment rates to be calculated. Results: OM augmented calcium-activated force at submaximal calcium levels that can be attributed to increased thick filament recruitment, increases in calcium sensitivity, an increased duty ratio, and from decelerated crossbridge detachment resulting in slowed crossbridge cycling kinetics. Piperine, in contrast, was able to increase activated force at submaximal calcium levels without appreciably affecting crossbridge cycling kinetics. Conclusions: Our study supports the notion that thick filament activation is primarily a process of myosin recruitment that is not necessarily coupled with the chemo-cycling of crossbridges. These new insights into thick filament activation mechanisms will need to be considered in the design of sarcomere-based therapies for treatment of myopathies.

Mavacamten Inhibits the Effect of the N-Terminal Fragment of Cardiac Myosin-Binding Protein C with the L352P Mutation on the Actin-Myosin Interaction at Low Calcium Concentrations

Hypertrophic cardiomyopathy (HCM)-associated mutations in sarcomeric proteins lead to the disruption of the actin-myosin interaction and its calcium regulation and cause myocardial hypercontractility. About half of such mutations are found in the MYBPC3 gene encoding cardiac myosin-binding protein C (cMyBP-C). A new approach to normalize cardiac contractile function in HCM is the use of β-cardiac myosin function inhibitors, one of which is mavacamten. We studied the effect of mavacamten on the calcium regulation of the actin-myosin interaction using isolated cardiac contractile proteins in the in vitro motility assay. The L352P mutation did not affect the maximum sliding velocity of regulated thin filaments on myosin in the in vitro motility assay and the calcium sensitivity of the velocity but led to the underinhibition of the actin-myosin interaction at low calcium concentrations. Mavacamten decreased the maximum sliding velocity of thin filaments in the presence of the WT and L352P C0-C2 fragments, and abolished their movement in the presence of the L352P C0-C2 fragment at low calcium concentrations. Slowing down the kinetics of cross-bridges and inhibition of actin-myosin interaction at low calcium concentrations by mavacamten may reduce the hypercontractility in HCM and the degree of myocardial hypertrophy.

Mavacamten inhibits myosin activity by stabilising the myosin interacting-heads motif and stalling motor force generation

Most sudden cardiac deaths in young people arise from hypertrophic cardiomyopathy, a genetic disease of the heart muscle, with many causative mutations found in the molecular motor beta-cardiac myosin that drives contraction. Therapeutic intervention has until recently been limited to symptomatic relief or invasive procedures. However, small molecule modulators of cardiac myosin are promising therapeutic options to target disease progression. Mavacamten is the first example to gain FDA approval but its molecular mode of action remains unclear, limiting our understanding of its functional effects in disease. To better understand this, we solved the cryoEM structures of beta-cardiac heavy meromyosin in three ADP.Pi-bound states, the primed motor domain in the presence and absence of mavacamten, and the sequestered autoinhibited interacting-heads motif (IHM) in complex with mavacamten, to 2.9 Å, 3.4 Å and 3.7 Å global resolution respectively. Together with quantitative crosslinking mass spectrometric analysis, these structures reveal how mavacamten inhibits myosin. Mavacamten stabilises ADP.Pi binding, stalling the motor domain in a primed state, reducing motor dynamics required for actin-binding cleft closure, and slowing progression through the force generation cycle. Within the two-headed myosin molecule, these effects are propagated and lead to stabilisation of the IHM, through increased contacts at the motor-motor interface. Critically, while mavacamten treatment can thus rescue cardiac muscle relaxation in diastole, it can also reduce contractile output in systole in the heart.

Clinically approved representative small-molecule drugs for cardiopathy therapy

The application of therapeutic agents for cardiopathy has brought about significant advancements in the treatment of cardiovascular diseases. The intervention of small-molecule drugs has led to substantial reductions in morbidity and mortality rates, along with decreased utilization of healthcare resources. However, current treatment modalities do not exhibit uniform efficacy across all patients, and the emergence of drug resistance poses a significant challenge to further therapeutic efforts. Additionally, chronic administration of these drugs can result in toxicities, adding complexity to long-term management. This review focuses on the application of clinically approved small-molecule drugs for the treatment of cardiopathy, covering major classes such as angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers, calcium channel blockers, β-blockers, and sodium-glucose co-transporter 2 inhibitors. The review provides an in-depth analysis of their synthetic routes, mechanisms of action, and roles in cardiopathy treatment. It also offers perspectives on future directions in the development of next-generation cardioprotective agents, aiming to optimize therapeutic strategies for cardiovascular disease management.

Mavacamten in Symptomatic Nonobstructive Hypertrophic Cardiomyopathy: Design, Rationale, and Baseline Characteristics of ODYSSEY-HCM

There are no approved therapies for patients with symptomatic nonobstructive hypertrophic cardiomyopathy (nHCM). The authors describe the baseline characteristics of ODYSSEY-HCM (A Study of Mavacamten in Non-Obstructive Hypertrophic Cardiomyopathy), a phase 3, randomized, double-blind, placebo-controlled trial conducted worldwide at 201 sites evaluating mavacamten in symptomatic adult patients with nHCM. The 2 primary endpoints are the changes from baseline to week 48 in: 1) Kansas City Cardiomyopathy Questionnaire 23-item Clinical Summary Score; and 2) peak oxygen consumption (pVO2) on cardiopulmonary exercise testing. Dose titrations are made on blinded core laboratory assessments. Of 1,088 patients screened, 580 are randomized (mean age 56 ± 15 years, 46% women, 43% with family histories). All patients are nonobstructive and symptomatic (70% in NYHA functional class II and 30% class III), with a mean Kansas City Cardiomyopathy Questionnaire 23-item Clinical Summary Score of 58 ± 20, and 77% are on beta-blockers. The mean left ventricular ejection fraction and pVO2 are 66% ± 4% and 18 ± 6 mL/kg/min, respectively. ODYSSEY-HCM will report if mavacamten improves patient-reported health status and exercise capacity in patients with symptomatic nHCM. (A Study of Mavacamten in Non-Obstructive Hypertrophic Cardiomyopathy (ODYSSEY-HCM); NCT05582395).

French-Speaking Network of Pharmacogenetics (RNPGx) Recommendations for Clinical Use of Mavacamten

Mavacamten, the first drug in the class of β-cardiac myosin modulator, is used for the treatment of patients with hypertrophic cardiomyopathy. This orally administered drug demonstrates wide interpatient variability in pharmacokinetics parameters, due in part to variant CYP2C19 alleles. Individuals who are CYP2C19 poor metabolizers have increased exposure and are at increased risk of reduced cardiac hypercontractility. To ensure the safety of all patients, European Medicines Agency recommends CYP2C19 preemptive genotyping, and consecutively, to adapt maintenance and initial mavacamten doses, and to manage drug-drug interactions, according to CYP2C19 phenotype. In this article, we summarize evidence from the literature supporting the association between CYP2C19 phenotype and pharmacological features of mavacamten and provide, beyond biologic guidelines, therapeutic recommendations for the use of mavacamten based on CYP2C19 and CYP3A4/CYP3A5 genotype.

Functional control of myosin motors in the cardiac cycle

Contraction of the heart is driven by cyclical interactions between myosin and actin filaments powered by ATP hydrolysis. The modular structure of heart muscle and the organ-level synchrony of the heartbeat ensure tight reciprocal coupling between this myosin ATPase cycle and the macroscopic cardiac cycle. The myosin motors respond to the cyclical activation of the actin and myosin filaments to drive the pressure changes that control the inflow and outflow valves of the heart chambers. Opening and closing of the valves in turn switches the myosin motors between roughly isometric and roughly isotonic contraction modes. Peak filament stress in the heart is much smaller than in fully activated skeletal muscle, although the myosin filaments in the two muscle types have the same number of myosin motors. Calculations indicate that only ~5% of the myosin motors in the heart are needed to generate peak systolic pressure, although many more motors are needed to drive ejection. Tight regulation of the number of active motors is essential for the efficient functioning of the healthy heart - this control is commonly disrupted by gene variants associated with inherited heart disease, and its restoration might be a useful end point in the development of novel therapies.

Load-dependence of the activation of myosin filaments in heart muscle

Contraction of heart muscle requires activation of both the actin and myosin filaments. The mechanism of myosin filament activation is unknown, but the leading candidate hypothesis is direct mechano-sensing by the filaments. Here, we tested this hypothesis by activating intact trabeculae from rat heart by electrical stimulation under different loads and measuring myosin filament activation by X-ray diffraction. Unexpectedly, we found that the distinct structural changes in the myosin filament associated with activation had different dependences on the load. In early activation, all the structural changes indicated faster activation at higher load, as expected from the mechano-sensing hypothesis, but, at later times, the helical order of the myosin motors characteristic of the inactivated state was lost even at very low load. We conclude that mechano-sensing does operate in heart muscle, but it is supplemented by a previously undescribed mechanism that links myosin filament activation to actin filament activation. KEY POINTS: Myosin filament activation controls the strength and speed of contraction in heart muscle. Early activation of the myosin filament is determined by the filament load. At later times, myosin filament activation is controlled by a load independent pathway. This load independent pathway provides new targets and assays for drug development.

Hypertrophic Cardiomyopathy with Special Focus on Mavacamten and Its Future in Cardiology

Hypertrophic cardiomyopathy (HCM) is a heterogeneous group of heart muscle disorders that affects millions, with an incidence from 1 in 500 to 1 in 200. Factors such as genetics, age, gender, comorbidities, and environmental factors may contribute to the course of this disease. Diagnosis of HCM has improved significantly in the past few decades from simple echocardiographic evaluations to a more complex, multimodal approach embracing advanced imaging, genetic, and biomarker studies. This review focuses on Mavacamten, a selective allosteric inhibitor of cardiac myosin, as a pharmacological treatment for HCM. Patients with HCM experience pathological actomyosin interactions, leading to impaired relaxation and increased energy expenditure. Mavacamten decreases available myosin heads, reducing actomyosin cross-bridges during systole and diastole. By reducing the number of bridges left ventricular outflow tract pressure is normalized and cardiac cavities are filled. This mechanism enhances patient performance and alleviates symptoms such as chest pain and dyspnea. The results suggest the potential for Mavacamten to transform the treatment of obstructive hypertrophic cardiomyopathy. Studies to date have shown significant improvement in exercise capacity, symptom relief, and a reduction in the need for invasive procedures such as septal myectomy. Further studies are needed to confirm the clinical results.

Mavacamten in hypertrophic obstructive cardiomyopathy: Prospects for AI integration and mitigating healthcare disparities

Hypertrophic obstructive cardiomyopathy (HOCM) is an autosomal dominant condition that still remains significantly under-diagnosed worldwide. Early detection through clinical evaluation, imaging, and familial history is crucial to prevent severe complications such as heart failure and sudden cardiac death. While cuddsnt management strategies primarily offer symptomatic relief through pharmacotherapy or invasive procedures, their effectiveness and accessibility are limited, revealing substantial gaps in care. The emergence of Mavacamten, a recently FDA-approved drug, could potentially revolutionize HOCM management as it addresses the underlying pathophysiology by inhibiting cardiac myosin ATPase, showing promise in reducing obstruction and improving cardiac function. Our review aims to assess mavacamten's efficacy, emphasizing the pivotal role of genetic testing in identifying at-risk individuals and guiding precise diagnoses for personalized treatments. Additionally, we aim to highlight disparities in access to advanced diagnostics and therapies, particularly affecting underserved populations globally and within communities, as well as explore the potential of artificial intelligence (AI) in enhancing early detection and monitoring treatment responses in HOCM. This review thus offers valuable insights to inform future research directions and clinical practices aimed at optimizing outcomes for individuals with HOCM.

From amoeboid myosin to unique targeted medicines for a genetic cardiac disease

The importance of fundamental basic research in the quest for much needed clinical treatments is a story that constantly must be retold. Funding of basic science in the USA by the National Institutes of Health and other agencies is provided under the assumption that fundamental research eventually will lead to improvements in healthcare worldwide. Understanding how basic research is connected to clinical developments is important, but just part of the story. Many basic science discoveries never see the light of day in a clinical setting because academic scientists are not interested in or do not have the inclination and/or support for entering the world of biotechnology. Even if the interest and inclination are there, often the unknowns about how to enter that world inhibit taking the initial step. Young investigators often ask me how I incorporated biotech opportunities into my otherwise purely academic research endeavors. Here I tell the story of the foundational basic science and early events of my career that led to forming the biotech companies responsible for the development of unique cardiac drugs, including mavacamten, a first in class human β-cardiac myosin inhibitor that is changing the lives of hypertrophic cardiomyopathy patients.

Riding the Waves of Novel Therapies in Hypertrophic Cardiomyopathy

We discuss a case of a 60-year-old man with hypertrophic cardiomyopathy treated with the novel cardiac myosin inhibitor, mavacamten. Dynamic electrocardiogram patterns of left ventricular hypertrophy and left ventricular strain coincided with the patient starting mavacamten, discontinuing the drug, and then restarting mavacamten, highlighting electrocardiograms as accessible and inexpensive potential tools to monitor drug efficacy. This case also shows the ability of myosin inhibition to positively alter the adverse electrical changes associated with hypertrophic cardiomyopathy.

Reassessing the unifying hypothesis for hypercontractility caused by myosin mutations in hypertrophic cardiomyopathy

Significant advances in structural and biochemical research validate the 9-year-old hypothesis that cardiac hypercontractility seen in patients with hypertrophic cardiomyopathy is primarily caused by sarcomeric mutations that increase the number of myosin molecules available for actin interaction.

Sleep duration and heart failure risk: Insights from a Mendelian Randomization Study

To investigate the causal relationship between sleep duration and heart failure (HF) in a European population. We focused on the continuous sleep duration of 460,099 European individuals as our primary exposure. Genome-wide significant single nucleotide polymorphisms (SNPs, n = 9851,867) linked to continuous sleep duration were adopted as instrumental variables. The outcome of interest was based on HF events in a European cohort (n = 977,323; with 930,014 controls and 47,309 cases). We employed a two-sample Mendelian randomization (MR) approach to infer causality between sleep duration and the incidence of HF. For validation purposes, an additional cohort of 336,965 European individuals diagnosed with insomnia was selected as a secondary exposure group. Using its SNPs, a subsequent two-sample MR analysis was conducted with the HF cohort to further corroborate our initial findings. Employing the MR methodology, we selected 57 SNPs that are associated with sleep duration, and 24 SNPs that are associated with insomnia as instrumental variables. We discerned a substantial association between genetically inferred sleep duration and HF risk (odds ratio: 0.61; 95% confidence interval: 0.47-0.78, P < .0001). Our subsequent analysis highlighted a pronounced increased HF risk associated with insomnia (odds ratio: 1.54; 95% confidence interval: 1.08-2.17, P < .02). These conclusions were further bolstered by consistent results from sensitivity analyses. Our study suggests a causal linkage between sleep duration and the onset risk of HF in the European population. Notably, shorter sleep durations were associated with a heightened risk of HF.

An overview of the treatments for hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a very prevalent inherited disease with a wide global distribution and a prevalence rate of approximately 0.2% in the general population. Left ventricular hypertrophy (LVH) caused by sarcomere mutation is the primary reason of HCM. The histopathology feature is that cardiomyocyte hypertrophy, myocyte disorder and myocardial fibrosis lead to diminished diastolic function, left ventricular outflow tract obstruction (LVOTO) and arrhythmia, all of which result in serious cardiac complications. Previously, HCM was considered a malignant disease that was almost untreatable. With the improvement of medical standards and increasing awareness of HCM, it has become a highly treatable disease in contemporary times, with a significant decrease in mortality rates. However, there are still significant unmet requirements in the therapy of HCM. This paper draws on more than 100 references from the past four decades and summarizes current advances in the treatment of HCM. The article will review the pathogenesis and types, recent development in pharmacotherapy, invasive treatments and gene therapies, as well as dilemma and future development of HCM.

Genetic Mutations and Mitochondrial Redox Signaling as Modulating Factors in Hypertrophic Cardiomyopathy: A Scoping Review

Hypertrophic cardiomyopathy (HCM) is a heart condition characterized by cellular and metabolic dysfunction, with mitochondrial dysfunction playing a crucial role. Although the direct relationship between genetic mutations and mitochondrial dysfunction remains unclear, targeting mitochondrial dysfunction presents promising opportunities for treatment, as there are currently no effective treatments available for HCM. This review adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Extension for Scoping Reviews guidelines. Searches were conducted in databases such as PubMed, Embase, and Scopus up to September 2023 using "MESH terms". Bibliographic references from pertinent articles were also included. Hypertrophic cardiomyopathy (HCM) is influenced by ionic homeostasis, cardiac tissue remodeling, metabolic balance, genetic mutations, reactive oxygen species regulation, and mitochondrial dysfunction. The latter is a common factor regardless of the cause and is linked to intracellular calcium handling, energetic and oxidative stress, and HCM-induced hypertrophy. Hypertrophic cardiomyopathy treatments focus on symptom management and complication prevention. Targeted therapeutic approaches, such as improving mitochondrial bioenergetics, are being explored. This includes coenzyme Q and elamipretide therapies and metabolic strategies like therapeutic ketosis. Understanding the biomolecular, genetic, and mitochondrial mechanisms underlying HCM is crucial for developing new therapeutic modalities.

Myosin-Catalyzed ATP Hydrolysis in the Presence of Disease-Causing Mutations: Mavacamten as a Way to Repair Mechanism

Hypertrophic cardiomyopathy is one of the most common forms of genetic cardiomyopathy. Mavacamten is a first-in-class myosin modulator that was identified via activity screening on the wild type, and it is FDA-approved for the treatment of obstructive hypertrophic cardiomyopathy (HCM). The drug selectively binds to the cardiac β-myosin, inhibiting myosin function to decrease cardiac contractility. Though the drug is thought to affect multiple steps of the myosin cross-bridge cycle, its detailed mechanism of action is still under investigation. Individual steps in the overall cross-bridge cycle must be queried to elucidate the full mechanism of action. In this study, we utilize the rare-event method of transition path sampling to generate reactive trajectories to gain insights into the action of the drug on the dynamics and rate of the ATP hydrolysis step for human cardiac β-myosin. We study three known HCM causative myosin mutations: R453C, P710R, and R712L to observe the effect of the drug on the alterations caused by these mutations in the chemical step. Since the crystal structure of the drug-bound myosin was not available at the time of this work, we created a model of the drug-bound system utilizing a molecular docking approach. We find a significant effect of the drug in one case, where the actual mechanism of the reaction is altered from the wild type by mutation. The drug restores both the rate of hydrolysis to the wildtype level and the mechanism of the reaction. This is a way to check the effect of the drug on untested mutations.

Emerging Concepts of Mechanisms Controlling Cardiac Tension: Focus on Familial Dilated Cardiomyopathy (DCM) and Sarcomere-Directed Therapies

Novel therapies for the treatment of familial dilated cardiomyopathy (DCM) are lacking. Shaping research directions to clinical needs is critical. Triggers for the progression of the disorder commonly occur due to specific gene variants that affect the production of sarcomeric/cytoskeletal proteins. Generally, these variants cause a decrease in tension by the myofilaments, resulting in signaling abnormalities within the micro-environment, which over time result in structural and functional maladaptations, leading to heart failure (HF). Current concepts support the hypothesis that the mutant sarcomere proteins induce a causal depression in the tension-time integral (TTI) of linear preparations of cardiac muscle. However, molecular mechanisms underlying tension generation particularly concerning mutant proteins and their impact on sarcomere molecular signaling are currently controversial. Thus, there is a need for clarification as to how mutant proteins affect sarcomere molecular signaling in the etiology and progression of DCM. A main topic in this controversy is the control of the number of tension-generating myosin heads reacting with the thin filament. One line of investigation proposes that this number is determined by changes in the ratio of myosin heads in a sequestered super-relaxed state (SRX) or in a disordered relaxed state (DRX) poised for force generation upon the Ca2+ activation of the thin filament. Contrasting evidence from nanometer-micrometer-scale X-ray diffraction in intact trabeculae indicates that the SRX/DRX states may have a lesser role. Instead, the proposal is that myosin heads are in a basal OFF state in relaxation then transfer to an ON state through a mechano-sensing mechanism induced during early thin filament activation and increasing thick filament strain. Recent evidence about the modulation of these mechanisms by protein phosphorylation has also introduced a need for reconsidering the control of tension. We discuss these mechanisms that lead to different ideas related to how tension is disturbed by levels of mutant sarcomere proteins linked to the expression of gene variants in the complex landscape of DCM. Resolving the various mechanisms and incorporating them into a unified concept is crucial for gaining a comprehensive understanding of DCM. This deeper understanding is not only important for diagnosis and treatment strategies with small molecules, but also for understanding the reciprocal signaling processes that occur between cardiac myocytes and their micro-environment. By unraveling these complexities, we can pave the way for improved therapeutic interventions for managing DCM.

A therapeutic leap: how myosin inhibitors moved from cardiac interventions to skeletal muscle myopathy solutions

The myosin inhibitor mavacamten has transformed the management of obstructive hypertrophic cardiomyopathy (HCM) by targeting myosin ATPase activity to mitigate cardiac hypercontractility. This therapeutic mechanism has proven effective for patients with HCM independent of having a primary gene mutation in myosin. In this issue of the JCI, Buvoli et al. report that muscle hypercontractility is a mechanism of pathogenesis underlying muscle dysfunction in Laing distal myopathy, a disorder characterized by mutations altering the rod domain of β myosin heavy chain. The authors performed detailed physiological, molecular, and biomechanical analyses and demonstrated that myosin ATPase inhibition can correct a large extent of muscle abnormalities. The findings offer a therapeutic avenue for Laing distal myopathy and potentially other myopathies. This Commentary underscores the importance of reevaluating myosin activity's role across myopathies in general for the potential development of targeted myosin inhibitors to treat skeletal muscle disorders.

Complex architecture of cardiac muscle thick filaments revealed

Muscle contraction is orchestrated by the well-understood thin filaments and the markedly complex thick filaments. Studies by Dutta et al. and Tamborrini et al., discussed here, have unravelled the structure of the mammalian heart thick filament in exquisite near-atomic detail and pave the way for understanding physiological modulation pathways and mutation-induced dysfunction and for designing potential drugs to modify defects.

Myosin in autoinhibited off state(s), stabilized by mavacamten, can be recruited in response to inotropic interventions

Mavacamten is a FDA-approved small-molecule therapeutic designed to regulate cardiac function at the sarcomere level by selectively but reversibly inhibiting the enzymatic activity of myosin. It shifts myosin toward ordered off states close to the thick filament backbone. It remains elusive whether these myosin heads in the off state(s) can be recruited in response to physiological stimuli when required to boost cardiac output. We show that cardiac myosins stabilized in these off state(s) by mavacamten are recruitable by 1) Ca2+, 2) increased chronotropy [heart rate (HR)], 3) stretch, and 4) β-adrenergic (β-AR) stimulation, all known physiological inotropic interventions. At the molecular level, we show that Ca2+ increases myosin ATPase activity by shifting mavacamten-stabilized myosin heads from the inactive super-relaxed state to the active disordered relaxed state. At the myofilament level, both Ca2+ and passive lengthening can shift mavacamten-ordered off myosin heads from positions close to the thick filament backbone to disordered on states closer to the thin filaments. In isolated rat cardiomyocytes, increased stimulation rates enhanced shortening fraction in mavacamten-treated cells. This observation was confirmed in vivo in telemetered rats, where left-ventricular dP/dtmax, an index of inotropy, increased with HR in mavacamten-treated animals. Finally, we show that β-AR stimulation in vivo increases left-ventricular function and stroke volume in the setting of mavacamten. Our data demonstrate that the mavacamten-promoted off states of myosin in the thick filament are at least partially activable, thus preserving cardiac reserve mechanisms.