Population pharmacokinetic-pharmacodynamic modeling of omecamtiv mecarbil, a cardiac myosin activator, in healthy volunteers and patients with stable heart failure

Harnessing molecular mechanism for precision medicine in dilated cardiomyopathy caused by a mutation in troponin T

Familial dilated cardiomyopathy (DCM) is frequently caused by autosomal dominant point mutations in genes involved in diverse cellular processes, including sarcomeric contraction. While patient studies have defined the genetic landscape of DCM, genetics are not currently used in patient care, and patients receive similar treatments regardless of the underlying mutation. It has been suggested that a precision medicine approach based on the molecular mechanism of the underlying mutation could improve outcomes; however, realizing this approach has been challenging due to difficulties linking genotype and phenotype and then leveraging this information to identify therapeutic approaches. Here, we used multiscale experimental and computational approaches to test whether knowledge of molecular mechanism could be harnessed to connect genotype, phenotype, and drug response for a DCM mutation in troponin T, deletion of K210. Previously, we showed that at the molecular scale, the mutation reduces thin filament activation. Here, we used computational modeling of this molecular defect to predict that the mutant will reduce cellular and tissue contractility, and we validated this prediction in human cardiomyocytes and engineered heart tissues. We then used our knowledge of molecular mechanism to computationally model the effects of a small molecule that can activate the thin filament. We demonstrate experimentally that the modeling correctly predicts that the small molecule can partially rescue systolic dysfunction at the expense of diastolic function. Taken together, our results demonstrate how molecular mechanism can be harnessed to connect genotype and phenotype and inspire strategies to optimize mechanism-based therapeutics for DCM.

Medical Management of Patients With Heart Failure and Reduced Ejection Fraction

The options for treating heart failure with reduced ejection fraction (HFrEF) have expanded considerably over the past decade. While neurohormonal modulation using angiotensin converting enzyme inhibitors and angiotensin receptor blockers, beta blockers and mineralocorticoid receptor antagonists remain the cornerstone of therapy, additional novel approaches including angiotensin receptor neprilysin inhibitors, sodium glucose cotransporter 2 inhibitors, ivrabradine, vericiguat and omecamtiv mecarbil have been shown to improve outcomes in patients with HFrEF. This reviews summarizes currently available approaches as well as promising additional strategies that may be used in the future.

Treatment options for patients with heart failure (HF) with reduced ejection fraction (HFrEF) have expanded considerably over the past few decades. Whereas neurohormonal modulation remains central to the management of patients with HFrEF, other pathways have been targeted with drugs that have novel mechanisms of action. The angiotensin receptor-neprilysin inhibitors (ARNIs) which enhance levels of compensatory molecules such as the natriuretic peptides while simultaneously providing angiotensin receptor blockade have emerged as the preferred strategy for inhibiting the renin angiotensin system. Sodium glucose cotransporter 2 (SGLT2) inhibitors which were developed as hypoglycemic agents have been shown to improve outcomes in patients with HF regardless of their diabetic status. These agents along with beta blockers and mineralocorticoid receptor antagonists are the core medical therapies for patients with HFrEF. Additional approaches using ivabradine to slow heart rate in patients with sinus rhythm, the hydralazine/isosorbide dinitrate combination to unload the heart, digoxin to provide inotropic support and vericiguat to augment cyclic guanosine monophosphate production have been shown in well-designed trials to have beneficial effects in the HFrEF population and are used as adjuncts to the core therapies in selected patients. This review provides an overview of the medical management of patients with HFrEF with focus on the major developments that have taken place in the field. It offers prospective of how these drugs should be employed in clinical practice and also a glimpse into some strategies that may prove to be useful in the future.

Population Pharmacokinetic Properties of Omecamtiv Mecarbil in Healthy Subjects and Patients with Heart Failure with Reduced Ejection Fraction

ABSTRACT

Omecamtiv mecarbil is a small molecule that has been shown to improve cardiac function in patients with heart failure with reduced ejection fraction and is currently being developed as an oral modified release (MR) tablet for subjects with chronic HF. The objectives of this study were to analyze the pharmacokinetic (PK) properties of omecamtiv mecarbil and to investigate the effects of potential covariates on pertinent PK parameters using population PK modeling of data from 3 clinical trials in healthy subjects (N=85) and 3 clinical trials in patients with heart failure (N=4261). The population PK analysis was performed using a non-linear mixed effects modeling approach. Omecamtiv mecarbil has a clearance of 11.7 L/hr (0.701 % RSE [relative standard error]) and a central volume of distribution of 275 L (2.12% RSE). The estimated half-life of omecamtiv mecarbil was 33 hours. Body weight and estimated glomerular filtration rate (eGFR) were significant covariates, but their effect on exposure was modest and lacked clinical relevance. Additional covariates including sex, race, bilirubin, albumin, concomitant medications, New York Heart Association Functional Classification, N-terminal-pro hormone B-type natriuretic peptide (NT-proBNP), troponin I, creatine kinase MB, serum hemoglobin, tablet formulation, aspartate aminotransferase, and serum urea was tested and found to have no impact on omecamtiv mecarbil exposures. The results of this integrated evaluation of the impact of covariates on the systemic exposure of omecamtiv mecarbil suggest dose adjustment is not required for the studied subpopulations of patients with heart failure.

Pharmacokinetic Drug-Drug Interaction Study of Omecamtiv Mecarbil With Amiodarone and Digoxin in Healthy Subjects

Omecamtiv mecarbil (OM), a novel cardiac myosin activator, is being evaluated for the treatment of heart failure with reduced ejection fraction. In vitro studies demonstrate OM as a substrate and inhibitor of P-glycoprotein (P-gp), which can result in drug-drug interactions. Two phase 1, open-label studies assessed the effect of coadministration of OM (50-mg single dose) on the pharmacokinetics of digoxin (0.5-mg single dose; N = 15), a P-gp substrate, and the effect of coadministration of amiodarone (600-mg single dose), a P-gp inhibitor, on the pharmacokinetics of OM (50-mg single dose; N = 14) in healthy subjects. The ratios of the geometric least squares mean (90% confidence interval [CI]) of digoxin coadministered with OM vs digoxin alone for area under the plasma concentration-time curve (AUC) from time 0 to infinity, AUC from time 0 to the time of the last quantifiable concentration, and maximum observed plasma concentration were 1.06 (90%CI, 0.99-1.14), 1.06 (90%CI, 0.98-1.14), and 1.08 (90%CI, 0.92-1.26), respectively. The ratios of the geometric least squares mean of OM coadministered with amiodarone vs OM alone for AUC from time 0 to infinity, AUC from time 0 to the time of the last quantifiable concentration, and maximum observed plasma concentration were 1.21 (90%CI, 1.08-1.36), 1.21 (90%CI, 1.07-1.36), and 1.08 (90%CI, 0.96-1.22), respectively. In conclusion, OM coadministered with digoxin or amiodarone did not result in any clinically relevant pharmacokinetic drug-drug interactions.

Pharmacokinetics, Tolerability, and Safety of Single and Multiple Omecamtiv Mecarbil Doses in Healthy Japanese and Caucasian Subjects

BACKGROUND AND OBJECTIVES

Omecamtiv mecarbil (OM) is a cardiac myosin activator under development for the treatment of heart failure. The pharmacokinetics of single and multiple doses of OM were investigated in healthy Japanese subjects in two clinical studies.

METHODS

Study 1 (n = 36) evaluated the bioavailability and pharmacokinetics after intravenous infusion (15 mg/h for 4 h) and an oral modified release (MR) tablet in healthy Japanese and Caucasian subjects using 25 mg single and multiple doses and 50 mg single dose. Study 2 (n = 50) evaluated the pharmacokinetics of OM with multiple oral doses of 25 mg MR tablets twice a day (BID) followed by up-titration to either 37.5 mg or 50 mg BID in healthy Japanese subjects.

RESULTS

In Study 1, the maximum observed plasma concentration (C_max) and area under the plasma concentration-time curve (AUC) from time 0 to infinity (AUC_inf) in Japanese subjects after a single oral dose of 50 mg were twice that at the 25 mg dose, consistent with that observed in Caucasian subjects. Following single oral doses of 25 mg and 50 mg, absolute bioavailability was 56.5% and 59.2% for Japanese subjects and 63.1 and 83.6% for Caucasian subjects, respectively. No ethnic differences were observed in the pharmacokinetics of OM and its metabolites following single and multiple doses of 25 mg and 50 mg. In Study 2, the mean accumulation ratios based on AUC from 0 to 12 h (AUC₁₂) were approximately four-fold from day 1 to day 8 and from day 20 to day 27 across ethnic groups. The mean ratios of C_max to predose concentrations (C_predose) ranged from 1.25 to 1.38 across subgroups.

CONCLUSIONS

OM showed consistent and predictable pharmacokinetics after multiple dosing in Japanese subjects.

Pharmacokinetic Evaluation of the CYP3A4 and CYP2D6 Drug-Drug Interaction and CYP3A4 Induction Potential of Omecamtiv Mecarbil: Two Open-Label Studies in Healthy Subjects

Omecamtiv mecarbil (OM) is a cardiac myosin activator under development for the treatment of heart failure. The effect of CYP3A4 and CYP2D6 inhibition on OM pharmacokinetics and the potential for OM to induce CYP3A4 was assessed in 2 studies. Study 1, part A, assessed the effect of ketoconazole 200 mg on the pharmacokinetics of OM 10 mg in CYP2D6 extensive metabolizers (EMs; n = 8) or poor metabolizers (PMs; n = 8). Study 1, part B, assessed the effect of diltiazem 240 mg on the pharmacokinetics of OM 10 mg (EM; n = 8). Study 2 assessed the effect of OM 25 mg on the pharmacokinetics of midazolam 5 mg (n = 14). Coadministration with ketoconazole led to 51% and 31% increases in OM AUC_inf in EM and PM subjects, respectively, whereas OM C_max remained similar (3% higher and 14% lower for EM and PM subjects, respectively). No changes in OM pharmacokinetics were observed in EM subjects following coadministration with diltiazem. Midazolam AUC_inf and C_max decreased by 18% and 10%, respectively, when coadministered with OM. In conclusion, CYP3A4 and CYP2D6 inhibitors are unlikely to have a clinically significant effect on the pharmacokinetics of OM. In addition, OM is unlikely to have a clinically relevant effect on the pharmacokinetics of CYP3A4 substrates.

Switchability and minimal effect of food on pharmacokinetics of modified release tablet strengths of omecamtiv mecarbil, a cardiac myosin activator

Omecamtiv mecarbil (OM) is a cardiac myosin activator in clinical development for the treatment of heart failure. The effect of food on the pharmacokinetics (PK) of 25, 37.5, and 50 mg strength modified release (MR) tablets and the bioequivalence of two 25 mg tablets versus one 50 mg MR tablet were evaluated in two open-label, randomized, cross-over studies in healthy subjects. Subjects received two 25 mg tablets or one 50 mg OM MR tablet under fed or fasted states in Study 1 (n = 39), and single oral doses of 25 and 37.5 mg OM MR tablets and to assess its relative bioavailability to the 25 mg MR tablet, a 25 mg oral solution under fed or fasted states in Study 2 (n = 34). The area under the concentration-time curve (AUC) and the maximum observed concentration (C_max ) of 25, 37.5, or 50 mg OM MR tablets were approximately 13%-22% higher and 31%-40% higher, respectively, when taken with food. The two 25 mg and one 50 mg OM MR tablets were bioequivalent (90% confidence intervals) of the geometric mean ratios for C_max and AUC of OM were within 0.8-1.25 under the fasted or fed state. OM was well tolerated and all treatment-emergent events were mild in severity and resolved by the end of the study. In conclusion, these studies demonstrated that the effect of food on the PK of OM was minimal at all three studied strengths of the MR tablets, and two 25 mg MR tablets may be switched for one 50 mg MR tablet (EudraCT Number: 2019-003683-44).

Omecamtiv mecarbil does not prolong QTc intervals at therapeutic concentrations

AIMS

Omecamtiv mecarbil (OM) is a novel selective cardiac myosin activator under investigation for the treatment of heart failure. This study aimed to evaluate the effect of therapeutic concentrations of OM on electrocardiogram (ECG) parameters and exclude a clinically concerning effect on the rate-corrected QT (QTc) interval.

METHODS

In part A, 70 healthy subjects received a 25 mg oral dose of OM, and pharmacokinetics were assessed. Only subjects with maximum observed plasma concentration ≤ 350 ng/mL (n = 60) were randomized into part B, where they received a single oral dose of placebo, 50 mg OM and 400 mg moxifloxacin in a 3-period, 3-treatment, 6-sequence crossover study with continuous ECG collection.

RESULTS

After a 50-mg dose of OM, mean placebo-corrected change from baseline QTcF (∆∆QTcF; Fridericia correction) ranged from -6.7 ms at 1 hour postdose to -0.8 ms at 4 hours postdose. The highest upper bound of the 1-sided 95% confidence interval (CI) was 0.7 ms (4 h postdose). Moxifloxacin resulted in a clear increase in mean ∆∆QTcF, with a peak value of 13.1 ms (90% CI: 11.71-14.57) at 3 hours; lower bound of the 1-sided 95% CI was > 5 ms at all of the 3 prespecified time points. Based on a concentration-QTc analysis, an effect on ∆∆QTcF exceeding 10 ms can be excluded up to OM plasma concentrations of ~800 ng/mL. There were no serious or treatment-emergent adverse events leading to discontinuation from the study.

CONCLUSION

OM does not have a clinically relevant effect on the studied ECG parameters.

Effect of Omecamtiv Mecarbil on the Pharmacokinetics of Metformin, a Probe Substrate for MATE1/MATE2-K, in Healthy Subjects

BACKGROUND AND OBJECTIVE

Omecamtiv mecarbil (OM) is a novel cardiac myosin activator in development for the treatment of heart failure with reduced ejection fraction. The objective of this study was to evaluate the potential for OM to affect the pharmacokinetics of metformin.

METHODS

This was an open-label, fixed-sequence study in 14 healthy subjects. On Day 1, subjects received an 850 mg oral dose of metformin. From Days 4 to 9, subjects received twice-daily 25 mg oral doses of OM tablets. On Day 10, subjects received an 850 mg oral dose of metformin and a single 25 mg tablet of OM. Blood and urine samples were collected up to 36 h post-dose following administration of metformin on Days 1 and 10 to characterize concentrations of metformin in plasma and urine.

RESULTS

The ratios of the geometric least square means of metformin coadministered with OM compared to metformin alone were 98.7%, 99.3%, and 110.2% for AUC_inf, AUC_last, and C_max, respectively. The mean renal clearance of metformin was similar following metformin administered alone (34.2 L/h) compared to metformin coadministered with OM (32.9 L/h). All adverse events were mild in severity and resolved prior to the end of the study. No serious adverse events or treatment-emergent adverse events led to discontinuation from the study.

CONCLUSIONS

There was no clinically relevant effect of OM on the pharmacokinetics of metformin in healthy subjects.

Myosin from the ventricle is more sensitive to omecamtiv mecarbil than myosin from the atrium

Omecamtiv mecarbil (OM), an activator of cardiac myosin, strongly affects contractile characteristics of the ventricles and, to a much lesser extent, the characteristics of atrial contraction. We compared the molecular mechanism of action of OM on the interaction of atrial and ventricular myosin with actin using an optical trap and an in vitro motility assay. In concentrations up to 0.5 μM, OM did not affect the step size of a myosin molecule but reduced it at a higher OM level. OM substantially prolonged the interaction of both isoforms of myosin with actin. However, the interaction characteristics of ventricular myosin with actin were more sensitive to OM than those of atrial myosin. Our results, obtained at the level of isolated proteins, can explain why the impact of OM in therapeutic concentrations on the contractile function of the atrium is less significant as compared to those of the ventricle.

Orthophosphate increases the efficiency of slow muscle-myosin isoform in the presence of omecamtiv mecarbil

Omecamtiv mecarbil (OM) is a putative positive inotropic tool for treatment of systolic heart dysfunction, based on the finding that in vivo it increases the ejection fraction and in vitro it prolongs the actin-bond life time of the cardiac and slow-skeletal muscle isoforms of myosin. OM action in situ, however, is still poorly understood as the enhanced Ca²⁺-sensitivity of the myofilaments is at odds with the reduction of force and rate of force development observed at saturating Ca²⁺. Here we show, by combining fast sarcomere-level mechanics and ATPase measurements in single slow demembranated fibres from rabbit soleus, that the depressant effect of OM on the force per attached motor is reversed, without effect on the ATPase rate, by physiological concentrations of inorganic phosphate (Pi) (1-10 mM). This mechanism could underpin an energetically efficient reduction of systolic tension cost in OM-treated patients, whenever [Pi] increases with heart-beat frequency.

Omecamtiv mecarbil is a small molecule effector under clinical trial for the treatment of systolic heart failure. Here the authors define the molecular mechanisms of its inotropic action and find it can increase the efficiency of contraction in muscle fibres when the orthophosphate concentration rises with the beat frequency.

Multiparametric Mechanistic Profiling of Inotropic Drugs in Adult Human Primary Cardiomyocytes

Effects of non-cardiac drugs on cardiac contractility can lead to serious adverse events. Furthermore, programs aimed at treating heart failure have had limited success and this therapeutic area remains a major unmet medical need. The challenges in assessing drug effect on cardiac contractility point to the fundamental translational value of the current preclinical models. Therefore, we sought to develop an adult human primary cardiomyocyte contractility model that has the potential to provide a predictive preclinical approach for simultaneously predicting drug-induced inotropic effect (sarcomere shortening) and generating multi-parameter data to profile different mechanisms of action based on cluster analysis of a set of 12 contractility parameters. We report that 17 positive and 9 negative inotropes covering diverse mechanisms of action exerted concentration-dependent increases and decreases in sarcomere shortening, respectively. Interestingly, the multiparametric readout allowed for the differentiation of inotropes operating via distinct mechanisms. Hierarchical clustering of contractility transient parameters, coupled with principal component analysis, enabled the classification of subsets of both positive as well as negative inotropes, in a mechanism-related mode. Thus, human cardiomyocyte contractility model could accurately facilitate informed mechanistic-based decision making, risk management and discovery of molecules with the most desirable pharmacological profile for the correction of heart failure.

Positive cardiac inotrope omecamtiv mecarbil activates muscle despite suppressing the myosin working stroke

Omecamtiv mecarbil (OM) is a positive cardiac inotrope in phase-3 clinical trials for treatment of heart failure. Although initially described as a direct myosin activator, subsequent studies are at odds with this description and do not explain OM-mediated increases in cardiac performance. Here we show, via single-molecule, biophysical experiments on cardiac myosin, that OM suppresses myosin's working stroke and prolongs actomyosin attachment 5-fold, which explains inhibitory actions of the drug observed in vitro. OM also causes the actin-detachment rate to become independent of both applied load and ATP concentration. Surprisingly, increased myocardial force output in the presence of OM can be explained by cooperative thin-filament activation by OM-inhibited myosin molecules. Selective suppression of myosin is an unanticipated route to muscle activation that may guide future development of therapeutic drugs.

Pharmacokinetic and pharmacodynamic modeling of oral mitiglinide on glucose lowering in healthy Chinese volunteers

Background

Mitiglinide is a widely used agent for diabetic treatment. We established a pharmacokinetic-pharmacodynamic (PK-PD) model to illustrate the relationship between mitiglinide plasma concentration and its glucose lowering effects in healthy volunteers.

Methods

The volunteers participated in the test after the administration of a single dose of 10 mg mitiglinide. The drug concentration in Plasma and the values of glucose levels were determined by LC-MS/MS assay and hexokinase method. A PK-PD model was established with a series of equations to describe the relationship between plasma medicine and glucose, and the equations were solved numerically and fitted to the data with the Phoenix NLME software.

Results

The results of the two-compartment model analysis were based on the maximum likelihood criterion and visual inspection of the fittings. The terminal elimination half-life (t_1/2) was 1.69 ± 0.16 h and the CL/F was 7.80 ± 1.84 L/h. The plasma glucose levels began to decline by 0.2 h, and hit its bottom decreasing values of 2.6 mg/L at 0.5 h after administration. The calculated parameter and fitting curve indicated that the model established in our experiment fitted well.

Conclusions

A PK/PD model illustrates that the relationship between mitiglinide concentration in plasma and glucose lowering effect in healthy volunteers was established. The results of our experiment suggested that the model can be used reasonably to predict the relationship between PK and PD in mitiglinide, which could be used in diabetes mellitus dosage control in clinical trials and other fields.

New developments in the pharmacotherapeutic management of heart failure in elderly patients: concerns and considerations

INTRODUCTION

Heart failure (HF) remains a major public health problem worldwide, affecting approximately 23 million patients, and is predominantly a disease of the elderly population. Elderly patients mostly suffer from HF with preserved ejection fraction (HFpEF), which often presents with multiple co-morbidities and they require multiple medical treatments. This, together with the heterogeneous phenotype of HFpEF, makes it a difficult syndrome to diagnose and treat. Areas covered: Although HF is most abundant in the elderly, this group is still underrepresented in clinical trials, which results in the lack of evidence-based medical regimens. The current review has focused on new potential therapies for this poorly studied population. The focus will be on several classes of drugs currently recommended or might be expected soon. These will include sacubitril/valsartan (former LCZ696), Omecamtiv mecarbil, Vericiguat, Ivabradine, mineralocorticoid receptor antagonists (MRAs) and potassium binders. Expert opinion: We discuss promising new treatments and hypothesize that personalized approaches will be needed to treat elderly patients optimally. Medical doctors should not only focus on HF therapy, but comorbidities and polypharmacy should also influence therapeutic decision making. Furthermore, the importance of quality of life as a management endpoint should not be underestimated in the frail elderly.

Perspective on precision medicine in paediatric heart failure

In 2015, President Obama launched the Precision Medicine Initiative (PMI), which introduced new funding to a method of research with the potential to study rare and complex diseases. Paediatric heart failure, a heterogeneous syndrome affecting approximately 1 in 100000 children, is one such condition in which precision medicine techniques may be applied with great benefit. Current heart failure therapies target downstream effects of heart failure rather than the underlying cause of heart failure. As such, they are often ineffective in paediatric heart failure, which is typically of primary (e.g. genetic) rather than secondary (e.g. acquired) aetiology. It is, therefore, important to develop therapies that can target the causes of heart failure in children with greater specificity thereby decreasing morbidity, mortality and burden of illness on both patients and their families. The benefits of co-ordinated research in genomics, proteomics, metabolomics, transcriptomics and phenomics along with dietary, lifestyle and social factors have led to novel therapeutic and prognostic applications in other fields such as oncology. Applying such co-ordinated research efforts to heart failure constitutes an important step in advancing care and improving the lives of those affected.

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

BACKGROUND

Impaired contractility is a feature of heart failure with reduced ejection fraction. We assessed the pharmacokinetics and effects on cardiac function and structure of the cardiac myosin activator, omecamtiv mecarbil.

METHODS

In this randomised, double-blind study, done at 87 sites in 13 countries, we recruited patients with stable, symptomatic chronic heart failure and left ventricular ejection fraction 40% or lower. Patients were randomly assigned equally, via an interactive web response system, to receive 25 mg oral omecamtiv mecarbil twice daily (fixed-dose group), 25 mg twice daily titrated to 50 mg twice daily guided by pharmacokinetics (pharmacokinetic-titration group), or placebo for 20 weeks. We assessed the maximum concentration of omecamtiv mecarbil in plasma (primary endpoint) and changes in cardiac function and ventricular diameters. This trial is registered with ClinicalTrials.gov, number NCT01786512.

FINDINGS

From March 17, 2014, to March 5, 2015, we enrolled 150 patients in the fixed-dose omecamtiv mecarbil group and 149 in the pharmacokinetic-titration and placebo groups. Mean maximum concentration of omecamtiv mecarbil at 12 weeks was 200 (SD 71) ng/mL in the fixed-dose group and 318 (129) ng/mL in the pharmacokinetic-titration group. For the pharmacokinetic-titration group versus placebo group at 20 weeks, least square mean differences were as follows: systolic ejection time 25 ms (95% CI 18-32, p<0·0001), stroke volume 3·6 mL (0·5-6·7, p=0·0217), left ventricular end-systolic diameter -1·8 mm (-2·9 to -0·6, p=0·0027), left ventricular end-diastolic diameter -1·3 mm, (-2·3 to 0·3, p=0·0128), heart rate -3·0 beats per min (-5·1 to -0·8, p=0·0070), and N-terminal pro B-type natriuretic peptide concentration in plasma -970 pg/mL (-1672 to -268, p=0·0069). The frequency of adverse clinical events did not differ between groups.

INTERPRETATION

Omecamtiv mecarbil dosing guided by pharmacokinetics achieved plasma concentrations associated with improved cardiac function and decreased ventricular diameter.

FUNDING

Amgen.

The myosin activator omecamtiv mecarbil: a promising new inotropic agent

Heart failure became a leading cause of mortality in the past few decades with a progressively increasing prevalence. Its current therapy is restricted largely to the suppression of the sympathetic activity and the renin-angiotensin system in combination with diuretics. This restrictive strategy is due to the potential long-term adverse effects of inotropic agents despite their effective influence on cardiac function when employed for short durations. Positive inotropes include inhibitors of the Na⁺/K⁺ pump, β-receptor agonists, and phosphodiesterase inhibitors. Theoretically, Ca²⁺ sensitizers may also increase cardiac contractility without resulting in Ca²⁺ overload; nevertheless, their mechanism of action is frequently complicated by other pleiotropic effects. Recently, a new positive inotropic agent, the myosin activator omecamtiv mecarbil, has been developed. Omecamtiv mecarbil binds directly to β-myosin heavy chain and enhances cardiac contractility by increasing the number of the active force-generating cross-bridges, presumably without major off-target effects. This review focuses on recent in vivo and in vitro results obtained with omecamtiv mecarbil, and discusses its mechanism of action at a molecular level. Based on clinical data, omecamtiv mecarbil is a promising new tool in the treatment of systolic heart failure.