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Introduction: Heart failure with preserved ejection fraction (HFpEF) is characterized by underlying contractile dysfunction and progressive myocardial fibrosis and stiffness. CK-3772271 (CK-271) is a novel small molecule cardiac myosin inhibitor that reduces cardiac myosin ATPase activity and reduces cardiac contractility in unloaded isolated cardiomyocytes in vitro and in healthy rats and dogs in vivo . The effect of chronic CK-271 treatment on cardiac function and morphology was evaluated in the Dahl/Salt Sensitive (DSS) rat hypertension model of HFpEF. Methods: DSS male rats were fed either a control low salt (LS, 0.3% NaCl) or high salt (HS, 4% NaCl) diet to induce a hypertension-driven HFpEF disease phenotype. 6 weeks after HS diet treatment, DSS rats were randomized into two sub-groups: continued HS diet or a HS diet formulated with CK-271 (100 ppm) for an additional 6 weeks. Body mass, systolic blood pressure, and cardiac function were measured longitudinally. After 12 weeks of HS treatment, hearts were collected to assess cardiac fibrosis. Results: HS diet treatment increased systolic blood pressure (LS:132.2 ± 4.7 mm Hg vs. HS: 163.5 ± 4.0 mm Hg, mean ± SEM, p< 0.001) and caused cardiac hypercontractility as evidenced by an increase in the end-systolic pressure-volume relationship (LS: 0.8 ± 0.17 vs. HS: 2.1 ± 0.46 mm Hg/ml). HS diet also increased isovolumic relaxation time (IVRT) (LS: 16.8 ± 0.6 vs. HS: 22.8 ± 0.6 ms, p2 , p2 , p Conclusion: The small molecule cardiac myosin inhibitor, CK-3772271, attenuated the development of cardiac hypercontractility, diastolic dysfunction and fibrosis in the DSS rat model of HFpEF. Cardiac myosin inhibition may be a novel approach to mitigate the development of HFpEF.

Introduction: Hypertrophic cardiomyopathy (HCM) is characterized by left ventricular (LV) hypertrophy in the absence of known causes. HCM can be due to genetic mutations that affect sarcomeric proteins, leading to myocardial hypercontractility. HCM is often complicated by left ventricular outflow tract obstruction (LVOTO) and patients may be at greater risk of cardiovascular death. Medications targeted to address the pathophysiology of HCM and ameliorate LVOTO are needed. CK-3773274 (CK-274) is a novel small molecule cardiac myosin inhibitor that reduces myocardial contractility in vitro and in vivo . Cats have naturally occurring HCM commonly complicated by LVOTO and are an excellent large animal model for investigation of HCM therapeutics. In this study, we aim to characterize the pharmacodynamic effect of a single oral dose of CK-274 on cardiac function in cats with hypertrophic cardiomyopathy and LVOTO. Methods: Eight purpose-bred cats with naturally occurring HCM and LVOTO due to the A31P mutation in cardiac myosin binding protein C (cMyBP-C) were included in a randomized, controlled, crossover study. Cats were randomized to receive vehicle, 0.3 mg/kg, or 1 mg/kg CK-274 treatment, and received echocardiograms at baseline, 6, 24, and 48 hours post-treatment. All cats were crossed over to all treatment groups. Results: CK-274 (1 mg/kg) reduced mean LV fractional shortening at 6, 24 and 48 hours post-treatment (mean reduction 13.6%, p=0.03; 15.4%, p=0.01; 11.6% p=0.02, respectively). CK-274 (1 mg/kg) increased LV systolic internal dimension at 6 and 24-hours post-treatment (mean increase 0.21 cm, p=0.046; 0.25 cm, p=0.03), and did not affect LV diastolic internal dimension. LVOT peak pressure gradient was reduced with CK-274 (0.3 mg/kg) treatment [median pressure gradient at baseline 27.1 mmHg (IQR 18.3-33.3) vs 24 hours post-drug, 7.3 mmHg (IQR 14.2-19.7) p=0.01]. Heart rate did not change for any treatment group over time. No differences were noted following vehicle administration at any time point. Conclusion: In HCM affected cats with the cMyBP-C A31P mutation, the cardiac myosin inhibitor CK-274 is well tolerated at the studied doses and caused dose-related changes in LV systolic function and reductions in LVOT peak pressure gradient.

Cardiac sarcomere hypercontractility appears to underlie pathological hypertrophy and fibrosis in select genetic hypertrophic cardiomyopathies. The small molecule, CK-3773274, is a novel cardiac myosin inhibitor that decreases contractility in vitro and in healthy animals in vivo . The objective of this study was to evaluate the effect of CK-3773274 in the genetic R403Q mouse model of hypertrophic cardiomyopathy. At approximately 40 weeks of age, left ventricular wall dimensions were determined by echocardiography in male wild type (WT) and heterozygous R403Q mice. As an indicator of cardiac hypertrophy, R403Q mice had significantly greater septal and posterior wall thickness than WT mice (septal wall WT: 0.93 ± 0.03 mm vs. R403Q: 1.22 ± 0.08 mm; posterior wall WT: 0.84 ± 0.04 mm vs. R403Q: 1.09 ± 0.04 mm; mean ± SEM, p< 0.05). R403Q mice were treated with single oral doses of CK-3773274 ranging from 0.25 to 1.5 mg/kg and fractional shortening (FS) and heart rate were assessed at select time points over a 24-hour period. One hour after dose administration, CK-3773274 significantly reduced FS in a dose-related fashion relative to pre-dose baseline values (FS % R403Q baseline: 55.5 ± 2%; 0.25 mg/kg: 43.9 ± 2%; 1 mg/kg: : 27.3 ± 2%; 1.5 mg/kg: 13.7 ± 1%; mean ±SEM, p10 and IC 50 ) was 0.11 and 0.78 μM, respectively. In summary, single oral dose administration of CK-3773274 reduced fractional shortening in a dose and concentration-dependent manner in the genetic R403Q mouse model of hypertrophic cardiomyopathy. Cardiac myosin inhibition may be a viable approach to reduce underlying hypercontractility of the cardiac sarcomere in hypertrophic cardiomyopathies.

Hypercontractility of the cardiac sarcomere appears to underlie pathological hypertrophy and fibrosis in select genetic hypertrophic cardiomyopathies. Here, we characterize the small molecule, CK-3773274, as a novel cardiac myosin inhibitor that decreases contractility in vitro and in vivo . In bovine cardiac myofibrils, CK-3773274 decreased myosin ATPase activity in a concentration-dependent fashion (IC 50 :1.26 μM). CK-3773274 specifically inhibited myosin activity, as it reduced myosin ATPase activity in a concentration-dependent manner in the absence of other sarcomere proteins, including actin, troponin, and tropomyosin. CK-3773274 (10 μM) reduced fractional shortening by 84% in electrically paced, isolated adult rat cardiomyocytes relative to control without any effect on the calcium transient. The effect of CK-3773274 on cardiac contractility in vivo was assessed in healthy male Sprague Dawley (SD) rats using single oral doses ranging from 0.5 to 4 mg/kg. Fractional shortening (FS) and left ventricular dimensions were determined by echocardiography at select time points over a 24-hour period. One hour after dose administration, CK-3773274 significantly reduced fractional shortening in a dose-related fashion by 20-70% relative to vehicle treatment (FS %: vehicle: 47.9± 1%; 0.5 mg/kg: 39 ± 2%; 4 mg/kg: 15 ± 4%; mean ±SEM, pin vitro and in vivo . Cardiac myosin inhibition may be a viable approach to treat the underlying hypercontractility of the cardiac sarcomere in hypertrophic cardiomyopathies.

We report the design, synthesis, and optimization of the first, selective activators of cardiac myosin. Starting with a poorly soluble, nitro-aromatic hit compound (1), potent, selective, and soluble myosin activators were designed culminating in the discovery of omecamtiv mecarbil (24). Compound 24 is currently in clinical trials for the treatment of systolic heart failure.

Decreased cardiac contractility is a central feature of systolic heart failure and yet we have no effective drugs to improve cardiac contractility. Existing drugs that increase cardiac contractility do so indirectly through signaling cascades and their use is limited by their mechanism-related adverse effects. Direct activation of the cardiac sarcomere to increase cardiac contractility may provide a means to avoid these limitations. Using a reconstituted version of the cardiac sarcomere, we screened a small molecule library and identified several chemical classes that directly activate cardiac myosin. One compound class has been optimized extensively using an iterative process; omecamtiv mecarbil, a small-molecule, selective, cardiac myosin activator is the most advanced exemplar of this novel mechanistic class. It accelerates the transition of myosin into the force-generating state without affecting cardiac myocyte calcium homeostasis. In animal models, omecamtiv mecarbil increases cardiac function by increasing the duration of ejection without changing the rates of contraction. Initial clinical studies have demonstrated the translation of this mechanism into humans, and further clinical studies of its use in acute and chronic heart failure are planned. Cardiac myosin activation may provide a new therapeutic approach for systolic heart failure. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure."

Inhibition of mitotic kinesins represents a novel approach for the discovery of a new generation of anti-mitotic cancer chemotherapeutics. We report here the discovery of the first potent and selective inhibitor of centromere-associated protein E (CENP-E) 3-chloro-N-{(1S)-2-[(N,N-dimethylglycyl)amino]-1-[(4-{8-[(1S)-1-hydroxyethyl]imidazo[1,2-a]pyridin-2-yl}phenyl)methyl]ethyl}-4-[(1-methylethyl)oxy]benzamide (GSK923295; 1), starting from a high-throughput screening hit, 3-chloro-4-isopropoxybenzoic acid 2. Compound 1 has demonstrated broad antitumor activity in vivo and is currently in human clinical trials.

CK-1909178 is a member of a class of fast skeletal troponin activators that sensitize skinned skeletal muscle fibers to calcium. In rat muscle preparations in vitro and in situ, CK-1909178 increased sub-tetanic force without altering maximum force. Given that a major cause of muscle fatigue during repeated muscle contraction is reduced myoplasmic Ca2+ due to impaired sarcoplasmic reticulum Ca2+ release, we tested whether increased calcium sensitivity with CK-1909178 would slow the development of fatigue. Rat flexor digitorum brevis muscle was pretreated in vitro with CK-1909178 and stimulated every 3 seconds at a frequency sufficient to achieve 50% of maximum force for 6 min at 30°C. CK-1909178 diminished the extent of fatigue as compared to control (terminal force 29.5±8% vs. 12.7±4%, p