Small-molecule inhibition of glycogen synthase 1 for the treatment of Pompe disease and other glycogen storage disorders.

Glycogen synthase 1 (GYS1), the rate-limiting enzyme in muscle glycogen synthesis, plays a central role in energy homeostasis and has been proposed as a therapeutic target in multiple glycogen storage diseases. Despite decades of investigation, there are no known potent, selective small-molecule inhibitors of this enzyme. Here, we report the preclinical characterization of MZ-101, a small molecule that potently inhibits GYS1 in vitro and in vivo without inhibiting GYS2, a related isoform essential for synthesizing liver glycogen. Chronic treatment with MZ-101 depleted muscle glycogen and was well tolerated in mice. Pompe disease, a glycogen storage disease caused by mutations in acid α glucosidase (GAA), results in pathological accumulation of glycogen and consequent autophagolysosomal abnormalities, metabolic dysregulation, and muscle atrophy. Enzyme replacement therapy (ERT) with recombinant GAA is the only approved treatment for Pompe disease, but it requires frequent infusions, and efficacy is limited by suboptimal skeletal muscle distribution. In a mouse model of Pompe disease, chronic oral administration of MZ-101 alone reduced glycogen buildup in skeletal muscle with comparable efficacy to ERT. In addition, treatment with MZ-101 in combination with ERT had an additive effect and could normalize muscle glycogen concentrations. Biochemical, metabolomic, and transcriptomic analyses of muscle tissue demonstrated that lowering of glycogen concentrations with MZ-101, alone or in combination with ERT, corrected the cellular pathology in this mouse model. These data suggest that substrate reduction therapy with GYS1 inhibition may be a promising therapeutic approach for Pompe disease and other glycogen storage diseases.

The structural mechanism of human glycogen synthesis by the GYS1-GYG1 complex.

Glycogen is the primary energy reserve in mammals, and dysregulation of glycogen metabolism can result in glycogen storage diseases (GSDs). In muscle, glycogen synthesis is initiated by the enzymes glycogenin-1 (GYG1), which seeds the molecule by autoglucosylation, and glycogen synthase-1 (GYS1), which extends the glycogen chain. Although both enzymes are required for proper glycogen production, the nature of their interaction has been enigmatic. Here, we present the human GYS1:GYG1 complex in multiple conformations representing different functional states. We observe an asymmetric conformation of GYS1 that exposes an interface for close GYG1 association, and propose this state facilitates handoff of the GYG1-associated glycogen chain to a GYS1 subunit for elongation. Full activation of GYS1 widens the GYG1-binding groove, enabling GYG1 release concomitant with glycogen chain growth. This structural mechanism connecting chain nucleation and extension explains the apparent stepwise nature of glycogen synthesis and suggests distinct states to target for GSD-modifying therapeutics.

Discovery of Reldesemtiv, a Fast Skeletal Muscle Troponin Activator for the Treatment of Impaired Muscle Function.

The discovery of reldesemtiv, a second-generation fast skeletal muscle troponin activator (FSTA) that increases force production at submaximal stimulation frequencies, is reported. Property-based optimization of high throughput screening hit 1 led to compounds with improved free exposure and in vivo muscle activation potency compared to the first-generation FSTA, tirasemtiv. Reldesemtiv demonstrated increased muscle force generation in a phase 1 clinical trial and is currently being evaluated in clinical trials for the treatment of amyotrophic lateral sclerosis.

Dual inhibition of αvß6 and αvß1 reduces fibrogenesis in lung tissue explants from patients with IPF.

RATIONALE: αv integrins, key regulators of transforming growth factor-ß activation and fibrogenesis in in vivo models of pulmonary fibrosis, are expressed on abnormal epithelial cells (αvß6) and fibroblasts (αvß1) in fibrotic lungs. OBJECTIVES: We evaluated multiple αv integrin inhibition strategies to assess which most effectively reduced fibrogenesis in explanted lung tissue from patients with idiopathic pulmonary fibrosis. METHODS: Selective αvß6 and αvß1, dual αvß6/αvß1, and multi-αv integrin inhibitors were characterized for potency, selectivity, and functional activity by ligand binding, cell adhesion, and transforming growth factor-ß cell activation assays. Precision-cut lung slices generated from lung explants from patients with idiopathic pulmonary fibrosis or bleomycin-challenged mouse lungs were treated with integrin inhibitors or standard-of-care drugs (nintedanib or pirfenidone) and analyzed for changes in fibrotic gene expression or TGF-ß signaling. Bleomycin-challenged mice treated with dual αvß6/αvß1 integrin inhibitor, PLN-74809, were assessed for changes in pulmonary collagen deposition and Smad3 phosphorylation. MEASUREMENTS AND MAIN RESULTS: Inhibition of integrins αvß6 and αvß1 was additive in reducing type I collagen gene expression in explanted lung tissue slices from patients with idiopathic pulmonary fibrosis. These data were replicated in fibrotic mouse lung tissue, with no added benefit observed from inhibition of additional αv integrins. Antifibrotic efficacy of dual αvß6/αvß1 integrin inhibitor PLN-74809 was confirmed in vivo, where dose-dependent inhibition of pulmonary Smad3 phosphorylation and collagen deposition was observed. PLN-74809 also, more potently, reduced collagen gene expression in fibrotic human and mouse lung slices than clinically relevant concentrations of nintedanib or pirfenidone. CONCLUSIONS: In the fibrotic lung, dual inhibition of integrins αvß6 and αvß1 offers the optimal approach for blocking fibrogenesis resulting from integrin-mediated activation of transforming growth factor-ß.

Discovery of Tirasemtiv, the First Direct Fast Skeletal Muscle Troponin Activator.

The identification and optimization of the first activators of fast skeletal muscle are reported. Compound 1 was identified from high-throughput screening (HTS) and subsequently found to improve muscle function via interaction with the troponin complex. Optimization of 1 for potency, metabolic stability, and physical properties led to the discovery of tirasemtiv (25), which has been extensively characterized in clinical trials for the treatment of amyotrophic lateral sclerosis.

Fast skeletal muscle troponin activator tirasemtiv increases muscle function and performance in the B6SJL-SOD1G93A ALS mouse model.

Amyotrophic Lateral Sclerosis (ALS) is a motor neuron disease characterized by progressive motor neuron loss resulting in muscle atrophy, declining muscle function, and eventual paralysis. Patients typically die from respiratory failure 3 to 5 years from the onset of symptoms. Tirasemtiv is a fast skeletal troponin activator that sensitizes the sarcomere to calcium; this mechanism of action amplifies the response of muscle to neuromuscular input producing greater force when nerve input is reduced. Here, we demonstrate that a single dose of tirasemtiv significantly increases submaximal isometric force, forelimb grip strength, grid hang time, and rotarod performance in a female transgenic mouse model (B6SJL-SOD1 G93A) of ALS with functional deficits. Additionally, diaphragm force and tidal volume are significantly higher in tirasemtiv-treated female B6SJL-SOD1 G93A mice. These results support the potential of fast skeletal troponin activators to improve muscle function in neuromuscular diseases.

Tirasemtiv amplifies skeletal muscle response to nerve activation in humans.

INTRODUCTION: In this study we tested the hypothesis that tirasemtiv, a selective fast skeletal muscle troponin activator that sensitizes the sarcomere to calcium, could amplify the response of muscle to neuromuscular input in humans. METHODS: Healthy men received tirasemtiv and placebo in a randomized, double-blind, 4-period, crossover design. The deep fibular nerve was stimulated transcutaneously to activate the tibialis anterior muscle and produce dorsiflexion of the foot. The force-frequency relationship of tibialis anterior dorsiflexion was assessed after dosing. RESULTS: Tirasemtiv increased force produced by the tibialis anterior in a dose-, concentration-, and frequency-dependent manner with the largest increases [up to 24.5% (SE 3.1), P < 0.0001] produced at subtetanic nerve stimulation frequencies (10 Hz). CONCLUSIONS: The data confirm that tirasemtiv amplifies the response of skeletal muscle to nerve input in humans. This outcome provides support for further studies of tirasemtiv as a potential therapy in conditions marked by diminished neuromuscular input.

Smooth muscle myosin inhibition: a novel therapeutic approach for pulmonary hypertension.

OBJECTIVE: Pulmonary hypertension remains a major clinical problem despite current therapies. In this study, we examine for the first time a novel pharmacological target, smooth muscle myosin, and determine if the smooth muscle myosin inhibitor, CK-2019165 (CK-165) ameliorates pulmonary hypertension. MATERIALS AND METHODS: Six domestic female pigs were surgically instrumented to measure pulmonary blood flow and systemic and pulmonary vascular dynamics. Pulmonary hypertension was induced by hypoxia, or infusion of the thromboxane analog (U-46619, 0.1 µg/kg/min, i.v.). In rats, chronic pulmonary hypertension was induced by monocrotaline. RESULTS: CK-165 (4 mg/kg, i.v.) reduced pulmonary vascular resistance by 22±3 and 28±6% from baseline in hypoxia and thromboxane pig models, respectively (p<0.01 and 0.01), while mean arterial pressure also fell and heart rate rose slightly. When CK-165 was delivered via inhalation in the hypoxia model, pulmonary vascular resistance fell by 17±6% (p<0.05) while mean arterial pressure and heart rate were unchanged. In the monocrotaline model of chronic pulmonary hypertension, inhaled CK-165 resulted in a similar (18.0±3.8%) reduction in right ventricular systolic pressure as compared with sildenafil (20.3±4.5%). CONCLUSION: Inhibition of smooth muscle myosin may be a novel therapeutic target for treatment of pulmonary hypertension.

Activation of fast skeletal muscle troponin as a potential therapeutic approach for treating neuromuscular diseases.

Limited neural input results in muscle weakness in neuromuscular disease because of a reduction in the density of muscle innervation, the rate of neuromuscular junction activation or the efficiency of synaptic transmission. We developed a small-molecule fast-skeletal-troponin activator, CK-2017357, as a means to increase muscle strength by amplifying the response of muscle when neural input is otherwise diminished secondary to neuromuscular disease. Binding selectively to the fast-skeletal-troponin complex, CK-2017357 slows the rate of calcium release from troponin C and sensitizes muscle to calcium. As a consequence, the force-calcium relationship of muscle fibers shifts leftwards, as does the force-frequency relationship of a nerve-muscle pair, so that CK-2017357 increases the production of muscle force in situ at sub-maximal nerve stimulation rates. Notably, we show that sensitization of the fast-skeletal-troponin complex to calcium improves muscle force and grip strength immediately after administration of single doses of CK-2017357 in a model of the neuromuscular disease myasthenia gravis. Troponin activation may provide a new therapeutic approach to improve physical activity in diseases where neuromuscular function is compromised.

Inhibition of smooth muscle myosin as a novel therapeutic target for hypertension.

We examined a novel therapeutic approach for hypertension, a small-molecule direct inhibitor of smooth muscle myosin, CK-2018448 (CK-448), which is an N,N'-alkylurea (U.S. Patent Publication 2009-0275537 A1) in conscious dogs with renal hypertension and compared its efficacy with that of a calcium channel blocker, amlodipine. Dogs were instrumented with a miniature left ventricular pressure gauge, an aortic pressure catheter, and ultrasonic flow probes in the ascending aorta and renal and iliac arteries for measurement of cardiac output and regional blood flow. In the hypertensive state, mean arterial pressure increased from 101 ± 3.8 to 142 ± 1.9 mm Hg. At the doses selected, CK-448 and amlodipine increased cardiac output similarly (30 ± 11% versus 33 ± 6.4%) and similarly reduced mean arterial pressure (-22 ± 3.6% versus -16 ± 3.4%) and total peripheral resistance (-36 ± 5.9% versus -37 ± 5.8%). CK-448 had the greatest vasodilator effect in the renal bed, where renal blood flow increased by 46 ± 9.0%, versus 11 ± 3.4% for amlodipine (p < 0.01). CK-488 produced significantly less vasodilation in the limb, where iliac blood flow did not change; in contrast, it rose by 48 ± 12% with amlodipine (p < 0.01). The minimal effects on limb blood flow could limit the development of peripheral edema, an adverse side effect of Ca(2+) channel blockers. In addition, in a rodent model of hypertension, oral administration of a smooth muscle myosin inhibitor resulted in a sustained antihypertensive effect. Thus, the smooth muscle myosin inhibitor's preferential effect on renal blood flow makes this drug mechanism particularly appealing, because many patients with hypertension have renal insufficiency, and patients with heart failure could benefit from afterload reduction coupled with enhanced renal blood flow.

Cardiac myosin activation: a potential therapeutic approach for systolic heart failure.

Decreased cardiac contractility is a central feature of systolic heart failure. Existing drugs increase cardiac contractility indirectly through signaling cascades but are limited by their mechanism-related adverse effects. To avoid these limitations, we previously developed omecamtiv mecarbil, a small-molecule, direct activator of cardiac myosin. Here, we show that it binds to the myosin catalytic domain and operates by an allosteric mechanism to increase the transition rate of myosin into the strongly actin-bound force-generating state. Paradoxically, it inhibits adenosine 5'-triphosphate turnover in the absence of actin, which suggests that it stabilizes an actin-bound conformation of myosin. In animal models, omecamtiv mecarbil increases cardiac function by increasing the duration of ejection without changing the rates of contraction. Cardiac myosin activation may provide a new therapeutic approach for systolic heart failure.

Improvement of cardiac function by a cardiac Myosin activator in conscious dogs with systolic heart failure.

BACKGROUND: Therapy for chronic systolic heart failure (sHF) has improved over the past 2 decades, but the armamentarium of drugs is limited and consequently sHF remains a leading cause of death and disability. In this investigation, we examined the effects of a novel cardiac myosin activator, omecamtiv mecarbil (formerly CK-1827452) in 2 different models of heart failure. METHODS AND RESULTS: Two different models of sHF were used: (1) pacing-induced sHF after myocardial infarction (MI-sHF) and (2) pacing-induced sHF after 1 year of chronic pressure overload left ventricular hypertrophy (LVH-sHF). Omecamtiv mecarbil increased systolic function in sHF dogs, chronically instrumented to measure LV pressure, wall thickness, and cardiac output. Omecamtiv mecarbil, infused for 24 hours, induced a sustained increase without desensitization (P<0.05) in wall thickening (25+/-6.2%), stroke volume (44+/-6.5%) and cardiac output (22+/-2.8%), and decreased heart rate (15+/-3.0%). The major differences between the effect of omecamtiv mecarbil on cardiac function and the effect induced by a catecholamine, for example, dobutamine, is that omecamtiv mecarbil did not increase LV dP/dt but rather increased LV systolic ejection time by 26+/-2.9% in sHF. Another key difference is that myocardial O(2) consumption (MVO(2)), which increases with catecholamines, was not significantly affected by omecamtiv mecarbil. CONCLUSIONS: These results demonstrate that chronic infusion of the cardiac myosin activator, omecamtiv mecarbil, improves LV function in sHF without the limitations of progressive desensitization and increased MVO(2.) This unique profile may provide a new therapeutic approach for patients with sHF.

Antitumor activity of an allosteric inhibitor of centromere-associated protein-E.

Centromere-associated protein-E (CENP-E) is a kinetochore-associated mitotic kinesin that is thought to function as the key receptor responsible for mitotic checkpoint signal transduction after interaction with spindle microtubules. We have identified GSK923295, an allosteric inhibitor of CENP-E kinesin motor ATPase activity, and mapped the inhibitor binding site to a region similar to that bound by loop-5 inhibitors of the kinesin KSP/Eg5. Unlike these KSP inhibitors, which block release of ADP and destabilize motor-microtubule interaction, GSK923295 inhibited release of inorganic phosphate and stabilized CENP-E motor domain interaction with microtubules. Inhibition of CENP-E motor activity in cultured cells and tumor xenografts caused failure of metaphase chromosome alignment and induced mitotic arrest, indicating that tight binding of CENP-E to microtubules is insufficient to satisfy the mitotic checkpoint. Consistent with genetic studies in mice suggesting that decreased CENP-E function can have a tumor-suppressive effect, inhibition of CENP-E induced tumor cell apoptosis and tumor regression.

Discovery of the First Potent and Selective Inhibitor of Centromere-Associated Protein E: GSK923295.

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.

Discovery of omecamtiv mecarbil the first, selective, small molecule activator of cardiac Myosin.

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.

Effective killing of the human pathogen Candida albicans by a specific inhibitor of non-essential mitotic kinesin Kip1p.

Kinesins from the bipolar (Kinesin-5) family are conserved in eukaryotic organisms and play critical roles during the earliest stages of mitosis to mediate spindle pole body separation and formation of a bipolar mitotic spindle. To date, genes encoding bipolar kinesins have been reported to be essential in all organisms studied. We report the characterization of CaKip1p, the sole member of this family in the human pathogenic yeast Candida albicans. C. albicans Kip1p appears to localize to the mitotic spindle and loss of CaKip1p function interferes with normal progression through mitosis. Inducible excision of CaKIP1 revealed phenotypes unique to C. albicans, including viable homozygous Cakip1 mutants and an aberrant spindle morphology in which multiple spindle poles accumulate in close proximity to each other. Expression of the C. albicans Kip1 motor domain in Escherichia coli produced a protein with microtubule-stimulated ATPase activity that was inhibited by an aminobenzothiazole (ABT) compound in an ATP-competitive fashion. This inhibition results in 'rigor-like', tight association with microtubules in vitro. Upon treatment of C. albicans cells with the ABT compound, cells were killed, and terminal phenotype analysis revealed an aberrant spindle morphology similar to that induced by loss of the CaKIP1 gene. The ABT compound discovered is the first example of a fungal spindle inhibitor targeted to a mitotic kinesin. Our results also show that the non-essential nature and implementation of the bipolar motor in C. albicans differs from that seen in other organisms, and suggest that inhibitors of a non-essential mitotic kinesin may offer promise as cidal agents for antifungal drug discovery.