Tirasemtiv (CK-2017357, CAS 1005491-05-3) Fast Skeletal Muscle Troponin Activator | FSTA for ALS & Neuromuscular Research

Tirasemtiv CAS 1005491-05-3
Fast Skeletal Muscle Troponin Activator (FSTA)

Tirasemtiv (CK-2017357, CK-357) is the first-in-class fast skeletal muscle troponin activator - a calcium sensitizer that binds the fast skeletal troponin complex (Kd ≈ 40 nM) and slows calcium release from troponin C. The result is amplified force generation at submaximal calcium concentrations, so muscle produces more force for the same neural input. This mechanism made tirasemtiv a landmark research tool for amyotrophic lateral sclerosis (ALS), myasthenia gravis, sarcopenia and other neuromuscular conditions where motor neuron drive to muscle is compromised.

FSTA Troponin Activator Calcium Sensitizer ALS Research Myasthenia Gravis Sarcopenia Muscle Force Click Chemistry Alkyne

Request a Quote Technical Specs

230.27

MW (C12H14N4O)

≥98%

Purity (HPLC)

40 nM

Kd, fast skeletal troponin

Molecular Information

Name: Tirasemtiv
CAS: 1005491-05-3
Formula: C12H14N4O
MW: 230.27 g/mol
SMILES: O=C1N(C(CC)CC)C2=NC(C#C)
=CN=C2N1
InChIKey: RSQGZEAXODVTOL
-UHFFFAOYSA-N
Purity: ≥98% (HPLC)
Appearance: White to off-white powder
Solubility: DMSO (≥30 mg/mL); ethanol
Synonyms: CK-2017357 / CK-357 /
Troponin Activator
Storage: -20°C, sealed, dry, dark

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CAS Number

1005491-05-3

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Molecular Weight

230.27

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Primary Activity

Fast Troponin Activator

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Purity

≥98%

Tirasemtiv Technical Specifications & Quality Control Parameters

Complete physicochemical properties and QC release data for research-grade tirasemtiv (CK-2017357, CAS 1005491-05-3)

📋 Physicochemical Properties

Product NameTirasemtiv
IUPAC Name6-Ethynyl-1-(pentan-3-yl)-1,3-dihydro-2H-imidazo[4,5-b]pyrazin-2-one
Alternative Name1-(1-Ethylpropyl)-6-ethynyl-1,3-dihydro-2H-imidazo[4,5-b]pyrazin-2-one
CAS Number1005491-05-3
Code NamesCK-2017357 / CK-357
Molecular FormulaC12H14N4O
Molecular Weight230.27 g/mol
SMILESO=C1N(C(CC)CC)C2=NC(C#C)=CN=C2N1
InChI1S/C12H14N4O/c1-4-8-7-13-10-11(14-8)16(12(17)15-10)9(5-2)6-3/h1,7,9H,5-6H2,2-3H3,(H,13,15,17)
InChIKeyRSQGZEAXODVTOL-UHFFFAOYSA-N
AppearanceWhite to off-white (to grey) crystalline powder
UV lambda-max258 nm, 330 nm
Chemical ClassImidazo[4,5-b]pyrazin-2-one; terminal alkyne
OriginatorCytokinetics (partnered with Astellas)

🔬 Quality Control & Handling

Purity (HPLC)≥98%
FormCrystalline powder
Identity1H-NMR / 13C-NMR / LC-MS conforming
Water Content (KF)≤0.5%
Residual SolventsMeets ICH Q3C limits
Storage Condition-20°C, sealed, protect from light and moisture
Solution Storage-80°C 2 years / -20°C 1 year in DMSO
SolubilityDMSO ≥30 mg/mL (up to ~46 mg/mL); ethanol ~30-46 mg/mL; DMF 30 mg/mL; water insoluble
In Vivo Vehicle10% DMSO / 40% PEG300 / 5% Tween-80 / 45% saline
QC DocumentationCOA / HPLC / NMR / MS / MSDS
Pack Sizes1g / 5g / 10g / 100g / 1KG
Stock StatusIn Stock
Use StatementResearch use only; not for human or veterinary use

Molecular Target: The Fast Skeletal Muscle Troponin Complex

Tirasemtiv is remarkably selective for the fast (type II) skeletal troponin complex, sparing slow skeletal and cardiac muscle - the basis of its clean pharmacological profile in muscle biology research

🦼 Fast Skeletal Troponin C (TNNC2) 🧠 Fast Skeletal Troponin Complex (Kd ≈ 40 nM) 🪕 Fast Skeletal Troponin I (TNNI2) 🧩 Fast Skeletal Troponin T (TNNT3) 🔵 Slow Skeletal Troponin (Kd ≈ 3,800 nM, weak) ❌ Cardiac Troponin (no activation) ⚡ Myofibrillar ATPase (EC50 ≈ 390 nM) 🎯 Sarcomere Calcium Sensitivity

How Tirasemtiv Works: Calcium Sensitization of the Sarcomere

Rather than increasing neural drive or calcium release, tirasemtiv makes the existing calcium signal work harder - a fundamentally different therapeutic strategy for neuromuscular weakness

1. Selective Binding to Fast Troponin

Tirasemtiv binds the purified fast skeletal troponin complex with a Kd of approximately 40 nM, versus roughly 3,800 nM for slow skeletal troponin, and does not activate cardiac troponin. This ~100-fold selectivity means the compound acts on type II (fast-twitch) fibres - exactly those preferentially lost in ALS, sarcopenia and disuse atrophy - without cardiac inotropic effects.

2. Slowed Calcium Dissociation

Binding to the troponin C-troponin I interface stabilises the calcium-bound conformation of troponin C and slows the rate of Ca2+ release from the regulatory complex. Calcium therefore remains bound longer during each twitch, prolonging the window in which the thin filament is switched on.

3. Leftward Shift of the Force-Calcium Curve

In skinned human and rabbit fast skeletal fibres, tirasemtiv shifts the force-pCa relationship leftward in a concentration-dependent manner. Submaximal calcium concentrations - the physiological range during ordinary contraction - now generate substantially more force, while maximal force is unchanged.

4. Amplified Response to Neural Input

Because the sarcomere is more calcium-responsive, each motor neuron action potential produces greater muscle force. In neuromuscular disease where motor units are lost or transmission fails, the surviving neural input is effectively amplified - increased force and reduced fatigue without full tetanic activation.

5. Functional and Preclinical Readouts

Tirasemtiv increases in situ extensor digitorum longus (EDL) force and forelimb grip strength in a rat model of myasthenia gravis, and improves grip strength, grid-hang and rotarod performance in the B6SJL-SOD1(G93A) ALS mouse at 10 mg/kg (Hwee et al., PLoS One 2014). It also increases isolated myofibrillar ATPase activity with an EC50 of ~390 nM.

6. Translational Endpoints

In human studies tirasemtiv increased slow vital capacity (SVC) and muscle function measures in ALS. Dose-limiting dizziness and nausea attributable to central nervous system exposure limited tolerability, which directly motivated development of the next-generation FSTA reldesemtiv (CK-2127107) with reduced CNS penetration.

Research Applications of Tirasemtiv in Muscle and Neuromuscular Biology

A selective chemical probe for dissecting sarcomere calcium sensitivity, muscle force generation and fatigue across disease models

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Amyotrophic Lateral Sclerosis (ALS)

The flagship application. Tirasemtiv improves muscle function in the B6SJL-SOD1(G93A) ALS mouse model and increased slow vital capacity in human ALS trials (BENEFIT-ALS, VITALITY-ALS). It remains the reference FSTA for studying how sarcomere-level pharmacology can compensate for motor neuron loss.

ALS / Motor Neuron

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Myasthenia Gravis & NMJ Transmission

In rat models of myasthenia gravis, tirasemtiv increases in situ EDL force and forelimb grip strength by amplifying the reduced endplate signal reaching the muscle. A clinical single-dose crossover study in AChR-antibody-positive myasthenia gravis was reported by Sanders et al. (Neurotherapeutics 2015).

Neuromuscular Junction

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Sarcopenia & Age-Related Muscle Weakness

Fast-twitch type II fibres are preferentially lost with ageing, making the fast troponin complex a rational target. Tirasemtiv is used to test whether calcium sensitization can restore functional strength and mobility endpoints in aged and disuse-atrophy models.

Ageing Muscle

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Skeletal Muscle Physiology & Force Mechanics

Skinned-fibre force-pCa protocols, myofibrillar ATPase assays and single-twitch/tetanus analyses with tirasemtiv define how troponin C calcium affinity governs contractile output - a core tool in sarcomere biophysics.

Muscle Biophysics

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Muscle Fatigue & Exercise Performance

By increasing force at submaximal calcium, tirasemtiv delays the decline in force during repetitive stimulation. It is used to interrogate excitation-contraction coupling failure and central versus peripheral contributions to fatigue.

Fatigue Research

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Spinal Muscular Atrophy & Peripheral Neuropathy

Any condition in which neural drive to muscle is reduced is a candidate for FSTA pharmacology. Tirasemtiv is applied in SMA, Charcot-Marie-Tooth and post-polio model systems to test force amplification independent of neuronal rescue.

Neuromuscular Disease

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Respiratory Muscle Function

Diaphragm and accessory respiratory muscles are predominantly fast-twitch. Tirasemtiv is used in diaphragm strip preparations and ventilatory-endpoint studies, reflecting the slow-vital-capacity signal observed in human ALS studies.

Respiratory Muscle

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Click Chemistry & Chemical Probe Design

Tirasemtiv carries a terminal alkyne and can undergo copper-catalysed azide-alkyne cycloaddition (CuAAC), enabling construction of tagged troponin probes for target engagement, pull-down and imaging studies.

Chemical Biology

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Metabolite Identification & Doping Control

Human metabolites of tirasemtiv and reldesemtiv have been characterised for anti-doping screening (Drug Testing and Analysis 2025), making tirasemtiv a reference material for LC-MS/MS method development in sports drug testing laboratories.

Analytical Reference

Key Publications on Tirasemtiv and Fast Skeletal Troponin Activation

Foundational mechanism papers and clinical trial reports defining the fast skeletal muscle troponin activator (FSTA) class

Authors & Title	Journal	Year	DOI / PMID
Russell AJ, Hartman JJ, Hinken AC, et al. Activation of fast skeletal muscle troponin as a potential therapeutic approach for treating neuromuscular diseases.	Nature Medicine	2012	10.1038/nm.2618
Shefner J, Cedarbaum JM, Cudkowicz ME, et al. Safety, tolerability and pharmacodynamics of a skeletal muscle activator in amyotrophic lateral sclerosis.	Amyotrophic Lateral Sclerosis	2012	10.3109/17482968.2012.684214
Hwee DT, Kennedy A, Ryans J, et al. Fast skeletal muscle troponin activator tirasemtiv increases muscle function and performance in the B6SJL-SOD1(G93A) ALS mouse model.	PLoS ONE	2014	10.1371/journal.pone.0096921
Sanders DB, Rosenfeld J, Dimachkie MM, et al. A double-blinded, randomized, placebo-controlled trial to evaluate efficacy, safety, and tolerability of single doses of tirasemtiv in patients with acetylcholine receptor-binding antibody-positive myasthenia gravis.	Neurotherapeutics	2015	10.1007/s13311-015-0345-y
Shefner JM, Wolff AA, Meng L, et al. A randomized, placebo-controlled, double-blind phase IIb trial evaluating the safety and efficacy of tirasemtiv in patients with amyotrophic lateral sclerosis (BENEFIT-ALS).	Amyotrophic Lateral Sclerosis and Frontotemporal Degeneration	2016	10.3109/21678421.2016.1148169
Shefner JM, Cudkowicz ME, Hardiman O, et al. A phase III trial of tirasemtiv as a potential treatment for amyotrophic lateral sclerosis (VITALITY-ALS).	Amyotrophic Lateral Sclerosis and Frontotemporal Degeneration	2019	10.1080/21678421.2019.1612922

Available Pack Sizes & Ordering

Research-grade tirasemtiv (CK-2017357, CAS 1005491-05-3) with full QC documentation - from 1 g analytical packs to 1 KG industrial batches

Pack sizes: 1 g / 5 g / 10 g / 100 g / 1 KG

Tier	Pack Size	Stock Status	Suitable For	Shipping & Lead Time
Standard	1 g	In Stock	Skinned-fibre force-pCa assays, myofibrillar ATPase, in vitro troponin binding	Same/next-day dispatch, ambient with ice pack
Medium	5 g	In Stock	Rodent grip strength, rotarod and in situ EDL force studies	Same/next-day dispatch, ambient with ice pack
Large	10 g	In Stock	Multi-cohort SOD1(G93A) ALS mouse programmes, chronic dosing	Same/next-day dispatch, double-bagged foil pouch
Bulk	100 g	In Stock	Large-animal studies, formulation and toxicology package preparation	2-5 business days, drum/foil pack, quote to confirm
Industrial	1 KG	Made to order	Pilot/production scale supply, CDMO and contract manufacturing programmes	Batch delivery, quote to confirm lead time

💡 Reference sizes shown above; for exact pricing and availability please contact us for a quote. Bulk orders qualify for tiered discounts.

Frequently Asked Questions (FAQ)

Common questions about tirasemtiv mechanism, FSTA class comparisons, ALS data and laboratory handling

What is Tirasemtiv (CK-2017357, CAS 1005491-05-3)?

Tirasemtiv is the first-in-class fast skeletal muscle troponin activator (FSTA), a small molecule with the formula C12H14N4O and molecular weight 230.27 g/mol. Discovered by Cytokinetics, it binds the fast skeletal troponin complex with a Kd of about 40 nM and sensitizes the sarcomere to calcium, increasing the force muscle generates for a given level of neural activation. It has been studied extensively in amyotrophic lateral sclerosis (ALS) and myasthenia gravis.

How exactly does tirasemtiv activate troponin?

Tirasemtiv binds at the interface of fast skeletal troponin C (TNNC2) and troponin I within the regulatory troponin complex, stabilising the calcium-bound conformation and slowing the rate of Ca2+ dissociation. Because calcium stays bound longer, the thin filament remains switched on for more of each twitch cycle. The functional consequence is a leftward shift of the force-calcium relationship: at submaximal calcium the muscle produces significantly more force, while maximal force capacity is unchanged. It does not increase intracellular calcium or motor neuron firing - it changes how efficiently the existing signal is converted into force.

How does tirasemtiv compare with reldesemtiv (CK-2127107)?

Both are fast skeletal muscle troponin activators sharing the same molecular target. Tirasemtiv is the first-generation compound; in human trials its efficacy signal on slow vital capacity was accompanied by dose-limiting dizziness, nausea and fatigue attributable to central nervous system exposure, causing high discontinuation rates in VITALITY-ALS. Reldesemtiv is the next-generation FSTA engineered for lower CNS penetration and better tolerability, allowing higher effective muscle exposure. For laboratory work, tirasemtiv remains the reference compound with the deepest preclinical characterisation of the FSTA mechanism.

Why is tirasemtiv selective for fast-twitch muscle?

The troponin C isoform in fast (type II) skeletal fibres, TNNC2, differs structurally from slow skeletal/cardiac troponin C (TNNC1). Tirasemtiv exploits this difference: Kd is approximately 40 nM at the fast skeletal complex versus ~3,800 nM at the slow skeletal complex, and it does not activate cardiac troponin at all. This is pharmacologically important because it avoids cardiac inotropic effects, and biologically convenient because type II fibres are the ones preferentially lost in ALS, sarcopenia and disuse atrophy.

What happened in the tirasemtiv ALS clinical trials?

The Phase IIb BENEFIT-ALS trial (Shefner et al., 2016) missed its primary ALSFRS-R endpoint but showed a significant benefit on slow vital capacity (SVC) and muscle strength measures - the first human evidence that sarcomere-level pharmacology could improve function in ALS. The Phase III VITALITY-ALS trial (2019) again showed SVC benefit in patients who tolerated the drug, but tolerability-driven discontinuation limited the overall result and development was stopped. The mechanism was validated even though the molecule was not advanced.

Is tirasemtiv useful in myasthenia gravis research?

Yes. Because tirasemtiv amplifies the muscle's response to whatever neural signal arrives, it is mechanistically well suited to conditions of impaired neuromuscular junction transmission. In a rat myasthenia gravis model it increased in situ EDL force and forelimb grip strength, and a randomised double-blind single-dose crossover study in AChR-antibody-positive myasthenia gravis patients was reported by Sanders et al. (Neurotherapeutics 2015).

Can tirasemtiv be used as a click chemistry reagent?

Yes. Tirasemtiv contains a terminal alkyne on the imidazo[4,5-b]pyrazinone core and can undergo copper-catalysed azide-alkyne cycloaddition (CuAAC) with azide-bearing partners. This allows researchers to build fluorescent or biotinylated tirasemtiv conjugates for troponin target-engagement, affinity pull-down and imaging experiments - a useful secondary application of the same lot of material.

How should tirasemtiv be dissolved and stored?

Prepare stock solutions in DMSO, where solubility is typically 30-46 mg/mL (approximately 130-200 mM); ethanol and DMF also dissolve the compound at similar concentrations, while it is essentially insoluble in water. A widely used in vivo cascade is 10% DMSO / 40% PEG300 / 5% Tween-80 / 45% saline, or 10% DMSO / 90% 20% SBE-beta-CD in saline. Store the powder at -20°C sealed and dry; DMSO stocks are stable for about 2 years at -80°C or 1 year at -20°C. Aliquot to avoid freeze-thaw cycles.

What in vivo doses are typically used in ALS mouse models?

In the B6SJL-SOD1(G93A) ALS mouse, Hwee et al. (PLoS One 2014) used cumulative intra-arterial bolus dosing to 10 mg/kg to establish the dose-response for grip strength, grid-hang and rotarod performance. Oral suspension dosing in CMC-Na is also used for chronic studies. Doses should always be re-optimised for strain, route and endpoint; we supply material only, not dosing guidance for any human or veterinary application.

What documentation and pack sizes are available?

Every lot is released at ≥98% purity by HPLC and ships with a Certificate of Analysis (COA) including HPLC chromatogram, NMR and mass spectrometry confirmation. MSDS/SDS, residual solvent data and Certificates of Origin are supplied on request. Pack sizes are 1 g, 5 g, 10 g and 100 g in stock, with 1 KG made to order for scale-up programmes. Please contact us for a quote, lead times and bulk pricing.

Need Research-Grade Tirasemtiv for Your Muscle Biology Programme?

Tirasemtiv (CK-2017357, CAS 1005491-05-3) - fast skeletal troponin activator, C12H14N4O, MW 230.27, ≥98% HPLC with COA
Available in 1g / 5g / 10g / 100g / 1KG - request your quote today

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Weight	1 g