Structural Basis of <i>Tirasemtiv</i> Activation of Fast Skeletal Muscle

Li, Monica X.; Mercier, Pascal; Hartman, James J.; Sykes, Brian D.

doi:10.1021/acs.jmedchem.0c01412

Cited by 12 publications

(15 citation statements)

References 43 publications

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“…Increased force was also observed at resting calcium concentrations, along with increased myosin ATP consumption in cardiac myofibrils. The behaviour of RPI-194 is more in keeping with what was observed for fast skeletal troponin activator tirasemtiv, with a leftward pCa 50 but no significant change in force generated at low or saturating calcium concentrations ( Russell et al, 2012 ), which is not surprising given that they both target the same homologous binding pocket ( Li et al, 2021 ). It is possible that TA1 is able to activate the thin filament through cTnI/cTnT, independent of the calcium binding activity of cTnC, unlike RPI-194 and tirasemtiv.…”

Section: Discussionsupporting

confidence: 69%

“…Reldesemtiv is currently undergoing clinical trials for the treatment of spinal muscular atrophy ( Rudnicki et al, 2021 ). These fsTnC-targeting drugs bind to a hydrophobic cavity in fsTnC that lies beneath the binding site for the fsTnI switch region ( Li et al, 2021 ). In theory, it should be possible to develop a compound that targets the homologous binding cavity in cTnC/ssTnC, though it would likely be active for both cardiac and slow skeletal muscle.…”

Section: Introductionmentioning

confidence: 99%

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Small Molecule RPI-194 Stabilizes Activated Troponin to Increase the Calcium Sensitivity of Striated Muscle Contraction

et al. 2022

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Small molecule cardiac troponin activators could potentially enhance cardiac muscle contraction in the treatment of systolic heart failure. We designed a small molecule, RPI-194, to bind cardiac/slow skeletal muscle troponin (Cardiac muscle and slow skeletal muscle share a common isoform of the troponin C subunit.) Using solution NMR and stopped flow fluorescence spectroscopy, we determined that RPI-194 binds to cardiac troponin with a dissociation constant KD of 6–24 μM, stabilizing the activated complex between troponin C and the switch region of troponin I. The interaction between RPI-194 and troponin C is weak (KD 311 μM) in the absence of the switch region. RPI-194 acts as a calcium sensitizer, shifting the pCa50 of isometric contraction from 6.28 to 6.99 in mouse slow skeletal muscle fibers and from 5.68 to 5.96 in skinned cardiac trabeculae at 100 μM concentration. There is also some cross-reactivity with fast skeletal muscle fibers (pCa50 increases from 6.27 to 6.52). In the slack test performed on the same skinned skeletal muscle fibers, RPI-194 slowed the velocity of unloaded shortening at saturating calcium concentrations, suggesting that it slows the rate of actin-myosin cross-bridge cycling under these conditions. However, RPI-194 had no effect on the ATPase activity of purified actin-myosin. In isolated unloaded mouse cardiomyocytes, RPI-194 markedly decreased the velocity and amplitude of contractions. In contrast, cardiac function was preserved in mouse isolated perfused working hearts. In summary, the novel troponin activator RPI-194 acts as a calcium sensitizer in all striated muscle types. Surprisingly, it also slows the velocity of unloaded contraction, but the cause and significance of this is uncertain at this time. RPI-194 represents a new class of non-specific troponin activator that could potentially be used either to enhance cardiac muscle contractility in the setting of systolic heart failure or to enhance skeletal muscle contraction in neuromuscular disorders.

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Section: Discussionsupporting

confidence: 69%

Section: Introductionmentioning

confidence: 99%

Small Molecule RPI-194 Stabilizes Activated Troponin to Increase the Calcium Sensitivity of Striated Muscle Contraction

et al. 2022

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“…Protein expression and labeling were analogous to previously described protocols. 11 The linker portion was optimized on the basis of the ITC binding data for a SM test compound and the quality of the one-dimensional (1D) 1 H NMR spectra of the chimera:Ca 2+ :SM complex. The human cardiac TnC−TnI chimera consists of an N-terminal hexahistidine tag and TEV cleavage site (ENLYFQG) fused to the N-terminal domain of human cardiac TnC (GenBank accession number P63316, residues D2−G91) followed by an -AGAG linker and the human cardiac TnI switch region (GenBank accession number P19429.3, residues V147−D180).…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

“…Protein expression and labeling were analogous to previously described protocols . The linker portion was optimized on the basis of the ITC binding data for a SM test compound and the quality of the one-dimensional (1D) 1 H NMR spectra of the chimera:Ca 2+ :SM complex.…”

Section: Methodsmentioning

confidence: 99%

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Structural and Thermodynamic Model for the Activation of Cardiac Troponin

et al. 2022

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Cardiac troponin is a regulatory protein complex located on the sarcomere that regulates the engagement of myosin on actin filaments. Low-molecular weight modulators of troponin that bind allosterically with the calcium ion have the potential to improve cardiac contractility in patients with reduced cardiac function. Here we propose an approach to the rational design of troponin modulators through the combined use of solution nuclear magnetic resonance and isothermal titration calorimetry methods. In contrast to traditional approaches limited to calcium and activator-bound troponin structures, here we analyzed the structural and thermodynamic impact of an activator in the context of the troponin functional cycle. This led us to propose a rationale for developing an efficacious troponin activator.

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Intermolecular And Dynamic Investigation of The Mechanism of Action of Reldesemtiv on Fast Skeletal Muscle Troponin Complex Toward the Treatment of Impaired Muscle Function

2023

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Muscle weakness as a secondary feature of attenuated neuronal input often leads to disability and sometimes death in patients with neurogenic neuromuscular diseases. These impaired muscle function has been observed in several diseases including amyotrophic lateral sclerosis, Charcot–Marie–Tooth, spinal muscular atrophy and Myasthenia gravis. This has spurred the search for small molecules which could activate fast skeletal muscle troponin complex as a means to increase muscle strength. Discovered small molecules have however been punctuated by off-target and side effects leading to the development of the second-generation small molecule, Reldesemtiv. In this study, we investigated the impact of Reldesemtiv binding to the fast skeletal troponin complex and the molecular determinants that condition the therapeutic prowess of Redesemtiv through computational techniques. It was revealed that Reldesemtiv binding possibly potentiates troponin C compacting characterized by reduced exposure to solvent molecules which could favor the slow release of calcium ions and the resultant sensitization of the subunit to calcium. These conformational changes were underscored by conventional and carbon hydrogen bonds, pi-alkyl, pi-sulfur and halogen interactions between Reldesemtiv the binding site residues. Arg113 (−3.96 kcal/mol), Met116 (−2.23 kcal/mol), Val114 (−1.28 kcal/mol) and Met121 (−0.63 kcal/mol) of the switch region of the inhibitory subunit were among the residues that contributed the most to the total free binding energy of Reldesemtiv highlighting their importance. These findings present useful insights which could lay the foundation for the development of fast skeletal muscle small molecule activators with high specificity and potency.

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Structural Basis of Tirasemtiv Activation of Fast Skeletal Muscle

Cited by 12 publications

References 43 publications

Small Molecule RPI-194 Stabilizes Activated Troponin to Increase the Calcium Sensitivity of Striated Muscle Contraction

Small Molecule RPI-194 Stabilizes Activated Troponin to Increase the Calcium Sensitivity of Striated Muscle Contraction

Structural and Thermodynamic Model for the Activation of Cardiac Troponin

Intermolecular And Dynamic Investigation of The Mechanism of Action of Reldesemtiv on Fast Skeletal Muscle Troponin Complex Toward the Treatment of Impaired Muscle Function

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