Novel Small-Molecule Troponin Activator Increases Cardiac Contractile Function Without Negative Impact on Energetics

Abstract

Background: Current heart failure (HF) therapies unload the failing heart without targeting the underlying problem of reduced cardiac contractility. Traditional inotropes (i.e. calcitropes) stimulate contractility via energetically costly augmentation of calcium cycling and worsen patient survival. A new class of agents - myotropes - activate the sarcomere directly, independent of calcium. We hypothesize that a novel myotrope TA1 increases contractility without the deleterious myocardial energetic impact of a calcitrope dobutamine. Methods: We determined the effect of TA1 in bovine cardiac myofibrils and human cardiac microtissues, ex vivo in mouse cardiac fibers and in vivo in anesthetized normal rats. Effects of increasing concentrations of TA1 or dobutamine on contractile function, phosphocreatine (PCr) and ATP concentrations and ATP production were assessed by 31 P NMR spectroscopy on isolated perfused rat hearts. Results: TA1 increased the rate of myosin ATPase activity in isolated bovine myofibrils and calcium sensitivity in intact mouse papillary fibers. Contractility increased dose dependently in human cardiac microtissues and in vivo in rats as assessed by echocardiography. In isolated rat hearts, TA1 and dobutamine similarly increased rate pressure product (RPP). Dobutamine increased both developed pressure (DevP) and heart rate (HR) accompanied by decreased PCr to ATP ratio and decreased free energy of ATP hydrolysis (ΔG~ ATP ) and elevated left ventricular end-diastolic pressure (LVEDP). In contrast, the TA1 increased DevP without any effect on HR, LVEDP, PCr/ATP ratio or ΔG~ ATP . Conclusions: Novel myotrope, TA1, increased myocardial contractility by sensitizing the sarcomere to calcium without impairing diastolic function or depleting the cardiac energy reserve. Since energetic depletion negatively correlates with long term survival, myotropes may represent a superior alternative to traditional inotropes in heart failure management.

L-2-Hydroxyglutarate Protects Against Cardiac Injury via Metabolic Remodeling

“…The sample size represents the number of independent experimental units per group. Sample sizes were determined based on our pilot and previous study 24 performing power analysis based on a 2-tailed Student t test to provide adequate power to detect a ≥20% difference, assuming a power of 80% (β=0.20) and an α of 0.05 for these studies. Seventeen animals or samples were excluded from the ex vivo studies.…”

Distinct Mechanisms for Increased Cardiac Contraction Through Selective Alteration of Either Myosin or Troponin Activity

“… 54 Similarly, T is a structural analog of CK-136 and was anticipated to exhibit a similar selectivity profile. 55 For T, we saw activity that tracked with the source of troponin. T increased myosin ATPase activity in the reconstituted assays containing cardiac thin filaments as well as in reconstituted assays containing cardiac troponin irrespective of the source of myosin or tropomyosin ( Supplemental Figures S1B and S1C ).…”

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

“…TA1/AMG-594/CK-136 is highly selective for cardiac muscle over slow skeletal muscle, which would not be possible if it were targeting the same binding site as RPI-194. Moreover, TA1 is more potent, not only causing a greater leftward shift for pCa 50 in cardiac trabeculae, but also markedly increasing the maximum force generated at saturating calcium concentrations, unlike RPI-194 ( He et al, 2021 ). Increased force was also observed at resting calcium concentrations, along with increased myosin ATP consumption in cardiac myofibrils.…”

“…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. Cytokinetics has developed a cardio-selective troponin activator, CK-136, formerly known as AMG 594, which appears to be selective for cardiac muscle, though a structure of its binding site on cardiac troponin is not yet available ( He et al, 2021 ).…”