Istaroxime Metabolite PST3093 Selectively Stimulates SERCA2a and Reverses Disease-Induced Changes in Cardiac Function

Abstract

Heart failure (HF) therapeutic toolkit would strongly benefit from the availability of ino-lusitropic agents with a favorable pharmacodynamics and safety profile. Istaroxime is a promising agent, which combines Na + /K + pump inhibition with SERCA2a stimulation; however, it has a very short half-life and extensive metabolism to a molecule, named PST3093. The present work aims to investigate whether PST3093, still retains the pharmacodynamic and pharmacokinetic properties of its parent compound. We studied PST3093 for its effects on SERCA2a and Na + /K + ATPase activities, Ca 2+ dynamics in isolated myocytes and hemodynamic effects in an in-vivo rat model of diabetic (streptozotocin (STZ)-induced) cardiomyopathy. Istaroxime infusion in HF patients led to accumulation of PST3093 in the plasma; clearance was substantially slower for PST3093 than for istaroxime. In cardiac rat preparations PST3093 did not inhibit the Na + /K + ATPase activity, but retained SERCA2a stimulatory activity. In in-vivo echocardiographic assessment, PST3093 improved overall cardiac performance and reversed most STZ-induced abnormalities. PST3093 i.v. toxicity was considerably lower than that of istaroxime and it failed to significantly interact with 50 off-targets. Overall, PST3093 is a "selective" SERCA2a activator, the prototype of a novel pharmacodynamic category with a potential in the ino-lusitropic approach to HF with prevailing diastolic dysfunction. Its pharmacodynamics are peculiar and its pharmacokinetics are suitable to prolong the cardiac beneficial effect of istaroxime infusion. Significance statementHeart failure (HF) treatment would benefit from the availability of ino-lusitropic agents with a favourable profile. PST3093 is the main metabolite of istaroxime, a promising agent combining Na + /K + pump inhibition and SERCA2a stimulation. PST3093 shows a longer half-life in human circulation compared to parent drug, activates SERCA2a, doesn't inhibit Na + /K + pump and improves cardiac performance in a model of diabetic cardiomyopathy. Overall, PST3093 as This article has not been copyedited and formatted. The final version may differ from this version.

Early consequences of the phospholamban mutation PLN‐R14del+/− in a transgenic mouse model

“…Next, we evaluated SERCA2a function in the context of an intact myocyte. To improve mechanistic interpretation of the mutation effect, studies with an agent known to increase SERCA2a function by preventing its interaction with PLN 10 were included. SERCA2a function may have different impact on intracellular Ca 2+ dynamics at different heart rates; therefore, the rate‐dependency of changes in Ca 2+ dynamics was also evaluated in a separate set of CMs field‐stimulated at four rates between 1 and 2 Hz.…”

“…The view that hyperdynamic Ca 2+ handling reflects enhanced SERCA2a activity is reinforced by (1) increased Ca 2+ sensitivity (lower Kd Ca ) of SERCA2a ATPase activity in myocardial homogenates; (2) similarity with the effect of PST‐3093, a SERCA2a stimulator. The latter is known to increase SERCA2a activity by weakening its interaction with PLN, 10 thus suggesting reduced affinity for SERCA2a as a mechanism of PLN R14del behavior. In the PLN R14del heterozygous state, PST‐3093 should have retained part of its stimulatory effect by displacing residual WT PLN.…”

FRET assay for live-cell high-throughput screening of the cardiac SERCA pump yields multiple classes of small-molecule allosteric modulators

“…Of all these SERCA2a activators only istaroxime, a known Na + /K + transporting ATPase inhibitor as well as an inotropic/lusitropic agent acting to enhance SERCA2a activity, has been in phase IIb clinical trials for treatment of heart failure 45,46 . However, because of its unsuitability for human usage (poor gastrointestinal absorption, high clearance rate, and extensive metabolic transformation) 46 , istaroxime derivatives were designed from QSAR studies and a new promising class of SERCA2a activators has been identified 47,48,49 .…”

Early consequences of the phospholamban mutation PLN-R14del+/-in a transgenic mouse model

“…The view that hyperdynamic Ca 2+ handling reflects enhanced SERCA2a activity is reinforced by 1) increased Ca 2+ sensitivity (lower Kd Ca ) of SERCA2a ATPase activity in myocardial homogenates; 2) similarity with the effect of PST-3093, a SERCA2a stimulator. The latter is known to increase SERCA2a activity by weakening its interaction with PLN, 9 thus suggesting reduced affinity for SERCA2a as a mechanism of PLN R14del effects. In the PLN R14del heterozygous state, PST-3093 should have retained part of its stimulatory effect by displacing residual WT PLN.…”

“…The "superinhibition" theory motivated us to test reversal of PLN R14del +/phenotype by a recently developed compound (PST-3093) that selectively stimulates SERCA2a by antagonizing its interaction with PLN. 9 Strikingly, human iPS-derived cardiomyocytes (hiPS-CMs) from a heterozygous human mutation carrier displayed a hyperdynamic Ca 2+ handling instead, a phenotype that obviously is incompatible with the SERCA2a "superinhibition". Notably, PST-3093 mimicked the effect of the mutation when applied to the WT hiPS-CMs, but it was ineffective in mutant ones.…”