ITI214

Effects of phosphodiesterase-1 inhibitor on pulmonary vein electrophysiology and arrhythmogenesis

Introduction: Phosphodiesterase (PDE) isoform inhibitors have mechanical and electrical effects on the heart. Inhibition of PDE-1 enzymes is a novel strategy for treating heart failure. However, the electrophysiological effects of PDE-1 inhibition on the heart remain unclear. This study explored the effects of PDE-1 inhibition using ITI-214 on electrical activity in the pulmonary vein (PV), the most common trigger of atrial fibrillation, and investigated the underlying ionic mechanisms. Methods: Conventional microelectrodes or whole-cell patch clamps were employed to study the effects of ITI-214 (0.1-10 μM) on PV electrical activity, mechanical responses and ionic currents in isolated rabbit PV tissue specimens and isolated single PV cardiomyocytes. Results: ITI-214 at 1 μM and 10 μM (but not 0.1 μM) significantly reduced PV spontaneous beating rate (10 ± 2% and 10 ± 3%, respectively) and PV diastolic tension (11 ± 3% and 17 ± 3%, respectively). ITI-24 (1 μM) significantly reduced late sodium current (INa-Late ), L-type calcium current (ICa-L ) and the reverse mode of the sodium-calcium exchanger (NCX), but it did not affect peak sodium currents. Conclusions: ITI-214 reduces PV spontaneous activity and PV diastolic tension by reducing INa-Late , ICa-L and NCX current. Considering its therapeutic potential in heart failure, targeting PDE-1 inhibition may provide a novel strategy for managing atrial arrhythmogenesis.

Phosphodiesterase-1 inhibitor modulates Ca2+ regulation in sirtuin 1-deficient mouse cardiomyocytes

Background: Phosphodiesterase inhibitors can be used to enhance second messenger signaling to regulate intracellular Ca²⁺ cycling. This study investigated whether ITI-214, a selective phosphodiesterase-1 inhibitor, modulates intracellular Ca²⁺ regulation, resulting in a positive inotropic effect in sirtuin 1 (Sirt1)-deficient cardiomyocytes.
Methods: Mice with cardiac-specific Sirt1 knockout (Sirt1^-/-) were used, with Sirt1^flox/flox mice serving as controls. Electromechanical analyses of ventricular tissues were conducted, and we monitored intracellular Ca²⁺ using Fluo-3 as well as reactive oxygen species production in isolated cardiomyocytes.
Results: Sirt1^-/- ventricles showed prolonged action potential duration at 90% repolarization and increased contractile force after treatment with ITI-214. The rates and sustained durations of burst firing in ventricles were higher and longer, respectively, in Sirt1^-/- ventricles than in controls. ITI-214 treatment decreased the rates and shortened the durations of burst firing in Sirt1^-/- mice. Sirt1^-/- cardiomyocytes showed reduced Ca²⁺ transient amplitudes and sarcoplasmic reticulum (SR) Ca²⁺ stores compared to those in control cardiac myocytes, which was reversed after ITI-214 treatment. SR Ca²⁺ leakage was larger in Sirt1^-/- cardiac myocytes than in control myocytes. ITI-214 reduced SR Ca²⁺ leakage in Sirt1^-/- cardiac myocytes. Increased levels of reactive oxygen species in Sirt1^-/- cardiomyocytes compared to those in controls were reduced after ITI-214 treatment. Levels of Ca²⁺ regulatory proteins, including ryanodine receptor 2, phospholamban, and sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2a were not affected by ITI-214 administration.
Conclusions: Our results suggest that ITI-214 improves intracellular Ca²⁺ regulation, which in turn exerts inotropic effects and suppresses arrhythmic events in Sirt1-deficient ventricular myocytes.

Inhibition of calcium-calmodulin-dependent phosphodiesterase (PDE1) suppresses inflammatory responses

A novel, potent, and highly specific inhibitor of calcium-calmodulin-dependent phosphodiesterases (PDE) of the PDE1 family, ITI-214, was used to investigate the role of PDE1 in inflammatory responses. ITI-214 dose-dependently suppressed lipopolysaccharide (LPS)-induced gene expression of pro-inflammatory cytokines in an immortalized murine microglial cell line, BV2 cells. RNA profiling (RNA-Seq) was used to analyze the impact of ITI-214 on the BV2 cell transcriptome in the absence and the presence of LPS. ITI-214 was found to regulate classes of genes that are involved in inflammation and cell migration responses to LPS exposure. The gene expression changes seen with ITI-214 treatment were distinct from those elicited by inhibitors of other PDEs with anti-inflammatory activity (e.g., a PDE4 inhibitor), indicating a distinct mechanism of action for PDE1. Functionally, ITI-214 inhibited ADP-induced migration of BV2 cells through a P2Y12-receptor-dependent pathway, possibly due to increases in the extent of cAMP and VASP phosphorylation downstream of receptor activation. Importantly, this effect was recapitulated in P2 rat microglial cells in vitro, indicating that these pathways are active in native microglial cells. These studies are the first to demonstrate that inhibition of PDE1 exerts anti-inflammatory effects through effects on microglia signaling pathways. The ability of PDE1 inhibitors to prevent or dampen excessive inflammatory responses of BV2 cells and microglia provides a basis for exploring their therapeutic utility in the treatment of neurodegenerative diseases associated with increased inflammation and microglia proliferation such as Parkinson's disease and Alzheimer's disease.

Acute Enhancement of Cardiac Function by Phosphodiesterase Type 1 Inhibition

Background: Phosphodiesterase type-1 (PDE1) hydrolyzes cAMP and cGMP and is constitutively expressed in the heart, although cardiac effects from its acute inhibition in vivo are largely unknown. Existing data are limited to rodents expressing mostly the cGMP-favoring PDE1A isoform. Human heart predominantly expresses PDE1C with balanced selectivity for cAMP and cGMP. Here, we determined the acute effects of PDE1 inhibition in PDE1C-expressing mammals, dogs, and rabbits, in normal and failing hearts, and explored its regulatory pathways.
Methods: Conscious dogs chronically instrumented for pressure-volume relations were studied before and after tachypacing-induced heart failure (HF). A selective PDE1 inhibitor (ITI-214) was administered orally or intravenously±dobutamine. Pressure-volume analysis in anesthetized rabbits tested the role of β-adrenergic and adenosine receptor signaling on ITI-214 effects. Sarcomere and calcium dynamics were studied in rabbit left ventricular myocytes.
Results: In normal and HF dogs, ITI-214 increased load-independent contractility, improved relaxation, and reduced systemic arterial resistance, raising cardiac output without altering systolic blood pressure. Heart rate increased, but less so in HF dogs. ITI-214 effects were additive to β-adrenergic receptor agonism (dobutamine). Dobutamine but not ITI-214 increased plasma cAMP. ITI-214 induced similar cardiovascular effects in rabbits, whereas mice displayed only mild vasodilation and no contractility effects. In rabbits, β-adrenergic receptor blockade (esmolol) prevented ITI-214-mediated chronotropy, but inotropy and vasodilation remained unchanged. By contrast, adenosine A_2B-receptor blockade (MRS-1754) suppressed ITI-214 cardiovascular effects. Adding fixed-rate atrial pacing did not alter the findings. ITI-214 alone did not affect sarcomere or whole-cell calcium dynamics, whereas β-adrenergic receptor agonism (isoproterenol) or PDE3 inhibition (cilostamide) increased both. Unlike cilostamide, which further enhanced shortening and peak calcium when combined with isoproterenol, ITI-214 had no impact on these responses. Both PDE1 and PDE3 inhibitors increased shortening and accelerated calcium decay when combined with forskolin, yet only cilostamide increased calcium transients.
Conclusions: PDE1 inhibition by ITI-214 in vivo confers acute inotropic, lusitropic, and arterial vasodilatory effects in PDE1C-expressing mammals with and without HF. The effects appear related to cAMP signaling that is different from that provided via β-adrenergic receptors or PDE3 modulation. ITI-214, which has completed phase I trials, may provide a novel therapy for HF.

Acute Hemodynamic Effects and Tolerability of Phosphodiesterase-1 Inhibition With ITI-214 in Human Systolic Heart Failure

Background: PDE1 (phosphodiesterase type 1) hydrolyzes cyclic adenosine and guanosine monophosphate. ITI-214 is a highly selective PDE1 inhibitor that induces arterial vasodilation and positive inotropy in larger mammals. Here, we assessed pharmacokinetics, hemodynamics, and tolerability of single-dose ITI-214 in humans with stable heart failure with reduced ejection fraction.
Methods: Patients with heart failure with reduced ejection fraction were randomized 3:1 to 10, 30, or 90 mg ITI-214 single oral dose or placebo (n=9/group). Vital signs and electrocardiography were monitored predose to 5 hours postdose and transthoracic echoDoppler cardiography predose and 2-hours postdose.
Results: Patient age averaged 54 years; 42% female, and 60% Black. Mean systolic blood pressure decreased 3 to 8 mm Hg (P<0.001) and heart rate increased 5 to 9 bpm (P≤0.001 for 10, 30 mg doses, RM-ANCOVA). After 4 hours, neither blood pressure or heart rate significantly differed among cohorts (supine or standing). ITI-214 increased mean left ventricular power index, a relatively load-insensitive inotropic index, by 0.143 Watts/mL²·10⁴ (P=0.03, a +41% rise; 5-71 CI) and cardiac output by 0.83 L/min (P=0.002, +31%, 13-49 CI) both at the 30 mg dose. Systemic vascular resistance declined with 30 mg (-564 dynes·s/cm-⁵, P<0.001) and 90 mg (-370, P=0.016). Diastolic changes were minimal, and no parameters were significantly altered with placebo. ITI-214 was well-tolerated. Five patients had mild-moderate hypotension or orthostatic hypotension recorded adverse events. There were no significant changes in arrhythmia outcome and no serious adverse events.
Conclusions: Single-dose ITI-214 is well-tolerated and confers inodilator effects in humans with heart failure with reduced ejection fraction. Further investigations of its therapeutic utility are warranted. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT03387215.