Phosphodiesterase inhibition and Ca2+ sensitization

Area of Science:

• Cardiovascular Pharmacology
• Medicinal Chemistry

Background:

• Phosphodiesterase type III (PDE III) inhibitors increase cardiac contractility by elevating intracellular calcium ([Ca2+]i) via cAMP.
• Long-term PDE III inhibitor use is limited by arrhythmia risk due to increased [Ca2+]i.
• Calcium sensitizers offer a potential alternative with reduced arrhythmia risk.

Purpose of the Study:

• To investigate novel thiadiazinone derivatives as potential cardiac therapeutics.
• To differentiate the PDE III inhibitory and Ca2+ sensitizing effects of enantiomers.

Main Methods:

• Synthesis of thiadiazinone derivatives, including enantiomers [+]-EMD 60263 and [-]-EMD 60264.
• Assessment of contractile force in isolated cardiac preparations, myocytes, and Langendorff-perfused guinea-pig hearts.
• Electrophysiological studies to evaluate action potential duration and ion channel effects.

Main Results:

• [+]-EMD 60263 significantly increased cardiac contractility and myocyte cell shortening, indicating potent Ca2+ sensitization.
• [-]-EMD 60264 showed weak PDE III inhibition and a negative inotropic effect.
• Both enantiomers reduced heart rate and prolonged action potential duration by blocking the delayed rectifier K+ current, suggesting Class III antiarrhythmic activity.
• All observed effects were reversible upon enantiomer washout.

Conclusions:

• The [+]-enantiomer of thiadiazinone derivatives exhibits potent Ca2+ sensitizing effects, enhancing cardiac contractility.
• Both enantiomers possess Class III antiarrhythmic properties, warranting further investigation.
• These compounds represent a promising new class of cardiovascular agents with potential therapeutic applications.