Diltiazem N-oxide, a novel ischaemia-activated prodrug, prevents ischaemia-induced ventricular fibrillation without off-target adverse effects.

BACKGROUND AND PURPOSE: Ventricular fibrillation (VF) in coronary heart disease accounts for up to 70% of sudden cardiac death. We examined whether diltiazem N-oxide (DNO) has ischaemia-selective antiarrhythmic activity.

EXPERIMENTAL APPROACH: Randomised and blinded experiments were performed in rat isolated hearts and in anaesthetised rats to determine antiarrhythmic effectiveness, adverse drug reaction (ADR) profile and mechanism of action of DNO, using diltiazem as a positive control. The ratio of the lowest concentration with antiarrhythmic activity to the highest concentration without ADRs was defined as the translational therapeutic index (TTI).

KEY

RESULTS

In Langendorff-perfused hearts, diltiazem (100 nM-6 µM) and DNO (1 µM-6 µM) reduced ischaemia-induced VF occurrence. Diltiazem caused vasodilation (≥100 nM), atrioventricular (AV) block (≥3 µM), and negative inotropy (≥3 µM) with a TTI ≤ 1 while DNO had no adverse effects (TTI > 6). Ultra-high performance liquid chromatography with tandem mass spectrometry analysis of hearts perfused with 1-μM DNO detected almost complete conversion of DNO to diltiazem in ischaemia, but not in normoxia. 31P nuclear magnetic resonance spectroscopy (NMR) revealed ischaemia-induced intracellular acidosis, decreased β-ATP and phosphocreatine, all unaffected by either 1-μM diltiazem or 1-μM DNO. Diltiazem (2 mg·kg-1 + 0.2 mg·kg-1·min-1) and DNO (6.5 mg·kg-1 + 0.65 mg·kg-1·min-1) prevented ischaemia-induced VF in anaesthetised rats, with diltiazem causing AV block and bradycardia and DNO causing no ADRs.

CONCLUSIONS AND IMPLICATIONS: DNO was converted to diltiazem selectively in ischaemic cardiac tissue where it mimicked diltiazem's effect on VF, but without its associated ADRs. Neither drug affected cardiac energetics.