BACKGROUND/AIMS: Lubeluzole is a benzothiazole derivative that has shown 
neuroprotective properties in preclinical models of ischemic stroke. However, 
clinical research on lubeluzole is now at a standstill, since lubeluzole seems 
to be associated with the acquired long QT syndrome and ventricular arrhythmias. 
Since the cardiac cellular effects of lubeluzole have not been described thus 
far, an explanation for the lubeluzole-induced QT interval prolongation is 
lacking.
METHODS: We tested the affinity of lubeluzole, its enantiomer, and the racemate 
for hERG channel using the patch-clamp technique. We synthesized and tested two 
simplified model compounds corresponding to two moieties included in the 
lubeluzole structure. The obtained experimental results were rationalized by 
docking simulation on the recently reported cryo-electron microscopy (cryo-EM) 
structure of hERG. Group efficiency analysis was performed in order to 
individuate the fragment most contributing to binding.
RESULTS: We found that lubeluzole and its R enantiomer are highly potent 
inhibitors of human ether-ago-go-related gene (hERG) channel with an IC50 value 
of 12.9 ± 0.7 nM and 11.3 ± 0.8 nM, respectively. In the presence of lubeluzole, 
steady-state activation and inactivation of hERG channel were shifted to more 
negative potentials and inactivation kinetics was accelerated. Mutations of 
aromatic residues (Y652A and F656A) in the channel inner cavity significantly 
reduced the inhibitory effect of lubeluzole. Molecular docking simulations 
performed on the near atomic resolution cryo-electron microscopy structures of 
hERG supported the role of Y652 and F656 as the main contributors to high 
affinity binding. Group efficiency analysis indicated that both 
1,3-benzothiazol-2-amine and 3-aryloxy-2-propanolamine moieties contribute to 
drug binding with the former giving higher contribution.
CONCLUSIONS: This study suggests the possibility to modulate lubeluzole hERG 
blockade by introducing suitable substituents onto one or both constituting 
portions of the parent compound in order to either reduce potency (i. e. 
torsadogenic potential) or potentiate affinity (useful for class III 
antiarrhythmic and anticancer agent development).