BI-8668

BI-8668 represents a good chemical probe for the endothelial sodium channel (ENaC). In Na+ transport cell-based assays it showed a low nanomolar IC50 value while the negative control compound BI-0337 showed an IC50 value greater then 10 micromolar. BI-8668 was designed to be delivered via inhalation. A lung retention study in rats showed that 55% of drug remained in the lung 3h post intratracheal instillation after a dose of 10 μg/kg. The ED50 3h after dosing in an acute rat lung fluid absorption model was 0.1 μg/kg.

BI-8668 is a potent (IC50 = 17 nM) and in vivo grade ENaC inhibitor with a structurally distinct scaffold from amiloride and idrevloride. At doses > 1 uM, off-target inhibition of M1/M2/M3 muscarinic receptors, the alpha1A adrenergic receptor, and acetylcholinesterase will be observed; therefore, 1 uM should not be exceeded. BI-8668 is positively charged and highly water soluble as the result of optimizing the compound for delivery via inhalation. When delivered to the lungs of rats via intratracheal instillation, BI-8668 achieves ENaC inhibition only in the lungs without acting in the kidney (at least at doses up to 3 ug/kg), making it an ideal in vivo tool compound. BI-8668 does contain a hinge binder, suggesting it might inhibit some kinases (no kinase profiling is reported). However, given its low permeability, it is not anticipated to inhibit intracellular kinases in cellular studies and therefore the lack of off-target kinase profiling is understandable. Use of BI-8668 alongside the negative control BI-0337, which retains the hinge binding motif but is completely dead against ENaC, will further ensure the on-target nature of cellular phenotypes. Therefore, BI-8668 is a high quality chemical probe suitable for cellular and in vivo studies exploring ENaC inhibition.

Selective and cell active probe with clear in Vigo activity. Nice SAR and good inactive probe. Overall, this probe should be used to interrogate this target across assay types