Kidney CLC-K Chloride Channels Inhibitors: Definition of Novel Structural Requirements and Efficacy in CLC-K Polymorphism Associated with Hypertension

The human chloride channels CLC-Ka and CLC-Kb play a pivotal role in kidney by controlling chloride and water absorption. Both channels require barttin as an accessory subunit for full activity. Mutations in CLC-Kb and barttin genes lead to severe renal salt loss while CLC-K gain of function polymorphisms could predispose to hypertension. Thus, compounds that selectively bind to CLC-Ka and/or CLC-Kb channels may have a significant therapeutic potential. Recently, we explored the pharmacological profile of CLC-K/barttin expressed in mammalian HEK-293 cells and demonstrated that HEK cells represent a valid biological system to screen CLC-K high affinity blockers (Imbrici et al., Biochim Biophys Acta, 2014). Here, by using molecular modeling and patch-clamp technique, we developed a new series of benzofuran derivatives and evaluated their efficacy on CLC-K channels expressed in HEK 293 cells. Chemical modifications regarding the hydrophobic group at C-5 and C-3 position of the benzofuran nucleus of the lead compounds RT-93 and JBL-44 (IC50 within 10-30 μM range), allowed us to define the structural requirements to ensure an efficacious CLC-Ka block, finally identifying SRA-36 the most potent compound so far described, with an IC50 of 2.6 ± 1 μM. Interestingly, besides capable of inhibiting CLC-Kb and CLC-K1 isoforms, this compound was also efficacious in blocking A447T CLC-Ka, a polymorphism associated with hypertension. Thus, the SRA-36 molecule could represent a useful probe for exploring CLC-K molecular mechanisms of gating as well as a new potential therapeutic option for hypertensive patients carrying CLC-K gene polymorphisms (Telethon GGP14096).