Towards the Development of Small-Molecule MO25Binders as Potential Indirect SPAK/OSR1 Kinase Inhibitors

The binding of the scaffolding protein MO25 to SPAK andOSR1 protein kinases, which regu late ion homeostasis, causesincreases of up to 100-fold in their catalytic activity. Variousanimal models have shown that the inhibition of SPAK andOSR1 lowers blood pressure, andsohere we present anewindirect approachtoinhibiting SPAK and OSR1 kinases by tar-geting their protein partner MO25. To explorethis approach,we developed afluorescent polarisation assay and used it inscreening of asmall in-house library of &4000 compounds.This led to the identification of one compound—H K01—as thefirst small-molecule inhibitor of the MO25-dependent activa-tion of SPAK and OSR1 in vitro. Our data confirm the feasibilityof targeting this protein–protein interaction by small-moleculecompounds and highlights their potential to modulate ion co-transporters and thus cellular electrolyte balance.