STO-609

STO-609 is a selective and cell-permeable inhibitor of the Ca²⁺/calmodulin-dependent protein kinase kinase (CaM-KK), with K_i values of 80 and 15 ng/mL for recombinant CaM-KKα and CaM-KKβ, respectively. STO-609 inhibits AMP-activated protein kinase kinase (AMPKK) activity in HeLa cell lysates with an IC₅₀ ~0.02 g/ml. IC50 & Target: Ki: 80 ng/mL (CaM-KKα), 15 ng/mL (CaM-KKβ)^[1] In Vitro: STO-609 inhibits the activities of recombinant CaM-KKα and CaM-KKβ isoforms, with K_i values of 80 and 15 ng/mL, respectively, and also inhibits their autophosphorylation activities. STO-609 is highly selective for CaM-KK without any significant effect on the downstream CaM kinases (CaM-KI and -IV), and the IC₅₀ value of the compound against CaM-KII is 10 μg/mL. STO-609 inhibits constitutively active CaM-KKα as well as the wild-type enzyme. In transfected HeLa cells, STO-609 suppresses the Ca²⁺-induced activation of CaM-KIV in a dose-dependent manner. STO-609 significantly reduces the endogenous activity of CaM-KK in SH-SY5Y neuroblastoma cells at a concentration of 1μg/mL (80% inhibitory rate)^[1].