Selective, cell-permeable inhibitor of Ca2+-calmodulin-dependent protein kinase kinase (Ki values are 80 and 15 ng/ml for inhibition of CaM-KKα and CaM-KKβ respectively); competes for the ATP-binding site. Displays > 80-fold selectivity over CaMK1, CaMK2, CaMK4, MLCK, PKC, PKA and p42 MAPK.