MRT199665 is an effective and ATP-competitive, selective MARK SIK AMPK inhibitor (IC50s of 2 2 3 2 nM, 10 10 nM, and 110 12 43 nM for MARK1 MARK2 MARK3 MARK14, AMPKα1 AMPKα2, and SIK1 SIK2 SIK3, respectively). MRT199665 suppresses the phosphorylation of S