TY - JOUR T1 - Activation of the Aryl Hydrocarbon Receptor by the Calcium/Calmodulin-Dependent Protein Kinase Kinase Inhibitor 7-Oxo-7<em>H</em>-benzimidazo[2,1-<em>a</em>]benz[de]isoquinoline-3-carboxylic Acid (STO-609) JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 2556 LP - 2563 DO - 10.1124/dmd.108.023333 VL - 36 IS - 12 AU - Patricia Monteiro AU - David Gilot AU - Sophie Langouet AU - Olivier Fardel Y1 - 2008/12/01 UR - http://dmd.aspetjournals.org/content/36/12/2556.abstract N2 - This study was designed to analyze the effects of the Ca2+/calmodulin-dependent protein kinase kinase (CaMKK) inhibitor STO-609 (7-oxo-7H-benzimidazo[2,1-a]benz[de]isoquinoline-3-carboxylic acid) toward the aryl hydrocarbon receptor (AhR) pathway because Ca2+/calmodulin-dependent protein kinase (CaMK) Iα, known as a downstream CaMKK effector, has been recently shown to contribute to the AhR cascade. STO-609 failed to alter up-regulation of the AhR target CYP1A1 in response to the potent AhR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in MCF-7 cells. STO-609, used at a 25 μM concentration known to fully inhibit CaMKK activity, was surprisingly found to markedly induce CYP1A1 expression and activity by itself in MCF-7 cells; it similarly up-regulated various other AhR target genes in human macrophages. STO-609-related CYP1A1 induction was prevented by chemical inhibition or small interfering RNA-mediated knockdown expression of AhR. Moreover, STO-609 was demonstrated to physically interact with the ligand-binding domain of AhR, as assessed by TCDD binding competition assay, and to induce AhR translocation to the nucleus. As already reported for AhR agonists, STO-609 triggered the increase of [Ca2+]i and activation of CaMKIα, whose inhibition through the use of the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid-acetoxymethyl ester or the CaMK inhibitor KN-93 (2-[N-(2-hydroxyethyl)]-N-(4-methoxybenzenesulfonyl)]amino-N-(4-chlorocinnamyl)-N-methylbenzylamine), respectively, prevented STO-609-mediated CYP1A1 activity induction. Taken together, these results demonstrate that the CaMKK inhibitor STO-609 can act as an AhR ligand and, in this way, fully activates the Ca2+/CaMKIα/AhR cascade. Such data, therefore, make unlikely any contribution of CaMKK activity to the AhR pathway and, moreover, suggest that caution may be required when using STO-609 as a specific inhibitor of CaMKKs. The American Society for Pharmacology and Experimental Therapeutics ER -