Activation of the p38 kinase pathway in immune cells leads to the transcriptional and translational regulation of proinflammatory cytokines. Mitogen-activated protein kinase-activated protein kinase 2 (MK2), a direct downstream substrate of p38 kinase, regulates lipopolysaccharide (LPS)-stimulated tumor necrosis factor ␣ (TNF␣) and interleukin-6 (IL-6) production through modulating the stability and translation of these mRNAs. Developing small-molecule inhibitors of MK2 may yield anti-inflammatory efficacy with a different safety profile relative to p38 kinase inhibitors. This article describes the pharmacologic properties of a benzothiophene MK2 inhibitor, PF-3644022 [(10R)-10-methyl-3-(6-methylpyridin-3-yl)-9,10,11,12-tetrahydro-8H-[1,4]diazepino[5Ј,6Ј:4,5]thieno[3,2-f]quinolin-8-one]. PF-3644022 is a potent freely reversible ATP-competitive compound that inhibits MK2 activity (K i ϭ 3 nM) with good selectivity when profiled against 200 human kinases. In the human U937 monocytic cell line or peripheral blood mononuclear cells, PF-3644022 potently inhibits TNF␣ production with similar activity (IC 50 ϭ 160 nM). PF-3644022 blocks TNF␣ and IL-6 production in LPS-stimulated human whole blood with IC 50 values of 1.6 and 10.3 M, respectively. Inhibition of TNF␣ in U937 cells and blood correlates closely with inhibition of phospho-heat shock protein 27, a target biomarker of MK2 activity. PF-3644022 displays good pharmacokinetic parameters in rats and is orally efficacious in both the rat acute LPS-induced TNF␣ model and the chronic streptococcal cell wall-induced arthritis model. Dose-dependent inhibition of TNF␣ production in the acute model and inhibition of paw swelling in the chronic model is observed with ED 50 values of 6.9 and 20 mg/kg, respectively. PF-3644022 efficacy in the chronic inflammation model is strongly correlated with maintaining a C min higher than the EC 50 measured in the rat LPS-induced TNF␣ model.

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