In vitro activity: PH-797804 blocks LPS-induced TNF-α production and p38 kinase activity in the human monocytic U937 cell line, with comparable IC50 of 5.9 nM and 1.1 nM. PH-797804 has no inhibitory effect on either the JNK pathway (c-Jun phosphorylation) or ERK pathway (ERK phosphorylation) in U937 cells at concentrations up to 1 μM. PH-797804 inhibits RANKL- and M-CSF-induced osteoclast formation in a concentration-dependent manner, with IC50 of 3 nM in primary rat bone marrow cells. IC50 values for PH-797804 against the following targets have been determined to be greater than 200 μM (unless specified): CDK2, ERK2, IKK1, IKK2, IKKi, MAPKAP2, MAPKAP3, MKK7 (>100 μM), MNK, MSK (>164 μM), PRAK, RSK2, and TBK1, which means the activity of PH-797804 is specific.

Kinase Assay: A resin capture assay method is used to determine the phosphorylation of epidermal growth factor receptor peptide (EGFRP) or GST-c-Jun by p38 kinases. Reactions mixtures contain 25 mM HEPES, pH 7.5, 10 mM magnesium acetate, ATP (at the indicated concentration), 0.05 to 0.3 μCi of [γ-33P]ATP, 0.8 mM dithiothreitol, and either 200 μM EGFRP or 10 μM GST-c-Jun for p38α kinase reactions. The reaction is initiated by the addition of 25 nM p38α kinase to give a final volume of 50 μl. The p38αkinase reactions are incubated at 25 °C for 30 minutes. Under these conditions, the formation of product for both p38αkinase is linear with time. The reaction is stopped, and the unreacted [γ-33P]ATP is removed by the addition of 150 μl of AG 1 × 8 ion exchange resin in 900 mM sodium formate, pH 3.0. Once thoroughly mixed, solutions are allowed to stand for 5 minutes. A 50-μl aliquot of head volume containing the phosphorylated substrate is removed from the mixture and transferred to a 96-well plate. MicroScint-40 scintillation cocktail (150 μL) is added to each well and the radioactivity quantities using a TopCount NXT microplate scintillation and luminescence counter.

Cell Assay: PH-797804 blocks LPS-induced TNF-α production and p38 kinase activity in the human monocytic U937 cell line, with comparable IC50 of 5.9 nM and 1.1 nM. PH-797804 has no inhibitory effect on either the JNK pathway (c-Jun phosphorylation) or ERK pathway (ERK phosphorylation) in U937 cells at concentrations up to 1 μM. PH-797804 inhibits RANKL- and M-CSF-induced osteoclast formation in a concentration-dependent manner, with IC50 of 3 nM in primary rat bone marrow cells

J Pharmacol Exp Ther. 2009 Dec;331(3):882-95; Biochemistry. 2009 Jul 14;48(27):6402-11.