In vitro activity: JNK-IN-8 inhibits c-Jun phosphorylation in HeLa and A375 cells with EC50 of 486 nM and 338 nM, respectively. JNK-IN-8 shows a dramatic improvement in selectivity and eliminated binding to IRAK1, PIK3C3, PIP4K2C, and PIP5K3. JNK-IN-8 requires Cys116 for JNK2 inhibition. JNK-IN-8 (10 mM) suppresses the IL-1β-stimulated phosphorylation of c-Jun in IL-1R cells, an established substrate of the JNKs. JNK-IN-8 covalently attaches to the JNK isoforms caused a small retardation in the electrophoretic mobility of the JNK isoforms. JNK-IN-8 is discovered to inhibit JNK kinase by broad-based kinase selectivity profiling of a library of acrylamide kinase inhibitors based on the structure of imatinib using the KinomeScan approach. JNK-IN-8 possesses distinct regiochemistry of the 1,4-dianiline and 1,3-aminobenzoic acid substructures relative to imatinib and uses an N,N-dimethyl butenoic acetamide warhead to covalently target Cys154. JNK-IN-8 adopts an L-shaped type I binding conformation to access Cys 154 located toward the lip of the ATP-binding site

Kinase Assay: JNK-IN-8 is a JNK1/2/3 inhibitor with high specificity. When JNK-IN-8 was profiled with a panel of 400 kinases, it exhibited specific binding to JNK 1/2/3 but not to other kinases. Crystallization study also found that JNK-IN-8 forms covalent bonds with conserved cysteine residue of JNK 1/2/3, resulting in a conformational change of the activation loop that blocks the substrate binding, thereby inhibiting the activity of JNK 1/2/3.

Cell Assay: In Hela cells and A375 cells, pretreatment of cells with JNK-IN-8 resulted in the inhibition of c-Jun which is a direct phosphorylation substrate of JNK 1/2/3, confirming the inhibitory action of JNK-IN-8 on JNK 1/2/3. In HEK293-ILR1 cells following stimulation by anisomycin, the JNK-IN-8 was observed to inhibit c-Jun but not MSK1 and p38, and the inhibition was not reversible by removing JNK-IN-8 from culture medium. Additionally, JNK-IN-8 only exhibited on-pathway inhibition of JNK signaling pathway, which can be monitored by the phosphorylation of c-Jun.

Chem Biol. 2012 Jan 27;19(1):140-54; Biochem J. 2012 Jan 1;441(1):339-46; Chem Biol. 2013 Feb 21;20(2):146-59.