BI-78D3, dose-dependently inhibits the phosphorylation of JNK substrates both in vitro and in cell. BI-78D3 is able to compete with the D-domain of JIP1 (amino acids 153-163; pepJIP1) for JNK1 binding (IC50=500 nM). Using the same in vitro LanthaScreen kinase assay and the same ATF2 substrate, BI-78D3 is found to be 100-fold less active vs. p38α, a member of the MAPK family with high structural similarity to JNK, and completely inactive against mTOR and PI3-kinase (α-isoform), both unrelated protein kinases. Furthermore, Lineweaver-Burk analysis clearly indicates that BI-78D3 is competitive with ATF2 for binding to JNK1 with an apparent Ki value of 200 nM. In an attempt to profile the properties of BI-78D3 in the context of a complex cellular milieu, the cell-based LanthaScreen kinase assay is used. In this assay BI-78D3 is able to inhibit TNF-α stimulated phosphorylation of c-Jun in cell (EC50=12.4 μM).