BI-78D3

BI-78D3 functions as a substrate competitive inhibitor of JNK, inhibit the JNK kinase activity (IC₅₀=280 nM). IC50 & Target: IC50: 280 nM (JNK)^[1] In Vitro: 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 K_i 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)^[1]. In Vivo: The link between ConA-induced liver failure, TNF receptor signaling, and JNK function has been established by studies employing JNK1^-/- and JNK2^-/- mice. For this analysis, insulin insensitive mice are injected only once with 25 mg/kg BI-78D3, 30 min before insulin injection. The effect of insulin on blood glucose levels is then measured. BI-78D3 results in a statistically significant reduction in blood glucose levels as compared with the vehicle control. Thus, the ability of BI-78D3 to abrogate ConA-induced liver damage and restore insulin sensitivity is consistent with its proposed function as an effective JNK inhibitor. Liquid chromatography/mass spectrometry bio-availability analysis demonstrates that BI-78D3 has favorable microsome and plasma stability (T_1/2=54 min)^[1].