SP600125 is a selective, reversible and ATP-competitive inhibitor of Jun N-terminal kinase (JNK) with IC50 values of 40, 40 and 90 nM for JNK1, 2 and 3, respectively [1].

SP600125 was screened out from a time-resolved f luorescence assay using the GST-c-Jun and recombinant human JNK2. In this assay, SP600125 showed a Ki value of 190 nM. SP600125 was also found to inhibit JNK1, 2 and 3 isoforms in the selectivity tests. The selectivity of SP600125 for JNK is 300-fold greater than that for ERK1 and p38-2. In Jurkat T cells, SP600125 suppressed the phosphorylation of c-Jun with IC50 of 5-10 μM. SP600125 also inhibited the expression of IL-2 and IFN-γ in cells stimulated with PMA and phytohemagglutinin, since JNK had been reported to regulate the transcription of IL-2. Besides that, SP600125 exerted differential inhibition of cytokines in CD4+ cells as well as inflammatory genes in monocytes. Moreover, SP600125 administration significantly inhibited TNF-α expression induced by LPS in a mouse model, suggesting that it had efficacy in endotoxin-induced inf lammation in vivo [1].