SP 600125 is a potent and reversible inhibitor of JNK1-3 with an IC50 value of 0.11 ?M.1 It is cell-permeable and dose-dependently inhibits c-Jun phosphorylation in cells, blocking the expression of COX-2 and TNF-α in monocytes and IL-10, TNF-α, and IFN-γ in T-cells. SP 600125 also prevents apoptosis in many cell types, including B-cells, and inhibits autophagy in HeLa cells. Competitively and reversibly inhibits JNK1, 2 and 3 (IC50 = 40 - 90 nM) with negligible activity at ERK2, p38β and a range of enzymes (IC50 > 10 ?M). Active in vivo. Shown to have reduced selectivity over other protein kinases under certain conditions. Protects renal tubular epithelial cells against ischemia/reperfusion-induced apoptosis. Prevents BMP9-induced osteogenic differentiation of MSCs.