U-0126 is a selective MAP Kinase Kinase (MKK, MEK) inhibitor with IC50 values of 72 nM and 58 nM for MEK1 and MEK2, respectively. It shows little to no inhibition against a number of other kinases including PKC, Ab1, Raf, MEKK, ERK, JNK, MKK-3, MKK-4, MKK-6, Cdk2, and Cdk4. U-0126 inhibition of MEK is noncompetitive with respect adenosine triphosphate (ATP) and its phosphorylation target ERK, which may partially explain its selectivity profile against other kinases.
