U-0126 is a MEK inhibitor with IC50 values of 72 nM and 58 nM for MEK1 and MEK2, respectively. It is noncompetitive with respect adenosine triphosphate (ATP) and its phosphorylation target ERK and it shows little to no inhibition against a number of other kinases including PKC, Ab1, Raf, MEKK, ERK, JNK, MKK-3,...

Selective inhibitor of the mitogen-activated protein kinase kinases, MEK-1 and MEK-2, with 100-fold higher potency than PD 98059, but is, at most, a weak inhibitor of PKC, Raf, ERK, JNK, MEKK, MKK-3, MKK-4/SEK, MKK-6, Abl, Cdk2 and Cdk4. U0126 is an inhibitor of AP-1 transactivation in cell-based reporter assays....

Soluble in DMSO at 200 mg/mL, very poorly soluble in ethanol, very poorly soluble in water, maximum solubility in plain water is estimated to be about 10-50 µM, buffers, serum, or other additives may increase or decrease the aqueous solubility