PD98059 (MEK1 Inhibitor) is soluble in DMSO at 10-100 mM. For use with in vitro or cell-based assays, it may be diluted into aqueous buffers to yield desired concentrations (<100 µM) with final DMSO concentrations of ~0.1%. IC50 values for inhibitory activity against MEK1 are around 5-10 µM. For experiments with cultured cells, CST recommends pretreating with this inhibitor for one hour prior to stimulation.