An orally bioavailable small-molecule inhibitor of mitogen-activated protein kinase kinase (MAP2K, MAPK/ERK kinase, or MEK) 1 and 2 with potential antineoplastic activity. MEK 1/2 inhibitor AS703988/MSC2015103B selectively binds to and inhibits the activity of MEK1/2, preventing the activation of MEK1/2-dependent effector proteins and transcription factors, which may result in the inhibition of growth factor-mediated cell signaling and tumor cell proliferation. MEK1 and MEK2 are dual-specificity threonine/tyrosine kinases that play key roles in the activation of the RAS/RAF/MEK/ERK pathway that regulates cell growth and are often upregulated in a variety of tumor cell types.