An orally bioavailable inhibitor of mitogen-activated protein kinase kinase (MAP2K, MAPK/ERK kinase, or MEK), with potential antineoplastic activity. Upon administration, tunlametinib selectively binds to and inhibits the activity of MEK, preventing the activation of MEK-dependent effector proteins and transcription factors, which may result in the inhibition of growth factor-mediated cell signaling and tumor cell proliferation. MEK, a threonine/tyrosine kinase, plays a key role in the activation of the RAS/RAF/MEK/ERK pathway that regulates cell growth. This pathway is often dysregulated in a variety of tumor cell types through BRAF, KRAS and NRAS mutations.