7 It is a potent inhibitor of MEK1 and mitogen-activated protein kinase/extracellular signal-regulated kinase kinase kinase-1 (MEKK1), and other kinases with a role in cancer development, including Src tyrosine kinases.7–11 Cancers with elevated MEK1 activity, including those with an upstream activating BRAF mutation, may be therapeutic targets for E6201.12,13 Preclinical studies have demonstrated the ability of E6201 to inhibit growth and induce cell death in BRAF-mutated human cancer cell lines and xenografts, including melanoma.13–15. Here, MAP3K1 is linked to cancer.