MAP2K1 and cancer: In preclinical models, E6201 administration (on a Q4D x3 schedule) in BRAF-mutated human cancer xenograft models resulted in significant and prolonged anti-tumour activity lasting >20 days from first dose.13 MEK1 inhibition occurred only 8 h after dosing, and was sustained for 72 h postdose despite the short t1/2 of E6201 (~3–6 h).11,18 Anticipating a similarly delayed effect in humans, a weekly dosing regimen was proposed.