All MEK1 mutations examined conferred robust resistance to both RAF and MEK inhibition following doxycycline induction, with fold change in GI50 (half-maximal inhibitory concentration) of 10–80 fold for dabrafenib (Fig. 3C) and 3–20 fold for trametinib (Fig. 3D) as compared to wild-type MEK1, noting that only 50% growth inhibition was maximally achieved.