To test whether ERK blockade was efficacious in the context of these clinically observed resistance mechanisms, stable cell lines expressing each of these variants were engineered in a BRAFV600E A375 background. As shown in Fig. 3D, overexpression of KRASG13D (positive control), BRAFV600E (to simulate amplification), or BRAFV600EΔ2-8 all conferred resistance to PLX4032, whereas overexpression of MEK1P124L (residue proximal to N-terminal negative inhibitory domain) conferred resistance to GSK1120212.