BRAF and melanoma: To understand why melanoma cells harboring mutant forms of NRAS are resistant to MEKi, which are effective for treating BRAF-mutant melanomas, we established polyclonal cells with acquired trametinib resistance from cell lines harboring NRAS mutations (SK-MEL-2, Q61R; SK-MEL-30, Q61K; SK-MEL-147, Q61R; Figure 1A).