A sub-population of viable melanoma cells persist following BRAF inhibition. Invasive WM793 human melanoma cell layers treated 48 h with DMSO or pharmacological inhibitors targeting total BRAF (SB-590885) or mutant BRAF (PLX-4720) from B-Bridge Int. (Cupertino, CA). A) Cell layers were treated with increasing concentration (0.01, 0.05, 0.1, 0.5, 1.0 μM) of inhibitors, cell lysates were generated and analyzed by Western blot using antibodies from Cell Signaling Technology (Danvers, MA); phos-MEK1/2 (9121) and total MEK1 (9124). B) Western blot analysis of lysates from cells treated with 0.5 μM SB-590885, 0.5 μM PLX-4720 or DMSO, phos-ERK1/2 (sc7383) and total ERK2 (sc154) antibodies from Santa Cruz Biotech (Santa Cruz, CA). Graphed is the mean ± SD of phos-ERK1/2:ERK2 ratio from 3 experiments with the DMSO condition set to one. C) Micrographs depicting cell layers treated with inhibitors, as described above. D) Time-course indicating viable melanoma cells following BRAF inhibitor treatments, as determined by toludine blue staining; Graph shows average ± SD).