AUTHOR=Stones Clare J., Kim Ji Eun , Joseph Wayne R., Marshall Elaine S., Leung Euphemia , Finlay Graeme J., Shelling Andrew N., Baguley Bruce C.

TITLE=Comparison of responses of human melanoma cell lines to MEK and BRAF inhibitors

JOURNAL=Frontiers in Genetics

VOLUME=4

YEAR=2013

URL=https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2013.00066

DOI=10.3389/fgene.2013.00066

ISSN=1664-8021

ABSTRACT=<p>The <italic>NRAS</italic> and <italic>BRAF</italic> genes are frequently mutated in melanoma, suggesting that the NRAS-BRAF-MEK-ERK signaling pathway is an important target for therapy. Two classes of drugs, one targeting activated BRAF and one targeting MEK, are currently undergoing clinical evaluation. We have analysed the <italic>NRAS</italic> and <italic>BRAF</italic> mutational status of a series of 44 early passage lines developed from New Zealand patients with metastatic melanoma. 41% of the lines analysed had <italic>BRAF</italic> mutations, 23% had <italic>NRAS</italic> mutations, and 36% had neither. We then determined IC<sub>50</sub> values (drug concentrations for 50% growth inhibition) for CI-1040, a commonly used inhibitor of MEK kinase; trametinib, a clinical agent targeting MEK kinase; and vemurafenib, an inhibitor of mutant BRAF kinase. Cell lines with activating <italic>BRAF</italic> mutations were significantly more sensitive to vemurafenib than lines with <italic>NRAS</italic> mutations or lines lacking either mutation (<italic>p</italic> &lt; 0.001). IC<sub>50</sub> values for CI-1040 and trametinib were strongly correlated (<italic>r</italic> = 0.98) with trametinib showing ~100-fold greater potency. Cell lines sensitive to vemurafenib were also sensitive to CI-1040 and trametinib, but there was no relationship between IC<sub>50</sub> values and <italic>NRAS</italic> mutation status. A small number of lines lacking a <italic>BRAF</italic> mutation were sensitive to CI-1040 but resistant to vemurafenib. We used western blotting to investigate the effect on ERK phosphorylation of CI-1040 in four lines, of vemurafenib in two lines and of trametinib in two lines. The results support the view that MEK inhibitors might be combined with BRAF inhibitors in the treatment of melanomas with activated <italic>BRAF</italic>. The high sensitivity to trametinib of some lines with wildtype <italic>BRAF</italic> status also suggests that MEK inhibitors could have a therapeutic effect against some melanomas as single agents.</p>