Vemurafenib is a B-Raf enzyme inhibitor developed by Plexxikon (now part of the Daiichi Sankyo group) and Genentech for the treatment of late-stage melanoma. Vemurafenib has been shown to cause programmed cell death in melanoma cell lines. Vemurafenib interrupts the B-Raf/MEK step on the B-Raf/MEK/ERK pathway − if the B-Raf has the common V600E mutation. Vemurafenib only works in melanoma patients whose cancer has a V600E BRAF mutation (that is, at amino acid position number 600 on the B-Raf protein, the normal valine is replaced by glutamic acid). About 60% of melanomas have this mutation. It also has efficacy against the rarer BRAF V600K mutation. Melanoma cells without these mutations are not inhibited by vemurafenib; the drug paradoxically stimulates normal BRAF and may promote tumor growth in such cases.
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