GDC-0879 (AR-00341677) is a novel, potent and selective B-Raf inhibitor with IC50 of 0.13 nM with activity against c-Raf as well.

GDC-0879 also inhibits cellular pERK with IC50 of 63 nM. GDC-0879 shows comparable potency in A375 melanoma and Colo205 colorectal carcinoma cell lines, both of which are B-RafV600E mutant, with IC50 of 59 nM and 29 nM for pMEK1 inhibition respectively. GDC-0879 potently inhibits B-RafV600E in Malme3M cells with IC50 of 0.75 μM. GDC-0879 also shows EC50 values < 0.5 μM in many tumor cells (A375, 624, SK-MEL-28, Malme3M, C32, 928, 888, G-361, Colo205, Colo206, SW1417, CL34, and Colo201). [1]

In GDC-0879 treated mice, both cell line- and patient-derived BRAFV600E tumors exhibit stronger and more sustained pharmacodynamic inhibition (>90% for 8 hours) and improved survival compared to mutant KRAS-expressing tumors. Although there is involvement of activated RAF signaling in RAS-induced tumorigenesis, decreased time to progression is observed for some KRAS-mutant tumors following GDC-0879 administration. Whereas GDC-0879-mediated efficacy is associated strictly with B-RafV600E status, MEK inhibition also attenuates proliferation and tumor growth of cell lines expressing wild-type BRAF (81% KRAS mutant, 38% KRAS wild type). The responsiveness of B-RafV600E melanoma cells to GDC-0879 could be dramatically altered by pharmacologic and genetic modulation of PI3K pathway activity. [2]