AZD6244 (Selumetinib, ARRY-142886) is an orally active, highly potent and selective non-ATP competitive MEK inhibitor, inhibiting MEK1 with an IC50 of 14 nM. In vitro cell viability inhibition screening of a tumor cell line panel found that cell lines harboring BRAF or RAS mutations were more likely to be sensitive to AZD6244. Treatment of primary HCC cells with AZD6244 led to growth inhibition, caspase-3 and caspase-7 activation, poly(ADP)ribose polymerase cleavage, and inhibition of ERK1/2 and p90RSK phosphorylation. AZD6244 significantly inhibits phosphorylation of ERK1/2 in 2-1318, 5-1318, 26-1004 and 4-1318 xenografts and induces apoptosis in primary 2-1318 cells by activating the caspase pathway. Currently AZD6244 is undergoing Phase II/III clinical trials to treat solid tumors.