Because amplification of mutant BRAF in AR cells caused hyperactivation of MEK and resistance to AZD6244, we hypothesized that inhibiting excess BRAF activity might restore sensitivity to AZD6244. To test this hypothesis, we treated parental and AR cells with increasing concentrations of AZD6244 or the BRAF inhibitor AZ628, alone or in combination. Although AR cells were resistant to treatment with either compound alone, they were highly sensitive to the combination. In fact, the IC50s for th...