LAUSR

Simple Summary We demonstrate that the pan-RAF inhibitor LY3009120 induces apoptosis and inhibits proliferation in AML cells harboring RAS or FLT3 mutations through action on the RAS/RAF/MEK/ERK and the AKT/mTOR pathways. Notably, pan-RAF inhibition combined with Ara-C overcomes drug resistance mediated by bone marrow-derived mesenchymal stem cells. Furthermore, the combination of LY3009120 and tyrosine kinase inhibition with sorafenib appears to synergistically increase apoptosis in AML cells carrying FLT3-ITD mutation. Abstract RAF molecules play a critical role in cell signaling through their integral impact on the RAS/RAF/MEK/ERK signaling pathway, which is constitutively activated in a sizeable subset of acute myeloid leukemia (AML) patients. We evaluated the impact of pan-RAF inhibition using LY3009120 in AML cells harboring mutations upstream and downstream of RAF. LY3009120 had anti-proliferative and pro-apoptotic effects and suppressed pERK1/2 levels in leukemic cells with RAS and FLT3 mutations. Using reverse protein phase array analysis, we identified reductions in the expression/activation of cell signaling components downstream of RAF (activated p38) and cell cycle regulators (Wee1/cyclin B1, Cdc2/Cdk1, activated Rb, etc.). Notably, LY3009120 potentiated the effect of Ara-C on AML cells and overcame bone marrow mesenchymal stromal cell-mediated chemoresistance, with RAS-mutated cells showing a notable reduction in pAKT (Ser473). Furthermore, the combination of LY3009120 and sorafenib resulted in significantly higher levels of apoptosis in AML cells with heterozygous and hemizygous FLT3 mutations. In conclusion, pan-RAF inhibition in AML using LY3009120 results in anti-leukemic activity, and combination with Ara-C or sorafenib potentiates its effect.