Combination treatment has proven effective for patients with
acute promyelocytic leukemia, exemplifying the importance of
therapy targeting multiple components of oncogenic regulation for a successful outcome. However, recent studies have shown that the mutational complexity of
acute myeloid leukemia (AML) precludes the translation of molecular targeting into clinical success. Here, as a
complement to genetic profiling, we used unbiased, combinatorial in vitro
drug screening to identify pathways that drive AML and to develop personalized combinatorial treatments. First, we screened 513 natural compounds on primary AML cells and identified a novel
diterpene (H4) that preferentially induced differentiation of FLT3 wild-type AML, while FLT3-ITD/mutations conferred resistance. The samples responding to H4, displayed increased expression of myeloid markers, a clear decrease in the nuclear-cytoplasmic ratio and the potential of re-activation of the monocytic transcriptional program reducing
leukemia propagation in vivo. By combinatorial screening using H4 and molecules with defined targets, we demonstrated that H4 induces differentiation by the activation of the
protein kinase C (PKC) signaling pathway, and in line with this, activates PKC phosphorylation and translocation of PKC to the cell membrane. Furthermore, the combinatorial screening identified a bromo- and extra-terminal domain (BET) inhibitor that could further improve H4-dependent leukemic differentiation in FLT3 wild-type monocytic AML. These findings illustrate the value of an unbiased, multiplex screening platform for developing combinatorial therapeutic approaches for AML.