Study of novel targets for therapy of acute leukemia

Acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) are genetically complex leukemias that are caused by the cooperation of multiple oncogenic driver genes. Current treatment of ALL and AML consists of combination chemotherapy and/or stem cell transplantation, with variable outcome based on type of leukemia, molecular subclass and age of the patients. With the increasing molecular insights in the pathogenesis of AML and ALL, the introduction of targeted therapies could potentially improve the outcome and reduce the toxicities of the current therapies. In this work, we studied the MYB transcriptional pathway, the FLT3 kinase and the Hedgehog signaling pathway as potential targets for therapy in ALL or AML. The MYB transcription factor was previously shown to be deregulated in ALL and AML due to duplications and translocations of the MYB gene. In this work we performed a mutation analysis of the complete MYB gene in T-ALL to identify alternative oncogenic activation mechanisms, but we did not identify recurrent mutations. By gene expression profiles we determined genes that were regulated by MYB, of which some were critical for the observed effects of MYB on differentiation. In a second part, we performed a cell based high-throughput screening of 25607 compounds, with the aim to identify inhibitors of MYB dependent and FLT3 dependent leukemia cell lines. In this way, we identified new FLT3/PDGFR inhibitors, and also several inhibitors that did not act on FLT3 and for which we were investigating if their mechanism of action was through the MYB transcriptional pathway or still through other targets. Related to this work, we showed that the FLT3 mutations N676D and G697R conferred resistance against the currently used FLT3 inhibitor, AC220, stating the need for novel FLT3 inhibitors. In a third part, we investigated the effect of Hedgehog pathway inhibitors on the proliferation of T-ALL cells. The hedgehog pathway is important in development of many tissues and is known to be overactivated in various solid tumors. Treatment of T-ALL cell lines with different Hedgehog pathway antagonists showed a reduced proliferation of the cell lines and in the case of itraconazole we could even observe a block of cell cycle and induction of apoptosis. In addition, we identified mutations in the Hedgehog pathway, confirming activation of the pathway in a subset of T-ALL. Hedgehog pathway inhibitors are already in clinical development for the treatment of solid tumors, and our work demonstrates that they may also be applied for the treatment of specific leukemias. Our work contributes to the characterization of ALL and AML, and may lead to the development of new therapeutic strategies for the treatment of acute leukemia.status: publishe