Targeting PLCG1 in AML1-ETO-positive acute myeloid leukemia (AML)

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Acute myeloid leukemia (AML) is a clonal hematopoietic disorder characterized by the accumulation of immature and proliferating blasts in the bone marrow, peripheral blood and other organs. Molecular heterogeneity of AML remains a major therapeutic challenge. Different genomic AML profiles contribute to disease biology and translate to variable outcomes. This molecular and clinical heterogeneity may also depend on the cellular origin of the different AML subtypes. On the other hand, presence of specific aberrations can create secondary dependencies and vulnerabilities. Within the first funding period we aimed to identify novel molecular targets for fusion oncogene–induced acute myeloid leukemia (AML). We performed high-resolution proteomic analysis. In AML1-ETO (AE)-driven AML, we uncovered a deregulation of phospholipase C (PLC) signaling. Of note, highest expression levels were found in AML harboring the balanced translocation t(8;21), which gives rise to the oncogenic fusion AML1-ETO. We identified PLCgamma1 (PLCG1) as a specific target of the AE fusion protein that is induced after AE binding to intergenic regulatory DNA elements. Genetic inactivation of PLCG1 in a newly developed conditional mouse model and in human AML inhibited AML1-ETO dependent self-renewal programs, leukemic proliferation, and leukemia maintenance in vivo. In contrast, PLCG1 was dispensable for normal hematopoietic stem and progenitor cell function. These findings are extended to and confirmed by pharmacologic perturbation of calcium-signaling in AML1-ETO AML cells, indicating that the PLCG1 pathway poses an important therapeutic target for AML1-ETO1 leukemic stem cells. While the upstream regulation of PLCG1 in AE-AML has been characterized, its downstream regulation and mechanistic function remains elusive. According to our proposed working program we will identify relevant effectors and specify dependencies of PLCG1 in AE-AML and aim to uncover mechanistic roles of PLCG1 to facilitate targeting of PLCG1 in AE-AML. Using CRISPR-mediated screens, we have identified relevant domains of PLCG1 indicating targetable regions. Using global phospho-proteome analysis and functional genome editing approaches we will define effectors and dependencies of PLCG1 in AML1-ETO (AE) driven AML. Using the conditional mouse model created in the first funding period, we will conduct rescue experiments, genetic perturbation of relevant PLCG1 domains and interactome analyses to uncover targetable molecular mechanisms downstream of PLCG1 in AML1-ETO AML.