Project 2: Microenvironmental and inflammatory mechanisms in MDM4-driven AML pathogenesis.

Project Summary/Abstract Recent studies have demonstrated the existence of preleukemic (preL) HSPC (which includes the phenomenon of age-related clonal hematopoiesis (ARCH)) in human MDS and AML. In the majority of patients, the disease clone occurring at relapse/progression is not directly derived from the

initially transformed LSC clone through the acquisition of additional mutations, but is rather arising from preexisting preL-HSPC clones. These observations have fundamentally challenged the classical model of linear-divergent tumor progression, and indicate that heterogeneous preleukemic cell states early in the transformation process hold the key for understanding the

origin of tumor heterogeneity, stem cell subclonal dynamics, competition and selection, and progression and death of patients. We have previously discovered that mouse/human double minute 4 (MDM4/HDM4; synonym: MDMX/HDMX) is significantly overexpressed in the vast majority of patients with AML, including at the stem cell level. Elevated MDM4 expands and

increases competitiveness of preL HSPC, promotes ARCH/MDS-to-AML progression in several newly developed mouse models, and patient data indicates that MDM4high MDS patients are at significantly higher risk to progress to AML. For this project, and based on published and newer preliminary data, we hypothesize that MDM4 overexpression acts in ARCH/MDS-to-AML

progression in the context of microenvironmental changes and selection pressures that are frequently encountered during aging and inflammatory stress. Preliminary data imply specifically the βcat/Cnot6l axis as well as IL-1 signaling in the progression of Mdm4high ARCH/MDS to AML. We will determine the role of stromal and inflammatory changes in selection, expansion, and

progression of the MDM4high pre-leukemic stem cell pool; identify and functionally characterize molecular mechanisms employed by the stroma and inflammatory stress that mediate MDM4- dependent progression of ARCH and MDS, using a combination of CITE-seq, subclonal tracking, spatial mapping, and analysis of select targets on longitudinal samples during progression; and,

examine whether preemptive combinatorial targeting of the MDM4/TP53 interaction and cell extrinsically-driven pathways can prevent progression of ARCH and MDS by testing clinically available inhibitors of MDM4/TP53, combined with either genetic or pharmacologic targeting of identified stromal and inflammatory pathways. These studies will provide novel mechanistic

insights into combinatorial cell-intrinsic/extrinsic preleukemic to AML progression as well as a preclinical proof-of-concept for the design of preventative clinical trials in the future.