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Investigation into the Mechanisms of Acute Myeloid Leukemia (AML) Tumorigenesis and Chemoresistance via Systems Analysis of Mitochondrial Form and Function

Funded by the Department of Defense (DOD - W81XWH-19-1-0213)

Background: The present application aligns with the FY18 PRCRP Military Relevance Focus Area: Blood Cancer. While the proposed work specifically focuses on acute myeloid leukemia (AML), experimental findings from this work will likely have broad scientific relevance to other blood and non-blood cancers. Rationale for this application stems from a growing body of evidence linking multiple aspects of AML biology (e.g., tumorigenesis, chemoresistance) to altered mitochondrial quantity and quality. Related to this, several groups have recently demonstrated efficacy in treating both leukemic tumorigenesis and drug-resistance, the major cause of treatment failure, by targeting mitochondrial oxidative phosphorylation (OXPHOS). While these studies have ignited interest in mitochondrial-targeted chemotherapeutics, clinical success for these ‘mito-therapeutics’ will most certainly hinge upon their ability to specifically target only leukemic mitochondria. Functional interrogation of AML mitochondria using a recently described mitochondrial diagnostic platform unveiled a remarkable bioenergetic phenotype shared across chemo-sensitive and resistant AML. Specifically, when AML mitochondria were exposed to physiological ATP free energy (i.e., ΔGATP mimicking resting energy charge), they were found to be refractory to chemical uncoupling. Given the dependence of this effect on ΔGATP, we hypothesize that this unique bioenergetic phenotype is mediated by inhibitory phosphorylation of the ETS.

Objective/Hypothesis: Our primary objective is twofold: 1) fully characterize the unique bioenergetic signature(s) of AML tumorigenesis and chemoresistance; 2) identify the mitochondrial protein kinases responsible for identified alterations in the mitochondrial phosphoproteome of AML mitochondria. Our guiding hypothesis is that bioenergetic efficiency is differentially regulated in the setting of AML tumorigenesis and drug-resistance via a currently unidentified collection of discrete respiratory control parameters and phosphorylation signatures.

Specific Aims: 1) Determine the unique bioenergetic phenotypes that differentiate AML cells from non-cancerous hematopoietic controls, as well as those linked to AML chemoresistance, the major cause of treatment failure. 2) Determine the phosphoproteomic landscape of mitochondria derived from hematopoietic controls and AML cells (sensitive and refractory to several chemotherapeutics) using bottom-up mass spectrometry.

Study Design: To accomplish these aims, my team will leverage a state-of-the-art assay platform which unites discovery-based molecular omics with comprehensive bioenergetic characterization. Specifically, comprehensive bioenergetic characterization as well as global analysis of the mitochondrial phosphoproteome will be carried out in isolated mitochondrial populations derived from healthy human peripheral blood cells, as well as various chemo-sensitive and resistant AML cell lines.

Innovation: Until this point, most pharmacological interventions targeting the mitochondria of proliferating leukemic blasts have attempted to induce cell death via further interference with bioenergetic efficiency. While this strategy has proven effective in isolated systems and small organisms, such treatments when translated to the clinic will also interfere with bioenergetic efficiency across the >200 distinct cell types of the human body, the majority of which require high ΔGATP for optimal physiological function. The goal of targeted cancer treatment is to identity unique molecular pathways or mechanisms that are specific only to neoplastic growth and then develop drugs against those targets. The central goal of this application is to complete the requisite first step in this process: identify the unique bioenergetic signature(s) of AML tumorigenesis and chemoresistance. To illustrate the impact, if indeed lower bioenergetic efficiency in AML is successfully ascribed to inhibitory phosphorylation of the ETS, then it stands to reason that this unique feature, found only in AML mitochondria, could be effectively targeted via pharmacologic inhibition of the implicated kinase(s). Indeed, kinase inhibitors are common chemotherapeutics employed across several cancers; however, no such drugs currently exist for AML that target matrix kinase activity.

Military Relevance: Although the cause of AML is unknown, risk factors include age, prior chemotherapy and exposure to benzene, as well as ionizing radiation. This latter exposure is particularly relevant to military veterans, as the US Department of Veteran Affairs lists AML as a “presumptive disease” qualifying veterans exposed to “radiation-risk activity” for disability compensation. Thus, continuing research into mechanisms of AML tumorigenesis is within the scope of the FY18 PRCRP Military Relevance Focus Area: Blood Cancer.