Metabolic control of normal and malignant hematopoiesis

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PROJECT SUMMARY/ABSTRACT Somatic mutations in the isocitrate dehydrogenase (IDH) enzymes contribute to the pathogenesis of acute myeloid leukemia (AML) and other malignancies via production of the ‘oncometabolite’ D-2-hydroxyglutarate (D-2HG). D-2HG blocks differentiation of malignant cells by inhibiting alpha-ketoglutarate (KG)-dependent enzymes that regulate chromatin structure and gene expression. Small molecule inhibitors of mutant IDH enzymes are promising new therapies for AML, but their efficacy remains limited to the subset of patients with IDH mutations. This raises the question as to whether analogous metabolic aberrations might contribute to leukemogenesis in IDH-wildtype AML. Intriguingly, 2HG is a chiral molecule that can exist in either the D- or L- enantiomer. Although cancer-associated IDH mutants exclusively produce D-2HG, biochemical studies indicate that L-2HG can function as a ~10-fold more potent inhibitor of many KG-dependent enzymes, including chromatin modifiers and regulators of hypoxia-inducible factor (HIF) stability. However, biological sources and activities of L-2HG have been poorly understood. We identified a metabolic pathway wherein normal and malignant cells without IDH mutations selectively produce L-2HG in response to oxygen limitation (a.k.a. hypoxia) through an unusual reaction catalyzed by lactate dehydrogenase (LDHA). We show that hypoxia-induced L-2HG enhances stability of HIF, increases repressive chromatin modifications, and blocks differentiation of stem/progenitor cells. These findings suggest that L-2HG might account, at least in part, for the importance of hypoxic niches, HIF, and LDHA in balancing self-renewal and differentiation of stem cell populations, including hematopoietic stem/progenitor cells (HSPC) and leukemia stem cells. Thus, we hypothesize that L-2HG functions as a metabolic signal that couples hypoxic niches to the maintenance of normal blood stem cells and leukemia stem cells. This hypothesis will be rigorously addressed in three Specific Aims. Aim 1 will define the molecular mechanisms by which L-2HG regulates blood cell differentiation in vitro. In this Aim, we will define the effects of L-2HG on gene expression and chromatin structure and determine how these inputs balance HSPC stemness and lineage differentiation. Aim 2 will determine how L-2HG functions to control normal and malignant hematopoiesis in vivo. This Aim will use novel genetically engineered mouse models that allow for tissue-specific, inducible manipulation of L-2HG levels in order to dissect the role of L-2HG in normal hematopoiesis and leukemia. Aim 3 will elucidate the oncogenic mechanisms and therapeutic potential of L-2HG in human leukemia. In this Aim, we will use primary AML biospecimens and patient-derived xenografts to determine the mechanisms that lead to deregulated L- 2HG in a subset of AML and assess whether depleting L-2HG offers a promising strategy to treat human AML. The proposed studies will offer fundamental insights into the metabolic control of normal and malignant stem cell biology and expand the applicability of metabolic targeted therapies for leukemia and other cancers.