Somatic mutations in catalytic arginine residues of IDH1 and IDH2 contribute to the pathogenesis of acute myeloid leukemia (AML) through the production of the oncometabolite (R)-2-hydroxyglutarate (R-2-HG). Accumulating R-2HG causes epigenetic alterations by impairing αKG-dependent dioxygenases. Allosteric inhibitors of mutant IDH suppress R-2HG production and induce differentiation of leukemic blasts. These findings provide the basis of two targeted therapies for AML (ivosidenib and enasidenib), establishing the first example of personalized therapy based on cancer metabolism. However, the low response rate and the development of resistance to IDHmut inhibitors are major clinical challenges. Moreover, therapy resistance to IDH inhibition can occur through multiple mechanisms, including the selection of R-2HG-restoring second-site mutations or other sub-clonal mutations. These findings underscore the importance of developing more effective approaches for the treatment of IDH-mutant MDS and AML patients. Here we developed a panel of isogenic myeloid leukemia cell lines containing the most common IDH1 or IDH2 oncogenic mutations by CRISPR base editing. By saturation mutagenesis of IDH single-amino acid variants, we identified a repertoire of IDH second-site mutations responsible for therapy resistance through disabling uncompetitive enzyme inhibition. Recurrent mutations at NADPH binding sites within IDH heterodimers act in cis or trans to prevent the formation of stable enzyme-inhibitor complexes, restore R-2HG production in the presence of inhibitors, and drive therapy resistance in IDH-mutant AML cells and patients. Moreover, by transcriptomic and epigenomic profiling of base-edited isogenic cells, we identified a new regulatory axis involving the CD44-mediated rewiring of intracellular metabolism, which is required for mutant IDH-catalyzed R-2-HG production. More importantly, primary and resistant IDH-mutant leukemia cells are sensitive to combined IDH inhibition and genetic or pharmacologic inactivation of CD44 in vitro and in vivo. Taken together, our findings uncover a cell adhesion molecule-mediated metabolic signaling pathway as a new targetable dependency of IDH-mutant leukemia cells, with therapeutic implications for more effective treatment of primary and resistant IDH-mutant myeloid malignancies.

Citation Format: Jian Xu. Targeting IDH-mutant myeloid leukemia by disabling metabolic dependencies [abstract]. In: Proceedings of the AACR Special Conference: Acute Myeloid Leukemia and Myelodysplastic Syndrome; 2023 Jan 23-25; Austin, TX. Philadelphia (PA): AACR; Blood Cancer Discov 2023;4(3_Suppl):Abstract nr IA11.