Reductive TCA cycle catalyzed by wild-type IDH2 promotes acute myeloid leukemia and is a metabolic vulnerability for potential targeted therapy

Abstract

Background Isocitrate dehydrogenase-2 (IDH2) is a mitochondrial enzyme that catalyzes the metabolic conversion between isocitrate and alpha-ketoglutarate (α-KG) in the TCA cycle. IDH2 mutation is an oncogenic event in acute myeloid leukemia (AML) due to the generation of 2-hydroxyglutarate. However, the role of wild-type IDH2 in AML remains unknown, despite patients with it suffer worse clinical outcome than those harboring mutant type. Methods IDH2 expression in AML cell lines and patient samples was evaluated by RT-qPCR, western blotting and database analyses. The role of wild-type IDH2 in AML cell survival and proliferation was tested using genetic knockdown and pharmacological inhibition in AML cells and animal models. LC–MS, GC–MS, isotope metabolic tracing, and molecular analyses were performed to reveal the underlying mechanisms. Results We found that wild-type IDH2 was overexpressed in AML and played a major role in promoting leukemia cell survival and proliferation in vitro and in vivo. Metabolomic analyses revealed an active IDH2-mediated reductive TCA cycle that promoted the conversion of α-KG to isocitrate/citrate to facilitate glutamine utilization for lipid synthesis in AML cells. Suppression of wild-type IDH2 by shRNA resulted in elevated α-KG and decreased isocitrate/citrate, leading to reduced lipid synthesis, a significant decrease in c-Myc downregulated by α-KG, and an inhibition of AML viability and proliferation. Importantly, pharmacological inhibition of IDH2 showed significant therapeutic effect in mice inoculated with AML cells with wt-IDH2 and induced a downregulation of C-MYC in vivo. Conclusions Wt-IDH2 is an essential molecule for AML cell survival and proliferation by promoting conversion of α-KG to isocitrate for lipid synthesis and by upregulating c-Myc expression and could be a potential therapeutic target in AML.

Wild-Type Isocitrate Dehydrogenase-Dependent Oxidative Decarboxylation and Reductive Carboxylation in Cancer and Their Clinical Significance

“…Forward TCA is a catabolic pathway, while IDH1- and IDH2-mediated reverse TCA is the anabolic process of adding H and C. This process, known as reductive carboxylation, involves adding C of CO 2 directly to α-KG to form 6-C isocitrate, which isomerizes to form citrate. Studies have confirmed that the active IDH2-mediated reductive TCA cycle in acute myeloid leukemia (AML) cells promotes the conversion of α-KG to isocitrate/citrate, thereby facilitating the synthesis of lipids from glutamine [ 13 ].…”

“…Inhibition of IDH2 with AGI-6780 in mice carrying AML xenografts demonstrated significant therapeutic effects and potential clinical applications. The study also suggested that IDH2 inhibition could transform cancer treatment from cytotoxic to precision therapy and fundamentally change the cancer treatment landscape [ 13 ]. Recent research has found that shRNA inhibition of wild-type IDH2 increased α-KG, decreased c-Myc (an important oncogene), and suppressed AML viability and proliferation [ 13 ].…”

“…The study also suggested that IDH2 inhibition could transform cancer treatment from cytotoxic to precision therapy and fundamentally change the cancer treatment landscape [ 13 ]. Recent research has found that shRNA inhibition of wild-type IDH2 increased α-KG, decreased c-Myc (an important oncogene), and suppressed AML viability and proliferation [ 13 ]. Prolyl hydroxylase domain enzymes (PHDs) rely on oxygen (O 2 ), iron (Fe 2+ ), α-KG, and ascorbic acid (vitamin C), to hydroxylate HIF-1α, promoting the degradation of HIF-1α by proteases.…”

“…The reductive carboxylation provides a shortcut for this process of anabolism [ 10 , 11 ]. IDH1 and IDH2 mediate the direct generation of isocitrate from α-KG in the reductive carboxylation reaction [ 3 ], and some scholars describe this reaction process as reductive TCA or “counter-clockwise” TCA [ 12 , 13 , 14 ]. Interestingly, some studies have advocated that the reductive carboxylation catalyzed by IDH1 and 2 is inconsequential as it converts the α-KG back to isocitrate, creating an “ineffective cycle” [ 9 ].…”

Malignant transformation by oncogenic K‐ras requires IDH2‐mediated reductive carboxylation to promote glutamine utilization

“…The observations that tumorigenesis often requires multiple hits suggest that K‐ras mutation likely needs the coordination of other molecular events that enable adaptive cellular metabolism for a full malignant transformation. Based on our previous study on the impact of K‐ras on mitochondrial metabolism [ 1 , 5 ] and our recent findings that mitochondrial isocitrate dehydrogenase 2 (IDH2) could promote the “reverse” flow of the tricarboxylic acid (TCA) cycle from α‐KG to isocitrate and enhance the survival and proliferation of acute myeloid leukemia cells [ 6 ], we investigated the potential role of IDH2 in metabolic adaptation during K‐ras‐driven tumorigenesis.…”