Limited nutrient availability in the tumor microenvironment renders pancreatic tumors sensitive to allosteric IDH1 inhibitors

Articles https://doi.org/10.1038/s43018-022-00393-y Limited nutrient availability in the tumor microenvironment renders pancreatic tumors sensitive to allosteric IDH1 inhibitors Ali Vaziri-Gohar1, Joel Cassel2, Farheen S. Mohammed2, Mehrdad Zarei1,3, Jonathan J. Hue1,3, Omid Hajihassani1, Hallie J. Graor1, Yellamelli V. V. Srikanth2, Saadia A. Karim 4, Ata Abbas 1, Erin Prendergast5, Vanessa Chen6, Erryk S. Katayama 1, Katerina Dukleska7, Imran Khokhar7, Anthony Andren8, Li Zhang8, Chunying Wu9, Bernadette Erokwu9, Chris A. Flask10, Mahsa Zarei11, Rui Wang1, Luke D. Rothermel3, Andrea M. P. Romani12, Jessica Bowers13, Robert Getts13, Curtis Tatsuoka14, Jennifer P. Morton4,15, Ilya Bederman5, Henri Brunengraber16, Costas A. Lyssiotis Joseph M. Salvino 2, Jonathan R. Brody17 and Jordan M. Winter 1,3 ✉ , 8 Nutrient-deprived conditions in the tumor microenvironment (TME) restrain cancer cell viability due to increased free radicals and reduced energy production. In pancreatic cancer cells a cytosolic metabolic enzyme, wild-type isocitrate dehydrogenase 1 (wtIDH1), enables adaptation to these conditions. Under nutrient starvation, wtIDH1 oxidizes isocitrate to generate α-ketoglutarate (αKG) for anaplerosis and NADPH to support antioxidant defense. In this study, we show that allosteric inhibitors of mutant IDH1 (mIDH1) are potent wtIDH1 inhibitors under conditions present in the TME. We demonstrate that low magnesium levels facilitate allosteric inhibition of wtIDH1, which is lethal to cancer cells when nutrients are limited. Furthermore, the Food & Drug Administration (FDA)-approved mIDH1 inhibitor ivosidenib (AG-120) dramatically inhibited tumor growth in preclinical models of pancreatic cancer, highlighting this approach as a potential therapeutic strategy against wild-type IDH1 cancers. P ancreatic cancer (pancreatic ductal adenocarcinoma, PDAC) cells adapt to austere conditions created by a dense and hypovascular stroma in the TME1–6. These same adaptive survival pathways protect pancreatic cancer cells against chemotherapy7. Thus, the best available treatments against PDAC (that is, chemotherapy) are less effective under tumor-associated conditions. Investigative pursuits that identify metabolic dependencies in primary and metastatic pancreatic cancer1,8–15 should reveal attractive therapeutic alternatives that attack biologic vulnerabilities, especially in the context of the TME. Examples of relevant biologic processes utilized by PDAC cells to overcome nutrient limitation include autophagy16, macropinocytosis3,17 and the utilization of secreted alanine from pancreatic stellate cells18. A growing body of evidence shows that mitochondrial function and antioxidant defense are also crucial under low nutrient conditions. When energy substrates are scarce, oxidative phosphorylation is needed to maximize ATP generation19,20 and nutrient limitation is highly oxidative because glucose is the principal substrate for NADPH synthesis21–23. We previously determined that an RNA-binding protein, human antigen R (HuR; ELAVL1), enhanced both antioxidant defense and mitochondrial function under nutrient withdrawal. HuR accomplishes this in part through post-transcriptional stabilization of wtIDH1. Out of 40 antioxidant enzymes, only IDH1 expression was lost in multiple HuR-knockout cell lines, pointing to an HuR–IDH1 regulatory axis as a key component of the acute antioxidant response to stress2,24. Additional studies identified the regulatory HuR binding site on the IDH1 3'-UTR7. IDH1 is a cytosolic enzyme that catalyzes the reversible conversion of isocitrate and αKG. The reaction uses NADP+ or NADPH as a cofactor, depending on the direction of the reaction25–27. Surprisingly few studies have focused on the role of wtIDH1 in cancer cell survival and tumor growth7,25–31, and these studies generally did not consider the reliance of cancer cells on wtIDH1 in Case Comprehensive Cancer Center, Case Western Reserve University, Cleveland, OH, USA. 2Molecular and Cellular Oncogenesis Program, The Wistar Institute, Philadelphia, PA, USA. 3Department of Surgery, Division of Surgical Oncology, University Hospitals, Cleveland Medical Center, Cleveland, OH, USA. 4Cancer Research UK Beatson Institute, Glasgow, UK. 5Department of Genetics and Genome Sciences, Case Western Reserve University, Cleveland, OH, USA. 6Department of Nutrition, Case Western Reserve University, Cleveland, OH, USA. 7Jefferson Pancreas, Biliary and Related Cancer Center, Thomas Jefferson University, Philadelphia, PA, USA. 8Department of Molecular and Integrative Physiology, University of Michigan School of Medicine, Ann Arbor, MI, USA. 9Department of Radiology, Case Western Reserve University, Cleveland, OH, USA. 10Deptartments of Radiology, Biomedical Engineering, and Pediatrics, Case Western Reserve University, Cleveland, OH, USA. 11Department of Veterinary Physiology and Pharmacology, Texas A&M University, College Station, TX, USA. 12Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH, USA. 13Code Biotherapeutics Inc, Hatfield, PA, USA. 14Department of Population and Quantitative Health Sciences, Case Western Reserve University, Cleveland, OH, USA. 15Institute of Cancer Sciences, University of Glasgow, Glasgow, UK. 16Department of Nutrition and Biochemistry, Case Western Reserve University, Cleveland, OH, USA. 17 Brenden Colson Center for Pancreatic Care; Departments of Surgery and Cell, Developmental & Cancer Biology; Knight Cancer Institute, Oregon Health and Science University, Portland, OR, USA. ✉e-mail: 1 Nature Cancer | www.nature.com/natcancer Articles the context of nutrient limitation, which is a key feature of tumors7. However, this cancer-associated stress is relevant since studies suggest that glucose may be more limiting than oxygen within the TME32. Based on our previous studies revealing IDH1 as a regulatory target of HuR, and the enzyme’s direct role in the generation of NADPH and αKG through the oxidation of isocitrate, we hypothesized that wtIDH1 is essential for PDAC cells under metabolic stress. More specifically, we suspected that the products of the oxidative wtIDH1 reaction, NADPH and αKG, directly power antioxidant defense and mitochondrial function to promote PDAC survival. Herein, we also demonstrate that compounds developed to target mutant IDH1 can be repurposed as wild-type IDH1 inhibitors, because these drugs surprisingly become potent inhibitors of wtIDH1 in cancer cells under conditions present in tumors: specifically, we found that wtIDH1 is critical for PDAC cell survival under low-glucose conditions, and allosteric IDH inhibitors effectively block wtIDH1 activity under low magnesium. Results IDH1 protects PDAC cells from oxidative stress under nutrient limitation. Pancreatic ductal adenocarcinoma cells were cultured under low-glucose conditions (2.5 mM) to simulate the levels present in the pancreatic cancer microenvironment3. A surge i (...truncated)