Inhibition of glutamine metabolism counteracts pancreatic cancer stem cell features and sensitizes cells to radiotherapy

Abstract

Pancreatic ductal adenocarcinoma (PDAC) cells utilize a novel non-canonical pathway of glutamine metabolism that is essential for tumor growth and redox balance. Inhibition of this metabolic pathway in PDAC can potentially synergize with therapies that increase intracellular reactive oxygen species (ROS) such as radiation. Here, we evaluated the dependence of pancreatic cancer stem cells (PCSCs) on this non-canonical glutamine metabolism pathway and researched whether inhibiting this pathway can enhance radiosensitivity of PCSCs. We showed that glutamine deprivation significantly inhibited self-renewal, decreased expression of stemness-related genes, increased intracellular ROS, and induced apoptosis in PCSCs. These effects were countered by oxaloacetate, but not α-ketoglutarate. Knockdown of glutamic-oxaloacetic transaminase dramatically impaired PCSCs properties, while glutamate dehydrogenase knockdown had a limited effect, suggesting a dependence of PCSCs on non-canonical glutamine metabolism. Additionally, glutamine deprivation significantly increased radiation-induced ROS and sensitized PCSCs to fractionated radiation. Moreover, transaminase inhibitors effectively enhanced ROS generation, promoted radiation sensitivity, and attenuated tumor growth in nude mice following radiation exposure. Our findings reveal that inhibiting the non-canonical pathway of glutamine metabolism enhances the PCSC radiosensitivity and may be an effective adjunct in cancer radiotherapy.

Metabolism and Gut Microbiota in Cancer Immunoediting, CD8/Treg Ratios, Immune Cell Homeostasis, and Cancer (Immuno)Therapy: Concise Review

“…Gordon et al showed that the largest CSC subpopulation in breast cancer exhibited a glycolytic gene expression profile even in the presence of ample oxygen, suggesting preferential reliance on glycolysis. Li et al showed additionally dependence of pancreatic cancer stem cells (PCSCs) on glutamine; the authors showed that glutamine deprivation negatively affected self‐renewal and expression of stemness‐related genes, increased apoptosis, and enhanced PCSC radiosensitivity.…”

Spheroid cancer stem cells display reprogrammed metabolism and obtain energy by actively running the tricarboxylic acid (TCA) cycle

“…One of the experimental approaches for obtaining CSC-like properties in cells is to culture cancer cells in suspension, resulting in spheroid-shaped cells [6–8]. Indeed, a previous study has suggested that metabolic profiles in spheroid-derived cells from ovarian serous adenocarcinoma were different from those in cancer cells that were cultured in adherent plates [8].…”

“…Additionally, the differences in the metabolites generated under 3D and 2D conditions were attributable to the amino acids that are essential for actively and efficiently carrying out TCA cycle reactions; namely, serine, aspartate, glutamate and glutamine [6, 9–15]. Indeed, these amino acids were significantly increased in 3D conditions when compared to 2D conditions.…”

“…We herein report that activation of TCA cycles appears to be a metabolic feature of CSCs that distinguishes them from non-CSCs. Although metabolic pathways of the amino acids, especially serine and glutamine, are already considered as targets for cancer therapy [6, 14, 15], they are additionally proposed as potential targets for CSC treatment.…”

Targeting metabolic vulnerabilities of cancer: Small molecule inhibitors in clinic

“…While GLS inhibitors may serve as monotherapies, their combination with other concurrent therapies such as radiotherapy, chemotherapy or immunotherapy is equally intriguing. With respect to radio‐ and chemotherapy, studies in PDAC have demonstrated that GLS inhibition leads to increased radio‐sensitivity, largely due to increased ROS generation, an aspect likely linked to alterations in glutathione biosynthesis, a well‐documented contributor to drug resistance . Indeed, studies in triple‐negative breast cancer have demonstrated considerable effects of CB‐839 on reducing glutathione levels in a cell line‐dependent manner .…”