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

Abstract

// Doudou Li 1, 7, * , Zhiqiang Fu 2, 7, * , Ruiwan Chen 3, * , Xiaohui Zhao 4, 7 , Yu Zhou 2, 5, 7 , Bing Zeng 2 , Min Yu 2, 5 , Quanbo Zhou 2 , Qing Lin 2 , Wenchao Gao 2, 7 , Huilin Ye 2, 7 , Jiajia Zhou 6 , Zhihua Li 4 , Yimin Liu 1, 7 , Rufu Chen 2, 7 1 Department of Radiotherapy, Sun Yat-sen Memorial Hospital, Sun Yat-sen University, Guangzhou, China 2 Department of Hepato-Pancreato-Billiary Surgery, Sun Yat-sen Memorial Hospital, Sun Yat-sen University, Guangzhou, China 3 Department of Radiotherapy, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China 4 Department of Medical Oncology, Sun Yat-sen Memorial Hospital, Sun Yat-sen University, Guangzhou, China 5 Department of General Surgery, Guangdong General Hospital, Guangzhou, China 6 Department of Pediatric Surgery, Sun Yat-sen Memorial Hospital, Sun Yat-sen University, Guangzhou, China 7 Key Laboratory of Malignant Tumor Gene Regulation and Target Therapy of Guangdong Higher Education Institutes, Sun Yat-sen Memorial Hospital, Sun Yat-sen University, Guangzhou, China * These authors have contributed equally to this work Correspondence to: Rufu Chen, e-mail: chenrf_sysu@163.com Zhihua Li, e-mail: lizhihuasysu@163.com Yimin Liu, e-mail: liuyimin_sysu@163.com Keywords: pancreatic ductal adenocarcinoma, glutamine metabolism, cancer stem cells, reactive oxygen species, radiosensitivity Received: January 24, 2015      Accepted: August 21, 2015      Published: September 03, 2015 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.