Abstract 2411: The pentose-phosphate pathway induces pancreatic cancer radioresistance, a preclinical study with clinical validation
Authors: Shimoni-Sebag Ariel , Abramovich Ifat , Agranovich Bella , Sirovsky Yaarit , Stossel Chani , Atias Dikla , Raitses-Gurevich Maria , Glick-Gorman Yulia , Margalit Ofer , Regev David , Tal Rotem , Tirosh Itay , Golan Talia , Yizhak Keren , Gottlieb Eyal , Lawrence Yaacov R. 
Published: April 2023

Abstract
Purpose: Pancreatic ductal adenocarcinoma (PDAC) is remarkably resistant to standard modalities, including radiotherapy (RT). The mechanisms of radiation resistance in general, and pancreatic cancer in particular, are poorly understood. We hypothesized that metabolic reprogramming may underlie this radioresistance, and moreover, that it would be possible to exploit these changes in metabolism for therapeutic intent.
Experimental Design: We established multiple isogenic models of radioresistant PDAC cells. Metabolic profile was investigated using Nanostring technology, labeled-glucose tracing by liquid chromatography-mass spectrometry, Seahorse analysis and exposure to metabolic inhibitors. Patient-derived xenografts (PDXs) were established from patients treated with radiation and RNA sequencing performed. The PDXs were grouped according to clinical RECIST response to radiation (responsive/stable disease vs disease progression) and differential gene expression analysis was performed.
Results: The radioresistant cells overexpressed pyruvate dehydrogenase kinase (PDK) and were radiosensitized by the PDK inhibitor dichloroacetate. In keeping with PDK overexpression, radioresistant cells displayed increased glycolysis and downregulated both the tricarboxylic acid cycle and oxidative phosphorylation. Metabolic flux through the pentose-phosphate pathway (PPP) was increased, as were levels of reduced glutathione; PPP inhibition dramatically potentiated radiation-induced cell death. Critically, the PPP was upregulated in PDXs derived from patients who demonstrated clinical resistance to radiotherapy. High transcription levels of 6PGD, the rate-limiting enzyme of the PPP, were associated with a poor radiological response to radiation therapy (p=0.0004) and a lower overall survival (p=0.004).
Conclusions: We demonstrate that radioresistant PDAC cells divert the glycolytic flux from the tricarboxylic acid cycle and oxidative phosphorylation to the PPP, thereby increasing their antioxidant capacity and promoting nucleotide synthesis for DNA repair. Furthermore, we show that PDAC cells can be radiosensitized via PPP inhibition. Exploitation of metabolic vulnerabilities to radiosensitize tumors constitutes a novel approach to pancreatic cancer with a real potential to improve clinical outcomes.
Citation Format: Ariel Shimoni-Sebag, Ifat Abramovich, Bella Agranovich, Yaarit Sirovsky, Chani Stossel, Dikla Atias, Maria Raitses-Gurevich, Yulia Glick-Gorman, Ofer Margalit, David Regev, Rotem Tal, Itay Tirosh, Talia Golan, Keren Yizhak, Eyal Gottlieb, Yaacov R. Lawrence. The pentose-phosphate pathway induces pancreatic cancer radioresistance, a preclinical study with clinical validation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2411.