A metabolic switch to the pentose-phosphate pathway induces radiation resistance in pancreatic cancer.

Purpose: Pancreatic ductal adenocarcinoma (PDAC) is remarkably resistant to standard modalities, including radiotherapy. We hypothesized that metabolic reprogramming may underlie PDAC radioresistance, and moreover, that it would be possible to exploit these metabolic changes for therapeutic intent.
Methods and Materials: We established two matched models of radioresistant PDAC cells by exposing the AsPC-1 and MIAPaCa-2 human pancreatic cancer cells to incremental doses of radiation. The metabolic profile of parental and radioresistant cells was investigated using Nanostring technology, labeled-glucose tracing by liquid chromatography-mass spectrometry, Seahorse analysis and exposure to metabolic inhibitors. The synergistic effect of radiation combined with a pentose-phosphate pathway inhibitor, 6-aminonicotinamide (6-AN) was evaluated in a xenograft model established by subcutaneous injection of radioresistant-AsPC-1 cells into nude mice.
Results: The radioresistant cells overexpressed pyruvate dehydrogenase kinase (PDK) and consistently, displayed increased glycolysis and downregulated the tricarboxylic acid (TCA) cycle and oxidative phosphorylation. Metabolic flux through the pentose-phosphate pathway (PPP) was increased, as were levels of reduced glutathione; pharmacological inhibition of the PPP dramatically potentiated radiation-induced cell death. Furthermore, the combined treatment of radiation with the PPP inhibitor 6-AN synergistically inhibited tumor growth in-vivo.
Conclusions: We provide a mechanistic understanding of the metabolic changes that underlie radioresistance in PDAC. Furthermore, we demonstrate that pancreatic cancer cells can be re-sensitized to radiation via metabolic manipulation, in particular, inhibition of the PPP. Exploitation of the metabolic vulnerabilities of radioresistant pancreatic cancer cells constitutes a new approach to pancreatic cancer, with a potential to improve clinical outcomes.
Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: [Y.R.L, A.S.S and E.G have declared funding support in the Funding statement. T.G has declared relationship with AstraZeneca, AbbVie, Curesponse and MSD Merck. Y.R.L. has received consultancy fees from Roche Genetech and Zola Therapeutics Inc., he has stock ownership in Protean Biodiagnostics Inc. None of these are of relevance to this work. All remaining authors have declared no conflicts of interest.].
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