Abstract 5801: Xanthine oxidoreductase mediates the survival of starved lung adenocarcinoma cells by inducing UPR and autophagic degradation
Authors: Chen Manman , Guo Wei , Guo Xiaozhen , Xie Cen , Meng Linghua 
Published: June 2022

Abstract
Background & Purpose: Lung adenocarcinoma (LUAD) is the most common and aggressive subtype of non-small cell lung cancer, and is the leading cause of cancer-associated mortality worldwide. Upregulation of purine degradation pathway is observed in LUAD. Xanthine oxidoreductase (XOR) is the rate-limiting enzyme in purine catabolism by converting hypoxanthine to xanthine and xanthine to uric acid. The altered expression and activity of XOR in cancer tissues are usually associated with prognosis of cancer, while its role in LUAD remains unknown.
Methods: XOR expression in LUAD tissues were detected by immunohistochemistry. XOR knock-out LUAD cells were generated by CRISPR-Cas9 system. Clonogenic survival of LUAD cells was determined by crystal violet staining. The expression of genes involving in unfolded protein response (UPR) and autophagy was detected by RT-qPCR and the protein level was detected by Western blotting. Autophagic flux was observed by immunofluorescent microscopy. The level of amino acids and ATP/ADP/AMP were determined by UPLC-QTOFMS. Metabolic flux was analyzed by radio-labeled metabolites measured by UPLC-QTOFMS.
Results: XOR is highly expressed in LUAD and significantly associated with poor clinical prognosis. Knocking out or inhibition of XOR attenuated the survival of starved LUAD cells. Nucleoside supplementation rescued the survival of starved LUAD cells upon XOR inhibition, while inhibition of purine nucleoside phosphorylase (PNP) impended the process, indicating that ribose produced by nucleoside degradation is required for the XOR-mediated the survival of LUAD cells. Accordingly, metabolic flux revealed that ribose derived from nucleoside fueled key carbon metabolic pathways to sustain the survival of starved LUAD cells. Mechanistically, downregulation of XOR suppressed UPR and autophagic degradation in starved LUAD cells. Consistently, inhibition of XOR decreased the level of amino acids produced by autophagic degradation, which was accompanied with down-regulation of mTORC1 signaling. Supplementation of amino acids including glutamine, glutamate or aspartate rescued the survival of starved LUAD cells, indicating that autophagic degradation plays a key role in XOR-mediated LUAD cells survival under nutrient stress. Finally, XOR inhibitors potentiated the anti-proliferative activity of 2-deoxy-D-glucose that induced UPR and/or autophagy in LUAD cells.
Conclusions: We found that knock-out or inhibition of XOR attenuated UPR and autophagy in starved LUAD cells, which resulted in nutrients scarcity due to blockade of the degradation of nucleosides and proteins, and finally cell death. These findings demonstrate that XOR plays a crucial role in the survival of LUAD cells, suggesting that targeting XOR is a potential strategy to improve the efficacy of drugs that are able to induce UPR and autophagy.
Citation Format: Manman Chen, Wei Guo, Xiaozhen Guo, Cen Xie, Linghua Meng. Xanthine oxidoreductase mediates the survival of starved lung adenocarcinoma cells by inducing UPR and autophagic degradation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5801.