Poster Presentation 35th Lorne Cancer Conference 2023

Disruption of nucleotide homeostasis confers cancer cell susceptibility to oxidative phosphorylation inhibition independently of energy depletion (#370)

Xiao Hong Zhao 1 , Man Man Han 2 , Yi Meng Yue 2 , Qian Qian Yan 2 , Yuan Yuan Zhang 1 , Liang Xu 1 , Ting La 1 , Yuchen Feng 1 , Haijie Tang 1 , Ran Xu 1 , Vinod K. Narayana 3 , David De Souza 3 , Lake-Ee Quek 4 , Jeff Holst 5 , Rick Thorne 2 , Mark Baker 1 , Lei Jin 1 , Xu Dong Zhang 1
  1. Noncoding Cancer Biomarkers and Therapeutics Group, College of Health, Medicine and Wellbeing, The University of Newcastle, Callaghan, NSW, Australia
  2. Translational Research Institute, Henan Provincial and Zhengzhou City Key laboratory of Non-coding RNA and Cancer Metabolism, Henan International Join Laboratory of Non-coding RNA and Metabolism in Cancer, Henan Provincial People’s Hospital, Academy of Medical Sciences, Zhengzhou University, Zhengzhou, Henan, China
  3. Metabolomics Australia, University of Melbourne, Melbourne, Victoria, Australia
  4. School of Mathematics and Statistics, The University of Sydney, Sydney, NSW, Australia
  5. School of Medical Sciences and School of Clinical Medicine, The University of New South Wales, Sydney, NSW, Australia

Background: Cancer metabolism is highly heterogenous and flexible with the Warburg effect or oxidative phosphorylation (OXPHOS) prevailing in a cancer type- and context-dependent manner. Past studies have demonstrated that targeting OXPHOS robustly inhibits glycolysis-deficient cancer cell viability and tumorigenicity. However, the therapeutic potential of OXPHOS inhibition in metabolically flexible glycolysis-competent cancers is unclear. Moreover, whether the depletion of OXPHOS-derived ATP or the abolition of OXPHOS-supported biosynthesis is the major determinant of cancer cell susceptibility remains obscure.

Methods: A panel of metabolically flexible glycolysis-competent cancer cell lines along with those deficient in glycolysis were tested using OXPHOS inhibitors, including the mitochondrial complex I inhibitor IACS-010759. Metabolic phenotypes were determined using Seahorse metabolic flux assays. Targeted metabolomics was conducted using both GC- and LC-MS. Stable isotope tracing was carried out with uniformly labeled [15N]-/[13C]-aspartate. Patient-derived xenograft (PDX) models of colorectal cancer in NSG mice were used for in vivo validation.

Results: OXPHOS inhibition potently diminished metabolically flexible glycolysis-competent cancer cell proliferation and tumorigenicity without causing devastating energy stress. This was associated with S-phase cell cycle arrest and the enrichment of the G2/M DNA-damage checkpoint regulation pathway, suggestive of replication stress. Indeed, IACS treatment significantly reduced the purine/pyrimidine nucleotide pools, which was primarily caused by aspartate deficiency resulting from a shortage in the electron acceptor NAD+. The supplementation of exogenous nucleosides, aspartate, or pyruvate that can accept electron-generating NAD+, into the culture medium rescued cells from IACS-induced cell cycle arrest. Instructively, inhibition of GOT1, which catalyzes cytosolic aspartate biosynthesis when mitochondrial aspartate production is dampened, rendered cancer cells more susceptible to OXPHOS inhibition.   

Conclusion: 1) Disruption of nucleotide homeostasis is a major determinant of cancer cell susceptibility to OXPHOS inhibition; 2) OXPHOS inhibition is a promising avenue for the treatment of cancers that are metabolic flexible and glycolysis competent, and 3) GOT1 targeting is potentially a useful approach to improve the therapeutic efficacy of OXPHOS inhibition for cancer treatment.