Abstract
Pancreatic ductal adenocarcinoma (PDA) is a lethal, therapy-resistant cancer that thrives in a highly desmoplastic, nutrient-deprived microenvironment. Several studies investigated the effects of depriving PDA of either glucose or glutamine alone. However, the consequences on PDA growth and metabolism of limiting both preferred nutrients have remained largely unknown. Here, we report the selection for clonal human PDA cells that survive and adapt to limiting levels of both glucose and glutamine. We find that adapted clones exhibit increased growth in vitro and enhanced tumor-forming capacity in vivo. Mechanistically, adapted clones share common transcriptional and metabolic programs, including amino acid use for de novo glutamine and nucleotide synthesis. They also display enhanced mTORC1 activity that prevents the proteasomal degradation of glutamine synthetase (GS), the rate-limiting enzyme for glutamine synthesis. This phenotype is notably reversible, with PDA cells acquiring alterations in open chromatin upon adaptation. Silencing of GS suppresses the enhanced growth of adapted cells and mitigates tumor growth. These findings identify non-genetic adaptations to nutrient deprivation in PDA and highlight GS as a dependency that could be targeted therapeutically in pancreatic cancer patients.
Significance Pancreatic ductal adenocarcinoma (PDA) is a highly lethal malignancy with no effective therapies. PDA aggressiveness partly stems from its ability to grow within a uniquely dense stroma restricting nutrient access. This study demonstrates that PDA clones that survive chronic nutrient deprivation acquire reversible non-genetic adaptations allowing them to switch between metabolic states optimal for growth under nutrient-replete or nutrient-deprived conditions. One contributing factor to this adaptation mTORC1 activation, which stabilizes glutamine synthetase (GS) necessary for glutamine generation in nutrient-deprived cancer cells. Our findings imply that although total GS levels may not be a prognostic marker for aggressive disease, GS inhibition is of high therapeutic value, as it targets specific cell clusters adapted to nutrient starvation, thus mitigating tumor growth.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Whole exome sequencing (WES) analysis of all clones described in this manuscript revealed an inadvertent mistake in the identity of the adapted clones from one of the human pancreatic cancer cell lines used, PA-TU-8988T. As demonstrated in the revisions, the conclusions of the study were not affected. We found that 8988T adapted (but not non-adapted) clones were actually derived from the second cell line used, SUIT-2. To correct this, all figures and figure panels containing data from 8988T adapted and non-adapted clones were removed and replaced with newly generated data derived from newly adapted and non-adapted clones of the authenticated 8988T cell line. These include Figures 1C-F (left panels), 2A, 2C (left panel), 3B (right panel), 3E, 4E, S2A-F (left panels), S2G, S5A and B, S6A (left panel), S7B (right panel). Moreover, Figures 6A-E and S12A-F have been corrected to indicate that the adapted clones used in this experiment were from SUIT-2 cells (not 8988T), as authenticated by DNA sequencing (WES) and short tandem repeat profiling (STR). In addition, several figures, figure panels and 2 Datasets have been added, representing additional experiments and analyses that further strengthen the conclusions of our findings. These include Figure 1B, 1G and 1H, Supplementary Figures S1A-C, S4A-F, S6B, S8A-D, S9, S10A, S12G and S12H and Supplementary Datasets 1 and 2. All sequencing data have been deposited in Gene Expression Omnibus database and are accessible through GEO Series accession number GSE144833.
