Identification and molecular characterization of cancer cells surviving under glucose starvation

Tumors are heterogeneous, consisting of different cell subpopulations to allow tumor survival in variable conditions. We observed the survival of a small percentage of HCT116 cells under glucose starvation. We hypothesized that these cells represent a previously undescribed subpopulation able to adjust their metabolism in the absence of glucose. Here, we aimed to characterize the metabolic and molecular properties allowing these cells to survive. We propagated individual clones from HCT116 cells and further analyzed a single clone whose descendants were able to survive glucose starvation. Biochemical and molecular analyses were performed under standard glucose conditions, under glucose starvation during adaptation period, and under glucose starvation after resumption of proliferation. Metabolic analysis by Seahorse revealed that surviving cells completely shifted their metabolism from glycolysis to oxidative phosphorylation. LC-MS metabolomics analysis revealed that during senescence-like adaptation the cells accumulate metabolites required for NAD synthesis. FAD, a co-factor involved in the TCA cycle, was not found in the dormant cells, while higher levels of carnosine, essential for ROS elimination, were observed. The metabolic shift toward enhanced oxidative phosphorylation was accompanied by increased production of ROS leading to DNA damage, reflected in an upregulation of the genes NUPR, ST6GAL1, and EGRF as observed by RNAseq. Cells that resumed proliferation were also characterized by enhanced expression of DNA damage repair genes and upregulated subunits of ATP-synthase, a key enzyme in oxidative phosphorylation. We suggest that cells predisposed to effective DNA repair have more time and capabilities to adjust their metabolism and to survive extreme conditions.