Fig. 3

Serine synthesis from glucose and the impact of exogenous serine/glycine and glucose levels. Uniformly labeled [¹³C₆]-glucose was administered to normal BEC or cancer cells at two different concentrations, high (10 mM) or low (0.2 mM), in combination with high/low levels of serine (150 µM/15 µM) and glycine (300 µM/30 µM) and metabolites were quantified. A Label enrichment (% of total) in A549 cells from ¹³C₆-glucose after treatment with NCT-503 (NCT, 10 µM) or vehicle (Veh). B Serine labeling from ¹³C₆-glucose and relative glycine labeling from serine in normal and cancer cells. Label enrichments in the cancer cells were compared to BEC. C Serine and glycine isotopologue enrichments. M + 0 denotes unlabeled metabolites and M + 1, M + 2 and M + 3 contain one, two, or three ¹³C. Statistical analysis was performed on relative enrichment of the most informative isotopologue (##). D Enrichment ratios of (fully labeled) serine M + 3 normalized to (fully labeled) phosphoenolpyruvate (PEP) M + 3 and (fully labeled) glycine M + 2 normalized to serine M + 3. A-D Results are mean ± SEM from four (A549 and H1299) or three (BEC) experiments. Group comparisons were performed by Two-way ANOVA with Tukey (A,C-D) or Dunnett (B) post-hoc analysis; *P < 0.05; **P < 0.01; ***P < 0.001; n.s., not significant; #, versus high glucose conditions; Ser/Gly, serine/glycine; E Metabolic pathway for the conversion of glucose or glutamine to serine/glycine and cysteine. Filled circles represent ¹³C. TCA cycle, tricarboxylic acid cycle; PEP, phosphoenolpyruvate; PCK2, phosphoenolpyruvate carboxykinase mitochondrial isoform