Breast cancer is a heterogeneous disease with subtypes that vary by morphology, in 15.7% of human breast cancers and is more common in high grade tumors and the basal-like 62 subtype. 17 As a transcription factor, Myc affects numerous biological processes including 63 metabolism. 18, 19 Notably, Myc expression regulates several genes in glucose, amino acid, and 64 nucleotide metabolism. 20-22 Therefore, investigating metabolism of the MMTV-Myc model system may reveal metabolic features common to human cancer and could present new targeted 66 therapeutic options.
Here, we present a study investigating the metabolic profiles of two histologically distinct 
To determine metabolic profiles of histologically distinct mouse mammary tumor subtypes, 84 polar metabolites were extracted from tumor-derived cell lines and quantitated using LC-MS/MS.
We found metabolites involved in several central carbon metabolic pathways to be differentially 86 abundant between EMT and papillary tumor-derived cell lines (Figure 2 ).
In the EMT subtype, both oxidized and reduced forms of glutathione, a key metabolite in 88 redox homeostasis, are elevated ( Figure 2B ). Increased levels of both reduced and oxidized 89 glutathione imply that the EMT subtype has elevated glutathione biosynthetic activity. This could 90 reflect a greater dependency on glutathione biosynthesis in the EMT cells and targeting 91 glutathione biosynthesis would therefore be more effective against the EMT subtype. Metabolites 92 increased in the papillary subtype include fructose bisphosphate (FBP; glycolysis); acetyl-CoA indicating relative metabolite differences between EMT and papillary tumor derived cell lines. Metabolites are sorted by relationship to metabolic pathways. Yellow and blue boxes indicate increased or decreased metabolite levels relative to the average of the papillary subtype, respectively. Data for each sample is normalized to the average signal for all metabolites in the analysis. Metabolites with statistically significant differences (p-value < 0.05) are bolded and marked with asterisks (*). (B) Representative bar graphs of metabolites with statistically significant differences between EMT and papillary subtypes. Data are displayed as means ± S.D., N = 6.
A B * * * * metabolic pool size measurements to reveal more complete metabolic profiles. 24 We find the 108 papillary subtype has proportionally lower abundance of 13 
and ATP, as well as ribulose-5-phosphate and ribose-5-phosphate, two intermediates in the PPP production or decreased nucleotide consumption, we applied the same isotope labeling 