Figure 4. Contributions of systemic and tumor autonomous ammonia metabolism to amino acid synthesis.

A. Measurement of ammonia in the interstitial fluids of the tumor microenvironment (TME) compared to plasma isolated from ER(+) breast cancer xenograft models. Lines connect values of ammonia in the plasma to that in the interstitial fluid of the TME. B. Isotope abundance of ¹⁵N-isotopologues isolated from the liver, plasma and tumor of mice IP injected with a bolus (9.0 mmol/kg) of ¹⁵NH₄Cl. Tissues were harvested 1, 2, or 4 hours after injection. Values represent mean +/− SEM, n=4. ¹⁵N-isotopologues were corrected for natural abundance of tissues harvested from a control mouse treated with 9.0 mmol/kg NH₄Cl for 4 hours. C. Western blot of GDH knockdown in T47D xenograft tumors. D. In vivo tumor growth of T47D control and GDH-depleted xenograft models (n=15 mice per group). Values represent mean tumor volume +/− SEM. E. In vivo tracing of ¹⁵NH₄Cl in T47D control and GDH-depleted xenograft models. Values represent mean isotopologue abundance +/− SEM, n=4. F. Schematic of systemic and tumor autonomous ammonia metabolism. For all comparisons two-tailed t test was used. *P < 0.05, **P < 0.01, ***P<0.001, ****P<0.0001.