Figure 4.

Tryptophan-derived one-carbon units are incorporated into nucleotides in pancreatic tumors in vivo and can substitute for serine

(A) Schematic diagram outlining in vivo¹³C₁₁-tryptophan tracing.

(B) KPC cell line 2 (see Figures 1E and S1A) from C57Bl6/J Pdx1-Cre;Kras^G12D/+;Trp53^R172H/+ mice were engineered to stably express IDO1 (KPC-IDO1) or empty vector control (KPC-EV). Cells were injected into the flanks of C57Bl6/J mice. Once tumors had formed, the mice were given a single intraperitoneal injection of 800 μL 120 mM ¹³C₁₁ tryptophan and harvested after 3 h. The tumor tissue was excised and analyzed by LC-MS (EV n = 7, IDO1 n = 7, p values calculated with unpaired 2-sided t test, bars are SDs). y axis = ¹³C labeled fraction for the stated isotopologues.

(C) KPC-IDO1 cells were grown in culture medium with or without serine, with or without epacadostat (1 μM). The cell number was counted every 24 h for 5 days; n = 3 biological replicates, bars are SDs.

(D) KPC-IDO1 cells were grown in culture medium with or without serine, with or without epacadostat (1 μM) for 24 h, and intracellular metabolites were analyzed by LC-MS; n = 3 biological replicates, bars are SDs.

(E and F) KPC-IDO1 cells were injected as subcutaneous allografts into BALB/c nude mice and received vehicle or epacadostat (50 mg/kg twice per day) as oral gavage. Mice either received a control diet containing serine and glycine (E) or a matched diet lacking serine and glycine (F). Bars are SDs. p values calculated using unpaired 2-sided t test.