(A) Immunoblot of PHGDH, PSAT1, and PSPH expression in splenic B cells from WT (n = 3) and Eμ-Myc mice (n = 6). HSC70 was used as loading control. (B) Representative IHC staining (×20 magnification) for B220, Ki67, MYC, PHGDH, and PSAT1 abundance in sections of spleens from either WT (n = 3) or Eμ-Myc (n = 3) mice. (C) Isotope tracing analysis in splenic B cells isolated from either C57BL/6J WT mice or Eμ-MYC mice and cultured for 2 hours with ¹³C₆-labeled glucose. Serine and glycine levels were measured by LC-MS. The percent distribution of each isotopologue of their respective metabolite pool is represented as mean ± SEM of triplicate cultures and is representative of 3 independent experiments. (D) Schematic showing lymphoma transplantation model, in which Myc/+;Rosa26-CreER^T2/+;Phgdh^fl/fl lymphoma cells are injected via the tail vein into 9-week-old male C57BL/6J mice. Three days after lymphoma engraftment, mice were randomized to receive either vehicle or tamoxifen treatment by oral gavage for 4 days. Samples were collected 20 days after injection. (E) Representative pictures of spleens from mice (n = 3 per group) sacrificed 20 days after transplantation (left), and quantification of the spleen weight (right). (F) Schematic showing lymphoma transplantation model, in which Myc/+ lymphoma cells are injected via the tail vein into 9-week-old male C57BL/6J mice. Two days after lymphoma engraftment, mice were randomized to be treated with either vehicle or PH-755 by oral gavage for 14 days. (G) Representative pictures of spleens from mice (n = 3 per group) sacrificed after 7 or 14 days after transplantation (left), and quantification of the spleen weight (right). Data are shown as the mean ± SEM. *P < 0.05 and ***P < 0.001, by 2-tailed Student’s t test (E and G).