Fig. 4: Cooperation between serine synthesis pathway inhibition and modulation of hypoxanthine in limiting tumour cell growth.

A Growth curve of cells grown in DMEM lacking serine and glycine (-SG) supplemented (blue) or not (grey) with 5 or 0.2 µM of hypoxanthine. Data are represented as mean ± SD of triplicate wells and representative of 3 independent experiments. B Growth curve of cells grown in DMEM lacking serine (−S) but containing 1 mM glycine (+1 mM G) supplemented (blue) or not (grey) with 5 or 0.2 µM of hypoxanthine. Data are represented as mean ± SD of triplicate wells and representative of 3 independent experiments. C Growth fold change relative to the untreated Plasmax condition (HPX+ /PH755−) after 72 h of proliferation in the different conditions. Cells were treated with 10 µM PH755 where indicated. Data are represented as mean ± SD of triplicate wells and representative of three independent experiments (one-way Anova, *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001, ns: no significance). D, E Levels of hypoxanthine measured by LC–MS in plasma and tumour, respectively, collected at end-point from DLD-1 xenograft-bearing mice fed with control diet and treated with vehicle n = 10 (dark grey) or PH755 n = 10 (grey) or serine/glycine free diet and treated with vehicle (light blue) n = 10 or PH755 n = 9 (dark blue). Levels of hypoxanthine were normalised by total ion count. Data are represented as mean ± SEM (multiple comparison by one-way Anova, *p < 0.05). The samples were obtained from an experiment previously published⁹. F Fold change in growth relative to the untreated Plasmax condition (PH755-/6-MP-) after 72 h of proliferation in the different conditions. Cells were all treated with 10 µM PH755 where indicated and with 1 µM 6-MP for MDA-MB-468, 2.5 µM 6-MP for A549 and HCT116 and 5 µM 6-MP for DLD-1 when indicated. PH755-/6-MP- (light blue), PH755+ /6-MP− (dark blue), PH755−/6-MP+ (red), PH755+ /6-MP+ (pink). Data are represented as mean ± SD of triplicate wells and representative of three independent experiments (multiple comparison by one-way Anova, *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001). G Cells were transfected at day 0 with siHPRT1 or non-targeting siRNA. At day 1, cells were transferred into Plasmax media with or without 10 µM PH755 Graphs represent fold change of cell number after 72 h relative to day 1. PH755-/siHPRT- (light blue), PH755+ /siHPRT− (dark blue), PH755−/siHPRT+ (red), PH755+ /siHPRT+ (pink). Data are represented as mean ± SD of triplicate wells and representative of two independent experiments (one-way Anova, **p < 0.01, ***p < 0.001, ****p < 0.0001, ns no significance). Source data are provided as a Source Data file.