Fig. 3: Inhibiting GTP synthesis radiosensitizes RT-resistant GBM cell lines and patient-derived neurospheres.

a Purine synthesis schematic. R5P: Ribose 5-phosphate; IMP: inosine monophosphate; GTP: Guanosine-5’-triphosphate; ATP: Adenosine triphosphate; IMPDH: Inosine-5’-monophosphate dehydrogenase; HGPRT: hypoxanthine-guanine phosphoribosyltransferase; MPA: mycophenolic acid. b–d U87 MG cells were treated with MPA (10 μM) for 24 h, and then harvested and analyzed by targeted LC-MS/MS. Data are presented as mean ± SEM from four biologic replicates. p values are <0.0001, <0.0001, and 0.0237 for Fig. b–d, respectively. *p < 0.05, and ****p < 0.0001 compared with control. The p values indicated were obtained by two-tailed unpaired student's t test. e, f After treatment with indicated conditions, cells were replated for colonogenic assay and colonies were stained and counted 10 to 14 days later. Data are presented as mean ± SEM from 4 separate experiments. g, h HF2303 or MSP12 neurospheres were treated as the timeline shown in Supplementary Fig. 3e. In brief, cells were treated with nucleosides or MPA (10 µM), and retreated with nucleosides 2 h before RT. Cells were replated to 96-well plates (2000 cells/well) 24 h post-RT and cell viability were detected by the Celltiter-Glo kit ~7 days after replating. Fig. g and h are representative figures from three biologically independent experiments. Error bars show mean ± SEM from representative experiments, which were performed in five (g) or six (h) technical replicates. ER (mean ± SEM) of MPA from biologic replicates is shown on the lower left of each graph and is calculated as the GI50 of the control-treated cells divided by the GI50 of the MPA-treated cells. Source data are provided as a Source Data file.