P01.30.B TRANSLATIONAL INSIGHTS FROM THE B-FREE TRIAL (GLIOBLASTOMA THERAPY WITH SERINE AND GLYCINE FREE DIET)

Abstract BACKGROUND Malignant gliomas are characterized by profound therapeutic resistance, partly due to their metabolic plasticity. Emerging evidence highlights the crucial role of serine and glycine (SG) metabolism in glioblastoma survival, redox homeostasis, and immune evasion. Targeting these pathways through dietary interventions presents a novel therapeutic strategy. MATERIAL AND METHODS We conducted in vitro experiments assessing the effects of SG deprivation and 3-phosphoglycerate dehydrogenase (PHGDH) inhibition (via BI-4916) on GB cell lines. Assays included viability (CellTiter-Glo), clonogenicity, reactive oxygen species (ROS) production (H2DCFDA-FACS), cell death (LDH release), invasion (Boyden chamber) and migration (wound healing). Oxygen consumption and acidification rates were measured using Seahorse technology. In parallel, the investigator-initiated B-FREE Trial (Glioblastoma therapy with serine and glycine free diet) employs a window-of-opportunity design involving 10 days of SG-free normocaloric nutrition prior to surgical resection. Plasma, cerebrospinal fluid (CSF), and tumor tissue are collected pre- and post-intervention. Metabolomic profiling is performed via UHPLC-MS/MS and GC-MS. Additionally, formate - a downstream metabolite in SG metabolism - is assessed as a surrogate marker. Ultra-high field Magnetic resonance spectroscopy (MRS) is performed pre- and post-intervention to non-invasively monitor intratumoral metabolic alterations, including SG-related signatures. Immunological effects are analyzed in a co-clinical model using patient-derived organoids co-cultured with autologous T cells and evaluated through live-cell imaging, FACS, and multiplex immunofluorescence. RESULTS Our in vitro studies demonstrate that both dietary SG restriction and inhibition of serine de novo synthesis via PHGDH blockade using BI-4916 lead to reduced glioma cell viability and clonogenicity, along with ROS accumulation and increased hypoxia-induced cell death. Furthermore, PHGDH-inhibition impairs invasion, and both interventions reduce cellular migration, accompanied by a reduction in formate levels, a downstream metabolite known to promote these processes. Genetic and pharmacological inhibition of PHGDH also results in altered oxygen metabolism. CONCLUSION This translational project evaluates SG metabolism as a vulnerability in gliomas and explores dietary modulation as a therapeutic adjunct. The B-FREE Trial aims to identify metabolic and immunological biomarkers predictive of response and to lay the groundwork for future combinatorial therapies.