KS01.6.A THE LIPID DROPLET PHENOTYPE AS A TARGETABLE METABOLIC DEPENDENCY OF TUMOR CELLS AND PRO-TUMORAL MACROPHAGES IN THE PERI-NECROTIC GBM NICHE
Authors: Talbot H , Governa V , Cerezo-Magaña M , Gonçalves de Oliveira K , Boukredine A , Bång-Rudenstam A , Garza R , Jakobsson J , de Neergaard T , Nordenfelt P , Pietras A , Jeannot P , Darabi A , Forsberg-Nilsson K , Bengzon J , Belting M 
Published: October 2024

Abstract

BACKGROUND
The poorly vascularized, peri-necrotic GBM niche drives a metabolic switch towards adaptive lipid metabolism. Failure to adapt results in profound areas of necrosis, a GBM hallmark associated with worse outcome. Surprisingly few studies have addressed whether necrotic debris represents a passive terminus or could actively contribute to GBM progression. Peri-necrotic regions are enriched in intracellular lipid droplets (LDs), as shown by us and others, and highly infiltrated by macrophages. Here, we provide new mechanistic links between necrosis lipid scavenging by GBM cells, recruitment and metabolic rewiring of macrophages, and GBM aggressiveness.

MATERIAL AND METHODS
Macrophage infiltration, LD formation, and vacularization were characterized in GBM tissues and cells, including freshly resected GBM specimens, and primary GBM and macrophage cultures. Methods include snRNA-seq, immunophenotyping by FACS and imaging, LCM for spatial profiling, extracellular vesicle (EV) and necrotic material uptake, and phagocytic activity. Treatment studies targeted at LD formation and the cellular redox machinery were assessed for cytotoxicity and lipid peroxidation by live imaging. Biostatistcal methods were employed to correlate macrophage lipid phenotype with glioma grade, IDH status, and GBM patient survival. Mouse GBM models were employed for in vivo treatment studies.

RESULTS
We show that GBM peri-necrotic areas display abundant LDs not only in tumor cells but also in infiltrating macrophages. GBM cells scavenge necrotic material, resulting in LD formation, increased proliferation, resistance to radio and chemotherapy, induction of anti-ferroptotic and β-oxidation pathways, as well as a pro-inflammatory profile linked to macrophage recruitment (unpublished, under review). We reveal that macrophages engulfing necrotic material and tumor cell-derived EVs also acquire LDs, specifically at hypoxic conditions of the peri-necrotic niche. These newly described Tumor Associated Foam cells (TAFs) exhibit distinct pro-tumorigenic characteristics related to HIF signalling, mesenchymal transition, angiogenesis, impaired phagocytosis, and correlate with worse patient outcome (unpublished, under revision). Pharmacological targeting of LD formation disrupted TAF functionality, and simultaneously mitigated GBM cell proliferation and treatment resistance. Combined targeting of LD formation with SLC7A11 or CPT1A inhibitors induced strong lipotoxicity and ferroptotic cell death in GBM cells.

CONCLUSION
We show that tumor cells and macrophages enriched in LDs co-inhabit in the peri-necrotic GBM microenvironment to drive a pro-tumoral phenotype. Our findings open a new therapeutic avenue against the inherently treatment resistant peri-necrotic niche of GBM tumors.