Comprehensive Metabolic Profiling of MYC-Amplified Medulloblastoma Tumors Reveals Key Dependencies on Amino Acid, Tricarboxylic Acid and Hexosamine Pathways

Abstract

Reprograming of cellular metabolism is a hallmark of cancer. Altering metabolism allows cancer cells to overcome unfavorable microenvironment conditions and to proliferate and invade. Medulloblastoma is the most common malignant brain tumor of children. Genomic amplification of MYC defines a subset of poor-prognosis medulloblastoma. We performed comprehensive metabolic studies of human MYC-amplified medulloblastoma by comparing the metabolic profiles of tumor cells in three different conditions—in vitro, in flank xenografts and in orthotopic xenografts in the cerebellum. Principal component analysis showed that the metabolic profiles of brain and flank high-MYC medulloblastoma tumors clustered closely together and separated away from normal brain and in vitro MYC-amplified cells. Compared to normal brain, MYC-amplified medulloblastoma orthotopic xenograft tumors showed upregulation of the TCA cycle as well as the synthesis of nucleotides, hexosamines, amino acids and glutathione. There was significantly higher glucose uptake and usage in orthotopic xenograft tumors compared to flank xenograft tumors and cells in culture. In orthotopic tumors, glucose was the main carbon source for the de novo synthesis of glutamate, glutamine and glutathione through the TCA cycle. In vivo, the glutaminase II pathway was the main pathway utilizing glutamine. Glutathione was the most abundant upregulated metabolite in orthotopic tumors compared to normal brain. Glutamine-derived glutathione was synthesized through the glutamine transaminase K (GTK) enzyme in vivo. In conclusion, high MYC medulloblastoma cells have different metabolic profiles in vitro compared to in vivo, and key vulnerabilities may be missed by not performing in vivo metabolic analyses.

Pathological implications of metabolic reprogramming and its therapeutic potential in medulloblastoma

“…In neurons, glucose enters through the sodium-independent facilitative transporters GLUT1 and GLUT3 (encoded by SLC2A1 and SLC2A3 genes respectively), which are differentially distributed across the brain. GLUT1 is upregulated in embryonal tumors including MB (Loda et al, 2000), with a prominent expression in MYC-driven Group 3 MB (Park et al, 2019;Pham et al, 2022). GLUT1 overexpression determines a higher glucose influx into the cell that is avidly used for cytoplasmic glycolysis, supporting cell survival in low oxygen Frontiers in Cell and Developmental Biology frontiersin.org environments (Al Tameemi et al, 2019).…”

“…Lactate can be exported outside the cell and contributes to both intra- and extracellular acidification. High lactate levels have been primarily associated with Group 3/4 compared to SHH MB ( Blüml et al, 2016 ), and MB Group 3 orthotopic mouse models also exhibit high lactate levels ( Pham et al, 2022 ). Moreover, lactate dehydrogenase A (LDHA) levels are found overexpressed in the most aggressive MB subgroups ( Valvona and Fillmore, 2018 ).…”

“…Interestingly, a comparative analysis of metabolic profiles of MB cells in three different environments - in vitro , in flank and in orthotopic xenografts- suggests that orthotopic MYC-amplified MB tumors have increased levels of glucosamine-6-phosphate compared to normal brain, proposing dependence on HBP ( Pham et al, 2022 ). Similarly, RNA-sequencing data derived by the “Children’s Brain Tumor Network/Kids First Pediatric Brain Tumor Atlas'' indicate an increase in HBP enzymes expression in MB tumors compared to other pediatric brain tumors (i.e., glioma, ependymoma) ( Pham et al, 2022 ).…”

Metabolic determinants of stemness in medulloblastoma

“…On the other hand, a recent publication also questions the Warburg effect in MYC-amplified MBs: higher glucose incorporation into the tricarboxylic acid (TCA) cycle was detected in orthotopic tumours compared with normal brain, indicating that tumour cells use glycolysis and oxidative phosphorylation simultaneously. In addition, significant differences in glucose and glutamine metabolism were detected in high MYC-amplified MBs comparing in vitro , flank xenografts, and orthotopic xenograft MB models, evidencing the importance of using orthotopic models for metabolic analysis in these tumours[ 46 ].…”

“…Group 3 MB tumours not only display an enrichment of the glycolytic pathway but also the upregulation of proteins involved in other metabolic pathways such as gluconeogenesis (PCK2, PC), glutamine anabolism (GLUL), calcium signalling (RYR3, CAMK2D), fatty acid synthesis (ACLY), glutathione-mediated antioxidant pathway (PTGDS, GSTZ1), and the drug metabolism pathway (IMPDH1, GUSB)[ 47 ]. In addition, the upregulation of the TCA cycle, synthesis of nucleotides, hexosamines, amino acids, and glutathione was also detected in MYC-amplified orthotopic xenograft MBs[ 46 ]. This highly metabolic profile could be responsible for the aggressiveness and chemoresistance of Group 3 and MYC-amplified tumours.…”