The Leloir Cycle in Glioblastoma: Galactose Scavenging and Metabolic Remodeling.

Martyn A Sharpe,Alexandra M Baskin,Omkar B Ijare,David S Baskin,Kumar Pichumani,Brianna N Baskin

doi:10.3390/cancers13081815

Martyn A Sharpe, Alexandra M Baskin + Show 4 more

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https://doi.org/10.3390/cancers13081815

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Abstract

Simple SummaryProliferation of glioblastoma (GBM) depends on access to extracellular nutrients. Inadequate tumor perfusion creates a short supply of the most common nutrients, such as glucose (Glc) and glutamine. As a result, GBMs undergo metabolic remodeling and scavenge alternative nutrients from the tumor microenvironment for their growth and proliferation. GBM expresses sugar transporters, such as Glut3 and Glut14. Galactose (Gal) is a good substrate for Glut3/Glut14, and GBM cells can scavenge Gal from the circulation/extracellular space. The Leloir pathway allows GBM to transport and metabolize Gal at physiologic Glc concentrations, providing GBM cells with an alternate energy source. GBM cultures proliferated when grown solely on Gal. GBMs metabolize Gal via the Leloir pathway, glycolysis, and pentose phosphate pathway (PPP) to optimize ATP production, while the mitochondrial metabolism of Gal in GBM is limited. The selective targeting of the Leloir/PPP pathway may provide new treatment strategies for GBM.Background: Glioblastoma (GBM) can use metabolic fuels other than glucose (Glc). The ability of GBM to use galactose (Gal) as a fuel via the Leloir pathway is investigated. Methods: Gene transcript data were accessed to determine the association between expression of genes of the Leloir pathway and patient outcomes. Growth studies were performed on five primary patient-derived GBM cultures using Glc-free media supplemented with Gal. The role of Glut3/Glut14 in sugar import was investigated using antibody inhibition of hexose transport. A specific inhibitor of GALK1 (Cpd36) was used to inhibit Gal catabolism. Gal metabolism was examined using proton, carbon and phosphorous NMR spectroscopy, with 13C-labeled Glc and Gal as tracers. Results: Data analysis from published databases revealed that elevated levels of mRNA transcripts of SLC2A3 (Glut3), SLC2A14 (Glut14) and key Leloir pathway enzymes correlate with poor patient outcomes. GBM cultures proliferated when grown solely on Gal in Glc-free media and switching Glc-grown GBM cells into Gal-enriched/Glc-free media produced elevated levels of Glut3 and/or Glut14 enzymes. The 13C NMR-based metabolic flux analysis demonstrated a fully functional Leloir pathway and elevated pentose phosphate pathway activity for efficient Gal metabolism in GBM cells. Conclusion: Expression of Glut3 and/or Glut14 together with the enzymes of the Leloir pathway allows GBM to transport and metabolize Gal at physiological glucose concentrations, providing GBM cells with an alternate energy source. The presence of this pathway in GBM and its selective targeting may provide new treatment strategies.

Highlights

We performed kinetic modeling of their data and the analysis shows that dietary Gal uptake is rapid (t1/2 of ≈ 14 min) and the Gal is present in the plasma at a concentration >1 mM for extended periods, but the metabolism of Gal is slow (t1/2 of ≈ 23 min) (Supplemental Figure S1B) [27]
The impact of expression of Glut3/Glut14 and of other key enzymes of the Leloir pathway on the survival of GBM patients is presented in the form of Kaplan–Meier survival curves (Figure 2A)
When Glut3/Glut14 hexose transport is inhibited by antibody binding, we found a greater impact on GBM cell growth with Gal compared to Glc

Summary

Introduction

Glioblastoma (GBM) is a grade IV aggressive glial neoplasm, with an incidence in the Glioblastoma (GBM)is a grade aggressive neoplasm, with an incidence in the UnitedStates of 3.19 per 100,000 perIV year.Patient glial outcome in GBM remains poor, with a States of100,000 per year.Patient outcome in GBM remains poor, with median survival of 16.7 months at diagnosis and only 30% of patients surviving two years a median survivalcancers, of 16.7 including months atbrain diagnosis andprimarily only 30%metabolize of patientsglucose surviving [1].Many human tumors,(Glc)two to years [1].Manyproduction, human cancers, including known brain tumors, primarilyeffect metabolize glucose lactate for ATP a phenomenon as the Warburg [2,3,4]. Glioblastoma (GBM) is a grade IV aggressive glial neoplasm, with an incidence in the Glioblastoma (GBM). Patient glial outcome in GBM remains poor, with a States of. Patient outcome in GBM remains poor, with median survival of 16.7 months at diagnosis and only 30% of patients surviving two years a median survivalcancers, of 16.7 including months atbrain diagnosis andprimarily only 30%metabolize of patientsglucose surviving [1]. Manyproduction, human cancers, including known brain tumors, primarilyeffect metabolize glucose lactate for ATP a phenomenon as the Warburg [2,3,4]. Glioblastoma (GBM) can use metabolic fuels other than glucose (Glc). The ability of GBM to use galactose (Gal) as a fuel via the Leloir pathway is investigated.

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