Integrated analysis identifies different metabolic signatures for tumor-initiating cells in a murine glioblastoma model.

I Saga,O Sampetrean,K Urakami,S Fujita,M Kusuhara,S Osuka,J Okubo,K Yoshida,Y Kobayashi,S Yamada,H Saya,S Shibao

doi:10.1093/neuonc/nou096

Abstract

The metabolic preference of malignant glioma for glycolysis as an energy source is a potential therapeutic target. As a result of the cellular heterogeneity of these tumors, however, the relation between glycolytic preference, tumor formation, and tumor cell clonogenicity has remained unknown. To address this issue, we analyzed the metabolic profiles of isogenic glioma-initiating cells (GICs) in a mouse model. GICs were established by overexpression of H-Ras(V12) in Ink4a/Arf-null neural stem cells. Subpopulations of these cells were obtained by single-cell cloning, and clones differing in extracellular acidification potential were assessed for metabolic characteristics. Tumors formed after intracranial implantation of these clones in mice were examined for pathological features of glioma and expression of glycolytic enzymes. Malignant transformation of neural stem cells resulted in a shift in metabolism characterized by an increase in lactic acid production. However, isogenic clonal populations of GICs manifested pronounced differences in glucose and oxygen consumption, lactate production, and nucleoside levels. These differences were paralleled by differential expression of glycolytic enzymes such as hexokinase 2 and pyruvate kinase M2, with this differential expression also being evident in tumors formed by these clones in vivo. The metabolic characteristics of glioma cells appear early during malignant transformation and persist until the late stages of tumor formation. Even isogenic clones may be heterogeneous in terms of metabolic features, however, suggesting that a more detailed understanding of the metabolic profile of glioma is imperative for effective therapeutic targeting.

Highlights

The metabolic preference of malignant glioma for glycolysis as an energy source is a potential therapeutic target
Even isogenic clones may be heterogeneous in terms of metabolic features, suggesting that a more detailed understanding of the metabolic profile of glioma is imperative for effective therapeutic targeting
Glioma cells tend to present with a metabolic preference for glycolysis, with this feature having served as the basis for the development of PET-based diagnosis.[7]

Summary

Methods

GICs were established by overexpression of H-RasV12 in Ink4a/Arf –null neural stem cells. Subpopulations of these cells were obtained by single-cell cloning, and clones differing in extracellular acidification potential were assessed for metabolic characteristics. Primary Ink4a/Arf– null neural stem cells (NSCs) and neural progenitor cells (NPCs) were isolated as previously described.[16] Human H-RasV12 cDNA P. Pandolfi) was cloned into a modified form of the retroviral vector pMXs-IG Kitamura) in which the coding sequence for green fluorescent protein had been replaced with that for dsRed. Retroviral supernatants were prepared and used to infect the isolated NSCs/ NPCs. Cells sorted for dsRed fluorescence were designated RasR, cultured as spheres, and used for subsequent experiments

Results

Discussion

Conclusion