Metabolite Profiling For Cancer Stem Cells In Malignant Gliomas Revealed That Protoporphyrin-IX Is A Biomarker For Tumor-Propagating Cells And In _-Aminolevulinic Acid-Mediated Photodynamic/Radiosensitizing Therapy

Naosuke NONOGUCHI, Osaka Medical College, Japan
OHMURA N. 1 , PARK Y. 1 , IKEDA N. 1 , KAWABATA S. 1 , KAJIMOTO Y. 1 , KUROIWA T. 1

1 Department of Neurosurgery, Osaka Medical College, Takatsuki, Japan

Tumor heterogeneity of high-grade gliomas (HGGs) is recognized in 3 major subtypes based on core gene signatures: mesenchymeal, proneural and classical. Among them, HGGs profiled in the mesenchymeal subtype tend to show worse prognosis than others. Recently, also as for glioma stem cells, genome-wide transcriptional analysis identified two mutually exclusive subtypes of glioma stem cells (GSCs) with distinct dysregulated signaling and metabolic pathways; mesenchymal GSCs (MES-GSCs) and proneural GSCs (PN-GSCs). Similar to HGGs with a MES signature, MES-GSCs display more aggressive phenotypes and are markedly resistant to radiation as compared with PN-GSCs, consistent with the relative radiation resistance of MES-GBM.
 In the present study, we used 5 human GSC lines established from 3 MES-HGGs and 2 PN-HGGs. Metabolome analysis for these GSCs using liquid chromatography-tandem mass spectrometry (LC-MS/MS) revealed that the glycolytic pathway and porphyrin biosynthesis were significantly activated in MES-GSCs compared to PN-GSCs. Furthermore, exogenous administration of δ-aminolevurinic acid (ALA), the first metabolite in the porphyrin synthesis pathway, significantly increased the endogenous production of protoporphyrin-IX (PpIX), a heme precursor porphyrin with photosensitizing and radiosensitizing activities, in MES-GSCs than PN-GSCs. To reflect those difference, ALA/PpIX-mediated photodynamic and radio-sensitizing therapies were significantly more effective in MES-GSCs than in PN-GSCs both in vitro and in vivo. Furthermore, when MES-GSCs were sorted by PpIX-fluorescence intensity into three fractions by FACS, MES-GSCs with high intracellular PpIX level showed significantly higher expression of GSC marker genes (nestin, L1CAM, SSEA-1 etc.) and in vivo tumor-initiating ability compared to those with low intracellular PpIX. Those results seemed to suggest that PpIX could be a metabolic biomarker to detect and extract cells with high tumor-propagating phenotype among malignant gliomas.
 Porphyrin metabolism may therefore represent a metabolic vulnerability in MES-GSCs under photodynamic and radiosensitizing therapies that could in principle be targeted for therapeutic benefit.