Increased mitochondrial activity in a novel IDH1-R132H mutant human oligodendroglioma xenograft model: in situ detection of 2-HG and α-KG

Abstract

BackgroundPoint mutations in genes encoding NADP+-dependent isocitrate dehydrogenases (especially IDH1) are common in lower grade diffuse gliomas and secondary glioblastomas and occur early during tumor development. The contribution of these mutations to gliomagenesis is not completely understood and research is hampered by the lack of relevant tumor models. We previously described the development of the patient-derived high-grade oligodendroglioma xenograft model E478 that carries the commonly occurring IDH1-R132H mutation. We here report on the analyses of E478 xenografts at the genetic, histologic and metabolic level.ResultsLC-MS and in situ mass spectrometric imaging by LESA-nano ESI-FTICR revealed high levels of the proposed oncometabolite D-2-hydroxyglutarate (D-2HG), the product of enzymatic conversion of α-ketoglutarate (α-KG) by IDH1-R132H, in the tumor but not in surrounding brain parenchyma. α-KG levels and total NADP+-dependent IDH activity were similar in IDH1-mutant and -wildtype xenografts, demonstrating that IDH1-mutated cancer cells maintain α-KG levels. Interestingly, IDH1-mutant tumor cells in vivo present with high densities of mitochondria and increased levels of mitochondrial activity as compared to IDH1-wildtype xenografts. It is not yet clear whether this altered mitochondrial activity is a driver or a consequence of tumorigenesis.ConclusionsThe oligodendroglioma model presented here is a valuable model for further functional elucidation of the effects of IDH1 mutations on tumor metabolism and may aid in the rational development of novel therapeutic strategies for the large subgroup of gliomas carrying IDH1 mutations.

IDH1 R132H Mutation Generates a Distinct Phospholipid Metabolite Profile in Glioma

“…Despite their frequent occurrence, glioma xenografts carrying these mutations are very scarce (41,52,53), and in vitro propagation of IDH1-mutated glioma cell lines is challenging (54). Interestingly, and in line with clinical observations, E478 xenografts present with lower proliferation rates than IDHwt counterparts, as established via the Ki67 index, and mice carrying these xenografts have a longer survival time than mice carrying IDHwt xenografts (see Supplementary Materials).…”

“…In this study, we tested the hypothesis that IDH1 mutations affect the phospholipid metabolite profile of tumors by using IDH1-R132H E478 xenografts (41). Our major finding is that gliomas with an IDH1 mutation indeed have a phospholipid profile, which differs from that in gliomas with wild-type IDH1.…”

“…Two xenograft lines, labeled E468 and E473, were originally derived from human GBM biopsies, whereas E434 and E478 were established from high-grade oligodendroglioma specimens. The E478 xenograft model contains the heterozygous IDH1-R132H mutation (41). All xenografts grow via diffuse infiltration, whereas the E434 model additionally presents with some compact growth (40).…”

“…To test this hypothesis, we applied in vivo 31 P MR spectroscopic imaging (MRSI) to four unique and representative human glioma models growing orthotopically in mice (40), one carrying the IDH1-R132H mutation (41). The spectral findings were verified by 31 P NMR analyses of tumor tissue extracts.…”

Hominoid-specific enzyme GLUD2 promotes growth of IDH1 R132H glioma

“…Previous studies have demonstrated that IDH1 R132H human gliomas maintain normal concentrations of α-KG but have not identified a mechanism that compensates for diverted flux of α-KG into 2-HG (8,9,18,19). In human tumors, mutations in IDH1 and IDH2 are mutually exclusive and invariably heterozygous (7).…”