BI-27 ANALYSIS OF THE BIOCHEMICAL PROFILE OF LOW GRADE GLIOMA WITH DIFFERENT IDH1 MUTATION STATUS USING VIBRATIONAL SPECTROSCOPY

Mutations in human cytosolic isocitrate dehydrogenases 1 (IDH1) are a common feature of low grade gliomas (LGG) and cause profound changes of the metabolites of the Krebs cycle. Vibrational spectroscopy comprises label-free techniques that probe a sample's molecular composition. Therefore, we investigated the ability of fourier-transform infrared (FT-IR) spectroscopy to analyze the IDH1-mutation status in cell culture systems and human brain tumor samples. Cell lines (U87-MG, SVG p12 and the primary glioblastoma cell lines HT7606, HT12346 and HT12347) were transduced with either IDH1 wild-type or mutated IDH1. Clusteranalysis and principal-component-analysis were able to detect differences in the respective FT-IR spectral datasets in regions assigned to saccharides (1050 and 1120 cm-1) and proteins (1236, 1545 and 1651 cm-1). Brain tumor samples of human LGG were obtained during routine surgery and the IDH1 mutation status was determined by DNA sequencing (n = 17). Difference spectra (IDH1-mut vs. IDH1-wt) showed changes in the region around 1100 cm-1 which is attributed to saccharides. Additionally, amide I and amide II spectral bands (around 1550 and 1650 cm-1, respectively) were reduced in the IDH1-mut dataset whereas the band at 1740 cm-1 assigned to C = O stretching vibrations was more pronounced. Principal-component-analysis confirmed differences between the two groups based on spectral regions assigned to saccharides, proteins and to C = O stretching vibrations, as identified previously in the difference spectra. Supervised classification recognized relevant spectral regions at 974, 1005, 1038-1044, 1078-1082, 1267-1275, 1342, 1417-1421, 1479 cm-1 and was able to assign 16 of the 17 tumor samples to the correct group. On the basis of FT-IR spectroscopy samples of LGG carrying IDH1 mutations can be discerned from IDH1 wildtype tumors. Relevant spectral regions assigned to saccharides and C = O stretching vibrations can be explained by changes in the Krebs cycle and in particular by the accumulation of 2-hydroxyglutarate (rich in C = O bonds).