Abstract LB-308: Effects of the IDH1 R132H mutation on redox status and metabolism are cell type dependent but independent from D-2-hydroxyglutarate accumulation
Authors: Schrock Evelin , Biedermann Julia , Abou-El-Ardat Khalil , Lehmann Matthias , Conde Marina , Peitzsch Mirko , Richter Susan , Wiedemuth Ralf , Meinhardt Matthias , Leenders William P. J. , Herold-Mende Christel , Eisenhofer Graeme , Niclou Simone P. , Kunz-Schughart Leoni , Temme Achim , Klink Barbara 
Published: July 2016

Abstract
IDH1 R132H mutations are considered to play a key role in the development of low grade gliomas and therefrom derived secondary glioblastomas (GBM). Wild type IDH1 converts isocitrate to α-ketoglutarate (a-KG) while reducing NADP+. IDH1R132H has a neomorphic enzymatic function using a-KG to generate high amounts of the oncometabolite D-2-hydroxyglutarate (D-2-HG). While the effects of D-2-HG have been subject to intense research, D-2-HG independent effects of IDH1R132H on energy homeostasis and redox status are not well studied. Here we demonstrate that IDH1R132H transduction but not D-2-HG alone leads to significantly decreased Krebs cycle metabolite concentrations and proliferation in U87 and the primary GBM cell line HT7606 as well as in immortalized astrocytes SVGp12. Furthermore, IDH1R132H mutation, but not D-2-HG treatment, resulted in a significant drop in NADPH levels in tumor cells (U87 and HT7606), whereas immortalized astrocytes retained normal NADPH levels. Since NAPDH levels can be restored via the reaction of the NAD-kinase, we analyzed NAD levels and enzymes involved in NAD-synthesis in our cell lines. Indeed we found a significant drop of NAD levels and in the activity of the NAD-dependent enzyme sirtuin in IDH1R132H mutant U87 and HT7606 but not in NADPH stable SVGp12-IDH1R132H. Interestingly, there were marked differences in expression of NAD-synthesis enzymes between the different cell-lines. In particular, NAMPT-levels were much higher in U87 and HT7606 then in astrocytes (SVGp12) and significantly decreased in U87-IDH1R132H and HT7606-IDH1R132H. Importantly, we also found decreased levels of NAMPT in primary tumor tissues and patient derived glioma cell lines with IDH1 R132H compared to wild type gliomas. Altogether our results for the first time show that the IDH1 mutation directly affects energy homeostasis and redox status in a cell-type dependent manner. We hypothesize that this leads to a drop in NADPH and NAD-levels during malignant progression, resulting in a disadvantage for proliferating tumor cells. This is in line with the favorable prognosis and good response to chemo- and radiation therapy clinically observed in IDH-mutated gliomas. Our findings suggest that the impaired metabolism in IDH1-mutant tumors might be a promising target for future therapies.
Citation Format: Evelin Schrock, Julia Biedermann, Khalil Abou-El-Ardat, Matthias Lehmann, Marina Conde, Mirko Peitzsch, Susan Richter, Ralf Wiedemuth, Matthias Meinhardt, William P. J. Leenders, Christel Herold-Mende, Graeme Eisenhofer, Simone P. Niclou, Leoni Kunz-Schughart, Achim Temme, Barbara Klink. Effects of the IDH1 R132H mutation on redox status and metabolism are cell type dependent but independent from D-2-hydroxyglutarate accumulation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-308.