Myriam Chaumeil | University of California, San Francisco (original) (raw)
Papers by Myriam Chaumeil
Brain Pathology, 2015
This review is focused on describing the use of magnetic resonance (MR) spectroscopy for metaboli... more This review is focused on describing the use of magnetic resonance (MR) spectroscopy for metabolic imaging of brain tumors. We will first review the MR metabolic imaging findings generated from preclinical models, focusing primarily on in vivo studies, and will then describe the use of metabolic imaging in the clinical setting. We will address relatively well-established (1) H MRS approaches, as well as (31) P MRS, (13) C MRS and emerging hyperpolarized (13) C MRS methodologies, and will describe the use of metabolic imaging for understanding the basic biology of glioma as well as for improving the characterization and monitoring of brain tumors in the clinic.
Magn Reson Med, 2008
In the present work, diffusion-weighted (DW)-NMR spectroscopy of glutamate was performed during a... more In the present work, diffusion-weighted (DW)-NMR spectroscopy of glutamate was performed during a 13 C-labeled glucose infusion in monkey brain (six experiments). It is shown that glutamate 13 C labeling occurs significantly faster at higher diffusion weightings-slightly for glutamate in position C4, and more markedly for glutamate in position C3. This demonstrates the existence of different diffusion compartments for glutamate, associated with different metabolic rates. Metabolic modeling of 13 C enrichment time-courses suggests that these compartments might be gray and white matter, each having a specific oxidative metabolism rate possibly paralleled by a specific glutamate diffusion coefficient. Magn Reson Med 60: 306 -311, 2008.
Methods in Enzymology, 2015
First described in 2003, the dissolution dynamic nuclear polarization (DNP) technique, combined w... more First described in 2003, the dissolution dynamic nuclear polarization (DNP) technique, combined with (13)C magnetic resonance spectroscopy (MRS), has since been used in numerous metabolic studies and has become a valuable metabolic imaging method. DNP dramatically increases the level of polarization of (13)C-labeled compounds resulting in an increase in the signal-to-noise ratio (SNR) of over 50,000 fold for the MRS spectrum of hyperpolarized compounds. The high SNR enables rapid real-time detection of metabolism in cells, tissues, and in vivo. This chapter will present a comprehensive review of the DNP approaches that have been used to monitor metabolism in living systems. First, the list of (13)C DNP probes developed to date will be presented, with a particular focus on the most commonly used probe, namely [1-(13)C] pyruvate. In the next four sections, we will then describe the different factors that need to be considered when designing (13)C DNP probes for metabolic studies, conducting in vitro or in vivo hyperpolarized experiments, as well as acquiring, analyzing, and modeling hyperpolarized (13)C data.
Neuro-Oncology, 2012
The phosphatidylinositol-3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR) signaling pat... more The phosphatidylinositol-3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR) signaling pathway is activated in more than 88% of glioblastomas (GBM). New drugs targeting this pathway are currently in clinical trials. However, noninvasive assessment of treatment response remains challenging. By using magnetic resonance spectroscopy (MRS), PI3K/Akt/ mTOR pathway inhibition was monitored in 3 GBM cell lines (GS-2, GBM8, and GBM6; each with a distinct pathway activating mutation) through the measurement of 2 mechanistically linked MR biomarkers: phosphocholine (PC) and hyperpolarized lactate. 31 P MRS studies showed that treatment with the PI3K inhibitor LY294002 induced significant decreases in PC to 34 %+ + + + + 9% of control in GS-2 cells, 48% + + + + + 5% in GBM8, and 45% + + + + + 4% in GBM6. The mTOR inhibitor everolimus also induced a significant decrease in PC to 62% + + + + + 14%, 57% + + + + + 1%, and 58% + + + + + 1% in GS-2, GBM8, and GBM6 cells, respectively. Using hyperpolarized 13 C MRS, we demonstrated that hyperpolarized lactate levels were significantly decreased following PI3K/Akt/mTOR pathway inhibition in all 3 cell lines to 51% + + + + + 10%, 62% + + + + + 3%, and 58% + + + + + 2% of control with LY294002 and 72% + + + + + 3%, 61% + + + + + 2%, and 66% + + + + + 3% of control with everolimus in GS-2, GBM8, and GBM6 cells, respectively. These effects were mediated by decreases in the activity and expression of choline kinase a and lactate dehydrogenase, which respectively control PC and lactate production downstream of HIF-1. Treatment with the DNA damaging agent temozolomide did not have an effect on either biomarker in any cell line. This study highlights the potential of PC and hyperpolarized lactate as noninvasive MR biomarkers of response to targeted inhibitors in GBM.
Magnetic Resonance in Medicine, 2008
Journal of Cerebral Blood Flow & Metabolism, 2012
Early diagnosis and follow-up of neurodegenerative diseases are often hampered by the lack of rel... more Early diagnosis and follow-up of neurodegenerative diseases are often hampered by the lack of reliable biomarkers. Neuroimaging techniques like magnetic resonance spectroscopy (MRS) offer promising tools to detect biochemical alterations at early stages of degeneration. Intracellular pH, which can be measured noninvasively by 31 P-MRS, has shown variations in several brain diseases. Our purpose has been to evaluate the potential of MRS-measured pH as a relevant biomarker of early degeneration in Huntington's disease (HD). We used a translational approach starting with a preclinical validation of our hypothesis before adapting the method to HD patients. 31 P-MRS-derived cerebral pH was first measured in rodents during chronic intoxication with 3-nitropropionic acid (3NP). A significant pH increase was observed early into the intoxication protocol (pH = 7.17±0.02 after 3 days) as compared with preintoxication (pH = 7.08 ± 0.03). Furthermore, pH changes correlated with the 3NP-induced inhibition of succinate dehydrogenase and preceded striatum lesions. Using a similar MRS approach implemented on a clinical MRI, we then showed that cerebral pH was significantly higher in HD patients (n = 7) than in healthy controls (n = 6) (7.05±0.03 versus 7.02 ± 0.01, respectively, P = 0.026). Altogether, both preclinical and human data strongly argue in favor of MRS-measured pH being a promising biomarker for diagnosis and follow-up of HD.
European Biophysics Journal, 2006
Many questions in cell biology and biophysics involve the quantitation of co-localisation and the... more Many questions in cell biology and biophysics involve the quantitation of co-localisation and the interaction of proteins tagged with different fluorophores. However, the incomplete separation of the different colour channels due to the presence of autofluorescence, along with cross-excitation and emission ''bleed-through'' of one colour channel into the other, all combine to render the interpretation of multiband images ambiguous. Here we introduce a new live-cell epifluorescence spectral imaging and linear unmixing technique for classifying resolution-limited point objects containing multiple fluorophores. We demonstrate the performance of our technique by detecting, at the single-vesicle level, the co-expression of the vesicle-associated membrane protein, VAMP-2 (also called synaptobrevin-2), linked to either enhanced green fluorescent protein (EGFP) or citrine (a less pH-sensitive variant of enhanced yellow fluorescent protein (EYFP)), in mouse cortical astrocytes. In contrast, the co-expression of VAMP-2-citrine and the lysosomal transporter sialine fused to EGFP resulted in little overlap. Spectral imaging and linear unmixing permit us to fingerprint the expression of spectrally overlapping fluorescent proteins on single secretory organelles in the presence of a spectrally broad autofluorescence. Our technique provides a robust alternative to error-prone dual-or triple colour co-localisation studies.
Proceedings of the National Academy of Sciences, 2009
Neuroimaging methods have considerably developed over the last decades and offer various noninvas... more Neuroimaging methods have considerably developed over the last decades and offer various noninvasive approaches for measuring cerebral metabolic fluxes connected to energy metabolism, including PET and magnetic resonance spectroscopy (MRS). Among these methods, 31 P MRS has the particularity and advantage to directly measure cerebral ATP synthesis without injection of labeled precursor. However, this approach is methodologically challenging, and further validation studies are required to establish 31 P MRS as a robust method to measure brain energy synthesis. In the present study, we performed a multimodal imaging study based on the combination of 3 neuroimaging techniques, which allowed us to obtain an integrated picture of brain energy metabolism and, at the same time, to validate the saturation transfer 31 P MRS method as a quantitative measurement of brain ATP synthesis. A total of 29 imaging sessions were conducted to measure glucose consumption (CMRglc), TCA cycle flux (VTCA), and the rate of ATP synthesis (VATP) in primate monkeys by using 18 F-FDG PET scan, indirect 13 C MRS, and saturation transfer 31 P MRS, respectively. These 3 complementary measurements were performed within the exact same area of the brain under identical physiological conditions, leading to: CMRglc ؍ 0.27 ؎ 0.07 mol⅐g ؊1 ⅐min ؊1 , VTCA ؍ 0.63 ؎ 0.12 mol⅐g ؊1 ⅐min ؊1 , and VATP ؍ 7.8 ؎ 2.3 mol⅐g ؊1 ⅐min ؊1 . The consistency of these 3 fluxes with literature and, more interestingly, one with each other, demonstrates the robustness of saturation transfer 31 P MRS for directly evaluating ATP synthesis in the living brain.
Cancer Research, 2015
Mutant isocitrate dehydrogenase 1 (IDH1) catalyzes the production of 2-hydroxyglutarate but also ... more Mutant isocitrate dehydrogenase 1 (IDH1) catalyzes the production of 2-hydroxyglutarate but also elicits additional metabolic changes. Levels of both glutamate and pyruvate dehydrogenase (PDH) activity have been shown to be affected in U87 glioblastoma cells or normal human astrocyte (NHA) cells expressing mutant IDH1, as compared to cells expressing wild-type IDH1. In this study, we show how these phenomena are linked through the effects of IDH1 mutation, which also reprograms pyruvate metabolism. Reduced PDH activity in U87 glioblastoma and NHA IDH1 mutant cells was associated with relative increases in PDH inhibitory phosphorylation, expression of pyruvate dehydrogenase kinase-3 and levels of hypoxia inducible factor-1α. PDH activity was monitored in these cells by hyperpolarized 13C-magnetic resonance spectroscopy (13C-MRS), which revealed a reduction in metabolism of hyperpolarized 2-13C-pyruvate to 5-13C-glutamate, relative to cells expressing wild-type IDH1. 13C-MRS also revealed a reduction in glucose flux to glutamate in IDH1 mutant cells. Notably, pharmacological activation of PDH by cell exposure to dichloroacetate (DCA) increased production of hyperpolarized 5-13C-glutamate in IDH1 mutant cells. Further, DCA treatment also abrogated the clonogenic advantage conferred by IDH1 mutation. Using patient-derived mutant IDH1 neurosphere models, we showed that PDH activity was essential for cell proliferation. Taken together, our results established that the IDH1 mutation induces an MRS-detectable reprogramming of pyruvate metabolism which is essential for cell proliferation and clonogenicity, with immediate therapeutic implications.
PLOS ONE, 2015
Mutations in isocitrate dehydrogenase (IDH) 1 have been reported in over 70% of lowgrade gliomas ... more Mutations in isocitrate dehydrogenase (IDH) 1 have been reported in over 70% of lowgrade gliomas and secondary glioblastomas. IDH1 is the enzyme that catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate while mutant IDH1 catalyzes the conversion of α-ketoglutarate into 2-hydroxyglutarate. These mutations are associated with the accumulation of 2-hydroxyglutarate within the tumor and are believed to be one of the earliest events in the development of low-grade gliomas. The goal of this work was to determine whether the IDH1 mutation leads to additional magnetic resonance spectroscopy (MRS)detectable changes in the cellular metabolome.
ABSTRACT The IDH1 mutation is now recognized as an important driver in the etiology of low-grade ... more ABSTRACT The IDH1 mutation is now recognized as an important driver in the etiology of low-grade brain tumors. In contrast to wild-type IDH1, which catalyzes the conversion of isocitrate to α-ketoglutarate (αKG), mutant IDH1 converts αKG into the oncometabolite 2-hydroxygluatrate (2HG). In an effort to noninvasively image the activity of mutant IDH1, we have previously shown that we can use hyperpolarized αKG together with 13C magnetic resonance spectroscopy (MRS) to noninvasively detect the production of hyperpolarized 2HG in vivo. In more recent studies we have focused on identifying additional metabolic alterations associated with the presence of the IDH1 mutation in order to develop complementary metabolic imaging approaches that might serve to inform on the presence of mutant IDH1 and its modulation with targeted therapies.
Hyperpolarized (13) C magnetic resonance allows for the study of real-time metabolism in vivo, in... more Hyperpolarized (13) C magnetic resonance allows for the study of real-time metabolism in vivo, including significant hyperpolarized (13) C lactate production in many tumors. Other studies have shown that aggressive and highly metastatic tumors rapidly transport lactate out of cells. Thus, the ability to not only measure the production of hyperpolarized (13) C lactate but also understand its compartmentalization using diffusion-weighted MR will provide unique information for improved tumor characterization. We used a bipolar, pulsed-gradient, double spin echo imaging sequence to rapidly generate diffusion-weighted images of hyperpolarized (13) C metabolites. Our methodology included a simultaneously acquired B1 map to improve apparent diffusion coefficient (ADC) accuracy and a diffusion-compensated variable flip angle scheme to improve ADC precision. We validated this sequence and methodology in hyperpolarized (13) C phantoms. Next, we generated ADC maps of several hyperpolarized (13) C metabolites in a normal rat, rat brain tumor, and prostate cancer mouse model using both preclinical and clinical trial-ready hardware. ADC maps of hyperpolarized (13) C metabolites provide information about the localization of these molecules in the tissue microenvironment. The methodology presented here allows for further studies to investigate ADC changes due to disease state that may provide unique information about cancer aggressiveness and metastatic potential. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
The isocitrate dehydrogenase (IDH)1 mutation is associated with accumulation of 2-hydroxyglutarat... more The isocitrate dehydrogenase (IDH)1 mutation is associated with accumulation of 2-hydroxyglutarate (2-HG), but the metabolic fluxes associated with 2-HG production and cellular reprogramming of mutant IDH1 cells are not fully understood. The objective of this study was to use 13 C magnetic resonance spectroscopy (MRS) to probe the fate of 13 C-labeled metabolites (at thermal polarization and hyperpolarized by dynamic nuclear polarization) and to monitor the glycolytic pathway, the TCA cycle, and glutamine metabolism in wild-type and mutant IDH1 glioma cells. To achieve this goal, U87 cells expressing mutant IDH1 and wild-type IDH1 were generated by transduction with a lentiviral vector coding for mutant or wild-type IDH1 respectively. MRS studies were performed using a cell perfusion (bioreactor) system. Live cells were exposed to hyperpolarized 1-13 C or 2-13 C-labeled pyruvic acid, 1-13 C glucose or 3-13 C glutamine and cell metabolism was probed using 13 C MRS. We found that in mutant IDH1 cells pyruvate flux to lactate was increased relative to wild-type cells, and pyruvate flux to glutamate and 2-HG was decreased compared to pyruvate flux to glutamate in wild-type IDH1 cell. Glutamine flux to glutamate in wild-type cells, or to glutamate and 2-HG in mutant IDH1 cells was comparable. Accordingly, the total intracellular glutamate pool was reduced in mutant IDH1 cells. The drop in pyruvate flux to the TCA cycle was mediated by a significant drop in pyruvate dehydrogenase (PDH) activity, which was due to significantly increased inhibitory PDH phosphorylation. When considering 2-HG synthesis, our data also indicate that, consistent with previous work, the majority of 2-HG is produced from glutamine (82%). However in our cells a significant portion (18%) was also derived from glucose. Our findings thus point to metabolic reprogramming in IDH1 mutant cells beyond 2-HG production and highlight the value of MRS for characterizing the metabolic changes associated with the IDH1 mutation.
Brain Pathology, 2015
This review is focused on describing the use of magnetic resonance (MR) spectroscopy for metaboli... more This review is focused on describing the use of magnetic resonance (MR) spectroscopy for metabolic imaging of brain tumors. We will first review the MR metabolic imaging findings generated from preclinical models, focusing primarily on in vivo studies, and will then describe the use of metabolic imaging in the clinical setting. We will address relatively well-established (1) H MRS approaches, as well as (31) P MRS, (13) C MRS and emerging hyperpolarized (13) C MRS methodologies, and will describe the use of metabolic imaging for understanding the basic biology of glioma as well as for improving the characterization and monitoring of brain tumors in the clinic.
Magn Reson Med, 2008
In the present work, diffusion-weighted (DW)-NMR spectroscopy of glutamate was performed during a... more In the present work, diffusion-weighted (DW)-NMR spectroscopy of glutamate was performed during a 13 C-labeled glucose infusion in monkey brain (six experiments). It is shown that glutamate 13 C labeling occurs significantly faster at higher diffusion weightings-slightly for glutamate in position C4, and more markedly for glutamate in position C3. This demonstrates the existence of different diffusion compartments for glutamate, associated with different metabolic rates. Metabolic modeling of 13 C enrichment time-courses suggests that these compartments might be gray and white matter, each having a specific oxidative metabolism rate possibly paralleled by a specific glutamate diffusion coefficient. Magn Reson Med 60: 306 -311, 2008.
Methods in Enzymology, 2015
First described in 2003, the dissolution dynamic nuclear polarization (DNP) technique, combined w... more First described in 2003, the dissolution dynamic nuclear polarization (DNP) technique, combined with (13)C magnetic resonance spectroscopy (MRS), has since been used in numerous metabolic studies and has become a valuable metabolic imaging method. DNP dramatically increases the level of polarization of (13)C-labeled compounds resulting in an increase in the signal-to-noise ratio (SNR) of over 50,000 fold for the MRS spectrum of hyperpolarized compounds. The high SNR enables rapid real-time detection of metabolism in cells, tissues, and in vivo. This chapter will present a comprehensive review of the DNP approaches that have been used to monitor metabolism in living systems. First, the list of (13)C DNP probes developed to date will be presented, with a particular focus on the most commonly used probe, namely [1-(13)C] pyruvate. In the next four sections, we will then describe the different factors that need to be considered when designing (13)C DNP probes for metabolic studies, conducting in vitro or in vivo hyperpolarized experiments, as well as acquiring, analyzing, and modeling hyperpolarized (13)C data.
Neuro-Oncology, 2012
The phosphatidylinositol-3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR) signaling pat... more The phosphatidylinositol-3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR) signaling pathway is activated in more than 88% of glioblastomas (GBM). New drugs targeting this pathway are currently in clinical trials. However, noninvasive assessment of treatment response remains challenging. By using magnetic resonance spectroscopy (MRS), PI3K/Akt/ mTOR pathway inhibition was monitored in 3 GBM cell lines (GS-2, GBM8, and GBM6; each with a distinct pathway activating mutation) through the measurement of 2 mechanistically linked MR biomarkers: phosphocholine (PC) and hyperpolarized lactate. 31 P MRS studies showed that treatment with the PI3K inhibitor LY294002 induced significant decreases in PC to 34 %+ + + + + 9% of control in GS-2 cells, 48% + + + + + 5% in GBM8, and 45% + + + + + 4% in GBM6. The mTOR inhibitor everolimus also induced a significant decrease in PC to 62% + + + + + 14%, 57% + + + + + 1%, and 58% + + + + + 1% in GS-2, GBM8, and GBM6 cells, respectively. Using hyperpolarized 13 C MRS, we demonstrated that hyperpolarized lactate levels were significantly decreased following PI3K/Akt/mTOR pathway inhibition in all 3 cell lines to 51% + + + + + 10%, 62% + + + + + 3%, and 58% + + + + + 2% of control with LY294002 and 72% + + + + + 3%, 61% + + + + + 2%, and 66% + + + + + 3% of control with everolimus in GS-2, GBM8, and GBM6 cells, respectively. These effects were mediated by decreases in the activity and expression of choline kinase a and lactate dehydrogenase, which respectively control PC and lactate production downstream of HIF-1. Treatment with the DNA damaging agent temozolomide did not have an effect on either biomarker in any cell line. This study highlights the potential of PC and hyperpolarized lactate as noninvasive MR biomarkers of response to targeted inhibitors in GBM.
Magnetic Resonance in Medicine, 2008
Journal of Cerebral Blood Flow & Metabolism, 2012
Early diagnosis and follow-up of neurodegenerative diseases are often hampered by the lack of rel... more Early diagnosis and follow-up of neurodegenerative diseases are often hampered by the lack of reliable biomarkers. Neuroimaging techniques like magnetic resonance spectroscopy (MRS) offer promising tools to detect biochemical alterations at early stages of degeneration. Intracellular pH, which can be measured noninvasively by 31 P-MRS, has shown variations in several brain diseases. Our purpose has been to evaluate the potential of MRS-measured pH as a relevant biomarker of early degeneration in Huntington's disease (HD). We used a translational approach starting with a preclinical validation of our hypothesis before adapting the method to HD patients. 31 P-MRS-derived cerebral pH was first measured in rodents during chronic intoxication with 3-nitropropionic acid (3NP). A significant pH increase was observed early into the intoxication protocol (pH = 7.17±0.02 after 3 days) as compared with preintoxication (pH = 7.08 ± 0.03). Furthermore, pH changes correlated with the 3NP-induced inhibition of succinate dehydrogenase and preceded striatum lesions. Using a similar MRS approach implemented on a clinical MRI, we then showed that cerebral pH was significantly higher in HD patients (n = 7) than in healthy controls (n = 6) (7.05±0.03 versus 7.02 ± 0.01, respectively, P = 0.026). Altogether, both preclinical and human data strongly argue in favor of MRS-measured pH being a promising biomarker for diagnosis and follow-up of HD.
European Biophysics Journal, 2006
Many questions in cell biology and biophysics involve the quantitation of co-localisation and the... more Many questions in cell biology and biophysics involve the quantitation of co-localisation and the interaction of proteins tagged with different fluorophores. However, the incomplete separation of the different colour channels due to the presence of autofluorescence, along with cross-excitation and emission ''bleed-through'' of one colour channel into the other, all combine to render the interpretation of multiband images ambiguous. Here we introduce a new live-cell epifluorescence spectral imaging and linear unmixing technique for classifying resolution-limited point objects containing multiple fluorophores. We demonstrate the performance of our technique by detecting, at the single-vesicle level, the co-expression of the vesicle-associated membrane protein, VAMP-2 (also called synaptobrevin-2), linked to either enhanced green fluorescent protein (EGFP) or citrine (a less pH-sensitive variant of enhanced yellow fluorescent protein (EYFP)), in mouse cortical astrocytes. In contrast, the co-expression of VAMP-2-citrine and the lysosomal transporter sialine fused to EGFP resulted in little overlap. Spectral imaging and linear unmixing permit us to fingerprint the expression of spectrally overlapping fluorescent proteins on single secretory organelles in the presence of a spectrally broad autofluorescence. Our technique provides a robust alternative to error-prone dual-or triple colour co-localisation studies.
Proceedings of the National Academy of Sciences, 2009
Neuroimaging methods have considerably developed over the last decades and offer various noninvas... more Neuroimaging methods have considerably developed over the last decades and offer various noninvasive approaches for measuring cerebral metabolic fluxes connected to energy metabolism, including PET and magnetic resonance spectroscopy (MRS). Among these methods, 31 P MRS has the particularity and advantage to directly measure cerebral ATP synthesis without injection of labeled precursor. However, this approach is methodologically challenging, and further validation studies are required to establish 31 P MRS as a robust method to measure brain energy synthesis. In the present study, we performed a multimodal imaging study based on the combination of 3 neuroimaging techniques, which allowed us to obtain an integrated picture of brain energy metabolism and, at the same time, to validate the saturation transfer 31 P MRS method as a quantitative measurement of brain ATP synthesis. A total of 29 imaging sessions were conducted to measure glucose consumption (CMRglc), TCA cycle flux (VTCA), and the rate of ATP synthesis (VATP) in primate monkeys by using 18 F-FDG PET scan, indirect 13 C MRS, and saturation transfer 31 P MRS, respectively. These 3 complementary measurements were performed within the exact same area of the brain under identical physiological conditions, leading to: CMRglc ؍ 0.27 ؎ 0.07 mol⅐g ؊1 ⅐min ؊1 , VTCA ؍ 0.63 ؎ 0.12 mol⅐g ؊1 ⅐min ؊1 , and VATP ؍ 7.8 ؎ 2.3 mol⅐g ؊1 ⅐min ؊1 . The consistency of these 3 fluxes with literature and, more interestingly, one with each other, demonstrates the robustness of saturation transfer 31 P MRS for directly evaluating ATP synthesis in the living brain.
Cancer Research, 2015
Mutant isocitrate dehydrogenase 1 (IDH1) catalyzes the production of 2-hydroxyglutarate but also ... more Mutant isocitrate dehydrogenase 1 (IDH1) catalyzes the production of 2-hydroxyglutarate but also elicits additional metabolic changes. Levels of both glutamate and pyruvate dehydrogenase (PDH) activity have been shown to be affected in U87 glioblastoma cells or normal human astrocyte (NHA) cells expressing mutant IDH1, as compared to cells expressing wild-type IDH1. In this study, we show how these phenomena are linked through the effects of IDH1 mutation, which also reprograms pyruvate metabolism. Reduced PDH activity in U87 glioblastoma and NHA IDH1 mutant cells was associated with relative increases in PDH inhibitory phosphorylation, expression of pyruvate dehydrogenase kinase-3 and levels of hypoxia inducible factor-1α. PDH activity was monitored in these cells by hyperpolarized 13C-magnetic resonance spectroscopy (13C-MRS), which revealed a reduction in metabolism of hyperpolarized 2-13C-pyruvate to 5-13C-glutamate, relative to cells expressing wild-type IDH1. 13C-MRS also revealed a reduction in glucose flux to glutamate in IDH1 mutant cells. Notably, pharmacological activation of PDH by cell exposure to dichloroacetate (DCA) increased production of hyperpolarized 5-13C-glutamate in IDH1 mutant cells. Further, DCA treatment also abrogated the clonogenic advantage conferred by IDH1 mutation. Using patient-derived mutant IDH1 neurosphere models, we showed that PDH activity was essential for cell proliferation. Taken together, our results established that the IDH1 mutation induces an MRS-detectable reprogramming of pyruvate metabolism which is essential for cell proliferation and clonogenicity, with immediate therapeutic implications.
PLOS ONE, 2015
Mutations in isocitrate dehydrogenase (IDH) 1 have been reported in over 70% of lowgrade gliomas ... more Mutations in isocitrate dehydrogenase (IDH) 1 have been reported in over 70% of lowgrade gliomas and secondary glioblastomas. IDH1 is the enzyme that catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate while mutant IDH1 catalyzes the conversion of α-ketoglutarate into 2-hydroxyglutarate. These mutations are associated with the accumulation of 2-hydroxyglutarate within the tumor and are believed to be one of the earliest events in the development of low-grade gliomas. The goal of this work was to determine whether the IDH1 mutation leads to additional magnetic resonance spectroscopy (MRS)detectable changes in the cellular metabolome.
ABSTRACT The IDH1 mutation is now recognized as an important driver in the etiology of low-grade ... more ABSTRACT The IDH1 mutation is now recognized as an important driver in the etiology of low-grade brain tumors. In contrast to wild-type IDH1, which catalyzes the conversion of isocitrate to α-ketoglutarate (αKG), mutant IDH1 converts αKG into the oncometabolite 2-hydroxygluatrate (2HG). In an effort to noninvasively image the activity of mutant IDH1, we have previously shown that we can use hyperpolarized αKG together with 13C magnetic resonance spectroscopy (MRS) to noninvasively detect the production of hyperpolarized 2HG in vivo. In more recent studies we have focused on identifying additional metabolic alterations associated with the presence of the IDH1 mutation in order to develop complementary metabolic imaging approaches that might serve to inform on the presence of mutant IDH1 and its modulation with targeted therapies.
Hyperpolarized (13) C magnetic resonance allows for the study of real-time metabolism in vivo, in... more Hyperpolarized (13) C magnetic resonance allows for the study of real-time metabolism in vivo, including significant hyperpolarized (13) C lactate production in many tumors. Other studies have shown that aggressive and highly metastatic tumors rapidly transport lactate out of cells. Thus, the ability to not only measure the production of hyperpolarized (13) C lactate but also understand its compartmentalization using diffusion-weighted MR will provide unique information for improved tumor characterization. We used a bipolar, pulsed-gradient, double spin echo imaging sequence to rapidly generate diffusion-weighted images of hyperpolarized (13) C metabolites. Our methodology included a simultaneously acquired B1 map to improve apparent diffusion coefficient (ADC) accuracy and a diffusion-compensated variable flip angle scheme to improve ADC precision. We validated this sequence and methodology in hyperpolarized (13) C phantoms. Next, we generated ADC maps of several hyperpolarized (13) C metabolites in a normal rat, rat brain tumor, and prostate cancer mouse model using both preclinical and clinical trial-ready hardware. ADC maps of hyperpolarized (13) C metabolites provide information about the localization of these molecules in the tissue microenvironment. The methodology presented here allows for further studies to investigate ADC changes due to disease state that may provide unique information about cancer aggressiveness and metastatic potential. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
The isocitrate dehydrogenase (IDH)1 mutation is associated with accumulation of 2-hydroxyglutarat... more The isocitrate dehydrogenase (IDH)1 mutation is associated with accumulation of 2-hydroxyglutarate (2-HG), but the metabolic fluxes associated with 2-HG production and cellular reprogramming of mutant IDH1 cells are not fully understood. The objective of this study was to use 13 C magnetic resonance spectroscopy (MRS) to probe the fate of 13 C-labeled metabolites (at thermal polarization and hyperpolarized by dynamic nuclear polarization) and to monitor the glycolytic pathway, the TCA cycle, and glutamine metabolism in wild-type and mutant IDH1 glioma cells. To achieve this goal, U87 cells expressing mutant IDH1 and wild-type IDH1 were generated by transduction with a lentiviral vector coding for mutant or wild-type IDH1 respectively. MRS studies were performed using a cell perfusion (bioreactor) system. Live cells were exposed to hyperpolarized 1-13 C or 2-13 C-labeled pyruvic acid, 1-13 C glucose or 3-13 C glutamine and cell metabolism was probed using 13 C MRS. We found that in mutant IDH1 cells pyruvate flux to lactate was increased relative to wild-type cells, and pyruvate flux to glutamate and 2-HG was decreased compared to pyruvate flux to glutamate in wild-type IDH1 cell. Glutamine flux to glutamate in wild-type cells, or to glutamate and 2-HG in mutant IDH1 cells was comparable. Accordingly, the total intracellular glutamate pool was reduced in mutant IDH1 cells. The drop in pyruvate flux to the TCA cycle was mediated by a significant drop in pyruvate dehydrogenase (PDH) activity, which was due to significantly increased inhibitory PDH phosphorylation. When considering 2-HG synthesis, our data also indicate that, consistent with previous work, the majority of 2-HG is produced from glutamine (82%). However in our cells a significant portion (18%) was also derived from glucose. Our findings thus point to metabolic reprogramming in IDH1 mutant cells beyond 2-HG production and highlight the value of MRS for characterizing the metabolic changes associated with the IDH1 mutation.