Non-invasive assessment of telomere maintenance mechanisms in brain tumors

AbstractTelomere maintenance is a universal hallmark of cancer. Most tumors including low-grade oligodendrogliomas use telomerase reverse transcriptase (TERT) expression for telomere maintenance while astrocytomas use the alternative lengthening of telomeres (ALT) pathway. Although TERT and ALT are hallmarks of tumor proliferation and attractive therapeutic targets, translational methods of imaging TERT and ALT are lacking. Here we show that TERT and ALT are associated with unique 1H-magnetic resonance spectroscopy (MRS)-detectable metabolic signatures in genetically-engineered and patient-derived glioma models and patient biopsies. Importantly, we have leveraged this information to mechanistically validate hyperpolarized [1-13C]-alanine flux to pyruvate as an imaging biomarker of ALT status and hyperpolarized [1-13C]-alanine flux to lactate as an imaging biomarker of TERT status in low-grade gliomas. Collectively, we have identified metabolic biomarkers of TERT and ALT status that provide a way of integrating critical oncogenic information into non-invasive imaging modalities that can improve tumor diagnosis and treatment response monitoring.

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TAMI-08. A TALE OF TWO TELOMERE MAINTENANCE MECHANISMS: TERT EXPRESSION AND THE ALT PATHWAY INDUCE UNIQUE MRS-DETECTABLE METABOLIC REPROGRAMMING IN LOW-GRADE GLIOMAS

Neuro-Oncology ◽

10.1093/neuonc/noaa215.897 ◽

2020 ◽

Vol 22 (Supplement_2) ◽

pp. ii214-ii214

Author(s):

Pavithra Viswanath ◽

Georgios Batsios ◽

Anne Marie Gillespie ◽

Hema Artee Luchman ◽

Joseph Costello ◽

...

Keyword(s):

Treatment Response ◽

Metabolic Reprogramming ◽

Telomere Maintenance ◽

Imaging Biomarker ◽

Low Grade ◽

Tumor Proliferation ◽

Nicotinamide Phosphoribosyltransferase ◽

Non Invasive ◽

Key Enzyme ◽

Tert Expression

Abstract Telomeres are nucleoprotein structures at chromosomal ends that shorten with cell division and constitute a natural barrier to proliferation. In order to proliferate indefinitely, all tumors require a telomere maintenance mechanism (TMM). Telomerase reverse transcriptase (TERT) expression is the TMM in most tumors, including low-grade oligodendrogliomas (LGOGs). In contrast, low-grade astrocytomas (LGAs) use the alternative lengthening of telomeres (ALT) pathway as their TMM. As molecular hallmarks of tumor proliferation, TMMs are attractive tumor biomarkers and therapeutic targets. Non-invasive imaging of TMM status will, therefore, allow assessment of tumor proliferation and treatment response. However, translational methods of imaging TMM status are lacking. Here, we show that TERT expression and the ALT pathway are associated with unique magnetic resonance spectroscopy (MRS)-detectable metabolic reprogramming in LGOGs and LGAs respectively. In genetically-engineered and patient-derived LGOG models, TERT expression is linked to elevated 1H-MRS-detectable NAD(P)/H, glutathione, aspartate and AXP. In contrast, the ALT pathway in LGAs is associated with higher α-ketoglutarate, glutamate, alanine and AXP. Importantly, elevated flux of hyperpolarized [1-13C]-alanine to pyruvate, which depends on α-ketoglutarate, is a non-invasive in vivo imaging biomarker of the ALT pathway in LGAs while elevated flux of hyperpolarized [1-13C]-alanine to lactate, which depends on NADH, is an imaging biomarker of TERT expression in LGOGs. Mechanistically, the ALT pathway in LGAs is linked to higher glutaminase (GLS), a key enzyme for α-ketoglutarate biosynthesis while TERT expression in LGOGs is associated with elevated nicotinamide phosphoribosyltransferase (NAMPT), a key enzyme for NADH biosynthesis. Notably, TERT expression and the ALT pathway are linked to MRS-detectable metabolic reprogramming in LGOG and LGA patient biopsies, emphasizing the clinical validity of our observations. Collectively, we have identified unique metabolic signatures of TMM status that integrate critical oncogenic information with noninvasive imaging modalities that can improve diagnosis and treatment response monitoring for LGOG and LGA patients.

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BIMG-08. DEUTERIUM MAGNETIC RESONANCE SPECTROSCOPY USING 2H-PYRUVATE ALLOWS NON-INVASIVE IN VIVO IMAGING OF TERT EXPRESSION IN BRAIN TUMORS

Neuro-Oncology Advances ◽

10.1093/noajnl/vdab024.007 ◽

2021 ◽

Vol 3 (Supplement_1) ◽

pp. i2-i2

Author(s):

Georgios Batsios ◽

Celine Taglang ◽

Meryssa Tran ◽

Anne Marie Gillespie ◽

Joseph Costello ◽

...

Keyword(s):

Magnetic Resonance ◽

Magnetic Resonance Spectroscopy ◽

In Vivo Imaging ◽

Lactate Production ◽

Telomere Maintenance ◽

Resonance Spectroscopy ◽

Low Grade ◽

Non Invasive ◽

Tert Expression

Abstract Telomere shortening constitutes a natural barrier to uncontrolled proliferation and all tumors must find a mechanism of maintaining telomere length. Most human tumors, including high-grade primary glioblastomas (GBMs) and low-grade oligodendrogliomas (LGOGs) achieve telomere maintenance via reactivation of the expression of telomerase reverse transcriptase (TERT), which is silenced in normal somatic cells. TERT expression is, therefore, a driver of tumor proliferation and, due to this essential role, TERT is also a therapeutic target. However, non-invasive methods of imaging TERT are lacking. The goal of this study was to identify magnetic resonance spectroscopy (MRS)-detectable metabolic biomarkers of TERT expression that will enable non-invasive visualization of tumor burden in LGOGs and GBMs. First, we silenced TERT expression by RNA interference in patient-derived LGOG (SF10417, BT88) and GBM (GS2) models. Our results linked TERT silencing to significant reductions in steady-state levels of NADH in all models. NADH is essential for the conversion of pyruvate to lactate, suggesting that measuring pyruvate flux to lactate could be useful for imaging TERT status. Recently, deuterium (2H)-MRS has emerged as a novel, clinically translatable method of monitoring metabolic fluxes in vivo. However, to date, studies have solely examined 2H-glucose and the use of [U-2H]pyruvate for non-invasive 2H-MRS has not been tested. Following intravenous injection of a bolus of [U-2H]pyruvate, lactate production was higher in mice bearing orthotopic LGOG (BT88 and SF10417) and GBM (GS2) tumor xenografts relative to tumor-free mice, suggesting that [U-2H]pyruvate has the potential to monitor TERT expression in vivo. In summary, our study, for the first time, shows the feasibility and utility of [U-2H]pyruvate for in vivo imaging. Importantly, since 2H-MRS can be implemented on clinical scanners, our results provide a novel, non-invasive method of integrating information regarding a fundamental cancer hallmark, i.e. TERT, into glioma patient management.

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NIMG-51. DEUTERIUM METABOLIC IMAGING OF BRAIN TUMOR IMMORTALITY USING 2H-PYRUVATE

Neuro-Oncology ◽

10.1093/neuonc/noab196.549 ◽

2021 ◽

Vol 23 (Supplement_6) ◽

pp. vi140-vi141

Author(s):

Georgios Batsios ◽

Céline Taglang ◽

Meryssa Tran ◽

Anne Marie Gillespie ◽

Sabrina Ronen ◽

...

Keyword(s):

Brain Tumor ◽

Lactate Production ◽

Response To Therapy ◽

Telomere Maintenance ◽

Metabolic Imaging ◽

Resonance Spectroscopy ◽

Low Grade ◽

Tumor Proliferation ◽

Non Invasive ◽

Tert Expression

Abstract Telomere maintenance is essential for tumor immortality and sustained tumor proliferation. Most tumors, including high-grade glioblastomas and low-grade oligodendrogliomas achieve telomere maintenance via reactivation of the expression of telomerase reverse transcriptase (TERT), which is silenced in normal somatic cells. Due to this essential role, TERT is a therapeutic target and TERT inhibitors such as 6-thio-2’-deoxyguanosine are in clinical trials. Non-invasive methods of imaging TERT, therefore, have the potential to provide a readout of tumor proliferation and response to therapy. We previously showed that TERT expression is associated with elevated levels of NADH in gliomas. Since NADH is essential for the conversion of pyruvate to lactate, measuring pyruvate flux to lactate could be useful for imaging TERT expression. In this context, deuterium magnetic resonance spectroscopy (2H-MRS) recently emerged as a novel, clinically translatable method of monitoring metabolic fluxes. The goal of this study was to assess the potential of [U-2H]pyruvate for non-invasive imaging of TERT status in gliomas. Following intravenous injection of [U-2H]pyruvate, lactate production was significantly higher in mice bearing orthotopic oligodendroglioma (SF10417, BT88) or glioblastoma (GBM1, GBM6) tumors relative to tumor-free controls. 2D chemical shift imaging showed localization of lactate production to tumor vs. contralateral normal brain. Importantly, following treatment of mice bearing orthotopic GBM6 or BT88 tumors with the TERT inhibitor 6-thio-2’-deoxyguanosine, lactate production from [U-2H]pyruvate was significantly reduced at early timepoints when alterations in tumor volume could not be detected by anatomical imaging, pointing to the ability of [U-2H]pyruvate to report on pseudoprogression. Collectively, we have, for the first time, demonstrated the utility of [U-2H]pyruvate for metabolic imaging of brain tumor burden and treatment response in vivo. Importantly, since 2H-MRS can be implemented on clinical scanners, our results provide a novel, non-invasive method of integrating information regarding a fundamental tumor hallmark, i.e. TERT, into glioma patient management.

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CBMT-41. IMAGING A HALLMARK OF CANCER: HYPERPOLARIZED 13C-MAGNETIC RESONANCE SPECTROSCOPY CAN NON-INVASIVELY MONITOR TERT EXPRESSION IN LOW-GRADE GLIOMAS IN VIVO

Neuro-Oncology ◽

10.1093/neuonc/noz175.163 ◽

2019 ◽

Vol 21 (Supplement_6) ◽

pp. vi42-vi42

Author(s):

Pavithra Viswanath ◽

Georgios Batsios ◽

Anne Marie Gillespie ◽

Russell O Pieper ◽

Sabrina Ronen

Keyword(s):

Lactate Production ◽

Metabolic Imaging ◽

Imaging Biomarkers ◽

Resonance Spectroscopy ◽

Low Grade ◽

Normal Brain ◽

Non Invasive ◽

Glucose Flux ◽

Tert Expression

Abstract Telomerase reverse transcriptase (TERT) expression is a hallmark of cancer, including in primary glioblastomas and low-grade oligodendrogliomas. Since TERT is essential for glioma proliferation and is an attractive therapeutic target, metabolic imaging of TERT status can inform on tumor progression and response to therapy. To that end, the goal of this study was to identify non-invasive, translational, hyperpolarized 13C-magnetic resonance spectroscopy-detectable metabolic imaging biomarkers of TERT in low-grade oligodendrogliomas. Unbiased metabolomic analysis of immortalized normal human astrocytes without (NHAcontrol) and with TERT (NHAtert) indicated that TERT induced unique metabolic reprogramming. Notably, TERT increased NADPH and NADH levels. Glucose flux through the pentose phosphate pathway (PPP) is a major producer of NADPH. Non-invasive imaging of PPP flux using hyperpolarized [U-13C,U-2H]-glucose indicated that production of the PPP metabolite 6-phosphogluconate (6-PG) was elevated in NHAtert cells relative to NHAcontrol. Importantly, hyperpolarized [U-13C,U-2H]-glucose flux to 6-PG clearly differentiated tumor from normal brain in orthotopic NHAtert tumor xenografts. Next, we exploited the observation that TERT expression increased NADH, which is essential for the metabolism of hyperpolarized [1-13C]-alanine to lactate. Lactate production from hyperpolarized [1-13C]-alanine was higher in NHAtert cells relative to NHAcontrol. Importantly, hyperpolarized [1-13C]-alanine imaging in orthotopic NHAtert tumors revealed pronounced differences in lactate production between tumor tissue and normal brain. Mechanistically, TERT increased expression of glucose-6-phosphate dehydrogenase (G6PDH), the rate-limiting enzyme for 6-PG and NADPH production, and of nicotinamide phosphoribosyltransferase (NAMPT), a rate-limiting enzyme for NADH biosynthesis. Silencing TERT reversed G6PDH and NAMPT expression and normalized hyperpolarized [U-13C,U-2H]-glucose and [1-13C]-alanine metabolism, validating our imaging biomarkers. Finally, hyperpolarized [U-13C,U-2H]-glucose and [1-13C]-alanine could monitor TERT status in the clinically relevant, patient-derived BT54 oligodendroglioma model. In summary, we demonstrate, for the first time, non-invasive in vivo imaging of TERT status in gliomas that can enable longitudinal analysis of tumor burden and treatment response in the clinic.

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CBMT-10. MUTANT ISOCITRATE DEHYDROGENASE 1 INHIBITION INDUCES A UNIQUE MRS-DETECTABLE METABOLIC SIGNATURE IN LOW-GRADE GLIOMAS

Neuro-Oncology ◽

10.1093/neuonc/noz175.132 ◽

2019 ◽

Vol 21 (Supplement_6) ◽

pp. vi34-vi35

Author(s):

Abigail Molloy ◽

Aliya Lakhani ◽

Chloé Najac ◽

Elavarasan Subramani ◽

Anne Marie Gillespie ◽

...

Keyword(s):

Cell Lines ◽

Isocitrate Dehydrogenase ◽

Phase 1 ◽

Genetically Engineered ◽

Resonance Spectroscopy ◽

Low Grade ◽

Isocitrate Dehydrogenase 1 ◽

1H Mrs ◽

Low Grade Gliomas ◽

Non Invasive

Abstract Mutations in isocitrate dehydrogenase 1/2 (IDHmut) are reported in 70–90% of low-grade gliomas and secondary glioblastomas. IDHmut catalyzes the reduction of a-ketoglutarate (a-KG) to 2-hydroxyglutarate (2-HG), an oncometabolite that drives tumorigenesis. Inhibition of IDHmut is therefore a rapidly emerging therapeutic approach and IDHmut inhibitors such as AG-120 and AG-881 have shown promising results in phase 1 and 2 clinical studies. The goal of this study was to identify early non-invasive metabolic biomarkers of IDHmut inhibition that can serve to moniter response to these therapies. We used 1H and 13C magnetic resonance spectroscopy (MRS) to investigate the response of two genetically-engineered IDHmut cell lines (U87-based and normal human astrocyte-based) to AG-120 and AG-881 treatment. As expected, in both cell lines, our 1H-MRS data indicated that AG-120 and AG-881 induced a significant decrease in 2-HG. Interestingly however, we also observed a significant increase in phosphocholine and glutamate, pointing to broader changes in the metabolism of treated cells and a unique MRS signature. To further investigate the increase in glutamate induced by AG-120 and AG-881 in our models, we used 13C-MRS and quantified the flux of [1-13C] glucose and [3-13C] glutamine to 13C-labeled glutamate. Our results indicate that both AG-120 and AG-881 significantly increase the flux of 13C-labeled glutamine to 13C glutamate, while the flux of 13C-labeled glucose to 13C glutamate remained unchanged. Further studies are currently underway to explore the utility of using hyperpolarized [1-13C]-glutamine and hyperpolarized [1-13C]-a-KG for monitoring flux to glutamate and 2-HG, and to validate these probes as additional biomarkers of response to IDHmut inhibition. Taken together, our studies indicate that IDHmut inhibition induces a unique MRS-detectable metabolic profile that can potentially be exploited for early non-invasive, clinically translatable detection of response to emerging IDHmut inhibitors.

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NIMG-50. DEUTERIUM METABOLIC IMAGING OF THE ALTERNATIVE LENGTHENING OF TELOMERES PATHWAY REPORTS ON TUMOR BURDEN AND PSEUDOPROGRESSION IN LOW-GRADE GLIOMAS

Neuro-Oncology ◽

10.1093/neuonc/noab196.548 ◽

2021 ◽

Vol 23 (Supplement_6) ◽

pp. vi140-vi140

Author(s):

Céline Taglang ◽

Georgios Batsios ◽

Joydeep Mukherjee ◽

Meryssa Tran ◽

Anne Marie Gillespie ◽

...

Keyword(s):

Magnetic Resonance ◽

Tumor Burden ◽

Telomere Maintenance ◽

Metabolic Imaging ◽

Glycolytic Flux ◽

Low Grade ◽

Non Invasive ◽

Glucose Flux ◽

Alternative Lengthening

Abstract Glioma patient management relies heavily on magnetic resonance imaging (MRI). However, MRI is often inadequate for assessment of tumor burden and pseudoprogression. Non-invasive methods that report on molecular pathways such as telomere maintenance that drive tumor proliferation are needed. Among brain tumors, low-grade astrocytomas (LGAs) use the alternative lengthening of telomeres (ALT) pathway for telomere maintenance. The goal of this study was to identify ALT-linked metabolic alterations that can be exploited for non-invasive magnetic resonance spectroscopy (MRS)-based imaging of LGAs. We examined the patient-derived BT257 model and compared neurospheres that are ALT-dependent (BT257 ALT+) with those in which the ALT pathway has been silenced (BT257 ALT-). Our studies suggest that expression and activity of the rate-limiting glycolytic enzyme phosphofructokinase-1 are significantly higher in BT257 ALT+ neurospheres relative to ALT-, an effect that is associated with elevated glucose flux to lactate. Studies indicate that poly(ADP-ribose) polymerase inhibitors such as niraparib selectively induce telomeric fusion and cell death in ALT-dependent cells. We find that the telomeric fusion-mediated cytotoxicity of niraparib is associated with significantly reduced glycolytic flux in BT257 ALT+ neurospheres. We then examined whether 2H-MRS using [6,6’-2H]-glucose, which is a clinically translatable method of imaging glycolytic flux, can be used to monitor the ALT pathway in vivo. [6,6’-2H]-glucose flux to lactate is elevated in tumor relative to normal brain in mice bearing orthotopic BT257 tumors. Importantly, following treatment of BT257 tumor-bearing mice with niraparib, lactate production from [6,6’-2H]-glucose is significantly reduced at early timepoints when alterations in tumor volume cannot be observed by MRI, pointing to the ability of [6,6’-2H]-glucose to report on pseudoprogression in vivo. Collectively, our studies mechanistically link the ALT pathway with elevated glycolytic flux via phosphofructokinase-1 and identify deuterium metabolic imaging as a novel, non-invasive method of imaging tumor burden and treatment response in LGAs in vivo.

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Early Noninvasive Metabolic Biomarkers of Mutant IDH Inhibition in Glioma

Metabolites ◽

10.3390/metabo11020109 ◽

2021 ◽

Vol 11 (2) ◽

pp. 109

Author(s):

Marina Radoul ◽

Donghyun Hong ◽

Anne Marie Gillespie ◽

Chloé Najac ◽

Pavithra Viswanath ◽

...

Keyword(s):

Magnetic Resonance ◽

Genetically Engineered ◽

Response To Treatment ◽

Driver Mutations ◽

Resonance Spectroscopy ◽

Low Grade ◽

Isocitrate Dehydrogenase 1 ◽

1H Mrs ◽

Metabolic Biomarkers

Approximately 80% of low-grade glioma (LGGs) harbor mutant isocitrate dehydrogenase 1/2 (IDH1/2) driver mutations leading to accumulation of the oncometabolite 2-hydroxyglutarate (2-HG). Thus, inhibition of mutant IDH is considered a potential therapeutic target. Several mutant IDH inhibitors are currently in clinical trials, including AG-881 and BAY-1436032. However, to date, early detection of response remains a challenge. In this study we used high resolution 1H magnetic resonance spectroscopy (1H-MRS) to identify early noninvasive MR (Magnetic Resonance)-detectable metabolic biomarkers of response to mutant IDH inhibition. In vivo 1H-MRS was performed on mice orthotopically-implanted with either genetically engineered (U87IDHmut) or patient-derived (BT257 and SF10417) mutant IDH1 cells. Treatment with either AG-881 or BAY-1436032 induced a significant reduction in 2-HG. Moreover, both inhibitors led to a significant early and sustained increase in glutamate and the sum of glutamate and glutamine (GLX) in all three models. A transient early increase in N-acetylaspartate (NAA) was also observed. Importantly, all models demonstrated enhanced animal survival following both treatments and the metabolic alterations were observed prior to any detectable differences in tumor volume between control and treated tumors. Our study therefore identifies potential translatable early metabolic biomarkers of drug delivery, mutant IDH inhibition and glioma response to treatment with emerging clinically relevant therapies.

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OS02.6.A The TeloDIAG: How telomeric parameters can help in glioma rapid diagnosis and liquid biopsies approaches

Neuro-Oncology ◽

10.1093/neuonc/noab180.015 ◽

2021 ◽

Vol 23 (Supplement_2) ◽

pp. ii5-ii6

Author(s):

P Billard ◽

C Guerriau ◽

C Carpentier ◽

F Juillard ◽

N Grandin ◽

...

Keyword(s):

Telomere Maintenance ◽

Molecular Characteristics ◽

Low Grade ◽

New Classification ◽

Liquid Biopsies ◽

Efficient Tool ◽

Isocitrate Dehydrogenase 1 ◽

Mutational Status ◽

Alternative Lengthening

Abstract BACKGROUND The integration of molecular markers into the WHO 2016 classification has clarified the complex diagnosis of gliomas. Among these biomarkers, the TERT promoter mutation and the loss of ATRX (ATRX loss) are mutually exclusive alterations associated with re-activation of telomerase or alternative lengthening of telomeres (ALT), respectively. Strangely, 25% of gliomas display neither or both these alterations, a situation referred to as abnormal telomere maintenance mechanism (aTMM). MATERIAL AND METHODS To investigate the TMM actually involved in gliomas, the C-circle (CC) assay was adapted to tumor (FFPE and frozen) samples. RESULTS We constructed a CC-based algorithm able to identify the TMM of 284 gliomas with either TERT or ATRX alteration, with a sensitivity of 100% and a specificity of 97.3%, and succeeded in deciphering the TMM involved in 122 aTMM gliomas. Additionally, the combination of the TMM, the mutational status of the Isocitrate dehydrogenase 1/2 (IDH) gene, and the histological grading was used as base for a new classification: TeloDIAG. Six subtypes are defined in this classification: tOD, tLGA, tGBM_IDHmt, tGBM, and tAIV, corresponding to oligodendroglioma, IDHmt low grade astrocytoma, IDHmt glioblastoma, and IDHwt glioblastoma, respectively, the last class gathers ALT+ IDHwt glioma. The TeloDIAG diagnosis is 99% concordant with the WHO classification for glioma displaying typical molecular characteristics (N=312). It modified the classification of 38% (N=156) discordant tumors, such as IDHwt Astrocytoma, aTMM tumors, or gliomas with unexpected TMM (e.g. TERTwt oligodendroglioma, ATRX loss GBM). Interestingly, 20% (N=69) of TERTwt, ATRXwt, or IDHwt GBM were actually tAIV, which is remarkable as tAIV-glioma patients’ survival tended to be longer (21.2 months) than tGBM patients’ survival (16.5 months). Importantly, CC in blood sampled from IDHmt astrocytoma patients was detected with a sensitivity of 56% and a specificity of 95% (N = 206). CONCLUSION In sum, the TeloDIAG is a new, simple, and efficient tool helping in glioma diagnosis and a promising option for liquid biopsy

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Glycine by MR spectroscopy is an imaging biomarker of glioma aggressiveness

Neuro-Oncology ◽

10.1093/neuonc/noaa034 ◽

2020 ◽

Vol 22 (7) ◽

pp. 1018-1029 ◽

Cited By ~ 5

Author(s):

Vivek Tiwari ◽

Elena V Daoud ◽

Kimmo J Hatanpaa ◽

Ang Gao ◽

Song Zhang ◽

...

Keyword(s):

Cell Proliferation ◽

Patient Survival ◽

Inverse Correlation ◽

Metabolic Imaging ◽

Imaging Biomarker ◽

Resonance Spectroscopy ◽

Nucleotide Biosynthesis ◽

Glycine Concentration ◽

Non Invasive ◽

Mib 1

Abstract Background High-grade gliomas likely remodel the metabolic machinery to meet the increased demands for amino acids and nucleotides during rapid cell proliferation. Glycine, a non-essential amino acid and intermediate of nucleotide biosynthesis, may increase with proliferation. Non-invasive measurement of glycine by magnetic resonance spectroscopy (MRS) was evaluated as an imaging biomarker for assessment of tumor aggressiveness. Methods We measured glycine, 2-hydroxyglutarate (2HG), and other tumor-related metabolites in 35 glioma patients using an MRS sequence tailored for co-detection of glycine and 2HG in gadolinium-enhancing and non-enhancing tumor regions on 3T MRI. Glycine and 2HG concentrations as measured by MRS were correlated with tumor cell proliferation (MIB-1 labeling index), expression of mitochondrial serine hydroxymethyltransferase (SHMT2), and glycine decarboxylase (GLDC) enzymes, and patient overall survival. Results Elevated glycine was strongly associated with presence of gadolinium enhancement, indicating more rapidly proliferative disease. Glycine concentration was positively correlated with MIB-1, and levels higher than 2.5 mM showed significant association with shorter patient survival, irrespective of isocitrate dehydrogenase status. Concentration of 2HG did not correlate with MIB-1 index. A high glycine/2HG concentration ratio, >2.5, was strongly associated with shorter survival (P < 0.0001). GLDC and SHMT2 expression were detectable in all tumors with glycine concentration, demonstrating an inverse correlation with GLDC. Conclusions The data suggest that aggressive gliomas reprogram glycine-mediated one-carbon metabolism to meet the biosynthetic demands for rapid cell proliferation. MRS evaluation of glycine provides a non-invasive metabolic imaging biomarker that is predictive of tumor progression and clinical outcome. Key Points 1. Glycine and 2-hydroxyglutarate in glioma patients are precisely co-detected using MRS at 3T. 2. Tumors with elevated glycine proliferate and progress rapidly. 3. A high glycine/2HG ratio is predictive of shortened patient survival.

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