Vorasidenib in IDH1- or IDH2-Mutant Low-Grade Glioma

BACKGROUND

Isocitrate dehydrogenase (IDH)-mutant grade 2 gliomas are malignant brain tumors that cause considerable disability and premature death. Vorasidenib, an oral brain-penetrant inhibitor of mutant IDH1 and IDH2 enzymes, showed preliminary activity in IDH-mutant gliomas.

METHODS

In a double-blind, phase 3 trial, we randomly assigned patients with residual or recurrent grade 2 IDH-mutant glioma who had undergone no previous treatment other than surgery to receive either oral vorasidenib (40 mg once daily) or matched placebo in 28-day cycles. The primary end point was imaging-based progression-free survival according to blinded assessment by an independent review committee. The key secondary end point was the time to the next anticancer intervention. Crossover to vorasidenib from placebo was permitted on confirmation of imaging-based disease progression. Safety was also assessed.

RESULTS

A total of 331 patients were assigned to receive vorasidenib (168 patients) or placebo (163 patients). At a median follow-up of 14.2 months, 226 patients (68.3%) were continuing to receive vorasidenib or placebo. Progression-free survival was significantly improved in the vorasidenib group as compared with the placebo group (median progression-free survival, 27.7 months vs. 11.1 months; hazard ratio for disease progression or death, 0.39; 95% confidence interval [CI], 0.27 to 0.56; P<0.001). The time to the next intervention was significantly improved in the vorasidenib group as compared with the placebo group (hazard ratio, 0.26; 95% CI, 0.15 to 0.43; P<0.001). Adverse events of grade 3 or higher occurred in 22.8% of the patients who received vorasidenib and in 13.5% of those who received placebo. An increased alanine aminotransferase level of grade 3 or higher occurred in 9.6% of the patients who received vorasidenib and in no patients who received placebo.

CONCLUSIONS

In patients with grade 2 IDH-mutant glioma, vorasidenib significantly improved progression-free survival and delayed the time to the next intervention. (Funded by Servier; INDIGO ClinicalTrials.gov number, NCT04164901.).

Vorasidenib and ivosidenib in IDH1-mutant low-grade glioma: a randomized, perioperative phase 1 trial

Vorasidenib and ivosidenib inhibit mutant forms of isocitrate dehydrogenase (mIDH) and have shown preliminary clinical activity against mIDH glioma. We evaluated both agents in a perioperative phase 1 trial to explore the mechanism of action in recurrent low-grade glioma (IGG) and select a molecule for phase 3 testing. Primary end-point was concentration of D-2-hydroxyglutarate (2-HG), the metabolic product of mIDH enzymes, measured in tumor tissue from 49 patients with mIDH1-R132H nonenhancing gliomas following randomized treatment with vorasidenib (50 mg or 10 mg once daily, q.d.), ivosidenib (500 mg q.d. or 250 mg twice daily) or no treatment before surgery. Tumor 2-HG concentrations were reduced by 92.6% (95% credible interval (CrI), 76.1-97.6) and 91.1% (95% CrI, 72.0-97.0) in patients treated with vorasidenib 50 mg q.d. and ivosidenib 500 mg q.d., respectively. Both agents were well tolerated and follow-up is ongoing. In exploratory analyses, 2-HG reduction was associated with increased DNA 5-hydroxymethylcytosine, reversal of 'proneural' and 'stemness' gene expression signatures, decreased tumor cell proliferation and immune cell activation. Vorasidenib, which showed brain penetrance and more consistent 2-HG suppression than ivosidenib, was advanced to phase 3 testing in patients with mIDH LGGs. Funded by Agios Pharmaceuticals, Inc. and Servier Pharmaceuticals LLC; ClinicalTrials.gov number NCT03343197.

Impact of CDKN2A/B, MTAP, and TERT Genetic Alterations on Survival in IDH Wild Type Glioblastomas

PURPOSE

Poor outcomes in IDH wild-type (IDHwt) glioblastomas indicate the need to determine which genetic alterations can indicate poor survival and guidance of patient specific treatment options. We sought to identify the genetic alterations in these patients that predict for survival when adjusting particularly for treatments and other genetic alterations.

METHODS

A cohort of 167 patients with pathologically confirmed IDHwt glioblastomas treated at our institution was retrospectively reviewed. Next generation sequencing was performed for each patient to determine tumor genetic alterations. Multivariable cox proportional hazards analysis for overall survival (OS) was performed to control for patient variables.

RESULTS

CDKN2A, CDKN2B, and MTAP deletion predict for worse OS independently of other genetic alterations and patient characteristics (hazard ratio [HR] 2.192, p = 0.0017). Patients with CDKN2A copy loss (HR 2.963, p = 0.0037) or TERT mutated (HR 2.815, p = 0.0008) glioblastomas exhibited significant associations between radiation dose and OS, while CDKN2A and TERT wild type patients did not. CDKN2A deleted patients with NF1 mutations had worse OS (HR 1.990, p = 0.0540), while CDKN2A wild type patients had improved OS (HR 0.229, p = 0.0723). Patients with TERT mutated glioblastomas who were treated with radiation doses < 45 Gy (HR 3.019, p = 0.0010) but not those treated with ≥ 45 Gy exhibited worse OS compared to those without TERT mutations.

CONCLUSION

In IDHwt glioblastomas, CDKN2A, CDKN2B, and MTAP predict for poor prognosis. TERT and CDKN2A mutations are associated with worse survival only when treated with lower radiation doses, thus potentially providing a genetic marker that can inform clinicians on proper dose-fractionation schemes.

Neutrophilia and post-radiation thrombocytopenia predict for poor prognosis in radiation-treated glioma patients

Introduction

Poor outcomes in glioma patients indicate a need to determine prognostic indicators of survival to better guide patient specific treatment options. While preoperative neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and monocyte-to-lymphocyte ratio (MLR) have been suggested as prognostic systemic inflammation markers, the impact of post-radiation changes in these cell types is unclear. We sought to identify which hematologic cell measurements before, during, or after radiation predicted for patient survival.

Methods

A cohort of 182 patients with pathologically confirmed gliomas treated at our institution was retrospectively reviewed. Patient blood samples were collected within one month before, during, or within 3 months after radiation for quantification of hematologic cell counts, for which failure patterns were evaluated. Multivariable cox proportional hazards analysis for overall survival (OS) and progression-free survival (PFS) was performed to control for patient variables.

Results

Multivariable analysis identified pre-radiation NLR > 4.0 (Hazard ratio = 1.847, p = 0.0039) and neutrophilia prior to (Hazard ratio = 1.706, p = 0.0185), during (Hazard ratio = 1.641, p = 0.0277), or after (Hazard ratio = 1.517, p = 0.0879) radiation as significant predictors of worse OS, with similar results for PFS. Post-radiation PLR > 200 (Hazard ratio = 0.587, p = 0.0062) and a percent increase in platelets after radiation (Hazard ratio = 0.387, p = 0.0077) were also associated with improved OS. Patients receiving more than 15 fractions of radiation exhibited greater post-radiation decreases in neutrophil and platelet counts than those receiving fewer. Patients receiving dexamethasone during radiation exhibited greater increases in neutrophil counts than those not receiving steroids. Lymphopenia, changes in lymphocyte counts, monocytosis, MLR, and changes in monocyte counts did not impact patient survival.

Conclusion

Neutrophilia at any time interval surrounding radiotherapy, pre-radiation NLR, and post-radiation thrombocytopenia, but not lymphocytes or monocytes, are predictors of poor patient survival in glioma patients.

Optimization of spectrally selective 180° radiofrequency pulse timings in J-difference editing (MEGA) of lactate

PURPOSE

J-Difference editing (MEGA) provides an effective spectroscopic means of selectively measuring low-concentration metabolites having weakly coupled spins. The fractional inphase and antiphase coherences are determined by the radiofrequency (RF) pulses and inter-RF pulse intervals of the sequence. We examined the timings of the spectrally selective editing 180° pulses (E180) in MEGA-PRESS to maximize the edited signal amplitude in lactate at 3T.

METHODS

The time evolution of the lactate spin coherences was analytically and numerically calculated for non-volume localized and single-voxel localized MEGA sequences. Single-voxel localized MEGA-PRESS simulations and phantom experiments were conducted for echo time (TE) 60-160 ms and for all possible integer-millisecond timings of the E180 pulses. Optimized E180 timings of 144, 103, and 109 ms TEs, tailored with simulation and phantom data, were tested in brain tumor patients in vivo. Lactate signals, broadened to singlet linewidths (~6 Hz), were compared between simulation, phantom, and in vivo data.

RESULTS

Theoretical and experimental data indicated consistently that the MEGA-edited signal amplitude and width are sensitive to the E180 timings. In volume-localized MEGA, the lactate peak amplitudes in E180-on and difference spectra were maximized at specific E180 timings for individual TEs, largely due to the chemical-shift displacement effects. The E180 timings for maximum lactate peak amplitude were different from those of maximum inphase coherence in in vivo linewidth situations.

CONCLUSION

In in vivo MEGA editing, the E180 pulse timings can be effectively used for manipulating the inphase and antiphase coherences and increasing the edited signal amplitude, following TE optimization.

Vorasidenib, a Dual Inhibitor of Mutant IDH1/2, in Recurrent or Progressive Glioma; Results of a First-in-Human Phase I Trial

PURPOSE

Lower grade gliomas (LGGs) are malignant brain tumors. Current therapy is associated with short- and long-term toxicity. Progression to higher tumor grade is associated with contrast enhancement on MRI. The majority of LGGs harbor mutations in the genes encoding isocitrate dehydrogenase 1 or 2 (IDH1/IDH2). Vorasidenib (AG-881) is a first-in-class, brain-penetrant, dual inhibitor of the mutant IDH1 and mutant IDH2 enzymes.

PATIENTS AND METHODS

We conducted a multicenter, open-label, phase I, dose-escalation study of vorasidenib in 93 patients with mutant IDH1/2 (mIDH1/2) solid tumors, including 52 patients with glioma that had recurred or progressed following standard therapy. Vorasidenib was administered orally, once daily, in 28-day cycles until progression or unacceptable toxicity. Enrollment is complete; this trial is registered with ClinicalTrials.gov, NCT02481154.

RESULTS

Vorasidenib showed a favorable safety profile in the glioma cohort. Dose-limiting toxicities of elevated transaminases occurred at doses ≥100 mg and were reversible. The protocol-defined objective response rate per Response Assessment in Neuro-Oncology criteria for LGG in patients with nonenhancing glioma was 18% (one partial response, three minor responses). The median progression-free survival was 36.8 months [95% confidence interval (CI), 11.2-40.8] for patients with nonenhancing glioma and 3.6 months (95% CI, 1.8-6.5) for patients with enhancing glioma. Exploratory evaluation of tumor volumes in patients with nonenhancing glioma showed sustained tumor shrinkage in multiple patients.

CONCLUSIONS

Vorasidenib was well tolerated and showed preliminary antitumor activity in patients with recurrent or progressive nonenhancing mIDH LGG.

Spectral fitting strategy to overcome the overlap between 2-hydroxyglutarate and lipid resonances at 2.25 ppm

PURPOSE

¹ H MRS provides a noninvasive tool for identifying mutations in isocitrate dehydrogenase (IDH). Quantification of the prominent 2-hydroxyglutarate (2HG) resonance at 2.25 ppm is often confounded by the lipid resonance at the same frequency in tumors with elevated lipids. We propose a new spectral fitting approach to separate these overlapped signals, therefore, improving 2HG evaluation.

METHODS

TE 97 ms PRESS was acquired at 3T from 42 glioma patients. New lipid basis sets were created, in which the small lipid 2.25-ppm signal strength was preset with reference to the lipid signal at 0.9 ppm, incorporating published fat relaxation data. LCModel fitting using the new lipid bases (Fitting method 2) was conducted along with fitting using the LCModel built-in lipid basis set (Fitting method 1), in which the lipid 2.25-ppm signal is assessed with reference to the lipid 1.3-ppm signal. In-house basis spectra of low-molecular-weight metabolites were used in both fitting methods.

RESULTS

Fitting method 2 showed marked improvement in identifying IDH mutational status compared with Fitting method 1. 2HG estimates from Fitting method 2 were overall smaller than those from Fitting method 1, which was because of differential assignment of the signal at 2.25 ppm to lipids. In receiver operating characteristic analysis, Fitting method 2 provided a complete distinction between IDH mutation and wild-type whereas Fitting method 1 did not.

CONCLUSION

The data suggest that ¹ H MR spectral fitting using the new lipid basis set provides a robust fitting strategy that improves 2HG evaluation in brain tumors with elevated lipids.

Glycine by MR spectroscopy is an imaging biomarker of glioma aggressiveness

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.

Translating Basic Science Discoveries into Improved Outcomes for Glioblastoma

Members of the scientific and clinical neuro-oncology community met in April 2019 to discuss the current challenges and opportunities associated with translating basic science discoveries in glioblastoma for improved survival of patients. A summary of key points of these discussions is presented in this article.

In vivo MRS measurement of 2-hydroxyglutarate in patient-derived IDH-mutant xenograft mouse models versus glioma patients

PURPOSE

To generate a preclinical model of isocitrate dehydrogenase (IDH) mutant gliomas from glioma patients and design a MRS method to test the compatibility of 2-hydroxyglutarate (2HG) production between the preclinical model and patients.

METHODS

Five patient-derived xenograft (PDX) mice were generated from two glioma patients with IDH1 R132H mutation. A PRESS sequence was tailored at 9.4 T, with computer simulation and phantom analyses, for improving 2HG detection in mice. 2HG and other metabolites in the PDX mice were measured using the optimized MRS at 9.4 T and compared with 3 T MRS measurements of the metabolites in the parental-tumor patients. Spectral fitting was performed with LCModel using in-house basis spectra. Metabolite levels were quantified with reference to water.

RESULTS

The PRESS TE was optimized to be 96 ms, at which the 2HG 2.25 ppm signal was narrow and inverted, thereby leading to unequivocal separation of the 2HG resonance from adjacent signals from other metabolites. The optimized MRS provided precise detection of 2HG in mice compared to short-TE MRS at 9.4 T. The 2HG estimates in PDX mice were in excellent agreement with the 2HG measurements in the patients.

CONCLUSION

The similarity of 2HG production between PDX models and parental-tumor patients indicates that PDX tumors retain the parental IDH metabolic fingerprint and can serve as a preclinical model for improving our understanding of the IDH-mutation associated metabolic reprogramming.

A phase I, open label, perioperative study of AG-120 and AG-881 in recurrent IDH1 mutant, low-grade glioma: Results from cohort 1

2003

Background: AG-120 (ivosidenib [IVO]) is a first-in-class oral inhibitor of mutant isocitrate dehydrogenase 1 (mIDH1) evaluated in 66 glioma patients (pts) in an ongoing phase 1 study. AG-881 (vorasidenib [VOR]) is an oral, potent, brain-penetrant inhibitor of mIDH1/2 evaluated in 52 glioma pts in an ongoing phase 1 study. In an orthotopic glioma model, IVO and VOR reduced 2-hydroxyglutarate (2-HG) by 85% and 98%, respectively, despite different brain:plasma ratios (<0.04 vs 1.33). Methods: Primary endpoint: brain tumor 2-HG concentration with IVO or VOR treatment in mIDH1 low-grade glioma. Pts with recurrent non-enhancing WHO-2016 Grade (Gr) 2 or 3 mIDH1-R132H oligodendroglioma or astrocytoma undergoing craniotomy were randomized 2:2:1 to IVO 500mg QD, VOR 50mg QD, or no treatment for 4 wks preoperatively in Cohort 1. Post-operatively, pts continued to receive IVO or VOR and control pts were randomized 1:1 to IVO or VOR. Tumors were assessed for mIDH1 status, cellularity, 2-HG, and drug concentration. Treated samples were compared to control pts and mIDH1 and wild type (WT) banked reference (ref) samples. Plasma and CSF 2-HG were assessed. Pts with non-evaluable tissue were replaced. Results: As of 29 Nov 2018, 26 pts (17M, 9F; 25 Gr 2, 1 Gr 3) were randomized preoperatively (IVO 10, VOR 11, control 5), 25 received drug (IVO 12, VOR 13). At the data cut, 19 tumors were analyzed with 16 evaluable. Common (>10%) TEAEs (all grade 1/2): diarrhea (36%), hypocalcemia and constipation (each 20%), anemia, hyperglycemia, pruritus, headache and nausea (each 16%), and hypokalemia and fatigue (each 12%). Mean brain:plasma ratio: 0.16 for IVO, 2.4 for VOR. Tumor 2-HG results are shown in Table. Updated data from Cohort 1 will be presented. Conclusions: In Cohort 1 of this phase 1 perioperative study, IVO and VOR were CNS penetrant and lowered 2-HG compared to untreated samples. Cohort 2 is open and will evaluate IVO 250mg BID and VOR 10mg QD. Brain tumor 2-HG concentration. Clinical trial information: NCT03343197. [Table: see text]

Genome-Wide Analysis of Glioblastoma Patients with Unexpectedly Long Survival

Glioblastoma (GBM), representing WHO grade IV astrocytoma, is a relatively common primary brain tumor in adults with an exceptionally dismal prognosis. With an incidence rate of over 10 000 cases in the United States annually, the median survival rate ranges from 10-15 months in IDH1/2-wildtype tumors and 24-31 months in IDH1/2-mutant tumors, with further variation depending on factors such as age, MGMT methylation status, and treatment regimen. We present a cohort of 4 patients, aged 37-60 at initial diagnosis, with IDH1-mutant GBMs that were associated with unusually long survival intervals after the initial diagnosis, currently ranging from 90 to 154 months (all still alive). We applied genome-wide profiling with a methylation array (Illumina EPIC Array 850k) and a next-generation sequencing panel to screen for genetic and epigenetic alterations in these tumors. All 4 tumors demonstrated methylation patterns and genomic alterations consistent with GBM. Three out of four cases showed focal amplification of the CCND2 gene or gain of the region on 12p that included CCND2, suggesting that this may be a favorable prognostic factor in GBM. As this study has a limited sample size, further evaluation of patients with similar favorable outcome is warranted to validate these findings.

Isotope Tracing of Human Clear Cell Renal Cell Carcinomas Demonstrates Suppressed Glucose Oxidation In Vivo

Clear cell renal cell carcinoma (ccRCC) is the most common form of human kidney cancer. Histological and molecular analyses suggest that ccRCCs have significantly altered metabolism. Recent human studies of lung cancer and intracranial malignancies demonstrated an unexpected preservation of carbohydrate oxidation in the tricarboxylic acid (TCA) cycle. To test the capacity of ccRCC to oxidize substrates in the TCA cycle, we infused 13C-labeled fuels in ccRCC patients and compared labeling patterns in tumors and adjacent kidney. After infusion with [U-13C]glucose, ccRCCs displayed enhanced glycolytic intermediate labeling, suppressed pyruvate dehydrogenase flow, and reduced TCA cycle labeling, consistent with the Warburg effect. Comparing 13C labeling among ccRCC, brain, and lung tumors revealed striking differences. Primary ccRCC tumors demonstrated the highest enrichment in glycolytic intermediates and lowest enrichment in TCA cycle intermediates. Among human tumors analyzed by intraoperative 13C infusions, ccRCC is the first to demonstrate a convincing shift toward glycolytic metabolism.

3D high-resolution imaging of 2-hydroxyglutarate in glioma patients using DRAG-EPSI at 3T in vivo

PURPOSE

To develop 3D high-resolution imaging of 2-hydroxyglutarate (2HG) at 3T in vivo.

METHODS

Echo-planar spectroscopic imaging with dual-readout alternated-gradients (DRAG-EPSI), which was recently reported for 2D imaging of 2HG at 7T, was tested for 3D imaging of 2HG at 3T. The frequency drifts and acoustic noise induced by DRAG-EPSI were investigated in comparison with conventional EPSI. Four patients with IDH-mutant gliomas were enrolled for 3D imaging of 2HG and other metabolites. A previously reported 2HG-tailored TE 97-ms PRESS sequence preceded the DRAG-EPSI readout gradients. Unsuppressed water, acquired with EPSI, was used as reference for multi-channel combination, eddy-current compensation, and metabolite quantification. Spectral fitting was conducted with the LCModel using in-house basis sets.

RESULTS

With gradient strength of 4 mT/m and slew rate of 20 mT/m/ms, DRAG-EPSI produced frequency drifts smaller by 5.5-fold and acoustic noise lower by 25 dB compared to conventional EPSI. In a 19-min scan, 3D DRAG-EPSI provided images of 2HG with precision (CRLB <10%) at a resolution of 10 × 10 × 10 mm³ for a field of view of 240 × 180 × 80 mm³ . 2HG was estimated to be 5 mM in a pre-treatment patient. In 3 post-surgery patients, 2HG estimates were 3-6 mM, and the 2HG distribution was different from the water-T₂ image pattern or highly concentrated in the post-contrast enhancing region.

CONCLUSION

Together with 2HG-optimized PRESS, DRAG-EPSI provides an effective tool for reliable 3D high-resolution imaging of 2HG at 3T in vivo.

Oncogenes Activate an Autonomous Transcriptional Regulatory Circuit That Drives Glioblastoma

Efforts to identify and target glioblastoma (GBM) drivers have primarily focused on receptor tyrosine kinases (RTKs). Clinical benefits, however, have been elusive. Here, we identify an SRY-related box 2 (SOX2) transcriptional regulatory network that is independent of upstream RTKs and capable of driving glioma-initiating cells. We identified oligodendrocyte lineage transcription factor 2 (OLIG2) and zinc-finger E-box binding homeobox 1 (ZEB1), which are frequently co-expressed irrespective of driver mutations, as potential SOX2 targets. In murine glioma models, we show that different combinations of tumor suppressor and oncogene mutations can activate Sox2, Olig2, and Zeb1 expression. We demonstrate that ectopic co-expression of the three transcription factors can transform tumor-suppressor-deficient astrocytes into glioma-initiating cells in the absence of an upstream RTK oncogene. Finally, we demonstrate that the transcriptional inhibitor mithramycin downregulates SOX2 and its target genes, resulting in markedly reduced proliferation of GBM cells in vivo.

Measurement of 13 C turnover into glutamate and glutamine pools in brain tumor patients

Malignant brain tumors are known to utilize acetate as an alternate carbon source in the citric acid cycle for their bioenergetics. ¹³ C NMR-based isotopomer analysis has been used to measure turnover of ¹³ C-acetate carbons into glutamate and glutamine pools in tumors. Plasma from the patients infused with [1,2-¹³ C]acetate further revealed the presence of ¹³ C isotopomers of glutamine, glucose, and lactate in the circulation that were generated due to metabolism of [1,2-¹³ C]acetate by peripheral organs. In the tumor cells, [4-¹³ C] and [3,4-¹³ C]glutamate and glutamine isotopomers were generated from blood-borne ¹³ C-labeled glucose and lactate which were formed due to [1,2-¹³ C[acetate metabolism of peripheral tissues. [4,5-¹³ C] and [3,4,5-¹³ C]glutamate and glutamine isotopomers were produced from [1,2-¹³ C]acetyl-CoA that was derived from direct oxidation of [1,2-¹³ C] acetate in the tumor. Major portion of C4 ¹³ C fractional enrichment of glutamate (93.3 ± 0.02%) and glutamine (90.9 ± 0.03%) were derived from [1,2-¹³ C]acetate-derived acetyl-CoA.

Measurement of glycine in healthy and tumorous brain by triple-refocusing MRS at 3 T in vivo

Glycine (Gly) has been implicated in several neurological disorders, including malignant brain tumors. The precise measurement of Gly is challenging largely as a result of the spectral overlap with myo-inositol (mI). We report a new triple-refocusing sequence for the reliable co-detection of Gly and mI at 3 T and for the evaluation of Gly in healthy and tumorous brain. The sequence parameters were optimized with density-matrix simulations and phantom validation. With a total TE of 134 ms, the sequence gave complete suppression of the mI signal between 3.5 and 3.6 ppm and, consequently, well-defined Gly (3.55 ppm) and mI (3.64 ppm) peaks. In vivo ¹ H magnetic resonance spectroscopy (MRS) data were acquired from the gray matter (GM)-dominant medial occipital and white matter (WM)-dominant left parietal regions in six healthy subjects, and analyzed with LCModel using in-house-calculated basis spectra. Tissue segmentation was performed to obtain the GM and WM contents within the MRS voxels. Metabolites were quantified with reference to GM-rich medial occipital total creatine at 8 mM. The Gly and mI concentrations were estimated to be 0.63 ± 0.05 and 8.6 ± 0.6 mM for the medial occipital and 0.34 ± 0.05 and 5.3 ± 0.8 mM for the left parietal regions, respectively. From linear regression of the metabolite estimates versus fractional GM content, the concentration ratios between pure GM and pure WM were estimated to be 2.6 and 2.1 for Gly and mI, respectively. Clinical application of the optimized sequence was performed in four subjects with brain tumor. The Gly levels in tumors were higher than those of healthy brain. Gly elevation was more extensive in a post-contrast enhancing region than in a non-enhancing region. The data indicate that the optimized triple-refocusing sequence may provide reliable co-detection of Gly and mI, and alterations of Gly in brain tumors can be precisely evaluated.

Echo-planar spectroscopic imaging with dual-readout alternated gradients (DRAG-EPSI) at 7 T: Application for 2-hydroxyglutarate imaging in glioma patients

PURPOSE

To develop echo-planar spectroscopic imaging (EPSI) with large spectral width and accomplish high-resolution imaging of 2-hydroxyglutarate (2HG) at 7 T.

METHODS

We designed a new EPSI readout scheme at 7 T. Data were recorded with dual-readout alternated gradients and combined according to the gradient polarity. Following validation of its performance in phantoms, the new readout scheme, together with previously reported 2HG-optimized magnetic resonance spectroscopy (point-resolved spectroscopy echo time of 78 ms), was used for time-efficient and high-resolution imaging of 2HG and other metabolites in five glioma patients before treatment. Unsuppressed water, acquired with EPSI, was used as reference for multichannel combination, eddy-current compensation, and metabolite quantification. Spectral fitting was conducted with the LCModel using in-house calculated basis sets.

RESULTS

Using a readout gradient strength of 9.5 mT/m and slew rate of 90 mT/m/ms, dual-readout alternated gradients EPSI permitted 1638-Hz spectral width with 6 × 6 mm² in-plane resolution at 7 T. Phantom data indicated that dual-readout alternated gradients EPSI provides proper metabolite signals and induces much less frequency drifts than conventional EPSI. For a spatial resolution of 0.5 mL, 2HG was detected in tumors with precision (Cramer-Rao lower bound < 10%). The 2HG was estimated to be 2.3 to 3.3 mM in tumors of three patients with biopsy-proven isocitrate dehydrogenase (IDH) mutant gliomas. The 2HG was undetectable in an IDH wild-type glioblastoma. For a radiographically suggested glioma, the estimated 2HG of 2.3 ± 0.2 mM (Cramer-Rao lower bound < 10%) indicated that the lesion may be an IDH mutant glioma.

CONCLUSIONS

The data indicated that the dual-readout alternated gradients EPSI can provide reliable high-resolution imaging of 2HG in glioma patients at 7 T in vivo. Magn Reson Med 79:1851-1861, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Quantifying the benefit of chemotherapy and radiation in low-grade glioma: A systematic review and meta-analysis of numbers needed to treat

2057

Background: The optimal role of chemotherapy and radiation (RT) in adult low-grade glioma (LGG, WHO grade 1 & 2) is unclear. We conducted a systematic review and study-level meta-analysis of the literature on overall survival (OS) and progression free survival (PFS) in patients with LGG. Methods: Pubmed was queried with MeSH terms. All comparative studies of adults with newly diagnosed, supratentorial LGG were included. Comparisons of interest were OS and PFS at 2, 5, and 10 years in chemotherapy versus no chemotherapy and early RT versus delayed or no RT. Data were extracted from studies and synthesized with a random effects model. Quality of evidence was determined by American Academy of Neurology criteria and further analysis was performed, separating high quality (class I and II) from low quality (class III and IV) evidence. Numbers needed to treat (NNT) were determined from the risk difference. Results: 1531 articles were screened; 18 studies were included. Chemotherapy was not associated with a significant survival advantage compared to control. However, an analysis of high quality data revealed a survival advantage at 10 years associated with chemotherapy compared to control with NNT 5 (relative risk death chemo vs control 0.69 [0.56-0.86] p = 0.0006). Furthermore, NNT to prevent one progression with chemotherapy at 5 and 10 years was 6 and 3, respectively. Early RT was not associated with an OS advantage compared to control. However, early RT had progression benefit at all time points, with NNT of 10, 6, and 5 at 2, 5, and 10 years. Conclusions: Further study will be needed to confirm the optimal role of chemotherapy and RT. Caution must be used in interpretation as much of the literature consists of low-quality studies. [Table: see text]

Phase I study of AG-120, an IDH1 mutant enzyme inhibitor: Results from the cholangiocarcinoma dose escalation and expansion cohorts

4015

Background: Mutations in the metabolic enzyme isocitrate dehydrogenase 1 (mIDH1) occur in patients (pts) with cholangiocarcinoma (CC) and are detected in up to 25% of intrahepatic CC. mIDH1 produce the oncometabolite, D-2-hydroxyglutarate (2-HG), resulting in epigenetic and genetic dysregulation and oncogenesis. AG-120 is a first-in-class, potent, oral inhibitor of mIDH1 tested in this phase I study in mIDH1 solid tumors, including CC. Methods: AG-120 was escalated in a 3+3 design from 100 mg twice daily to 1200 mg once daily (QD) in 28-day cycles (N = 60, mIDH1 advanced solid tumors). Key eligibility for CC: recurrence of progressive mIDH1 CC following standard therapy (dose escalation) or at least a prior gemcitabine-based regimen (expansion cohort). Response (RECIST 1.1) was assessed every 8 weeks. Plasma and tumor tissue were collected for exploratory analyses. Results: Based on the safety, pharmacokinetic, and pharmacodynamic data from dose escalation, the 500 mg QD dose was selected for expansion in mIDH1 CC and other mIDH1 solid tumors. As of Dec 16, 2016, 73 pts with mIDH1 CC had been dosed in the dose escalation (n = 24) and expansion (n = 49) cohorts. Demographics: M/F = 24/49, median number of prior therapies = 2 (range 1–5), ECOG 0–1 = 26/47. There were no dose-limiting toxicities. Treatment-related adverse events (AEs) in ≥5% pts: fatigue (21%), nausea (18%), vomiting (12%), diarrhea (10%), decreased appetite (8%), dysgeusia (5%), QT prolongation (5%). Two (3%) pts experienced related grade 3 AEs: fatigue and low phosphorus. There were no AG-120-related AEs leading to discontinuation. Among the 72 efficacy evaluable (≥1 post baseline response assessment or discontinued prematurely) mIDH1 CC pts (24 in escalation and 48 in expansion cohort), 6% (n = 4) had a confirmed partial response and 56% (n = 40) experienced stable disease. The progression-free survival rate at 6 months was 40%, and 8 pts have been treated with AG-120 for ≥1 year. Conclusions: In this pretreated mIDH1 CC population, AG-120 was associated with a favorable safety profile and prolonged stable disease. A global, phase III, randomized, placebo-controlled study of AG-120 in mIDH1 CC has been initiated (ClarIDHy). Clinical trial information: NCT02073994.

Association of aggressive resection with survival and progression-free survival in adult low-grade glioma: A systematic review and meta-analysis with numbers needed to treat

2025

Background: Low-grade gliomas (LGG) account for 17-22% of all primary brain tumors. Optimal surgical management consists of optimum safe resection with the goal of complete resection. We performed a systematic review and meta-analysis to quantify the association of extent of resection with likelihood of survival, expressing our results in numbers needed to treat (NNT). Methods: A systematic review and study-level meta-analysis to determine the association of resection with overall survival and progression-free survival in newly diagnosed, supratentorial LGG in adults was performed by querying PubMed. Data were extracted to compare gross total resection (GTR) to subtotal resection (STR) and STR to biopsy (Bx) to determine relative risks (RR) of death and progression at 2, 5, and 10 years. Data were analyzed using a random effects model. NNT were calculated from significant comparisons and rounded up to the nearest whole number. Quality of evidence was determined by American Academy of Neurology criteria. Results: The systematic review resulted in 283 potential studies. Ultimately 29 studies were included in at least one comparison. There were no high quality (class I and II) or prospective studies discovered in the review. Comparing GTR to STR, RR with 95% confidence intervals (CI) of death at 2, 5, and 10 years, and NNT to avoid one death at 2, 5, and 10 years (GTR vs. STR) were 0.29 [0.17-0.52, p < 0.0001, NNT 17], 0.39 [0.29-0.51, p < 0.00001, NNT 6], and 0.50 [0.35-0.70, p < 0.0001 NNT 4]. RR and NNT for progression (GTR vs. STR) at 2, 5, and 10 years were 0.37 [0.24-0.57, p < 0.0001 NNT 7], 0.50 [0.39-0.64, p < 0.0001 NNT 4], and 0.67 [0.53-0.84, p = 0.0005 NNT 4]. Comparing STR to Bx, RR of death at 2, 5, and 10 years were 0.55 [0.34-0.88, p = 0.01 NNT 10], 0.9 [0.61-1.34], and 0.95 [0.73-1.23]. Conclusions: Increasing resection thresholds appear to be associated with improved overall and progression free survival, but the body of literature consists of low quality studies. Prospective studies are required to explore whether extent of resection matters or whether resectable tumors share a favorable biology associated with better outcome.

Noninvasive assessment of isocitrate dehydrogenase mutation status in cerebral gliomas by magnetic resonance spectroscopy in a clinical setting

OBJECTIVE Mutations in the isocitrate dehydrogenase (IDH) genes are of proven diagnostic and prognostic significance for cerebral gliomas. The objective of this study was to evaluate the clinical feasibility of using a recently described method for determining IDH mutation status by using magnetic resonance spectroscopy (MRS) to detect the presence of 2-hydroxyglutarate (2HG), the metabolic product of the mutant IDH enzyme. METHODS By extending imaging time by 6 minutes, the authors were able to include a point-resolved spectroscopy (PRESS) MRS sequence in their routine glioma imaging protocol. In 30 of 35 patients for whom this revised protocol was used the lesions were subsequently diagnosed histologically as gliomas. Of the remaining 5 patients, 1 had a gangliocytoma, 1 had a primary CNS lymphoma, and 3 had nonneoplastic lesions. Immunohistochemistry and/or polymerase chain reaction were used to detect the presence of IDH mutations in the glioma tissue resected. RESULTS In vivo MRS for 2HG correctly identified the IDH mutational status in 88.6% of patients. The sensitivity and specificity was 89.5% and 81.3%, respectively, when using 2 mM 2HG as threshold to discriminate IDH-mutated from wildtype tumors. Two glioblastomas that had elevated 2HG levels did not have detectable IDH mutations, and in 2 IDH-mutated gliomas 2HG was not reliably detectable. CONCLUSIONS The noninvasive determination of the IDH mutation status of a presumed glioma by means of MRS may be incorporated into a routine diagnostic imaging protocol and can be used to obtain additional information for patient care.

Prospective Longitudinal Analysis of 2-Hydroxyglutarate Magnetic Resonance Spectroscopy Identifies Broad Clinical Utility for the Management of Patients With IDH-Mutant Glioma

Purpose Proton magnetic resonance spectroscopy (MRS) of the brain can detect 2-hydroxyglutarate (2HG), the oncometabolite produced in neoplasms harboring a mutation in the gene coding for isocitrate dehydrogenase ( IDH). We conducted a prospective longitudinal imaging study to determine whether quantitative assessment of 2HG by MRS could serve as a noninvasive clinical imaging biomarker for IDH-mutated gliomas. Patients and Methods 2HG MRS was performed in 136 patients using point-resolved spectroscopy at 3 T in parallel with standard clinical magnetic resonance imaging and assessment. Data were analyzed in patient cohorts representing the major phases of the glioma clinical course and were further subgrouped by histology and treatment type to evaluate 2HG. Histologic correlations were performed. Results Quantitative 2HG MRS was technically and biologically reproducible. 2HG concentration > 1 mM could be reliably detected with high confidence. During the period of indolent disease, 2HG concentration varied by less than ± 1 mM, and it increased sharply with tumor progression. 2HG concentration was positively correlated with tumor cellularity and significantly differed between high- and lower-grade gliomas. In response to cytotoxic therapy, 2HG concentration decreased rapidly in 1p/19q codeleted oligodendrogliomas and with a slower time course in astrocytomas and mixed gliomas. The magnitude and time course of the decrease in 2HG concentration and magnitude of the decrease in tumor volume did not differ between oligodendrogliomas treated with temozolomide or carmustine. Criteria for 2HG MRS were established to make a presumptive molecular diagnosis of an IDH mutation in gliomas technically unable to undergo a surgical procedure. Conclusion 2HG concentration as measured by MRS was reproducible and reliably reflected the disease state. These data provide a basis for incorporating 2HG MRS into clinical management of IDH-mutated gliomas.

Detection of 2-hydroxyglutarate in brain tumors by triple-refocusing MR spectroscopy at 3T in vivo

PURPOSE

To test the efficacy of triple-refocusing MR spectroscopy (MRS) for improved detection of 2-hydroxyglutarate (2HG) in brain tumors at 3T in vivo.

METHODS

The triple-refocusing sequence parameters were tailored at 3T, with density-matrix simulations and phantom validation, for enhancing the 2HG 2.25-ppm signal selectivity with respect to the adjacent resonances of glutamate (Glu), glutamine (Gln), and gamma-aminobutyric acid (GABA). In vivo MRS data were acquired from 15 glioma patients and analyzed with LCModel using calculated basis spectra. Metabolites were quantified with reference to water.

RESULTS

A triple-refocusing sequence (echo time = 137 ms) was obtained for 2HG detection. The 2HG 2.25-ppm signal was large and narrow while the Glu and Gln signals between 2.2 and 2.3 ppm were minimal. The optimized triple refocusing offered improved separation of 2HG from Glu, Gln and GABA when compared with published MRS methods. 2HG was detected in all 15 patients, the estimated 2HG concentrations ranging from 2.4 to 15.0 mM, with Cramer-Rao lower bounds of 2%-11%. The 2HG estimates did not show significant correlation with total choline.

CONCLUSION

The optimized triple refocusing provides excellent 2HG signal discrimination from adjacent resonances and may confer reliable in vivo measurement of 2HG at relatively low concentrations. Magn Reson Med 78:40-48, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Hepatic gluconeogenesis influences (13)C enrichment in lactate in human brain tumors during metabolism of [1,2-(13)C]acetate

(13)C-enriched compounds are readily metabolized in human malignancies. Fragments of the tumor, acquired by biopsy or surgical resection, may be acid-extracted and (13)C NMR spectroscopy of metabolites such as glutamate, glutamine, 2-hydroxyglutarate, lactate and others provide a rich source of information about tumor metabolism in situ. Recently we observed (13)C-(13)C spin-spin coupling in (13)C NMR spectra of lactate in brain tumors removed from patients who were infused with [1,2-(13)C]acetate prior to the surgery. We found, in four patients, that infusion of (13)C-enriched acetate was associated with synthesis of (13)C-enriched glucose, detectable in plasma. (13)C labeled glucose derived from [1,2-(13)C]acetate metabolism in the liver and the brain pyruvate recycling in the tumor together lead to the production of the (13)C labeled lactate pool in the brain tumor. Their combined contribution to acetate metabolism in the brain tumors was less than 4.0%, significantly lower than the direct oxidation of acetate in the citric acid cycle in tumors.

In vivo detection of 2-hydroxyglutarate in brain tumors by optimized point-resolved spectroscopy (PRESS) at 7T

PURPOSE

To test the efficacy of 7T MRS for in vivo detection of 2-hydroxyglutarate (2HG) in brain tumors.

METHODS

The subecho times of point-resolved spectroscopy (PRESS) were optimized at 7T with density-matrix simulations and phantom validation to improve the 2HG signal selectivity with respect to the neighboring resonances of γ-aminobutyric acid (GABA), glutamate (Glu), and glutamine (Gln). MRS data were acquired from 12 subjects with gliomas in vivo and analyzed with LCModel using calculated basis spectra. Metabolite levels were quantified using unsuppressed short echo time (TE) water as a reference.

RESULTS

The PRESS TE was optimized as TE = 78 ms (TE₁ = 58 ms and TE₂ = 20 ms), at which the 2HG 2.25 ppm resonance appeared as a temporally maximum inverted narrow peak and the GABA, Glu, and Gln resonances between 2.2 and 2.5 ppm were all positive peaks. The PRESS TE = 78 ms method offered improved discrimination of 2HG from Glu, Gln, and GABA when compared with short-TE MRS. 2HG was detected in all patients enrolled in the study, the estimated 2HG concentrations ranging from 1.0 to 6.2 mM, with percentage standard deviation of 2%-7%.

CONCLUSION

Data indicate that the optimized MRS provides good selectivity of 2HG from other metabolite signals and may confer reliable in vivo detection of 2HG at relatively low concentrations. Magn Reson Med 77:936-944, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Acetate is a bioenergetic substrate for human glioblastoma and brain metastases

Glioblastomas and brain metastases are highly proliferative brain tumors with short survival times. Previously, using (13)C-NMR analysis of brain tumors resected from patients during infusion of (13)C-glucose, we demonstrated that there is robust oxidation of glucose in the citric acid cycle, yet glucose contributes less than 50% of the carbons to the acetyl-CoA pool. Here, we show that primary and metastatic mouse orthotopic brain tumors have the capacity to oxidize [1,2-(13)C]acetate and can do so while simultaneously oxidizing [1,6-(13)C]glucose. The tumors do not oxidize [U-(13)C]glutamine. In vivo oxidation of [1,2-(13)C]acetate was validated in brain tumor patients and was correlated with expression of acetyl-CoA synthetase enzyme 2, ACSS2. Together, the data demonstrate a strikingly common metabolic phenotype in diverse brain tumors that includes the ability to oxidize acetate in the citric acid cycle. This adaptation may be important for meeting the high biosynthetic and bioenergetic demands of malignant growth.

In vivo (1)H MRSI of glycine in brain tumors at 3T

PURPOSE

MR spectroscopic imaging (SI) of glycine (Gly) in the human brain is challenging due to the interference of the abundant neighboring J-coupled resonances. Our aim is to accomplish reliable imaging of Gly in healthy brain and brain tumors using an optimized MR sequence scheme at 3 tesla.

METHODS

Two-dimensional (1)H SI was performed with a point-resolved spectroscopy scheme. An echo time of 160 ms was used for separation between Gly and myo-inositol signals. Data were collected from eight healthy volunteers and 14 subjects with gliomas. Spectra were analyzed with the linear combination model using numerically calculated basis spectra. Metabolite concentrations were estimated with reference to creatine in white matter (WM) regions at 6.4 molar concentrations (mM).

RESULTS

From a linear regression analysis with respect to the fractional gray matter (GM) content, the Gly concentrations in pure GM and WM in healthy brains were estimated to be 1.1 and 0.3 mM, respectively. Gly was significantly elevated in tumors. The tumor-to-contralateral Gly concentration ratio was more extensive with higher grades, showing ∼ 10-fold elevation of Gly in glioblastomas.

CONCLUSION

The Gly level is significantly different between GM and WM in healthy brains. Our data indicate that SI of Gly may provide a biomarker of brain tumor malignancy.

¹H MRS characterization of neurochemical profiles in orthotopic mouse models of human brain tumors

Glioblastoma (GBM), the most common primary brain tumor, is resistant to currently available treatments. The development of mouse models of human GBM has provided a tool for studying mechanisms involved in tumor initiation and growth as well as a platform for preclinical investigation of new drugs. In this study we used (1) H MR spectroscopy to study the neurochemical profile of a human orthotopic tumor (HOT) mouse model of human GBM. The goal of this study was to evaluate differences in metabolite concentrations in the GBM HOT mice when compared with normal mouse brain in order to determine if MRS could reliably differentiate tumor from normal brain. A TE =19 ms PRESS sequence at 9.4 T was used for measuring metabolite levels in 12 GBM mice and 8 healthy mice. Levels for 12 metabolites and for lipids/macromolecules at 0.9 ppm and at 1.3 ppm were reliably detected in all mouse spectra. The tumors had significantly lower concentrations of total creatine, GABA, glutamate, total N-acetylaspartate, aspartate, lipids/macromolecules at 0.9 ppm, and lipids/macromolecules at 1.3 ppm than did the brains of normal mice. The concentrations of glycine and lactate, however, were significantly higher in tumors than in normal brain.

High expression of the stem cell marker nestin is an adverse prognostic factor in WHO grade II-III astrocytomas and oligoastrocytomas

Infiltrating astrocytomas and oligoastrocytomas of low to anaplastic grade (WHO grades II and III), in spite of being associated with a wide range of clinical outcomes, can be difficult to subclassify and grade by the current histopathologic criteria. Unlike oligodendrogliomas and anaplastic oligodendrogliomas that can be identified by the 1p/19q codeletion and the more malignant glioblastomas (WHO grade IV astrocytomas) that can be diagnosed solely based on objective features on routine hematoxylin and eosin sections, no such objective criteria exist for the subclassification of grade II-III astrocytomas and oligoastrocytomas (A+OA II-III). In this study, we evaluated the prognostic and predictive value of the stem cell marker nestin in adult A+OA II-III (n = 50) using immunohistochemistry and computer-assisted analysis on tissue microarrays. In addition, the correlation between nestin mRNA level and total survival was analyzed in the NCI Rembrandt database. The results showed that high nestin expression is a strong adverse prognostic factor for total survival (p = 0.0004). The strength of the correlation was comparable to but independent of the isocitrate dehydrogenase 1/2 (IDH 1/2) mutation status. Histopathological grading and subclassification did not correlate significantly with outcome, although the interpretation of this finding is limited by the fact that grade III tumors were treated more aggressively than grade II tumors. These results suggest that nestin level and IDH 1/2 mutation status are strong prognostic features in A+OA II-III and possibly more helpful for treatment planning than routine histopathological variables such as oligodendroglial component (astrocytoma vs. oligoastrocytoma) and WHO grade (grade II vs. III).

In vivo detection of citrate in brain tumors by 1H magnetic resonance spectroscopy at 3T

PURPOSE

To test whether citrate is elevated in adult patients with gliomas using (1)H magnetic resonance spectroscopy (MRS) at 3T in vivo.

METHODS

Thirty-four adult patients were enrolled in the study, including six subjects with glioblastomas, eight subjects with astrocytomas (World Health Organization grade 3, n = 5; grade 2, n = 3), and 20 subjects with oligodendrogliomas (grade 3, n = 5; grade 2, n = 15). Five healthy volunteers were studied for baseline citrate data. Single-voxel localized spectra were collected with point-resolved spectroscopy (PRESS) echo times of 35 and 97 ms and were analyzed with LCModel software using numerically calculated basis spectra that included the effects of the PRESS radiofrequency and gradient pulses.

RESULTS

Citrate was not measurable by MRS in healthy brain but was detected in tumor patients at both echo times. The citrate concentration was estimated to be as high as 1.8 mM with reference to water at 42 M, with Cramér-Rao lower bounds (CRLB) as low as 5%. The mean citrate level was 0.7 ± 0.4 mM (mean ± SD, n = 32) with a median CRLB of ∼12%. No correlation was identified between citrate concentration and tumor grade or histological type.

CONCLUSION

Citrate was increased in the majority of gliomas in adult patients. The elevated citrate in our data indicates an altered metabolic state of tumor relative to healthy brain.

Metabolism of [U-13 C]glucose in human brain tumors in vivo

Glioblastomas and brain metastases demonstrate avid uptake of 2-[(18) F]fluoro-2-deoxyglucose by positron emission tomography and display perturbations of intracellular metabolite pools by (1) H MRS. These observations suggest that metabolic reprogramming contributes to brain tumor growth in vivo. The Warburg effect, excess metabolism of glucose to lactate in the presence of oxygen, is a hallmark of cancer cells in culture. 2-[(18) F]Fluoro-2-deoxyglucose-positive tumors are assumed to metabolize glucose in a similar manner, with high rates of lactate formation relative to mitochondrial glucose oxidation, but few studies have specifically examined the metabolic fates of glucose in vivo. In particular, the capacity of human brain cancers to oxidize glucose in the tricarboxylic acid cycle is unknown. Here, we studied the metabolism of human brain tumors in situ. [U-(13) C]Glucose (uniformly labeled glucose, i.e. d-glucose labeled with (13) C in all six carbons) was infused during surgical resection, and tumor samples were subsequently subjected to (13) C NMR spectroscopy. The analysis of tumor metabolites revealed lactate production, as expected. We also determined that pyruvate dehydrogenase, turnover of the tricarboxylic acid cycle, anaplerosis and de novo glutamine and glycine synthesis contributed significantly to the ultimate disposition of glucose carbon. Surprisingly, less than 50% of the acetyl-coenzyme A pool was derived from blood-borne glucose, suggesting that additional substrates contribute to tumor bioenergetics. This study illustrates a convenient approach that capitalizes on the high information content of (13) C NMR spectroscopy and enables the analysis of intermediary metabolism in diverse cancers growing in their native microenvironment.

Glucose metabolism via the pentose phosphate pathway, glycolysis and Krebs cycle in an orthotopic mouse model of human brain tumors

It has been hypothesized that increased flux through the pentose phosphate pathway (PPP) is required to support the metabolic demands of rapid malignant cell growth. Using orthotopic mouse models of human glioblastoma (GBM) and renal cell carcinoma metastatic to brain, we estimated the activity of the PPP relative to glycolysis by infusing [1,2-(13) C(2) ]glucose. The [3-(13) C]lactate/[2,3-(13) C(2) ]lactate ratio was similar for both the GBM and brain metastasis and their respective surrounding brains (GBM, 0.197 ± 0.011 and 0.195 ± 0.033, respectively (p = 1); metastasis: 0.126 and 0.119 ± 0.033, respectively). This suggests that the rate of glycolysis is significantly greater than the PPP flux in these tumors, and that the PPP flux into the lactate pool is similar in both tumors. Remarkably, (13) C-(13) C coupling was observed in molecules derived from Krebs cycle intermediates in both tumor types, denoting glucose oxidation. In the renal cell carcinoma, in contrast with GBM, (13) C multiplets of γ-aminobutyric acid (GABA) differed from its precursor glutamate, suggesting that GABA did not derive from a common glutamate precursor pool. In addition, the orthotopic renal tumor, the patient's primary renal mass and brain metastasis were all strongly immunopositive for the 67-kDa isoform of glutamate decarboxylase, as were 84% of tumors on a renal cell carcinoma tissue microarray of the same histology, suggesting that GABA synthesis is cell autonomous in at least a subset of renal cell carcinomas. Taken together, these data demonstrate that (13) C-labeled glucose can be used in orthotopic mouse models to study tumor metabolism in vivo and to ascertain new metabolic targets for cancer diagnosis and therapy.

Analysis of tumor metabolism reveals mitochondrial glucose oxidation in genetically diverse human glioblastomas in the mouse brain in vivo

Dysregulated metabolism is a hallmark of cancer cell lines, but little is known about the fate of glucose and other nutrients in tumors growing in their native microenvironment. To study tumor metabolism in vivo, we used an orthotopic mouse model of primary human glioblastoma (GBM). We infused (13)C-labeled nutrients into mice bearing three independent GBM lines, each with a distinct set of mutations. All three lines displayed glycolysis, as expected for aggressive tumors. They also displayed unexpected metabolic complexity, oxidizing glucose via pyruvate dehydrogenase and the citric acid cycle, and using glucose to supply anaplerosis and other biosynthetic activities. Comparing the tumors to surrounding brain revealed obvious metabolic differences, notably the accumulation of a large glutamine pool within the tumors. Many of these same activities were conserved in cells cultured ex vivo from the tumors. Thus GBM cells utilize mitochondrial glucose oxidation during aggressive tumor growth in vivo.

Compressive sensing could accelerate 1H MR metabolic imaging in the clinic

PURPOSE

To retrospectively evaluate the fidelity of magnetic resonance (MR) spectroscopic imaging data preservation at a range of accelerations by using compressed sensing.

MATERIALS AND METHODS

The protocols were approved by the institutional review board of the university, and written informed consent to acquire and analyze MR spectroscopic imaging data was obtained from the subjects prior to the acquisitions. This study was HIPAA compliant. Retrospective application of compressed sensing was performed on 10 clinical MR spectroscopic imaging data sets, yielding 600 voxels from six normal brain data sets, 163 voxels from two brain tumor data sets, and 36 voxels from two prostate cancer data sets for analysis. The reconstructions were performed at acceleration factors of two, three, four, five, and 10 and were evaluated by using the root mean square error (RMSE) metric, metabolite maps (choline, creatine, N-acetylaspartate [NAA], and/or citrate), and statistical analysis involving a voxelwise paired t test and one-way analysis of variance for metabolite maps and ratios for comparison of the accelerated reconstruction with the original case.

RESULTS

The reconstructions showed high fidelity for accelerations up to 10 as determined by the low RMSE (< 0.05). Similar means of the metabolite intensities and hot-spot localization on metabolite maps were observed up to a factor of five, with lack of statistically significant differences compared with the original data. The metabolite ratios of choline to NAA and choline plus creatine to citrate did not show significant differences from the original data for up to an acceleration factor of five in all cases and up to that of 10 for some cases.

CONCLUSION

A reduction of acquisition time by up to 80%, with negligible loss of information as evaluated with clinically relevant metrics, has been successfully demonstrated for hydrogen 1 MR spectroscopic imaging.

T2 measurement of J-coupled metabolites in the human brain at 3T

Proton T(2) relaxation times of metabolites in the human brain were measured using point resolved spectroscopy at 3T in vivo. Four echo times (54, 112, 246 and 374 ms) were selected from numerical and phantom analyses for effective detection of the glutamate multiplet at ~ 2.35 ppm. In vivo data were obtained from medial and left occipital cortices of five healthy volunteers. The cortices contained predominantly gray and white matter, respectively. Spectra were analyzed with LCModel software using volume-localized calculated spectra of brain metabolites. The estimate of the signal strength vs. TE was fitted to a monoexponential function for estimation of apparent T(2) (T(2)(†)). T(2)(†) was estimated to be similar between the brain regions for creatine, choline, glutamate and myo-inositol, but significantly different for N-acetylaspartate singlet and multiplet. T(2)(†)s of glutamate and myo-inositol were measured as 181 ± 16 and 197 ± 14 ms (mean ± SD, N = 5) for medial occipital cortices, and 180 ± 12 and 196 ± 17 ms for left occipital cortices, respectively.

2-hydroxyglutarate detection by magnetic resonance spectroscopy in IDH-mutated patients with gliomas

Mutations in isocitrate dehydrogenase 1 and 2 (IDH1, 2) have been demonstrated in the majority of World Health Organization grade 2 and grade 3 gliomas in adults. These mutations are associated with the accumulation of 2-hydroxyglutarate (2HG) within the tumor. Here we report the noninvasive detection of 2HG by proton magnetic resonance spectroscopy (MRS). The pulse sequence was developed and optimized with numerical and phantom analyses for 2HG detection. The concentrations of 2HG were estimated using spectral fitting in the tumors of 30 patients. Detection of 2HG correlated with mutations in IDH1 or IDH2 and with increased levels of D-2HG by mass spectrometry of resected tumor. Noninvasive detection of 2HG may prove to be a valuable diagnostic and prognostic biomarker.

Measurement of glycine in the human brain in vivo by 1H-MRS at 3 T: application in brain tumors

Glycine is a key metabolic intermediate required for the synthesis of proteins, nucleic acids, and other molecules, and its detection in cancer could, therefore, provide biologically relevant information about the growth of the tumor. Here, we report measurement of glycine in human brain and gliomas by an optimized point-resolved spectroscopy sequence at 3 T. Echo time dependence of the major obstacle, myo-inositol (mI) multiplet, was investigated with numerical simulations, incorporating the 3D volume localization. The simulations indicated that a subecho pair (TE(1) , TE(2) ) = (60, 100) ms permits detection of both glycine and mI with optimum selectivity. In vivo validation of the optimized point-resolved spectroscopy was conducted on the right parietal cortex of five healthy volunteers. Metabolite signals estimated from LC Model were normalized with respect to the brain water signal, and the concentrations were evaluated assuming the total creatine concentration at 8 mM. The glycine concentration was estimated as 0.6 ± 0.1 mM (mean ± SD, n = 5), with a mean Cramér-Rao lower bound of 9 ± 1%. The point-resolved spectroscopy sequence was applied to measure the glycine levels in patients with glioblastoma multiforme. Metabolite concentrations were obtained using the water signal from the tumor mass. The study revealed that a subset of human gliomas contains glycine levels elevated 1.5-8 fold relative to normal.

Improvement of resolution for brain coupled metabolites by optimized (1)H MRS at 7T

Resolution enhancement for glutamate (Glu), glutamine (Gln) and glutathione (GSH) in the human brain by TE-optimized point-resolved spectroscopy (PRESS) at 7 T is reported. Sub-TE dependences of the multiplets of Glu, Gln, GSH, γ-aminobutyric acid (GABA) and N-acetylaspartate (NAA) at 2.2-2.6 ppm were investigated with density matrix simulations, incorporating three-dimensional volume localization. The numerical simulations indicated that the C4-proton multiplets can be completely separated with (TE(1), TE(2)) = (37, 63) ms, as a result of a narrowing of the multiplets and suppression of the NAA 2.5 ppm signal. Phantom experiments reproduced the signal yield and lineshape from simulations within experimental errors. In vivo tests of optimized PRESS were conducted on the prefrontal cortex of six healthy volunteers. In spectral fitting by LCModel, Cramér-Rao lower bounds (CRLBs) of Glu, Gln and GSH were 2 ± 1, 5 ± 1 and 6 ± 2 (mean ± SD), respectively. To evaluate the performance of the optimized PRESS method under identical experimental conditions, stimulated-echo spectra were acquired with (TE, TM) = (14, 37) and (74, 68) ms. The CRLB of Glu was similar between PRESS and short-TE stimulated-echo acquisition mode (STEAM), but the CRLBs of Gln and GSH were lower in PRESS than in both STEAM acquisitions.

The telomerase antagonist, imetelstat, efficiently targets glioblastoma tumor-initiating cells leading to decreased proliferation and tumor growth

PURPOSE

Telomerase activity is one of the hallmarks of cancer and is a highly relevant therapeutic target. The effects of a novel human telomerase antagonist, imetelstat, on primary human glioblastoma (GBM) tumor-initiating cells were investigated in vitro and in vivo.

EXPERIMENTAL DESIGN

Tumor-initiating cells were isolated from primary GBM tumors and expanded as neurospheres in vitro. The GBM tumor-initiating cells were treated with imetelstat and examined for the effects on telomerase activity levels, telomere length, proliferation, clonogenicity, and differentiation. Subsequently, mouse orthotopic and subcutaneous xenografts were used to assess the in vivo efficacy of imetelstat.

RESULTS

Imetelstat treatment produced a dose-dependent inhibition of telomerase (IC(50) 0.45 micromol/L). Long-term imetelstat treatment led to progressive telomere shortening, reduced rates of proliferation, and eventually cell death in GBM tumor-initiating cells. Imetelstat in combination with radiation and temozolomide had a dramatic effect on cell survival and activated the DNA damage response pathway. Imetelstat is able to cross the blood-brain barrier in orthotopic GBM xenograft tumors. Fluorescently labeled GBM tumor cells isolated from orthotopic tumors, following systemic administration of imetelstat (30 mg/kg every day for three days), showed approximately 70% inhibition of telomerase activity. Chronic systemic treatment produced a marked decrease in the rate of xenograft subcutaneous tumor growth.

CONCLUSION

This preclinical study supports the feasibility of testing imetelstat in the treatment of GBM patients, alone or in combination with standard therapies.

Marked genomic differences characterize primary and secondary glioblastoma subtypes and identify two distinct molecular and clinical secondary glioblastoma entities

Glioblastoma is classified into two subtypes on the basis of clinical history: "primary glioblastoma" arising de novo without detectable antecedent disease and "secondary glioblastoma" evolving from a low-grade astrocytoma. Despite their distinctive clinical courses, they arrive at an indistinguishable clinical and pathologic end point highlighted by widespread invasion and resistance to therapy and, as such, are managed clinically as if they are one disease entity. Because the life history of a cancer cell is often reflected in the pattern of genomic alterations, we sought to determine whether primary and secondary glioblastomas evolve through similar or different molecular pathogenetic routes. Clinically annotated primary and secondary glioblastoma samples were subjected to high-resolution copy number analysis using oligonucleotide-based array comparative genomic hybridization. Unsupervised classification using genomic nonnegative matrix factorization methods identified three distinct genomic subclasses. Whereas one corresponded to clinically defined primary glioblastomas, the remaining two stratified secondary glioblastoma into two genetically distinct cohorts. Thus, this global genomic analysis showed wide-scale differences between primary and secondary glioblastomas that were previously unappreciated, and has shown for the first time that secondary glioblastoma is heterogeneous in its molecular pathogenesis. Consistent with these findings, analysis of regional recurrent copy number alterations revealed many more events unique to these subclasses than shared. The pathobiological significance of these shared and subtype-specific copy number alterations is reinforced by their frequent occurrence, resident genes with clear links to cancer, recurrence in diverse cancer types, and apparent association with clinical outcome. We conclude that glioblastoma is composed of at least three distinct molecular subtypes, including novel subgroups of secondary glioblastoma, which may benefit from different therapeutic strategies.

Phase I/II Study of Imatinib Mesylate for Recurrent Malignant Gliomas: North American Brain Tumor Consortium Study 99-08

PURPOSE

Phase I: To determine the maximum tolerated doses, toxicities, and pharmacokinetics of imatinib mesylate (Gleevec) in patients with malignant gliomas taking enzyme-inducing antiepileptic drugs (EIAED) or not taking EIAED. Phase II: To determine the therapeutic efficacy of imatinib.

EXPERIMENTAL DESIGN

Phase I component used an interpatient dose escalation scheme. End points of the phase II component were 6-month progression-free survival and response.

RESULTS

Fifty patients enrolled in the phase I component (27 EIAED and 23 non-EIAED). The maximum tolerated dose for non-EIAED patients was 800 mg/d. Dose-limiting toxicities were neutropenia, rash, and elevated alanine aminotransferase. EIAED patients received up to 1,200 mg/d imatinib without developing dose-limiting toxicity. Plasma exposure of imatinib was reduced by approximately 68% in EIAED patients compared with non-EIAED patients. Fifty-five non-EIAED patients (34 glioblastoma multiforme and 21 anaplastic glioma) enrolled in the phase II component. Patients initially received 800 mg/d imatinib; 15 anaplastic glioma patients received 600 mg/d after hemorrhages were observed. There were 2 partial response and 6 stable disease among glioblastoma multiforme patients and 0 partial response and 5 stable disease among anaplastic glioma patients. Six-month progression-free survival was 3% for glioblastoma multiforme and 10% for anaplastic glioma patients. Five phase II patients developed intratumoral hemorrhages.

CONCLUSIONS

Single-agent imatinib has minimal activity in malignant gliomas. CYP3A4 inducers, such as EIAEDs, substantially decreased plasma exposure of imatinib and should be avoided in patients receiving imatinib for chronic myelogenous leukemia and gastrointestinal stromal tumors. The evaluation of the activity of combination regimens incorporating imatinib is under way in phase II trials.

A rapid and sensitive enzymatic method for epidermal growth factor receptor mutation screening

PURPOSE

Mutations in the epidermal growth factor receptor (EGFR) are associated with clinical and radiographic responses to EGFR tyrosine kinase inhibitors gefitinib and erlotinib. Currently available methods of EGFR mutation detection rely on direct DNA sequencing, which requires isolation of DNA from a relatively pure population of tumor cells, cannot be done on small diagnostic specimens, and lack sensitivity. Here we describe the use of a sensitive screening method that overcomes many of these limitations.

EXPERIMENTAL DESIGN

We screened 178 non-small cell lung cancer specimens for mutations in exons 18 to 21 of EGFR using a DNA endonuclease, SURVEYOR, which cleaves mismatched heteroduplexed DNA. Samples were analyzed by high-performance liquid chromatography on the Transgenomic WAVE HS system. Selected specimens that produced digestion products using SURVEYOR were subsequently reanalyzed by size separation or under partially denaturing conditions, followed by fractionation and sequencing. The specimens included DNA isolated from frozen tumor specimens, dissected formalin-fixed, paraffin-embedded tumor specimens undergoing clinical sequencing, and undissected formalin-fixed, paraffin-embedded specimens. One hundred sixty specimens were independently analyzed using direct DNA sequencing in a blinded fashion.

RESULTS

EGFR mutations were detected in 16 of 61 fresh frozen tumor specimens, 24 of 91 dissected formalin-fixed, paraffin-embedded tumor specimens, and 11 of 26 undissected formalin-fixed, paraffin-embedded tumor specimens. Compared with sequencing, the sensitivity and specificity of the present method were 100% and 87%. The positive and negative predictive values were 74% and 100%, respectively. SURVEYOR analysis detected 7 (4%) mutations that were not previously detected by direct sequencing.

CONCLUSIONS

SURVEYOR analysis provides a rapid method for EGFR mutation screening with 100% sensitivity and negative predictive value. This unbiased scanning technique is superior to direct sequencing when used with undissected formalin-fixed, paraffin-embedded specimens.

Mouse Models of Human Cancers Consortium Workshop on Nervous System Tumors

Nervous system tumors are clinically challenging neoplasms that form within the central and peripheral nervous system. Although there have been many clinical trials using novel agents for the treatment of primary brain tumors, there have been few advances that positively affect overall patient survival. Over the past several years, there has been significant progress in the development of accurate small-animal spontaneous brain tumor models, small-animal neuroimaging, and tools for the bioinformatic analysis of complex molecular data sets, all of which have contributed to an improved understanding of the pathogenesis of human brain tumors. Whereas these models will continue to be of great value in basic science investigations, they can also be used to identify and validate potential therapies for brain tumors and to evaluate these drugs in preclinical trials. The National Cancer Institute recently convened a workshop to review the current state of small-animal brain tumor modeling and to make recommendations about the use of these models to improve the clinical outcome for patients with brain tumors. In this meeting report, we outline the current state of small-animal models for brain tumors, the potential applications of these models, and the recommendations made by the workshop participants for the use of mouse models in the preclinical evaluation of potential brain tumor therapies.

Hyperinsulinemic hypoglycemia in Beckwith-Wiedemann syndrome due to defects in the function of pancreatic beta-cell adenosine triphosphate-sensitive potassium channels

BACKGROUND

Beckwith-Wiedemann syndrome (BWS) is a congenital overgrowth syndrome that is clinically and genetically heterogeneous. Hyperinsulinemic hypoglycemia occurs in about 50% of children with BWS and, in the majority of infants, it resolves spontaneously. However, in a small group of patients the hypoglycemia can be persistent and may require pancreatectomy. The mechanism of persistent hyperinsulinemic hypoglycemia in this group of patients is unclear.

PATIENTS AND METHODS

Using patch-clamp techniques on pancreatic tissue obtained at the time of surgery, we investigated the electrophysiological properties of ATP-sensitive K(+) (K(ATP)) channels in pancreatic beta-cells in a patient with BWS and severe medically-unresponsive hyperinsulinemic hypoglycemia.

RESULTS

Persistent hyperinsulinism was found to be caused by abnormalities in K(ATP) channels of the pancreatic beta-cell. Immunofluorescence studies using a SUR1 antibody revealed perinuclear pattern of staining in the BWS cells, suggesting a trafficking defect of the SUR1 protein. No mutations were found in the genes ABCC8 and KCNJ11 encoding for the two subunits, SUR1 and KIR6.2, respectively, of the K(ATP) channel. Genetic analysis of this patients BWS showed evidence of mosaic paternal isodisomy.

CONCLUSIONS

In this novel case of BWS with mosaic paternal uniparental disomy for 11p15, persistent hyperinsulinism was due to abnormalities in K(ATP) channels of the pancreatic beta-cell. The mechanism/s by which mosaic paternal uniparental disomy for 11p15 causes a trafficking defect in the SUR1 protein of the K(ATP) channel remains to be elucidated.