Diagnostic and Prognostic Significance of Methionine Uptake and Methionine Positron Emission Tomography Imaging in Gliomas

Radiomics for residual tumour detection and prognosis in newly diagnosed glioblastoma based on postoperative [11C] methionine PET and T1c-w MRI

Personalized treatment strategies based on non-invasive biomarkers have potential to improve patient management in patients with newly diagnosed glioblastoma (GBM). The residual tumour burden after surgery in GBM patients is a prognostic imaging biomarker. However, in clinical patient management, its assessment is a manual and time-consuming process that is at risk of inter-rater variability. Furthermore, the prediction of patient outcome prior to radiotherapy may identify patient subgroups that could benefit from escalated radiotherapy doses. Therefore, in this study, we investigate the capabilities of traditional radiomics and 3D convolutional neural networks for automatic detection of the residual tumour status and to prognosticate time-to-recurrence (TTR) and overall survival (OS) in GBM using postoperative [11C] methionine positron emission tomography (MET-PET) and gadolinium-enhanced T1-w magnetic resonance imaging (MRI). On the independent test data, the 3D-DenseNet model based on MET-PET achieved the best performance for residual tumour detection, while the logistic regression model with conventional radiomics features performed best for T1c-w MRI (AUC: MET-PET 0.95, T1c-w MRI 0.78). For the prognosis of TTR and OS, the 3D-DenseNet model based on MET-PET integrated with age and MGMT status achieved the best performance (Concordance-Index: TTR 0.68, OS 0.65). In conclusion, we showed that both deep-learning and conventional radiomics have potential value for supporting image-based assessment and prognosis in GBM. After prospective validation, these models may be considered for treatment personalization.

Methionine-PET to differentiate between brain lesions appearing similar on conventional CT/MRI scans

BACKGROUND AND PURPOSE

11 C-Methionine (MET)-PET is a useful tool in neuro-oncology. This study aimed to examine whether a combination of diagnostic variables associated with MET uptake could help distinguish between brain lesions that are often difficult to discriminate in conventional CT and MRI.

METHODS

MET-PET was assessed in 129 patients with glioblastoma multiforme, primary central nervous lymphoma, metastatic brain tumor, tumefactive multiple sclerosis, or radiation necrosis. The accuracy of the differential diagnosis was analyzed using five diagnostic characteristics in combination: higher maximum standardized uptake value (SUV) of MET in the lesion/the mean normal cortical SUV of MET ratio, overextension beyond gadolinium, peripheral pattern indicating abundant MET accumulation in the peripheral region, central pattern denoting abundant MET accumulation in the central region, and dynamic-up suggesting increased MET accumulation during dynamic study. The analysis was conducted on sets of two of the five brain lesions.

RESULTS

Significant differences in the five diagnostic traits were observed among the five brain lesions, and differential diagnosis could be achieved by combining these diagnostic features. The area under the curve between each set of two of the five brain lesions using MET-PET features ranged from .85 to 1.0.

CONCLUSIONS

According to the findings, combining the five diagnostic criteria could help with the differential diagnosis of the five brain lesions. MET-PET is an auxiliary diagnostic technique that could help in distinguishing these five brain lesions.

Evaluation of Gliomas with Magnetic Resonance Fingerprinting with PET Correlation-A Comparative Study

OBJECTIVES

Advanced MR imaging of brain tumors is still mainly based on qualitative imaging. PET imaging offers additive metabolic information, and MR fingerprinting (MRF) offers a novel approach to quantitative data acquisition. The purpose of this study was to evaluate the ability of MRF to predict tumor regions and grading in combination with PET.

METHODS

Seventeen patients with histologically verified infiltrating gliomas and available amino-acid PET data were enrolled. ROIs for solid tumor parts (SPo), perifocal edema (ED1), and normal-appearing white matter (NAWM) were selected on conventional MRI sequences and aligned to the MRF and PET images. The predictability of gliomas by region and grading as well as intermodal correlations were assessed.

RESULTS

For MRF, we calculated an overall predictability by region (SPo, ED1, and NAWM) for all of the MRF parameters of 76.5%, 47.1%, and 94.1%, respectively. The overall ability to distinguish low- from high-grade gliomas using MRF was 88.9% for LGG and 75% for HGG, with an accuracy of 82.4%, a ppV of 85.71%, and an npV of 80%. PET positivity was found in 13/17 patients for solid tumor parts, and in 3/17 patients for the edema region. However, there was no significant difference in region-specific MRF values between PET positive and PET negative patients.

CONCLUSIONS

MRF and PET provide quantitative measurements of the tumor tissue characteristics of gliomas, with good predictability. Nonetheless, the results are dissimilar, reflecting the different underlying mechanisms of each method.

18F-Fluorodeoxy Glucose and 11C-Methionine Accumulation in Demyelinating Lesions

Background Few studies have evaluated the accumulation of 18F-fluorodeoxyglucose (FDG), 11C-methionine (MET), and other positron emission tomography (PET) tracers in patients with demyelinating disease.

Purpose This study aimed to investigate the accumulation of FDG-PET/computed tomography (CT) and MET-PET/CT in demyelinating lesions.

Material and Methods A retrospective search of the patient database in our hospital identified five patients with demyelinating disease in whom PET studies performed in the past 10 years revealed accumulation of FDG or MET. The clinical diagnoses were multiple sclerosis (n=1), myelitis (n=1), limbic encephalitis (n=1), chronic inflammatory demyelinating polyneuropathy (CIDP; n=1), and acute demyelinating encephalomyelitis (ADEM; n=1). Two patients received FDG-PET/CT alone and three patients received both FDG-PET/CT and MET-PET/CT on the same day. Images were visually and conjointly reviewed by two radiologists. In semiquantitative evaluation, the maximum standardized uptake value (SUVmax) of the lesion was measured. The lesion-to-normal brain uptake ratio (L/N ratio) was calculated.

Results FDG and/or MET accumulated to a part of the lesions seen on MRI. SUVmax on FDG-PET/CT ranged from 3.8 to 10.3, and L/N ratio on MET-PET/CT ranged from 16.6 to 2.4.

Conclusion It has been established that neoplastic and demyelinating lesions can be differentiated on the basis of FDG or MET uptake. However, as accumulation of FDG and MET can also occur in demyelinating lesions; knowledge of this possibility is of clinical importance.

Correlation of Intraoperative 5-ALA-Induced Fluorescence Intensity and Preoperative 11C-Methionine PET Uptake in Glioma Surgery

Simple Summary

In malignant brain tumor surgery, precise identification of the tumor is essential. 5-Aminolevulinic acid (5-ALA) labels tumor cells with red fluorescence to facilitate tumor resection. On the other hand, the nuclear medicine imaging technique, positron emission tomography with ¹¹C-methionine (MET-PET), can delineate tumors precisely but is not widely available. This study aimed to determine the correlation between intraoperative 5-ALA-induced fluorescence and preoperative MET-PET signals of gliomas. We quantitatively measured the fluorescence intensity from tumor samples and calculated the MET-PET uptake by the tumor. Our study showed that strong tumor fluorescence correlated with high MET-PET uptake and cellular proliferation. Our findings might be valuable to rapidly provide information on tumor biology at the time of surgery in circumstances where MET-PET is inaccessible.

Abstract

Background: 5-Aminolevulinic acid (5-ALA) is widely employed to assist fluorescence-guided surgery for malignant brain tumors. Positron emission tomography with ¹¹C-methionine (MET-PET) represents the activity of brain tumors with precise boundaries but is not readily available. We hypothesized that quantitative 5-ALA-induced fluorescence intensity might correlate with MET-PET uptake in gliomas. Methods: Adult patients with supratentorial astrocytic gliomas who underwent preoperative MET-PET and surgical tumor resection using 5-ALA were enrolled in this prospective study. The regional tumor uptake of MET-PET was expressed as the ratio of standardized uptake volume max to that of the normal contralateral frontal lobe. A spectrometric fluorescence detection system measured tumor specimens’ ex vivo fluorescence intensity at 635 nm. Ki-67 index and IDH mutation status were assessed by histopathological analysis. Use of an antiepileptic drug (AED) and contrast enhancement pattern on MRI were also investigated. Results: Thirty-two patients, mostly with Glioblastoma IDH wild type (46.9%) and anaplastic astrocytoma IDH mutant (21.9%), were analyzed. When the fluorescence intensity was ranked into four groups, the strongest fluorescence group exhibited the highest mean MET-PET uptake and Ki-67 index values. When rearranged into fluorescence Visible or Non-visible groups, the Visible group had significantly higher MET-PET uptake and Ki-67 index compared to the Non-visible group. Contrast enhancement on MRI and IDH wild type tumors were more frequent among the Visible group. AED use did not correlate with 5-ALA-induced fluorescence intensity. Conclusions: In astrocytic glioma surgery, visible 5-ALA-induced fluorescence correlated with high MET-PET uptake, along with a high Ki-67 index.

Interactions between Radiation and One-Carbon Metabolism

Metabolic reprogramming is a hallmark of cancer. Cancer cells rewire one-carbon metabolism, a central metabolic pathway, to turn nutritional inputs into essential biomolecules required for cancer cell growth and maintenance. Radiation therapy, a common cancer therapy, also interacts and alters one-carbon metabolism. This review discusses the interactions between radiation therapy, one-carbon metabolism and its component metabolic pathways.

Metabolic Drivers of Invasion in Glioblastoma

Glioblastoma is a primary malignant brain tumor with a median survival under 2 years. The poor prognosis glioblastoma caries is largely due to cellular invasion, which enables escape from resection, and drives inevitable recurrence. While most studies to date have focused on pathways that enhance the invasiveness of tumor cells in the brain microenvironment as the primary driving forces behind GBM’s ability to invade adjacent tissues, more recent studies have identified a role for adaptations in cellular metabolism in GBM invasion. Metabolic reprogramming allows invasive cells to generate the energy necessary for colonizing surrounding brain tissue and adapt to new microenvironments with unique nutrient and oxygen availability. Historically, enhanced glycolysis, even in the presence of oxygen (the Warburg effect) has dominated glioblastoma research with respect to tumor metabolism. More recent global profiling experiments, however, have identified roles for lipid, amino acid, and nucleotide metabolism in tumor growth and invasion. A thorough understanding of the metabolic traits that define invasive GBM cells may provide novel therapeutic targets for this devastating disease. In this review, we focus on metabolic alterations that have been characterized in glioblastoma, the dynamic nature of tumor metabolism and how it is shaped by interaction with the brain microenvironment, and how metabolic reprogramming generates vulnerabilities that may be ripe for exploitation.

Glycolysis on F-18 FDG PET/CT Is Superior to Amino Acid Metabolism on C-11 Methionine PET/CT in Identifying Advanced Renal Cell Carcinoma at Staging

Simple Summary

Alteration of metabolism, including glycolysis and glutaminolysis in malignant tumours, has become a hallmark of cancer and related biological aggressiveness. The metabolic signature of each cancer has been actively investigated for potential new drug development. Of the metabolic imaging biomarkers, F-18 fluorodeoxyglucose (FDG) and C-11 methionine positron emission tomography/computed tomography (PET/CT) are widely studied to evaluate the degree of glucose metabolism and amino acid metabolism, respectively. In this prospective study, we found that both F-18 FDG and C-11 methionine uptakes on PET/CT were heterogeneous in renal cell carcinomas, and increased uptake was associated with higher grades of both radiotracers. Additionally, metabolic tumour volume on F-18 FDG PET/CT but not C-11 methionine PET/CT was significant in predicting advanced-stage renal cell carcinoma. These metabolic features derived with PET/CT may help in the development of new drugs targeting glucose and amino acid metabolic pathways.

Abstract

We evaluated the value of F-18 fluorodeoxyglucose (FDG) and C-11 methionine positron emission tomography/computed tomography (PET/CT) to predict high-Fuhrman grade and advanced-stage tumours in patients with renal cell carcinoma (RCC). Forty patients with RCC underwent F-18 FDG and C-11 methionine PET/CT between September 2016 and September 2018. They were classified into limited (stages I and II, n = 15) or advanced stages (stages III and IV, n = 25) according to pathological staging. Logistic regressions were used to predict the advanced stage using various parameters, including maximum standardised uptake value (SUV_max) and metabolic tumour volume (MTV). Receiver operating characteristic analyses were performed to predict high-grade tumours (Fuhrman 3 and 4). On univariate analysis, tumour size, SUV_max and MTV of F-18 FDG and C-11 methionine, and Fuhrman grades were significant predictors for the advanced stage. On multivariate analysis, F-18 FDG MTV > 21.3 cm³ was the most significant predictor (p < 0.001). The area under the curve for predicting high-grade tumours was 0.830 for F-18 FDG (p < 0.001) and 0.726 for C-11 methionine PET/CT (p = 0.014). In conclusion, glycolysis on F-18 FDG PET/CT and amino acid metabolism on C-11 methionine PET/CT were variable but increased in high-grade RCCs. Increased MTV on F-18 FDG PET/CT is a powerful predictor of advanced-stage tumours.

Synthesis, Radiolabeling, and Biological Evaluation of the trans-Stereoisomers of 1-Amino-3-(fluoro-18F)-4-fluorocyclopentane-1-carboxylic Acid as PET Imaging Agents

The enantiomeric non-natural cyclic amino acids (3R,4R)-1-amino-3-fluoro-4-(fluoro-¹⁸F)cyclopentane-1-carboxylic acid and (3S,4S)-1-amino-3-fluoro-4-(fluoro-¹⁸F)cyclopentane-1-carboxylic acid ([ ¹⁸ F]5) have been prepared as a racemic mixture in 1.3% decay corrected radiochemical yield and in greater than 99% radiochemical purity. [ ¹⁸ F]5 is transported primarily via system L with some transport occurring via system ASC, as assessed in rat 9L gliosarcoma, human U87 ΔEGFR glioblastoma, and human DU145 androgen-independent prostate carcinoma tumor cells. In rats bearing intracranial 9L gliosarcoma, [ ¹⁸ F]5 gave tumor to contralateral brain tissue ratios of up to 2.8. Biodistribution studies in healthy rats demonstrated that bladder accumulation is delayed until 10 min postinjection.

Nanotechnology and Nanocarrier-Based Drug Delivery as the Potential Therapeutic Strategy for Glioblastoma Multiforme: An Update

Simple Summary

Glioblastoma multiforme (GBM) are among the most lethal tumors. The highly invasive nature and presence of GBM stem cells, as well as the blood brain barrier (BBB) which limits chemotherapeutic drugs from entering the tumor mass, account for the high chance of treatment failure. Recent developments have found that nanoparticles can be conjugated to liposomes, dendrimers, metal irons, or polymeric micelles, which enhance the drug-loaded compounds to efficiently penetrate the BBB, thus offering new possibilities for overcoming GBM stem cell-mediated resistance to chemotherapy and radiation therapy. In addition, there have been new emerging strategies that use nanocarriers for successful GBM treatment in animal models. This review highlights the recent development of nanotechnology and nanocarrier-based drug delivery for treatment of GBMs, which may be a promising therapeutic strategy for this tumor entity.

Abstract

Glioblastoma multiforme (GBM) is the most common and malignant brain tumor with poor prognosis. The heterogeneous and aggressive nature of GBMs increases the difficulty of current standard treatment. The presence of GBM stem cells and the blood brain barrier (BBB) further contribute to the most important compromise of chemotherapy and radiation therapy. Current suggestions to optimize GBM patients’ outcomes favor controlled targeted delivery of chemotherapeutic agents to GBM cells through the BBB using nanoparticles and monoclonal antibodies. Nanotechnology and nanocarrier-based drug delivery have recently gained attention due to the characteristics of biosafety, sustained drug release, increased solubility, and enhanced drug bioactivity and BBB penetrability. In this review, we focused on recently developed nanoparticles and emerging strategies using nanocarriers for the treatment of GBMs. Current studies using nanoparticles or nanocarrier-based drug delivery system for treatment of GBMs in clinical trials, as well as the advantages and limitations, were also reviewed.

Synthesis, Radiolabeling, and Biological Evaluation of the cis Stereoisomers of 1-Amino-3-Fluoro-4-(fluoro-18F)Cyclopentane-1-Carboxylic Acid as PET Imaging Agents

The non-natural cyclic amino acids (1S,3R,4S)-1-amino-3-fluoro-4-(fluoro-¹⁸F)cyclopentane-1-carboxylic acid ([¹⁸F]9) and (1S,3S,4R)-1-amino-3-fluoro-4-(fluoro-¹⁸F)cyclopentane-1-carboxylic acid ([¹⁸F]28) have been prepared in 10 and 1.7% decay corrected radiochemical yield, respectively, and in greater than 99% radiochemical purity. Cell assays in rat 9L gliosarcoma, human U87 ΔEGFR glioblastoma, and human DU145 androgen-independent prostate carcinoma tumor cells indicated that both compounds are substrates for amino acid transport primarily by system L, with some transport taking place via system ASC. In rats with 9L gliosarcoma, [¹⁸F]9 and [¹⁸F]28 provided high tumor to normal brain tissue ratios, with maximal ratios of 3.5 and 4.1, respectively. Biodistribution studies in healthy rats confirmed that both compounds are BBB permeable and that bladder accumulation is low until at least 5 min post injection.

A preliminary PET radiomics study of brain metastases using a fully automatic segmentation method

Background

Positron Emission Tomography (PET) is increasingly utilized in radiomics studies for treatment evaluation purposes. Nevertheless, lesion volume identification in PET images is a critical and still challenging step in the process of radiomics, due to the low spatial resolution and high noise level of PET images. Currently, the biological target volume (BTV) is manually contoured by nuclear physicians, with a time expensive and operator-dependent procedure.

This study aims to obtain BTVs from cerebral metastases in patients who underwent L-[¹¹C]methionine (11C-MET) PET, using a fully automatic procedure and to use these BTVs to extract radiomics features to stratify between patients who respond to treatment or not. For these purposes, 31 brain metastases, for predictive evaluation, and 25 ones, for follow-up evaluation after treatment, were delineated using the proposed method. Successively, 11C-MET PET studies and related volumetric segmentations were used to extract 108 features to investigate the potential application of radiomics analysis in patients with brain metastases. A novel statistical system has been implemented for feature reduction and selection, while discriminant analysis was used as a method for feature classification.

Results

For predictive evaluation, 3 features (asphericity, low-intensity run emphasis, and complexity) were able to discriminate between responder and non-responder patients, after feature reduction and selection. Best performance in patient discrimination was obtained using the combination of the three selected features (sensitivity 81.23%, specificity 73.97%, and accuracy 78.27%) compared to the use of all features. Secondly, for follow-up evaluation, 8 features (SUV_mean, SUL_peak, SUV_min, SUL_peak prod-surface-area, SUV_mean prod-sphericity, surface mean SUV 3, SUL_peak prod-sphericity, and second angular moment) were selected with optimal performance in discriminant analysis classification (sensitivity 86.28%, specificity 87.75%, and accuracy 86.57%) outperforming the use of all features.

Conclusions

The proposed system is able i) to extract 108 features for each automatically segmented lesion and ii) to select a sub-panel of 11C-MET PET features (3 and 8 in the case of predictive and follow-up evaluation), with valuable association with patient outcome. We believe that our model can be useful to improve treatment response and prognosis evaluation, potentially allowing the personalization of cancer treatment plans.

Enzyme-mediated depletion of serum l-Met abrogates prostate cancer growth via multiple mechanisms without evidence of systemic toxicity

Extensive studies in prostate cancer and other malignancies have revealed that l-methionine (l-Met) and its metabolites play a critical role in tumorigenesis. Preclinical and clinical studies have demonstrated that systemic restriction of serum l-Met, either via partial dietary restriction or with bacterial l-Met-degrading enzymes exerts potent antitumor effects. However, administration of bacterial l-Met-degrading enzymes has not proven practical for human therapy because of problems with immunogenicity. As the human genome does not encode l-Met-degrading enzymes, we engineered the human cystathionine-γ-lyase (hMGL-4.0) to catalyze the selective degradation of l-Met. At therapeutically relevant dosing, hMGL-4.0 reduces serum l-Met levels to >75% for >72 h and significantly inhibits the growth of multiple prostate cancer allografts/xenografts without weight loss or toxicity. We demonstrate that in vitro, hMGL-4.0 causes tumor cell death, associated with increased reactive oxygen species, S-adenosyl-methionine depletion, global hypomethylation, induction of autophagy, and robust poly(ADP-ribose) polymerase (PARP) cleavage indicative of DNA damage and apoptosis.

Met-PET uptake index for total tumor resection: identification of 11C-methionine uptake index as a goal for total tumor resection including infiltrating tumor cells in glioblastoma

Glioblastoma multiforme (GBM) is largely due to glioma stem cells (GSCs) that escape from total resection of gadolinium (Gd)-enhanced tumor on MRI. The aim of this study is to identify the imaging requirements for maximum resection of GBM with infiltrating GSCs. We investigated the relationship of tumor imaging volume between MRI and ¹¹C-methionine (Met)-PET and also the relationship between Met uptake index and tumor activity. In ten patients, tumor-to-contralateral normal brain tissue ratio (TNR) was calculated to evaluate metabolic activity of Met uptake areas which were divided into five subareas by the degrees of TNR. In each GBM, tumor tissue was obtained from subareas showing the positive Met uptake. Immunohistochemistry was performed to examine the tumor proliferative activity and existence of GSCs. In all patients, the volume of Met uptake area at TNR ≦ 1.4 was larger than that of the Gd-enhanced area. The Met uptake area at TNR 1.4 beyond the Gd-enhanced tumor was much wider in high invasiveness-type GBMs than in those of low invasiveness type, and survival was much shorter in the former than the latter types. Immunohistochemistry revealed the existence of GSCs in the area showing Met uptake at TNR 1.4 and no Gd enhancement. Areas at TNR > 1.4 included active tumor cells with relatively high Ki-67 labeling index. In addition, it was demonstrated that GSCs could exist beyond the border of Gd-enhanced tumor. Therefore, to obtain maximum resection of GBMs, including infiltrating GSCs, aggressive surgical excision that includes the Met-positive area at TNR 1.4 should be considered.

The Molecular Effects of Ionizing Radiations on Brain Cells: Radiation Necrosis vs. Tumor Recurrence

The central nervous system (CNS) is generally resistant to the effects of radiation, but higher doses, such as those related to radiation therapy, can cause both acute and long-term brain damage. The most important results is a decline in cognitive function that follows, in most cases, cerebral radionecrosis. The essence of radio-induced brain damage is multifactorial, being linked to total administered dose, dose per fraction, tumor volume, duration of irradiation and dependent on complex interactions between multiple brain cell types. Cognitive impairment has been described following brain radiotherapy, but the mechanisms leading to this adverse event remain mostly unknown. In the event of a brain tumor, on follow-up radiological imaging often cannot clearly distinguish between recurrence and necrosis, while, especially in patients that underwent radiation therapy (RT) post-surgery, positron emission tomography (PET) functional imaging, is able to differentiate tumors from reactive phenomena. More recently, efforts have been done to combine both morphological and functional data in a single exam and acquisition thanks to the co-registration of PET/MRI. The future of PET imaging to differentiate between radionecrosis and tumor recurrence could be represented by a third-generation PET tracer already used to reveal the spatial extent of brain inflammation. The aim of the following review is to analyze the effect of ionizing radiations on CNS with specific regard to effect of radiotherapy, focusing the attention on the mechanism underling the radionecrosis and the brain damage, and show the role of nuclear medicine techniques to distinguish necrosis from recurrence and to early detect of cognitive decline after treatment.

Folate can promote the methionine-dependent reprogramming of glioblastoma cells towards pluripotency

Methionine dependency of tumor growth, although not well-understood, is detectable by ¹¹C-methionine positron emission tomography and may contribute to the aggressivity of glioblastomas (GBM) and meningiomas. Cytosolic folate cycle is required for methionine synthesis. Its dysregulation may influence cell reprogramming towards pluripotency. We evaluated methionine-dependent growth of monolayer (ML) cells and stem cell-like tumor spheres (TS) derived from 4 GBM (U251, U87, LN299, T98G) and 1 meningioma (IOMM-LEE) cell lines. Our data showed that for all cell lines studied, exogenous methionine is required for TS formation but not for ML cells proliferation. Furthermore, for GBM cell lines, regardless of the addition of folate cycle substrates (folic acid and formate), the level of 3 folate isoforms, 5-methytetrahydrofolate, 5,10-methenyltetrahydrofolate, and 10-formyltetrahydrofolate, were all downregulated in TS relative to ML cells. Unlike GBM cell lines, in IOMM-LEE cells, 5-methyltetrahydrofolate was actually more elevated in TS than ML, and only 5,10-methenyltetrahydrofolate and 10-formyltetrahydrofolate were downregulated. The functional significance of this variation in folate cycle repression was revealed by the finding that Folic Acid and 5-methyltetrahydrofolate promote the growth of U251 TS but not IOMM-LEE TS. Transcriptome-wide sequencing of U251 cells revealed that DHFR, SHMT1, and MTHFD1 were downregulated in TS vs ML, in concordance with the low activity cytosolic folate cycle observed in U251 TS. In conclusion, we found that a repressed cytosolic folate cycle underlies the methionine dependency of GBM and meningioma cell lines and that 5-methyltetrahydrofolate is a key metabolic switch for glioblastoma TS formation. The finding that folic acid facilitates TS formation, although requiring further validation in diseased human tissues, incites to investigate whether excessive folate intake could promote cancer stem cells formation in GBM patients.

IDH-wildtype glioblastomas and grade III/IV IDH-mutant gliomas show elevated tracer uptake in fibroblast activation protein-specific PET/CT

PURPOSE

Targeting fibroblast activation protein (FAP) is a new diagnostic approach allowing the visualization of tumor stroma. Here, we applied FAP-specific PET imaging to gliomas. We analyzed the target affinity and specificity of two FAP ligands (FAPI-02 and FAPI-04) in vitro, and the pharmacokinetics and biodistribution in mice in vivo. Clinically, we used ⁶⁸Ga-labeled FAPI-02/04 for PET imaging in 18 glioma patients (five IDH-mutant gliomas, 13 IDH-wildtype glioblastomas).

METHODS

For binding studies with ¹⁷⁷Lu-radiolabeled FAPI-02/04, we used the glioblastoma cell line U87MG, FAP-transfected fibrosarcoma cells, and CD26-transfected human embryonic kidney cells. For pharmacokinetic and biodistribution studies, U87MG-xenografted mice were injected with ⁶⁸Ga-labeled compounds followed by small-animal PET imaging and ¹⁷⁷Lu-labeled FAPI-02/04, respectively. Clinical PET/CT scans were performed 30 min post intravenous administration of ⁶⁸Ga-FAPI-02/04. PET and MRI scans were co-registrated. Immunohistochemistry was done on 14 gliomas using a FAP-specific antibody.

RESULTS

FAPI-02 and FAPI-04 showed high binding specificity to FAP. FAPI-04 demonstrated higher tumor accumulation and delayed elimination compared with FAPI-02 in preclinical studies. IDH-wildtype glioblastomas and grade III/IV, but not grade II, IDH-mutant gliomas showed elevated tracer uptake. In glioblastomas, we observed spots with increased uptake in projection on contrast-enhancing areas. Immunohistochemistry showed FAP-positive cells with mainly elongated cell bodies and perivascular FAP-positive cells in glioblastomas and an anaplastic IDH-mutant astrocytoma.

CONCLUSIONS

Using FAP-specific PET imaging, increased tracer uptake in IDH-wildtype glioblastomas and high-grade IDH-mutant astrocytomas, but not in diffuse astrocytomas, may allow non-invasive distinction between low-grade IDH-mutant and high-grade gliomas. Therefore, FAP-specific imaging in gliomas may be useful for follow-up studies although further clinical evaluation is required.

Comparison of L-Methyl-11C-Methionine PET With Magnetic Resonance Spectroscopy in Detecting Newly Diagnosed Glioma

AIMS

Amino acid PET and magnetic resonance spectroscopy (MRS) are at the forefront of noninvasive imaging techniques used for detection and subtyping of glioma-suspicious lesions. In this pilot study, we compare L-methyl-C-methionine PET and MRS for their ability to predict glioma subtypes.

METHODS

Nineteen patients with histologically, confirmed newly diagnosed glioma underwent preoperative L-methyl-C-methionine PET and MRS in 1 diagnostic session. According to the molecular portfolio and histopathologic diagnosis, patients were subdivided in isocitrate dehydrogenase (IDH) wild-type glioblastoma, IDH wild-type grade II/III glioma, IDH-mutant grade II/III glioma without 1p/19q codeletion, and with 1p/19q codeletion subgroups. Maximum tumor-to-brain ratio (TBRmax), creatine, choline, and N-acetyl aspartate peaks were correlated with postoperative histopathologic tumor diagnoses.

RESULTS

Maximum tumor-to-brain ratio was highest in glioblastoma patients (4.18) followed by patients with IDH wild-type grade II and III glioma (3.41). The latter TBRmax values were higher compared with those in patients with IDH-mutant grade II/III glioma without 1p/19q codeletion (1.95) and in patients with IDH-mutant 1p/19q codeleted grade II and III glioma (2.79). Magnetic resonance spectroscopy marker distribution showed no clear trend. Receiver operating characteristic analysis revealed TBRmax to be the best performing parameter in identifying IDH status (area under the curve, 0.67) and all spectroscopy markers combined in identifying glioma subgroups (area under the curve, 0.68), respectively.

CONCLUSIONS

L-Methyl-C-methionine PET and MRS bear limited potential in glioma subgrouping. L-Methyl-C-methionine PET appears to be superior in differentiating IDH status, whereas MRS is more helpful in glioma subgrouping.

Relationship between Malignant Brain Tumors and Values of Homocysteine, Folic Acid and Vitamin B12

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults. Homocysteine (Hcy) has a detrimental influence on human neurons, considering that human GBM cells undergo cell death already at D,L-Hcy concentrations in culture medium of 50 μM. Th is data demonstrate that Hcy is a potent gliotoxic agent capable of inducing the death of human glial cells already at concentrations reached in brain during hyperhomocysteinemia. The one retrospective study found that the serum vitamin B12 level can be used to predict survival time in metastatic cancer patients including neurological cancer. Cancer risk increases with elevated vitamin B12 level, mostly within the first year of the follow-up period, suggesting that vitamin B12 level could be used as a cancer diagnostic marker. In addition, the relationship between elevated vitamin B12 level and poor cancer survival time has been reported. Previous investigation suggests that the folate supplementation could be used as an adjuvant in antiglioma therapy to limit the low DNA methylation level because this confers a poor prognosis in glioblastoma multiforme patients. Taking into account all presented data, it can be concluded that effect of homocystein, folic acid and vitamin B12 on formation, development and outcome of treatment in patients with carcinoma is very intriguing question, whose response requires additional both experimental and clinical research. There lack of data in the literature on the incidence of elevated levels of Hcy in the blood, as well as the disorders of folic acid and vitamin B12, at malignant tumors of the brain.

Evaluation of 11C-Methionine PET and Anatomic MRI Associations in Diffuse Intrinsic Pontine Glioma

The role of metabolic imaging in the diagnosis, treatment, and response assessment of diffuse intrinsic pontine glioma (DIPG) is poorly defined. We investigated the uptake of ¹¹C-methionine in pediatric patients with newly diagnosed DIPG and evaluated the associations of ¹¹C-methionine PET metrics with conventional MRI indices and survival outcomes. Methods: Twenty-two patients with newly diagnosed DIPG were prospectively enrolled on an institutional review board-approved investigational study of ¹¹C-methionine PET. All patients underwent baseline ¹¹C-methionine PET/CT, and initial treatment-response scans after chemotherapy or radiation therapy were obtained for 17 patients. Typical and atypical DIPGs were assessed clinically and radiographically and defined by multidisciplinary consensus. Three-dimensional regions of interest, reviewed by consensus between a nuclear medicine physician and a radiation oncologist, were delineated after coregistration of PET and MR images. Associations of ¹¹C-methionine uptake intensity and uniformity with survival, along with associations between ¹¹C-methionine uptake and conventional MRI tumor indices over time, were evaluated. ¹¹C-methionine PET voxel values within regions of interest were assessed as threshold values across proportions of the study population, and ¹¹C-methionine uptake at baseline was assessed relative to MRI-defined tumor progression. Results: ¹¹C-methionine uptake above that of uninvolved brain tissue was observed in 18 of 22 baseline scans (82%) and 15 of 17 initial response scans (88%). ¹¹C-methionine avidity within MRI-defined tumor was limited in extent, with 11 of 18 positive baseline ¹¹C-methionine PET scans (61%) showing less than 25% ¹¹C-methionine-avid tumor. The increase in total tumor volume with ¹¹C-methionine PET was relatively limited (17.2%; interquartile range, 6.53%-38.90%), as was the extent of ¹¹C-methionine uptake beyond the MRI-defined tumor (2.2%; interquartile range, 0.55%-10.88%). Although baseline ¹¹C-methionine PET intensity and uniformity metrics did not correlate with survival outcomes, initial ¹¹C-methionine avidity overlapped with recurrent tumor in 100% of cases. A clinical diagnosis of atypical DIPG was associated with borderline significantly prolonged progression-free survival (P  =  0.07), yet ¹¹C-methionine PET indices at diagnosis did not differ significantly between atypical and typical DIPGs. Conclusion: Most newly diagnosed DIPGs are successfully visualized by ¹¹C-methionine PET. Baseline ¹¹C-methionine uptake delineates regions at increased risk for recurrence, yet intensity and uniformity metrics did not correlate with treatment outcomes in children with DIPG in this study.