Evaluation of brain tumors using dynamic 11C-methionine-PET

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.

Methionine metabolism and endocrine function of the pituitary gland in patients with suprasellar germinoma

PURPOSE

The aim of this study was to investigate the association between methionine (MET) metabolism and endocrine function of the pituitary gland in patients with suprasellar region tumor.

MATERIALS AND METHODS

Twenty patients with intracranial germinoma were included in this study. Initial staging and all surveillance MET PET/CT scans and comparable serum levels of follicle stimulating hormone (FSH), luteinizing hormone (LH), and thyroid stimulating hormone (TSH) were analyzed. The patients were divided into two groups according to tumor location, with tumors in the suprasellar region (condition) or not (control). MET uptake of the pituitary gland (i.e., SUVR [standardized uptake value ratio]) and levels of FSH, LH, TSH were compared in the condition and control groups and in the before and after treatment phases of each group.

RESULTS

The SUVR in the control group was like that found in normal pituitary glands in previous studies, whereas the SUVR of the untreated condition group was high and that of treated condition group was low with significance compared to the control group. Serum levels of pituitary hormones in before and after treatment condition groups were significantly lower than those in the control group. The FSH and LH levels of curatively treated patients in the control group were positively correlated with SUVR with respective ß values of 3.71 and 0.98 (p < .001). The TSH level of the treated condition group was negatively correlated with SUVR (ß = -1.02, p < .001).

CONCLUSION

This study is the first known investigation to examine the association between MET metabolism and endocrine function of the pituitary gland, and it confirmed that MET metabolism reflects endocrine function. A future study validating the result of correlation analysis is warranted.

Differentiation of astrocytoma between grades II and III using a combination of methionine positron emission tomography and magnetic resonance spectroscopy

Objective

This study aimed to establish a method for differentiating between grades II and III astrocytomas using preoperative imaging.

Methods

We retrospectively analyzed astrocytic tumors, including 18 grade II astrocytomas (isocitrate dehydrogenase (IDH)-mutant: IDH-wildtype = 8:10) and 56 grade III anaplastic astrocytomas (37:19). We recorded the maximum methionine (MET) uptake ratios (tumor-to-normal: T/N) on positron emission tomography (PET) and three MRS peak ratios: choline (Cho)/creatine (Cr), N-acetyl aspartate (NAA)/Cr, and Cho/NAA, between June 2015 and June 2020. We then evaluated the cut-off values to differentiate between grades II and III. We compared the grading results between contrast enhancement effects on MR and combinational diagnostic methods (CDM) on a scatter chart using the cutoff values of the T/N ratio and MRS parameters.

Results

The IDH-mutant group showed significant differences in the Cho/NAA ratio between grades II and III using univariate analysis; however, multiple regression analysis results negated this. The IDH-wildtype group showed no significant differences between the groups. Contrast enhancement effects also showed no significant differences in IDH status. Accordingly, regardless of the IDH status, no statistically independent factors differentiated between grades II and III. However, CDMs showed higher sensitivity and negative predictive value in distinguishing them than MRI contrast examinations for both IDH statuses. We demonstrated a significantly higher diagnostic rate of grade III than of grade II with CDM, which was more striking in the IDH-mutant group than in the wild-type group.

Conclusions

CDM could be valuable in differentiating between grade II and III astrocytic tumors.

Selective resection of cushing microadenoma guided by preoperative hybrid 18-fluoroethyl-L-tyrosine and 11-C-methionine PET/MRI

PURPOSE

11-C-methionine (MET)-positron emission tomography (PET) as an adjunct to magnetic resonance imaging (MRI) has been proposed as a suitable molecular imaging modality for localizing pituitary adenomas in Cushing's disease. 18-F-Fluoroethyl-L-tyrosine (FET)-PET, which is more widely available has not yet been reported in this context.

METHODS

Retrospective double-center cohort study on 15 patients who underwent transsphenoidal surgery for biochemically proven Cushing's disease between 2011 and 2019. Preoperative MET-PET/MRI and/or FET-PET/MRI were compared with intraoperative and histopathological examinations using the Mann Whitney U test and the Fisher's Exact test, along with positive predictive value calculations.

RESULTS

Fifteen patients were included, with a mean age of 47.2 (18-69) years. Six patients received either a MET-PET/MRI or a FET-PET/MRI and 3 patients both exams, respectively. 67% of the tumors were detected by MRI (MET-PET-group [56%]; FET-PET-group [78%]). All tumors were microadenomas with a mean adenoma volume of 0.19 cm³ (0.02-0.78), all of which displayed a circumscribed pathological FET- and/or MET-uptake. FET-PET/MRI results positively correlated with the localization of the tumor confirmed intraoperatively and histopathologically in all cases, resulting in a sensitivity and specificity of FET-PET/MRI for tumor localization of 100% (95% CI 66.37-100%). One MET-PET/MRI suggested a localization contralateral to the expected spot. The sensitivity and specificity of MET-PET for tumor localization hence was 89% (95% CI 51.75-99.72%).

CONCLUSIONS

Preoperative hybrid FET-PET/MRI and MET-PET/MRI have a high predictive value in localizing corticotroph adenoma for selective adenomectomy in Cushing's disease.

Dynamic 11C-Methionine PET-CT: Prognostic Factors for Disease Progression and Survival in Patients with Suspected Glioma Recurrence

Simple Summary

Recurrence after initial treatments is an expected event in glioma patients, particularly for high-grade glioma, with a median progression-free survival of 8–11 weeks. The prognostic evaluation of disease is a crucial step in the planning of therapeutic strategies, in both the primary and recurrence stages of disease. The aim of our retrospective study was to assess the prognostic value of ¹¹C-methionine PET-CT dynamic and semiquantitative parameters in patients with suspected glioma recurrence at MR, in terms of progression-free survival and overall survival. In a population of sixty-seven consecutive patients, both static and kinetic analyses provided parameters (i.e., tumour-to-background ratio and SUVmax associated with time-to-peak, respectively) able to predict both progression-free and overall survival in the whole population and in the high-grade glioma subgroup of patients. Dynamic ¹¹C-methionine PET-CT can be a useful diagnostic tool, in patients with suspicion of glioma recurrence, able to produce significant prognostic indices.

Abstract

Purpose: The prognostic evaluation of glioma recurrence patients is important in the therapeutic management. We investigated the prognostic value of ¹¹C-methionine PET-CT (MET-PET) dynamic and semiquantitative parameters in patients with suspected glioma recurrence. Methods: Sixty-seven consecutive patients who underwent MET-PET for suspected glioma recurrence at MR were retrospectively included. Twenty-one patients underwent static MET-PET; 46/67 underwent dynamic MET-PET. In all patients, SUVmax, SUVmean and tumour-to-background ratio (T/B) were calculated. From dynamic acquisition, the shape and slope of time-activity curves, time-to-peak and its SUVmax (SUVmax_TTP) were extrapolated. The prognostic value of PET parameters on progression-free (PFS) and overall survival (OS) was evaluated using Kaplan–Meier survival estimates and Cox regression. Results: The overall median follow-up was 19 months from MET-PET. Recurrence patients (38/67) had higher SUVmax (p = 0.001), SUVmean (p = 0.002) and T/B (p < 0.001); deceased patients (16/67) showed higher SUVmax (p = 0.03), SUVmean (p = 0.03) and T/B (p = 0.006). All static parameters were associated with PFS (all p < 0.001); T/B was associated with OS (p = 0.031). Regarding kinetic analyses, recurrence (27/46) and deceased (14/46) patients had higher SUVmax_TTP (p = 0.02, p = 0.01, respectively). SUVmax_TTP was the only dynamic parameter associated with PFS (p = 0.02) and OS (p = 0.006). At univariate analysis, SUVmax, SUVmean, T/B and SUVmax_TTP were predictive for PFS (all p < 0.05); SUVmax_TTP was predictive for OS (p = 0.02). At multivariate analysis, SUVmax_TTP remained significant for PFS (p = 0.03). Conclusion: Semiquantitative parameters and SUVmax_TTP were associated with clinical outcomes in patients with suspected glioma recurrence. Dynamic PET-CT acquisition, with static and kinetic parameters, can be a valuable non-invasive prognostic marker, identifying patients with worse prognosis who require personalised therapy.

[Dynamic11C-methionine PET/CT in differential diagnosis of brain gliomas]

OBJECTIVE

To evaluate the possibilities of dynamic preoperative ¹¹C-methionine (MET) PET/CT in differential diagnosis of various types of brain gliomas in adults.

MATERIAL AND METHODS

The study included 74 patients aged 48±14 years with supratentorial gliomas: Grade IV - glioblastoma (GB, n=33), Grade III - anaplastic oligodendroglioma (AOD, n=10) and anaplastic astrocytoma (AA, n=12), Grade II - diffuse astrocytoma (DA, n=13) and oligodendroglioma (OD, n=6). All patients underwent standard MRI and dynamic MET PET/CT within 20 minutes after intravenous injection of radiopharmaceutical. Then, we compared MRI and PET/CT data and comprehensively analyzed the early stages of time-activity curve using 2 parameters: the first pass peak (FPP) and the first peak of maximum uptake (Pmax).

RESULTS

We have significantly distinguished high-grade tumors (GB and AA+AOD) and certain benign gliomas (DA and OD) (p<0.05). AUC was over 0.7 and 0.8 for FPP and Pmax in differential diagnosis of various gliomas, respectively. We found that difficulties in differential diagnosis of gliomas arise mainly if oligodendrogliomas are included in the control group.

CONCLUSION

Dynamic PET/CT with analysis of FPP and Pmax increases specificity of differential diagnosis of various gliomas compared to standard static imaging. These data are valuable for choice of optimal treatment strategy, as well as fundamental research of metabolic processes and vascularization of various tumors.

Combination Methionine-methylation-axis Blockade: A Novel Approach to Target the Methionine Addiction of Cancer

BACKGROUND/AIM

Cancers are selectively sensitive to methionine (MET) restriction (MR) due to their addiction to MET which is overused for elevated methylation reactions. MET addiction of cancer was discovered by us 45 years ago. MR of cancer results in depletion of S-adenosylmethionine (SAM) for transmethylation reactions, resulting in selective cancer-growth arrest in the late S/G₂-phase of the cell cycle. The aim of the present study was to determine if blockade of the MET-methylation axis is a highly-effective strategy for cancer chemotherapy.

MATERIALS AND METHODS

In the present study, we demonstrated the efficacy of MET-methylation-axis blockade using MR by oral-recombinant methioninase (o-rMETase) combined with decitabine (DAC), an inhibitor of DNA methylation, and an inhibitor of SAM synthesis, cycloleucine (CL). We determined a proof-of-concept of the efficacy of the MET-methylation-axis blockade on a recalcitrant undifferentiated/unclassified soft-tissue sarcoma (USTS) patient-derived orthotopic xenograft (PDOX) mouse model.

RESULTS

The o-rMETase-CL-DAC combination regressed the USTS PDOX with extensive cancer necrosis.

CONCLUSION

The new concept of combination MET-methylation-axis blockade is effective and can now be tested on many types of recalcitrant cancer.

Validation of PET/MRI attenuation correction methodology in the study of brain tumours

BACKGROUND

This study aims to compare proton density weighted magnetic resonance imaging (MRI) zero echo time (ZTE) and head atlas attenuation correction (AC) to the reference standard computed tomography (CT) based AC for 11C-methionine positron emission tomography (PET)/MRI.

METHODS

A retrospective cohort of 14 patients with suspected or confirmed brain tumour and 11C-Methionine PET/MRI was included in the study. For each scan, three AC maps were generated: ZTE-AC, atlas-AC and reference standard CT-AC. Maximum and mean standardised uptake values (SUV) were measured in the hotspot, mirror region and frontal cortex. In postoperative patients (n = 8), SUV values were additionally obtained adjacent to the metal implant and mirror region. Standardised uptake ratios (SUR) hotspot/mirror, hotspot/cortex and metal/mirror were then calculated and analysed with Bland-Altman, Pearson correlation and intraclass correlation reliability in the overall group and subgroups.

RESULTS

ZTE-AC demonstrated narrower SD and 95% CI (Bland-Altman) than atlas-AC in the hotspot analysis for all groups (ZTE overall ≤ 2.84, - 1.41 to 1.70; metal ≤ 1.67, - 3.00 to 2.20; non-metal ≤ 3.04, - 0.96 to 3.38; Atlas overall ≤ 4.56, - 1.05 to 3.83; metal ≤ 3.87, - 3.81 to 4.64; non-metal ≤ 4.90, - 1.68 to 5.86). The mean bias for both ZTE-AC and atlas-AC was ≤ 2.4% compared to CT-AC. In the metal region analysis, ZTE-AC demonstrated a narrower mean bias range-closer to zero-and narrower SD and 95% CI (ZTE 0.21-0.48, ≤ 2.50, - 1.70 to 2.57; Atlas 0.56-1.54, ≤ 4.01, - 1.81 to 4.89). The mean bias for both ZTE-AC and atlas-AC was within 1.6%. A perfect correlation (Pearson correlation) was found for both ZTE-AC and atlas-AC compared to CT-AC in the hotspot and metal analysis (ZTE ρ 1.00, p < 0.0001; atlas ρ 1.00, p < 0.0001). An almost perfect intraclass correlation coefficient for absolute agreement was found between Atlas-, ZTE and CT maps for maxSUR and meanSUR values in all the analyses (ICC > 0.99).

CONCLUSIONS

Both ZTE and atlas-AC showed a good performance against CT-AC in patients with brain tumour.

Preliminary clinical assessment of dynamic carbon-11 methionine positron-emission tomography/computed tomography for the diagnosis of the pathologies in patients with musculoskeletal lesions: a prospective study

Background

This study prospectively assessed the diagnostic capacity of dynamic carbon-11 methionine (C-11 MET) positron-emission tomography (PET)/computed tomography for the diagnosis of pathologies in patients with primary unknown musculoskeletal lesions (MSLs). In total, 13 patients with MSLs underwent dynamic scans (5–10 [phase 1], 10–15 [phase 2], 15–20 [phase 3], 20–25 [phase 4], 25–30 [phase 5], and 30–35 [phase 6] min post-injection of C-11 MET). We statistically compared the maximum standardised uptake values (SUVmax) and corresponding retention index for dynamic scans (RI-SUV) for five benign MSLs (BMSLs), five primary malignant musculoskeletal tumours (PMMSTs), four metastatic musculoskeletal tumours (MMSTs), and three malignant lymphoma (ML) cases and explored their diagnostic capacities using receiver operating characteristic (ROC) curve analyses.

Results

SUVmax gradually decreased or remained similar with minimal fluctuations in all BMSL cases and four of five PMMST cases. In contrast, SUVmax increased over time in one case of PMMST and in all cases of MMST and ML. Significant differences were observed in SUVmax for all time phases and RI-SUV between BMSLs and MMSLs, in SUVmax for all time phases between PMMSTs and BMSLs, in SUVmax for all time phases and RI-SUV between non-PMMST-malignant tumours and BMSL, and in RI-SUV between non-PMMST-malignant tumours and PMMST. In ROC analyses, the areas under the curve yielded the highest values at 1.00 for differentiating most intergroup comparisons.

Conclusions

Dynamic C-11 MET PET scans have the potential to be good predictors of discriminating MSLs in patients with primary unknown MSLs in clinical practice.

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.

Dissociation Between 11C-Methionine-Positron Emission Tomography and Gadolinium-Enhanced Magnetic Resonance Imaging in Longitudinal Features of Glioblastoma After Postoperative Radiotherapy

The aims of the present study were to compare the longitudinal changes of glioblastoma multiforme after radiotherapy (RT) between 11C-methionine positron emission tomography (MET-PET) and gadolinium (Gd)-enhanced magnetic resonance imaging (MRI) and to clarify whether these changes were predictive of survival. We included 30 patients, who had undergone MET-PET and Gd-MRI before and every 3 months after RT. The lesion/normal brain uptake (L/N) ratio and contrast-enhancing lesion volume were examined. The L/N ratio was decreased until 9 months after RT with significance until 3 months. The contrast-enhancing lesion volume was decreased until 3 months and thereafter increased until 9 months with significance. The variation rates of the L/N ratio between pre-RT and 3 months differentiated survival of >23 months from ≤23 months. A dissociation could exist in the longitudinal changes of GBM after RT between MET-PET and Gd-MRI. The variation rate of the L/N ratio could be related to survival.

Nuclear medicine of the cerebellum

Single-photon emission computed tomography (SPECT) and positron emission tomography (PET) with different radiotracers enable regional evaluation of blood flow and glucose metabolism, of receptors and transporters of several molecules, and of abnormal deposition of peptides and proteins in the brain. The cerebellum has been used as a reference region for different radiotracers in several disease conditions. Whole-brain voxel-wise analysis is not affected by a priori knowledge bias and should be preferred. SPECT and PET have contributed to establishing the cerebellum role in motion, cognition, and emotion control in physiologic and pathophysiologic conditions. The basic abnormal imaging findings include decreased or increased uptake of flow or metabolism tracers in the cerebellum alone or as part of a network. Decreased uptake is generally observed in primary structural damage of the cerebellum, but can also represent a distant effect of cerebral damage (crossed diaschisis). Increased uptake can be observed in Freidreich ataxia, inflammatory or immune-mediated diseases of the cerebellum, and in status epilepticus. The possibility is also recognized that primary structural damage of the cerebellum might determine distance effects on other brain structures (reversed diaschisis). So far, SPECT and PET have been predominantly used in clinical studies to investigate cerebellar changes in neurologic and psychiatric diseases and in connection with pharmacologic, transcranial magnetic stimulation, deep-brain stimulation, or surgical treatments.

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

The present most common image diagnostic tracer in clinical practice for glioma is ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET) for brain tumors diagnosis and prognosis. PET is a promising molecular imaging technique, which provides real-time information on the metabolic behavior of the tracer. The diffusive nature of glioblastoma (GBM) and heterogeneity often make the radiographic detection by FDG-PET inaccurate, and there is no gold standard. FDG-PET often leads to several controversies in making clinical decisions due to their uptake by normal surrounding tissues, and pose a challenge in delineating treatment-induced necrosis, edema, inflammation, and pseudoprogression. Thus, it is imperative to find new criteria independent of conventional morphological diagnosis to demarcate normal and tumor tissues. We have provided proof of concept studies for ¹¹C methionine-PET (MET-PET) imaging of gliomas, along with prognostic and diagnostic significance. MET-PET is not widely used in the United States, though clinical trials from Japan and Germany suggesting the diagnostic ability of MET-PET imaging are superior to FDG-PET imaging for brain tumors. A major impediment is the availability of the onsite cyclotron and isotopic carbon chemistry facilities. In this article, we have provided the scientific rationale and advantages of the use of MET-PET as GBM tracers. We extend our discussion on the expected pitfalls of using MET-PET and ways to overcome them by incorporating a translational component of profiling gene status in the methionine metabolic pathway. This translational correlative component to the MET-PET clinical trials can lead to a better understanding of the existing controversies and can enhance our knowledge for future randomization of GBM patients based on their tumor gene signatures to achieve better prognosis and treatment outcome.

Uptake of AV-1451 in meningiomas

AIM

AV-1451 is an imaging agent labeled with the positron-emitting radiolabel Fluorine-18. 18F-AV-1451 binds paired helical filament tau (PHF-tau), a pathology related to Alzheimer's disease. In our study of AV-1451 uptake in the brains of cognitively normal subjects, we noted a case of a meningioma with visually significant uptake of AV-1451.

OBJECTIVE

We initiated the present retrospective study to further examine cases of meningioma that underwent AV-1451 imaging.

METHODS

We searched the patient records of 650 patients who had undergone AV-1451 at our institution for the keyword "meningioma" to identify potential cases. PET/CT and MRI results were visually reviewed and semi-quantitative analysis of PET was performed. A paired student's t test was run between background and tumor standard uptake values. Fisher's exact test was used to examine the association between AV-1451 uptake and presence of calcifications on CT.

RESULTS

We identified 12 cases of meningioma, 58% (7/12) of which demonstrated uptake greater than background using both visual analysis and tumor-to-normal cortex ratios (T/N + 1.90 ± 0.83). The paired student's t test revealed no statistically significant difference between background and tumor standard uptake values (p = 0.09); however, cases with a T/N ratio greater than one showed statistically higher uptake in tumor tissue (p = 0.01). A significant association was noted between AV-1451 uptake and presence of calcifications (p = 0.01).

CONCLUSION

AV-1451 PET imaging should be reviewed concurrently with anatomic imaging to prevent misleading interpretations of PHF-tau distribution due to meningiomas.

Clinical Utility of Positron Emission Tomography in Patients with Malignant Glioma

Positron emission tomography (PET) is being increasingly utilized for the management of brain tumors. Herein, we primarily review our previous studies on the use of PET in glioma that utilize three types of tracers: ¹¹C-methionine (MET), ¹¹C-choline, and ¹⁸F-fluorodeoxyglucose. These studies included aspects such as tumor behavior, diagnosis, grade of malignancy, spread and invasion, viability, and genetic deletions; moreover, they also evaluated PET as a tool for planning radiation therapy (RT) and determining its outcome. MET-PET in particular is considered to be the most informative for diagnosis and therapeutic decision-making for glioma patients; it is therefore considered crucial for brain tumor therapy. MET-PET is expected to be widely used for brain tumor patients going forward.

Structural Snapshots of an Engineered Cystathionine-γ-lyase Reveal the Critical Role of Electrostatic Interactions in the Active Site

Enzyme therapeutics that can degrade l-methionine (l-Met) are of great interest as numerous malignancies are exquisitely sensitive to l-Met depletion. To exhaust the pool of methionine in human serum, we previously engineered an l-Met-degrading enzyme based on the human cystathionine-γ-lyase scaffold (hCGL-NLV) to circumvent immunogenicity and stability issues observed in the preclinical application of bacterially derived methionine-γ-lyases. To gain further insights into the structure-activity relationships governing the chemistry of the hCGL-NLV lead molecule, we undertook a biophysical characterization campaign that captured crystal structures (2.2 Å) of hCGL-NLV with distinct reaction intermediates, including internal aldimine, substrate-bound, gem-diamine, and external aldimine forms. Curiously, an alternate form of hCGL-NLV that crystallized under higher-salt conditions revealed a locally unfolded active site, correlating with inhibition of activity as a function of ionic strength. Subsequent mutational and kinetic experiments pinpointed that a salt bridge between the phosphate of the essential cofactor pyridoxal 5'-phosphate (PLP) and residue R62 plays an important role in catalyzing β- and γ-eliminations. Our study suggests that solvent ions such as NaCl disrupt electrostatic interactions between R62 and PLP, decreasing catalytic efficiency.

Optimization of scan initiation timing after 11C-methionine administration for the diagnosis of suspected recurrent brain tumors

OBJECTIVE

¹¹C-Methionine (MET) positron emission tomography (PET) imaging is a valuable technique for the evaluation of primary and recurrent brain tumors. Many studies have used MET-PET for data acquisition starting at 20 min after the tracer injection, while others have used scan initiation times at 5-15 min postinjection. No previous studies have identified the best acquisition timing during MET-PET imaging for suspected recurrent brain tumors. Here we sought to determine the optimal scan initiating timing after MET administration for the detection of recurrent brain tumors.

MATERIALS AND METHODS

Twenty-three consecutive patients with suspected recurrent brain tumors underwent MET-PET examinations. Brain PET images were reconstructed from the four serial data sets (10-15, 15-20, 20-25, and 25-30 min postinjection) that were obtained using the list-mode acquisition technique. We determined the maximal standardized uptake values (SUVmax) of the target lesions and the target-to-normal-tissue ratios (TNRs), calculated as the SUVmax to the SUVmean of a region of interest placed on the normal contralateral frontal cortex. Target lesions without significant MET uptake were excluded.

RESULTS

Thirty-one lesions from 23 patients were enrolled. There were no significant differences in MET SUVmax or TNR values among the PET images that were reconstructed with the data extracted from the four phases postinjection.

CONCLUSION

The MET uptake in the suspected recurrent brain tumors was comparable among all data extraction time phases from 10 to 30 min postinjection. The scan initiation time of MET-PET at 10 min after the injection is allowable for the detection of recurrent brain tumors. The registration identification number of the original study is 1002.

Neuroradiologic characteristics of astroblastoma and systematic review of the literature: 2 new cases and 125 cases reported in 59 publications

BACKGROUND

Astroblastoma is a rare tumor of uncertain origin most commonly presenting in the cerebrum of children and young adults. The literature contains only case reports and small series regarding its radiologic features. This systematic review is the largest study of imaging findings of astroblastoma to date and serves to identify features that might differentiate it from other neoplasms.

OBJECTIVE

This study describes the imaging features of astroblastoma based on a systematic review of the literature and two new cases.

MATERIALS AND METHODS

We conducted a PubMed and Google Scholar database search that identified 59 publications containing 125 cases of pathology-confirmed astroblastoma, and we also added two new cases from our own institution. Data collected include patient age, gender, tumor location, morphology, calcifications and calvarial changes. We recorded findings on CT, MRI, diffusion-weighted imaging (DWI), MR spectroscopy, positron emission tomography (PET) and catheter angiography.

RESULTS

Age at diagnosis ranged 0-70 years (mean 18 years; median 14 years). Female-to-male ratio was 8:1. Of 127 cases, 66 reported CT, 78 reported MRI and 47 reported both findings. Not all authors reported all features, but the tumor features reported included supratentorial in 96% (122/127), superficial in 72% (48/67), well-demarcated in 96% (79/82), mixed cystic-solid in 93% (79/85), and enhancing in 99% (78/79). On CT, 84% (26/31) of astroblastomas were hyperattenuated, 73% (27/37) had calcifications and 7 cases reported adjacent calvarial erosion. Astroblastomas were hypointense on T1-W in 58% (26/45) and on T2-W in 50% (23/46) of MRI sequences. Peritumoral edema was present in 80% (40/50) of cases but was typically described as slight. Six cases included DWI findings, with 100% showing restricted diffusion. On MR spectroscopy, 100% (5/5) showed nonspecific tumor spectra with elevated choline and decreased N-acetylaspartate (NAA). PET revealed nonspecific reduced uptake of [F-18] 2-fluoro-2-deoxyglucose ((18)F-FDG) and increased uptake of [11C]-Methionine in 100% (3/3) of cases. Catheter angiography findings (n=12) were variable, including hypervascularity in 67%, arteriovenous shunting in 33% and avascular areas in 25%.

CONCLUSION

Astroblastomas occur most often in adolescent girls. Imaging often shows a supratentorial, superficial, well-defined, cystic-solid enhancing mass. On CT, most are hyperattenuated, have calcifications, and may remodel adjacent bone if superficial. MRI characteristically reveals a hypointense mass on T1-W and T2-W sequences with restricted diffusion. MR spectroscopy, PET and catheter angiography findings are nonspecific.

Molecular imaging correlates of tryptophan metabolism via the kynurenine pathway in human meningiomas

BACKGROUND

Increased tryptophan metabolism via the kynurenine pathway (KP) is a key mechanism of tumoral immune suppression in gliomas. However, details of tryptophan metabolism in meningiomas have not been elucidated. In this study, we evaluated in vivo tryptophan metabolism in meningiomas and compared it with gliomas using α-[(11)C]-methyl-L-tryptophan (AMT)-PET. We also explored expression patterns of KP enzymes in resected meningiomas.

METHODS

Forty-seven patients with MRI-detected meningioma (n = 16) and glioma (n = 31) underwent presurgical AMT-PET scanning. Tumoral AMT uptake and tracer kinetic parameters (including K and k3' evaluating unidirectional uptake and trapping, respectively) were measured, correlated with meningioma grade, and compared between meningiomas and gliomas. Patterns of KP enzyme expression were assessed by immunohistochemistry in all meningiomas.

RESULTS

Meningioma grade showed a positive correlation with AMT k3' tumor/cortex ratio (r = 0.75, P = .003), and this PET parameter distinguished grade I from grade II/III meningiomas with 92% accuracy. Kinetic AMT parameters could differentiate meningiomas from both low-grade gliomas (97% accuracy by k3' ratios) and high-grade gliomas (83% accuracy by K ratios). Among 3 initial KP enzymes (indoleamine 2,3-dioxygenase 1/2, and tryptophan 2,3-dioxygenase 2 [TDO2]), TDO2 showed the strongest immunostaining, particularly in grade I meningiomas. TDO2 also showed a strong negative correlation with AMT k3' ratios (P = .001).

CONCLUSIONS

PET imaging of tryptophan metabolism can provide quantitative imaging markers for differentiating grade I from grade II/III meningiomas. TDO2 may be an important driver of in vivo tryptophan metabolism in these tumors. These results can have implications for pharmacological targeting of the KP in meningiomas.

Developing biomarker-specific end points in lung cancer clinical trials

In cancer-drug development, a number of different end points have been used to establish efficacy and support regulatory approval, such as overall survival, progression-free survival (PFS), and radiographic response rate. However, these traditional end points have important limitations. For example, in lung cancer clinical trials, evaluating overall survival end points is a protracted process and these end points are most reliable when crossover to the investigational therapy is not permitted. Furthermore, although radiographic surrogate end points, such as PFS and response rate, generally correlate with clinical benefit in the setting of cytotoxic chemotherapy and molecular targeted therapies, novel immunotherapies might have atypical response kinetics, which confounds radiographic interpretation. In this Review, we discuss the need to develop alternative or surrogate end points for lung cancer clinical trials, and focus on several new biomarkers that could serve as surrogate end points, including functional imaging biomarkers, circulating factors (tumour proteins, DNA, and cells), and pharmacodynamic tumour markers. By enabling the size, duration, and complexity of cancer trials to be reduced, biomarker end points hold the promise to accelerate drug development and improve patient outcomes.

Hypofractionated high-dose irradiation with positron emission tomography data for the treatment of glioblastoma multiforme

This research paper presents clinical outcomes of hypofractionated high-dose irradiation by intensity-modulated radiation therapy (Hypo-IMRT) with ¹¹C-methionine positron emission tomography (MET-PET) data for the treatment of glioblastoma multiforme (GBM). A total of 45 patients with GBM were treated with Hypo-IMRT after surgery. Gross tumor volume (GTV) was defined as the area of enhanced lesion on MRI, including MET-PET avid region; clinical target volume (CTV) was the area with 5 mm margin surrounding the GTV; planning target volume (PTV) was the area with 15 mm margin surrounding the CTV, including MET-PET moderate region. Hypo-IMRT was performed in 8 fractions; planning the dose for GTV was escalated to 68 Gy and that for CTV was escalated to 56 Gy, while keeping the dose delivered to the PTV at 40 Gy. Concomitant and adjuvant TMZ chemotherapy was administered. At a median follow-up of 18.7 months, median overall survival (OS) was 20.0 months, and median progression-free survival was 13.0 months. The 1- and 2-year OS rates were 71.2% and 26.3%, respectively. Adjuvant TMZ chemotherapy was significantly predictive of OS on multivariate analysis. Late toxicity included 7 cases of Grade 3-4 radiation necrosis. Hypo-IMRT with MET-PET data appeared to result in favorable survival outcomes for patients with GBM.

Bevacizumab treatment leads to observable morphological and metabolic changes in brain radiation necrosis

We investigated morphological and metabolic changes of radiation necrosis (RN) of the brain following bevacizumab (BEV) treatment by using neuroimaging. Nine patients with symptomatic RN, who had already been treated with radiation therapy for malignant brain tumors (6 glioblastomas, 1 anaplastic oligodendroglioma, and 2 metastatic brain tumors), were enrolled in this prospective clinical study. RN diagnosis was neuroradiologically determined with Gd-enhanced MRI and 11C-methionine positron emission tomography (MET-PET). RN clinical and radiological changes in MRI, magnetic resonance spectroscopy (MRS) and PET were assessed following BEV therapy. Karnofsky performance status scores improved in seven patients (77.8 %). Both volumes of the Gd-enhanced area and FLAIR-high area from MRI decreased in all patients after BEV therapy and the mean size reduction rates of the lesions were 80.0 and 65.0 %, respectively. MRS, which was performed in three patients, showed a significant reduction in Cho/Cr ratio after BEV therapy. Lesion/normal tissue (L/N) ratios in MET- and 11C-choline positron emission tomography (CHO-PET) decreased in 8 (89 %) and 9 patients (100 %), respectively, and the mean L/N ratio reduction rates were 24.4 and 60.7 %, respectively. BEV-related adverse effects of grade 1 or 2 (anemia, neutropenia and lymphocytopenia) occurred in three patients. These results demonstrated that BEV therapy improved RN both clinically and radiologically. BEV therapeutic mechanisms on RN have been suggested to be related not only to the effect on vascular permeability reduction by repairing the blood-brain barrier, but also to the effect on suppression of tissue biological activity, such as immunoreactions and inflammation.

Diagnostic and prognostic application of positron emission tomography in breast imaging: emerging uses and the role of PET in monitoring treatment response

Positron emission tomography (PET) is an imaging modality that using radiotracers, permits real-time dynamic monitoring of biologic processes such as cell metabolic behavior and proliferation, and has proven useful as a research tool for understanding tumor biology. While it does not have a well-defined role in breast cancer for the purposes of screening, diagnosis, or prognosis, emerging PET technologies and uses could expand the applications of PET in breast cancer. Positron emission mammography may provide an alternative adjunct imaging modality for the screening and diagnosis of high-risk patients unable to tolerate MRI. The development of radiotracers with the ability to measure hormonal activity could provide a non-invasive way to assess hormone receptor status and functionality. Finally, the role of PET technologies in monitoring early treatment response may prove particularly useful to research involving new therapeutic interventions.