Amino Acid Tracer Research Articles

Age-Specific Differences in Whole-Body Amino Acid Kinetics

Abstract Objectives Aging is associated with changes in body composition (eg. sarcopenia) but the overall effects of aging on systemic amino acid kinetics need further exploration. We previously reported metabolic differences in certain amino acids between young and older adults using comprehensive metabolic flux analysis. We expanded this novel single stable tracer pulse approach by the addition of several other isotopically-labeled amino acids to confirm and extend our findings in a new cohort of young and older adults. Methods We studied 18 healthy young (∼23 y, 9 females and 9 males) and 16 older adults (∼67 y, 8 females and 8 males) by administering a single dose of a mixture of stable amino acid tracers related to arginine-citrulline, glutamate, branched-chain amino acid (BCAA: leucine, isoleucine, valine), and protein-related metabolism. A baseline blood sample was collected before administration of the pulse tracer followed by 1.5 hours blood sampling protocol. We measured plasma enrichments by LC-MS/MS to calculate their whole body production (WBP) rates and metabolite interconversions. In addition, body composition by dual-energy X-ray absorptiometry was measured. Statistics were performed by unpaired student t-test. Results Older adults had a 13% higher Body Mass Index (P = 0.005) and 13% lower appendicular skeletal muscle index than the younger group (P = 0.04). WBP of glutamate was 26% lower (P < 0.05) in older adults whereas WBP of tau-methylhistidine was higher (31%, P = 0.045), in line with our previously reported data. In addition, older adults were characterized by lower WBP of all 3 BCAAs (P = 0.007), histidine (P = 0.001) and tryptophan (P = 0.003) by 17%, 16%, and 15%, respectively. However, higher whole-body production rates were observed for citrulline (24%, P = 0.036) and de novo arginine synthesis (21%, P = 0.027) in older adults. Conclusions Metabolic flux analysis reveals that the kinetics of a large set of amino acids differ between younger and older adults which indicates that amino acid metabolism is age-related. The clinical relevance of those changes needs further investigation. Funding Sources CTRAL Internal Funds.

Selective synthesis of L-2-[18 F]fluoro-alpha-methylphenylalanine via copper-mediated 18 F-fluorination of (mesityl)(aryl)iodonium salt.

L-2-[18 F]fluoro-alpha-methylphenylalanine (2-[18 F]FAMP) is a promising amino acid tracer for positron emission tomography (PET) imaging, yet the low production yield of direct electrophilic radiofluorination with [18 F]F2 necessitates further optimization of the radiolabeling process. This paper describes a two-step preparation method for L-2-[18 F]fluoro-alpha-methylphenylalanine (2-[18 F]FAMP) starting from [18 F]fluoride. The (Mesityl)(L-alpha-methylphenylalanine)-2-iodonium tetrafluoroborate precursors with various protecting groups were prepared. The copper-mediated 18 F-fluorination of the iodonium salt precursors successfully produced 2-[18 F]FAMP. The highest radio chemical conversion of 57.6% was noted with N-Piv-protected (mesityl)(aryl)iodonium salt in the presence of 5 equivalent of Cu (OTf)2 . Subsequent deprotection with 57% hydrogen iodide produced 2-[18 F]FAMP within 120 min in 21.4 ± 11.7% overall radiochemical yield with >95% radiochemical purity and an enantiomeric excess >99%. The obtained 2-[18 F]FAMP showed comparable biodistribution profiles in normal mice with that of the carrier-added 2-[18 F]FAMP. These results indicate that usefulness of copper mediated 18 F-fluorination for the production of 2-[18 F]FAMP, which would facilitate clinical translation of the promising tumor specific amino acid tracer. Individual facilities could adopt either production method based on radioactivity demand and equipment availability.

An Acute Reduction in Habitual Protein Intake Attenuates Post Exercise Anabolism and May Bias Oxidation-Derived Protein Requirements in Resistance Trained Men.

Protein recommendations for resistance-trained athletes are generally lower than their habitual intakes. Excess protein consumption increases the capacity to oxidize amino acids, which can attenuate post-exercise anabolism and may impact protein requirements determined by stable isotope techniques predicated on amino acid tracer oxidation. We aimed to determine the impact of an acute (5d) reduction in dietary protein intake on post-exercise anabolism in high habitual consumers using the indicator amino acid oxidation (IAAO) technique. Resistance trained men [n = 5; 25 ± 7 y; 73.0 ± 5.7 kg; 9.9 ± 2.9% body fat; 2.69 ± 0.38 g·kg−1·d−1 habitual protein intake) consumed a high (H; 2.2 g·kg−1·d−1) and moderate (M; 1.2 g·kg−1·d−1) protein diet while training every other day. During the High protein phase, participants consumed a 2d controlled diet prior to determining whole body phenylalanine turnover, net balance (NB), and 13CO2 excretion (F13CO2) after exercise via oral [13C]phenylalanine. During the Moderate phase, participants consumed 2.2 g protein·kg−1·d−1 for 2d prior to consuming 1.2 g protein·kg−1·d−1 for 5d. Phenylalanine metabolism was measured on days 1, 3, and 5 (M1, M3, and M5, respectively) of the moderate intake. F13CO2, the primary outcome for IAAO, was ~72 and ~55% greater on the 1st day (M1, P < 0.05) and the third day of the moderate protein diet (M3, P = 0.07), respectively, compared to the High protein trial. Compared to the High protein trial, NB was ~25% lower on the 1st day (M1, P < 0.01) and 15% lower on the third day of the moderate protein diet (M3, P = 0.09). High habitual protein consumption may bias protein requirements determined by traditional IAAO methods that use only a 2d pre-trial controlled diet. Post-exercise whole body anabolism is attenuated following a reduction in protein intake in resistance trained men and may require ~3–5d to adapt. This trial is registered at clinicaltrials.gov as NCT03845569.

Presence or Absence of Skeletal Muscle Dysfunction in Chronic Obstructive Pulmonary Disease is Associated With Distinct Phenotypes

IntroductionReduced skeletal muscle function and cognitive performance are common extrapulmonary features in Chronic Obstructive Pulmonary Disease (COPD) but their connection remains unclear. Whether presence or absence of skeletal muscle dysfunction in COPD patients is linked to a specific phenotype consisting of reduced cognitive performance, comorbidities and nutritional and metabolic disturbances needs further investigation. MethodsThirty-seven patients with COPD (grade II–IV) were divided into two phenotypic cohorts based on the presence (COPD dysfunctional, n=25) or absence (COPD functional, n=12) of muscle dysfunction. These cohorts were compared to 28 healthy, age matched controls. Muscle strength (dynamometry), cognitive performance (Trail Making Test and STROOP Test), body composition (Dual-energy X-Ray Absorptiometry), habitual physical activity, comorbidities and mood status (questionnaires) were measured. Pulse administration of stable amino acid tracers was performed to measure whole body production rates. ResultsPresence of muscle dysfunction in COPD was independent of muscle mass or severity of airflow obstruction but associated with impaired STROOP Test performance (p=0.04), reduced resting O2 saturation (p=0.003) and physical inactivity (p=0.01), and specific amino acid metabolic disturbances (enhanced leucine (p=0.02) and arginine (p=0.06) production). In contrast, COPD patients with normal muscle function presented with anxiety, increased fat mass, plasma glucose concentration, and metabolic syndrome related comorbidities (hypertension and dyslipidemia). ConclusionCOPD patients with muscle dysfunction show characteristics of a cognitive – metabolic impairment phenotype, influenced by the presence of hypoxia, whereas those with normal muscle function present a phenotype of metabolic syndrome and mood disturbances.

Excitatory glutamate transporter EAAC1 as an important transporter of N-(2-[18F]fluoropropionyl)-L-glutamate in oncology PET imaging

IntroductionWe have reported that N-(2-[18F]fluoropropionyl)-L-glutamate ([18F]FPGLU) was a potential amino acid tracer for tumor imaging with positron emission tomography (PET). In this study, the relationship between glutamate transporter excitatory amino acid carrier 1 (EAAC1) expression and [18F]FPGLU uptake in rat C6 glioma cell lines and human SPC-A-1 lung adenocarcinoma cell lines was investigated. MethodsThe uptake of [18F]FPGLU was assessed in ATRA-treated and untreated C6 cell lines, and also in EAAC1 knock-down SPC-A-1(shRNA) cells and SPC-A-1(NT) control cells. PET imaging of [18F]FPGLU was performed on the SPC-A-1 and SPC-A-1 (shRNA)-bearing mice models. ResultsThe uptake of [18F]FPGLU in C6 cells increased significantly after induced by ATRA for 24, 48, and 72 h, which was closely related to expression of EAAC1 in C6 cells (R2 = 0.939). Compared with the SPC-A-1(NT) control cells, the uptake of [18F]FPGLU on EAAC1 knock-down SPC-A-1(shRNA) cells significantly decreased to 64.0%. Moreover, the uptake of [18F]FPGLU in EAAC1 knock-down SPC-A-1(shRNA) xenografts was significantly lower than that in SPC-A-1 xenografts, with tumor/muscle ratios of 3.01 vs. 1.67 at 60 min post-injection of [18F]FPGLU. ConclusionThe transport mechanism of [18F]FPGLU in glioma C6 and lung adenocarcinoma SPC-A-1 cell lines mainly involves in glutamate transporter EAAC1. EAAC1 is an important transporter of N-(2-[18F]fluoropropionyl)-L-glutamate in oncologic PET imaging.

Comprehensive metabolic flux analysis to explain skeletal muscle weakness in COPD.

Metabolic characterization of a well-defined group of patients could be a powerful tool in revealing metabolic signatures to explain limb muscle weakness in chronic diseases. Studies are currently limited in Chronic Obstructive Pulmonary Disease (COPD) to the identification of differential amino acid concentrations but lack comprehensive analysis of the flux through relevant muscle function related metabolic pathways. In 23 stable patients with moderate to very severe COPD and 19 healthy controls, a comprehensive metabolic flux analysis was conducted by administering an intravenous pulse and primed constant infusion of multiple stable tracers of amino acids known to play a role in muscle health. Blood samples were obtained to calculate production (WBP) and interconversion rates, and plasma concentrations of these amino acids. Lower and upper limb muscle strength, muscle mass, lung function, physical activity level, and disease history and characteristics were assessed. The COPD group was characterized by lower and upper limb muscle weakness (P<0.01) despite preserved muscle mass. Higher values were found in COPD for plasma glutamine, WBP of leucine (P<0.001), 3-methylhistidine (P<0.01) (marker of enhanced myofibrillar protein breakdown), citrulline (P<0.05), and arginine to citrulline conversion (P<0.05) (reflecting enhanced nitric oxide synthesis). Plasma concentration of β-hydroxy β-methylbutyrate (HMB with anticatabolic, anabolic and contractile properties), WBP of glycine (precursor of creatine and glutathione), and transcutaneous O2 saturation explained up to 79% and 65% of the variation in strength of the lower and upper limb muscles, respectively, in COPD. Comprehensive metabolic flux analysis revealed a homogenous metabolic signature in stable patients with COPD and a specific metabolic profile in those with skeletal muscle weakness. ClinicalTrials.gov; No. NCT01787682; URL: www.clinicaltrials.gov.

A novel stable isotope tracer method to simultaneously quantify skeletal muscle protein synthesis and breakdown

Background/aimsMethodological challenges have been associated with the dynamic measurement of muscle protein breakdown (MPB), as have the measurement of both muscle protein synthesis (MPS) and MPB within the same experiment. Our aim was to use the transmethylation properties of methionine as proof-of-concept to measure rates of MPB via its methylation of histidine within skeletal muscle myofibrillar proteins, whilst simultaneously utilising methionine incorporation into bound protein to measure MPS. ResultsDuring the synthesis measurement period, incorporation of methyl[D3]-13C-methionine into cellular protein in C2C12 myotubes was observed (representative of MPS), alongside an increase in the appearance of methyl[D3]-methylhistidine into the media following methylation of histidine (representative of MPB). For further validation of this approach, fractional synthetic rates (FSR) of muscle protein were increased following treatment of the cells with the anabolic factors insulin-like growth factor-1 (IGF-1) and insulin, while dexamethasone expectedly reduced MPS. Conversely, rates of MPB were reduced with IGF-1 and insulin treatments, whereas dexamethasone accelerated MPB. ConclusionsThis is a novel stable isotope tracer approach that permits the dual assessment of muscle cellular protein synthesis and breakdown rates, through the provision of a single methionine amino acid tracer that could be utilised in a wide range of biological settings.

NI-11 PATHOLOGICAL ASSESSMENT IN THE IMPACT OF ONE-SHOT BEVACIZUMAB ON UPTAKE OF 11C-METHIONINE

BACKGROUNDThis study aimed to clarify how one-time administration of bevacizumab (BEV) changes histological features in glioblastoma, and how histological changes affect the uptake of 11C-methyl-L-methionine (11C-met) as an amino-acid tracer.MATERIALS AND METHODSSubjects were 18 patients with newly diagnosed glioblastoma who were assigned to 2 groups: BEV group, single intravenous administration of BEV before surgical tumor removal; and control group, surgical tumor removal alone. After surgery, we compared the densities of tumor cells and microvessels, and microvascular structures including vascular pericytes and L-type amino acid transporter-1 (LAT1), between the BEV and control groups. Correlations between 11C-met uptake on positron emission tomography before surgery, microvascular density, and LAT1 expression were assessed in each group.RESULTSBEV induced significant reductions in microvascular density, while tumor cell density and proliferation were retained in the BEV group. Percentages of vessels with pericytes and vascular endothelium with LAT1 expression were lower in the BEV group than in controls. Uptake of 11C-met correlated significantly with microvascular density in the BEV group, but not with LAT1expression.CONCLUSIONSThe present study showed that even one course of BEV administration induced reductions in microvessels, vascular pericytes, and LAT1 expression in glioblastomas. One course of BEV therapy also reduced 11C-met uptake, which might have been largely attributed to reductions in microvessels rather than reductions in LAT1 expression, in addition to reduction of vascular permeability.

Diagnostic Accuracy of PET Tracers for the Differentiation of Tumor Progression from Treatment-Related Changes in High-Grade Glioma: A Systematic Review and Metaanalysis.

Posttreatment high-grade gliomas are usually monitored with contrast-enhanced MRI, but its diagnostic accuracy is limited as it cannot adequately distinguish between true tumor progression and treatment-related changes. According to recent Response Assessment in Neuro-Oncology recommendations, PET overcomes this limitation. However, it is currently unknown which tracer yields the best results. Therefore, a systematic review and metaanalysis were performed to compare the diagnostic accuracy of the different PET tracers in differentiating tumor progression from treatment-related changes in high-grade glioma patients. Methods: PubMed, Web of Science, and Embase were searched systematically. Study selection, data extraction, and quality assessment were performed independently by 2 authors. Metaanalysis was performed using a bivariate random-effects model when at least 5 studies were included. Results: The systematic review included 39 studies (11 tracers). 18F-FDG (12 studies, 171 lesions) showed a pooled sensitivity and specificity of 84% (95% confidence interval, 72%-92%) and 84% (95% confidence interval, 69%-93%), respectively. O-(2-18F-fluoroethyl)-l-tyrosine (18F-FET) (7 studies, 172 lesions) demonstrated a sensitivity of 90% (95% confidence interval, 81%-95%) and specificity of 85% (95% confidence interval, 71%-93%). For S-11C-methyl)-l-methionine (11C-MET) (8 studies, 151 lesions), sensitivity was 93% (95% confidence interval, 80%-98%) and specificity was 82% (95% confidence interval, 68%-91%). The numbers of included studies for the other tracers were too low to combine, but sensitivity and specificity ranged between 93%-100% and 0%-100%, respectively, for 18F-FLT; 85%-100% and 72%-100%, respectively, for 3,4-dihydroxy-6-18F-fluoro-l-phenylalanine (18F-FDOPA); and 100% and 70%-88%, respectively, for 11C-choline. Conclusion:18F-FET and 11C-MET, both amino-acid tracers, showed a comparably higher sensitivity than 18F-FDG in the differentiation between tumor progression and treatment-related changes in high-grade glioma patients. The evidence for other tracers is limited; thus, 18F-FET and 11C-MET are preferred when available. Our results support the incorporation of amino-acid PET tracers for the treatment evaluation of high-grade gliomas.

Diagnostic Performance and Prognostic Value of PET/CT with Different Tracers for Brain Tumors: A Systematic Review of Published Meta-Analyses.

Background: Several meta-analyses reporting data on the diagnostic performance or prognostic value of positron emission tomography (PET) with different tracers in detecting brain tumors have been published so far. This review article was written to summarize the evidence-based data in these settings. Methods: We have performed a comprehensive literature search of meta-analyses published in the Cochrane library and PubMed/Medline databases (from inception through July 2019) about the diagnostic performance or prognostic value of PET with different tracers in patients with brain tumors. Results: We have summarized the results of 24 retrieved meta-analyses on the use of PET or PET/computed tomography (CT) with different tracers in brain tumors. The tracers included were: fluorine-18 fluorodeoxyglucose (18F-FDG), carbon-11 methionine (11C-methionine), fluorine-18 fluoroethyltyrosine (18F-FET), fluorine-18 dihydroxyphenylalanine (18F-FDOPA), fluorine-18 fluorothymidine (18F-FLT), and carbon-11 choline (11C-choline). Evidence-based data demonstrated good diagnostic performance of PET with different tracers in detecting brain tumors, in particular, radiolabelled amino acid tracers showed the highest diagnostic performance values. All the PET tracers evaluated had significant prognostic value in patients with glioma. Conclusions: Evidence-based data showed a good diagnostic performance for some PET tracers in specific indications and significant prognostic value in brain tumors.

An exploration of the methods to determine the protein-specific synthesis and breakdown rates in vivo in humans.

The present study explores the methods to determine human in vivo protein‐specific myofibrillar and collagenous connective tissue protein fractional synthesis and breakdown rates. We found that in human myofibrillar proteins, the protein‐bound tracer disappearance method to determine the protein fractional breakdown rate (FBR) (via 2H2O ingestion, endogenous labeling of 2H‐alanine that is incorporated into proteins, and FBR quantified by its disappearance from these proteins) has a comparable intrasubject reproducibility (range: 0.09–53.5%) as the established direct‐essential amino acid, here L‐ring‐13C6‐phenylalanine, incorporation method to determine the muscle protein fractional synthesis rate (FSR) (range: 2.8–56.2%). Further, the determination of the protein breakdown in a protein structure with complex post‐translational processing and maturation, exemplified by human tendon tissue, was not achieved in this experimentation, but more investigation is encouraged to reveal the possibility. Finally, we found that muscle protein FBR measured with an essential amino acid tracer prelabeling is inappropriate presumably because of significant and prolonged intracellular recycling, which also may become a significant limitation for determination of the myofibrillar FSR when repeated infusion trials are completed in the same participants.

Impacts on Histological Features and 11C-Methyl-L-methionine Uptake After “One-Shot” Administration with Bevacizumab Before Surgery in Newly Diagnosed Glioblastoma

BACKGROUND: Bevacizumab (BEV), an antiangiogenic agent, induces dramatic normalization of the tumor vasculature in glioblastoma. This study aimed to clarify how one-time administration of BEV changes histological features in glioblastoma and how histological changes affect the uptake of 11C-methyl-L-methionine (11C-met) as an amino-acid tracer. MATERIALS AND METHODS: Subjects were 18 patients with newly diagnosed glioblastoma who were assigned to two groups: BEV group, single intravenous administration of BEV before surgical tumor removal; and control group, surgical tumor removal alone. After surgery, we compared the densities of tumor cells and microvessels, and microvascular structures including vascular pericytes and L-type amino acid transporter-1 (LAT1) between the BEV and control groups. Correlations between 11C-met uptake on positron emission tomography before surgery, microvascular density, and LAT1 expression were assessed in each group. RESULTS: BEV induced significant reductions in microvascular density, while tumor cell density and proliferation were retained in the BEV group. Percentages of vessels with pericytes and vascular endothelium with LAT1 expression were lower in the BEV group than in controls. Uptake of 11C-met correlated significantly with microvascular density in the BEV group but not with LAT1expression. CONCLUSIONS: The present study showed that even one course of BEV administration induced reductions in microvessels, vascular pericytes, and LAT1 expression in glioblastomas. One course of BEV therapy also reduced 11C-met uptake, which might have been largely attributed to reductions in microvessels rather than reductions in LAT1 expression.

Facile fully automated radiosynthesis and quality control of O-(2-[18F]fluoroethyl)-l-tyrosine ([18F]FET) for human brain tumor imaging

O-(2-[18F]Fluoroethyl)-l-tyrosine ([18F]FET) has become one of the most successful amino acid tracers for human brain tumor imaging with positron emission tomography (PET). Facile fully automated radiosynthesis and quality control (QC) of [18F]FET using our home-built automated multi-purpose 18F-radiosynthesis module are described. [18F]FET was produced in 75–80 min overall synthesis time with 20–25% radiochemical yield decay corrected to end of bombardment (EOB), based on H[18F]F. The radiochemical and enantiomeric purities were >99%, and the molar activity (Am) was 189–411 GBq/μmol at EOB. The [18F]FET dose meets all QC criteria for clinical use, and is suitable for clinical PET study of brain tumor.

MLTI-18. PRECISION IMAGING OF METASTATIC AND PRIMARY BRAIN TUMORS AFTER RADIATION WITH 18F-FDOPA PET-MRI IS FEASIBLE AND COST EFFECT

PURPOSE: Post-radiation changes in the brain can mimic tumor recurrence on MRI, requiring multiple short term follow-ups to differentiate tumor progression from radiation necrosis. We propose combining functional and anatomic imaging with FDOPA PET tracer in hybrid PET-MRI to improve detection of tumor recurrence. MATERIALS AND METHODS: Seventeen adult patients treated with radiation therapy were identified - four with metastatic disease from breast and lung cancer and thirteen with primary brain glioma (11 IDH wildtype glioblastoma and 2 astrocytoma). Patients were scanned on hybrid PET-MRI (GE Healthcare) with clinical MRI brain sequences and dynamic FDOPA uptake. Dynamic FDOPA uptake within these tumors over 45 minutes after tracer injection was analyzed and compared to ADC histogram analysis. RESULTS: For each of the patients, clinical multi sequence gadolinium enhanced MRI and dynamic PET imaging for up to 45 minutes with 18F-FDOPA amino acid tracer was obtained. The total cost savings of scanning 17 patients in groups was 51.4% ($28,321), as opposed to the cost of individual radiosynthesis performed for each study. Quantitative analysis of tracer uptake in striatum, internal carotid artery, and superior sagittal sinus were performed with appropriate accumulation and subsequent washout of tracer respectively. Successful dynamic FDOPA uptake within the tumor was seen in all patients and ratio of tumor to contralateral ROI were found to range from 1.8–4.5. While raw SUV values did not differentiate between recurrent tumor and radiation changes, T/C SUVmax ratios were elevated to 4.5 in recurrent glioblastoma, 2.5 in hypoxic treated glioblastoma, and 1.8 in non-recurrent metastatic breast cancer after gamma knife treatment. CONCLUSION: Batch imaging of patients with [18F]FDOPA PET-MRI is feasible and cost effective. Understanding radionuclide synthesis process is critical for increasing accessibility of novel PET tracers to patients and results in significant cost savings.

Influx rate of 18F-fluoroaminosuberic acid reflects cystine/glutamate antiporter expression in tumour xenografts.

18F-fluoroaminosuberic acid (18F-FASu) is a recently developed amino acid tracer for positron emission tomography (PET) of oxidative stress that may offer improved tumour assessment over the conventional tracer 18F-fluorodeoxyglucose (18F-FDG). Our aim was to evaluate and relate dynamic 18F-FASu and 18F-FDG uptake with pharmacokinetic modelling to transporter protein expression levels in a panel of diverse tumour xenograft lines. Four different tumour xenograft lines were implanted in female athymic nude mice: MAS98.12 and HBCx3 (breast), TPMX (osteosarcoma) and A549 (lung). Dynamic PET over 60min was performed on a small animal unit. The time-activity curves (TACs) for 18F-FASu and 18F-FDG in individual tumours were used to extract early (SUVE; 2min p.i.) and late (SUVL; 55min p.i.) standardised uptake values. Pharmacokinetic two-tissue compartment models were applied to the TACs to estimate rate constants K1-k4 and blood volume fraction vB. Relative levels of cystine/glutamate antiporter subunit xCT were assessed by western blotting, and expression of GLUT1 and CD31 by immunohistochemistry. 18F-FASu showed higher SUVE, whilst 18F-FDG exhibited higher SUVL. Influx rate K1 for 18F-FASu was significantly correlated with xCT levels (p = 0.001) and was significantly higher than K1 for 18F-FDG (p < 0.001). K1 for 18F-FDG was significantly correlated with GLUT1 levels (p = 0.002). vB estimated from 18F-FASu and 18F-FDG TACs was highly consistent and significantly correlated (r = 0.85, p < 0.001). Two qualitatively different 18F-FASu uptake profiles were identified: type α with low xCT expression and low K1 (A549 and HBCx3), and type β with high xCT expression and high K1 (MAS98.12 and TPMX). The influx rate of 18F-FASu reflects xCT activity in tumour xenografts. Dynamic PET with pharmacokinetic modelling is needed to fully appraise 18F-FASu distribution routes.

Quantifying terrestrial carbon in freshwater food webs using amino acid isotope analysis: Case study with an endemic cavefish

Abstract Flow of terrestrial carbon though aquatic ecosystems (allochthony) is an important but underestimated component of the global carbon cycle. A lack of clear consensus about the importance of allochthonous (terrestrial) organic carbon is sometimes attributed to uncertainties associated with conventional ‘bulk’ isotope data, the most widely used ecological tracer. Amino acid‐specific isotope analysis is an emerging research method promising to address existing limitations of bulk C and N isotope analyses. We tested the efficacy of amino acid δ13C data as a generalizable measure of allochthony by analysing an aggregated dataset (n = 168) of primary and secondary data of carbon sources from disparate geographical locations across the globe. We found the δ13C fingerprints amino acids to be consistently distinct between allochthonous (terrestrial) and autochthonous (aquatic) carbon sources. We also found that our approach is most effective when we use only essential amino acid tracers (i.e. isoleucine, leucine, phenylalanine, threonine and valine). Predictive trends in δ13C fingerprints appear to be largely compatible across studies and/or laboratories. As a case study, we used this approach to quantify the contribution of terrestrial carbon to an endemic cavefish, Cryptotora thamicola, and found that its biomass was comprised largely of autochthonous carbon (~75%).

PET Imaging and Glioblastoma

Abstract INTRODUCTION Patients who present with Glioblastoma have a median survival of around 15 mo, even when treated with the most aggressive methods available. Imaging of glial cell tumours is faced with multiple challenges, including the accurate delineation of abnormal tissue and the identification of low-grade gliomas. PET imaging depicts aspects of tissue activity in Vivo and thus, helps us improve our understanding of the tumor's size and behavior. While functional imaging is already an established modality in other fields of oncology, the appropriate tracer for the imaging of glial cancers remains under investigation since FDG, the traditional oncological tracer, proves suboptimal due to the high physiological glucose uptake of the cerebral grey matter. METHODS In this literature review, I discuss the physiological characteristics as well as the opportunities for clinical application of the tracers FDG, C-MET, FET, FDOPA and FLT. RESULTS Although PET imaging remains expensive and availability of tracers is limited by their mode of production and decaying nature, integration of PET scanning into the treatment pathway offers clear patient benefits. While sensitivity of the PET tracers C-MET and FET exceeds that of traditional imaging modalities, application in screening is limited by associated expenses. Combining amino-acid PET tracers with traditional modalities has shown significant benefits in biopsy and radiotherapy planning. CONCLUSION All amino acid tracers show good results in distinguishing treatment response from early recurrence, a task where MRI, the current gold standard, is lacking in reliability. FET shows especially good results in monitoring residual tumour mass.

Early Postoperative 18F-FET PET/MRI for Pediatric Brain and Spinal Cord Tumors.

Complete resection is the treatment of choice for most pediatric brain tumors, but early postoperative MRI for detection of residual tumor may be misleading because of MRI signal changes caused by the operation. PET imaging with amino acid tracers in adults increases the diagnostic accuracy for brain tumors, but the literature in pediatric neurooncology is limited. A hybrid PET/MRI system is highly beneficial in children, reducing the number of scanning procedures, and this is to our knowledge the first larger study using PET/MRI in pediatric neurooncology. We evaluated if additional postoperative 18F-fluoro-ethyl-tyrosine (18F-FET) PET in children and adolescents would improve diagnostic accuracy for the detection of residual tumor as compared with MRI alone and would assist clinical management. Methods: Twenty-two patients (7 male; mean age, 9.5 y; range, 0-19 y) were included prospectively and consecutively in the study and had 27 early postoperative 18F-FET PET exams performed preferentially in a hybrid PET/MRI system (NCT03402425). Results: Using follow-up (93%) or reoperation (7%) as the reference standard, PET combined with MRI discriminated tumor from treatment effects with a lesion-based sensitivity/specificity/accuracy (95% confidence intervals) of 0.73 (0.50-1.00)/1.00 (0.74-1.00)/0.87 (0.73-1.00) compared with MRI alone: 0.80 (0.57-1.00)/0.75 (0.53-0.94)/0.77 (0.65-0.90); that is, the specificity for PET/MRI was 1.00 as compared with 0.75 for MRI alone (P = 0.13). In 11 of 27 cases (41%), results from the 18F-FET PET scans added relevant clinical information, including one scan that directly influenced clinical management because an additional residual tumor site was identified. 18F-FET uptake in reactive changes was frequent (52%), but correct interpretation was possible in all cases. Conclusion: The high specificity for detecting residual tumor suggests that supplementary 18F-FET PET is relevant in cases where reoperation for residual tumor is considered.

Synthesis of enantiopure 18F-trifluoromethyl cysteine as a structure-mimetic amino acid tracer for glioma imaging.

Although 11C-labelled sulfur-containing amino acids (SAAs) including L-methyl-[11C]methionine and S-[11C]-methyl-L-cysteine, are attractive tracers for glioma positron emission tomography (PET) imaging, their applications are limited by the short half-life of the radionuclide 11C (t1/2 = 20.4 min). However, development of 18F-labelled SAAs (18F, t1/2 = 109.8 min) without significant structural changes or relying on prosthetic groups remains to be a great challenge due to the absence of adequate space for chemical modification.Methods: We herein present 18F-trifluoromethylated D- and L-cysteines which were designed by replacing the methyl group with 18F-trifluoromethyl group using a structure-based bioisosterism strategy. These two enantiomers were synthesized stereoselectively from serine-derived cyclic sulfamidates via a nucleophilic 18F-trifluoromethylthiolation reaction followed by a deprotection reaction. Furthermore, we conducted preliminary in vitro and in vivo studies to investigate the feasibility of using 18F-trifluoromethylated cysteines as PET tracers for glioma imaging.Results: The two-step radiosynthesis provided the desired products in excellent enantiopurity (ee > 99%) with 14% ± 3% of radiochemical yield. In vitro cell study demonstrated that both enantiomers were taken up efficiently by C6 tumor cells and were mainly transported by systems L and ASC. Among them, the D-enantiomer exhibited relatively good stability and high tumor-specific accumulation in the animal studies.Conclusion: Our findings indicate that 18F-trifluoromethylated D-cysteine, a new SAA tracer, may be a potential candidate for glioma imaging. Taken together, our study represents a first step toward developing 18F-trifluoromethylated cysteines as structure-mimetic tracers for PET tumor imaging.

PET in brain tumors

The aim of this Pictorial Essay is to illustrate the metabolic aspect of PET (positron emission tomography) imaging in relation to conventional and advanced MR (magnetic resonance) of brain neoplasms. 10 patients, who performed PET–CT with amino acid tracers and/or FDG were selected from a series of more than 250 cases from a single institution. The selection was made to illustrate and discuss each of the indications reported in the European guidelines. Fusion imaging was obtained merging PET–CT with MR T1-CE (contrast enhanced) and/or T2/FLAIR sequences. The SUVmax of the lesion and the SUVmax lesion to SUVmax background ratio were evaluated. The lesion uptake was also assessed using a five-point visual scale with a range from − 2 to + 2 in relation to basal ganglia uptake. The Hospital Information System (HIS) and the proton therapy data archives have been used for clinical history. For each case, the critical issues were described and the physiopathological correlations were provided to explain the imaging findings. The complexity of illustrated cases demonstrates the need for a multidisciplinary board evaluation to reach a more accurate diagnosis.