Highlight selection of radiochemistry and radiopharmacy developments by editorial board.

BACKGROUND: The Editorial Board of EJNMMI Radiopharmacy and Chemistry releases a biannual highlight commentary to update the readership on trends in the field of radiopharmaceutical development. MAIN BODY: This selection of highlights provides commentary on 24 different topics selected by each coauthoring Editorial Board member addressing a variety of aspects ranging from novel radiochemistry to first-in-human application of novel radiopharmaceuticals. CONCLUSION: Trends in radiochemistry and radiopharmacy are highlighted. Hot topics cover the entire scope of EJNMMI Radiopharmacy and Chemistry, demonstrating the progress in the research field in many aspects.

Macrophage mannose receptor CD206 targeting of fluoride-18 labeled mannosylated dextran: A validation study in mice.

PURPOSE: Aluminum fluoride-18-labeled 1,4,7-triazacyclononane-1,4,7-triacetic acid-conjugated mannosylated dextran derivative (Al[18F]F-NOTA-D10CM) is a new tracer for PET imaging. We report here on in vitro and in vivo validation of the tracer's ability to target the macrophage mannose receptor CD206. METHODS: First, the uptake of intravenously (i.v.) administered Al[18F]F-NOTA-D10CM was compared between wild-type (WT) and CD206-/- knockout (KO) mice. C57BL/6N mice were injected with complete Freund's adjuvant (CFA) in the left hind leg and the uptake of Al[18F]F-NOTA-D10CM after i.v. or intradermal (i.d.) injection was studied at 5 and 14 days after CFA induction of inflammation. Healthy C57BL/6N mice were studied as controls. Mice underwent PET/CT on consecutive days with [18F]FDG, i.v. Al[18F]F-NOTA-D10CM, and i.d. Al[18F]F-NOTA-D10CM. After the last imaging, Al[18F]F-NOTA-D10CM was i.v. injected for an ex vivo biodistribution study and autoradiography of inflamed tissues. Blood plasma samples were analyzed using high-performance liquid chromatography. To evaluate the specificity of Al[18F]F-NOTA-D10CM binding, an in vitro competitive displacement study was performed on inflamed tissue sections using autoradiography. CD206 expression was assessed by immunohistochemical staining. RESULTS: Compared with WT mice, the uptake of Al[18F]F-NOTA-D10CM was significantly lower in several CD206-/- KO mice tissues, including liver (SUV 8.21 ± 2.51 vs. 1.06 ± 0.16, P < 0.001) and bone marrow (SUV 1.63 ± 0.37 vs. 0.22 ± 0.05, P < 0.0001). The uptake of i.v. injected Al[18F]F-NOTA-D10CM was significantly higher in inflamed ankle joint (SUV 0.48 ± 0.13 vs. 0.18 ± 0.05, P < 0.0001) and inflamed foot pad skin (SUV 0.41 ± 0.10 vs. 0.04 ± 0.01, P < 0.0001) than in the corresponding tissues in healthy mice. The i.d.-injected Al[18F]F-NOTA-D10CM revealed differences between CFA-induced lymph node activation and lymph nodes in healthy mice. Ex vivo γ-counting, autoradiography, and immunohistochemistry supported the results, and a decrease of ~ 80% in the binding of Al[18F]F-NOTA-D10CM in the displacement study with excess NOTA-D10CM confirmed that tracer binding was specific. At 60 min after i.v. injection, an average 96.70% of plasma radioactivity was derived from intact Al[18F]F-NOTA-D10CM, indicating good in vivo stability. The uptake of Al[18F]F-NOTA-D10CM into inflamed tissues was positively associated with the area percentage of CD206-positive staining. CONCLUSION: The uptake of mannosylated dextran derivative Al[18F]F-NOTA-D10CM correlated with CD206 expression and the tracer appears promising for inflammation imaging.

Radiosynthesis, structural identification and in vitro tissue binding study of [18F]FNA-S-ACooP, a novel radiopeptide for targeted PET imaging of fatty acid binding protein 3.

BACKGROUND: Fatty acid binding protein 3 (FABP3) is a target with clinical relevance and the peptide ligand ACooP has been identified for FABP3 targeting. ACooP is a linear decapeptide containing a free amino and thiol group, which provides opportunities for conjugation. This work is to develop methods for radiolabeling of ACooP with fluorine-18 (18F) for positron emission tomography (PET) applications, and evaluate the binding of the radiolabeled ACooP in human tumor tissue sections with high FABP3 expression. RESULTS: The prosthetic compound 6-[18F]fluoronicotinic acid 4-nitrophenyl ester was conveniently prepared with an on-resin 18F-fluorination in 29.9% radiochemical yield and 96.6% radiochemical purity. Interestingly, 6-[18F]fluoronicotinic acid 4-nitrophenyl ester conjugated to ACooP exclusively by S-acylation instead of the expected N-acylation, and the chemical identity of the product [18F]FNA-S-ACooP was confirmed. In the in vitro binding experiments, [18F]FNA-S-ACooP exhibited heterogeneous and high focal binding in malignant tissue sections, where we also observed abundant FABP3 positivity by immunofluorescence staining. Blocking study further confirmed the [18F]FNA-S-ACooP binding specificity. CONCLUSIONS: FABP3 targeted ACooP peptide was successfully radiolabeled by S-acylation using 6-[18F]fluoronicotinic acid 4-nitrophenyl ester as the prosthetic compound. The tissue binding and blocking studies together with anti-FABP3 immunostaining confirmed [18F]FNA-S-ACooP binding specificity. Further preclinical studies of [18F]FNA-S-ACooP are warranted.

Imaging of Myocardial αvß3 Integrin Expression for Evaluation of Myocardial Injury After Acute Myocardial Infarction.

[68Ga]Ga-NODAGA-Arg-Gly-Asp (RGD) is a PET tracer targeting αvß3 integrin, which is upregulated during angiogenesis soon after acute myocardial infarction (AMI). We prospectively evaluated determinants of myocardial uptake of [68Ga]Ga-NODAGA-RGD and its associations with left ventricular (LV) function in patients after AMI. Methods: Myocardial blood flow and [68Ga]Ga-NODAGA-RGD uptake (60 min after injection) were evaluated by PET in 31 patients 7.7 ± 3.8 d after primary percutaneous coronary intervention for ST-elevation AMI. Transthoracic echocardiography of LV function was performed on the day of PET and at the 6-mo follow-up. Results: PET images showed increased uptake of [68Ga]Ga-NODAGA-RGD in the ischemic area at risk (AAR), predominantly in injured myocardial segments. The SUV in the segment with the highest uptake (SUVmax) in the ischemic AAR was higher than the SUVmean of the remote myocardium (0.73 ± 0.16 vs. 0.51 ± 0.11, P < 0.001). Multivariable predictors of [68Ga]Ga-NODAGA-RGD uptake in the AAR included high peak N-terminal pro-B-type natriuretic peptide (P < 0.001), low LV ejection fraction, low global longitudinal strain (P = 0.01), and low longitudinal strain in the AAR (P = 0.01). [68Ga]Ga-NODAGA-RGD uptake corrected for myocardial blood flow and perfusable tissue fraction in the AAR predicted improvement in global longitudinal strain at follow-up (P = 0.002), independent of peak troponin, N-terminal pro-B-type natriuretic peptide, and LV ejection fraction. Conclusion: [68Ga]Ga-NODAGA-RGD uptake shows increased αvß3 integrin expression in the ischemic AAR early after AMI that is associated with regional and global systolic dysfunction, as well as increased LV filling pressure. Increased [68Ga]Ga-NODAGA-RGD uptake predicts improvement of global LV function 6 mo after AMI.

Detection of Intestinal Inflammation by Vascular Adhesion Protein-1-Targeted [68Ga]Ga-DOTA-Siglec-9 Positron Emission Tomography in Murine Models of Inflammatory Bowel Disease.

PURPOSE: Inflammatory bowel disease (IBD) can be imaged with positron emission tomography (PET), but existing PET radiopharmaceuticals have limited diagnostic accuracy. Vascular adhesion protein-1 (VAP-1) is an endothelial cell surface molecule that controls leukocyte extravasation into sites of inflammation. However, the role of inflammation-induced VAP-1 expression in IBD is still unclear. Therefore, this study investigated the utility of VAP-1-targeted [68Ga]Ga-DOTA-Siglec-9 positron emission tomography/computed tomography (PET/CT) for assessing inflammation in two mouse models of IBD. PROCEDURES: Studies were performed using K8-/- mice that develop a chronic colitis-phenotype and C57Bl/6NCrl mice with acute intestinal inflammation chemically-induced using 2.5% dextran sodium sulfate (DSS) in drinking water. In both diseased and control mice, uptake of the VAP-1-targeting peptide [68Ga]Ga-DOTA-Siglec-9 was assessed in intestinal regions of interest using in vivo PET/CT, after which ex vivo gamma counting, digital autoradiography, and histopathological analyses were performed. Immunofluorescence staining was performed to determine VAP-1-expression in the intestine, including in samples from patients with ulcerative colitis. RESULTS: Intestinal inflammation could be visualized by [68Ga]Ga-DOTA-Siglec-9 PET/CT in two murine models of IBD. In both models, the in vivo PET/CT and ex vivo studies of [68Ga]Ga-DOTA-Siglec-9 uptake were significantly higher than in control mice. The in vivo uptake was increased on average 1.4-fold in the DSS model and 2.0-fold in the K8-/- model. Immunofluorescence staining revealed strong expression of VAP-1 in the inflamed intestines of both mice and patients. CONCLUSIONS: This study suggests that the VAP-1-targeting [68Ga]Ga-DOTA-Siglec-9 PET tracer is a promising tool for non-invasive imaging of intestinal inflammation. Future studies in patients with IBD and evaluation of the potential value of [68Ga]Ga-DOTA-Siglec-9 in diagnosis and monitoring of the disease are warranted.

Tetrazine Glycoconjugate for Pretargeted Positron Emission Tomography Imaging of trans-Cyclooctene-Functionalized Molecular Spherical Nucleic Acids.

Pretargeted concept in positron emission tomography (PET) together with bioorthogonal chemistry is an elegant solution to study processes with slow pharmacokinetics by utilizing radiotracers labeled with short-lived radionuclides. Namely, radiotracers based on tetrazine ligation with trans-cyclooctene (TCO) via the inverse electron demand Diels-Alder (IEDDA) reaction have become a state-of-the-art for the pretargeted PET imaging. For radiolabeling of tetrazine scaffolds, indirect radiofluorination methods are often preferred, as tetrazines are vulnerable to harsh conditions typically necessary for the direct radiofluorination. 18F-Fluoroglycosylation is an indirect radiofluorination method, which allows the introduction of a widely accessible glucose analog 2-[18F]fluoro-2-deoxy-d-glucose ([18F]FDG) to aminooxy-functionalized precursors via oxime formation. Here, we report the biological evaluation of [18F]FDG-Tz as a tracer for pretargeted PET imaging of TCO-functionalized molecular spherical nucleic acids (MSNA) against human epidermal growth factor receptor 2 (HER2) mRNA. The oxime ether formation between [18F]FDG and tetrazine oxyamine resulted in [18F]FDG-Tz with high radiochemical purity (>99%) and moderate yields (6.5 ± 3.6%, n = 5). Biological evaluation of [18F]FDG-Tz in healthy mice indicated favorable pharmacokinetics with quick blood clearance, urinary excretion as the main elimination route, and the absence of GLUT1 transportation. The successful pretargeted experiments with TCO-functionalized MSNA revealed higher tumor uptake compared to preclicked MSNA in HER2-expressing human breast cancer xenograft-bearing mice.

Vascular adhesion protein-1-targeted PET imaging in autoimmune myocarditis.

BACKGROUND: Vascular adhesion protein-1 (VAP-1) is an adhesion molecule and primary amine oxidase, and Gallium-68-labeled 1,4,7,10-tetraazacyclododecane-N,N',N″,N‴-tetra-acetic acid conjugated sialic acid-binding immunoglobulin-like lectin 9 motif containing peptide ([68Ga]Ga-DOTA-Siglec-9) is a positron emission tomography (PET) tracer targeting VAP-1. We evaluated the feasibility of PET imaging with [68Ga]Ga-DOTA-Siglec-9 for the detection of myocardial lesions in rats with autoimmune myocarditis. METHODS: Rats (n = 9) were immunized twice with porcine cardiac myosin in complete Freund's adjuvant. Control rats (n = 6) were injected with Freund's adjuvant alone. On day 21, in vivo PET/computed tomography (CT) imaging with [68Ga]Ga-DOTA-Siglec-9 was performed, followed by ex vivo autoradiography, histology, and immunohistochemistry of tissue sections. In addition, myocardial samples from three patients with cardiac sarcoidosis were studied. RESULTS: [68Ga]Ga-DOTA-Siglec-9 PET/CT images of immunized rats showed higher uptake in myocardial lesions than in myocardium outside lesions (SUVmean, 0.5 ± 0.1 vs 0.3 ± 0.1; P = .003) or control rats (SUVmean, 0.2 ± 0.03; P < .0001), which was confirmed by ex vivo autoradiography of tissue sections. Immunohistochemistry showed VAP-1-positive staining in lesions of rats with myocarditis and in patients with cardiac sarcoidosis. CONCLUSION: VAP-1-targeted [68Ga]Ga-DOTA-Siglec-9 PET is a potential novel technique for the detection of myocardial lesions.

Atomic Local Ordering and Alloying Effects on the Mg3(Sb1-xBix)2 Thermoelectric Material.

Mg3(Sb1-xBix)2 alloy has been extensively studied in the last 5 years due to its exceptional thermoelectric (TE) performance. The absence of accurate force field for inorganic alloy compounds presents great challenges for computational studies. Here, we explore the atomic microstructure, thermal, and elastic properties of the Mg3(Sb1-xBix)2 alloy at different solution concentrations through atomic simulations with a highly accurate machine learning interatomic potential (ML-IAP). We find atomic local ordering in the optimized structure with the Bi-Bi pair inclined to join adjacent layers and Sb-Sb pair preferring to stay within the same layer. The thermal conductivity changes with the solution concentrations can be correctly predicted through ML-IAP-based molecular dynamics simulations. Spectral thermal conductance analysis shows that the continuous movement of low-frequency peak to high frequency is responsible for the reduction of the thermal conductivity upon alloying. Elastic calculations reveal that similar to the thermal conductivity, solid solution alloying can reduce the overall elastic properties at both Mg3Sb2 and Mg3Bi2 ends, while anisotropic behavior is clearly observed with linear interpolation relationship upon alloying along the interlayer direction and nonlinearity along the intralayer direction. Although the atomic local ordering shows little effects on the properties of the Mg3(Sb1-xBix)2 alloy with only two alloying elements, it possesses potential important impacts on multiprincipal element inorganic TE alloys. This work provides a recipe for computational studies on the TE alloy systems and thus can accelerate the discovery and optimization of TE materials with high TE performance.

High folate receptor expression in gliomas can be detected in vivo using folate-based positron emission tomography with high tumor-to-brain uptake ratio divulging potential future targeting possibilities.

Introduction: Non-invasive imaging techniques such as positron emission tomography (PET) are extremely important for cancer detection and characterization especially for difficult to biopsy or extremely delicate organs such as the brain. The folate analogue 1,4,7-triazacylononane-1,4,7-triacetic acid-conjugated folate radiolabeled with aluminum fluoride-18 ([18F]FOL) has been previously shown to accumulate preferentially in tumor cells with an overexpression of folate receptors (FRs) and here was investigated for its ability to detect orthotopic gliomas in a rat model. In addition, we studied the expression of FRs in human glioblastoma samples to investigate if an analogous relationship may exist. Methods: Nine BDIX rats were injected with BT4C rat glioma cells into the right hemisphere of the brain. Animals were imaged with gadolinium-enhanced magnetic resonance imaging at on days prior to PET/computed tomography (CT) imaging. Animals were divided into two groups, and were PET/CT imaged with either [18F]FOL or 2-deoxy-2-18F-fluoro-D-glucose ([18F]FDG) on 19 and 32-days post glioma grafting. Two subjects were also PET/CT imaged with [18F]FOL on day 16. Biodistribution was studied and brains were cryosectioned for autoradiography, immunofluorescence, and histological studies. Patient-derived paraffin-embedded glioblastomas were sectioned and stained with similar methods. Results: PET imaging showed an increase of [18F]FOL tumor-to-brain uptake ratio (TBR) over the study duration from day 16/19 (3.3 ± 0.9) increasing to 5.7 ± 1.0 by day 32. [18F]FDG PET-imaged rats had a consistent TBR of 1.6 ± 0.1 throughout the study. Ex vivo autoradiography results revealed an exceptionally high TBR of 116.1 ± 26.9 for [18F]FOL while the [18F]FDG values were significantly lower giving 2.9 ± 0.6 (P<0.0001). Immunostaining demonstrated an increased presence of FR-α in the BT4C gliomas versus the contralateral brain tissue, while FR-ß was present only on glioma periphery. Human sections assayed showed similar FRs expression characteristics. Conclusion: This study shows upregulation of FR-α inside glioma regions in both human and animal tissue, providing a biochemical basis for the observed increased [18F]FOL uptake in animal PET images. These results suggest that FRs targeting imaging and therapeutic compounds may possess clinically relevant translational abilities for the detection and treatment of gliomas.

Aluminum Fluoride-18 Labeled Mannosylated Dextran: Radiosynthesis and Initial Preclinical Positron Emission Tomography Studies.

PURPOSE: In addition to being expressed on liver sinusoidal endothelial cells, mannose receptors are also found on antigen-presenting cells, including macrophages, which are mainly involved in the inflammation process. Dextran derivatives of various sizes containing cysteine and mannose moieties have previously been labeled with 99mTc and used for single-photon emission computed tomography imaging of sentinel lymph nodes. In this study, we radiolabeled 21.3-kDa D10CM with positron-emitting 18F for initial positron emission tomography (PET) studies in rats. PROCEDURES: D10CM was conjugated with 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) chelator and radiolabeled with the aluminum fluoride-18 method. The whole-body distribution kinetics and stability of the intravenously administered tracer were studied in healthy male Sprague-Dawley rats by in vivo PET/CT imaging, ex vivo gamma counting, and high-performance liquid chromatography analysis. RESULTS: Al[18F]F-NOTA-D10CM was obtained with a radiochemical purity of >99% and molar activity of 9.9 GBq/µmol. At 60 minutes after injection, an average of 84% of the intact tracer was found in the blood, indicating excellent in vivo stability. The highest radioactivity concentration was seen in the liver, spleen, and bone marrow, in which mannose receptors are highly expressed under physiological conditions. The uptake specificity was confirmed with in vivo blocking experiments. CONCLUSIONS: Our results imply that Al[18F]F-NOTA-D10CM is a suitable tracer for PET imaging. Further studies in disease models with mannose receptor CD206-positive macrophages are warranted to clarify the tracer's potential for imaging of inflammation.

Preclinical Evaluation of 89Zr-Desferrioxamine-Bexmarilimab, a Humanized Antibody Against Common Lymphatic Endothelial and Vascular Endothelial Receptor-1, in a Rabbit Model of Renal Fibrosis.

Bexmarilimab is a new humanized monoclonal antibody against common lymphatic endothelial and vascular endothelial receptor-1 (CLEVER-1) and is in clinical trials for macrophage-guided cancer immunotherapy. In addition being associated with cancer, CLEVER-1 is also associated with fibrosis. To facilitate prospective human PET studies, we preclinically evaluated 89Zr-labeled bexmarilimab in rabbits. Methods: Bexmarilimab was conjugated with desferrioxamine (DFO) and radiolabeled with 89Zr. Retained immunoreactivity was confirmed by flow cytometry. The distribution kinetics of intravenously administered 89Zr-DFO-bexmarilimab (0.1 mg/kg) were determined for up to 7 d in a rabbit model of renal fibrosis mediated by unilateral ureteric obstruction. The in vivo stability of 89Zr-DFO-bexmarilimab was evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis in combination with autoradiography. Additionally, we estimated the human radiation dose from data obtained in healthy rabbits. Results: 89Zr-DFO-bexmarilimab cleared rapidly from the blood circulation and distributed to the liver and spleen. At 24 h after injection, PET/CT, ex vivo γ-counting, and autoradiography demonstrated that there was significantly higher 89Zr-DFO-bexmarilimab uptake in unilateral ureteric obstruction-operated fibrotic renal cortex, characterized by abundant CLEVER-1-positive cells, than in contralateral or healthy kidneys. The estimated effective dose for a 70-kg human was 0.70 mSv/MBq. Conclusion: The characteristics of 89Zr-DFO-bexmarilimab support future human PET studies to, for example, stratify patients for bexmarilimab treatment, evaluate the efficacy of treatment, or monitor disease progression.

[68Ga]Ga-DOTA-Siglec-9 Detects Pharmacodynamic Changes of FAP-Targeted IL2 Variant Immunotherapy in B16-FAP Melanoma Mice.

Vascular adhesion protein-1 (VAP-1) is an inflammation-inducible adhesion molecule, which supports contact between leukocytes and inflamed endothelium. There is evidence that VAP-1 is involved in the recruitment of leukocytes to melanoma tumors. Interleukin-2 (IL-2)-based immunotherapy is an efficient therapy that promotes immune system activity against cancers but is associated with toxicity. In the present study, we evaluated the feasibility of PET/CT imaging using the radiotracer [68Ga]Ga-DOTA-Siglec-9, which is targeted to VAP-1, to monitor pharmacodynamic effects of a novel FAP-IL2v immunocytokine (a genetically engineered variant of IL-2 fused with fibroblast activation protein) in the B16-FAP melanoma model. At 9 days after the inoculation of B16-FAP melanoma cells, mice were studied with [68Ga]Ga-DOTA-Siglec-9 PET/CT as a baseline measurement. Immediately after baseline imaging, mice were treated with FAP-IL2v or vehicle, and treatment was repeated 3 days later. Subsequent PET/CT imaging was performed 3, 5, and 7 days after baseline imaging. In addition to in vivo PET imaging, ex vivo autoradiography, histology, and immunofluorescence staining were performed on excised tumors. B16-FAP tumors were clearly detected with [68Ga]Ga-DOTA-Siglec-9 PET/CT during the follow-up period, without differences in tumor volume between FAP-IL2v-treated and vehicle-treated groups. Tumor-to-muscle uptake of [68Ga]Ga-DOTA-Siglec-9 was significantly higher in the FAP-IL2v-treated group than in the vehicle-treated group 7 days after baseline imaging, and this was confirmed by tumor autoradiography analysis. FAP-IL2v treatment did not affect VAP-1 expression on the tumor vasculature. However, FAP-IL2v treatment increased the number of CD8+ T cells and natural killer cells in tumors. The present study showed that [68Ga]Ga-DOTA-Siglec-9 can detect B16-FAP tumors and allows monitoring of FAP-IL2v treatment.

Corrigendum: Exploiting Glutamine Consumption in Atherosclerotic Lesions by Positron Emission Tomography Tracer (2S,4R)-4-18F-Fluoroglutamine.

[This corrects the article DOI: 10.3389/fimmu.2022.821423.].

68Ga-Citrate PET of Healthy Men: Whole-Body Biodistribution Kinetics and Radiation Dose Estimates.

68Ga-citrate has one of the simplest chemical structures of all 68Ga-radiopharmaceuticals, and its clinical use is justified by the proven medical applications using its isotope-labeled compound 67Ga-citrate. To support broader application of 68Ga-citrate in medical diagnosis, further research is needed to gain clinical data from healthy volunteers. In this work, we studied the biodistribution of 68Ga-citrate and subsequent radiation exposure from it in healthy men. Methods: 68Ga-citrate was prepared with an acetone-based radiolabeling procedure compliant with good manufacturing practices. Six healthy men (age 41 ± 12 y, mean ± SD) underwent sequential whole-body PET/CT scans after an injection of 204 ± 8 MBq of 68Ga-citrate. Serial arterialized venous blood samples were collected during PET imaging, and the radioactivity concentration was measured with a γ-counter. Urinary voids were collected and measured. The MIRD bladder-voiding model with a 3.5-h voiding interval was used. A model using a 70-kg adult man and the MIRD schema was used to estimate absorbed doses in target organs and effective doses. Calculations were performed using OLINDA/EXM software, version 2.0. Results: Radioactivity clearance from the blood was slow, and relatively high radioactivity concentrations were observed over the whole of the 3-h measuring period. Although radioactivity excretion via urine was rather slow (biologic half-time, 69 ± 24 h), the highest decay-corrected concentrations in urinary bladder contents were measured at the 90- and 180-min time points. Moderate concentrations were also seen in kidneys, liver, and spleen. The source organs showing the largest residence times were muscle, liver, lung, and heart contents. The heart wall received the highest absorbed dose, 0.077 ± 0.008 mSv/MBq. The mean effective dose (International Commission on Radiological Protection publication 103) was 0.021 ± 0.001 mSv/MBq. Conclusion: PET imaging with 68Ga-citrate is associated with modest radiation exposure. A 200-MBq injection of 68Ga-citrate results in an effective radiation dose of 4.2 mSv, which is in the same range as other 68Ga-labeled tracers. This suggests the feasibility of clinical studies using 68Ga-citrate imaging in humans and the possibility of performing multiple scans in the same subjects across the course of a year.

Exploiting Glutamine Consumption in Atherosclerotic Lesions by Positron Emission Tomography Tracer (2S,4R)-4-18F-Fluoroglutamine.

Increased glutamine metabolism by macrophages is associated with development of atherosclerotic lesions. Positron emission tomography/computed tomography (PET/CT) with a glutamine analog (2S,4R)-4-18F-fluoroglutamine (18F-FGln) allows quantification of glutamine consumption in vivo. Here, we investigated uptake of 18F-FGln by atherosclerotic lesions in mice and compared the results with those obtained using the glucose analog 2-deoxy-2-18F-fluoro-D-glucose (18F-FDG). Uptake of 18F-FGln and 18F-FDG by healthy control mice (C57BL/6JRj) and atherosclerotic low-density lipoprotein receptor-deficient mice expressing only apolipoprotein B100 (LDLR-/-ApoB100/100) was investigated. The mice were injected intravenously with 18F-FGln or 18F-FDG for in vivo PET/CT imaging. After sacrifice at 70 minutes post-injection, tracer uptake was analyzed by gamma counting of excised tissues and by autoradiography of aorta cryosections, together with histological and immunohistochemical analyses. We found that myocardial uptake of 18F-FGln was low. PET/CT detected lesions in the aortic arch, with a target-to-background ratio (SUVmax, aortic arch/SUVmean, blood) of 1.95 ± 0.42 (mean ± standard deviation). Gamma counting revealed that aortic uptake of 18F-FGln by LDLR-/-ApoB100/100 mice (standardized uptake value [SUV], 0.35 ± 0.06) was significantly higher than that by healthy controls (0.20 ± 0.08, P = 0.03). More detailed analysis by autoradiography revealed that the plaque-to-healthy vessel wall ratio of 18F-FGln (2.90 ± 0.42) was significantly higher than that of 18F-FDG (1.93 ± 0.22, P = 0.004). Immunohistochemical staining confirmed that 18F-FGln uptake in plaques co-localized with glutamine transporter SLC7A7-positive macrophages. Collectively these data show that the 18F-FGln PET tracer detects inflamed atherosclerotic lesions. Thus, exploiting glutamine consumption using 18F-FGln PET may have translational relevance for studying atherosclerotic inflammation.

Comparison of: (2S,4R)-4-[18F]Fluoroglutamine, [11C]Methionine, and 2-Deoxy-2-[18F]Fluoro-D-Glucose and Two Small-Animal PET/CT Systems Imaging Rat Gliomas.

PURPOSE: The three positron emission tomography (PET) imaging compounds: (2S,4R)-4-[18F]Fluoroglutamine ([18F]FGln), L-[methyl-11C]Methionine ([11C]Met), and 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) were investigated to contrast their ability to image orthotopic BT4C gliomas in BDIX rats. Two separate small animal imaging systems were compared for their tumor detection potential. Dynamic acquisition of [18F]FGln was evaluated with multiple pharmacokinetic models for future quantitative comparison. PROCEDURES: Up to four imaging studies were performed on each orthotopically grafted BT4C glioma-bearing BDIX rat subject (n = 16) on four consecutive days. First, a DOTAREM® contrast enhanced MRI followed by attenuation correction CT and dynamic PET imaging with each radiopharmaceutical (20 min [11C]Met, 60 min [18F]FDG, and 60 min [18F]FGln with either the Molecubes PET/CT (n = 5) or Inveon PET/CT cameras (n = 11). Ex vivo brain autoradiography was completed for each radiopharmaceutical and [18F]FGln pharmacokinetics were studied by injecting 40 MBq into healthy BDIX rats (n = 10) and collecting blood samples between 5 and 60 min. Erythrocyte uptake, plasma protein binding and plasma parent-fraction were combined to estimate the total blood bioavailability of [18F]FGln over time. The corrected PET-image blood data was then applied to multiple pharmacokinetic models. RESULTS: Average BT4C tumor-to-healthy brain tissue uptake ratios (TBR) for PET images reached maxima of: [18F]FGln TBR: 1.99 ± 0.19 (n = 13), [18F]FDG TBR: 1.41 ± 0.11 (n = 6), and [11C]Met TBR: 1.08 ± 0.08, (n = 12) for the dynamic PET images. Pharmacokinetic modeling in dynamic [18F]FGln studies suggested both reversible and irreversible uptake play a similar role. Imaging with Inveon and Molecubes yielded similar end-result ratios with insignificant differences (p > 0.25). CONCLUSIONS: In orthotopic BT4C gliomas, [18F]FGln may offer improved imaging versus [11C]Met and [18F]FDG. No significant difference in normalized end-result data was found between the Inveon and Molecubes camera systems. Kinetic modelling of [18F]FGln uptake suggests that both reversible and irreversible uptake play an important role in BDIX rat pharmacokinetics.

Graph network based deep learning of bandgaps.

Recent machine learning models for bandgap prediction that explicitly encode the structure information to the model feature set significantly improve the model accuracy compared to both traditional machine learning and non-graph-based deep learning methods. The ongoing rapid growth of open-access bandgap databases can benefit such model construction not only by expanding their domain of applicability but also by requiring constant updating of the model. Here, we build a new state-of-the-art multi-fidelity graph network model for bandgap prediction of crystalline compounds from a large bandgap database of experimental and density functional theory (DFT) computed bandgaps with over 806 600 entries (1500 experimental, 775 700 low-fidelity DFT, and 29 400 high-fidelity DFT). The model predicts bandgaps with a 0.23 eV mean absolute error in cross validation for high-fidelity data, and including the mixed data from all different fidelities improves the prediction of the high-fidelity data. The prediction error is smaller for high-symmetry crystals than for low symmetry crystals. Our data are published through a new cloud-based computing environment, called the "Foundry," which supports easy creation and revision of standardized data structures and will enable cloud accessible containerized models, allowing for continuous model development and data accumulation in the future.

Atomistic simulations of dislocation mobility in refractory high-entropy alloys and the effect of chemical short-range order.

Refractory high-entropy alloys (RHEAs) are designed for high elevated-temperature strength, with both edge and screw dislocations playing an important role for plastic deformation. However, they can also display a significant energetic driving force for chemical short-range ordering (SRO). Here, we investigate mechanisms underlying the mobilities of screw and edge dislocations in the body-centered cubic MoNbTaW RHEA over a wide temperature range using extensive molecular dynamics simulations based on a highly-accurate machine-learning interatomic potential. Further, we specifically evaluate how these mechanisms are affected by the presence of SRO. The mobility of edge dislocations is found to be enhanced by the presence of SRO, whereas the rate of double-kink nucleation in the motion of screw dislocations is reduced, although this influence of SRO appears to be attenuated at increasing temperature. Independent of the presence of SRO, a cross-slip locking mechanism is observed for the motion of screws, which provides for extra strengthening for refractory high-entropy alloy system.

Association between [68Ga]NODAGA-RGDyK uptake and dynamics of angiogenesis in a human cell-based 3D model.

Radiolabeled RGD peptides targeting expression of αvß3 integrin have been applied to in vivo imaging of angiogenesis. However, there is a need for more information on the quantitative relationships between RGD peptide uptake and the dynamics of angiogenesis. In this study, we sought to measure the binding of [68Ga]NODAGA-RGDyK to αvß3 integrin in a human cell-based three-dimensional (3D) in vitro model of angiogenesis, and to compare the level of binding with the amount of angiogenesis. Experiments were conducted using a human cell-based 3D model of angiogenesis consisting of co-culture of human adipose stem cells (hASCs) and of human umbilical vein endothelial cells (HUVECs). Angiogenesis was induced with four concentrations (25%, 50%, 75%, and 100%) of growth factor cocktail resulting in a gradual increase in the density of the tubule network. Cultures were incubated with [68Ga]NODAGA-RGDyK for 90 min at 37 °C, and binding of radioactivity was measured by gamma counting and digital autoradiography. The results revealed that tracer binding increased gradually with neovasculature density. In comparison with vessels induced with a growth factor concentration of 25%, the uptake of [68Ga]NODAGA-RGDyK was higher at concentrations of 75% and 100%, and correlated with the amount of neovasculature, as determined by visual evaluation of histological staining. Uptake of [68Ga]NODAGA-RGDyK closely reflected the amount of angiogenesis in an in vitro 3D model of angiogenesis. These results support further evaluation of RGD-based approaches for targeted imaging of angiogenesis.

Evaluation of glucagon-like peptide-1 receptor expression in nondiabetic and diabetic atherosclerotic mice using PET tracer 68Ga-NODAGA-exendin-4.

Cardiovascular effects of glucagon-like peptide-1 receptor (GLP-1R) agonist therapies are potentially mediated by anti-inflammatory effects on atherosclerosis. Our study demonstrates that 68Ga-NODAGA-exendin-4, a radioligand specifically targeting GLP-1R, detects GLP-1R expression in inflamed atherosclerotic lesions in nondiabetic and diabetic hypercholesterolemic mice. Immunofluorescence staining suggests that GLP-1R is primarily localized in M2 macrophages in lesions. This study describes a new potential tool that may have translational relevance for studies of pharmacological modification of GLP-1R signaling in atherosclerosis.