Discovery and evaluation of a novel 18F-labeled vasopressin 1a receptor PET ligand with peripheral binding specificity.

The arginine-vasopressin (AVP) hormone plays a pivotal role in regulating various physiological processes, such as hormone secretion, cardiovascular modulation, and social behavior. Recent studies have highlighted the V1a receptor as a promising therapeutic target. In-depth insights into V1a receptor-related pathologies, attained through in vivo imaging and quantification in both peripheral organs and the central nervous system (CNS), could significantly advance the development of effective V1a inhibitors. To address this need, we develop a novel V1a-targeted positron emission tomography (PET) ligand, [18F]V1A-2303 ([18F]8), which demonstrates favorable in vitro binding affinity and selectivity for the V1a receptor. Specific tracer binding in peripheral tissues was also confirmed through rigorous cell uptake studies, autoradiography, biodistribution assessments. Furthermore, [18F]8 was employed in PET imaging and arterial blood sampling studies in healthy rhesus monkeys to assess its brain permeability and specificity, whole-body distribution, and kinetic properties. Our research indicated [18F]8 as a valuable tool for noninvasively studying V1a receptors in peripheral organs, and as a foundational element for the development of next-generation, brain-penetrant ligands specifically designed for the CNS.

The Bifunctional Dimer Caffeine-Indan Attenuates α-Synuclein Misfolding, Neurodegeneration and Behavioral Deficits after Chronic Stimulation of Adenosine A1 Receptors.

We previously found that chronic adenosine A1 receptor stimulation with N6-Cyclopentyladenosine increased α-synuclein misfolding and neurodegeneration in a novel α-synucleinopathy model, a hallmark of Parkinson's disease. Here, we aimed to synthesize a dimer caffeine-indan linked by a 6-carbon chain to cross the blood-brain barrier and tested its ability to bind α-synuclein, reducing misfolding, behavioral abnormalities, and neurodegeneration in our rodent model. Behavioral tests and histological stains assessed neuroprotective effects of the dimer compound. A rapid synthesis of the 18F-labeled analogue enabled Positron Emission Tomography and Computed Tomography imaging for biodistribution measurement. Molecular docking analysis showed that the dimer binds to α-synuclein N- and C-termini and the non-amyloid-ß-component (NAC) domain, similar to 1-aminoindan, and this binding promotes a neuroprotective α-synuclein "loop" conformation. The dimer also binds to the orthosteric binding site for adenosine within the adenosine A1 receptor. Immunohistochemistry and confocal imaging showed the dimer abolished α-synuclein upregulation and aggregation in the substantia nigra and hippocampus, and the dimer mitigated cognitive deficits, anxiety, despair, and motor abnormalities. The 18F-labeled dimer remained stable post-injection and distributed in various organs, notably in the brain, suggesting its potential as a Positron Emission Tomography tracer for α-synuclein and adenosine A1 receptor in Parkinson's disease therapy.

Imaging finding of renal masses associated with pathogenic variation in succinate dehydrogenase subunit B gene.

PURPOSE: Succinate dehydrogenase (SDH)-deficient renal cell carcinoma (RCC) is a newly defined, rare subtype of renal cancer, associated with pathogenic variations in the Succinate Dehydrogenase Subunit B (SDHB) gene. Our aim is to investigate the imaging findings of SDHB-associated renal tumors, utilizing cross-sectional and FDG-PET imaging in patients with pathogenic variations in SDHB gene, to facilitate accurate tumor characterization. METHODS: Twenty SDH-deficient tumors from 16 patients with pathogenic variations in SDHB gene were retrospectively evaluated using cross-sectional and FDG-PET imaging. Clinical findings such as demographics, family history, extra-renal findings and metastases were recorded. Tumor imaging characteristics on CT/MRI included were laterality, size, homogeneity, morphology, margins, internal content, T1/T2 signal intensity, enhancement features, and restricted diffusion. RESULTS: Sixteen patients (median age 31 years, IQR 19-41, 8 males) were identified with 68.8 % of patients having a known family history of SDHB variation. 81.3 % of lesions were solitary and majority were solid (86.7 % on CT, 87.5 % on MRI) with well-defined margins in >62.5 % of lesions, without evidence of internal fat, calcifications, or vascular invasion. 100 % of lesions demonstrated restricted diffusion and avid enhancement, with degree >75 % for most lesions on CT and MRI. On FDG-PET, all renal masses showed increased radiotracer uptake. 43.8 % of patients demonstrated extra-renal manifestations and 43.8 % had distant metastasis. CONCLUSION: SDHB-associated RCC is predominantly noted in young patients with no gender predilection. On imaging, SDH-deficient RCC are frequently unilateral, solitary, and solid with well-defined margins demonstrating avid enhancement with variability in enhancement pattern and showing restricted diffusion.

Structure-based discovery of a 4,5-Dihydropyrazole-cored PET ligand for imaging of receptor-interacting serine/threonine-protein kinase 1 (RIPK1) in the brain.

Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) regulates programmed cell death and inflammation, contributing to a wide range of human pathologies, including inflammatory disorders, neurodegenerative conditions, and cancer. Despite this, no RIPK1 positron emission tomography (PET) ligand with significant in vivo specificity has been reported to date. In this work, we designed and synthesized a new family of dihydropyrazole-cored ligands suitable for 18F-labeling at the late stage. Among these, WL8 showed a strong binding affinity to RIPK1 (EC50 = 19.9 nM, Kd = 25 nM) and was successfully labeled with 18F in the 6-position of pyridine ring, yielding a high radiochemistry yield of 27.9 % (decay-corrected) and a high molar activity of 18.8-31.2 GBq/µmol. In in vitro autoradiography, [18F]WL8 showed some specific binding in the brain sections of rats and lipopolysaccharide (LPS) model mice. Preliminary PET studies in rat brains revealed that [18F]WL8 could efficiently penetrate the blood-brain barrier and was rapidly washed out. As anticipated, [18F]WL8 exhibited a high initial uptake (brain2min = 4.80 % ID/g) in mouse brains, followed by a rapid washout (brain60min = 0.14 % ID/g), although no clear specific binding to RIPK1 was observed. Moderate in vivo stability was noted for [18F]WL8 in mouse brains with 35.2 % of the parent fraction remaining after 30 min post-administration. Altogether, our work broadens the landscape and offers a new chemotype for RIPK1 PET ligand development.

Medial temporal lobe atrophy patterns in early-versus late-onset amnestic Alzheimer's disease.

BACKGROUND: The medial temporal lobe (MTL) is hypothesized to be relatively spared in early-onset Alzheimer's disease (EOAD). Yet, detailed examination of MTL subfields and drivers of atrophy in amnestic EOAD is lacking. METHODS: BioFINDER-2 participants with memory impairment, abnormal amyloid-ß and tau-PET were included. Forty-one amnestic EOAD individuals ≤65 years and, as comparison, late-onset AD (aLOAD, ≥70 years, n = 154) and amyloid-ß-negative cognitively unimpaired controls were included. MTL subregions and biomarkers of (co-)pathologies were measured. RESULTS: AD groups showed smaller MTL subregions compared to controls. Atrophy patterns were similar across AD groups: aLOAD showed thinner entorhinal cortices than aEOAD; aEOAD showed thinner parietal regions than aLOAD. aEOAD showed lower white matter hyperintensities than aLOAD. No differences in MTL tau-PET or transactive response DNA binding protein 43-proxy positivity were found. CONCLUSIONS: We found evidence for MTL atrophy in amnestic EOAD and overall similar levels to aLOAD of MTL tau pathology and co-pathologies.

DOTATATE PET Imaging in Olfactory Neuroblastoma and Association with SSTR Expression.

Introduction Olfactory neuroblastoma (ONB), or esthesioneuroblastoma, is a rare neuroectodermal tumor of the nasal cavity and paranasal sinuses. Most of these tumors express somatostatin receptors (SSTRs), providing a potential target for radionuclide imaging with Ga-68 DOTATATE. However, this imaging modality has not been extensively studied in ONB. Methods We conducted a retrospective chart review of 96 endoscopic endonasal skull base surgery cases for ONB performed at our institution between 2000 and 2021. Histo (H) scores were assigned to each tumor and normalized DOTATATE standardized uptake values (nSUVs) were measured as well. Results Nine patients (5 males and 4 females) with ONB were ultimately included in the study. The average age of the patients was 50 years. All ONBs had a positive SSTR2 expression (H-score > 105; mean: 180). All ONBs showed DOTATATE avidity (mean nSUV for ONB: 6.7). However, there was no correlation between H-score and nSUV, with an r 2 of 0.24 ( p = 0.18). Conclusion Our study shows that SSTR2 expression is found in all ONBs with associated DOTATATE avidity, which may serve as a valuable imaging modality to monitor for recurrent and metastatic disease in ONB.

Development and Evaluation of [68Ga]Ga-Labeled Riboflavin Derivative for RFVT3-Targeted PET Imaging of Melanoma in Mice.

The limited progress in treatment options and the alarming survival rates in advanced melanoma emphasize the significant research importance of early melanoma diagnosis. RFVT3, a crucial protein at the core of energy metabolism reprogramming in melanoma, might play a pivotal role in early detection. In this study, [68Ga]Ga-NOTA-RF, based on riboflavin (RF), was rationally developed and validated, serving as an innovative tool for positron emission tomography (PET) imaging of RFVT3 expression in melanoma. The in vitro assays of RFVT3 specificity of [68Ga]Ga-NOTA-RF were performed on B16F10 melanoma cells. Then, PET imaging of melanoma was investigated in B16F10 allograft mouse models with varying volumes. Biodistribution studies are used to clarify the behavior of [68Ga]Ga-NOTA-RF in vivo. [68Ga]Ga-NOTA-RF was obtained with high radiochemical purity (>95%). A significant uptake (37.79 ± 6.86%, n = 4) of [68Ga]Ga-NOTA-RF was observed over time in B16F10 melanoma cells, which was significantly inhibited by RFVT3 inhibitors RF or methylene blue (MB), demonstrating the specific binding of [68Ga]Ga-NOTA-RF. At 60 min postinjection, the tumor-to-muscle (T/M) ratio of [68Ga]Ga-NOTA-RF was 4.03 ± 0.34, higher than that of the RF-blocked group (2.63 ± 0.19) and MB-blocked group (2.14 ± 0.20). The T/M ratios for three distinct tumor volumes-small (5 mm), medium (10 mm), and large (15 mm) were observed to be 5.25 ± 0.28, 4.03 ± 0.34, and 3.19 ± 0.55, respectively. The expression of RFVT3 was validated by immunohistochemical staining in various tumor models, with small B16F10 tumors exhibiting the highest expression. [68Ga]Ga-NOTA-RF demonstrates promising properties for the early diagnosis of melanoma and the examination of minute metastatic lesions, indicating its potential to assist in guiding clinical treatment decisions.

Utilizing integrin αvß6-targeted PET imaging to longitudinally monitor radiation- induced pulmonary fibrosis in vivo.

PURPOSE: Radiation-induced pulmonary fibrosis (RIPF) is a potentially serious and disabling late complication of radiation therapy. Monitoring RIPF progression is challenging due to the absence of early detection tools and the difficulty in distinguishing RIPF from other lung diseases using standard imaging methods. In the lungs, integrin αvß6 is crucial in the development of RIPF, acting as a significant activator of TGF-ß after radiation injury. This study aims to investigate integrin αvß6-targeted PET imaging ([64Cu]Cu-αvß6-BP) to study RIPF development in vivo. METHODS AND MATERIALS: We used a focal RIPF model (70 Gy delivered focally to a 3 mm spot in the lung) and a whole lung RIPF model (14 Gy delivered to the whole lung) in adult C57BL/6J mice. Small animal PET/CT images were acquired 1h post-injection of 11.1 MBq of [64Cu]Cu-αvß6-BP. Animals were imaged for eight weeks in the focal RIPF model and six months for the whole lung RIPF model. Immunohistochemistry for integrin αvß6 and trichrome staining were performed. RESULTS: In the focal RIPF model, there was focal uptake of [64Cu]Cu-αvß6-BP in the irradiated region at week four that progressively increased at week 6 and 8. In the whole lung RIPF model, minimal uptake of the probe was observed at four months post-RT, which significantly increased at months five and six. Expression of integrin αvß6 was validated histologically by immunohistochemistry in both models. CONCLUSIONS: Integrin αvß6-targeted PET imaging using [64Cu]Cu-αvß6-BP can serve as a useful tool to identify radiation-induced pulmonary fibrosis in vivo.

Development and preclinical characterization of a novel radiotheranostic EphA2-targeting bicyclic peptide.

Erythropoietin-producing hepatocellular receptor A2 (EphA2), is a receptor tyrosine kinase involved in cell-cell interactions. It is known to be overexpressed in various tumors and is associated with poor prognosis. EphA2 has been proposed as a target for theranostic applications. Low molecular weight peptide-based scaffolds with low nanomolar affinities have been shown to be ideal in such applications. Bicyclic peptides have emerged as an alternative to traditional peptides for this purpose, offering affinities comparable to antibodies due to their constrained nature, along with high tissue penetration, and improved stability compared to linear counterparts. This study presents the development and comprehensive in vitro and in vivo preclinical evaluation of BCY18469, a novel EphA2-targeting bicyclic peptide-based radiotheranostic agent. Methods: The EphA2-targeting Bicycle® peptide BCY18469 was identified through phage-display and chemically optimized. BCY18469 was radiolabeled with 68Ga, 177Lu and 111In. The physicochemical properties, binding affinity and internalization as well as specificity of the peptide were evaluated in vitro. In vivo PET/MR and SPECT/CT imaging studies were performed using [68Ga]Ga-BCY18469 and [111In]In-BCY18469, respectively, along with biodistribution of [177Lu]Lu-BCY18469 up to 24 h post injection in HT1080- and PC-3-tumor bearing BALB/c nu/nu EphA2-overexpressing xenograft mouse models. Results: The EphA2-targeting bicyclic peptide BCY18469 showed high binding affinity toward human and mouse EphA2 (1.9 and 3.8 nM, respectively). BCY18469 specifically bound and internalized into EphA2-expressing HT1080 cells. Imaging studies showed high tumor enrichment at early time-points (SUV of 1.7 g/mL at 1 h p.i. and 1.2 g/mL at 2 h p.i. in PET/MRI, HT1080 xenograft) with tumor contrast as early as 5 min p.i. and kidney-mediated clearance. Biodistribution studies revealed high early tumor uptake (19.5 ± 3.5 %ID/g at 1 h p.i., HT1080 xenograft) with SPECT/CT imaging further confirming these findings (5.7 ± 1.5 %ID/g at 1 h p.i., PC-3 xenograft). Conclusion: BCY18469 demonstrated high affinity, specific targeting of EphA2, a favorable biodistribution profile, and clearance through renal pathways. These findings underscore the potentially important role of bicyclic peptides in advancing radiotheranostic approaches and encourage additional translational research.

[18F]RS-127445 radiosynthesis and evaluation as a 5-HT2B receptor PET radiotracer in rat brain.

Serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter involved in many physiological and pathological mechanisms through its numerous receptors. Among these, the 5-HT2B receptor is known to play a key role in multiple brain disorders but remains poorly understood. Positron emission tomography (PET) can contribute to a better understanding of pathophysiological mechanisms regulated by the 5-HT2B receptor. To develop the first PET radiotracer for the 5-HT2B receptor, RS-127445, a well-known 5-HT2B receptor antagonist, was labeled with fluorine-18. [18F]RS-127445 was synthesized in a high radiochemical purity and with a good molar activity and radiochemical yield. Preliminary PET scans in rats showed good brain penetration of [18F]RS-127445. However, competition experiments and in vitro autoradiography showed high non-specific binding, especially to brain white matter.

Cyclotron production of manganese-52: a promising avenue for multimodal PET/MRI imaging.

BACKGROUND: The integration of positron emission tomography (PET) and magnetic resonance imaging (MRI) holds promise for advancing diagnostic imaging capabilities. The METRICS project aims to develop cyclotron-driven production of 52Mn for PET/MRI imaging. RESULTS: Using the 52Cr(p,n)52Mn reaction, we designed chromium metal targets via Spark Plasma Sintering and developed a separation procedure for isolating 52Mn. Labeling tests were conducted with traditional chelators (i.e. S-2-(4-Isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane tetraacetic acid) and the 1.4-dioxa-8-azaspiro[4.5]decane-8- carbodithioate ligand to produce radioactive complexes suitable for PET/MRI applications. Our methodology yielded high-quality 52Mn suitable for PET radiopharmaceuticals and PET/MRI imaging. Preliminary studies on phantom imaging using microPET and clinical MRI demonstrated the efficacy of our approach. CONCLUSIONS: The developed technology offers a promising avenue for producing 52Mn and enhancing PET/MRI imaging capabilities. Further in vivo investigations are warranted to evaluate the potential advantages of this hybrid imaging technique.

[18F]AlF-CBP imaging of type I collagen for non-invasive monitoring of pulmonary fibrosis in preclinical models.

PURPOSE: Pulmonary fibrosis is an irreversible scar-forming condition for which there is a lack of non-invasive and specific methods for monitoring its progression and therapy efficacy. However, the disease is known to be accompanied by collagen accumulation. Here, we developed a novel positron emission tomography (PET) probe targeting type I collagen to evaluate its utility for the non-invasive assessment of pulmonary fibrosis. METHODS: We designed a 18F-labeled PET probe ([18F]AlF-CBP) to target type I collagen and evaluated its binding affinity, specificity and stability in vitro. PET with [18F]AlF-CBP, CT, histopathology, immunofluorescence, and biochemical indice were performed to assess and quantify type I collagen levels and pulmonary fibrosis progression and treatment in murine models. Dynamic PET/CT studies of [18F]AlF-CBP were conducted to assess lung fibrosis in non-human primate models. RESULTS: [18F]AlF-CBP was successfully prepared, and in vitro and in vivo tests showed high stability (> 95%) and type I collagen specificity (IC50 = 0.36 µM). The lungs of the fibrotic murine model showed more elevated probe uptake and retention compared to the control group, and there was a positive correlation between the radioactivity uptake signals and the degree of fibrosis (CT: R2 = 0.89, P < 0.0001; hydroxyproline levels: R2 = 0.89, P < 0.0001). PET signals also correlated well with mean lung density in non-human primate models of pulmonary fibrosis (R2 = 0.84, P < 0.0001). CONCLUSION: [18F]AlF-CBP PET imaging is a promising non-invasive method for specific monitoring of lung fibrosis progression and therapy efficacy.

Imaging Identifies Superior Inflammation Targeting of M1 Macrophages for Cryo-Shocked Cell Pulmonary Drug Delivery to Treat Acute Lung Injury.

In the realm of combating acute lung injury (ALI) induced by a myriad of triggers including sepsis, pneumonia, aspiration, trauma, and pancreatitis, macrophages emerge as crucial players. However, traditional treatments such as systemic administration of glucocorticoids come with the baggage of severe side effects, curtailing their utility. Enter an innovative solution: a biomimetic drug delivery system fashioned from cryo-shocked macrophages, tailored for pulmonary drug delivery. Positron emission tomography (PET) imaging has shed light on the remarkable targeting abilities of live M1 macrophages, showcasing their unparalleled efficacy in homing in on local inflammatory foci when contrasted with naive, M1, and M2 macrophages. Building upon this foundation, liquid nitrogen-treated (LNT) M1 macrophages are developed, engineered to preserve their inflammation-targeting prowess while sidestepping the release of pro-inflammatory cytokines. This breakthrough allows for the delivery of glucocorticoids directly to inflamed lung tissues, efficiently quelling inflammation and mitigating pulmonary edema while drastically reducing systemic drug exposure. Inspired by the effectiveness of live M1 macrophages, the potential of glucocorticoid-loaded LNT M1 macrophages are harnessed, utilizing them as a stealthy "Trojan horse" in the battle against pneumonia-induced ALI. This innovative approach holds promise as a safe and potent treatment avenue for acute lung injury.

Development of caspase-3-selective activity-based probes for PET imaging of apoptosis.

BACKGROUND: The cysteine-aspartic acid protease caspase-3 is recognized as the main executioner of apoptosis in cells responding to specific extrinsic and intrinsic stimuli. Caspase-3 represents an interesting biomarker to evaluate treatment response, as many cancer therapies exert their effect by inducing tumour cell death. Previously developed caspase-3 PET tracers were unable to reach routine clinical use due to low tumour uptake or lack of target selectivity, which are two important requirements for effective treatment response evaluation in cancer patients. Therefore, the goal of this study was to develop and preclinically evaluate novel caspase-3-selective activity-based probes (ABPs) for apoptosis imaging. RESULTS: A library of caspase-3-selective ABPs was developed for tumour apoptosis detection. In a first attempt, the inhibitor Ac-DW3-KE (Ac-3Pal-Asp-ßhLeu-Phe-Asp-KE) was 18F-labelled on the N-terminus to generate a radiotracer that was incapable of adequately detecting an increase in apoptosis in vivo. The inability to effectively detect active caspase-3 in vivo was likely attributable to slow binding, as demonstrated with in vitro inhibition kinetics. Hence, a second generation of caspase-3 selective ABPs was developed based on the Ac-ATS010-KE (Ac-3Pal-Asp-Phe(F5)-Phe-Asp-KE) with greatly improved binding kinetics over Ac-DW3-KE. Our probes based on Ac-ATS010-KE were made by modifying the N-terminus with 6 different linkers. All the linker modifications had limited effect on the binding kinetics, target selectivity, and pharmacokinetic profile in healthy mice. In an in vitro apoptosis model, the least hydrophilic tracer [18F]MICA-316 showed an increased uptake in apoptotic cells in comparison to the control group. Finally, [18F]MICA-316 was tested in an in vivo colorectal cancer model, where it showed a limited tumour uptake and was unable to discriminate treated tumours from the untreated group, despite demonstrating that the radiotracer was able to bind caspase-3 in complex mixtures in vitro. In contrast, the phosphatidylethanolamine (PE)-binding radiotracer [99mTc]Tc-duramycin was able to recognize the increased cell death in the disease model, making it the best performing treatment response assessment tracer developed thus far. CONCLUSIONS: In conclusion, a novel library of caspase-3-binding PET tracers retaining similar binding kinetics as the original inhibitor was developed. The most promising tracer, [18F]MICA-316, showed an increase uptake in an in vitro apoptosis model and was able to selectively bind caspase-3 in apoptotic tumour cells. In order to distinguish therapy-responsive from non-responsive tumours, the next generation of caspase-3-selective ABPs will be developed with higher tumour accumulation and in vivo stability.

Zirconium- 89 Labeled Antibody K1-70 for PET Imaging of Thyroid-stimulating Hormone Receptor Expression in Thyroid Cancer.

PURPOSE: Thyroid-stimulating hormone receptor (TSHR) is a G-protein coupled receptor that is highly expressed on benign and malignant thyroid tissues. TSHR binding and activation has long been a component of thyroid cancer molecular imaging and radiotherapy, by promoting expression of the sodium-iodide symporter (NIS) and incorporation of I-131 into thyroid hormones. Here, we report the radiosynthesis and preclinical evaluation of a Zirconium-89 (89Zr) labeled TSHR antibody to serve as a positron emission tomography (PET) diagnostic correlate for therapeutic agents targeting TSHR without reliance on NIS. PROCEDURES: TSHR human monoclonal antibody K1-70 was conjugated to chelator desferrioxamine-p-benzyl-isothiocyanate, followed by labeling with Zr-89, yielding the radiotracer 89Zr-DFO-TSHR-Ab. The in vitro cellar uptake and binding affinity of 89Zr-DFO-TSHR-Ab were analyzed in three new TSHR stable overexpressing tumor cell lines and their corresponding wild types (WT) with low or no TSHR expression. 89Zr-DFO-TSHR-Ab PET/CT imaging of TSHR expression was evaluated in tumor mouse models bearing one TSHR-positive tumor and other negative control with or without the coinjection of antibody K1-70, and then verified by radiotracer biodistribution study and tumor immunohistochemistry (IHC). RESULTS: The conjugate DFO-TSHR-Ab was labeled with Zr-89 at 37 °C for 60 min and purified by PD-10 column in radiochemical yields of 68.8 ± 9.9%, radiochemical purities of 98.7 ± 0.8%, and specific activities of 19.1 ± 2.7 mCi/mg (n = 5). In vitro cell studies showed 89Zr-DFO-TSHR-Ab had significantly high uptake on TSHR expressing tumor cells with nanomolar affinity and high potency. Preclinical PET/CT imaging revealed that 89Zr-DFO-TSHR-Ab selectively detected TSHR expressing thyroid tumors and displayed improved in vivo performance with the coinjection of unlabeled TSHR antibody K1-70 leading to higher uptake in TSHR expressing tumors than parental WT tumors and physiologic tissues; this observation was confirmed by the biodistribution and immunostaining analyses. CONCLUSIONS: We synthesized 89Zr-labeled antibody K1-70 as a new radiopharmaceutical for PET imaging of TSHR. 89Zr-DFO-TSHR-Ab has high radioactive uptake and retention in TSHR expressing tumors and cleared quickly from most background tissues in mouse models. Our study demonstrated that 89Zr-DFO-TSHR-Ab has the potential for PET imaging of TSHR-positive thyroid cancer and monitoring TSHR-targeted therapy.

Application of Dynamic [18F]FDG PET/CT Multiparametric Imaging Leads to an Improved Differentiation of Benign and Malignant Lung Lesions.

PURPOSE: To evaluate the potential of whole-body dynamic (WBD) 2-deoxy-2-[18F]fluoro-D-glucose positron emission tomography/computed tomography ([18F]FDG PET/CT) multiparametric imaging in the differential diagnosis between benign and malignant lung lesions. PROCEDURES: We retrospectively analyzed WBD PET/CT scans from patients with lung lesions performed between April 2020 and March 2023. Multiparametric images including standardized uptake value (SUV), metabolic rate (MRFDG) and distribution volume (DVFDG) were visually interpreted and compared. We adopted SUVmax, metabolic tumor volume (MTV) and total lesion glycolysis (TLG) for semi-quantitative analysis, MRmax and DVmax values for quantitative analysis. We also collected the patients' clinical characteristics. The variables above with P-value < 0.05 in the univariate analysis were entered into a multivariate logistic regression. The statistically significant metrics were plotted on receiver-operating characteristic (ROC) curves. RESULTS: A total of 60 patients were included for data evaluation. We found that most malignant lesions showed high uptake on MRFDG and SUV images, and low or absent uptake on DVFDG images, while benign lesions showed low uptake on MRFDG images and high uptake on DVFDG images. Most malignant lesions showed a characteristic pattern of gradually increasing FDG uptake, whereas benign lesions presented an initial rise with rapid fall, then kept stable at a low level. The AUC values of MRmax and SUVmax are 0.874 (95% CI: 0.763-0.946) and 0.792 (95% CI: 0.667-0.886), respectively. DeLong's test showed the difference between the areas is statistically significant (P < 0.001). CONCLUSIONS: Our study demonstrated that dynamic [18F]FDG PET/CT imaging based on the Patlak analysis was a more accurate method of distinguishing malignancies from benign lesions than conventional static PET/CT scans.

Postoperative 68Ga-DOTATATE positron emission tomography has a low yield in incidental appendiceal neuroendocrine tumours.

INTRODUCTION: Rarely, appendiceal neuroendocrine tumours (NET) are an incidental finding when an appendicectomy is undertaken for suspected appendicitis. The role of further imaging in this setting is poorly defined. Positron emission tomography (PET) using 68Ga-DOTATATE is requested to evaluate post-surgical status, however, there is little evidence to guide how it should be employed. The aims of this project are to: (i) characterize 68Ga-DOTATATE PET findings in patients with incidental appendiceal NETs and (ii) discuss how these data might inform post-surgical imaging with PET. METHODS: We reviewed 47 PET scans in 30 patients, undertaken from 2009 to 2018. Scintigraphic findings, histopathological characteristics of the initial appendiceal lesion and medical records were reviewed. RESULTS: Most patients (n = 15) had small (<10 mm) appendiceal NETs with low grade (Ki67 < 2%) features. Eight patients had tumours between 10 and 20 mm, and seven had tumours >20 mm. Goblet cell features were identified in two patients. Three positive PET scans were reported in one patient with an index tumour measuring 40 mm and Ki67 < 2%. The remaining 29 patients had 44 negative scans. Clinical outcome data were available in 27 patients (mean follow-up time 57 months; range 6-123 months). There was no evidence of recurrent neuroendocrine disease at the time of the last follow-up. CONCLUSION: These data indicate that in most cases, post-surgical 68Ga-DOTATATE PET is negative in patients with incidentally detected appendiceal NETs. Clinical outcome data suggest that 68Ga-DOTATATE PET should be reserved for patients with large tumours (>20 mm) or those displaying goblet cell features.

Spatial-temporal dynamic evolution of lewy body dementia by metabolic PET imaging.

PURPOSE: Lewy body dementia (LBD) is a neurodegenerative disease with high heterogeneity and complex pathogenesis. Our study aimed to use disease progression modeling to uncover spatial-temporal dynamic evolution of LBD in vivo, and to explore differential profiles of clinical features, glucose metabolism, and dopaminergic function among different evolution-related subtypes. METHODS: A total of 123 participants (31 healthy controls and 92 LBD patients) who underwent 18F-FDG PET scans were retrospectively enrolled. 18F-FDG PET-based Subtype and Stage Inference (SuStaIn) model was established to illustrate spatial-temporal evolutionary patterns and categorize relevant subtypes. Then subtypes and stages were further related to clinical features, glucose metabolism, and dopaminergic function of LBD patients. RESULTS: This 18F-FDG PET imaging-based approach illustrated two distinct patterns of neurodegenerative evolution originating from the neocortex and basal ganglia in LBD and defined them as subtype 1 and subtype 2, respectively. There were obvious differences between subtypes. Compared with subtype 1, subtype 2 exhibited a greater proportion of male patients (P = 0.045) and positive symptoms such as visual hallucinations (P = 0.033) and fluctuating cognitions (P = 0.033). Cognitive impairment, metabolic abnormalities, dopaminergic dysfunction and progression were all more severe in subtype 2 (all P < 0.05). In addition, a strong association was observed between SuStaIn subtypes and two clinical phenotypes (Parkinson's disease dementia and dementia with Lewy bodies) (P = 0.005). CONCLUSIONS: Our findings based on 18F-FDG PET and data-driven model illustrated spatial-temporal dynamic evolution of LBD and categorized novel subtypes with different evolutionary patterns, clinical and imaging features in vivo. The evolution-related subtypes are associated with LBD clinical phenotypes, which supports the perspective of existence of distinct entities in LBD spectrum.

Parametric imaging of myocardial blood flow with 82Rb position emission tomography: An accuracy and image-quality analysis.

BACKGROUND: We aimed to develop a framework for generating three-dimensional (3D) myocardial blood flow (MBF) images, computing their accuracy against clinically validated two-dimensional (2D) polar MBF maps of the left ventricle, and evaluating their improvements in image quality over relative myocardial perfusion imaging (MPI). METHODS: N = 40 patients with a wide range of defect severities and uptake dynamics were retrospectively studied. The FlowQuant™ software was used to generate reference MPI and polar MBF maps and was adapted for voxel-wise MBF mapping. We evaluated agreement between parametric vs polar values for MBF at rest and stress and for reserve (stress/rest MBF). We also assessed improvements in image quality, assessed by signal-to-noise ratio, contrast-to-noise ratio, tissue-to-blood ratio, and defect severity, from relative MPI to MBF. RESULTS: There was excellent agreement between 3D parametric and 2D polar maps for all flow parameters (interclass correlation coefficient >0.96), albeit with minimal bias (<8%) for rest and stress MBF at the patient level. Image quality substantially improved from MPI to MBF in every patient for all image-quality metrics (P < 0.0001) CONCLUSIONS: We developed a robust methodology for producing highly accurate 3D MBF images exhibiting considerably improved image quality compared to relative MPI commonly used in clinical practice.

[89Zr]ZrCl4 for direct radiolabeling of DOTA-based precursors.

INTRODUCTION: Zirconium-89 (89Zr) is a positron emitter with several advantages over other shorter-lived positron emission tomography (PET) compatible radiometals such as gallium-68 or copper-64. These include practically unlimited availability, extremely low cost, greatly facilitated distribution logistics, positron energy fit for medical PET imaging, and sufficiently long physical half-life to enable PET imaging at later time points for patient-specific dosimetry estimations. Despite these apparent benefits, the reception of 89Zr in the nuclear medicine community has been tepid. The driving factor for the absence of broader adaptation is mostly routed in its final formulation - [89Zr]zirconium oxalate. While serving as a suitable precursor solution for the gold standard chelator deferoxamine (DFO), [89Zr]Zr-oxalate is inaccessible for the most commonly used chelators, such as the macrocyclic DOTA, due to its pre-chelated state. Consequently, pioneering work has been conducted by multiple research groups to create oxalate-free forms of [89Zr]Zr4+, either via chemical conversion of oxalate into other counterion forms or via direct radiochemical isolation of [89Zr]ZrCl4, showing that [89Zr]Zr-DOTA complexes are possible and stable. However, this success was accompanied by challenges, including complex and labor-intensive radiochemical processing and radiolabeling procedures as well as the relatively minuscule conversion rates. Here, we report on the direct production of [89Zr]ZrCl4 avoiding oxalate and metal contaminants to enable efficient radiolabeling of DOTA constructs. METHODS: We based our direct production of [89Zr]ZrCl4 on previously reported methods and further optimized its quality by including an additional iron-removing step using the TK400 Resin. Here, we avoided using oxalic acid and effectively minimized the content of trace metal contaminants. Our two-step purification procedure was automated, and we confirmed excellent radionuclide purity, minimal trace metals content, great reactivity over time, and high specific molar activity. In addition, DOTA-based PSMA-617 and DOTAGA-based PSMA-I&T were radiolabeled to demonstrate the feasibility of direct radiolabeling and to estimate the maximum apparent specific activities. Lastly, the biodistribution of [89Zr]Zr-PSMA-617 was assessed in mice bearing PC3-PIP xenografts, and the results were compared to the previously published data. RESULTS: A total of 18 batches, ranging from 6.9 to 20 GBq (186 to 541 mCi), were produced. The specific molar activity for [89Zr]ZrCl4 exceeded 0.96 GBq (26 mCi) per nanomole of zirconium. The radionuclidic purity was >99 %, and the trace metals content was in the <1 ppm range. The [89Zr]ZrCl4 remained in its reactive chemical form for at least five days when stored in cyclic olefin polymer (COP) vials. Batches of 11.1 GBq (300 mCi) of [89Zr]Zr-PSMA-617 and 14.4 GBq (390 mCi) of [89Zr]Zr-PSMA-I&T, corresponding to specific activities of 11.1 MBq/µg (0.3 mCi/µg), and 14.4 MBq/µg (0.39 mCi/µg), respectively, were produced. [89Zr]Zr-PSMA-617 animal PET imaging results were in agreement with the previously published data. CONCLUSION: In this work, we report on a suitable application of TK400 Resin to remove iron during [89Zr]ZrCl4 radiochemical isolation. The breakthrough allows for direct radiolabeling of DOTA-based constructs with [89Zr]ZrCl4, leading to high apparent molar activities and excellent conversion rates.