EJNMMI Radiopharmacy and Chemistry最新文献

Background

Siglec-9, a member of the Siglec family of receptors, plays a crucial role in modulating immune cell trafficking and inflammation, with significant clinical implications. It is predominantly expressed on immune cells such as neutrophils, monocytes, and dendritic cells –key components of both innate and adaptive immunity. Siglec-9 binds to sialic acid residues on glycoproteins, commonly found on endothelial cells, a mechanism central to immune regulation during inflammation and tissue injury. Notably, its interaction with vascular adhesion protein 1 (VAP-1), an endothelial adhesion molecule, is of particular interest for therapeutic development in chronic inflammatory diseases, autoimmune disorders, and cancer. Recent studies have demonstrated that a Siglec-9 motif-containing peptide conjugated with 1,4,7,10-tetraazacyclododecane-N, N′,N′′,N′′′-tetraacetic acid (DOTA) and radiolabelled with gallium-68 ([⁶⁸Ga]Ga-DOTA-Siglec-9) enables effective positron emission tomography (PET) imaging of these pathological conditions. This study aimed to develop a new automated radiolabelling protocol for the preparation of [⁶⁸Ga]Ga-DOTA-Siglec-9 for clinical use. The synthesis was carried out using a fully automated module with real-time monitoring of key parameters including time, temperature, and radioactivity.

Results

Following optimization of labelling conditions and assessment of peptide stability, [⁶⁸Ga]Ga-DOTA-Siglec-9 was successfully synthesized with a radiochemical yield (RY) of 55.04%, radiochemical purity (RCP) of 99.48%, and molar activity (Am) of 23.15 GBq/µmol at 65 °C in 6 min. Process validation yielded consistent mean values of RY (56.16%), RCP (99.40%). and Am (20.26 GBq/µmol). Stability testing at room temperature over 3 h demonstrated that [⁶⁸Ga]Ga-DOTA-Siglec-9 maintained acceptable RCP (mean99.29%), pH, appearance, and sterility.

Conclusion

The final product meets Ph. Eur. quality requirements and is suitable for clinical application.

Background

Mercury-197m (^197mHg, t_1/2 = 23.8 h) and mercury-197g (^197gHg, t_1/2 = 64.14 h) possess favorable nuclear properties for imaging and targeted therapy, but the development of suitable chelators for mercury-based radiopharmaceuticals remains underexplored. Additionally, accurate imaging and quantification of mercury isotopes, particularly in dual-isotope formats, require tools that account for their complex decay schemes. Phantom imaging studies are essential for validating spatial resolution, quantitative accuracy, and isotope-specific calibration prior to in vivo application. In this study, we investigated the commercially available ligand H₄Tetrathiol for chelation of [^197m/gHg]Hg²⁺ and developed a robust imaging and quantification pipeline to support the use of these nuclear isomers in preclinical imaging.

Results

Radiolabeling of H₄Tetrathiol yielded exceptionally efficient complexation, achieving the lowest ligand-to-metal ratio reported for radio-mercury. The resulting [^197m/gHg]Hg²⁺-complex demonstrated high in vitro stability in the presence of serum proteins, glutathione, and competing biologically relevant metal ions, though it exhibited kinetic lability when challenged with excess HgCl₂. In vivo biodistribution studies in mice showed a distinct pharmacokinetic profile from unchelated [^197m/gHg]HgCl₂, suggesting in vivo complex stability. Phantom imaging studies with a high sensitivity collimator demonstrated submillimeter resolution (≥ 1.1 mm) for both ^197gHg and ^197mHg, with decay behavior consistent with known half-lives. To facilitate accurate quantification, we developed HgQuant, a Python-based tool for isotope-specific calibration, Bateman decay correction, and automated dual-isotope analysis. This tool enabled reproducible, time-resolved quantification in both phantom and in vivo settings.

Conclusions

These results establish Tetrathiol as a promising scaffold for mercury-based theranostics, offering efficient radiolabeling and in vivo stability. The integration of high-resolution imaging and HgQuant-based quantification of each isomer establishes a comprehensive framework for advancing [^197m/gHg]Hg radiopharmaceutical development.

Background

Chronic kidney disease (CKD) poses a significant global health burden with limited effective treatments for its prevention, progression, and associated complications. Mitochondrial dysfunction is recognized as a pivotal factor in the development of kidney diseases, with mitochondrial complex-I (MC-I) playing a crucial role in assessing overall mitochondrial function. Recent advancements in selective MC-I positron emission tomography (PET) radioligands now allow for non-invasive visualization and quantification of renal mitochondrial status in vivo. The aim of the present study was to evaluate the utility of [¹⁸F]BCPP-BF in the adenine induced tubulointerstitial nephropathy model.

Results

Binding of the MC-I targeted PET radioligand, [¹⁸F]BCPP-BF, showed a gradual decline in the kidneys of mice on an adenine-rich diet. [¹⁸F]BCPP-BF binding decreased by 59–61% compared to baseline after two weeks of adenine treatment. These results of reduced uptake were further confirmed by in vitro autoradiography. In kidneys from adenine-fed mice, [¹⁸F]BCPP-BF specific binding was reduced by 65.6% compared to control kidney sections.

Conclusions

Altogether, the findings suggest that [¹⁸F]BCPP-BF holds potential as an imaging biomarker for renal failure. However, further preclinical studies and validation in human subjects are necessary before it can be established as a reliable indicator for the progression of CKD.

Background

Due to promising preclinical studies and clinical case reports, Tb-161 labeled radiopharmaceuticals for targeted radionuclide therapy (TRT) have gained interest. Unlike Lu-177, Tb-161 not only emits β⁻ particles, but also Auger and conversion electrons, which may improve the current therapeutic efficacy of TRT. However, before implementing Tb-161 for clinical use, several steps are required (E.g., development, optimization, validation). Therefore, this study focuses on the purity of Tb-161 as well as the detection and quantification of Tb–Tb-161-labeled radiopharmaceuticals. As multiple studies are currently aiming to determine the therapeutic effect of Tb-161 labeled radiopharmaceuticals, standardizing and evaluating Tb-161 is essential to be able to compare its therapeutic potential against Lu-177 and other radionuclides. Therefore, we established accurate detection methods, impurity measurements, radiolabeling protocols, and quality control for Tb-161 labeled pharmaceuticals. Parameters of Tb-161 labeled radiopharmaceuticals were investigated and exemplified by [¹⁶¹ Tb]Tb-DOTA-TATE, in comparison with [¹⁷⁷Lu]Lu-DOTA-TATE.

Results

Analysis of Tb-161 stock solution demonstrated the presence of metal impurities (ΣFe, Zn, Cu, Gd, and Dy) at the reference day and increased over time. The geometric effect of vial type demonstrated a decrease in activity when a vial was used without point-source. For both Lu-177 and Tb-161 labeled DOTA-TATE, high radiochemical yield and purity (> 95%) were obtained and remained stable (> 90%) up to 24 h in solution.

Conclusion

Analysis of Tb-161 stock showed an increase in metal impurities over time, which could interfere with the production of Tb-161 labeled radiopharmaceuticals. The low gamma energy (48.9 keV and 74.6 keV) of Tb-161 needs to be considered in (pre)clinical applications when quantifying activity. For Tb-161 labeled pharmaceuticals, similar radiolabeling conditions as Lu-177 have been shown to be successful and highly stable.

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 and application of radiopharmaceuticals.

Main Body

This selection of highlights provides commentary on 18 different topics selected by each co-authoring 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.

Background

Hsp90 is a molecular chaperone that is often overexpressed across multiple cancer types and has a potential value as a prognostic marker as well as a therapeutic target. Given the high interest in Hsp90 therapies, positron emission tomography or PET imaging of Hsp90 can be a valuable tool for patient selection. The limitations of the previously developed Hsp90 tracers prompted us to evaluate the recently developed brain-permeable [¹¹C]HSP990 PET probe to advance the development of Hsp90-targeted therapeutics. Given the brain accumulation of [¹¹C]HSP990 probe, application for glioblastoma imaging of this tracer is of particular interest.

Results

In vitro [¹¹C]HSP990 binding was assessed in breast cancer and glioma cell lines including patient-derived cells using Hsp90 inhibitors and RNA interference knockdown of Hsp90 isoforms. Saturation binding studies were conducted on these cells and tumour tissue homogenates, and autoradiography was performed on tissue sections. Ex vivo biodistribution and in vivo dynamic µPET/CT studies were performed in healthy mice and tumour-bearing mice, including immunocompromised subcutaneous human U87 and MDA-MB-231models and immunocompetent intracranial murine NS/CT-2A models at baseline and following a pre-treatment with Hsp90 inhibitors. High Hsp90-specific tracer uptake was observed in breast cancer and glioma cells, with Hsp90β inhibition resulting in the most substantial reduction in uptake. In vivo uptake was high in U87 tumours but low in MDA-MB-231, presumably due to the differences in Hsp90 expression in tumour tissue versus cultured cells. Differences in maximum binding capacity or B_max across cell and tissue types support this hypothesis, especially given that the affinity measured as dissociation constant K_d remained similar across all tissue types. Despite high NS/CT-2A tumour uptake in vitro, no contrast between the healthy brain tissue and the NS/CT-2A glioma was observed in vivo due to the high uptake by the healthy brain.

Conclusion

[¹¹C]HSP990 is a promising tracer for identifying Hsp90-overexpressing tumours and may hold potential for patient stratification, prognosis, and therapy monitoring of novel Hsp90 therapeutics. High healthy brain uptake of this tracer precluded the differentiation of the tumour in the intracranial NS/CT-2A tumour model, therefore [¹¹C]HSP990 might not be a suitable tracer for the glioblastoma imaging. Tracer with a longer half-life might be needed to compare the washout of the tracer from the brain and the tumour tissue over several hours to identify a suitable imaging window.

Background

Prostate-specific membrane antigen (PSMA) is an established target for the imaging and treatment of prostate cancer. This study focused on the preclinical evaluation of three novel PSMA inhibitors—P15, P16, and P19—which were structurally modified compared to the clinically used PSMA-617. Two main strategies were pursued: a chemical approach following the so-called reversed synthetic strategy, and the replacement of the naphthyl-based linker moiety with an analogous diphenyl-based moiety. The aim was to assess the impact of these modifications on physicochemical properties, in vitro behaviour, and in vivo pharmacokinetics following radiolabelling with ⁶⁸Ga.

Results

Radiolabelling of all three novel compounds with ⁶⁸Ga resulted in high radiochemical purity above 98% under physiological pH conditions and above 97% during stability testing in human plasma. All compounds exhibited hydrophilic characteristics based on partition coefficient measurements. Notable differences were observed in plasma protein binding, with P15 and P16 showing significantly lower binding compared to PSMA-617 and P19. In vitro assays using LNCaP prostate cancer cells demonstrated similar cellular uptake and internalization across all tested compounds. In vivo evaluation using Positron Emission Tomography/Computed Tomography (PET/CT) imaging in LNCaP tumour-bearing mice confirmed the tumour-targeting ability of all three inhibitors. These findings were further supported by biodistribution studies, which highlighted efficient and specific accumulation in tumour tissue. Among the tested compounds, P19 demonstrated the most promising overall profile in terms of stability, binding characteristics, and tumour uptake.

Conclusions

The stereochemical modifications in the linker region significantly influenced the in vitro and in vivo behaviour of the PSMA inhibitors. Despite similar cellular uptake, differences in plasma protein binding and pharmacokinetics were evident. Among the three novel compounds, P19 emerged as a particularly promising candidate for further investigation, also indicating that the diphenyl moiety might serve as a favourable linker building block in analogy to the naphthyl moiety. Our observations suggest potential not only for diagnostic imaging with ⁶⁸Ga, but also for therapeutic applications using ¹⁷⁷Lu, which offers a longer half-life suitable for delayed imaging and treatment intervals in prostate cancer management.

Background

The March 2022 approval of [¹⁷⁷Lu]Lu-PSMA-617—the first targeted radioligand therapy (TRT) for metastatic castration-resistant prostate cancer (mCRPC)—addressed a critical need in therapeutic diagnostics. However, approximately 30% of patients fail to respond to PSMA-targeted therapies, with suboptimal pharmacokinetics implicated as a key factor. To address this challenge, fatty acids, known for their role in binding albumin and enhancing drug pharmacokinetics, were explored. Although commonly used in small molecules and peptides, their application in radiopharmaceuticals remains limited. In response, a novel fatty acid-modified PSMA-targeting agent was developed to optimize pharmacokinetics by enhancing circulation half-life, tumor uptake, radioligand selectivity, and safety while reducing off-target accumulation. This innovative approach aims to maximize therapeutic efficacy, improve patient outcomes in mCRPC care, and reduce the overall treatment burden.

Results

In vitro studies confirmed the strong binding affinity and high specificity of [¹⁷⁷Lu]Lu-BT-117016 for PSMA. Biodistribution studies in LNCaP clone FGC tumor-bearing mice demonstrated significantly enhanced tumor uptake and retention of [¹⁷⁷Lu]Lu-BT-117016 compared to [¹⁷⁷Lu]Lu-PSMA-617. SPECT/CT imaging and therapy studies highlighted the superior profile of [¹⁷⁷Lu]Lu-BT-117016. It achieved significant tumor growth suppression with favorable tolerability at a minimal dose of 3 MBq, demonstrating comparable efficacy to a nearly 6-fold higher dose (20 MBq) of [177Lu]Lu-PSMA-617. The improved safety profile of [¹⁷⁷Lu]Lu-BT-117016 over [¹⁷⁷Lu]Lu-PSMA-617 was confirmed through radiation dosimetry.

Conclusion

Preclinical studies demonstrate that [¹⁷⁷Lu]Lu-BT-117016, a novel fatty acid-modified PSMA-targeting agent, optimizes albumin binding and harmonizes ligand-isotope half-lives. This results in advantageous biodistribution—characterized by high tumor uptake, rapid non-target clearance, and extended circulation—leading to complete tumor remission in LNCaP models with reduced toxicity. Crucially, [¹⁷⁷Lu]Lu-BT-117016 achieved equivalent efficacy to [¹⁷⁷Lu]Lu-PSMA-617 at 3–6 times lower doses. These findings indicate [¹⁷⁷Lu]Lu-BT-117016’s potential as a safer, more potent CRPC therapy enabling reduced dosages and less frequent administration. Further clinical trials are warranted to confirm these benefits.

Background

Alzheimer’s disease (AD) is increasingly recognized as a multifactorial disorder with vascular contributions, including a pro-coagulant state marked by fibrin deposition in the brain. Fibrin accumulation may exacerbate cerebral hypoperfusion and neuroinflammation, leading to neurodegeneration. Identifying patients with this pathology could enable targeted anticoagulant therapy. However, current imaging tools lack the specificity and sensitivity to detect fibrin in the brain non-invasively. This study aimed to develop and evaluate brain-penetrating peptide- and antibody-based PET radioligands targeting fibrin to enable individualized treatment strategies in AD.

Results

A fibrin-binding peptide (FBP) was conjugated to the antibody fragment scFv8D3, which targets the transferrin receptor (TfR), to facilitate transcytosis across the blood-brain barrier. FBP-scFv8D3 bound TfR and with modest affinity to fibrin. In vivo studies in Tg-ArcSwe mice, that exhibit fibrin along with brain amyloid-β pathology, and wild-type mice showed that [¹²⁵I]FBP-scFv8D3 retained brain-penetrating properties but did not demonstrate significant fibrin-specific retention. In contrast, the monoclonal antibody 1101 and its bispecific, brain penetrant variant 1101-scFv8D3 exhibited higher fibrin selectivity and TfR binding. Both antibodies showed a trend towards higher brain retention in Tg-ArcSwe mice and [¹²⁵I]1101-scFv8D3 showed a higher brain-to-blood ratio compared to [¹²⁴I]1101. PET imaging with [¹²⁴I]1101 and [¹²⁴I]1101-scFv8D3 revealed low global brain uptake. However, ex vivo autoradiography and regional PET quantification (ROI-to-cerebellum ratios) indicated significant cortical and caudate retention of [¹²⁴I]1101-scFv8D3 in Tg-ArcSwe mice, supporting region-specific target engagement.

Conclusion

This proof-of-concept study demonstrates the feasibility of using bispecific antibody-based PET radioligands to target fibrin in the AD brain. While the FBP-scFv8D3 conjugate showed limited specificity, the bispecific antibody 1101-scFv8D3 exhibited higher brain penetration and fibrin selectivity. These findings support further development of antibody-based imaging tools toward the goal to stratify AD patients who may benefit from anticoagulant therapy.

Background

Copper-mediated radiofluorination (CMRF) is a breakthrough in ¹⁸F-radiochemistry, enabling ¹⁸F incorporation into molecules even at electron-rich aromatic positions. In recent years, several improved protocols have been reported to advance the application of CMRF. These advancements primarily focus on improving radiochemical conversion, expanding substrate scope, and enabling scalability for remote-controlled radiotracer production. Despite these improvements, one major challenge remains: the protodemetallation. Protodemetallation is a common side reaction in transition metal-mediated cross-couplings that takes place by a mechanism that is not yet fully elucidated. In ¹⁸F-chemistry, the formation of the hydrogenated side product (HSP) can interfere with the chromatographic purification of the desired radiotracer, resulting in complex radiotracer production.

Results

The present work investigates the factors influencing the rate of the hydrogenation reaction as well as the source of hydrogen in the CMRF by use of model precursors bearing -B(OH)₂, -Bpin, -BEpin and -SnBu₃ as leaving groups. While the CMRF reactions are usually carried out under anhydrous conditions, the formation rate of the HSP was evaluated by controlling the chemical constituents (type and molarity of reagents) as well as the physical parameters (time and temperature). Moreover, experiments with deuterated reagents complemented by high-resolution mass spectrometry (HRMS) analysis were carried out to identify the source of hydrogen for the reductive elimination step.

Conclusion

This study identifies reaction parameters that influence hydrogenation side reactions in CMRF, enabling high RCC with minimal HSP formation. The optimal reaction conditions include low temperature, short reaction time, and minimal amount of precursor, copper, and ideally no base and alcohols as solvents. Among the evaluated precursors, –BEpin afforded the lowest HSP formation, while –B(OH)₂ afforded the highest. Overall, this study showed that the selection of proper reaction reagents and the fine-tuning of reaction parameters can substantially reduce the HSP formation while maintaining optimal radiochemical conversion.

Graphical abstract