EJNMMI Radiopharmacy and Chemistry最新文献

Background: Infection imaging plays a crucial role in clinical decision making, guiding antibiotic therapy and surgical management. Nuclear medicine offers molecular level approaches using three main techniques: [¹⁸F]FDG PET/CT, radiolabelled white blood cell (WBC) scintigraphy, and anti-granulocyte monoclonal antibody scintigraphy with [^99mTc]Tc-besilesomab. Among these, [^99mTc]Tc-besilesomab was developed to simplify infection imaging compared with in vitro WBC labelling, improving accessibility for hospitals without cell-labelling facilities. However, its use is restricted by the need for prior testing for human anti-mouse antibodies (HAMA) to prevent hypersensitivity reactions.

Main body: In recent years, significant regulatory changes in the European framework for in vitro diagnostics (IVDR 2017/746) have coincided with the withdrawal of the quantitative HAMA enzyme-linked immunosorbent assay from the market and its replacement with a qualitative rapid test. Although this shift aimed to streamline in vitro testing procedures, it has complicated the interpretation of HAMA results and raised concerns about diagnostic accessibility. In some centres, an increase in positive results has been observed with rapid tests, suggesting that patients may be inappropriately excluded from [^99mTc]Tc-besilesomab imaging. This situation highlights a paradox: a radiopharmaceutical designed to improve accessibility is now constrained by regulatory and methodological factors. The issue also reflects a broader challenge in nuclear medicine, ensuring patient safety and compliance without limiting access to essential diagnostic tools.

Conclusion: This debate argues that restoring accessibility to [^99mTc]Tc-besilesomab immunoscintigraphy requires both technological and regulatory innovation. Developing quantitative point-of-care HAMA assays, promoting humanised or nanobody-based tracers, and establishing harmonised European guidelines could help balance patient safety with diagnostic availability. The [^99mTc]Tc-besilesomab case exemplifies how well-intentioned regulatory transitions may have unintended consequences, underscoring the need for a pragmatic equilibrium between innovation, safety, and accessibility in infection imaging.

Background: Fibroblast activation protein (FAP) has emerged as a critical biomarker in the tumor microenvironment of various cancers. Radioligands targeting FAP have shown promise for cancer theranostics. To advance cancer imaging, we synthesized a dimeric radioligand based on a 4-quinolinoyl-glycyl-2-cyanopyrrolidine scaffold and conducted studies in cells and mouse tumor models to evaluate its target-binding affinity and PET imaging performance.

Results: OncoFAP, a commercially available FAP ligand, was conjugated via amide coupling with 1,4-butanediamine to generate a monomeric intermediate, hmFAP₁. A homodimeric molecule, hmFAP₂, was synthesized by tethering two hmFAP₁ moieties into a single construct. In enzymatic inhibition assays, both hmFAP₁ and hmFAP₂ demonstrated specific antagonist activity against FAP, with hmFAP₂ exhibiting a 14-fold increase in inhibitory potency compared to hmFAP₁. Cy5.5 fluorescent derivatives of hmFAP₁ and hmFAP₂ were generated for cell-binding assays in HeLa cells and xenografted tumors with positive FAP expression, revealing enhanced targeting efficacy of Cy5.5-hmFAP₂. The IC₅₀ values derived from cell-binding curves were 130 nM for hmFAP₁ and 8 nM for hmFAP₂ (P < 0.001). Using DOTA as the chelator, both ligands were radiolabeled with ⁶⁸Ga, yielding stable products [⁶⁸Ga]Ga-DOTA-hmFAP₁ and [⁶⁸Ga]Ga-DOTA-hmFAP₂ for PET imaging. Consistently, [⁶⁸Ga]Ga-DOTA-hmFAP₂ demonstrated superior tumor uptake with high specificity in mice bearing HeLa, MDA-MB-231, and HEK293T xenografts with variable levels of FAP expression. The liver and intestinal radioactivity showed no difference between the groups of mice imaged with [⁶⁸Ga]Ga-DOTA-hmFAP₂ and [⁶⁸Ga]Ga-DOTA-hmFAP₁.

Conclusions: hmFAP₂ markedly enhances FAP-targeting efficiency, providing higher binding affinity, improved tumor uptake, and reduced nonspecific distribution compared with its monomeric counterpart. The favorable imaging properties of hmFAP₂ position it as a promising candidate for translation into clinical PET imaging and as a potential scaffold for developing FAP-targeted theranostic agents.

Background: The αvβ6 integrin has emerged as a valuable target for theranostic applications in nuclear medicine with high applicability across a variety of cancers, including head-and-neck, lung, breast, and pancreatic carcinomas. [⁶⁸Ga]Ga-Trivehexin is a prominent example of a diagnostic tracer targeting this integrin. In this work, we aimed to expand on this concept by developing FSC(PEG4-αvβ6)₃, a novel tracer that retains the Trivehexin design, but features PEGylated spacers and replaces the TRAP chelator with Fusarinine C (FSC), enabling labelling with Zirconium-89 in addition to Gallium-68. Preclinical characterization of [⁶⁸Ga]Ga/[⁸⁹Zr]Zr-FSC(PEG4-αvβ6)₃ included affinity determination towards the αvβ6 integrin and cellular uptake studies in αvβ6-positive H2009 cells. A subcutaneously xenografted H2009 tumor model was used to assess the PET imaging potential and biodistribution at early time points with the Gallium-68 labelled compound, and at later time points (up to 6 days post-injection) with the Zirconium-89 labelled version.

Results: While [⁶⁸Ga]Ga-FSC(PEG4-αvβ6)₃ exhibited moderate binding to αvβ6, its affinity, cellular internalization, and tumor uptake in vivo were lower compared to [⁶⁸Ga]Ga-Trivehexin. Notably, this decreased target engagement was associated with reduced nonspecific binding, which we primarily attributed to the incorporation of PEGylated linkers. Despite indication of in vivo degradation of [⁸⁹Zr]Zr-FSC(PEG4-αvβ6)₃, still a meaningful evaluation of pharmacokinetics and biodistribution at extended time points was feasible, revealing prolonged tumor persistence up to 6 days post-injection.

Conclusions: FSC(PEG4-αvβ6)₃ represents the first-generation tracer targeting the αvβ6 integrin based on the multifunctional chelator Fusarinine C, thereby expanding the repertoire of radionuclides applicable from Gallium-68 to Zirconium-89. Following further optimization, this novel class of compounds holds significant promise for enabling clinical translation and advancing the development of next-generation αvβ6-directed imaging agents.

Background: Glutamate carboxypeptidase II (GCPII), also known as prostate-specific membrane antigen (PSMA) is overexpressed in 90-100% of prostate cancer cells. The radiopharmaceutical [¹⁸F]PSMA-1007, recognised as a PET tracer for prostate cancer imaging, is based on PSMA inhibitor [Glu-CO-Lys(2Nal-Amb-Glu-Glu-PyTMA)] bound to the radioisotope Fluorine-18. [¹⁸F]Fluoride was obtained via the ¹⁸O(p,n)¹⁸F reaction using a cyclotron for medical use, while synthesis of [¹⁸F]PSMA-1007 was performed with two different platforms: FASTlab2 and NEPTIS^® Perform. Both modules enabled synthesis through nucleophilic substitution reaction and subsequent purification in solid phase extraction (SPE). Quality control process was validated according to the current specific monograph (3116) of the European Pharmacopoeia (Ph. Eur.) before clinical use.

Results: Twenty syntheses of [¹⁸F]PSMA-1007 for each module were performed in order to evaluate and compare radiochemical purity (96.58% ± 1.25 with FASTlab2 vs 95.86% ± 0.79 with NEPTIS^® Perform) and decay-corrected radiochemical yield (43.7% ± 3 with FASTlab2 vs 28.5% ± 3.1 with NEPTIS^® Perform).

Conclusion: Both platforms produced [¹⁸F]PSMA-1007 that consistently met all pharmacopoeial quality control standards. However, the FASTlab2 system demonstrated a statistically significant higher decay-corrected radiochemical yield (43.7% ± 3% vs. 28.5% ± 3.1%, p-value < 0.001 after statistical testing). While this yield difference does not impact radiochemical purity or product safety, it may represent a relevant advantage in terms of production efficiency and available activity for clinical use, which may influence the choice of synthesizer.

Background: Positron emission tomography is a useful tool for quantitative imaging of neuroinflammation in human subjects; however, more suitable radiotracers are sought. One of the promising targets for imaging neuroinflammation is macrophage colony-stimulating factor 1 receptor (CSF1R) because of its expression on activated microglia. Several PET radiotracers for imaging CSF1R have been developed, however, a suitable CSF1R radiotracer radiolabeled with ¹⁸F is not yet available. We synthesized and performed preclinical evaluation of a new series of high-affinity, ¹⁸F-labeled PET radiotracers for imaging CSF1R.

Results: A new series of CSF1R ligands with nanomolar binding affinities and structural properties suitable for brain PET was synthesized. Five compounds of the series were radiolabeled with ¹⁸F to give the corresponding radiotracers [¹⁸F]1, [¹⁸F]3, [¹⁸F]4, [¹⁸F]5 and [¹⁸F]6. The radiotracers were tested in biodistribution experiments in control mice and demonstrated brain uptake above 1% injected dose per gram (%ID/g) of tissue, with [¹⁸F]3 exhibiting the highest uptake (12.5%ID/g) at 5 min after injection, followed by rapid washout. In the liposaccharide (LPS)-induced murine model of neuroinflammation all new radiotracers demonstrated a significant increase in brain uptake corrected for blood radioactivity vs. baseline controls, with [¹⁸F]3 showing the greatest increase (97%). The highest binding potential value in LPS-treated mice was seen for [¹⁸F]3 (BP = 1.05). In control baboon PET studies [¹⁸F]3 manifested high brain uptake (standardized uptake value, SUV = 5.2), reversible kinetics in baseline scan and moderate specific binding (up to 20%) in the blocking scans with two CSF1R inhibitors, CPPC and GW2580. In mice and baboon, [¹⁸F]3 undergoes metabolism with formation of a radiometabolite with insignificant brain penetration. The [¹⁸F]3 formulation in saline with 7% ethanol was stable for 2.5 h of storage. In vitro assay showed that 3 was selective for CSF1R (K_i = 5 nM) against several kinases associated with inflammation. Radiation dosimetry in mice demonstrated that [¹⁸F]3 is safe for future translation to human subjects.

Conclusions: A series of new PET radiotracers for imaging CSF1R was synthesized and tested in vitro and in animals. One member of the series, 2-[¹⁸F]fluoro-N-(4-(4-methylpiperazin-1-yl)-2-(piperidin-1-yl)phenyl)pyrimidine-4-carboxamide ([¹⁸F]3), manifests PET imaging properties that may be suitable for further testing on non-human primate models of neuroinflammation and translation to human subjects.

Background: Several platinum radionuclides, including ¹⁹¹Pt, are promising candidates for DNA-targeted Auger electron radiotherapy; however, effective compound designs are needed for this application. In this study, we developed six novel ¹⁹¹Pt-labeled compounds and evaluated their DNA-targeting properties in PSMA-positive tumors.

Results: Six trithiol-Hoechst-PSMA (THP) conjugates that consist of a trithiol ligand for ¹⁹¹Pt labeling, Hoechst33258 for DNA binding, and a PSMA-targeted moiety were synthesized and labeled with ¹⁹¹Pt, achieving radiochemical yields of 60-80%. The six [¹⁹¹Pt]Pt-THP compounds were evaluated for DNA-binding ability and PSMA targeting specificity in vitro, and biodistribution experiments were performed with five of the compounds in mice bearing subcutaneous PSMA-positive and PSMA-negative xenografts. Among them, [¹⁹¹Pt]Pt-THP3-4 and [¹⁹¹Pt]Pt-THP3-8, in which Hoechst33258 is linked on one side of the trithiol ligand via a linear PEG linker and the PSMA-targeting moiety is linked on the other side via a C4 linker, had the best properties. These compounds maintained higher PSMA targeting specificity and DNA-binding ability both in vitro and in vivo than the other [¹⁹¹Pt]Pt-THP compounds, exhibiting similar DNA binding in PSMA-positive PC3 PIP tumors in vivo as in the cultured cells from which the xenograft was derived.

Conclusions: This study highlighted the importance of the linkers between the three components (trithiol-Hoechst-PSMA) and demonstrated binding of intravenously administered [¹⁹¹Pt]Pt-THP3-4 and [¹⁹¹Pt]Pt-THP3-8 to DNA in PSMA-positive tumors. Our compound designs and findings could be a useful foundation for DNA-targeted Auger electron cancer therapy, especially with Pt radionuclides.

Background: Understanding the interaction between radiopharmaceuticals and human serum albumin (HSA) is essential for optimizing pharmacokinetics and therapeutic efficacy. This study evaluated the binding properties of ^natLu-FAPi-46 and ^natLu-FAP-2286 to HSA using theoretical and experimental techniques.

Results: Docking results revealed moderate affinities for ^natLu-FAPi-46 (- 9.7 kcal/mol) and ^natLu-FAP-2286 (- 7.8 kcal/mol), correlating with their lower blood retention (0.43% and 0.03% I.A./g at 4 h p.i.). Comparative docking of albumin-binding derivatives of FAPi-46 showed stronger binding, consistent with increased blood retention. Experimental analyses (fluorescence quenching, circular dichroism, and cyclic voltammetry) confirmed complex formation and conformational changes in HSA, validating the computational findings.

Conclusions: Together, the computational and experimental results underscore the importance of albumin-binding in shaping the pharmacokinetic properties of FAP-targeted radiopharmaceuticals. Strategic optimization of albumin-binding linkers may improve stability, circulation time, and overall therapeutic performance in next-generation FAP-based agents.

Background: One of the challenges in optimizing PSMA-based therapies for the treatment of prostate cancer is the stability of the radiopharmaceutical, defined by the degradation of radiolabeled compounds due to exposure to ionizing radiation (radiolysis). Radiolysis of a radiopharmaceutical is difficult to measure and can influence the biodistrubion of radiopharmaceuticals in vivo, possibly leading to toxicity or suboptimal outcomes. Therefore, an inter-laboratory study was performed to confirm accurate detection of radiolysed [¹⁷⁷Lu]Lu-PSMA-I&T, and the biodistribution of radiolysed radiopharmaceutical was investigated in vivo, and HPLC methods are compared.

Results: Multiple HPLC-methods were compared to evaluate the analysis of degraded radiopharmaceutical and an inter-laboratory comparison was conducted to evaluate the consistency of current analytical methods across various institutions and with current methods from literature. Additionally, for the biodistribution experiments, a radiolabeling of [¹⁷⁷Lu]Lu-PSMA-I&T was adjusted to achieve a radiochemical purity of 50%, 70%, and 97% of the final product. A PC3-PIP patient-derived xenograft mouse model was used to investigate in vivo behavior of the formed impurity, followed by SPECT/CT imaging and biodistribution. When evaluating radio-HPLC methods for the impurity detection, the European Pharmacopoeia method (with a phosphate buffered eluent) shows no significant difference in radiochemical purity, an increased peak separation but decreased recovery (< 75%). The inter-laboratory comparison demonstrated the ability to measure the radiolysed radiopharmaceutical across multiple hospitals, with a maximum standard deviation of 6.6%. The in vivo SPECT/CT and biodistribution results show that as ingrowth of impurities caused by radiolysis increasing the tumor-to-kidney ratio is decreasing (97%/50% RCP, p < 0.05).

Conclusion: The inter-laboratory study confirms that impurities caused by radiolysis can be measured accurately across different institutions, ensuring consistency and reliability in clinical diagnostics and therapy, contributing to improved patient safety. Phosphate buffered HPLC-methods showed no significant benefits in quality control. Increased impurities caused by radiolysis lead to lower tumor-to-kidney ratios, with a decrease in specific tumor binding.