Radiolabeling Method Research Articles

Convenient PET-tracer production via SuFEx 18F-fluorination of nanomolar precursor amounts

Recently, a protocol for radiolabeling of aryl fluorosulfates (“SuFEx click radiolabeling”) using ultrafast 18F/19F isotopic exchange has been reported. Although promising, the original procedure turned out to be rather inefficient. However, systematic optimization of the reaction parameters allowed for development of a robust method for SuFEx radiolabeling which obviates the need for azeotropic drying, base addition and HPLC purification. The developed protocol enabled efficient 18F-fluorination of low nanomolar amounts of aryl fluorosulfates in highly diluted solution (micromolar concentrations). It was successfully used to prepare a series of 29 18F-fluorosulfurylated phenols – including modified ezetimibe, α-tocopherol and etoposide, the two tyrosine derivatives Boc-Tyr([18F]FS)-OMe and H-Tyr([18F]FS)-OMe, the FAP-specific ligand [18F]FS-UAMC1110, and the DPA-714 analog [18F]FS-DPA – in fair to excellent yields. Preliminary evaluation demonstrated sufficient in vivo stability of radiofluorinated electron rich or neutral {Boc-Tyr([18F]FS)-OMe), H-Tyr([18F]FS)-OMe and [18F]FS-DPA} aryl fluorosulfates. Furthermore, [18F]FS-DPA was identified as a promising tracer for visualization of TSPO expression.

Radiolabeling Method for Lyophilizate for Dry Powder Inhalation Formulations

Human lung deposition data is non-mandatory for drug approval but very useful for the development of orally inhaled drug products. Lung deposition of inhaled drugs can be quantified by radionuclide imaging, for which one of the first considerations is the method used to radiolabel formulations. In this study, we report the development of a radiolabeling method for lyophilizate for dry powder inhalation (LDPI) formulations. TechneCoatTM is one method that can radiolabel drug particles without using solvents. In this method, particles are radiolabeled with a dispersion of 99mTc-labeled nanoparticles called TechnegasTM. Because a LDPI formulation is not comprised of particles but is a lyophilized cake aerosolized by air impact, the TechneCoat method cannot be used for the radiolabeling of LDPI formulations. We therefore modified the TechneCoat apparatus so that LDPI formulations were not aerosolized by the Technegas flow. Radiolabeling using a modified TechneCoat apparatus was validated with model LDPI formulations of interferon alpha (IFN). IFN of 99mTc-unlabeled, IFN of 99mTc-labeled, and 99mTc of 99mTc-labeled LDPI formulations showed similar behavior, and differences from IFN of 99mTc-unlabeled LDPI formulations were within ±15% in aerodynamic particle size distribution measurement. Our radiolabeling method for LDPI formulations may be useful for the quantification of drug deposition in human lungs.

A Radiolabeling Method for Precise Quantification of Polymers

Radiolabeling a protein, molecule, or polymer can provide accurate and precise quantification in biochemistry, biomaterials, pharmacology, and drug delivery research. Herein, we describe a method to 125I label two different polymers for precise quantification in different applications. The surfaces of model contact lenses were modified with phenylboronic acid to bind and release the natural polymer, hyaluronic acid (HA); HA uptake and release were quantified by radiolabeling. In the second example, the in vivo distribution of a mucoadhesive micelle composed of the block copolymer of poly(lactide)-b-poly(methacrylic acid-co-acrylamidophenylboronic acid) was investigated. The presence of phenyl boronic acid groups (PBA), which bind to mucosal surfaces, was proposed to improve the retention of the micelle. 125I labeling of polymers was examined for quantification of microgram amounts of HA present on a contact lens or to evaluate the enhanced retention of PBA micelles on mucosal surfaces in vivo. The introduction of phenol groups onto the polymers allowed for the labeling. HA was modified with phenol groups through a coupling reaction of its carboxylic acid with hydroxybenzylamine. Phenol functional block copolymer micelles with and without PBA were synthesized by including N-(4-hydroxyphenethyl)acrylamide during polymerization. The phenol groups of HA and the block copolymers were labeled with 125I using a modified ICl labeling method. 125I labeling enabled quantification of HA loading and release including the effect of varying amounts of PBA on the contact lens surfaces. Micelles made from 125I-labeled block copolymers with and without PBA were administered intranasally to Brown Norway rats. The animals were sacrificed either immediately after or 4 h after their last nasal instillation, and the nasopharyngeal tissues were removed and quantified. Radioactivity measurements demonstrated that the presence of the PBA mucosal binding groups led to approximately four times higher retention. The HA and block copolymer 125I labeling presented in this article demonstrates the utility of the method for quantification and tracking of microgram quantities of polymers in diverse applications.

Development of a Radiotracer for PET Imaging of the SNAP Tag.

Cell therapies have progressed to cures for hematopoietic disorders, neurodegenerative diseases, and cancer. However, only some patients can benefit from cell therapies even with prior screening. Due to the limited clinical methods to monitor the in vivo therapeutic functions of these transferred cells over time, the uncertain prognosis is hard to attenuate. Positron emission tomography (PET) cell tracking can provide comprehensive dynamic and spatial information on the proliferation status and whole-body distribution of the therapeutic cell. In this work, we designed and synthesized the first SNAP-tagged PET radiotracer. SNAP tag is an O6-alkylguanine-DNA alkyltransferase that can form an irreversible bond with 18F-BG-surface for in vivo cell tracking based on a reporter gene system. 18F-BG-surface was obtained by the F-Al radiolabeling method in 32 ± 7% radiochemical yield and showed a high in vitro stability in mouse serum. SNAP-tagged cells could be selectively targeted by 18F-BG-surface both in vitro (4.81 ± 0.08%AD/106 cell vs 2.26 ± 0.10%AD/106 cell) and in vivo (1.90 ± 0.05 vs 0.55 ± 0.02% ID/g, p < 0.01).

Cold Kit Labeling: The Future of 68Ga Radiopharmaceuticals?

Over the last couple of decades, gallium-68 (68Ga) has gained a formidable interest for PET molecular imaging of various conditions, from cancer to infection, through cardiac pathologies or neuropathies. It has gained routine use, with successful radiopharmaceuticals such as somatostatin analogs ([68Ga]Ga-DOTATOC and [68Ga]GaDOTATATE) for neuroendocrine tumors, and PSMA ligands for prostate cancer. It represents a major clinical impact, particularly in the context of theranostics, coupled with their 177Lu-labeled counterparts. Beside those, a bunch of new 68Ga-labeled molecules are in the preclinical and clinical pipelines, with some of them showing great promise for patient care. Increasing clinical demand and regulatory issues have led to the development of automated procedures for the production of 68Ga radiopharmaceuticals. However, the widespread use of these radiopharmaceuticals may rely on simple and efficient radiolabeling methods, undemanding in terms of equipment and infrastructure. To make them technically and economically accessible to the medical community and its patients, it appears mandatory to develop a procedure similar to the well-established kit-based 99mTc chemistry. Already available commercial kits for the production of 68Ga radiopharmaceuticals have demonstrated the feasibility of using such an approach, thus paving the way for more kit-based 68Ga radiopharmaceuticals to be developed. This article discusses the development of 68Ga cold kit radiopharmacy, including technical issues, and regulatory aspects.

Anchoring Group-Mediated Radiolabeling of Inorganic Nanoparticles─A Universal Method for Constructing Nuclear Medicine Imaging Nanoprobes.

Nuclear medicine imaging has aroused great interest in the design and synthesis of versatile radioactive nanoprobes, while most of the methods developed for radiolabeling nanoprobes are difficult to satisfy the criteria of clinical translation, including easy operation, mild labeling conditions, high efficiency, and high radiolabeling stability. Herein, we demonstrated the universality of a simple but efficient radiolabeling method recently developed for constructing nuclear imaging nanoprobes, that is, ligand anchoring group-mediated radiolabeling (LAGMERAL). In this method, a diphosphonate-polyethylene glycol (DP-PEG) decorating on the surface of inorganic nanoparticles plays an essential role. In principle, owing to the strong binding affinity to a great variety of metal ions, it can not only endow the underlying nanoparticles containing metal ions including some main group metal ions, transition metal ions, and lanthanide metal ions with excellent colloidal stability and biocompatibility but also enable efficient radiolabeling through the diphosphonate group. Based on this assumption, inorganic nanoparticles such as Fe3O4 nanoparticles, NaGdF4:Yb,Tm nanoparticles, and Cu2-xS nanoparticles, as representatives of functional inorganic nanoparticles suitable for different imaging modalities including magnetic resonance imaging (MRI), upconversion luminescence imaging (UCL), and photoacoustic imaging (PAI), respectively, were chosen to be radiolabeled with different kinds of radionuclides such as SPECT nuclides (e.g., 99mTc), PET nuclides (e.g., 68Ga), and therapeutic SPECT nuclides (e.g., 177Lu) to demonstrate the reliability of the LAGMERAL approach. The experimental results showed that the obtained nanoprobes exhibited high radiolabeling stability, and the whole radiolabeling process had negligible impacts on the physical and chemical properties of the initial nanoparticles. Through passive targeting SPECT/MRI of glioma tumor, active targeting SPECT/UCL of colorectal cancer, and SPECT/PAI of lymphatic metastasis, the outstanding potentials of the resulting radioactive nanoprobes for sensitive tumor diagnosis were demonstrated, manifesting the feasibility and efficiency of LAGMERAL.

89Zr-labeled PSMA ligands for pharmacokinetic PET imaging and dosimetry of PSMA-617 and PSMA-I&T: a preclinical evaluation and first in man.

Prolonged in vivo evaluation of PSMA tracers could improve tumor imaging and patient selection for 177Lu-PSMA-617 and 177Lu-PSMA-I&T. In this study, we present the radiolabeling method of PSMA-617 and PSMA-I&T with the long-lived positron emitter 89Zr to enable PET imaging up to 7days post-injection. We compared the biodistribution of 89Zr-PSMA-617 and 89Zr-PSMA-I&T to those of 177Lu-PSMA-617 and 177Lu-PSMA-I&T, respectively, in a PSMA+ xenograft model. Moreover, we provide the first human 89Zr-PSMA-617 images. PSMA ligands were labeled with 50-55MBq [89Zr]ZrCl4 using a two-step labeling protocol. For biodistribution, BALB/c nude mice bearing PSMA+ and PSMA- xenografts received 0.6µg (0.6-1MBq) of 89Zr-PSMA-617, 89Zr-PSMA-I&T, 177Lu-PSMA-617, or 177Lu-PSMA-I&T intravenously. Ex vivo biodistribution and PET/SPECT imaging were performed up to 168h post-injection. Dosimetry was performed from the biodistribution data. The patient received 90.5MBq 89Zr-PSMA-617 followed by PET/CT imaging. 89Zr-labeled PSMA ligands showed a comparable ex vivo biodistribution to its respective 177Lu-labeled counterparts with high tumor accumulation in the PSMA+ xenografts. However, using a dose estimation model for 177Lu, absorbed radiation dose in bone and kidneys differed among the 177Lu-PSMA and 89Zr-PSMA tracers. 89Zr-PSMA-617 PET in the first human patient showed high contrast of PSMA expressing tissues up to 48h post-injection. PSMA-617 and PSMA-I&T were successfully labeled with 89Zr and demonstrated high uptake in PSMA+ xenografts, which enabled PET up to 168h post-injection. The biodistribution of 89Zr-PSMA-I&T and 89Zr-PSMA-617 resembled that of 177Lu-PSMA-I&T and 177Lu-PSMA-617, respectively. The first patient 89Zr-PSMA-617 PET images were of high quality warranting further clinical investigation.

Radiolabeling of Nanomaterials: Advantages and Challenges.

Quantifying the distribution of nanomaterials in complex samples is of great significance to the toxicological research of nanomaterials as well as their clinical applications. Radiotracer technology is a powerful tool for biological and environmental tracing of nanomaterials because it has the advantages of high sensitivity and high reliability, and can be matched with some spatially resolved technologies for non-invasive, real-time detection. However, the radiolabeling operation of nanomaterials is relatively complicated, and fundamental studies on how to optimize the experimental procedures for the best radiolabeling of nanomaterials are still needed. This minireview looks back into the methods of radiolabeling of nanomaterials in previous work, and highlights the superiority of the “last-step” labeling strategy. At the same time, the problems existing in the stability test of radiolabeling and the suggestions for further improvement are also addressed.

Biodistribution of Mesoporous Carbon Nanoparticles via Technetium-99m Radiolabelling after Oral Administration to Mice.

The use of ordered mesoporous matrices, and in particular carbon-based mesoporous nanoparticles has shown great potential towards enhancing the bioavailability of orally administered drugs. Nevertheless, elucidation of the in vivo absorption, distribution, and excretion of such carriers is essential for understanding their behaviour, and radiolabelling provides a very useful way to track their occurrence inside the body. In this work, uniform spherical CMK-1-type ordered mesoporous carbon nanoparticles have been radiolabelled with Technetium-99m (99mTc) and traced after oral administration to mice. Ex vivo biodistribution studies showed that the radiolabelled nanoparticles accumulated almost exclusively in the gastrointestinal tract; complete elimination of the radiotracer was observed within 24 h after administration, with practically no uptake into other main organs. These findings along with the results from in vitro stability studies indicate that the spherical carbon nanoparticles examined could be safely used as drug carriers with minimal side effects, but also support the great value of radiolabelling methods for monitoring the particles’ behaviour in vivo.

Evaluation of Traumatic Spinal Cord Injury in a Rat Model Using 99mTc-GA-5 as a Potential In Vivo Tracer.

Spinal cord injury (SCI) refers to the damage suffered in the spinal cord by any trauma or pathology. The purpose of this work was to determine whether 99mTc-GA-5, a radiotracer targeting Glial Fibrillary Acidic Protein (GFAP), can reveal in vivo the reactivation of astrocytes in a murine model with SCI. A method for the 99mTc radiolabeling of the mouse anti-GFAP monoclonal antibody GA-5 was implemented. Radiochemical characterization was performed, and radioimmunohistochemistry assays were used to evaluate the integrity of 99mTc-GA-5. MicroSPECT/CT was used for in vivo imaging to trace SCI in the rats. No alterations in the GA-5’s recognition/specificity ability were observed after the radiolabeling. The GA-5’s radiolabeling procedure implemented in this work offers a practical method to allow the in vivo following of this monoclonal antibody to evaluate its biodistribution and specificity for GFAP receptors using SPECT/CT molecular imaging.

Anchoring Group Mediated Radiolabeling for Achieving Robust Nanoimaging Probes.

Radiolabeling counts for much in the functionalization of inorganic nanoparticles (NPs) because it endows NPs with high-sensitive imaging capacities apart from providing accurate pharmacokinetic information on the labeled particles, which makes the development of relevant radiolabeling chemistry highly desirable. Herein, a novel Ligand Anchoring Group MEdiated RAdioLabeling (LAGMERAL) method is reported, in which a polyethylene glycol (PEG) ligand with a diphosphonate (DP) terminal group plays a key role. It offers possibilities to radiolabel NPs through the spare coordination sites of the DP anchoring group. Through X-ray absorption spectroscopy studies, the coordination states of the foreign metal ions on the particle surface are investigated. In addition, radioactive Fe3 O4 NPs are prepared by colabeling the particles with 125 I at the outskirt of the particles through a phenolic hydroxyl moiety of the PEG ligand, and 99m Tc at the root of the ligand, respectively. In this way, the stabilities of these types of radiolabeling are compared both in vitro and in vivo to show the advantages of the LAGMERAL method. The outstanding stability of probe and simplicity of the labeling process make the current approach universal for creating advanced NPs with different combinations of functionalities of the inorganic NPs and radioactive properties of the metal radioisotopes.

Nanobody-Based Theranostic Agents for HER2-Positive Breast Cancer: Radiolabeling Strategies.

The overexpression of human epidermal growth factor 2 (HER2) in breast cancer (BC) has been associated with a more aggressive tumor subtype, poorer prognosis and shorter overall survival. In this context, the development of HER2-targeted radiotracers is crucial to provide a non-invasive assessment of HER2 expression to select patients for HER2-targeted therapies, monitor response and identify those who become resistant. Antibodies represent ideal candidates for this purpose, as they provide high contrast images for diagnosis and low toxicity in the therapeutic setting. Of those, nanobodies (Nb) are of particular interest considering their favorable kinetics, crossing of relevant biological membranes and intratumoral distribution. The purpose of this review is to highlight the unique characteristics and advantages of Nb-based radiotracers in BC imaging and therapy. Additionally, radiolabeling methods for Nb including direct labeling, indirect labeling via prosthetic group and indirect labeling via complexation will be discussed, reporting advantages and drawbacks. Furthermore, the preclinical to clinical translation of radiolabeled Nbs as promising theranostic agents will be reported.

Labeling the 5' Termini of DNA with Bacteriophage T4 Polynucleotide Kinase.

The removal of 5' phosphates from nucleic acids with phosphatases and their readdition in radiolabeled form by bacteriophage T4 polynucleotide kinase is a widely used technique for generating 32P-labeled probes. When the reaction is performed efficiently, 40%-50% of the protruding 5' termini in the reaction becomes radiolabeled. However, the specific activity of the resulting probes is not as high as that obtained by other radiolabeling methods because only one radioactive atom is introduced per DNA molecule. Nevertheless, the availability of [γ-32P]ATP with specific activities in the 3000-7000 Ci/mmol range allows the synthesis of probes suitable for many purposes. This protocol includes procedures for labeling the 5' ends of dsDNA and oligonucleotides.

Biodistribution of 68/67Ga-Radiolabeled Sphingolipid Nanoemulsions by PET and SPECT Imaging.

Background and PurposeNon-invasive imaging methodologies, especially nuclear imaging techniques, have undergone an extraordinary development over the last years. Interest in the development of innovative tracers has prompted the emergence of new nanomaterials with a focus on nuclear imaging and therapeutical applications. Among others, organic nanoparticles are of the highest interest due to their translational potential related to their biocompatibility and biodegradability. Our group has developed a promising new type of biocompatible nanomaterials, sphingomyelin nanoemulsions (SNs). The aim of this study is to explore the potential of SNs for nuclear imaging applications.MethodsReady-to-label SNs were prepared by a one-step method using lipid derivative chelators and characterized in terms of their physicochemical properties. Stability was assessed under storage and after incubation with human serum. Chelator-functionalized SNs were radiolabeled with 67Ga and 68Ga, and the radiochemical yield (RCY), radiochemical purity (RCP) and radiochemical stability (RCS) were determined. Finally, the biodistribution of 67/68Ga-SNs was evaluated in vivo and ex vivo.ResultsHere, we describe a simple and mild one-step method for fast and efficient radiolabeling of SNs with 68Ga and 67Ga radioisotopes. In vivo experiments showed that 67/68Ga-SNs can efficiently and indistinctly be followed up by PET and SPECT. Additionally, we proved that the biodistribution of the 67/68Ga-SNs can be conveniently modulated by modifying the surface properties of different hydrophilic polymers, and therefore the formulation can be further adapted to the specific requirements of different biomedical applications.ConclusionThis work supports 67/68Ga-SNs as a novel probe for nuclear imaging with tunable biodistribution and with great potential for the future development of nanotheranostics.

Metabolic radiolabeling and in vivo PET imaging of cytotoxic T lymphocytes to guide combination adoptive cell transfer cancer therapy

BackgroundAdoptive T cell transfer-based immunotherapy yields unsatisfactory results in the treatment of solid tumors, partially owing to limited tumor infiltration and the immunosuppressive microenvironment in solid tumors. Therefore, strategies for the noninvasive tracking of adoptive T cells are critical for monitoring tumor infiltration and for guiding the development of novel combination therapies.MethodsWe developed a radiolabeling method for cytotoxic T lymphocytes (CTLs) that comprises metabolically labeling the cell surface glycans with azidosugars and then covalently conjugating them with 64Cu-1,4,7-triazacyclononanetriacetic acid-dibenzo-cyclooctyne (64Cu-NOTA-DBCO) using bioorthogonal chemistry. 64Cu-labeled control-CTLs and ovalbumin-specific CTLs (OVA-CTLs) were tracked using positron emission tomography (PET) in B16-OVA tumor-bearing mice. We also investigated the effects of focal adhesion kinase (FAK) inhibition on the antitumor efficacy of OVA-CTLs using a poly(lactic-co-glycolic) acid (PLGA)-encapsulated nanodrug (PLGA-FAKi).ResultsCTLs can be stably radiolabeled with 64Cu with a minimal effect on cell viability. PET imaging of 64Cu-OVA-CTLs enables noninvasive mapping of their in vivo behavior. Moreover, 64Cu-OVA-CTLs PET imaging revealed that PLGA-FAKi induced a significant increase in OVA-CTL infiltration into tumors, suggesting the potential for a combined therapy comprising OVA-CTLs and PLGA-FAKi. Further combination therapy studies confirmed that the PLGA-FAKi nanodrug markedly improved the antitumor effects of adoptive OVA-CTLs transfer by multiple mechanisms.ConclusionThese findings demonstrated that metabolic radiolabeling followed by PET imaging can be used to sensitively profile the early-stage migration and tumor-targeting efficiency of adoptive T cells in vivo. This strategy presents opportunities for predicting the efficacy of cell-based adoptive therapies and for guiding combination regimens.Graphic

Enzymatic Methods for the Site-Specific Radiolabeling of Targeting Proteins.

Site-specific conjugation of proteins is currently required to produce homogenous derivatives for medicine applications. Proteins derivatized at specific positions of the polypeptide chain can actually show higher stability, superior pharmacokinetics, and activity in vivo, as compared with conjugates modified at heterogeneous sites. Moreover, they can be better characterized regarding the composition of the derivatization sites as well as the conformational and activity properties. To this aim, several site-specific derivatization approaches have been developed. Among these, enzymes are powerful tools that efficiently allow the generation of homogenous protein–drug conjugates under physiological conditions, thus preserving their native structure and activity. This review will summarize the progress made over the last decade on the use of enzymatic-based methodologies for the production of site-specific labeled immunoconjugates of interest for nuclear medicine. Enzymes used in this field, including microbial transglutaminase, sortase, galactosyltransferase, and lipoic acid ligase, will be overviewed and their recent applications in the radiopharmaceutical field will be described. Since nuclear medicine can benefit greatly from the production of homogenous derivatives, we hope that this review will aid the use of enzymes for the development of better radio-conjugates for diagnostic and therapeutic purposes.

Copper-mediated radioiodination reaction through aryl boronic acid or ester precursor and its application to direct radiolabeling of a cyclic peptide.

A copper-mediated radioiodination using aryl boronic precursors is attracting attention as a solution to oxidative iododestannylation and nickel-mediated radioiodination drawbacks. The copper-mediated radiolabeling method allows radioiodination at room temperature with stable aryl boronic precursors without preparing complex starting materials or reagents and can be performed in a reaction vessel exposed to air. This method has good potential in radiochemistry; however, studies on the scope of copper-mediated radioiodination through boronic precursors are insufficient. In particular, few reports have demonstrated the effect of protecting groups on radiolabeling efficiency. Therefore, the effect of the protecting group of aryl boronic acids on the copper-mediated radioiodination was investigated. In addition, this method, which does not require heating, is expected to be useful for direct radiolabeling of peptides. Thus, we attempted direct radioiodination of c(RGDyk) as an example. The resulting radioiodination method was well tolerated in various substrates and was unaffected by the pinacol ester-type protecting group. Also, c(RGDyk) was labeled with 125 I via copper-mediated radioiodination using an aryl boronic acid precursor. The reaction time and yield were improved, compared with the indirect method. Furthermore, the large difference in polarity between the boronic acid precursor and the radiolabeled compound facilitated purification.

Novel late-stage radiosynthesis of 5-[18F]-trifluoromethyl-1,2,4-oxadiazole (TFMO) containing molecules for PET imaging

Small molecules that contain the (TFMO) moiety were reported to specifically inhibit the class-IIa histone deacetylases (HDACs), an important target in cancer and the disorders of the central nervous system (CNS). However, radiolabeling methods to incorporate the [18F]fluoride into the TFMO moiety are lacking. Herein, we report a novel late-stage incorporation of [18F]fluoride into the TFMO moiety in a single radiochemical step. In this approach the bromodifluoromethyl-1,2,4-oxadiazole was converted into [18F]TFMO via no-carrier-added bromine-[18F]fluoride exchange in a single step, thus producing the PET tracers with acceptable radiochemical yield (3–5%), high radiochemical purity (> 98%) and moderate molar activity of 0.33–0.49 GBq/umol (8.9–13.4 mCi/umol). We validated the utility of the novel radiochemical design by the radiosynthesis of [18F]TMP195, which is a known TFMO containing potent inhibitor of class-IIa HDACs.

An HPLC and UHPLC-HRMS approach to study PSMA-11 instability in aqueous solution

BackgroundThe stability of precursors and reagents is of utmost importance for developing a robust radiolabelling method that provides high and constant radiochemical yield and radiochemical purity.While performing the QC of the [68Ga]Ga-PSMA-11 injectable solutions according to Ph. Eur. Monograph that has recently been published, a trend to the instability of the standard PSMA-11, the same used as a precursor for [68Ga]Ga-PSMA-11 radiosynthesis, has been observed. This instability led to the formation of a side product in a time-dependent manner. The formation of this compound, besides making the implementation of the Ph. Eur. analytical method more difficult, negatively influenced the radiochemical yield and the radiochemical purity by increasing gallium-68 in colloidal and ionic forms.ResultsThe nature of the side product was investigated by adding chelators, such as EDTA, to PSMA-11 solutions and using the combination of UHPLC-HRMS. The results led to the definition of the side product structure, as natFe-PSMA-11, from the combination of the high-affinity chelator HBED-CC, present in the molecule of PSMA-11, and environmental Fe (III).ConclusionsStrategies to reduce the risk of low radiolabeling yields and to increase the stability of the PSMA-11 in an aqueous solution were also discussed.

FAPI-04 PET/CT Using [18F]AlF Labeling Strategy: Automatic Synthesis, Quality Control, and In Vivo Assessment in Patient.

68Ga labeled FAPI is the current standard for FAPI-PET, but its batch activity is limited. [18F]AlF-NOTA-FAPI-04 is a promising alternative combining the advantages of a chelator-based radiolabeling method with the unique properties of fluorine-18. The objective of this study was to develop a quick automatic method for synthesis of [18F]AlF-NOTA-FAPI-04 using a AllinOne synthesis system, and perform PET imaging with [18F]AlF-NOTA-FAPI-04 on patients. [18F]AlF-NOTA-FAPI-04 was produced, and its quality control was conducted by HPLC equipped with a radioactive detector. [18F]AlF-NOTA-FAPI-04 PET/CT imaging was performed in normal BALB/c mice (n = 3) and 4T1 breast cancer models (n = 3) to determine its biodistribution. Then [18F]AlF-NOTA-FAPI-04 and 18F-fluorodeoxyglucose (FDG) PET/CT imaging were performed in an invasive ductal carcinoma patient (female, 54 years old). The synthesis time of [18F]AlF-NOTA-FAPI-04 was about 25 min, and the radiochemical yield was 26.4 ± 1.5% (attenuation correction, n = 10). The radiochemical purity was above 99.0% and was above 98.0% after 6 h. The product was colorless transparent solution with pH value of 7.0–7.5, and the specific activity was 49.41 ± 3.19 GBq/μmol. PET/CT imaging in mice showed that physiological uptake of [18F]AlF-NOTA-FAPI-04 was mainly in the biliary system and bladder, and [18F]AlF-NOTA-FAPI-04 highly concentrated in tumor xenografts. PET/CT imaging in the patient showed that [18F]AlF-NOTA-FAPI-04 obtained high tumor background ratio (TBR) value of 8.44 in segment V and VI, while TBR value was 2.55 by 18F-FDG. [18F]AlF-NOTA-FAPI-04 could be synthesized with high radiochemical yield and batch production by AllinOne module and show excellent diagnosis performance in cancer patients.