Positron Emission Tomography Probe Research Articles

Molecular Imaging of Alzheimer's Disease-Related Sigma-1 Receptor in the Brain via a Novel Ru-Mediated Aromatic 18F-deoxyfluorination Probe.

Sigma-1 receptor (σ1R) is an intracellular protein implicated in a spectrum of neurodegenerative conditions, notably Alzheimer's disease (AD). Positron emission tomography (PET) imaging of brain σ1R could provide a powerful tool for better understanding the underlying pathomechanism of σ1R in AD. In this study, we successfully developed a 18F-labeled σ1R radiotracer [18F]CNY-05 via an innovative ruthenium (Ru)-mediated 18F-deoxyfluorination method. [18F]CNY-05 exhibited preferable brain uptake, high specific binding, and slightly reversible pharmacokinetics within the PET scanning time window. PET imaging of [18F]CNY-05 in nonhuman primates (NHP) indicated brain permeability, metabolic stability, and safety. Moreover, autoradiography and PET studies of [18F]CNY-05 in the AD mouse model found a significantly decreased brain uptake compared to that in wild-type mice. Collectively, we have provided a novel 18F-radiolabeled σ1R PET probe, which enables visualizing brain σ1R in health and neurological diseases.

Synthesis and Evaluation of [18F]AlF-NOTA-c-DVAP: A Novel PET Probe for Imaging GRP78 in Cancer.

GRP78, a member of the HSP70 superfamily, is an endoplasmic reticulum chaperone protein overexpressed in various cancers, making it a promising target for cancer imaging and therapy. Positron emission tomography (PET) imaging offers unique advantages in real time, noninvasive tumor imaging, rendering it a suitable tool for targeting GRP78 in tumor imaging to guide targeted therapy. Several studies have reported successful tumor imaging using PET probes targeting GRP78. However, existing PET probes face challenges such as low tumor uptake, inadequate in vivo distribution, and high abdominal background signal. Therefore, this study introduces a novel peptide PET probe, [18F]AlF-NOTA-c-DVAP, for targeted tumor imaging of GRP78. [18F]AlF-NOTA-c-DVAP was radiolabeled with fluoride-18 using the aluminum-[18F]fluoride ([18F]AlF) method. The study assessed the partition coefficients, stability in vitro, and metabolic stability of [18F]AlF-NOTA-c-DVAP. Micro-PET imaging, pharmacokinetic analysis, and biodistribution studies were carried out in tumor-bearing mice to evaluate the probe's performance. Docking studies and pharmacokinetic analyses of [18F]AlF-NOTA-c-DVAP were also performed. Immunohistochemical and immunofluorescence analyses were conducted to confirm GRP78 expression in tumor tissues. The probe's binding affinity to GRP78 was analyzed by molecular docking simulation. [18F]AlF-NOTA-c-DVAP was radiolabeled in just 25 min with a high yield of 51 ± 16%, a radiochemical purity of 99%, and molar activity within the range of 20-50 GBq/μmol. [18F]AlF-NOTA-c-DVAP demonstrated high stability in vitro and in vivo, with a logD value of -3.41 ± 0.03. Dynamic PET imaging of [18F]AlF-NOTA-c-DVAP in tumors showed rapid uptake and sustained retention, with minimal background uptake. Biodistribution studies revealed rapid blood clearance and excretion through the kidneys following a single-compartment reversible metabolic model. In PET imaging, the T/M ratios for A549 tumors (high GRP78 expression), MDA-MB-231 tumors (medium expression), and HepG2 tumors (low expression) at 60 min postintravenous injection were 10.48 ± 1.39, 6.25 ± 0.47, and 3.15 ± 1.15% ID/g, respectively, indicating a positive correlation with GRP78 expression. This study demonstrates the feasibility of using [18F]AlF-NOTA-c-DVAP as a PET tracer for imaging GRP78 in tumors. The probe shows promising results in terms of stability, specificity, and tumor targeting. Further research may explore the clinical utility and potential therapeutic applications of this PET tracer for cancer diagnosis.

Controllable Dopamine Conjugation Boosts Fluorescence, Biocompatibility, and PET Imaging‐Guided Toxicity Assessment of Polycations

AbstractAs well known in bioactives delivery and cancer/inflammation theranostics, polycations have recently extended their biomedical potentials in reducing visceral fat, embolizing body fluid, modulating blood coagulation, and ameliorating hyperammonemia. However, positive charges that dominate various action mechanisms, often raise risks in biosafety concerns. Also, the lack of intrinsic imaging properties of polycations makes it challenging to uncover their pharmacokinetic profiles in living objects. Herein, dopamine conjugation is demonstrated controllable and highly efficient in boosting the fluorescence or even white color emission of various polycations including hyperbranched poly(amido amine) (HPAA), polyethyleneimine and poly‐L‐lysine. By shielding partial surface positive charges, increasing hydrophobicity, and inducing aqueous self‐assembly, dopamine conjugation can significantly enhance the biocompatibility and decrease the toxicity and immunogenicity of polycations. Furthermore, the catechol‐metal binding interaction facilitates the accessibility of polycation‐based positron emission tomography (PET) probes. Different tissue uptake and biodistributions of gallium‐68‐radiolabeled HPAA before and after dopamine conjugation indicate that PET imaging can be a useful supplement to evaluate the dynamic toxicities of polycations.

Synthesis and preclinical evaluation of 11C-labeled 7-Oxo-2,4,5,7-tetrahydro-6H-pyrazolo[3,4-c]pyridine radioligands for RIPK1 positron emission tomography imaging

Targeting receptor-interacting protein kinase 1 (RIPK1) has emerged as a promising therapeutic strategy for various neurodegenerative disorders. The development of a positron emission tomography (PET) probe for brain RIPK1 imaging could offer a valuable tool to assess therapeutic effectiveness and uncover the neuropathology associated with RIPK1. In this study, we present the development and characterization of two new PET radioligands, [11C]PB218 and [11C]PB220, which have the potential to facilitate brain RIPK1 imaging. [11C]PB218 and [11C]PB220 were successfully synthesized with a high radiochemical yield (34 % − 42 %) and molar activity (293 – 314 GBq/µmol). PET imaging characterization of two radioligands was conducted in rodents, demonstrating that both newly developed tracers have good brain penetration (maximum SUV = 0.9 – 1.0) and appropriate brain clearance kinetic profiles. Notably, [11C]PB218 has a more favorable binding specificity than [11C]PB220. A PET/MR study of [11C]PB218 in a non-human primate exhibited good brain penetration, desirable kinetic properties, and a safe profile, thus supporting the translational applicability of our new probe. These investigations enable further translational exploration of [11C]PB218 for drug discovery and PET probe development targeting RIPK1.

A novel PET probe to selectively image heat shock protein 90α/β isoforms in the brain

BackgroundHeat shock proteins (HSPs) are present throughout the brain. They function as molecular chaperones, meaning they help with the folding and unfolding of large protein complexes. These chaperones are vital in the development of neuropathological conditions such as Alzheimer’s disease and Lewy body disease, with HSP90, a specific subtype of HSP, playing a key role. Many studies have shown that drugs that inhibit HSP90 activity have beneficial effects in the neurodegenerative diseases. Therefore, HSP90 PET imaging ligand can be used effectively to study HSP90 in neurodegenerative diseases. Among four HSP90 isoforms, two cytosolic isoforms (HSP90α and HSP90β) thought to be involved in the structural homeostasis of the proteins related to the neurodegenerative diseases. Currently, no useful PET imaging ligands selectively targeting the two cytosolic isoforms of HSP90 have been available yet.ResultsIn this study, we developed a novel positron emission tomography (PET) imaging ligand, [11C]BIIB021, by 11C-radiolabeling (a positron emitter with a half-life of 20.4 min) 6-Chloro-9-[(4-methoxy-3,5-dimethylpyridin-2-yl)methyl]-9H-purin-2-amine (BIIB021), an inhibitor with a high affinity for and selectivity to HSP90α and HSP90β. [11C]BIIB021 was synthesized with a high yield, molar activity and radiochemical purity. [11C]BIIB021 showed a high binding affinity for rat brain homogenate as well as human recombinant HSP90α and HSP90β proteins. Radioactivity was well detected in the rat brain (SUV 1.4). It showed clear specific binding in PET imaging of healthy rats and autoradiography of healthy rat and human brain sections. Radiometabolite was detected in the brain, however, total distribution volume was well quantified using dual-input graphical model. Inhibition of p-glycoprotein increased brain radioactivity concentrations. However, total distribution volume values with and without p-glycoprotein inhibition were nearly the same.ConclusionsWe have developed a new PET imaging agent, [11C]BIIB021, specifically targeting HSP90α/β. We have been successful in synthesizing [11C]BIIB021 and in vitro and in vivo imaging HSP90α/β. However, the quantification of HSP90α/β is complicated by the presence of radiometabolites in the brain and the potential to be a substrate for p-glycoprotein. Further efforts are needed to develop radioligand suitable for imaging of HSP90α/β.

Radiosynthesis and In Vitro Evaluation of [11C]tozadenant as Adenosine A2A Receptor Radioligand.

Tozadenant (4-hydroxy-N-(4-methoxy-7-morpholinobenzo[d]thiazol-2-yl)-4-methylpiperidine-1-carboxamide) is a highly selective adenosine A2A receptor (A2AR) antagonist and a promising lead structure for the development of A2AR-selective positron emission tomography (PET) probes. Although several 18F-labelled tozadenant derivatives showed favorable in vitro properties, recent in vivo PET studies observed poor brain penetration and lower specific binding than anticipated from the in vitro data. While these findings might be attributable to the structural modification associated with 18F-labelling, they could also reflect inherent properties of the parent compound. However, PET studies with radioisotopologues of tozadenant to evaluate its cerebral pharmacokinetics and brain distribution are still lacking. In the present work, we applied N-Boc-O-desmethyltozadenant as a suitable precursor for the preparation of [O-methyl-11C]tozadenant ([11C]tozadenant) by O-methylation with [11C]methyl iodide followed by acidic deprotection. This approach afforded [11C]tozadenant in radiochemical yields of 18 ± 2%, with molar activities of 50-60 GBq/µmol (1300-1600 mCi/µmol) and radiochemical purities of 95 ± 3%. In addition, in vitro autoradiography in pig and rat brain slices demonstrated the expected striatal accumulation pattern and confirmed the A2AR specificity of the radioligand, making it a promising tool for in vivo PET studies on the cerebral pharmacokinetics and brain distribution of tozadenant.

Lysosome-targeting and legumain-triggered 68Ga-labeled probe for enhanced tumor PET imaging

Legumain is overexpressed in diverse tumors, serving as a significant tumor biomarker. Our study aimed to develop a new positron emission tomography (PET) probe [68Ga]Ga-NOTA-SF-AANM for imaging the expression level of legumain in vivo. The radio-labeling of [68Ga]Ga-NOTA-SF-AANM was accomplished within 15 min. The probe has good stability in vitro. NOTA-SF-AANM exhibited rapid response to recombinant human legumain enzyme, enabling intramolecular condensation cyclization. Cellular uptake and lysosomal co-localization experiments demonstrated that the probe was able to differentiate specifically between MDA-MB-468 and PC-3 cancer cells with varying degrees of legumain expression. PET imaging displayed a significant and persistent signal (3.59 ± 0.30 %ID/mL at 60 min) in MDA-MB-468 tumors, while PC-3 tumors exhibited lower radioactivity (1.08 ± 0.35 %ID/mL at 60 min), further validating the specific targeting of [68Ga]Ga-NOTA-SF-AANM towards legumain. [68Ga]Ga-NOTA-SF-AANM is a promising tool for precise diagnosis of legumain-related diseases due to its advantages in radio-labeling and accurate monitoring of legumain expression levels.

Synthesis and biological evaluation of novel 18F-labeled 2,4-diaminopyrimidine derivatives for detection of ghrelin receptor in the brain

The ghrelin receptor (GHSR) is known to regulate various physiological processes including appetite, food intake, and growth hormone release. Its expression is mainly observed in the brain, pancreas, stomach, and intestine. However, the functions of the receptor have not been fully elucidated. GHSR imaging with positron emission tomography (PET) is expected to further understanding of the functions and pathologies of the receptor. In this study, we newly designed and synthesized diaminopyrimidine derivatives ([18F]BPP-1 and [18F]BPP-2) and evaluated their utility as novel PET probes targeting GHSR. In in vitro competitive binding assays, the binding affinity of BPP-2 for GHSR (Ki = 274 nM) was comparable to that of the diaminopyimidine lead compound Abb8a (Ki = 109 nM). In a biodistribution study using normal mice, [18F]BPP-2 displayed low uptake in the brain and moderate uptake in the pancreas, but high radioactivity accumulation in bone was observed due to its defluorination in vivo. Taken together, although further improvement of the pharmacokinetics is needed, the diaminopyrimidine scaffold has potential for the development of useful GHSR-targeting PET probes.

Characterization of (R)- and (S)-[18F]OF-NB1 in Rodents as Positron Emission Tomography Probes for Imaging GluN2B Subunit-Containing N-Methyl-d-Aspartate Receptors.

The N-methyl-d-aspartate receptor (NMDAR) subtype 2B (GluN1/2B) is implicated in various neuropathologies. Given the lack of a validated radiofluorinated positron emission tomography (PET) probe for the imaging of GluN1/2B receptors, we comprehensively investigated the enantiomers of [18F]OF-NB1 in rodents. Particularly, the (R)- and (S)- enantiomers were evaluated using in silico docking, in vitro autoradiography, in vivo PET imaging, and ex vivo biodistribution studies. A select panel of GluN1/2B antagonists (CP-101,606, CERC-301, and eliprodil) and the off-target sigma-1 receptor ligands (fluspidine and SA4503) were used to determine the specificity and selectivity of the tested enantiomers. Additionally, a nonmetal-mediated radiofluorination strategy was devised that harnesses the potential of diaryliodoniums in the nucleophilic radiofluorination of nonactivated aromatic compounds. Both enantiomers exhibited known GluN1/2B binding patterns; however, the R-enantiomer showed higher GluN1/2B-specific accumulation in rodent autoradiography and higher brain uptake in PET imaging experiments compared to the S-enantiomer. Molecular simulation studies provided further insights with respect to the difference in binding, whereby a reduced ligand-receptor interaction was observed for the S-enantiomer. Nonetheless, both enantiomers showed dose dependency when two different doses (1 and 5 mg/kg) of the GluN1/2B antagonist, CP-101,606, were used in the PET imaging study. Taken together, (R)-[18F]OF-NB1 appears to exhibit the characteristics of a suitable PET probe for imaging of GluN2B-containing NMDARs in clinical studies.

Repurposing of the PET Probe Prototype PiB for Label and Radiation-Free CEST MRI Molecular Imaging of Amyloid.

Positron emission tomography (PET) probes are specific and sensitive while suffering from radiation risk. It is worthwhile to explore the chemical emission saturation transfer (CEST) effects of the probe prototypes and repurpose them for CEST imaging to avoid radiation. In this study, we used 11C-PiB as an example of a PET probe for detecting amyloid and tested the feasibility of repurposing this PET probe prototype, PiB, for CEST imaging. After optimizing the parameters through preliminary phantom experiments, we used APP/PS1 transgenic mice and age-matched C57 mice for in vivo CEST magnetic resonance imaging (MRI) of amyloid. Furthermore, the pathological assessment was conducted on the same brain slices to evaluate the correlation between the CEST MRI signal abnormality and β-amyloid deposition detected by immunohistochemical staining. In our results, the Z-spectra revealed an apparent CEST effect that peaked at approximately 6 ppm. APP/PS1 mice as young as 9 months injected with PiB showed a significantly higher CEST effect compared to the control groups. The hyperintense region was correlated with the Aβ deposition shown by pathological staining. In conclusion, repurposing the PET probe prototype for CEST MRI imaging is feasible and enables label- and radiation-free detection of the amyloid while maintaining the sensitivity and specificity of the ligand. This study opens the door to developing CEST probes based on PET probe prototypes.

PET Tracer-Based Glucose Uptake Predicts Clinical Response to Induction Therapy in Acute Myeloid Leukaemia

Metabolic re-programming enables cancer cells to harness various carbon substrates for energy production and biomass synthesis. Cell-intrinsic mechanisms of preferential glucose uptake is reported in acute myeloid leukaemia (AML). We previously identified leukaemia cells uptake more glucose compared with bone marrow micro-environment (BMME) cells in a MLL-AF9-driven AML mouse model (Leukemia 2023;37:1407). It is unknown how glucose is partitioned in the bone marrow, and whether glucose uptake variation correlates with response to induction chemotherapy in persons with newly-diagnosed AML. The radionuclide-labeled glucose analog 18F-2′-deoxy-2′-fluorodeoxyglucose ( 18F-FDG), a positron emission tomography (PET) probe, can be used to quantify in vivo glucose uptake in this setting. We studied this via a prospective pilot study (NCT05919199) in subjects with newly-diagnosed AML before receiving induction chemotherapy. Of 7 patients who have been enrolled in the study to date, all subjects were presented with various intensities of diffuse bone marrow 18F-FDG uptake in PET/CT images (maximum standardized uptake value (SUV max) mean, 6.0; range, 3.8-10.6). Subjects with higher SUV max in bone marrow had a higher likelihood of achieving a remission after induction therapy (Figure A). We use a 18F-FDG probe combined with magnetic-activated cell sorting (MACS) to quantify glucose uptake ( 18F radioactivity) in bulk and/or fractionated cell populations from subjects with AML at diagnosis. The associations between 18F-FDG uptake and response was better defined by per-cell glucose uptake quantification ( 18F counts per minute (CPM) per million cells) of bulk bone marrow cells. Higher 18F-FDG uptake correlated with a higher remission rate (Figure B). Notably, leukaemia cells from responders metabolized more glucose compared with micro-environment cells both of which had higher glucose uptake compared with non-responders. In contrast, leukaemia cells from non-responders had markedly decreased glucose uptake compared with micro-environment cells even they were sharing the same metabolic pool. These data indicate subject-specific glucose uptake is not directly affected by glucose availability but by cell-intrinsic glucose uptake programs. In light of data implicating mitochondrial metabolism in preserving leukaemia stem cells we speculated other energy sources such as amino acids and, fatty acids might compensate for decreased glucose uptake in non-responders. We utilized a computationally metabolic fluxome model, scFEA (Genome Res 2021;31:1867), which characterizes stochiometric relationships of metabolic networks and principal component analyses based on metabolism-related transcripts clustered samples by response. scFEA analysis of RNA-seq indicated responders had higher flux in the glucose import module, while flux of glutamine uptake were enriched in non-responders. These results suggest a switch from glucose (“Hot” AML) to glutamine metabolism (“Cold” AML) may protect leukaemia cells from chemotherapy stress. Taken together, we provide a rationale for in vivo evaluation of glucose uptake in AML patients, which is of potential use in discriminating patient response or resistance to induction therapies.

＜Editors' Choice＞ Pattern of THK 5351 retention in normal aging involves core regions of resting state networks associated with higher cognitive function.

We aimed to elucidate the distribution pattern of the positron emission tomography probe [18F]THK 5351, a marker for astrogliosis and tau accumulation, in healthy aging. We also assessed the relationship between THK5351 retention and resting state networks. We enrolled 62 healthy participants in this study. All participants underwent magnetic resonance imaging/positron emission tomography scanning consisting of T1-weighted images, resting state functional magnetic resonance imaging, Pittsburgh Compound-B and THK positron emission tomography. The preprocessed THK images were entered into a scaled subprofile modeling/principal component analysis to extract THK distribution patterns. Using the most significant THK pattern, we generated regions of interest, and performed seed-based functional connectivity analyses. We also evaluated the functional connectivity overlap ratio to identify regions with high between-network connectivity. The most significant THK distributions were observed in the medial prefrontal cortex and bilateral putamen. The seed regions of interest in the medial prefrontal cortex had a functional connectivity map that significantly overlapped with regions of the dorsal default mode network. The seed regions of interest in the putamen showed strong overlap with the basal ganglia and anterior salience networks. The functional connectivity overlap ratio also showed that three peak regions had the characteristics of connector hubs. We have identified an age-related spatial distribution of THK in the medial prefrontal cortex and basal ganglia in normal aging. Interestingly, the distribution's peaks are located in regions of connector hubs that are strongly connected to large-scale resting state networks associated with higher cognitive function.

Optimization of a 1,4,7-Triazacyclononane-1,4-diacetic acid (NODA) Derivative Radiofluorination by Al18 F Complexation Using a Design of Experiments Approach.

Fluorine-18 (18 F) is the most favorable positron emitter for radiolabeling Positron Emission Tomography (PET) probes. However, conventional 18 F labeling through covalent C-F bond formation is challenging, involving multiple steps and stringent conditions unsuitable for sensitive biomolecular probes whose integrity may be altered. Over the past decade, an elegant new approach has been developed involving the coordination of an aluminum fluoride {Al18 F} species in aqueous media at a late-stage of the synthetic process. The objective of this study was to implement this method and to optimize radiolabeling efficiency using a Design of Experiments (DoE). To assess the impact of various experimental parameters on {Al18 F} incorporation, a pentadentate chelating agent NODA-MP-C4 was prepared as a model compound. This model carried a thiourea function present in the final conjugates resulting from the grafting of the chelating agent onto the probe. The formation of the radioactive complex Al18 F-NODA-MP-C4 was studied to achieve the highest radiochemical conversion. A complementary "cold" series study using the natural isotope 19 F was also conducted to guide the radiochemical operating conditions. Ultimately, Al18 F-NODA-MP-C4 was obtained with a reproducible and satisfactory radiochemical conversion of 79±3.5 % (n=5).

Deoxyfluorination of phenols for chemoselective 18F-labeling of peptides.

The challenge of forming C-18F bonds is often a bottleneck in the development of new 18F-labeled tracer molecules for noninvasive functional imaging studies using positron emission tomography (PET). Nucleophilic aromatic substitution is the most widely employed reaction to functionalize aromatic substrates with the radioactive fluorine-18 but its scope is restricted to arenes containing electron-withdrawing substituents. Furthermore, many protic functional groups are incompatible with basic fluoride anions. Peptide substrates, which are highly desirable targets for PET molecular imaging, are particularly challenging to label with fluorine-18 because they are densely functionalized and sensitive to high temperatures and basic conditions. To expand the utility of nucleophilic aromatic substitution with fluorine-18, we describe two complementary procedures for the radiodeoxyfluorination of bench-stable and easy-to-access phenols that ensure rapid access to densely functionalized electron-rich and electron-poor 18F-aryl fluorides. The first procedure details the synthesis of an 18F-synthon and its subsequent ligation to the cysteine residue of Arg-Gly-Asp-Cys in 10.5 h from commercially available starting materials (189-min radiosynthesis). The second procedure describes the incorporation of commercially available CpRu(Fmoc-tyrosine)OTf into a fully protected peptide Lys-Met-Glu-(CpRu-Tyr)-Leu via solid-phase peptide synthesis and subsequent ruthenium-mediated uronium deoxyfluorination with fluorine-18 followed by deprotection, accomplished within 7 d (116-min radiosynthesis). Both radiolabeling methods are highly chemoselective and have conveniently been automated using commercially available radiosynthesis equipment so that the procedures described can be employed for the synthesis of peptide-based PET probes for in vivo imaging studies according to as low as reasonably achievable (ALARA) principles.

Characterization of Structurally Diverse 18F-Labeled d-TCO Derivatives as a PET Probe for Bioorthogonal Pretargeted Imaging.

Background: The pretargeted imaging strategy using inverse electron demand Diels-Alder (IEDDA) cycloaddition between a trans-cyclooctene (TCO) and tetrazine (Tz) has emerged and rapidly grown as a promising concept to improve radionuclide imaging and therapy in oncology. This strategy has mostly relied on the use of radiolabeled Tz together with TCO-modified targeting vectors leading to a rapid growth of the number of available radiolabeled tetrazines, while only a few radiolabeled TCOs are currently reported. Here, we aim to develop novel and structurally diverse 18F-labeled cis-dioxolane-fused TCO (d-TCO) derivatives to further expand the bioorthogonal toolbox for in vivo ligation and evaluate their potential for positron emission tomography (PET) pretargeted imaging. Results: A small series of d-TCO derivatives were synthesized and tested for their reactivity against tetrazines, with all compounds showing fast reaction kinetics with tetrazines. A fluorescence-based pretargeted blocking study was developed to investigate the in vivo ligation of these compounds without labor-intensive prior radiochemical development. Two compounds showed excellent in vivo ligation results with blocking efficiencies of 95 and 97%. Two novel 18F-labeled d-TCO radiotracers were developed, from which [18F]MICA-214 showed good in vitro stability, favorable pharmacokinetics, and moderate in vivo stability. Micro-PET pretargeted imaging with [18F]MICA-214 in mice bearing LS174T tumors treated with tetrazine-modified CC49 monoclonal antibody (mAb) (CC49-Tz) showed significantly higher uptake in tumor tissue in the pretargeted group (CC49-Tz 2.16 ± 0.08% ID/mL) when compared to the control group with nonmodified mAb (CC49 1.34 ± 0.07% ID/mL). Conclusions: A diverse series of fast-reacting fluorinated d-TCOs were synthesized. A pretargeted blocking approach in tumor-bearing mice allowed the choice of a lead compound with fast reaction kinetics with Tz. A novel 18F-labeled d-TCO tracer was developed and used in a pretargeted PET imaging approach, allowing specific tumor visualization in a mouse model of colorectal cancer. Although further optimization of the radiotracer is needed to enhance the tumor-to-background ratios for pretargeted imaging, we anticipate that the 18F-labeled d-TCO will find use in studies where increased hydrophilicity and fast bioconjugation are required.

Melanin-targeted [18F]-PFPN PET imaging may shed light for clear cell sarcoma.

Intracytoplasmic melanin pigment is a characteristic of clear cell sarcoma (CCS), which is a particularly deadly type of soft-tissue sarcoma. [18F]-N-(2-(diethylamino)ethyl)-5-(2-(2-(2-fluoroethoxy)ethoxy)ethoxy)picolinamide ([18F]-PFPN) is a positron emission tomography (PET) probe characterized by high melanin affinity. Therefore, this study aimed to investigate the feasibility of melanin-targeted [18F]-PFPN PET in patients with CCS. This prospective single-centre study recruited patients with pathologically confirmed CCS. [18F]-FDG PET/computed tomography and [18F]-PFPN PET/magnetic resonance imaging scans were performed within 1week of each other. The lesion numbers and [18F]-FDG and [18F]-PFPN PET parameters (maximum standardized uptake value [SUVmax], mean standardized uptake value [SUVmean], metabolic/melanotic tumour volume [MTV/MLTV], and total lesion glycolysis/melanin [TLG/TLM]) were collected. Three patients with CCS were recruited and received PET imaging. A total of 56 lesions were detected on [18F]-PFPN PET, including primary tumour and distant metastases. Identical lesions were not detected on [18F]-PFPN and [18F]-FDG PET. Twelve lesions (12/39, 30.77%) on [18F]-FDG imaging were missed on [18F]-PFPN, and 20 lesions (20/47,42.55%) on [18F]-PFPN imaging were missed on [18F]-FDG. In quantitative analysis, the [18F]-FDG SUVmean (4.60 ± 3.24) was higher than the [18F]-PFPN SUVmean (3.0 ± 2.63) in all lesions (P = 0.01). No significant correlations were found between the SUVmax, SUVmean, MLTV/MTV, and TLM/TLG values of [18F]-PFPN and [18F]-FDG (P > 0.05). Melanin-targeted [18F]-PFPN PET imaging is feasible for the diagnosis of CCS. Different imaging features were displayed on [18F]-PFPN and [18F]-FDG PET imaging, demonstrating the complementary role of the tracers. Combined use of the two imaging modalities would be preferred in patients with CCS. NCT05963035.

New Advances in the Exploration of Esterases with PET and Fluorescent Probes.

Esterases are hydrolases that catalyze the hydrolysis of esters into the corresponding acids and alcohols. The development of fluorescent probes for detecting esterases is of great importance due to their wide spectrum of biological and industrial applications. These probes can provide a rapid and sensitive method for detecting the presence and activity of esterases in various samples, including biological fluids, food products, and environmental samples. Fluorescent probes can also be used for monitoring the effects of drugs and environmental toxins on esterase activity, as well as to study the functions and mechanisms of these enzymes in several biological systems. Additionally, fluorescent probes can be designed to selectively target specific types of esterases, such as those found in pathogenic bacteria or cancer cells. In this review, we summarize the recent fluorescent probes described for the visualization of cell viability and some applications for in vivo imaging. On the other hand, positron emission tomography (PET) is a nuclear-based molecular imaging modality of great value for studying the activity of enzymes in vivo. We provide some examples of PET probes for imaging acetylcholinesterases and butyrylcholinesterases in the brain, which are valuable tools for diagnosing dementia and monitoring the effects of anticholinergic drugs on the central nervous system.

One-Pot Formal Carboradiofluorination of Alkenes: A Toolkit for Positron Emission Tomography Imaging Probe Development.

We report the first one-pot formal alkene carboradiofluorination reaction employing easily accessible alkenes as both prosthetic group precursors and coupling partners. The methodology features rapid sequential Markovnikov-selective iodofluorination and photoinduced Pd(0/I/II)-catalyzed alkyl Heck reaction as a mild and robust fluorine-18 (18F) radiochemical approach for positron emission tomography (PET) imaging probe development. A new class of prosthetic groups for PET imaging probe synthesis was isolated as iodofluorinated intermediates in moderate to excellent yields. The one-pot formal alkenylfluorination reaction was carried out to produce over 30 analogues of a wide range of bioactive molecules. Further application of the Pd(0/I/II) manifold in PET probe development was illustrated by the direct carbo(radio)fluorination of electron-rich alkenes. The methods were successfully translated to radiolabel a broad scope of medicinally relevant small molecules in generally good radiochemical conversion. The protocol was further optimized to accommodate no-carrier-added conditions with similar efficiency for future (pre)clinical translation. Moreover, the radiosynthesis of prosthetic groups was automated in a radiochemistry module to facilitate its practical use in multistep radiochemical reactions.

Imaging Cholinergic Receptors in the Brain by Positron Emission Tomography.

Cholinergic receptors represent a promising class of diagnostic and therapeutic targets due to their significant involvement in cognitive decline associated with neurological disorders and neurodegenerative diseases as well as cardiovascular impairment. Positron emission tomography (PET) is a noninvasive molecular imaging tool that has helped to shed light on the roles these receptors play in disease development and their diverse functions throughout the central nervous system (CNS). In recent years, there has been a notable advancement in the development of PET probes targeting cholinergic receptors. The purpose of this review is to provide a comprehensive overview of the recent progress in the development of these PET probes for cholinergic receptors with a specific focus on ligand structure, radiochemistry, and pharmacology as well as in vivo performance and applications in neuroimaging. The review covers the structural design, pharmacological properties, radiosynthesis approaches, and preclinical and clinical evaluations of current state-of-the-art PET probes for cholinergic receptors.

The Glutaminase-1 Inhibitor [11C-carbony]BPTES: Synthesis and Positron Emission Tomography Study in Mice.

Bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl)ethyl sulfide (BPTES) is a selective inhibitor of glutaminase-1 (GLS1), consequently inhibiting glutaminolysis. BPTES is known for its potent antitumor activity and plays a significant role in senescent cell removal. In this study, we synthesized [11C-carbonyl]BPTES ([11C]BPTES) as a positron emission tomography (PET) probe for the first time and assessed its biodistribution in mice using PET. [11C]BPTES was synthesized by the reaction of an amine precursor () with [11C-carbonyl]phenylacetyl acid anhydride ([11C]2), which was prepared from [11C]CO2 and benzyl magnesium chloride, followed by in situ treatment with isobutyl chloroformate. The decay-corrected isolated radiochemical yield of [11C]BPTES was 9.5% (based on [11C]CO2) during a synthesis time of 40 min. A PET study with [11C]BPTES showed high uptake levels of radioactivity in the liver, kidney, and small intestine of mice.