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Purpose: We aimed to assess the effect of concomitant medication, age, sex, body mass index and 18-kDa translocator protein (TSPO) binding affinity status on the metabolism and plasma pharmacokinetics of [18F]DPA-714 and their influence on the plasma input function in a large cohort of 201 subjects who underwent brain and whole-body PET imaging to investigate the role of neuroinflammation in neurological diseases. Methods: The non-metabolized fraction of [18F]DPA-714 was estimated in venous plasma of 138 patients and 63 healthy controls (HCs; including additional arterial sampling in 16 subjects) during the 90 min brain PET acquisition using a direct solid-phase extraction method. The mean fraction between 70 and 90 min post-injection ([18F]DPA-71470–90) and corresponding normalized plasma concentration (SUV70-90) were correlated with all factors using a multiple linear regression model. Differences between groups (arterial vs venous measurements; HCs vs patients; high- (HAB), mixed- (MAB) and low-affinity binders (LAB); subjects with vs without co-medications, females vs males were also assessed using the non-parametric Mann–Whitney or Kruskal–Wallis ANOVA tests. Finally, the impact of co-medications on the brain uptake of [18F]DPA-714 at equilibrium was investigated. Results: As no significant differences were observed between arterial and venous [18F]DPA-71470–90 and SUV70-90, venous plasma was used for correlations. [18F]DPA-71470–90 was not significantly different between patients and HCS (59.7 ± 12.3% vs 60.2 ± 12.9%) despite high interindividual variability. However, 47 subjects exhibiting a huge increase or decrease of [18F]DPA-71470–90 (up to 88% or down to 23%) and SUV70-90 values (2–threefold) were found to receive co-medications identified as inhibitors or inducers of CYP3A4, known to catalyse [18F]DPA-714 metabolism. Comparison between cortex-to-plasma ratios using individual input function (VTIND) or population-based input function derived from untreated HCs (VTPBIF) indicated that non-considering the individual metabolism rate led to a bias of about 30% in VT values. Multiple linear regression model analysis of subjects free of these co-medications suggested significant correlations between [18F]DPA-71470–90 and age, BMI and sex while TSPO polymorphism did not influence the metabolism of the radiotracer. [18F]DPA-714 metabolism fell with age and BMI and was significantly faster in females than in males. Whole-body PET/CT exhibited a high uptake of the tracer in TSPO-rich organs (heart wall, spleen, kidneys...) and those involved in metabolism and excretion pathways (liver, gallbladder) in HAB and MAB with a strong decrease in LAB (-89% and -85%) resulting in tracer accumulation in plasma (4.5 and 3.3-fold increase). Conclusion: Any co-medication that inhibits or induces CYP3A4 as well as TSPO genetic status, age, BMI and sex mostly contribute to interindividual variations of the radiotracer metabolism and/or concentration that may affect the input function of [18F]DPA-714 and consequently its human brain and peripheral uptake. Trial registration: INFLAPARK, NCT02319382, registered December 18, 2014, retrospectively registered; IMABIO 3, NCT01775696, registered January 25, 2013, retrospectively registered; INFLASEP, NCT02305264, registered December 2, 2014, retrospectively registered; EPI-TEP, EudraCT 2017–003381-27, registered September 24, 2018. [ABSTRACT FROM AUTHOR]

Background: Positron emission tomography is widely used to study biological processes without disrupting normal physiological functions. Traditional radiotracer synthesis and industrial market is focused on producing large batches of 18 F-labelled tracers, especially [ 18 F]FDG. Accessibility to smaller quantity of diverse radiopharmaceuticals is a key to enable a more personalised approach in nuclear medicine. A novel microfluidic module, iMiDEV™, has earlier been shown to be a versatile labelling platform as it has been used in the production of Na[ 18 F]F and various 11 C- and 68  Ga-labelled tracers. In the current study our aim was to utilise iMiDEV™ in the synthesis of fluorine-18-labelled radiotracers, specifically [ 18 F]DPA-714, [ 18 F]LBT-999 and [ 18 F]fallypride., Results: [ 18 F]DPA-714, [ 18 F]LBT-999 and [ 18 F]fallypride have been produced in up to 24%, 12% and 11% radiochemical yield, respectively, using the microfluidics based iMiDEV™ labelling platform. Activity yields at the end of synthesis were 3.6 GBq, 2.1 GBq and 2.3 GBq, respectively. All individual synthesis steps were studied for efficient activity transfer and labelling and the optimised synthesis sequence was fully automated., Conclusion: In this paper, we have demonstrated fully automated production of different 18 F-tracers of clinical relevance with moderate to good yields using microfluidic iMiDEV™ platform. Our work is a step towards more personalised, dose-on-demand manufacturing of PET radiopharmaceuticals., Competing Interests: Declarations. Ethics approval and consent to participate: Not applicable. Consent for publication: Not applicable. Competing interests: The authors declare that they have no competing interests., (© 2024. The Author(s).)

The accurate quantification of biomarkers is paramount in modern medicine, particularly in cancer where precise diagnosis is imperative for targeted therapy selection. In this paper we described a multiplexed analysis diagnostic approach based on cleavable MS-tagged antibodies. The technology uses MS-tag isotopologues and the sydnonimine-cyclooctyne click-and-release bioorthogonal reaction. In a proof of concept study, we demonstrated the potential of this approach for cancer cell immunoprofiling in culture cells, tissues and in vivo as well, thereby unveiling promising diagnostic avenues., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Positron emission tomography imaging using radiolabeled dolutegravir (DTG) is an interesting approach to understand the biodistribution of this antiretroviral drug at HIV-1 sanctuary sites. In the course of clinical translation, we depict herein an improved and pharmaceutically compliant radiosynthesis of [ 18 F]DTG from an original tin precursor. The radiosynthesis was achieved in two steps by copper-mediated radiofluorination, followed by enol ether deprotection using a kit-based AllInOne module. Ready-to-inject [ 18 F]DTG was obtained in 20 ± 5% ( n = 12) decay-corrected radiochemical yield within 90 min, representing a 4-fold increase compared to the previously published three-step radiosynthesis. Quality control was carried out with three consecutive [ 18 F]DTG productions according to the current European Pharmacopoeia guidelines, which include pH determination, identity and purity (chemical, radiochemical, and radionuclide) assessments, residual solvent quantification, dosage of lithium, copper, and tin traces, sterility and bacterial endotoxin tests. [ 18 F]DTG (∼2 GBq) was obtained with a molar activity of 59 ± 2 GBq/μmol at the time of injection and was suitable for human applications., Competing Interests: The authors declare the following competing financial interest(s): Thomas Bonasera is employed by GSK. Chris M. Parry is employed by ViiV Healthcare and has stock/shares in GSK., (© 2024 The Authors. Published by American Chemical Society.)

We have previously developed seven fluorinated analogues of A-836339 as new PET tracers for cannabinoid type 2 receptor (CB 2 R) imaging, among which ( Z )- N -(3-(2-(2-[ 18 F]fluoroethoxy)ethyl)-4,5-dimethylthiazol-2(3 H )-ylidene)-2,2,3,3-tetramethylcyclopropane-1-carboxamide ([ 18 F]FC0324) displayed high affinity and selectivity for CB 2 R in healthy rats. In the present study, we have further evaluated the imaging and metabolic properties of [ 18 F]FC0324 in a rat model of human CB 2 R overexpression in the brain (AAV- h CB 2 ) and in non-human primates (NHPs). Autoradiography with AAV- h CB 2 rat brain sections exhibited a signal of [ 18 F]FC0324 8-fold higher in the ipsilateral region than in the contralateral region. Blocking with NE40, a CB 2 R-specific agonist, resulted in a 91% decrease in the radioactivity. PET experiments showed a signal 7-fold higher in the ipsilateral region, and the specificity of [ 18 F]FC0324 for h CB 2 R in vivo was confirmed by the 80% decrease after blocking with NE40. In NHPs, brain time-activity curves displayed a fast and homogeneous distribution followed by a rapid washout, in accordance with the low amount of CB 2 Rs in healthy brain. Whole-body PET-CT suggested a high and specific uptake of the radiotracer in the spleen, a CB 2 R-rich organ, and in the organs involved in metabolism and excretion, with a low bone uptake. In vitro metabolism with monkey liver microsomes (MLMs) led to the formation of six main hydroxylated metabolites of FC0324. Five of them were produced by human liver microsomes, being much less active than MLMs. In vivo, in NHPs, the main radiometabolite was likely to result from further oxidation of hydroxylated compounds, and parent [ 18 F]FC0324 accounted for 8 ± 3% of plasma radioactivity (at 120 min p.i.) with a low level of potential interfering radiometabolites. Furthermore, this metabolism should be significantly reduced in humans due to species differences. In conclusion, [ 18 F]FC0324 appears to be a promising candidate for further human studies with suitable kinetics, selectivity, and metabolic profile for CB 2 R PET imaging., Competing Interests: The authors declare no competing financial interest., (© 2024 American Chemical Society.)

18 F-labelled radiopharmaceuticals are indispensable in positron emission tomography. The critical step in the preparation of 18 F-labelled tracers is the anhydrous F-18 nucleophilic substitution reaction, which involves [ 18 F]F - anions generated in aqueous media by the cyclotron. For this, azeotropic drying by distillation is widely used in standard synthesisers, but microfluidic systems are often not compatible with such a process. To avoid this step, several methods compatible with aqueous media have been developed. We summarised the existing approaches and two of them have been studied in detail. [ 18 F]fluoride elution efficiencies have been investigated under different conditions showing high 18 F-recovery. Finally, a large scope of precursors has been assessed for radiochemical conversion, and these hydrous labelling techniques have shown their potential for tracer production using a microfluidic approach, more particularly compatible with iMiDEV™ cassette volumes.

Biomolecules labeled with positron-emitting radionuclides like fluorine-18 or radiometals like copper-64 and zirconium-89 are increasingly employed in nuclear medicine for diagnosis purposes. Given the fragility and complexity of these compounds, their labeling requires mild conditions. Besides, it is essential to develop methods inducing minimal modification of the tertiary structure, as it is fundamental for the biological activity of such complex entities. Given these requirements, disulfide rebridging represents a promising possibility since it allows protein modification as well as conservation of the tertiary structure. In this context, we have developed an original radiofluorinated dibromopyridazine dione prosthetic group for labeling of disulfide-containing biomolecules via rebridging. We employed it to radiolabel octreotide, a somatostatin analogue, and to radiolabel fragment antigen binding (Fab) targeting programmed death-ligand 1 (PD-L1), whose properties were then evaluated in vitro and in vivo by positron emission tomography (PET) imaging. We next extended our strategy to the radiolabeling of cetuximab, a monoclonal antibody, with various radiometals commonly used in PET imaging (zirconium-89, copper-64) by developing various rebridging molecules bearing the appropriate chelators. The stabilities of the radiolabeled antibody conjugates were assessed in biological conditions.

Positron emission tomography (PET) imaging of the myelin sheath is a powerful tool to investigate multiple sclerosis, monitor its evolution, and support drug development. Radiotracers based on N,N -dimethylaminostilbene (MeDAS) fluorinated analogs have been designed for myelin PET imaging but were never translated to humans. We have synthesized three original fluorinated analogs of MeDAS with low metabolic rates for which binding to myelin in a healthy rat brain was demonstrated by fluorescence microscopy. A tosyl precursor was synthesized for the lead compound PEGMeDAS and automated fluorine-18 radiolabeling afforded [ 18 F]PEGMeDAS in 25 ± 5% radiochemical yield and 102 ± 15 GBq/μmol molar activity. Biodistribution in healthy rats demonstrated the brain penetration with low penetration of radiometabolites. However, E to Z isomerization observed in plasma hampers further investigations of this family of molecules and requires complementary data on the in vivo behavior of the Z isomer.

Crizotinib is a tyrosine kinase inhibitor approved for the treatment of non-small-cell lung cancer, but it is inefficient on brain metastases. Crizotinib is a substrate of the P-glycoprotein, and non-invasive nuclear imaging can be used to assess the brain penetration of crizotinib. Positron emission tomography (PET) imaging using fluorine-18-labeled crizotinib would be a powerful tool for investigating new strategies to enhance the brain distribution of crizotinib. We have synthesized a spirocyclic hypervalent iodine precursor for the isotopic labeling of crizotinib in a 2.4% yield. Because crizotinib is an enantiomerically pure drug, a chiral separation was performed to afford the (R) -precursor. A two-step radiolabeling process was optimized and automated using the racemic precursor to afford [ 18 F] (R,S) -crizotinib in 15 ± 2 radiochemical yield and 103 ± 18 GBq/µmol molar activity. The same radiolabeling process was applied to the (R) -precursor to afford [ 18 F] (R) -crizotinib with comparable results. As a proof-of-concept, PET was realized in a single non-human primate to demonstrate the feasibility of [ 18 F] (R) -crizotinib in in vivo imaging. Whole-body PET highlighted the elimination routes of crizotinib with negligible penetration in the brain (SUVmean = 0.1). This proof-of-concept paves the way for further studies using [ 18 F] (R) -crizotinib to enhance its brain penetration depending on the P-glycoprotein function.

Despite an apparently silent imaging, some patients with mild traumatic brain injury (TBI) experience cognitive dysfunctions, which may persist chronically. Brain changes responsible for these dysfunctions are unclear and commonly overlooked. It is thus crucial to increase our understanding of the mechanisms linking the initial event to the functional deficits, and to provide objective evidence of brain tissue alterations underpinning these deficits. We first set up a murine model of closed-head controlled cortical impact, which provoked persistent cognitive and sensorimotor deficits, despite no evidence of brain contusion or bleeding on MRI, thus recapitulating features of mild TBI. Molecular MRI for P-selectin, a key adhesion molecule, detected no sign of cerebrovascular inflammation after mild TBI, as confirmed by immunostainings. By contrast, in vivo PET imaging with the TSPO ligand [ 18 F]DPA-714 demonstrated persisting signs of neuroinflammation in the ipsilateral cortex and hippocampus after mild TBI. Interestingly, immunohistochemical analyses confirmed these spatio-temporal profiles, showing a robust parenchymal astrogliosis and microgliosis, at least up to 3 weeks post-injury in both the cortex and hippocampus. In conclusion, we show that even one single mild TBI induces long-term behavioural deficits, associated with a persistent neuro-inflammatory status that can be detected by PET imaging.

Considering the individual characteristics of positron emission tomography (PET) and optical imaging (OI) in terms of sensitivity, spatial resolution, and tissue penetration, the development of dual imaging agents for bimodal PET/OI imaging is a growing field. A current major breakthrough in this field is the design of monomolecular agent displaying both a radioisotope for PET and a fluorescent dye for OI. We took advantage of the multifunctionalities allowed by a clickable C -glycosyl scaffold to gather the different elements. We describe, for the first time, the synthesis of a cyanine-based dual PET/OI imaging probe based on a versatile synthetic strategy and its direct radiofluorination via [ 18 F]F-C bond formation. The non-radioactive dual imaging probe coupled with two c (RGDfK) peptides was evaluated in vitro and in vivo in fluorescence imaging. The binding on α v β 3 integrin (IC 50 = 16 nM) demonstrated the efficiency of the dimeric structure and PEG linkers in maintaining the affinity. In vivo fluorescence imaging of U-87 MG engrafted nude mice showed a high tumor uptake (40- and 100-fold increase for orthotopic and ectopic brain tumors, respectively, compared to healthy brain). In vitro and in vivo evaluations and resection of the ectopic tumor demonstrated the potential of the conjugate in glioblastoma cancer diagnosis and image-guided surgery.

Molecular imaging with PET offers an alternative method to quantify programmed-death-ligand 1 (PD-L1) to accurately select patients for immunotherapies. More and more clinical and preclinical trials involve radiolabeling of antibody fragments for their desirably fast clearance and high tumor penetration. As the radiolabeling strategy can significantly impact pharmacokinetics and biodistribution, we explored in this work a site-specific radiofluorination strategy on an anti-PD-L1 fragment antigen-binding (Fab) and compared the pharmacokinetic and biodistribution properties with the same Fab labeled using stochastic radiolabeling chemistry. We applied an enzymatic bioconjugation mediated by a variant of the lipoic acid ligase (LplA) that promotes the formation of an amide bond between a short peptide cloned onto the C terminus of the Fab. A synthetic analogue of the enzyme natural substrate, lipoic acid, was radiolabeled with fluorine-18 for site-specific conjugation by LplA. We compared the biodistribution of the site-specifically labeled Fab with a stochastically labeled Fab on lysine side chains in tumor-bearing mice. The two methods of fluorination demonstrate a comparable whole-body biodistribution. The 89 Zr-labeled Fab had different biodistribution compared to either 18 F-labeled Fab. We attribute the difference to [ 89 Zr] metabolism. Fab-LAP-[ 18 F]FPyOctA therefore reflects better the true pharmacokinetic profile of the Fab.

Deciphering the drug/virus/host interactions at infected cell reservoirs is a key leading to HIV-1 remission for which positron emission tomography (PET) imaging using radiolabeled antiretroviral (ARV) drugs is a powerful asset. Dolutegravir (DTG) is one of the preferred therapeutic options to treat HIV and can be isotopically labeled with fluorine-18. [18F]DTG was synthesized via a three-step approach of radiofluorination/nitrile reduction/peptide coupling with optimization for each step. Radiofluorination was performed on 2-fluoro-4-nitrobenzonitrile in 90% conversion followed by nitrile reduction using sodium borohydride and aqueous nickel(II) chloride with 72% conversion. Final peptide coupling reaction followed by HPLC purification and formulation afforded ready-to-inject [18F]DTG in 5.1 ± 0.8% (n = 10) decay-corrected radiochemical yield within 95 min. The whole process was automatized using a TRACERlab® FX NPro module, and quality control performed by analytical HPLC showed that [18F]DTG was suitable for in vivo injection with >99% chemical and radiochemical purity and a molar activity of 83 ± 18 GBq/µmol (n = 10). Whole-body distribution of [18F]DTG was performed by PET imaging on a healthy macaque and highlighted the elimination routes of the tracer. This study demonstrated the feasibility of in vivo [18F]DTG PET imaging and paved the way to explore drug/virus/tissues interactions in animals and humans.