Radiolabeling and brain penetration of [11C]VU0071063, a ligand of type 1 sulfonylurea receptors for positron emission tomography imaging

Sulfonylurea receptor 1 (SUR1) overexpression in the central nervous system is a potential biomarker for positron emission tomography (PET) imaging of brain damage and recovery. VU0071063, a selective ligand of SUR1 able to cross the blood–brain barrier, was isotopically radiolabeled with carbon-11 from a desmethyl precursor obtained quantitatively in one step. Ready-to-inject [11C]VU0071063 was obtained in 18 ± 2% radiochemical yield and 103 ± 22 GBq/μmol molar activity. PET imaging in healthy rats demonstrated a significant brain penetration and rapid elimination of the tracer in vivo, encouraging further investigation in animal models of SUR1 overexpression.     

Targeted 64Cu‐labeled gold nanoparticles for dual imaging with positron emission tomography and optical imaging

Gold nanoparticles (AuNPs) have been used for many years in cancer treatment mainly for brachytherapy, but in the last 15 years, the focus has shifted to the development of ultrasmall target‐specific AuNPs with homogeneous size and, ultimately, tailored shapes for use in various imaging modalities such as computed tomography (CT), Raman, or photoacoustic imaging. Here, we report on the development of tumor‐specific AuNPs as diagnostic tools intended for the dual detection of prostate cancer via optical imaging (OI) and positron emission tomography (PET). The AuNPs were decorated with a near‐infrared dye and NODAGA chelator for complexation with radiometals. Radiolabeling with ⁶⁴Cu was performed either indirect by complexation with NODAGA‐AuNPs or by direct reduction of [⁶⁴Cu]Cu(0) onto the surface of the AuNPs. Both methods yielded stable ⁶⁴Cu‐AuNPs with radiochemical yield more than 95% confirmed by HPLC. ⁶⁴Cu‐AuNPs were evaluated in a dual‐imaging setting in vitro and in vivo and exhibited favorable diagnostic properties concerning detection, biodistribution, and clearance. Furthermore, the first therapeutic properties of the ⁶⁴Cu‐AuNPs were evaluated in vitro concerning acute and long‐term toxicity, indicating that these ⁶⁴Cu‐AuNPs could be used in therapeutic concepts in the future.     

Fully automated radiosynthesis of [1‐(2‐[18F]fluoroethyl),1H[1,2,3]triazole 4‐ethylene] triphenylphosphonium bromide as a potential positron emission tomography tracer for imaging apoptosis

A novel phosphonium salt bearing a fluorine‐18 labelled triazole has been designed as a potential imaging agent for apoptosis. The radiosynthesis of [1‐(2‐[¹⁸F]fluoroethyl),1H[1,2,3]triazole 4‐ethylene] triphenylphosphonium bromide ([¹⁸F]MitoPhos_01) has been carried out on a fully automated system in a two‐step reaction. Radiolabelling an ethyl azide and then carrying out a copper‐mediated 1,3‐cycloaddition reaction has allowed for total synthesis time to be slightly more than 1 h from aqueous [¹⁸F]fluoride. After purification by HPLC, the average radiochemical yield was determined to be 9% (not decay corrected); the specific activity was on average 70 GBq/µmol at the end of synthesis, and the radiochemical purity was >99%.     

Improved synthesis and application of [11C]benzyl iodide in positron emission tomography radiotracer production

Positron emission tomography has increased the demand for new carbon‐11 radiolabeled tracers and building blocks. A promising radiolabeling synthon is [¹¹C]benzyl iodide ([¹¹C]BnI), because the benzyl group is a widely present functionality in biologically active compounds. Unfortunately, synthesis of [¹¹C]BnI has received little attention, resulting in limited application. Therefore, we investigated the synthesis in order to significantly improve, automate, and apply it for labeling of the dopamine D₂ antagonist [¹¹C]clebopride as a proof of concept. [¹¹C]BnI was synthesized from [¹¹C]CO₂ via a Grignard reaction and purified prior the reaction with desbenzyl clebopride. According to a one‐pot procedure, [¹¹C]BnI was synthesized in 11 min from [¹¹C]CO₂ with high yield, purity, and specific activity, 52 ± 3% (end of the cyclotron bombardment), 95 ± 3%, and 123 ± 17 GBq/µmol (end of the synthesis), respectively. Changes in the [¹¹C]BnI synthesis are reduced amounts of reagents, a lower temperature in the Grignard reaction, and the introduction of a solid‐phase intermediate purification. [¹¹C]Clebopride was synthesized within 28 min from [¹¹C]CO₂ in an isolated decay‐corrected yield of 11 ± 3% (end of the cyclotron bombardment) with a purity of >98% and specific activity (SA) of 54 ± 4 GBq/µmol (n = 3) at the end of the synthesis. Conversion of [¹¹C]BnI to product was 82 ± 11%. The reliable synthesis of [¹¹C]BnI allows the broad application of this synthon in positron emission tomography radiopharmaceutical development. Copyright © 2015 John Wiley & Sons, Ltd.     

A new technique for the radiolabelling of mixed leukocytes with zirconium‐89 for inflammation imaging with positron emission tomography

Mixed leukocyte (white blood cells [WBCs]) trafficking using positron emission tomography (PET) is receiving growing interest to diagnose and monitor inflammatory conditions. PET, a high sensitivity molecular imaging technique, allows precise quantification of the signal produced from radiolabelled moieties. We have evaluated a new method for radiolabelling WBCs with either zirconium‐89 (⁸⁹Zr) or copper‐64 (⁶⁴Cu) for PET imaging. Chitosan nanoparticles (CNs) were produced by a process of ionotropic gelation and used to deliver radiometals into WBCs. Experiments were carried out using mixed WBCs freshly isolated from whole human blood. WBCs radiolabelling efficiency was higher with [⁸⁹Zr]‐loaded CN (76.8 ± 9.6% (n = 12)) than with [⁶⁴Cu]‐loaded CN (26.3 ± 7.0 % (n = 7)). [⁸⁹Zr]‐WBCs showed an initial loss of 28.4 ± 5.8% (n = 2) of the radioactivity after 2 h. This loss was then followed by a plateau as ⁸⁹Zr remains stable in the cells. [⁶⁴Cu]‐WBCs showed a loss of 85 ± 6% (n = 3) of the radioactivity after 1 h, which increased to 96 ± 6% (n = 3) loss after 3 h. WBC labelling with [⁸⁹Zr]‐loaded CN showed a fast kinetic of leukocyte association, high labelling efficiency and a relatively good retention of the radioactivity. This method using ⁸⁹Zr has a potential application for PET imaging of inflammation.     

A fully automated synthesis of [18F]‐FEAU and [18F]‐FMAU using a novel dual reactor radiosynthesis module

2′‐Deoxy‐2′‐[¹⁸F]fluoro‐5‐substituted‐1‐β‐D ‐arabinofuranosyluracils, including 2′‐deoxy‐2′‐[¹⁸F]fluoro‐5‐methyl‐1‐β‐D ‐arabinofuranosyluracil [¹⁸F]FMAU and [¹⁸F]FEAU are established radiolabeled probes to monitor cellular proliferation and herpes simplex virus type 1 thymidine kinase (HSV1‐tk) reporter gene expression with positron emission tomography. For clinical applications, a fully automated CGMP‐compliant radiosynthesis is necessary for production of these probes. However, due to multiple steps in the synthesis, no such automated synthetic protocols have been developed. We report here a fully automated synthesis of [¹⁸F]‐FEAU and [¹⁸F]‐FMAU on a prototype dual reactor module TRACERlab FX FN. The synthesis was performed by using a computer‐programmed standard operating procedure, and the product was purified on a semipreparative high‐performance liquid chromatography (HPLC) integrated with the synthesis module using 12% EtOH in 50 mM Na₂HPO₄. Finally, the percentage of alcohol was adjusted to 7% by adding Na₂HPO₄ and filtered through a Millipore filter to make dose for human. The radiochemical yield on the fluorination was 40±10% (n=10), and the overall yields were 4±1% (d. c.), from the end of the bombardment; [¹⁸F]FEAU (n=7) and [¹⁸F]FMAU (n=3). The radiochemical purity was >99%, specific activity was 1200–1300 mCi/µmol. The synthesis time was 2.5 h. This automated synthesis should be suitable for production of [¹⁸F]FIAU, [¹⁸F]FFAU, [¹⁸F]FCAU, [¹⁸F]FBAU and other 5‐substitued thymidine analogues. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and characterization of novel radiofluorinated probes for positron emission tomography imaging of monoamine oxidase B

Monoamine oxidase B (MAO‐B), predominantly expressed in glial cells, plays an important role in neurotransmitter regulation, and MAO‐B activity relates to several neuronal diseases. Here, we aimed to develop a radiofluorinated MAO‐B imaging probe based on the structure of a selective MAO‐B inhibitor, MD‐230254. We synthesized and evaluated a series of compounds in vitro and in vivo. A series of fluorinated analogs of MD‐230254 were synthesized and evaluated for inhibitory potency and selectivity toward MAO‐B. 5‐[4‐(2‐[¹⁸F]Fluorobenzyloxy)phenyl]‐3‐(2‐cyanoethyl)‐1,3,4‐oxadiazol‐2(3H)‐one (2‐[¹⁸F]FBPO) was synthesized from a corresponding tributylstannyl precursor and [¹⁸F]CH₃COOF. Biodistribution after intravenous injection of 2‐[¹⁸F]FBPO was evaluated in male ddY mice with or without pretreatment by inhibitors. Among the compounds synthesized and evaluated, 2‐FBPO showed high inhibitory potency and selectivity toward MAO‐B comparable with MD‐230254. 2‐[¹⁸F]FBPO was successfully synthesized by an electrophilic reaction with a high radiochemical purity of more than 99%. 2‐[¹⁸F]FBPO was efficiently taken up by the brain and showed rapid blood clearance, which provided a brain/blood radioactivity ratio of 3.7 at 90 minutes postinjection. The brain radioactivity was significantly decreased by pretreatment with an MAO‐B selective inhibitor. The great potential of 2‐[¹⁸F]FBPO as an MAO‐B imaging probe, applicable to a variety of diseases, is indicated.     

An updated synthesis of [11C]carfentanil for positron emission tomography (PET) imaging of the μ‐opioid receptor

[¹¹C]Carfentanil ([¹¹C]CFN) is a selective radiotracer for in vivo positron emission tomography imaging studies of the μ‐opioid system that, in our laboratories, is synthesized by methylation of the corresponding carboxylate precursor with [¹¹C]MeOTf, and purified using a C2 solid‐phase extraction cartridge. Changes in the commercial availability of common C2 cartridges have necessitated future proofing the synthesis of [¹¹C]CFN to maintain reliable delivery of the radiotracer for clinical imaging studies. An updated synthesis of [¹¹C]CFN is reported that replaces a now obsolete purification cartridge with a new commercially available version and also substitutes the organic solvents used in traditional production methods with ethanol.     

A simplified protocol for the automated production of succinimidyl 4‐[18F]fluorobenzoate on an IBA Synthera module

The important peptide labelling reagent succinimidyl 4‐[¹⁸F]fluorobenzoate ([¹⁸F]SFB) has been synthesised in 75–85% decay corrected radiochemical yield using the IBA Synthera platform (IBA Cyclotron Solutions, Louvain‐la‐neuve, Belgium) with the fluorodeoxyglucose‐integrated fluidic processor nucleophilic and only four reagent vials in a single reactor. (4‐ethoxycarbonylphenyl) trimethylammonium triflate was used as the labelling precursor and 1 M aqueous tetramethylammonium hydroxide for the hydrolysis of the intermediate ethyl 4‐[¹⁸F]fluorobenzoate. N,N,N′,N′‐tetramethyl‐O‐(N‐succinimidyl)uronium tetrafluoroborate (TSTU) was then used to form [¹⁸F]SFB from 4‐[¹⁸F]fluorobenzoate. By omitting the addition of acetic acid and introducing a combined hydrolysis/water removal step, the synthesis time was shortened to 58 minutes. After SepPak purification, the radiochemical purity of [¹⁸F]SFB was 95.8–98.2%. These simplifications might be of significance to users of other automated synthesis modules.     

Preparation and stability of ethanol‐free solution of [18F]florbetapir ([18F]AV‐45) for positron emission tomography amyloid imaging

We have developed an ethanol‐free formulation method of [¹⁸F]florbetapir ([¹⁸F]AV‐45) using a commercially available automated JFE multi‐purpose synthesizer. We have also evaluated the radiochemical stability in an ethanol‐free solution of [¹⁸F]AV‐45 under visible light irradiation and dark conditions by comparison with a conventional 10% ethanol solution of [¹⁸F]AV‐45. [¹⁸F]AV‐45 was obtained with a radiochemical yield of 55.1 ± 2.2% (decay‐corrected to end of bombardment), specific activity of 591.6 ± 90.3 GBq/µmol and radiochemical purity of >99% within a total synthesis time of about 73 min. The radiochemical purity of [¹⁸F]AV‐45 formulated by dissolving the ethanol‐free solution was found to decrease as a function of the period of exposure to visible light. In contrast, the visible light photolysis could be suppressed by adding 10% ethanol to the formulation or by avoiding exposure to visible light. In the radiosynthesis of [¹⁸F]AV‐45 formulated by dissolving the ethanol‐free solution, [¹⁸F]AV‐45 could be obtained with high radiochemical purity and high stability by avoiding exposure to visible light. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and evaluation of an 18F‐labeled trifluoroborate derivative of 2‐nitroimidazole for imaging tumor hypoxia with positron emission tomography

2‐Nitroimidazole‐based hypoxia imaging tracers such as ¹⁸F‐FMISO are normally imaged at late time points (several hours post‐injection) due to their slow clearance from background tissues. Here, we investigated if a hydrophilic zwitterion‐based ammoniomethyl‐trifluoroborate derivative of 2‐nitroimidazole, ¹⁸F‐AmBF₃‐Bu‐2NI, could have the potential to image tumor hypoxia at earlier time points. AmBF₃‐Bu‐2NI was prepared in 4 steps. ¹⁸F labeling was conducted via ¹⁸F‐¹⁹F isotope exchange reaction, and ¹⁸F‐AmBF₃‐Bu‐2NI was obtained in 14.8 ± 0.4% (n = 3) decay‐corrected radiochemical yield with 24.5 ± 5.2 GBq/μmol specific activity and >99% radiochemical purity. Imaging and biodistribution studies in HT‐29 tumor‐bearing mice showed that ¹⁸F‐AmBF₃‐Bu‐2NI cleared quickly from blood and was excreted via the hepatobiliary and renal pathways. However, the tumor was not visualized in PET images until 3 hours post‐injection due to low tumor uptake (0.54 ± 0.13 and 0.19 ± 0.04%ID/g at 1 and 3 hours post‐injection, respectively). The low tumor uptake is likely due to the highly hydrophilic motif of ammoniomethyl‐trifluoroborate that prevents free diffusion of ¹⁸F‐AmBF₃‐Bu‐2NI across the cell membrane. Our results suggest that highly hydrophilic ¹⁸F‐labeled ammoniomethyl‐trifluoroborate derivatives might not be suitable for imaging intracellular targets including nitroreductase, a common tumor hypoxia imaging target.     

正电子发射断层显像在药物研究和开发中的应用

正电子发射断层显像（PET）是通过探测某些超短寿命放射性核素放射出的正电子与介质中的负电子发生碰撞（即“湮灭”）过程中,产生的一对方向相反、能量均为511KeV的光子的数量实现的一种定量、多维影像技术。它主要用于研究生物体（活体）的主要器官（或组织）在完成其生理功能过程中所伴随的生物化学反应。也可用于直接研究某些药物在生物活体内的生物学行为、疗效和毒性,因此,在药物研究开发中具有广泛的应用前景。本文简要综述了正电子发射断层显像技术的仪器和原理、正电子发射断层显像用放射性标记化合物、在药物研究和开发中的应用及其局限性。     

Efficient radiosynthesis and preclinical evaluation of [18F]FOMPyD as a positron emission tomography tracer candidate for TrkB/C receptor imaging

Herein we report an efficient radiolabeling of a ¹⁸F-fluorinated derivative of dual inhibitor GW2580, with its subsequent evaluation as a positron emission tomography (PET) tracer candidate for imaging of two neuroreceptor targets implicated in the pathophysiology of neurodegeneration: tropomyosin receptor kinases (TrkB/C) and colony stimulating factor receptor (CSF-1R). [¹⁸F]FOMPyD was synthesized from a boronic acid pinacolate precursor via copper-mediated ¹⁸F-fluorination concerted with thermal deprotection of the four Boc groups on a diaminopyrimidine moiety in an 8.7±2.8% radiochemical yield, a radiochemical purity >99%, and an effective molar activity of 187±93 GBq/μmol. [¹⁸F]FOMPyD showed moderate brain permeability in wild-type rats (SUV_max = 0.75) and a slow washout rate. The brain uptake was partially reduced (ΔAUC_40–90 = 11.6%) by administration of the nonradioactive FOMPyD (up to 30 μg/kg). In autoradiography, [¹⁸F]FOMPyD exhibits ubiquitous distribution in rat and human brain tissues with relatively high nonspecific binding revealed by self-blocking experiment. The binding was blocked by TrkB/C inhibitors, but not with a CSF-1R inhibitor, suggesting selective binding to the former receptor. Although an unfavorable pharmacokinetic profile will likely preclude application of [¹⁸F]FOMPyD as a PET tracer for brain imaging, the concomitant one-pot copper-mediated ¹⁸F-fluorination/Boc-deprotection is a practical technique for the automated radiosynthesis of acid-sensitive PET tracers.     

Radiosynthesis of 55Co‐ and 58mCo‐labelled DOTATOC for positron emission tomography imaging and targeted radionuclide therapy

The SPECT compound ⁵⁷Co‐DOTATOC has recently been shown to have the highest affinity ever found for somatostatin receptor subtype 2. Moreover, the internalization rate into the tumour cell line AR42J was also the highest found for any somatostatin‐based radiopharmaceutical. We here present a method to prepare the positron emission tomography compound ⁵⁵Co‐DOTATOC as a new promising radiopharmaceutical for positron emission tomography via solid target irradiations of enriched Fe‐metal. Also, the new, potent Auger‐electron‐emitting radioisotope ^58mCo and the resulting therapeutic compound ^58mCo‐DOTATOC as candidate for targeted radionuclide therapy of somatostatin receptor‐positive tumours have been prepared with high yield and high radiochemical purity. Copyright © 2011 John Wiley & Sons, Ltd.     

A fast,simple, and reproducible automated synthesis of [18F]FPyKYNE‐c(RGDyK) for αvβ3 receptor positron emission tomography imaging

[¹⁸ F]FPyKYNE‐c(RGDyK) was successfully synthesized by the Cu(I) catalyzed Huisgen 1,3‐dipolar cycloaddition of alkynes to azides using [¹⁸ F]FPyKYNE as a prosthetic group in an overall radiochemical yield of 12%–18% (decay‐corrected) and >99.5% chemical and radiochemical purities in 125 min including quality control. This simple, fully automated two‐step, two‐reactor approach consists of a quick and convenient purification of the prosthetic group using silica gel cartridges and its subsequent use for the labeling of the azido‐c(RGDyK) peptide via click chemistry.     

Novel radioligands for imaging sigma-1 receptor in brain using positron emission tomography (PET)

The sigma-1 receptor (σ₁R) is a unique intracellular protein. σ₁R plays a major role in various pathological conditions in the central nervous system (CNS), implicated in several neuropsychiatric disorders. Imaging of σ₁R in the brain using positron emission tomography (PET) could serve as a noninvasively tool for enhancing the understanding of the disease's pathophysiology. Moreover, σ₁R PET tracers can be used for target validation and quantification in diagnosis. Herein, we describe the radiosynthesis, in vivo PET/CT imaging of novel σ₁R ¹¹C-labeled radioligands based on 6-hydroxypyridazinone, [¹¹C]HCC0923 and [¹¹C]HCC0929. Two radioligands have high affinities to σ₁R, with good selectivity. In mice PET/CT imaging, both radioligands showed appropriate kinetics and distributions. Additionally, the specific interactions of two radioligands were reduced by compounds 13 and 15 (self-blocking). Of the two, [¹¹C]HCC0929 was further investigated in positive ligands blocking studies, using classic σ₁R agonist SA 4503 and σ₁R antagonist PD 144418. Both σ₁R ligands could extensively decreased the uptake of [¹¹C]HCC0929 in mice brain. Besides, the biodistribution of major brain regions and organs of mice were determined in vivo. These studies demonstrated that two radioligands, especially [¹¹C]HCC0929, possessed ideal imaging properties and might be valuable tools for non-invasive quantification of σ₁R in brain.     

Synthesis of [11C]gefitinib for imaging epidermal growth factor receptor tyrosine kinase with positron emission tomography

We have synthesized N‐(3‐chloro‐4‐fluorophenyl)‐7‐[¹¹C]methoxy‐6‐[3‐(morpholin‐4‐yl)propoxy]quinazolin‐4‐amine, [¹¹C]gefitinib ([¹¹C]Iressa), a high affinity (IC₅₀ = 2 nM) inhibitor of the epidermal growth factor receptor tyrosine kinase (EGFR‐TK), in solution and in a semi‐automated stainless loop methylation system using [¹¹C]methyl triflate. The trapping efficiency for [¹¹C]methyl triflate in solution was higher than in the solvent film generated in the loop system, thus the overall radiochemical yield was considerably higher for the synthesis in solution. The average radiochemical yield for the solution chemistry was 15% with an average specific radioactivity of approximately 9000 mCi/µmole at EOS in one step from its corresponding desmethyl phenol precursor. Copyright © 2006 John Wiley & Sons, Ltd.     

An optimized radiosynthesis of [18F]FNDP,a positron emission tomography radiotracer for imaging soluble epoxide hydrolase (sEH)

In this concise practitioner protocol, the radiochemical synthesis of [¹⁸F]FNDP suitable for human positron emission tomography studies is described and the results from validation productions are presented. The high specific activity radiotracer product is prepared as a sterile, apyrogenic solution that conforms to current Good Manufacturing Practice requirements.     

Synthesis of a radiotracer for studying serotonin uptake sites with positron emission tomography: [11C]McN-5652-Z

The highly potent serotonin (5-HT) uptake blocker, McN-5652-Z (trans-1,2,3,5,6,10b - hexahydro - 6 - [4 - (methylthio)phenyl] pyrrolo - [2,1-a]-isoquinoline) was labeled with ¹¹C for studying serotonin uptake sites using positron emission tomography (PET). [¹¹C]McN-5652-Z was synthesized by S-methylation of the normethyl precursor with [¹¹C]iodomethane in DMF at 30 - 35° C. The radiosyntheses including purification by HPLC and formulation for injection were completed in an average of 16 minutes following the end of bombardment (E.O.B.) with an overall radiochemical yield of 12%. The average specific activity determined at the end of synthesis (E.O.S.) was approximately 4250 mCi/μmole; this corresponds to approximately 7350 mCi/μmole at E.O.B. [¹¹C]McN-5655-Z, a less potent blocker, was also prepared by the same procedure.     

Radiosynthesis and biological evaluation of L- and D-S-(3-[18F]fluoropropyl)homocysteine for tumor imaging using positron emission tomography

Interest in radiolabeled amino acids for metabolic imaging of cancer and limitations with [(11)C]methionine has prompted the development of a new (18)F-labeled methionine derivative S-(3-[(18)F]fluoropropyl)homocysteine ([(18)F]FPHCys). The L and D enantiomers of [(18)F]FPHCys were prepared from their respective protected S-(3-tosyloxypropyl)homocysteine precursors 1 by [(18)F]fluoride substitution using K(2.2.2) and potassium oxalate, followed by acid hydrolysis on a Tracerlab FX(FN) synthesis module. [(18)F]-L-FPHCys and [(18)F]-D-FPHCys were isolated in 20 ± 5% radiochemical yield and >98% radiochemical and enantiomeric purity in 65 min. Competitive uptake studies in A375 and HT29 tumor cells suggest that L- and D-[(18)F]FPHCys are taken up by the L-transporter system. [(18)F]-L-FPHCys and [(18)F]-D-FPHCys displayed good stability In Vivo without incorporation into protein at least 2 h postinjection. Biodistribution studies demonstrate good uptake in A375 tumor-bearing rodents with tumor to blood ratios of 3.5 and 5.0 for [(18)F]-L-FPHCys and [(18)F]-D-FPHCys, respectively, at 2 h postinjection.