First human use of a radiopharmaceutical prepared by continuous-flow microfluidic radiofluorination: proof of concept with the tau imaging agent [18F]T807.

Despite extensive preclinical imaging with radiotracers developed by continuous-flow microfluidics, a positron emission tomographic (PET) radiopharmaceutical has not been reported for human imaging studies by this technology. The goal of this study was to validate the synthesis of the tau radiopharmaceutical 7-(6-fluoropyridin-3-yl)-5H-pyrido[4,3-b]indole ([18F]T807) and perform first-in-human PET scanning enabled by microfluidic flow chemistry. [18F]T807 was synthesized by our modified one-step method and adapted to suit a commercial microfluidic flow chemistry module. For this proof of concept, the flow system was integrated to a GE Tracerlab FXFN unit for high-performance liquid chromatography purification and formulation. Three consecutive productions of [18F]T807 were conducted to validate this radiopharmaceutical. Uncorrected radiochemical yields of 17 ± 1% of crude [18F]T807 (≈ 500 mCi, radiochemical purity 95%) were obtained from the microfluidic device. The crude material was then purified, and > 100 mCi of the final product was obtained in an overall uncorrected radiochemical yield of 5 ± 1% (n  =  3), relative to starting [18F]fluoride (end of bombardment), with high radiochemical purity (≥ 99%) and high specific activities (6 Ci/µmol) in 100 minutes. A clinical research study was carried out with [18F]T807, representing the first reported human imaging study with a radiopharmaceutical prepared by this technology.

A concise radiosynthesis of the tau radiopharmaceutical, [(18) F]T807.

Fluorine-18 labeled 7-(6-fluoropyridin-3-yl)-5H-pyrido[4,3-b]indole ([(18) F]T807) is a potent and selective agent for imaging paired helical filaments of tau and is among the most promising PET radiopharmaceuticals for this target in early clinical trials. The present study reports a simplified one-step method for the synthesis of [(18) F]T807 that is broadly applicable for routine clinical production using a GE TRACERlab™ FXFN radiosynthesis module. Key facets of our optimized radiosynthesis include development and use of a more soluble protected precursor, tert-butyl 7-(6-nitropyridin-3-yl)-5H-pyrido[4,3-b]indole-5-carboxylate, as well as new HPLC separation conditions that enable a facile one-step synthesis. During the nucleophilic fluorinating reaction with potassium cryptand [(18) F]fluoride (K[(18) F]/K222 ) in DMSO at 130 °C over 10 min the precursor is concurrently deprotected. Formulated [(18) F]T807 was prepared in an uncorrected radiochemical yield of 14 ± 3%, with a specific activity of 216 ± 60 GBq/µmol (5837 ± 1621 mCi/µmol) at the end of synthesis (60 min; n = 3) and validated for human use. This methodology offers the advantage of faster synthesis in fewer steps, with simpler automation that we anticipate will facilitate widespread clinical use of [(18) F]T807.

Evidence For Cannabidiol Modulation of Serotonergic Transmission in a Model of Osteoarthritis via in vivo PET Imaging and Behavioral Assessment.

Background: Preclinical studies indicate that cannabidiol (CBD), the primary nonaddictive component of cannabis, has a wide range of reported pharmacological effects such as analgesic and anxiolytic actions; however, the exact mechanisms of action for these effects have not been examined in chronic osteoarthritis (OA). Similar to other chronic pain syndromes, OA pain can have a significant affective component characterized by mood changes. Serotonin (5-HT) is a neurotransmitter implicated in pain, depression, and anxiety. Pain is often in comorbidity with mood and anxiety disorders in patients with OA. Since primary actions of CBD are analgesic and anxiolytic, in this first in vivo positron emission tomography (PET) imaging study, we investigate the interaction of CBD with serotonin 5-HT1A receptor via a combination of in vivo neuroimaging and behavioral studies in a well-validated OA animal model. Methods: The first aim of this study was to evaluate the target involvement, including the evaluation of modulation by acute administration of CBD, or a specific target antagonist/agonist intervention, in control animals. The brain 5-HT1A activity/availability was assessed via in vivo dynamic PET imaging (up to 60 min) using a selective 5-HT1A radioligand ([18F]MeFWAY). Tracer bindings of 17 ROIs were evaluated based on averaged SUVR values over the last 10 min using CB as the reference region. We subsequently examined the neurochemical and behavioral alterations in OA animals (induction with monosodium iodoacetate (MIA) injection), as compared to control animals, via neuroimaging and behavioral assessment. Further, we examined the effects of repeated low-dose CBD treatment on mechanical allodynia (von Frey tests) and anxiety-like (light/dark box tests, L/D), depressive-like (forced swim tests, FST) behaviors in OA animals, as compared to after vehicle treatment. Results: The tracer binding was significantly reduced in control animals after an acute dose of CBD administered intravenously (1.0 mg/kg, i.v.), as compared to that for baseline. This binding specificity to 5-HT1A was further confirmed by a similar reduction of tracer binding when a specific 5-HT1A antagonist WAY1006235 was used (0.3 mg/kg, i.v.). Mice subjected to the MIA-induced OA for 13-20 days showed a decreased 5-HT1A tracer binding (25% to 41%), consistent with the notion that 5-HT1A plays a role in the modulation of pain in OA. Repeated treatment with CBD administered subcutaneously (5 mg/kg/day, s.c., for 16 days after OA induction) increased 5-HT1A tracer binding, while no significant improvement was observed after vehicle. A trend of increased anxiety or depressive-like behavior in the light/dark box or forced swim tests after OA induction, and a decrease in those behaviors after repeated low-dose CBD treatment, are consistent with the anxiolytic action of CBD through 5HT1A receptor activation. There appeared to be a sex difference: females seem to be less responsive at the baseline towards pain stimuli, while being more sensitive to CBD treatment. Conclusion: This first in vivo PET imaging study in an OA animal model has provided evidence for the interaction of CBD with the serotonin 5-HT1A receptor. Behavioral studies with more pharmacological interventions to support the target involvement are needed to further confirm these critical findings.

Microfluidic continuous-flow radiosynthesis of [18F]FPEB suitable for human PET imaging.

The synthesis of fluorine-18 labeled 3-fluoro-5-[(pyridin-3-yl)ethynyl] benzonitrile ([18F]FPEB) for imaging metabotropic glutamate receptor subtype type 5 (mGluR5) was achieved with a commercial continuous-flow microfluidics device. This work represents the first positron emission tomography (PET) radiopharmaceutical that is suitable for human use with this technology. We also describe a validated synthesis of [18F]FPEB with a commercial reactor-based system.