A microwave radiosynthesis of the 4-[18F]-fluorobenzyltriphenylphosphonium ion

cGMP compliant one-step, one-pot automated [18F]FBnTP production for clinical imaging of mitochondrial activity

BACKGROUND

4-[18F]fluorobenzyl-triphenylphosphonium ([18F]FBnTP) is a lipophilic cation PET tracer. The cellular uptake of [18F]FBnTP is correlated with oxidative phosphorylation by mitochondria, which has been associated with multiple critical diseases. To date, [18F]FBnTP has been successfully applied for imaging myocardial perfusion, assessment of severity of coronary artery stenosis, delineation of the ischemic area after transient coronary occlusion, and detection/quantification of apoptosis in various animal models. Recent preclinical and clinical studies have also expanded the possibilities of using [18F]FBnTP in oncological diagnosis and therapeutic monitoring. However, [18F]FBnTP is typically prepared through a tediously lengthy four-step, three-pot reaction and required multiple synthesizer modules; Thus, such an approach remains a challenge for this promising radiopharmaceutical to be implemented for routine clinical studies. Herein, we report an optimized one-step, one-pot automated approach to produce [18F]FBnTP through a single standard commercially-available radiosynthesizer that enables centralized production for clinical use.

RESULTS

The fully automated production of [18F]FBnTP took less than 55 min with radiochemical yields ranging from 28.33 ± 13.92% (non-decay corrected), apparent molar activity of 69.23 ± 45.62 GBq/µmol, and radiochemical purities of 99.79 ± 0.41%. The formulated [18F]FBnTP solution was determined to be sterile and colorless with a pH of 4.0-6.0. Our data has indicated no observable radiolysis after 8 h from the time of final product formulation and maximum assay of 7.88 GBq.

CONCLUSIONS

A simplified and cGMP-compliant radiosynthesis of [18F]FBnTP has been established on the commercially available synthesizer in high activity concentration and radiochemical purity. While the preclinical and clinical studies using [18F]FBnTP PET are currently underway, the automated approaches reported herein facilitate clinical adoption of this radiotracer and warrant centralized production of [18F]FBnTP for imaging multiple patients.

Scalable droplet-based radiosynthesis of [18F]fluorobenzyltriphenylphosphonium cation ([18F]FBnTP) via a "numbering up" approach

The [18F]fluorobenzyltriphenylphosphonium cation ([18F]FBnTP) has emerged as a highly promising positron emission tomography (PET) tracer for myocardial perfusion imaging (MPI) due to its uniform distribution in the myocardium and favorable organ biodistribution demonstrated in preclinical studies. However, a complex and low-efficiency radiosynthesis procedure has significantly hindered its broader preclinical and clinical explorations. Recently, Zhang et al. developed a pinacolyl arylboronate precursor, enabling a one-step synthesis process that greatly streamlines the production of [18F]FBnTP. Building upon this progress, our group successfully adapted the approach to a microdroplet reaction format and demonstrated improved radiosynthesis performance in a preliminary optimization study. However, scaling up to clinical dose amounts was not explored. In this work, we demonstrate that scale-up can be performed in a straightforward manner using a "numbering up" strategy (i.e. performing multiple droplet reactions in parallel and pooling the crude products). The resulting radiochemical yield after purification and formulation was high, up to 66 ± 1% (n = 4) for a set of experiments involving pooling of 4 droplet reactions, accompanied by excellent radiochemical purity (>99%) and molar activity (339-710 GBq μmol-1). Notably, we efficiently achieved sufficient activity yield (0.76-1.84 GBq) for multiple clinical doses from 1.6 to 3.7 GBq of [18F]fluoride in just 37-47 min.

An improved radiosynthesis of [18 F]FAraG, a PET radiotracer for imaging T-cell activation

In this concise practitioner protocol, the radiochemical synthesis of 2'-deoxy-2'-[¹⁸ F]fluoro-9-β-d-arabinofuranosylguanine ([¹⁸ F]FAraG) suitable for human positron emission tomography (PET) studies is described and the results from validation productions are presented. The high specific activity (sometimes referred to as molar activity) radiotracer product is prepared as a sterile, apyrogenic solution that conforms to current Good Manufacturing Practice (cGMP) requirements established by the U.S. Food and Drug Administration.

An Automated Multidose Synthesis of the Potentiometric PET Probe 4-[18F]Fluorobenzyl-Triphenylphosphonium ([18F]FBnTP)

PURPOSE

The aim of this study was the automated synthesis of the mitochondrial membrane potential sensor 4-[¹⁸F]fluorobenzyl-triphenylphosphonium ([¹⁸F]FBnTP) on a commercially available synthesizer in activity yields (AY) that allow for imaging of multiple patients.

PROCEDURES

A three-pot, four-step synthesis was implemented on the ELIXYS FLEX/CHEM radiosynthesizer (Sofie Biosciences) and optimized for radiochemical yield (RCY), radiochemical purity (RCP) as well as chemical purity during several production runs (n = 24). The compound was purified by solid-phase extraction (SPE) with a Sep-Pak Plus Accell CM cartridge, thereby avoiding HPLC purification.

RESULTS

Under optimized conditions, AY of 1.4-2.2 GBq of [¹⁸F]FBnTP were obtained from 9.4 to 12.0 GBq [¹⁸F]fluoride in 90-92 min (RCY = 28.6 ± 5.1 % with n = 3). Molar activities ranged from 80 to 99 GBq/μmol at the end of synthesis. RCP of final formulations was > 99 % at the end of synthesis and > 95 % after 8 h. With starting activities of 23.2-33.0 GBq, RCY decreased to 16.1 ± 0.4 % (n = 3). The main cause of the decline in RCY when high amounts of [¹⁸F]fluoride are used is radiolytic decomposition of [¹⁸F]FBnTP during SPE purification.

CONCLUSIONS

In initial attempts, the probe was synthesized with RCY < 0.6 % when starting activities up to 44.6 GBq were used. Rapid radiolysis of the intermediate 4-[¹⁸F]fluorobenzaldehyde and the final product [¹⁸F]FBnTP during purification was identified as the main cause for low yields in high-activity runs. Radiolytic decomposition was hindered by the addition of radical scavengers during synthesis, purification, and formulation, thereby improving AY and RCP. The formulated probe in injectable form was synthesized without the use of HPLC and passed all applicable quality control tests.

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

In this concise practitioner protocol, the radiochemical synthesis of [¹⁸ F]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.

Research Progress on 18F-Labeled Agents for Imaging of Myocardial Perfusion with Positron Emission Tomography

Coronary artery disease (CAD) is the leading cause of death in the world. Myocardial perfusion imaging (MPI) plays a significant role in non-invasive diagnosis and prognosis of CAD. However, neither single-photon emission computed tomography nor positron emission tomography clinical MPI agents can absolutely satisfy the demands of clinical practice. In the past decades, tremendous developments happened in the field of ¹⁸F-labeled MPI tracers. This review summarizes the current state of ¹⁸F-labeled MPI tracers, basic research data of those tracers, and the future direction of MPI tracer research.

Fluorine-18 labelled building blocks for PET tracer synthesis

This review presents a comprehensive overview of the synthesis and application of fluorine-18 labelled building blocks since 2010.

One-step synthesis of 4-[(18) F]fluorobenzyltriphenylphosphonium cation for imaging with positron emission tomography

4-[(18) F]Fluorobenzyltriphenylphosphonium cation ((18) F-FBnTP) is a promising negative membrane potential targeting positron emission tomography tracer. However, the reported multistep radiolabeling approach for the synthesis of (18) F-FBnTP poses a challenge for routine clinical applications. In this study, we demonstrated that (18) F-FBnTP can be prepared in good conversion yields (~60%, nondecay corrected) in just one step via a copper-mediated (18) F-fluorination reaction using a pinacolyl arylboronate precursor. In addition, our data suggest that (18) F-labeled (phosphonium) cations can be efficiently prepared via a copper-mediated (18) F-fluoronation by using triflate as the counterion.

An improved synthesis of the radiolabeled prostate-specific membrane antigen inhibitor, [(18) F]DCFPyL

The radiosynthesis of [(18) F]DCFPyL on 2 distinct automated platforms with full regulatory compliant quality control specifications is described. The radiotracer synthesis was performed on a custom-made radiofluorination module and the Sofie Biosciences ELIXYS. The radiofluorination module synthesis was accomplished in an average of 66 minutes from end of bombardment with an average specific activity at end of synthesis (EOS) of 4.4 TBq/μmol (120 Ci/μmol) and an average radiochemical yield of 30.9% at EOS. The ELIXYS synthesis was completed in an average of 87 minutes with an average specific activity of 2.2 TBq/μmol (59.3 Ci/μmol) and an average radiochemical yield of 19% at EOS. Both synthesis modules produced large millicurie quantities of [(18) F]DCFPyL while conforming to all standard US Pharmacopeia Chapter <823> acceptance testing criteria.

Synthesis and quality control of [(18) F]T807 for tau PET imaging

The detailed synthesis and quality control of [(18) F]T807, radiotracer for tau protein aggregate imaging, are described. The radiotracer synthesis was accomplished in an average of 48 min with an average specific activity at end-of-synthesis of over 4.4 TBq/µmole (120 Ci/µmole) and an average radiochemical yield of 32%. Compliance with all standard US Pharmacopeia Chapter <823> acceptance tests was observed.

Microwave-assisted radiosynthesis of [(18) F]ASEM, a radiolabeled α7-nicotinic acetylcholine receptor antagonist

An improvement of the original radiochemical synthesis of [(18) F]ASEM, an α7-nicotinic acetylcholinergic receptor radioligand, is reported. The new procedure utilizes microwave-assisted radiofluorination. In addition, a new preparative HPLC method was developed to eliminate a chemical impurity in the final product. Quality control procedures were also enhanced to improve detection of product with enhanced resolution of potential impurities. [(18) F]ASEM was produced in 20.1 ± 8.9% non-decay corrected (NDC) yield with an average synthesis time of 57 min and an average specific radioactivity of 856 ± 332 GBq/µmol (23 ± 9 Ci/µmol).