Dataset Information

Initial Evaluation of AF78: a Rationally Designed Fluorine-18-Labelled PET Radiotracer Targeting Norepinephrine Transporter.

ABSTRACT: PURPOSE:Taking full advantage of positron emission tomography (PET) technology, fluorine-18-labelled radiotracers targeting norepinephrine transporter (NET) have potential applications in the diagnosis and assessment of cardiac sympathetic nerve conditions as well as the delineation of neuroendocrine tumours. However, to date, none have been used clinically. Drawbacks of currently reported radiotracers include suboptimal kinetics and challenging radiolabelling procedures. PROCEDURES:We developed a novel fluorine-18-labelled radiotracer targeting NET, AF78, with efficient one-step radiolabelling based on the phenethylguanidine structure. Radiosynthesis of AF78 was undertaken, followed by validation in cell uptake studies, autoradiography, and in vivo imaging in rats. RESULTS:[18F]AF78 was successfully synthesized with 27.9?±?3.1 % radiochemical yield, >?97 % radiochemical purity and >?53.8 GBq/mmol molar activity. Cell uptake studies demonstrated essentially identical affinity for NET as norepinephrine and meta-iodobenzylgaunidine. Both ex vivo autoradiography and in vivo imaging in rats showed homogeneous and specific cardiac uptake. CONCLUSIONS:The new PET radiotracer [18F]AF78 demonstrated high affinity for NET and favourable biodistribution in rats. A structure-activity relationship between radiotracer structures and affinity for NET was revealed, which may serve as the basis for the further design of NET targeting radiotracers with favourable features.

SUBMITTER: Chen X

PROVIDER: S-EPMC7250802 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature

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Initial Evaluation of AF78: a Rationally Designed Fluorine-18-Labelled PET Radiotracer Targeting Norepinephrine Transporter.

Chen Xinyu X Fritz Alexander A Werner Rudolf A RA Nose Naoko N Yagi Yusuke Y Kimura Hiroyuki H Rowe Steven P SP Koshino Kazuhiro K Decker Michael M Higuchi Takahiro T

Molecular imaging and biology 20200601 3

<h4>Purpose</h4>Taking full advantage of positron emission tomography (PET) technology, fluorine-18-labelled radiotracers targeting norepinephrine transporter (NET) have potential applications in the diagnosis and assessment of cardiac sympathetic nerve conditions as well as the delineation of neuroendocrine tumours. However, to date, none have been used clinically. Drawbacks of currently reported radiotracers include suboptimal kinetics and challenging radiolabelling procedures.<h4>Procedures</ ...[more]

PMID: 31332629

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Project description:IntroductionPrimary aldosteronism accounts for 6-15% of hypertension cases, the single biggest contributor to global morbidity and mortality. Whilst ~50% of these patients have unilateral aldosterone-producing adenomas, only a minority of these have curative surgery as the current diagnosis of unilateral disease is poor. Carbon-11 radiolabelled metomidate ([11C]MTO) is a positron emission tomography (PET) radiotracer able to selectively identify CYP11B1/2 expressing adrenocortical lesions of the adrenal gland. However, the use of [11C]MTO is limited to PET centres equipped with on-site cyclotrons due to its short half-life of 20.4?min. Radiolabelling a fluorometomidate derivative with fluorine-18 (radioactive half life 109.8?min) in the para-aromatic position ([18F]FAMTO) has the potential to overcome this disadvantage and allow it to be transported to non-cyclotron-based imaging centres.MethodsTwo strategies for the one-step radio-synthesis of [18F]FAMTO were developed. [18F]FAMTO was obtained via radiofluorination via use of sulfonium salt (1) and boronic ester (2) precursors. [18F]FAMTO was evaluated in vitro by autoradiography of pig adrenal tissues and in vivo by determining its biodistribution in rodents. Rat plasma and urine were analysed to determine [18F]FAMTO metabolites.Results[18F]FAMTO is obtained from sulfonium salt (1) and boronic ester (2) precursors in 7% and 32% non-isolated radiochemical yield (RCY), respectively. Formulated [18F]FAMTO was obtained with >99% radiochemical and enantiomeric purity with a synthesis time of 140?min from the trapping of [18F]fluoride ion on an anion-exchange resin (QMA cartridge). In vitro autoradiography of [18F]FAMTO demonstrated exquisite specific binding in CYP11B-rich pig adrenal glands. In vivo [18F]FAMTO rapidly accumulates in adrenal glands. Liver uptake was about 34% of that in the adrenals and all other organs were <12% of the adrenal uptake at 60?min post-injection. Metabolite analysis showed 13% unchanged [18F]FAMTO in blood at 10?min post-administration and rapid urinary excretion. In vitro assays in human blood showed a free fraction of 37.5%.Conclusions[18F]FAMTO, a new 18F-labelled analogue of metomidate, was successfully synthesised. In vitro and in vivo characterization demonstrated high selectivity towards aldosterone-producing enzymes (CYP11B1 and CYP11B2), supporting the potential of this radiotracer for human investigation.

Project description:BACKGROUND:Targeted therapy of HER2 positive breast cancer has led to clinical success in some cases with primary and secondary resistance being major obstacles. Due to the substantial involvement of mTOR kinase in cell growth and proliferation pathways it is now targeted in combination treatments to counteract HER2 targeted therapy resistance. However, the selection of receptive patient populations for a specific drug combination is crucial. This work aims to develop a molecular probe capable of identifying patients with tumour populations which are receptive to RAD001 combination therapy. Based on the structure of a mTOR inhibitor specific for mTORC1, we designed, synthesised and characterised a novel benzofuran based molecular probe which suits late stage fluorination via Click chemistry. RESULTS:Synthesis of the alkyne precursor 5 proceeded in 27.5% yield over 7 linear steps. Click derivatisation gave the non-radioactive standard in 25% yield. Radiosynthesis of [18F]1-((1-(2-Fluoroethyl)-1H-1,2,3-triazol-4-yl) methyl)-4-((5-methoxy-2-phenylbenzofuran-4-yl) methyl) piperazine ([18F]mBPET-1) proceeded over two steps which were automated on an iPhase FlexLab synthesis module. In the first step, 2-[18F]fluoroethylazide ([18F]6) was produced, purified by automated distillation in 60% non-decay-corrected yield and subjected to Click conditions with 5. Semi-preparative RP-HPLC purification and reformulation gave [18F]mBPET-1 in 40%?±?5% (n?=?6) overall RCY with a process time of 90?min. Radiochemical purity was ?99% at end of synthesis (EOS) and???98% after 4?h at room temperature. Molar activities ranged from typically 24.8?GBq/?mol (EOS) to a maximum of 78.6?GBq/?mol (EOS). Lipophilicity of [18F]mBPET-1 was determined at pH?7.4 (logD7.4?=?0.89). [18F]mBPET-1 showed high metabolic stability when incubated with mouse S9 liver fractions which resulted in a 0.8% drop in radiochemical purity after 3?h. Cell uptake assays showed 1.3-1.9-fold increased uptake of the [18F]mBPET-1 in RAD001 sensitive compared to insensitive cells across a panel of 4 breast cancer cell lines. CONCLUSION:Molecular targeting of mTOR with [18F]mBPET-1 distinguishes mTOR inhibitor sensitive and insensitive cell lines. Future studies will explore the ability of [18F]mBPET-1 to predict response to mTOR inhibitor treatment in in vivo models.

Dataset Information

Initial Evaluation of AF78: a Rationally Designed Fluorine-18-Labelled PET Radiotracer Targeting Norepinephrine Transporter.

Publications

Initial Evaluation of AF78: a Rationally Designed Fluorine-18-Labelled PET Radiotracer Targeting Norepinephrine Transporter.

Similar Datasets

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