Development of [18F]FAMTO: A novel fluorine-18 labelled positron emission tomography (PET) radiotracer for imaging CYP11B1 and CYP11B2 enzymes in adrenal glands
作者:Salvatore Bongarzone、Filippo Basagni、Teresa Sementa、Nisha Singh、Caleb Gakpetor、Vincent Faugeras、Jayanta Bordoloi、Antony D. Gee
DOI:10.1016/j.nucmedbio.2018.11.002
日期:2019.1
Introduction: Primary aldosteronism accounts for 6-15% of hypertension cases, the single biggest contributor to global morbidity and mortality. Whilst similar to 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 ([C-11]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 [C-11]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 ([F-18]FAMTO) has the potential to overcome this disadvantage and allow it to be transported to noncyclotron-based imaging centres.Methods: Two strategies for the one-step radio-synthesis of [F-18]FAMTO were developed. [F-18]FAMTO was obtained via radiofluorination via use of sulfonium salt (1) and boronic ester (2) precursors. [ 18 F]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 [F-18]FAMTO metabolites.Results: [F-18]FAMTO is obtained from sulfonium salt (1) and boronic ester (2) precursors in 7% and 32% nonisolated radiochemical yield (RCY), respectively. Formulated [F-18]FAMTO was obtained with >99% radiochemical and enantiomeric purity with a synthesis time of 140 min from the trapping of [F-18]fluoride ion on an anionexchange resin (QMA cartridge). In vitro autoradiography of [F-18]FAMTO demonstrated exquisite specific binding in CYP11B-rich pig adrenal glands. In vivo [F-18]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 [F-18]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: [F-18]FAMTO, a new F-18-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. (C) 2018 The Authors. Published by Elsevier Inc.