Radioactice labelling of the beta-2 adrenergic agonist Fenoterol with F-18 and C-11

Der b-2 adrenerge Rezeptor in der Lunge wird im Zusammenhang mit Erkrankungen wie Asthma diskutiert. Bislang gibt es keine Möglichkeit, den high-affinity Zustand des Rezeptors in vivo quantitativ zu erfassen. Ein Ansatz besteht in der radioaktiven Markierung eines hoch-selektiven, hoch-affinen sowie hydrophilen Agonisten wie Fenoterol, das als Asthma-Therapeutikum in der Medizin eingesetzt wird. Ziel dieser Arbeit war deshalb, Fenoterol durch Einführung der Isotope F-18 und C-11 dahingehend zu derivatisieren, dass die Affinität, die Selektivität und die Hydrophilie des originalen Fenoterols möglichst erhalten bleiben. Die nicht-radioaktive Verbindung 2-(Benzyl-(2-[4-(2-fluorethoxy)phenyl]-1-methylethyl)amino)-1-(3,5-bisbenzyloxy-phenyl)ethanol (20) und der nicht-radioaktive 19F-Standard 5-(2-(2-[4-(2-Fluoroethoxy)phenyl]-1-methylethylamino)-1-hydroxyethyl)benzen-1,3-diol (25) wurden in mehrstufigen Synthesen dargestellt. Die nicht-radioaktive Verbindung 2-(Benzyl-[2-(4-methoxyphenyl)-1-methylethyl]amino)-1-(3,5-bisbenzyloxy-phenyl)ethanol sowie der nicht-radioaktive 12C-Standard 5-(1-Hydroxy-2-[2-(4-methoxyphenyl)-1-methylethylamino]-ethyl)benzen-1,3-diol wurde analog zum 19F-Standard 20 in einer mehrstufigen konvergenten Synthese dargestellt. Die Markierungsvorläufer 4-(2-(Benzyl-[2-(3,5-bisbenzyloxy-phenyl)-2-hydroxyethyl]amino)propyl)phenol, 5-(1-Hydroxy-2-[2-(4-hydroxyphenyl)-1-methylethylamino]ethyl)benzen-1,3-diol und Essigsäure-2-[benzyl-(1-methyl-2-(4-[2-(toluol-4-sulfonyloxy)ethoxy]phenyl)ethyl)amino]-1-(3,5-bisbenzyloxy-phenyl)-ethylester wurden ebenfalls dargestellt. Die radioaktiven Markierungen wurden bezüglich Lösungsmittel, Vorläuferkonzentration, Reaktionstemperatur und Basenzusatz optimiert. Mit dem fluorethylierten Derivat von Fenoterol, 25, wurden vorläufige in vitro-Evaluierung an isolierten Meerschweinchen-Tracheen, mit dem radioaktiv markierten Fluorethyl-Fenoterol wurden vorläufige PET-Studien an Meerschweinchen durchgeführt.The role of the beta-2 adrenergic receptor in diseases such as asthma has long been discussed. Up to now, there exists no possibility to measure the beta-2 adrenoceptor status in lung in vivo. If a highly selective, subtype specific agonist were labelled with a positron emitting isotope like fluorine-18 or carbon-11 with minimal change to any of its biochemical properties, this would be an important tool to elucidate the role of the beta-2 adrenoceptor in the above mentioned diseases. The aim of this study therefore was to label Fenoterol, an agonist commonly used in asthma therapy with F-18 and C-11. The non-radioactive standard compounds 2-(benzyl-(2-[4-(2-fluoroethoxy)phenyl]-1-methylethyl)amino)-1-(3,5-bisbenzyloxy-phenyl)ethanol (20), 5-(2-(2-[4-(2-fluoroethoxy)phenyl]-1-methylethylamino)-1-hydroxyethyl)benzene-1,3-diol (25), 2-(benzyl-[2-(4-methoxyphenyl)-1-methylethyl]amino)-1-(3,5-bisbenzyloxy-phenyl)ethanol (32) and 5-(1-hydroxy-2-[2-(4-methoxyphenyl)-1-methylethylamino]-ethyl)benzene-1,3-diol were all prepared in multistep syntheses. The labelling precursors 4-(2-(benzyl-[2-(3,5-bisbenzyloxy-phenyl)-2-hydroxyethyl]amino)propyl)phenol, 5-(1-hydroxy-2-[2-(4-hydroxyphenyl)-1-methylethylamino]ethyl)benzene-1,3-diol und acetic acid-2-[benzyl-(1-methyl-2-(4-[2-(toluol-4-sulfonyloxy)ethoxy]phenyl)ethyl)amino]-1-(3,5-bisbenzyloxy-phenyl)-ethylester were synthesised analogously. The labelling reactions were optimised as to their reaction temperatures, solvents, precursor concentrations and bases. With the F-19 standard compound 5-(2-(2-[4-(2-fluoroethoxy)phenyl]-1-methylethylamino)-1-hydroxyethyl)benzene-1,3-diol (25) in vitro experiments on isolated guinea pig trachea were undertaken. As the results showed that the affinity of the ligand to the receptor was unchanged, preliminary in vivo PET studies on guinea pigs were performed

18F-Labeled Silicon-Based Fluoride Acceptors: Potential Opportunities for Novel Positron Emitting Radiopharmaceuticals

Background. Over the recent years, radiopharmaceutical chemistry has experienced a wide variety of innovative pushes towards finding both novel and unconventional radiochemical methods to introduce fluorine-18 into radiotracers for positron emission tomography (PET). These “nonclassical” labeling methodologies based on silicon-, boron-, and aluminium-18F chemistry deviate from commonplace bonding of an [18F]fluorine atom (18F) to either an aliphatic or aromatic carbon atom. One method in particular, the silicon-fluoride-acceptor isotopic exchange (SiFA-IE) approach, invalidates a dogma in radiochemistry that has been widely accepted for many years: the inability to obtain radiopharmaceuticals of high specific activity (SA) via simple IE. Methodology. The most advantageous feature of IE labeling in general is that labeling precursor and labeled radiotracer are chemically identical, eliminating the need to separate the radiotracer from its precursor. SiFA-IE chemistry proceeds in dipolar aprotic solvents at room temperature and below, entirely avoiding the formation of radioactive side products during the IE. Scope of Review. A great plethora of different SiFA species have been reported in the literature ranging from small prosthetic groups and other compounds of low molecular weight to labeled peptides and most recently affibody molecules. Conclusions. The literature over the last years (from 2006 to 2014) shows unambiguously that SiFA-IE and other silicon-based fluoride acceptor strategies relying on 18F− leaving group substitutions have the potential to become a valuable addition to radiochemistry

In-vivo confocal real-time mini-microscopy in animal models of human inflammatory and neoplastic diseases

BACKGROUND AND STUDY AIMS: Although various improvements in tissue imaging modalities have recently been achieved, in-vivo molecular and subsurface imaging in the field of gastroenterology remains a technical challenge. In this study we evaluated a newly developed, handheld, miniaturized confocal laser microscopy probe for real-time in-vivo molecular and subsurface imaging in rodent models of human disease. MATERIALS AND METHODS: The minimicroscope uses a 488-nm, single line laser for fluorophore excitation. The optical slice thickness is 7 microm, the lateral resolution 0.7 microm. The range of the z-axis is 0-250 microm below the tissue surface. Imaging was performed using different fluorescent staining protocols; 5-carboxyfluorescein-labeled octreotate was synthesized for targeted molecular imaging. RESULTS: Cellular and subcellular details of the gastrointestinal tract could be visualized in vivo at high resolution. Confocal real-time microscopy allowed in-vivo identification of tumor vessels and liver metastases, as well as diagnosis of focal hepatic inflammation, necrosis, and associated perfusion anomalies. Somatostatin-receptor targeting permitted in-vivo molecular staining of AR42-J-induced carcinoma and pancreatic islet cells. CONCLUSIONS: Confocal mini-microscopy allows rapid in-vivo molecular and subsurface imaging of normal and pathological tissue in the gastrointestinal tract at high resolution. Because this technology is applicable to humans, it might impact on future in-vivo microsocpic and molecular diagnosis of diseases such as cancer and inflammation

Cholinergic Depletion in Alzheimer’s Disease Shown by [18F]FEOBV Autoradiography

Rationale. Alzheimer’s Disease (AD) is a neurodegenerative condition characterized in part by deficits in cholinergic basalocortical and septohippocampal pathways. [18F]Fluoroethoxybenzovesamicol ([18F]FEOBV), a Positron Emission Tomography ligand for the vesicular acetylcholine transporter (VAChT), is a potential molecular agent to investigate brain diseases associated with presynaptic cholinergic losses. Purpose. To demonstrate this potential, we carried out an [18F]FEOBV autoradiography study to compare postmortem brain tissues from AD patients to those of age-matched controls. Methods. [18F]FEOBV autoradiography binding, defined as the ratio between regional grey and white matter, was estimated in the hippocampus (13 controls, 8 AD) and prefrontal cortex (13 controls, 11 AD). Results. [18F]FEOBV binding was decreased by 33% in prefrontal cortex, 25% in CA3, and 20% in CA1. No changes were detected in the dentate gyrus of the hippocampus, possibly because of sprouting or upregulation toward the resilient glutamatergic neurons of the dentate gyrus. Conclusion. This is the first demonstration of [18F]FEOBV focal binding changes in cholinergic projections to the cortex and hippocampus in AD. Such cholinergic synaptic (and more specifically VAChT) alterations, in line with the selective basalocortical and septohippocampal cholinergic losses documented in AD, indicate that [18F]FEOBV is indeed a promising ligand to explore cholinergic abnormalities in vivo

Radioligands for Tropomyosin Receptor Kinase (Trk) Positron Emission Tomography Imaging

The tropomyosin receptor kinases family (TrkA, TrkB, and TrkC) supports neuronal growth, survival, and differentiation during development, adult life, and aging. TrkA/B/C downregulation is a prominent hallmark of various neurological disorders including Alzheimer’s disease (AD). Abnormally expressed or overexpressed full-length or oncogenic fusion TrkA/B/C proteins were shown to drive tumorigenesis in a variety of neurogenic and non-neurogenic human cancers and are currently the focus of intensive clinical research. Neurologic and oncologic studies of the spatiotemporal alterations in TrkA/B/C expression and density and the determination of target engagement of emerging antineoplastic clinical inhibitors in normal and diseased tissue are crucially needed but have remained largely unexplored due to the lack of suitable non-invasive probes. Here, we review the recent development of carbon-11- and fluorine-18-labeled positron emission tomography (PET) radioligands based on specifically designed small molecule kinase catalytic domain-binding inhibitors of TrkA/B/C. Basic developments in medicinal chemistry, radiolabeling and translational PET imaging in multiple species including humans are highlighted