New systematically modified vesamicol analogs and their affinity and selectivity for the vesicular acetylcholine transporter - A critical examination of the lead structure.

To verify vesamicol as lead structure in the development of radioligands for imaging of VAChT in the brain by PET, we systematically modified this molecule and investigated four different groups of derivatives. Structural changes were conducted in all three ring systems A, B, and C resulting in a library of different vesamicol analogs. Based on their in vitro binding affinity toward VAChT as well as σ1 and σ2 receptors, we performed a structure-affinity relationship (SAR) study regarding both affinity and selectivity.

Pyrrolovesamicols--synthesis, structure and VAChT binding of two 4-fluorobenzoyl regioisomers.

This Letter describes the synthesis of two regioisomers of a new class of vesamicol analogs as possible ligands for imaging the vesicular acetylcholine transporter in future PET studies. The two pyrrolovesamicols (±)-6a and (±)-6b were synthesized by nucleophilic ring opening reaction of a tetrahydroindole epoxide precursor with 4-phenylpiperidine. The reaction mechanism of the synthesis was studied by HPLC and the molecular structures were determined by X-ray structure analysis.

Imaging of the brain serotonin transporters (SERT) with 18F-labelled fluoromethyl-McN5652 and PET in humans.

Purpose: [(11)C]DASB is currently the most frequently used highly selective radiotracer for visualization and quantification of central SERT. Its use, however, is hampered by the short half-life of (11)C, the moderate cortical test-retest reliability, and the lack of quantifying endogenous serotonin. Labelling with (18)F allows in principle longer acquisition times for kinetic analysis in brain tissue and may provide higher sensitivity.

Decreased cerebral α4β2* nicotinic acetylcholine receptor availability in patients with mild cognitive impairment and Alzheimer's disease assessed with positron emission tomography.

Purpose: Postmortem studies indicate a loss of nicotinic acetylcholine receptor (nAChRs) in Alzheimer's disease (AD). In order to establish whether these changes in the cholinergic system occur at an early stage of AD, we carried out positron emission tomography (PET) with a specific radioligand for the α4β2* nicotinic acetylcholine receptor (α4β2* nAChR) in patients with mild to moderate AD and in patients with amnestic mild cognitive impairment (MCI), who have a high risk to progress to AD.

Methods: Nine patients with moderate AD, eight patients with MCI and seven age-matched healthy controls underwent 2-[(18)F]fluoro-3-(2(S)-azetidinylmethoxy)pyridine (2-[(18)F]FA-85380) PET.

Reduced alpha4beta2*-nicotinic acetylcholine receptor binding and its relationship to mild cognitive and depressive symptoms in Parkinson disease.

Context: Cognitive or depressive disorders are frequently noted in patients with Parkinson disease (PD) and may be related to altered signaling through alpha4beta2*-nicotinic acetylcholine receptors (alpha4beta2*-nAChRs).

Objective: To assess the availability of alpha4beta2*-nAChRs and their relationship to mild cognitive and mild depressive symptoms in vivo in patients with PD.

Design: Crossover comparison between patients with PD and healthy volunteers (control group) using the alpha4beta2*-nAChR-specific radioligand 2-[(18)F]fluoro-3-(2[S]-2-azetidinylmethoxy)-pyridine (2-[(18)F]FA-85380) and positron emission tomography.

Neuroimaging of the vesicular acetylcholine transporter by a novel 4-[18F]fluoro-benzoyl derivative of 7-hydroxy-6-(4-phenyl-piperidin-1-yl)-octahydro-benzo[1,4]oxazines.

Phenylpiperidinyl-octahydro-benzo[1,4]oxazines represent a new class of conformationally restrained vesamicol analogues. Derived from this morpholine-fused vesamicol structure, a new fluorine-18-labeled 4-fluorobenzoyl derivative ([(18)F]FBMV) was synthesized with an average specific activity of 75 GBq/micromol and a radiochemical purity of 99%. The radiolabeling method included an exchange reaction of a 4-nitro group of the precursor by fluorine-18, a reduction procedure to eliminate excess of the nitro compound, followed by a high-performance liquid chromatography purification.

A new 18F-labeled fluoroacetylmorpholino derivative of vesamicol for neuroimaging of the vesicular acetylcholine transporter.

With the aim of producing selective radiotracers for in vivo imaging of the vesicular acetylcholine transporter (VAChT) using positron mission tomography (PET), here, we report synthesis and analysis of a new class of conformationally constrained vesamicol analogues with moderate lipophilicity. The sequential ring opening on trans-1,4-cyclohexadiene dioxide enabled an approach to synthesize 6-arylpiperidino-octahydrobenzo[1,4]oxazine-7-ols [morpholino vesamicols]. The radiosynthesis of the [18F]fluoroacetyl-substituted derivative ([18F]FAMV) was achieved starting from a corresponding bromo precursor [2-Bromo-1-[7-hydroxy-6-(4-phenyl-piperidin-1-yl)-octahydro-benzo[1,4]oxazin-4-yl]-ethanone] and using a modified commercial computer-controlled module system with a radiochemical yield of 27+/-4%, a high radiochemical purity (99%) and a specific activity of 35 GBq/micromol.

In vivo measurement of nicotinic acetylcholine receptors with [18F]norchloro-fluoro-homoepibatidine.

Functional changes of nicotinic acetylcholine receptors (nAChR) are important during age-related neuronal degeneration. Recent studies demonstrate the applicability of the nAChR ligand 2-[(18)F]F-A-85380 for neuroimaging of patients with dementias. However, its binding kinetics demands a 7-h acquisition time limiting its practicality for clinical PET studies.

Measurement of the alpha4beta2* nicotinic acetylcholine receptor ligand 2-[(18)F]Fluoro-A-85380 and its metabolites in human blood during PET investigation: a methodological study.

2-[(18)F]fluoro-A-85380 (2-[(18)F]FA) is a new radioligand for noninvasive imaging of alpha4beta2* nicotinic acetylcholine receptors (nAChRs) by positron emission tomography (PET) in human brain. In most cases, quantification of 2-[(18)F]FA receptor binding involves measurement of free nonmetabolized radioligand concentration in blood. This requires an efficient and reliable method to separate radioactive metabolites from the parent compound.

Binding properties of the cerebral alpha4beta2 nicotinic acetylcholine receptor ligand 2-[18F]fluoro-A-85380 to plasma proteins.

Introduction: To determine the availability of nicotinic acetylcholine receptors in different human brain regions using the positron emission tomography (PET) radioligand 2-[18F]fluoro-A-85380 (2-[18F]FA) and invasive approaches for quantification, it is important to correct the arterial input function as well for plasma protein binding (PPB) of the radioligand as for radiolabeled metabolites accumulating in blood. This study deals with some aspects of PPB of 2-[18F]FA.

Methods: Patients with different neurological disorders (n=72), such as Parkinson's disease, Alzheimer's disease and multiple sclerosis, and a group of healthy volunteers (n=15) subjected for PET imaging were analyzed for their PPB level of 2-[18F]FA using ultrafiltration.

Developmental and amyloid plaque-related changes in cerebral cortical capillaries in transgenic Tg2576 Alzheimer mice.

There is experimental evidence that cerebral perfusion is decreased during aging and in Alzheimer's disease. To characterize the temporal relationship between amyloid deposition, plaque size and cerebrovascular abnormalities, a semiquantitative immunohistochemical study was performed in transgenic Tg2576 mice that express the Swedish double mutation of human amyloid precursor protein (APP) and progressively develop Alzheimer-like beta-amyloid deposits. Cortical cryocut sections, obtained from mice at ages ranging between 4 and 18 months, were immunostained to label glucose transporter type 1 (GLUT1), a marker of vascular endothelial cells, and thioflavine-S to visualize plaques.

Structural changes of benzylether derivatives of vesamicol and their influence on the binding selectivity to the vesicular acetylcholine transporter.

18F labelled vesamicol analogues, which bind to the vesicular acetylcholine transporter (VAChT) in central cholinergic nerve terminals, are expected to be potential radioligands for the visualisation of cholinergic transmission deficits via positron emission tomography (PET). In this report the regioselective synthesis of five novel vesamicol analogues as well as their in vitro binding properties to the VAChT are described. Beside having the 4-fluorobenzylether-substitution at the cyclohexyl ring as an unique structural feature, the new compounds are additionally modified at the phenyl and piperidine moiety of the vesamicol skeleton.

Synthesis of novel 4- and 5-substituted benzyl ether derivatives of vesamicol and in vitro evaluation of their binding properties to the vesicular acetylcholine transporter site.

Detection of the central cholinergic deficits, a consistent feature of Alzheimer's disease, is essential to allow preventive measures and/or symptomatic treatment already at a very early stage of the disease. The vesicular acetylcholine transporter (VAChT) represents an appropriate target to establish PET radiotracer that are adequate for brain imaging the loss of cholinergic terminals. Here we describe the synthesis and binding characteristics of novel derivatives of vesamicol, known to represent a specific antagonist of VAChT sites.

Alterations in cholinergic and non-cholinergic neurotransmitter receptor densities in transgenic Tg2576 mouse brain with beta-amyloid plaque pathology.

Cholinergic deficits in Alzheimer's disease are accompanied by a number of alterations in other transmitter systems including glutamate, noradrenaline and serotonin, suggesting the involvement also of other neurotransmitter systems in the pathogenesis of the disease. To address the question whether beta-amyloid may contribute to these deficits, brain tissue from transgenic Tg2576 mice with Alzheimer plaque pathology at ages of 5 (still no significant plaque load) and 17 months (moderate to high cortical beta-amyloid plaque load) were examined for a number of cholinergic and non-cholinergic markers. Transgenic mice with no significant plaque load demonstrated reduced hemicholinium-3 (HCh-3) binding to choline uptake sites in anterior brain regions as compared to non-transgenic littermates, while in aged transgenic mice with high number of plaque deposits decreased HCh-3 binding levels were accompanied by increased vesicular acetylcholine transporter binding in selected cortical brain regions.

Neuroimaging of serotonin transporters in post-stroke pathological crying.

Pathological crying (PC) is a neuropsychiatric disorder characterized by an excessive tendency towards crying after brain damage. To elucidate the role of serotonin neurotransmission for PC, a pilot study was performed using single photon emission computed tomography with [123I]beta-CIT to estimate central (midbrain/pons and thalamus/hypothalamus) serotonin transporter (SERT) densities in 15 stroke patients who did or did not have PC. SERT binding ratios in midbrain/pons were significantly lower in the PC subgroup.

[18F]Fluoroazomycinarabinofuranoside (18FAZA) and [18F]Fluoromisonidazole (18FMISO): a comparative study of their selective uptake in hypoxic cells and PET imaging in experimental rat tumors.

The present study compares the uptake of [(18)F]Fluoroazomycinarabinofuranoside ((18)FAZA), a recently developed hypoxia tracer for PET imaging of tissue hypoxia, with an established tracer [(18)F]Fluoromisonidazole ((18)FMISO) both in vitro, using Walker 256 rat carcinosarcoma cells, and in vivo in experimental rat tumors eleven to twelve days after tumor cell implantation. In vitro studies indicated that hypoxia-selective uptake of both (18)FAZA and (18)FMISO in tumor cells, 20 and 100 minutes post-incubation was of the same magnitude (20 min: 1.24 +/- 0.

Adduct of 2-[18F]FDG and 2-nitroimidazole as a putative radiotracer for the detection of hypoxia with PET: synthesis, in vitro- and in vivo-characterization.

A new sugar-coupled 2-nitroimidazole derivative ([18F](see structure in text)) has been prepared in good radiochemical yields starting from peracetylated 2-[18F]FDG obtained from an automated 2-[18F]FDG production module. The corresponding glucose derivative (see structure in text) has proved to be able to inhibit 2-[18F]FDG uptake into tumor cells in a concentration dependent way. However, [18F](see structure in text) failed to show a retention in hypoxic tumor tissue thus excluding itself from further investigations.