Background and Aims: Smooth muscle cells (SMCs) show immense plasticity. In atherosclerosis, they can switch from contractile to modulated plaque cells with different phenotypes. We aimed to develop a transgenic mouse model for noninvasive monitoring of smooth muscle cell populations and their progeny during atherogenesis. Methods: We used a novel Cre/lox-based approach combined with the Apolipoprotein E deficient mouse model of atherosclerosis. The animals express a modified Herpes simplex virus thymidine kinase (sr39tk) reporter gene specifically in SMCs and SMC-derived cells. After [18F]FHBG (fluoro-3-[hydroxymethyl]butyl)guanine) tracer injection, these cells can be detected by positron emission tomography (PET) which is combined with magnetic resonance imaging (MRI) for anatomical co-registration. Results: In atherosclerotic reporter mice SMCs and SMC-derived cells were detected noninvasively in vivoby PET/MRI. Distinct hot spots of tracer uptake in the atherosclerotic aortic arch were identified and quantified. To confirm that tracer accumulation correlated with SMC-derived plaque cells, we dissected the aorta and analysed it in detail. Autoradiography, biodistribution analysis and analysis of sections from the aortic arch indicated that the hot spots detected by PET indeed represent a combination of SMCs and large patches of SMC-derived cells in the atherosclerotic plaque. Conclusions: Our data show that PET/MRI in SMC-specific sr39tk reporter mice enables noninvasive, longitudinal and quantitative detection of clonally grown SMC-derived cell clusters in atherosclerotic plaques in vivoduring atherogenesis.

Background. 1--D-(5-Deoxy-5-[ 18 F]fluoroarabinofuranosyl)-2-nitroimidazole ([ 18 F]FAZA) is a PET radiotracer currently used to image regional hypoxia in a wide range of solid tumors in cancer patients. [ 18 F]FAZA is radiofluorinated in moderate recovered radiochemical yield (rRCY) via nucleophilic substitution of the 1-α-D-(2,3-di-O-acetyl-5-tosyl)-AZA precursor. Hypothesis. It is postulated that the β-conformer of FAZA, 1--D-(5-fluoro-5-deoxyarabinofuranosyl)2-nitroimidazole (β-FAZA), by dint of the relative stability of the C1’ β-anomeric bond to basecatalysed hydrolysis and / or the fidelity of nucleophilic substitution at C5’, may offer improved rRCY. Preliminary PET images of the biodistribution of -[ 18 F]FAZA in a hypoxic tumor-bearing animal

An improved, automated synthesis of [18F]FDOPA including four synthetic steps (fluorination, reductive iodination, alkylation and hydrolysis) is reported with each step optimized individually. In a home-made automatic synthesizer, 9064±3076MBq of [18F]FDOPA were produced within 120min from EOB (n=5). Radiochemical purity and enantiomeric excess were both ⩾95%. Specific activity was ca. 50GBq/μmol at EOS. This automatically operable synthesis is well suited for the multi-patient-dose routine production of n.c.a. [18F]FDOPA.

1-[2-(2-Fluoroethoxy)ethyl]-2-1H-nitroimidazole (3a), 1-{2-[2-(2-fluoroethoxy)ethoxy]ethyl}-2-1H-nitroimidazole (3b) and 1-(2-{2-[2-(2-fluoroethoxy)ethoxy]ethoxy}ethyl)-2-1H-nitroimidazole (3c) were synthesized in a two step sequence.Coupling the ditosylate of di-, tri- or tetraethylene glycol with 2-nitroimidazole followed by fluoride substitution afforded the reference compounds in high yield and18F labeling gave the corresponding markers in 70-82% radiochemical yield.

Summary3′[18F]Fluoro-3′-deoxy-thymidine ([18F]FLT) (III) has been discussed to be a promising tracer for assessing tumor proliferation. In order to perform clinical studies for evaluating [18F]FLT a simplified labeling procedure was developed using 2,3′-anhydrothymidine with benzoyl as a protecting group in the 5′-position (I). In DMSO the labeling yield was 46% at 160 °C in 10 min. Hydrolysis was efficiently performed with 0.25% NaOH at room temperature within 10 min. The labeling procedure was transferred to a remote controlled synthesis module allowing the production of [18F]FLT in high activities. The overall radiochemical yield was 18.1 ± 5.4% (n= 55) with absolute yields of 9.2 ± 2.6 GBq of [18F]FLT at EOS ready for injection (60 min after EOB; irradiation parameters: 35 μA, 60 min) and specific activities of 100–220 GBq/μmol. A convenient cartridge method for metabolite analysis was developed and validatedversusHPLC showing that after 90 min 69.0 ± 7.0% of the radioactivity in plasma (less than 20% of initial radioactivity) was unchanged [18F]FLT (26 patients with various tumors).

18F-labeling of the nitroimidazole nucleoside analogue 1-(5-fluoro-5-deoxy-α-D-arabinofuranosyl)-2-nitroimidazole (FAZA) was developed to use this tracer in PET for detection of hypoxia. Parameters for labeling and hydrolysis were optimized with regard to amount of precursor, temperature and time. Labeling yields reached a maximum of 62±4% at 100 °C within 5 min using 5 mg of precursor. Hydrolysis was best performed with 1 mL of 0.1 N NaOH at 20 °C for 2 min. Transfer of these conditions to an automated synthesizer resulted in an overall radiochemical yield of 20.7±3.5%. Absolute yields at EOS were 9.8±2.3 GBq of [18F]FAZA ready for injection (n=21; 50 min after EOB; irradiation parameters: 35 μA, 60 min). Thus, a convenient approach suitable for large-scale production of [18F]FAZA was developed by an automated process.

The efficiency of serotonergic signal transduction is controlled by the density of serotonegic synapses and by the activity of the serotonin transporter (SERT), which selectively clears the synaptic cleft of the neurotransmitter. SERT is located in axons, where it is concentrated in varicosities and terminal boutons and thus is an exquisite marker for serotonergic synapses. This finding has been taken advantage of for neuroimaging serotonergic synaptic contact sites. Previous positron emission tomography (PET) and single photon emission computed tomography (SPECT) studies were often carried out using radioligands that bind with high affinity to SERTs in the brainstem but also exhibit high affinity for dopamine and norepinephrine transporters and therefore did not allow quantification of serotonergic innervations in brain regions also containing dopaminergic or noradrenergic terminals. In order to visualize SERT availability more selectively, in recent years new tracers have been developed, one of which is [11C]DASB (N,N-dimethyl-2-2-amino-4-cyanophenylthiobenzylamine). Here, we have performed a detailed pharmacological characterization of unlabelled as well as radioactive DASB on recombinant human monoamine transporter proteins. Our results show that DASB selectively binds to SERT with high affinity (KD = 3.5 nm) to a site distinct from the serotonin (5-HT) recognition/translocation site. 5-HT inhibits DASB binding to SERT with more than one order of magnitude lower affinity than that of DASB binding (IC50 = 82.4 nm). These findings suggest DASB to be a highly selective PET tracer to visualize the density of serotonergic synapses in human brain.

For labeling reactions [18F]fluoride has to be separated from [18O]water and transferred into an organic solvent suitable for nucleophilic substitutions. An electrolytical method is described for depositing [18F]fluoride on a vitreous carbon electrode and releasing it directly into CH3CN or DMSO. In the presence of Et3N×3HF, [18F]fluoride is almost quantitatively released into acetonitrile. When using n.c.a conditions, i.e., Et3N.HCl, desorption of the 18F activity is almost 70% and 60% in acetonitrile and DMSO, respectively, already within 5 minutes.