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| 2. |
- Bergman, Sara, et al.
(författare)
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Synthesis and Labelling of a Piperazine-Based Library of 11C-Labeled Ligands for Imaging of the Vesicular Acetylcholine Transporter
- 2014
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Ingår i: Journal of labelled compounds & radiopharmaceuticals. - : Wiley. - 0362-4803 .- 1099-1344. ; 57:8, s. 525-532
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Tidskriftsartikel (refereegranskat)abstract
- The cholinergic system is involved in neurodegenerative diseases, and visualization of cholinergic innervations with positron emission tomography (PET) would be a useful tool in understanding these diseases. A ligand for the vesicular acetylcholine transporter (VAChT), acknowledged as a marker for cholinergic neurons, could serve as such a PET tracer. The aim was to find a VAChT PET tracer using a library concept to create a small but diverse library of labeled compounds. From the same precursor and commercially available aryl iodides 6a-f, six potential VAChT PET tracers, [C-11]-(+/-)5a-f, were C-11-labeled by a palladium (0)-mediated aminocarbonylation, utilizing a standard protocol. The labeled compounds [C-11]-(+/-)5a-f were obtained in radiochemical purities >95% with decay-corrected radiochemical yields and specific radioactivities between 4-25% and 124-597 GBq/mu mol, respectively. Autoradiography studies were then conducted to assess the compounds binding selectivity for VAChT. Labeled compounds [C-11]-(+/-)5d and [C-11]-(+/-)5e showed specific binding but not enough to permit further preclinical studies. To conclude, a general method for a facile synthesis and labeling of a small piperazine-based library of potential PET tracers for imaging of VAChT was shown, and in upcoming work, another scaffold will be explored using this approach.
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| 3. |
- Kehler, Jan, et al.
(författare)
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Discovery and Development of C-11-Lu AE92686 as a Radioligand for PET Imaging of Phosphodiesterase10A in the Brain
- 2014
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Ingår i: Journal of Nuclear Medicine. - : Society of Nuclear Medicine. - 0161-5505 .- 1535-5667 .- 2159-662X. ; 55:9, s. 1513-1518
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Tidskriftsartikel (refereegranskat)abstract
- Phosphodiesterase 10A (PDE10A) plays a key role in the regulation of brain striatal signaling, and several pharmaceutical companies currently investigate PDE10A inhibitors in clinical trials for various central nervous system diseases. A PDE10A PET ligand may provide evidence that a clinical drug candidate reaches and binds to the target. Here we describe the successful discovery and initial validation of the novel radiolabeled PDE10A ligand 5,8-dimethyl-2-[2-((1-C-11-methyl)-4-phenyl-1H-imidazol-2-yl)-ethyl]-[1,2,4]triazolo[1,5-a]pyridine (C-11-Lu AE92686) and its tritiated analog H-3-Lu AE92686. Methods: Initial in vitro experiments suggested Lu AE92686 as a promising radioligand, and the corresponding tritiated and C-11-labeled compounds were synthesized. 3H-Lu AE92686 was evaluated as a ligand for in vivo occupancy studies in mice and rats, and C-11-Lu AE92686 was evaluated as a PET tracer candidate in cynomolgus monkeys and in humans. Results: C-11-Lu AE92686 displayed high specificity and selectivity for PDE10A-expressing regions in the brain of cynomolgus monkeys and humans. Similar results were found in rodents using 3H-Lu AE92686. The binding of C-11-Lu AE92686 and 3H-Lu AE92686 to striatum was completely and dose-dependently blocked by the structurally different PDE10A inhibitor 2-[4-(1-methyl-4-pyridin-4-yl-1H-pyrazol-3-yl)-phenoxymethyl]-quinoline (MP-10) in rodents and in monkeys. In all species, specific binding of the radioligand was seen in the striatum but not in the cerebellum, supporting the use of the cerebellum as a reference region. The binding potentials (BPND) of C-11-Lu AE92686 in the striatum of both cynomolgus monkeys and humans were evaluated by the simplified reference tissue model with the cerebellum as the reference tissue, and BPND was found to be high and reproducible-that is, BP(ND)s were 6.5 +/- 0.3 (n = 3) and 7.5 +/- 1.0 (n = 12) in monkeys and humans, respectively. Conclusion: Rodent, monkey, and human tests of labeled Lu AE92686 suggest that C-11-Lu AE92686 has great potential as a human PET tracer for the PDE10A enzyme.
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| 5. |
- Rosik, Daniel, et al.
(författare)
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Incorporation of a Triglutamyl Spacer Improves the Biodistribution of Synthetic Affibody Molecules Radiofluorinated at the N-Terminus via Oxime Formation with F-18-4-Fluorobenzaldehyde
- 2014
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Ingår i: Bioconjugate chemistry. - : American Chemical Society (ACS). - 1043-1802 .- 1520-4812. ; 25:1, s. 82-92
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Tidskriftsartikel (refereegranskat)abstract
- Affibody molecules are a class of affinity agents for molecular imaging based on a non-immunoglobulin protein scaffold. Previous studies have demonstrated high contrast for in vivo imaging of cancer-associated molecular abnormalities using Affibody molecules. Using the radionuclide F-18 for labeling and PET as the imaging modality, the sensitivity of molecular imaging using Affibody molecules can be further increased. The use of oxime formation between an aminooxy-functionalized peptide and F-18-fluorobenzaldehyde (F-18-FBA) is a promising way of radiolabeling of targeting peptides. However, previous studies demonstrated that application of this method to Affibody molecules is associated with high liver uptake. We hypothesized that incorporation of a triglutamyl spacer between the aminooxy moiety and the N-terminus of a synthetic Affibody molecule would decrease the hepatic uptake of the F-18-N-(4-fluorobenzylidine)oxime) (F-18-FBO)-labeled tracer. To verify this, we have produced two variants of the HER2-targeting Z(HER2:342) Affibody molecule by peptide synthesis: OA-PEP4313, where aminooxyacetic acid was conjugated directly to the N-terminal alanine, and OA-E-3-PEP4313, where a triglutamyl spacer was introduced between the aminooxy moiety and the N-terminus. We have found that the use of the spacer is associated with a minor decrease of affinity, from K-D = 49 pM to K-D = 180 pM. Radiolabeled F-18-FBO-E-3-PEP4313 demonstrated specific binding to HER2-expressing ovarian carcinoma SKOV-3 cells and slow internalization. Biodistribution studies in mice demonstrated that the use of a triglutamyl linker decreased uptake of radioactivity in liver 2.7-fold at 2 h after injection. Interestingly, radioactivity uptake in kidneys was also reduced (2.4-fold). Experiments in BALB/C nu/nu mice bearing SKOV-3 xenografts demonstrated HER2-specific uptake of F-18-FBO-E-3-PEP4313 in tumors. At 2 h pi, the tumor uptake (20 +/- 2% ID/g) exceeded uptake in liver 5-fold and uptake in kidneys 3.6-fold. The tumor-to-blood ratio was 21 +/- 3. The microPET/CT imaging experiment confirmed the biodistribution data. In conclusion, the use of a triglutamyl spacer is a convenient way to improve the biodistribution profile of Affibody molecules labeled at the N-terminus using F-18-FBA. It provides a tracer capable of producing high-contrast images of HER2-expressing tumors.
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