Hide and seek: a comparative autoradiographic in vitro investigation of the adenosine A3 receptor.

PURPOSE: Since the adenosine A3 receptor (A3R) is considered to be of high clinical importance in the diagnosis and treatment of ischaemic conditions (heart and brain), glaucoma, asthma, arthritis, cancer and inflammation, a suitable and selective A3R PET tracer such as [(18)F]FE@SUPPY would be of high clinical value for clinicians as well as patients. A3R was discovered in the late 1990s, but there is still little known regarding its distribution in the CNS and periphery. Hence, in autoradiographic experiments the distribution of A3R in human brain and rat tissues was investigated and the specific binding of the A3R antagonist FE@SUPPY and MRS1523 compared. Immunohistochemical staining (IHC) experiments were also performed to validate the autoradiographic findings. METHODS: For autoradiographic competition experiments human post-mortem brain and rat tissues were incubated with [(125)I]AB-MECA and highly selective compounds to block the other adenosine receptor subtypes. Additionally, IHC was performed with an A3 antibody. RESULTS: Specific A3R binding of MRS1523 and FE@SUPPY was found in all rat peripheral tissues examined with the highest amounts in the spleen (44.0% and 46.4%), lung (44.5% and 45.0%), heart (39.9% and 42.9%) and testes (27.4% and 29.5%, respectively). Low amounts of A3R were found in rat brain tissues (5.9% and 5.6%, respectively) and human brain tissues (thalamus 8.0% and 9.1%, putamen 7.8% and 8.2%, cerebellum 6.0% and 7.8%, hippocampus 5.7% and 5.6%, caudate nucleus 4.9% and 6.4%, cortex 4.9% and 6.3%, respectively). The outcome of the A3 antibody staining experiments complemented the results of the autoradiographic experiments. CONCLUSION: The presence of A3R protein was verified in central and peripheral tissues by autoradiography and IHC. The specificity and selectivity of FE@SUPPY was confirmed by direct comparison with MRS1523, providing further evidence that [(18)F]FE@SUPPY may be a suitable A3 PET tracer for use in humans.

Quantification of the radio-metabolites of the serotonin-1A receptor radioligand [carbonyl-11C]WAY-100635 in human plasma: an HPLC-assay which enables measurement of two patients in parallel.

[Carbonyl-(11)C]WAY-100635 is a potent and effective antagonist for the 5-HT(1A) receptor subtype. We aimed to assess the status of [carbonyl-(11)C]WAY-100635 and its main radio-metabolites, [carbonyl-(11)C]desmethyl-WAY-100635 and [carbonyl-(11)C]cyclohexanecarboxylic acid, on the basis of an improved radio-HPLC method. Common methods were characterized by preparative HPLC columns with long runtimes and/or high flow rates. Considering the short half-life of C-11, we developed a more rapid and solvent saving HPLC assay, allowing a fast, efficient and reliable quantification of these major metabolites.

Optimization of the radiosynthesis of the Alzheimer tracer 2-(4-N-[11C]methylaminophenyl)-6-hydroxybenzothiazole ([11C]PIB).

[(11)C]PIB is still the standard PET compound for Alzheimer imaging targeting beta-amyloid plaques. We aimed to establish a fully-automated procedure for the synthesis and purification of [(11)C]PIB with a high degree of reliability and improved specific activity as well as a suitable and fast quality control assay. The optimum reaction conditions were 75°C, 4 mg/mL precursor yielding at 48.0±2.7% (EOS, based on [(11)C]CH(3)OTf, corrected for decay), 183±14 GBq/µmol specific activity and >99% radiochemical purity. Time consumption was kept to a minimum (40 min from EOB) and overall yields were enough to serve 2 consecutive patients with a single preparation.

Simple and rapid preparation of [11C]DASB with high quality and reliability for routine applications.

[(11)C]DASB combines all major prerequisites for a successful SERT-ligand, providing excellent biological properties and in-vivo behaviour. Thus, we aimed to establish a fully automated procedure for the synthesis and purification of [(11)C]DASB with a high degree of reliability reducing the overall synthesis time while conserving high yields and purity. The optimized [(11)C]DASB synthesis was applied in more than 60 applications with a very low failure rate (3.2%). We obtained yields up to 8.9 GBq (average 5.3+/-1.6 GBq). Radiochemical yields based on [(11)C]CH(3)I, (corrected for decay) were 66.3+/-6.9% with a specific radioactivity (A(s)) of 86.8+/-24.3 GBq/micromol (both at the end of synthesis, EOS). Time consumption was kept to a minimum, resulting in 43 min from end of bombardment to release of the product after quality control. From our data, it is evident that the presented method can be implemented for routine preparations of [(11)C]DASB with high reliability.