| 1. |
- Schlein, Eva, et al.
(författare)
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Synthesis and evaluation of fluorine-18 labelled tetrazines as pre-targeting imaging agents for PET
- 2024
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Ingår i: EJNMMI Radiopharmacy and Chemistry. - : Springer Nature. - 2365-421X. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- The brain is a challenging target for antibody-based positron emission tomography (immunoPET) imaging due to the restricted access of antibody-based ligands through the blood-brain barrier (BBB). To overcome this challenge we have previously developed bispecific antibody ligands that pass through the BBB via receptor-mediated transcytosis. These ligands, when radiolabelled, can be used for brain imaging with high affinity and specificity, but their long residence time in the blood and brain can be challenging for their use as PET radioligands. This could be solved by using a two-step approach which involves the administration of a tagged antibody that accumulates at the target site in the brain and then clears from the blood, followed by administration of a radiolabelled molecule, with fast kinetics. This radiolabelled molecule can couple to the tagged antibody and thereby make the antibody localisation visible by PET imaging. The in vivo linkage can be achieved using the inverse electron demand Diels-Alder reaction (IEDDA), with trans-cyclooctene (TCO) and tetrazine groups participating as reactants.In this study, two 18F-labelled tetrazines were synthesized and evaluated for their potential as agents for pre-targeted imaging, i.e. for their ability to rapidly enter the brain and then, if non-bound, be sufficiently cleared with low background retention. The two compounds, a methyl tetrazine [18F]MeTz and an H-tetrazine [18F]HTz were radiolabelled using a two-step procedure via [18F]F-Py-TFP synthesized on solid support followed by amidation with amine-bearing tetrazines, resulting in radiochemical yields of 24% and 22%, respectively, and a radiochemical purity of > 96%. In vivo PET imaging was performed to assess their suitability for in vivo pre-targeting. Time-activity curves from PET-scans revealed that the [18F]MeTz had the most favourable profile for an imaging agent for pre-targeting, due to its fast and homogenous brain distribution and rapid clearance from the brain.
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| 2. |
- Shalgunov, Vladimir, et al.
(författare)
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Blocking of efflux transporters in rats improves translational validation of brain radioligands
- 2020
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Ingår i: EJNMMI Research. - : SPRINGER. - 2191-219X. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Background Positron emission tomography (PET) is a molecular imaging technique that can be used to investigate the in vivo pharmacology of drugs. Initial preclinical evaluation of PET tracers is often conducted in rodents due to the accessibility of disease models as well as economic considerations. Compared to larger species, rodents display a higher expression and/or activity of efflux transporters such as the P-glycoprotein (P-gp). Low brain uptake could, therefore, be species-specific and uptake in rodents not be predictive for that in humans. We hypothesized that a better prediction from rodent data could be achieved when a tracer is evaluated under P-gp inhibition. Consequently, we compared the performance of eight neuroreceptor tracers in rats with and without P-gp inhibition including a specific binding blockade. This data set was then used to predict the binding of these eight tracers in pigs. Methods PET tracers targeting serotonin 5-HT(2A)receptors ([F-18]MH.MZ, [F-18]Altanserin, [C-11]Cimbi-36, [C-11]Pimavanserin), serotonin 5-HT(7)receptors ([C-11]Cimbi-701, [C-11]Cimbi-717 and [C-11]BA-10) and dopamine D(2/3)receptors ([F-18]Fallypride) were used in the study. The brain uptake and target-specific binding of these PET radiotracers were evaluated in rats with and without inhibition of P-gp. Rat data were subsequently compared to the results obtained in pigs. Results Without P-gp inhibition, the amount of target-specific binding in the rat brain was sufficient to justify further translation for three out of eight evaluated tracers. With P-gp inhibition, results for five out of eight tracers justified further translation. The performance in pigs could correctly be predicted for six out of eight tracers when rat data obtained under P-gp inhibition were used, compared to four out of eight tracers without P-gp inhibition. Conclusions P-gp strongly affects the uptake of PET tracers in rodents, but false prediction outcomes can be reduced by evaluating a tracer under P-gp inhibition.
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| 3. |
- van den Broek, Sara Lopes, et al.
(författare)
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Pretargeted Imaging beyond the Blood-Brain Barrier-Utopia or Feasible?
- 2022
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Ingår i: Pharmaceuticals. - : MDPI. - 1424-8247. ; 15:10
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Tidskriftsartikel (refereegranskat)abstract
- Pretargeting is a promising nuclear imaging technique that allows for the usage of antibodies (Abs) with enhanced imaging contrast and reduced patient radiation burden. It is based on bioorthogonal chemistry with the tetrazine ligation-a reaction between trans-cyclooctenes (TCOs) and tetrazines (Tzs)-currently being the most popular reaction due to its high selectivity and reactivity. As Abs can be designed to bind specifically to currently 'undruggable' targets such as protein isoforms or oligomers, which play a crucial role in neurodegenerative diseases, pretargeted imaging beyond the BBB is highly sought after, but has not been achieved yet. A challenge in this respect is that large molecules such as Abs show poor brain uptake. Uptake can be increased by receptor mediated transcytosis; however, it is largely unknown if the achieved brain concentrations are sufficient for pretargeted imaging. In this study, we investigated whether the required concentrations are feasible to reach. As a model Ab, we used the bispecific anti-amyloid beta (A beta) anti-transferrin receptor (TfR) Ab 3D6scFv8D3 and conjugated it to a different amount of TCOs per Ab and tested different concentrations in vitro. With this model in hand, we estimated the minimum required TCO concentration to achieve a suitable contrast between the high and low binding regions. The estimation was carried out using pretargeted autoradiography on brain sections of an Alzheimer's disease mouse model. Biodistribution studies in wild-type (WT) mice were used to correlate how different TCO/Ab ratios alter the brain uptake. Pretargeted autoradiography showed that increasing the number of TCOs as well as increasing the TCO-Ab concentration increased the imaging contrast. A minimum brain concentration of TCOs for pretargeting purposes was determined to be 10.7 pmol/g in vitro. Biodistribution studies in WT mice showed a brain uptake of 1.1% ID/g using TCO-3D6scFv8D3 with 6.8 TCO/Ab. According to our estimations using the optimal parameters, pretargeted imaging beyond the BBB is not a utopia. Necessary brain TCO concentrations can be reached and are in the same order of magnitude as required to achieve sufficient contrast. This work gives a first estimate that pretargeted imaging is indeed possible with antibodies. This could allow the imaging of currently 'undruggable' targets and therefore be crucial to monitor (e.g., therapies for intractable neurodegenerative diseases).
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| 4. |
- Bratteby, Klas, et al.
(författare)
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In Vivo Veritas : 18F-Radiolabeled Glycomimetics Allow Insights into the Pharmacological Fate of Galectin-3 Inhibitors
- 2020
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Ingår i: Journal of Medicinal Chemistry. - : American Chemical Society (ACS). - 0022-2623 .- 1520-4804. ; 63:2, s. 747-755
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Tidskriftsartikel (refereegranskat)abstract
- Glycomimetic drugs have attracted increasing interest as unique targeting vectors or surrogates for endogenous biomolecules. However, it is generally difficult to determine the in vivo pharmacokinetic profile of these compounds. In this work, two galectin-3 inhibitors were radiolabeled with fluorine-18 and used as surrogate PET tracers of TD139 and GB1107. Both compounds are promising drugs for clinical applications. In vivo evaluation revealed that both surrogates strongly differed with respect to their biodistribution profile. The disaccharide (TD139 surrogate) was rapidly eliminated from blood while the monosaccharide (GB1107 surrogate) showed no sign of excretion. The data obtained allowed us to infer the different in vivo fate of TD139 and GB1107 and rationalize how different administration routes could boost efficacy. Whereas the fast excretion profile of the TD139 surrogate indicated that systemic application of disaccharides is unfavorable, the extended biological half-life of the GB1107 surrogate indicated that systemic administration is possible for monosaccharides.
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