| 1. |
- Schlein, Eva, et al.
(författare)
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Aβ targeting ImmunoPET : Brain pharmacokinetics comparison between a brain penetrating and a regular antibody
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Bispecific antibodies utilizing the transferrin receptor (TfR) for transport into the brain are being developed for both therapeutic and diagnostic applications. Compared with regular monospecific antibodies, the brain uptake of TfR-binding bispecific antibodies is rapid and efficient. However, due to differences in pharmacokinetic properties, it has been challenging to directly compare their brain uptake in vivo. In this study, we have studied the amyloid-β (Aβ) antibody Bapineuzumab (Bapi) and its bispecific variant Bapi-Fab8D3, which contains a fragment of the TfR-binding antibody 8D3. Both antibodies were recombinantly engineered to harbour a mutation that reduces binding to the neonatal Fc receptor (FcRn) and thus contributes to an increased clearance rate from blood.The antibodies were labelled with fluorine-18 (18F) and administered to wildtype (WT) mice, which were PET scanned for 2 h in an alternating manner to cover a period of 9 h, followed by ex vivo analyses. Next, the bispecific antibody [18F]Bapi-Fab8D3 was used for PET imaging if Aβ pathology in the AD mouse model AppNL-G-F compared with WT mice at 12 h after antibody administration. [18F]Bapi and [18F]Bapi-Fab8D3 had identical blood elimination curves in WT mice and PET data quantification demonstrated that [18F]Bapi brain concentration declined from the start and throughout the 9 h time period, while [18F]Bapi-Fab8D3 displayed a higher brain concentration, indicative of its active transport into the brain.[18F]Bapi-Fab PET imaging discriminated AppNL-G-F from WT mice already at 12 h after administration, suggesting that this novel antibody-based ligand could be used for same-day PET imaging.
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| 2. |
- 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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| 3. |
- Shalgunov, Vladimir, et al.
(författare)
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Pretargeted imaging beyond the blood-brain barrier
- 2023
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Ingår i: RSC Medicinal Chemistry. - : Royal Society of Chemistry. - 2632-8682. ; 14:3, s. 444-453
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Tidskriftsartikel (refereegranskat)abstract
- Pretargeting is a powerful nuclear imaging strategy to achieve enhanced imaging contrast for nanomedicines and reduce the radiation burden to healthy tissue. Pretargeting is based on bioorthogonal chemistry. The most attractive reaction for this purpose is currently the tetrazine ligation, which occurs between trans-cyclooctene (TCO) tags and tetrazines (Tzs). Pretargeted imaging beyond the blood-brain barrier (BBB) is challenging and has not been reported thus far. In this study, we developed Tz imaging agents that are capable of ligating in vivo to targets beyond the BBB. We chose to develop F-18-labeled Tzs as they can be applied to positron emission tomography (PET) - the most powerful molecular imaging technology. Fluorine-18 is an ideal radionuclide for PET due to its almost ideal decay properties. As a non-metal radionuclide, fluorine-18 also allows for development of Tzs with physicochemical properties enabling passive brain diffusion. To develop these imaging agents, we applied a rational drug design approach. This approach was based on estimated and experimentally determined parameters such as the BBB score, pretargeted autoradiography contrast, in vivo brain influx and washout as well as on peripheral metabolism profiles. From 18 initially developed structures, five Tzs were selected to be tested for their in vivo click performance. Whereas all selected structures clicked in vivo to TCO-polymer deposited into the brain, [F-18]18 displayed the most favorable characteristics with respect to brain pretargeting. [F-18]18 is our lead compound for future pretargeted neuroimaging studies based on BBB-penetrant monoclonal antibodies. Pretargeting beyond the BBB will allow us to image targets in the brain that are currently not imageable, such as soluble oligomers of neurodegeneration biomarker proteins. Imaging of such currently non-imageable targets will allow early diagnosis and personalized treatment monitoring. This in turn will accelerate drug development and greatly benefit patient care.
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| 4. |
- 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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