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Preclinical PET imaging of Alzheimer's disease progression
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences. (Geriatrics)
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Amyloid PET imaging with [11C]PIB enabled detection of Aβ for the first time in vivo. However, [11C]PIB is a small molecule that binds only the insoluble Aβ plaque. Rather, the soluble Aβ aggregates are considered the cause of Alzheimer’s disease (AD). As such, a more sensitive and specific PET tracer is needed for tracking longitudinal AD pathology.

Soluble Aβ aggregates likely interact with the metabotropic glutamate receptor 5 (mGluR5) to cause neurotoxic effects. However, with [11C]ABP688 PET we were unable to detect aberrant mGluR5 binding in AD mouse models, although we find elevated mGluR5 protein levels with immunoblotting.

Antibodies are highly specific large molecules that can bind specifically to soluble Aβ aggregates, thus they can be a good marker for AD pathology. Unfortunately, due to their large size they cannot cross the blood-brain barrier (BBB). However, it is possible to shuttle antibodies into the brain by taking advantage of endogenous transporter systems on the BBB. By creating bispecific antibodies binding both to soluble Aβ aggregates and to the transferrin receptor (BBB target), we successfully transported the antibody into the brain and could visually detect soluble Aβ aggregates with PET.

Recombinant expression further improved and optimized antibody design, creating smaller bispecific antibody-based constructs that had better pharmacokinetic properties allowing for earlier PET scanning (1 day instead of 3), and more sensitive signal.

Lastly, using TCO-tetrazine click chemistry, we indirectly labeled our antibodies with fluorine-18, and could successfully perform PET already 11 h post-injection with a fluorine-18 labeled antibody.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. , p. 59
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1395
Keywords [en]
Alzheimer's disease, transgenic mice, PET, antibody-based tracer, mGluR5, ABP688, di-scFv, amyloid-β
National Category
Neurosciences Pharmaceutical Sciences Radiology, Nuclear Medicine and Medical Imaging
Identifiers
URN: urn:nbn:se:uu:diva-333220ISBN: 978-91-513-0151-8 (print)OAI: oai:DiVA.org:uu-333220DiVA, id: diva2:1156029
Public defence
2018-01-19, Rudbecksalen, Dag Hammarskjölds väg 20, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2017-12-21 Created: 2017-11-10 Last updated: 2018-03-08
List of papers
1. Brain mGluR5 in mice with amyloid beta pathology studied with in vivo [(11)C]ABP688 PET imaging and ex vivo immunoblotting
Open this publication in new window or tab >>Brain mGluR5 in mice with amyloid beta pathology studied with in vivo [(11)C]ABP688 PET imaging and ex vivo immunoblotting
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2017 (English)In: Neuropharmacology, ISSN 0028-3908, E-ISSN 1873-7064, Vol. 113, no Pt A, p. 293-300, article id S0028-3908(16)30459-2Article in journal (Refereed) Published
Abstract [en]

Alzheimer's disease (AD) is characterized by aggregation of amyloid beta (Aβ) into insoluble plaques. Intermediates, Aβ oligomers (Aβo), appear to be the mechanistic cause of disease. The de facto PET AD ligand, [(11)C]PIB, binds and visualizes Aβ plaque load, which does not correlate well with disease severity. Therefore, finding a dynamic target that changes with pathology progression in AD is of great interest. Aβo alter synaptic plasticity, inhibit long-term potentiation, and facilitate long-term depression; key mechanisms involved in memory and learning. In order to convey these neurotoxic effects, Aβo requires interaction with the metabotropic glutamate 5 receptor (mGluR5). The aim was to investigate in vivo mGluR5 changes in an Aβ pathology model using PET. Wild type C57/BL6 (wt) and AβPP transgenic mice (tg-ArcSwe), 4, 8, and 16 months old, were PET scanned with [(11)C]ABP688, which is highly specific to mGluR5, to investigate changes in mGluR5. Mouse brains were extracted postscan and mGluR5 and Aβ protofibril levels were assessed with immunoblotting and ELISA respectively. Receptor-dense brain regions (hippocampus, thalamus, and striatum) displayed higher [(11)C]ABP688 concentrations corresponding to mGluR5 expression pattern. Mice had similar uptake levels of [(11)C]ABP688 regardless of genotype or age. Immunoblotting revealed general decline in mGluR5 expression and elevated levels of mGluR5 in 16 months old tg-ArcSwe compared with wt mice. [(11)C]ABP688 could visualize mGluR5 in the mouse brain. In conclusion, mGluR5 levels were found to decrease with age and tended to be higher in tg-ArcSwe compared with wt mice, however these changes could not be quantified with PET.

Keywords
Alzheimer's disease, PET, [(11)C]ABP688, mGluR5
National Category
Geriatrics Radiology, Nuclear Medicine and Medical Imaging Neurology Pharmacology and Toxicology
Identifiers
urn:nbn:se:uu:diva-317721 (URN)10.1016/j.neuropharm.2016.10.009 (DOI)000390502200028 ()27743932 (PubMedID)
Available from: 2017-03-17 Created: 2017-03-17 Last updated: 2018-01-13Bibliographically approved
2. Antibody-based PET imaging of amyloid beta in mouse models of Alzheimer's disease
Open this publication in new window or tab >>Antibody-based PET imaging of amyloid beta in mouse models of Alzheimer's disease
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2016 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 7, article id 10759Article in journal (Refereed) Published
Abstract [en]

Owing to their specificity and high-affinity binding, monoclonal antibodies have potential as positron emission tomography (PET) radioligands and are currently used to image various targets in peripheral organs. However, in the central nervous system, antibody uptake is limited by the blood-brain barrier (BBB). Here we present a PET ligand to be used for diagnosis and evaluation of treatment effects in Alzheimer's disease. The amyloid beta (A beta) antibody mAb158 is radiolabelled and conjugated to a transferrin receptor antibody to enable receptor-mediated transcytosis across the BBB. PET imaging of two different mouse models with Ab pathology clearly visualize A beta in the brain. The PET signal increases with age and correlates closely with brain A beta levels. Thus, we demonstrate that antibody-based PET ligands can be successfully used for brain imaging.

National Category
Geriatrics Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:uu:diva-282384 (URN)10.1038/ncomms10759 (DOI)000371037200021 ()26892305 (PubMedID)
Funder
Swedish Research Council, 2012-1593Swedish Research Council, 2012-2172The Swedish Brain Foundation
Available from: 2016-04-05 Created: 2016-04-05 Last updated: 2017-11-30Bibliographically approved
3. Efficient and inexpensive transient expression of multispecific multivalent antibodies in expi293 cells
Open this publication in new window or tab >>Efficient and inexpensive transient expression of multispecific multivalent antibodies in expi293 cells
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2017 (English)In: Biological Procedures Online, ISSN 1480-9222, E-ISSN 1480-9222Article in journal (Refereed) Published
National Category
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
Identifiers
urn:nbn:se:uu:diva-332463 (URN)
Available from: 2017-10-27 Created: 2017-10-27 Last updated: 2017-11-29
4. High detection sensitivity with antibody-based PET radioligand for amyloid beta in brain
Open this publication in new window or tab >>High detection sensitivity with antibody-based PET radioligand for amyloid beta in brain
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2019 (English)In: NeuroImage, ISSN 1053-8119, E-ISSN 1095-9572, Vol. 184, p. 881-888Article in journal (Refereed) Published
Abstract [en]

PET imaging of amyloid-beta (A beta) deposits in brain has become an important aid in Alzheimer's disease diagnosis, and an inclusion criterion for patient enrolment into clinical trials of new anti-A beta treatments. Available PET radioligands visualizing A beta bind to insoluble fibrils, i.e. A beta plaques. Levels of prefibrillar A beta forms, e.g. soluble oligomers and protofibrils, correlate better than plaques with disease severity and these soluble species are the neurotoxic form of A beta leading to neurodegeneration. The goal was to create an antibody-based radioligand, recognizing not only fibrillary A beta , but also smaller and still soluble aggregates. We designed and expressed a small recombinant bispecific antibody construct, di-scFv 3D6-8D3, targeting the A beta N-terminus and the transferrin receptor (TfR). Natively expressed at the blood-brain barrier (BBB), TfR could thus be used as a brain-blood shuttle. Di-scFv 3D6-8D3 bound to A beta 1-40 with high affinity and to TfR with moderate affinity. Di-scFv [I-124] 3D6-8D3 was injected in two transgenic mouse models overexpressing human A beta and wild-type control mice and PET scanned at 14, 24 or 72 h after injection. Di-scFv [I-124] 3D6-8D3 was retained in brain of transgenic animals while it was cleared from wild-type lacking A beta . This difference was observed from 24 h onwards, and at 72 h, 18 months old transgenic animals, with high load of A beta pathology, displayed SUVR of 2.2-3.5 in brain while wildtype showed ratios close to unity. A subset of the mice were also scanned with [C-11] PIB. Again wt mice displayed ratios of unity while transgenes showed slightly, non-significantly, elevated SUVR of 1.2, indicating improved sensitivity with novel di-scFv [I-124] 3D6-8D3 compared with [C-11] PIB. Brain concentrations of di-scFv [I-124] 3D6-8D3 correlated with soluble A beta (p < 0.0001) but not with total A beta, i.e. plaque load (p = 0.34). We have successfully created a small bispecific antibody-based radioligand capable of crossing the BBB, subsequently binding to and visualizing intrabrain A beta in vivo. The radioligand displayed better sensitivity compared with [C-11] PIB, and brain concentrations correlated with soluble neurotoxic A beta aggregates.

Keywords
Alzheimer's disease, Amyloid beta, PET, Antibody-based radioligand, Transferrin receptor, Brain
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:uu:diva-332464 (URN)10.1016/j.neuroimage.2018.10.011 (DOI)000449385000075 ()30300753 (PubMedID)
Funder
Swedish Research Council, 2012-1593Swedish Research Council, 2017-02413
Available from: 2017-10-27 Created: 2017-10-27 Last updated: 2019-01-15Bibliographically approved
5. Fluorine-18 labeling of antibody-based radioligands for PET imaging of amyloid beta in brain
Open this publication in new window or tab >>Fluorine-18 labeling of antibody-based radioligands for PET imaging of amyloid beta in brain
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(English)Manuscript (preprint) (Other academic)
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:uu:diva-332466 (URN)
Available from: 2017-11-02 Created: 2017-11-02 Last updated: 2017-11-10

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