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- Bonvicini, Gillian
(författare)
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Harnessing the molecular Trojan horse : Evaluating properties of preclinical Aβ immunoPET radioligands for optimized brain delivery via the transferrin receptor
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With high specificity and selectivity to targets, antibodies are prime candidates for positron emission tomography (PET) radioligands. They do not passively cross the blood-brain barrier which has hindered their development for imaging intrabrain targets, like amyloid-β (Aβ) in Alzheimer’s disease. The molecular Trojan horse strategy with antibodies that bind to both the transferrin receptor (TfR) and an intrabrain target improves brain delivery of therapeutic antibodies. However, therapeutic antibodies are typically dosed substantially higher than antibody-based PET (immunoPET) radioligands.This thesis evaluated the effects of affinity, valency, and dose on the brain delivery of preclinical Aβ immunoPET radioligands via the TfR.Paper I investigated whether immunoPET with TfR-mediated brain delivery could image Aβ with similar sensitivity in rats as it has in mice. To our knowledge, this was the first time TfR-hijacking to deliver a radioligand to image Aβ was successfully demonstrated in rats; suggesting this strategy could eventually be translated to clinics.Affinity to TfR influences therapeutic delivery to the brain. In Paper II, we compared four Biacore setups and one on-cell assay for determining apparent affinities to the TfR. Absolute affinity determination was challenging since several assay conditions impacted the kinetic parameters. A directional TfR capture in Biacore may be optimal since it determined kinetic parameters while mimicking in vivo receptor conditions. Papers I and III investigated how antibody affinity affects brain delivery at tracer doses and indicated that stronger TfR affinity yielded higher brain delivery. The antibodies in Paper III lacked effector function. The resulting pharmacokinetic profiles in Aβ pathology-presenting mice indicated this may have improved target accumulation of the immunoPET radioligand.In Paper IV, we screened a novel library of monovalent and bivalent affinity variants of the anti-mouse TfR antibody, 8D3. A pair of monovalent and bivalent antibodies with an apparent affinity of 10 nM was identified and evaluated in vivo. Monovalent binding yielded higher brain uptake at a tracer dose but whether bivalent binding steered the antibody towards lysosomal degradation was unclear.In conclusion, monovalency, high affinity binding, and ablated effector function are likely beneficial properties for TfR-mediated brain delivery of an immunoPET radioligand at a tracer dose.
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| 2. |
- Rofo, Fadi
(författare)
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Enhancing the therapeutic effect of biological drugs with protein engineering : Focusing on pre-clinical Alzheimer’s disease therapy
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aggregation of the amyloid-β peptide (Aβ) is one of the main pathological hallmarks in Alzheimer’s disease (AD). The soluble Aβ aggregates (oligomers and protofibrils) have shown to be the most harmful species. Hence, targeting these aggregates can be of therapeutic potential.Protein therapy is one of the fastest growing fields in drug development with more than 100 FDA approved protein-drugs in the last decade. Despite that, protein-drugs (mainly antibodies) targeting Aβ displayed limited beneficial effects in AD clinical trials. This might be attributed to the presence of the blood-brain barrier (BBB) that hinders the entry of big molecules such as proteins into the brain. In paper I, we fused somatostatin peptide (SST) to the previously developed BBB transporter (scFv8D3). The new protein, SST-scFv8D3, exhibited a 120-times longer plasma half-life compared to SST, and reached the brain at high levels when intravenously administered. When tested in APPswe mouse model of AD, SST-scFv8D3 significantly enhanced neprilysin (NEP)-mediated degradation of hippocampal Aβ42 after only three injections. In paper II, treatment with SST-scFv8D3 displayed a wide-ranging effect on AD brain proteome. Mitochondrial and neuronal growth proteins were among the most altered protein-groups, where SST-scFv8D treatment shifted them towards wild-type levels.There is potential to increase the binding strength and selectivity of antibodies to small Aβ aggregates (oligomers), which are thought to be the most toxic Aβ species. In paper III, we developed a multivalent antibody format with additional binding sites having short distances between them. The new antibody format displayed a 40-fold reduction in the dissociation rate from Aβ protofibrils. Furthermore, the multivalent antibody could strongly bind small Aβ oligomers, which has been difficult to achieve with conventional IgG antibodies. In paper IV, we developed a bispecific version of the multivalent antibody capable of passing the BBB. A single intravenous injection of the new antibody format was enough to significantly clear soluble Aβ aggregates from the brain of tg-ArcSwe mice. In paper V, we developed recombinant proteins with NEP linked to an Fc-fragment to provide long half-life and to the above-mentioned BBB transporter. When applied at therapeutic doses, these proteins significantly degraded plasma Aβ, but displayed limited effects on brain Aβ concentration, probably due to their short retention times in the brain.In conclusion, we developed new protein-drugs with improved binding properties to Aβ, ability to cross the BBB, and therapeutic potential in pre-clinical mouse models of AD.
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