In Vivo Amyloid-β Imaging in the APPPS1–21 Transgenic Mouse Model with a 89Zr-Labeled Monoclonal Antibody

Abstract

Introduction: The accumulation of amyloid-β is a pathological hallmark of Alzheimer’s disease and is a target for molecular imaging probes to aid in diagnosis and disease monitoring. This study evaluated the feasibility of using a radiolabeled monoclonal anti-amyloid-β antibody (JRF/AβN/25) to non-invasively assess amyloid-β burden in aged transgenic mice (APPPS1–21) with μPET imaging.Methods: We investigated the antibody JRF/AβN/25 that binds to full-length Aβ. JRF/AβN/25 was radiolabeled with a [89Zr]-desferal chelate and intravenously injected into 12–13 month aged APPPS1–21 mice and their wild-type (WT) controls. Mice underwent in vivo μPET imaging at 2, 4, and 7 days post injection and were sacrificed at the end of each time point to assess brain penetrance, plaque labeling, biodistribution, and tracer stability. To confirm imaging specificity we also evaluated brain uptake of a non-amyloid targeting [89Zr]-labeled antibody (trastuzumab) as a negative control, additionally we performed a competitive blocking study with non-radiolabeled Df-Bz-JRF/AβN/25 and finally we assessed the possible confounding effects of blood retention.Results: Voxel-wise analysis of μPET data demonstrated significant [89Zr]-Df-Bz-JRF/AβN/25 retention in APPPS1–21 mice at all time points investigated. With ex vivo measures of radioactivity, significantly higher retention of [89Zr]-Df-Bz-JRF/AβN/25 was found at 4 and 7 days pi in APPPS1–21 mice. Despite the observed genotypic differences, comparisons with immunohistochemistry revealed that in vivo plaque labeling was low. Furthermore, pre-treatment with Df-Bz-JRF/AβN/25 only partially blocked [89Zr]-Df-Bz-JRF/AβN/25 uptake indicative of a high contribution of non-specific binding.Conclusion: Amyloid plaques were detected in vivo with a radiolabeled monoclonal anti-amyloid antibody. The low brain penetrance of the antibody in addition to non-specific binding prevented an accurate estimation of plaque burden. However, it should be noted that [89Zr]-Df-Bz-JRF/AβN/25 nevertheless demonstrated in vivo binding and strategies to increase brain penetrance would likely achieve better results.

Advancing 89Zr-immuno-PET in neuroscience with a bispecific anti-amyloid-beta monoclonal antibody - The choice of chelator is essential

“…To test this, the bispecific anti-amyloid-beta aducanumab derivate mAbAdu-scFab8D3 (Adu-8D3) was used. This bispecific antibody was designed to overcome the low passive BBB permeability of monospecific mAbs, which have shown limited 89 Zr-immuno-PET potential for imaging amyloid-beta in the past [6,7]. The use of this bispecific mAb, consisting of an amyloid-beta targeting aducanumab derivate and the BBB shuttling moiety 8D3, for immuno-PET imaging, has previously been established by Syvänen et al using iodine-124 as the PET radionuclide [9][10][11].…”

“…Previous work by Fissers et al and Waldron et al showed that a 89 Zr-radiolabeled monoclonal anti-amyloid antibody [ 89 Zr]-Df-Bz-JRF/ AβN/25 indeed binds to amyloid plaques in vivo. However, low brain penetrance and high non-specific binding limited its usefulness as a plaque imaging agent [6,7]. It was suggested that strategies to enhance brain uptake would lead to better results.…”

PET Imaging in Preclinical Anti-Aβ Drug Development

“…In contrast to current amyloid-PET radioligands for which the binding is dependent on the structure of the protein aggregates, antibodies generally bind to specific epitopes based on the amino acid sequences of the protein. Antibodies are large molecules that show very limited and slow distribution to the brain and have therefore not been used for imaging intrabrain targets, although there have been some attempts in the preclinical setting (22)(23)(24)(25). Increased interest in immunotherapy of brain disorders has prompted the development of different strategies to increase antibody delivery to the brain, including the use of the transferrin receptor (TfR) as a shuttle for therapeutic proteins and antibodies across the blood-brain barrier (BBB) (26)(27)(28)(29)(30)(31)(32).…”

Mass spectrometric characterization of intact desferal‐conjugated monoclonal antibodies for immuno‐positron emission tomography imaging

“…We have recently developed an immuno‐PET tracer based on JRF/AβN/25, a mAb directed against amyloid β (Aβ) 1‐x peptide that recognizes an epitope in the first seven residues of Aβ . We showed that the JRF/AβN/25‐based tracer was able to penetrate the blood–brain‐barrier and detect Aβ plaques in the APPPS1–21 transgenic mouse model in vivo . In these studies, zirconium‐89 ( 89 Zr) was used as radioisotope and this was complexed to the mAb after conjugation with a bifunctional chelator, p ‐isothiocyanatobenzyl‐desferrioxamine (Df‐Bz‐NCS, further referred to as desferal), as previously optimized by Vosjan and colleagues .…”