Application of 89Zr-DFO*-immuno-PET to assess improved target engagement of a bispecific anti-amyloid-ß monoclonal antibody

PURPOSE

The recent conditional FDA approval of Aducanumab (Adu) for treating Alzheimer's disease (AD) and the continued discussions around that decision have increased interest in immunotherapy for AD and other brain diseases. Reliable techniques for brain imaging of antibodies may guide decision-making in the future but needs further development. In this study, we used ⁸⁹Zr-immuno-PET to evaluate the targeting and distribution of a bispecific brain-shuttle IgG based on Adu with transferrin receptor protein-1 (TfR1) shuttling mechanism, mAbAdu-scFab8D3, designated Adu-8D3, as a candidate theranostic for AD. We also validated the ⁸⁹Zr-immuno-PET platform as an enabling technology for developing new antibody-based theranostics for brain disorders.

METHODS

Adu, Adu-8D3, and the non-binding control construct B12-8D3 were modified with DFO*-NCS and radiolabeled with ⁸⁹Zr. APP/PS1 mice were injected with ⁸⁹Zr-labeled mAbs and imaged on days 3 and 7 by positron emission tomography (PET). Ex vivo biodistribution was performed on day 7, and ex vivo autoradiography and immunofluorescence staining were done on brain tissue to validate the PET imaging results and target engagement with amyloid-β plaques. Additionally, [⁸⁹Zr]Zr-DFO*-Adu-8D3 was evaluated in 3, 7, and 10-month-old APP/PS1 mice to test its potential in early stage disease.

RESULTS

A 7-fold higher brain uptake was observed for [⁸⁹Zr]Zr-DFO*-Adu-8D3 compared to [⁸⁹Zr]Zr-DFO*-Adu and a 2.7-fold higher uptake compared to [⁸⁹Zr]Zr-DFO*-B12-8D3 on day 7. Autoradiography and immunofluorescence of [⁸⁹Zr]Zr-DFO*-Adu-8D3 showed co-localization with amyloid plaques, which was not the case with the Adu and B12-8D3 conjugates. [⁸⁹Zr]Zr-DFO*-Adu-8D3 was able to detect low plaque load in 3-month-old APP/PS1 mice.

CONCLUSION

⁸⁹Zr-DFO*-immuno-PET revealed high and specific uptake of the bispecific Adu-8D3 in the brain and can be used for the early detection of Aβ plaque pathology. Here, we demonstrate that ⁸⁹Zr-DFO*-immuno-PET can be used to visualize and quantify brain uptake of mAbs and contribute to the evaluation of biological therapeutics for brain diseases.

Autoantibodies are highly prevalent in non-SARS-CoV-2 respiratory infections and critical illness

The widespread presence of autoantibodies in acute infection with SARS-CoV-2 is increasingly recognized, but the prevalence of autoantibodies in non-SARS-CoV-2 infections and critical illness has not yet been reported. We profiled IgG autoantibodies in 267 patients from 5 independent cohorts with non-SARS-CoV-2 viral, bacterial, and noninfectious critical illness. Serum samples were screened using Luminex arrays that included 58 cytokines and 55 autoantigens, many of which are associated with connective tissue diseases (CTDs). Samples positive for anti-cytokine antibodies were tested for receptor blocking activity using cell-based functional assays. Anti-cytokine antibodies were identified in > 50% of patients across all 5 acutely ill cohorts. In critically ill patients, anti-cytokine antibodies were far more common in infected versus uninfected patients. In cell-based functional assays, 11 of 39 samples positive for select anti-cytokine antibodies displayed receptor blocking activity against surface receptors for Type I IFN, GM-CSF, and IL-6. Autoantibodies against CTD-associated autoantigens were also commonly observed, including newly detected antibodies that emerged in longitudinal samples. These findings demonstrate that anti-cytokine and autoantibodies are common across different viral and nonviral infections and range in severity of illness.

Alpha-synuclein deficiency in the C57BL/6JOlaHsd strain does not modify disease progression in the ME7-model of prion disease

We previously detailed how intrahippocampal inoculation of C57BL/6J mice with murine modified scrapie (ME7) leads to chronic neurodegeneration (Cunningham C, Deacon R, Wells H, Boche D, Waters S, Diniz CP, Scott H, Rawlins JN, Perry VH (2003) Eur J Neurosci 17:2147-2155.). Our characterization of the ME7-model is based on inoculation of this murine modified scrapie agent into C57BL/6J mice from Harlan laboratories. This agent in the C57BL/6J host generates a disease that spans a 24-week time course. The hippocampal pathology shows progressive misfolded prion (PrP(Sc)) deposition, astrogliosis and leads to behavioural dysfunction underpinned by the early synaptic loss that precedes neuronal death. The Harlan C57BL/6J, although widely used as a wild type mouse, are a sub-strain harbouring a spontaneous deletion of alpha-synuclein with the full description C57BL/6JOlaHsd. Recently alpha-synuclein has been shown to ameliorate the synaptic loss in a mouse model lacking the synaptic chaperone CSP-alpha. This opens a potential confound of the ME7-model, particularly with respect to the signature synaptic loss that underpin the physiological and behavioural dysfunction. To investigate if this strain-selective loss of a candidate disease modifier impacts on signature ME7 pathology, we compared cohorts of C57BL/6JOlaHsd (alpha-synuclein negative) with the founder strain from Charles Rivers (C57BL/6JCrl, alpha-synuclein positive). There were subtle changes in behaviour when comparing control animals from the two sub-strains indicating potentially significant consequences for studies assuming neurobiogical identity of both strains. However, there was no evidence that the absence of alpha-synuclein modifies disease. Indeed, accumulation of PrP(Sc), synaptic loss and the behavioural dysfunction associated with the ME7-agent was the same in both genetic backgrounds. Our data suggest that alpha-synuclein deficiency does not contribute to the compartment specific processes that give rise to prion disease mediated synaptotoxicity and neurodegeneration.

GSK-3beta inhibition reverses axonal transport defects and behavioural phenotypes in Drosophila

The tauopathies are a group of disorders characterised by aggregation of the microtubule-associated protein tau and include Alzheimer's disease (AD) and the fronto-temporal dementias (FTD). We have used Drosophila to analyse how tau abnormalities cause neurodegeneration. By selectively co-expressing wild-type human tau (0N3R isoform) and a GFP vesicle marker in motorneurons, we examined the consequences of tau overexpression on axonal transport in vivo. The results show that overexpression of tau disrupts axonal transport causing vesicle aggregation and this is associated with loss of locomotor function. All these effects occur without neuron death. Co-expression of constitutively active glycogen-synthase kinase-3beta (GSK-3beta) enhances and two GSK-3beta inhibitors, lithium and AR-A014418, reverse both the axon transport and locomotor phenotypes, suggesting that the pathological effects of tau are phosphorylation dependent. These data show that tau abnormalities significantly disrupt neuronal function, in a phosphorylation-dependent manner, before the classical pathological hallmarks are evident and also suggest that the inhibition of GSK-3beta might have potential therapeutic benefits in tauopathies.

Presenilin 1 independently regulates beta-catenin stability and transcriptional activity

Presenilin 1 (PS1) regulates beta-catenin stability; however, published data regarding the direction of the effect are contradictory. We examined the effects of wild-type and mutant forms of PS1 on the membrane, cytoplasmic, nuclear, and signaling pools of endogenous and exogenous beta-catenin by immunofluorescence microscopy, subcellular fractionation, and in a transcription assay. We found that PS1 destabilizes the cytoplasmic and nuclear pools of beta-catenin when stabilized by Wnt or Dvl but not when stabilized at lower levels of the Wnt pathway. The PS1 mutants examined were less able to reduce the stability of beta-catenin. PS1 also inhibited the transcriptional activity of endogenous beta-catenin, and the PS1 mutants were again less inhibitory at the level of Dvl but showed a different pattern of inhibition toward transcription below Dvl. The transcriptional activity of exogenously expressed wild-type beta-catenin and two mutants, DeltaN89beta-catenin and DeltaSTbeta-catenin, were also inhibited by wild-type and mutant PS1. We conclude that PS1 negatively regulates the stability and transcriptional activity of beta-catenin at different levels in the Wnt pathway, that the effect on transcriptional activity appears to be independent of the GSK-3beta mediated degradation of beta-catenin, and that mutations in PS1 differentially affect the stability and transcriptional activity of beta-catenin.