Standardized Preclinical In Vitro Blood-Brain Barrier Mouse Assay Validates Endocytosis-Dependent Antibody Transcytosis Using Transferrin-Receptor-Mediated Pathways

Systemic Treatment with Fas-Blocking Peptide Attenuates Apoptosis in Brain Ischemia

Apoptosis plays a crucial role in neuronal injury, with substantial evidence implicating Fas-mediated cell death as a key factor in ischemic strokes. To address this, inhibition of Fas-signaling has emerged as a promising strategy in preventing neuronal cell death and alleviating brain ischemia. However, the challenge of overcoming the blood-brain barrier (BBB) hampers the effective delivery of therapeutic drugs to the central nervous system (CNS). In this study, we employed a 30 amino acid-long leptin peptide to facilitate BBB penetration. By conjugating the leptin peptide with a Fas-blocking peptide (FBP) using polyethylene glycol (PEG), we achieved specific accumulation in the Fas-expressing infarction region of the brain following systemic administration. Notably, administration in leptin receptor-deficient db/db mice demonstrated that leptin facilitated the delivery of FBP peptide. We found that the systemic administration of leptin-PEG-FBP effectively inhibited Fas-mediated apoptosis in the ischemic region, resulting in a significant reduction of neuronal cell death, decreased infarct volumes, and accelerated recovery. Importantly, neither leptin nor PEG-FBP influenced apoptotic signaling in brain ischemia. Here, we demonstrate that the systemic delivery of leptin-PEG-FBP presents a promising and viable strategy for treating cerebral ischemic stroke. Our approach not only highlights the therapeutic potential but also emphasizes the importance of overcoming BBB challenges to advance treatments for neurological disorders.

Subcellular trafficking and transcytosis efficacy of different receptor types for therapeutic antibody delivery at the blood‒brain barrier

Here, we report an experimental setup to benchmark different receptors for targeted therapeutic antibody delivery at the blood-brain barrier. We used brain capillary endothelial-like cells derived from induced pluripotent stem cells (hiPSC-BECs) as a model system and compared them to colon epithelial Caco-2 cells. This approach helped to identify favourable receptors for transport into the cell layer itself or for directing transport for transcytosis across the cell layer. The sorting receptors transferrin receptor and sortilin were shown to be efficient as antibody cargo receptors for intracellular delivery to the cell layer. In contrast, the cell surface receptors CD133 and podocalyxin were identified as static and inefficient receptors for delivering cargo antibodies. Similar to in vivo studies, the hiPSC-BECs maintained detectable transcytotic transport via transferrin receptor, while transcytosis was restricted using sortilin as a cargo receptor. Based on these findings, we propose the application of sortilin as a cargo receptor for delivering therapeutic antibodies into the brain microvascular endothelium.

Age, dose, and binding to TfR on blood cells influence brain delivery of a TfR-transported antibody

BACKGROUND

Transferrin receptor 1 (TfR1) mediated brain delivery of antibodies could become important for increasing the efficacy of emerging immunotherapies in Alzheimer's disease (AD). However, age, dose, binding to TfR1 on blood cells, and pathology could influence the TfR1-mediated transcytosis of TfR1-binders across the blood-brain barrier (BBB). The aim of the study was, therefore, to investigate the impact of these factors on the brain delivery of a bispecific TfR1-transported Aβ-antibody, mAb3D6-scFv8D3, in comparison with the conventional antibody mAb3D6.

METHODS

Young (3-5 months) and aged (17-20 months) WT and tg-ArcSwe mice (AD model) were injected with ¹²⁵I-labeled mAb3D6-scFv8D3 or mAb3D6. Three different doses were used in the study, 0.05 mg/kg (low dose), 1 mg/kg (high dose), and 10 mg/kg (therapeutic dose), with equimolar doses for mAb3D6. The dose-corrected antibody concentrations in whole blood, blood cells, plasma, spleen, and brain were evaluated at 2 h post-administration. Furthermore, isolated brains were studied by autoradiography, nuclear track emulsion, and capillary depletion to investigate the intrabrain distribution of the antibodies, while binding to blood cells was studied in vitro using blood isolated from young and aged mice.

RESULTS

The aged WT and tg-ArcSwe mice showed significantly lower brain concentrations of TfR-binding [¹²⁵I]mAb3D6-scFv8D3 and higher concentrations in the blood cell fraction compared to young mice. For [¹²⁵I]mAb3D6, no significant differences in blood or brain delivery were observed between young and aged mice or between genotypes. A low dose of [¹²⁵I]mAb3D6-scFv8D3 was associated with increased relative parenchymal delivery, as well as increased blood cell distribution. Brain concentrations and relative parenchymal distribution of [¹²⁵I]mAb3D6-scFv8D6 did not differ between tg-ArcSwe and WT mice at this early time point but were considerably increased compared to those observed for [¹²⁵I]mAb3D6.

CONCLUSION

Age-dependent differences in blood and brain concentrations were observed for the bispecific antibody mAb3D6-scFv8D3 but not for the conventional Aβ antibody mAb3D6, indicating an age-related effect on TfR1-mediated brain delivery. The lowest dose of [¹²⁵I]mAb3D6-scFv8D3 was associated with higher relative BBB penetration but, at the same time, a higher distribution to blood cells. Overall, Aβ-pathology did not influence the early brain distribution of the bispecific antibody. In summary, age and bispecific antibody dose were important factors determining brain delivery, while genotype was not.