Brain Shuttle Antibody for Alzheimer’s Disease with Attenuated Peripheral Effector Function due to an Inverted Binding Mode

Quantifying antibody binding: techniques and therapeutic implications

The binding kinetics of an antibody for its target antigen represent key determinants of its biological function and success as a novel biotherapeutic. Defining these interactions and kinetics is critical for understanding the pharmacological and pharmacodynamic profiles of antibodies in therapeutic applications, with line of sight to clinical translation. In this review, we discuss the latest developments in approaches to measure and modulate antibody-antigen interactions, including antibody engineering, novel antibody formats, current, and emerging technologies for measuring antibody-antigen binding interactions, and emerging perspectives within the field. We also explore how emerging computational methods are set to become powerful tools for modeling antibody-binding interactions under physiologically relevant conditions. Finally, we consider the therapeutic implications of modulating target engagement in terms of pharmacodynamics and pharmacokinetics.

Leveraging neonatal Fc receptor (FcRn) to enhance antibody transport across the blood brain barrier

The blood-brain barrier (BBB) restricts efficient penetration of systemically delivered therapeutic antibodies into the brain, limiting the development of this class of drugs to treat neurodegenerative diseases. Here we demonstrate that the neonatal Fc receptor (FcRn), which is highly expressed at the BBB, can be used to facilitate IgG transport to the brain. Engineering of the antibody Fc region to promote binding to FcRn at neutral pH enhances antibody transcytosis in a cellular model. In vivo, these modifications improve brain penetration, as well as brain target engagement and activity, of systemically administered antibodies in both mice and non-human primates. This engineering approach can be broadly implemented to enhance central nervous system (CNS) exposure of antibody- and Fc-based drugs, improving the clinical potential of biotherapeutics for the treatment of human brain diseases.

The blood-brain barrier as a treatment target for neurodegenerative disorders

INTRODUCTION

The blood-brain barrier (BBB) is a vascular endothelial membrane which restricts entry of toxins, cells, and microorganisms into the brain. At the same time, the BBB supplies the brain with nutrients, key substrates for DNA and RNA synthesis, and regulatory molecules, and removes metabolic waste products from brain to blood. BBB breakdown and/or dysfunction have been shown in neurogenerative disorders including Alzheimer's disease (AD). Current data suggests that these BBB changes may initiate and/or contribute to neuronal, synaptic, and cognitive dysfunction, and possibly other aspects of neurodegenerative processes.

AREAS COVERED

We first briefly review recent studies uncovering molecular composition of brain microvasculature and examine the BBB as a possible therapeutic target in neurodegenerative disorders with a focus on AD. Current strategies aimed at protecting and/or restoring altered BBB functions are considered. The relevance of BBB-directed approaches to improve neuronal and synaptic function, and to slow progression of neurodegenerative processes are also discussed. Lastly, we review recent advancements in drug delivery across the BBB.

EXPERT OPINION

BBB breakdown and/or dysfunction can significantly affect neuronal and synaptic function and neurodegenerative processes. More attention should focus on therapeutics to preserve or restore BBB functions when considering treatments of neurodegenerative diseases and AD.

Comparative Radiotracing Quantifies Brain Cellular Uptake and Catabolism of Bispecific Antibodies Targeting Transferrin Receptor and CD98hc

Bispecific antibodies (bAbs) that engage cerebrovascular targets, induce transport across the blood-brain barrier (BBB), and redistribute to secondary targets within the brain parenchyma have the potential to transform the diagnosis and treatment of a wide range of central nervous system disorders. Full understanding of the pharmacokinetics (PK) of these agents, including their potential for delivering cargo into brain parenchymal cells, is a key priority for the development of numerous potential therapeutic applications. To date, the brain PK of bAbs that target transferrin receptor (TfR-1) and CD98 heavy chain (CD98hc) has been characterized using techniques incapable of distinguishing between CNS clearance of intact protein from uptake and catabolism by brain parenchymal cells. Herein, we address this knowledge gap via a comparative radiotracing strategy using two radioisotopes with distinct residualizing properties, iodine-125 (I-125) and zirconium-89 (Zr-89). We first identify reaction conditions for tetravalent chelator modification and Zr-89 radiolabeling that do not adversely affect in vitro or in vivo function. We then use comparative radiotracing to define the PK of TfR-1 and CD98hc targeted bAbs without a parenchymal target, generating quantitative evidence of TfR-1-mediated cellular uptake and catabolism that implicates these processes in previously reported differences in the brain retention of IgGs shuttled across the BBB via these two pathways. Finally, we perform comparative radiotracing on a TfR-1 bAb with an internalizing neuronal target (TrkB), demonstrating rapid divergence of Zr-89 and I-125 PK curves, with a > 30-fold difference in brain content of the two radioisotopes. Together, these results establish comparative radiotracing as a valuable technique for identifying internalizing cellular targets within the brain parenchyma and quantifying the extent and timing of bAb uptake and catabolism following target engagement.

Brain-penetrant complement inhibition mitigates neurodegeneration in an Alzheimer's disease mouse model

Complement activation is implicated in driving brain inflammation, self-cell damage and progression of injury in Alzheimer's disease and other neurodegenerative diseases. Here, we investigate the impact of brain delivery of a complement-blocking antibody on neurodegeneration in an Alzheimer's mouse model. We engineered a brain-penetrant recombinant antibody targeting the pro-inflammatory membrane attack complex. Systemic administration of this antibody in APPNL-G-F mice reduced brain levels of complement activation products, demonstrating successful brain entry and target engagement. Prolonged treatment decreased synapse loss, amyloid burden and brain inflammatory cytokine levels, concomitant with cognitive improvement compared to controls. These results underscore the potential of brain-penetrant complement-inhibiting drugs as promising therapeutics, targeting downstream of amyloid plaques in Alzheimer's disease.

Preclinical B cell depletion and safety profile of a brain-shuttled crystallizable fragment-silenced CD20 antibody

BACKGROUND

The blood-brain barrier (BBB) presents a major challenge for the development of monoclonal antibody (mAb)-based therapies for brain disorders. To improve the likelihood of success of such therapies, Roche Brainshuttle technology utilizes a single anti-transferrin receptor 1 (TfR1)-antigen-binding antibody fragment linked to a therapeutic antibody, allowing engagement with TfR1 to transport the therapeutic antibody into the brain via receptor-mediated transcytosis.

METHODS

We compared Fc-silenced and Fc-competent variants of the Brainshuttle and the parental (non-shuttled) type II CD20 mAb, obinutuzumab in in vitro and in vivo (mouse and cynomolgus macaque) models. Endpoints assessed included B cell binding, B cell killing, tolerability, and ability to cross the BBB.

RESULTS

The Fc-silenced Brainshuttle construct showed a superior safety profile compared with the Fc-competent construct while maintaining the ability to cross the BBB and to deplete B cells in head-to-head comparisons in human and mouse in vitro and in mouse and cynomolgus macaque in vivo models.

CONCLUSION

Together, our data provide a path forward for the future development of safe and efficacious brain-targeted B-cell-depleting therapies.

KEY POINTS

The BBB hinders mAb-based brain disorder therapies A brain-targeted B-cell-depleting mAb for MS that efficiently crosses the BBB via hTfR1 was developed using Brainshuttle™ technology (1a and 1b) The Brainshuttle™-CD20 mAb was well tolerated (2a and 2b) and displayed B-cell-killing properties (1c), paving the way for future development and clinical translation of TfR1-targetingtherapies for increased brain penetration.

Fc-engineered large molecules targeting blood-brain barrier transferrin receptor and CD98hc have distinct central nervous system and peripheral biodistribution

Blood brain barrier-crossing molecules targeting transferrin receptor (TfR) and CD98 heavy chain (CD98hc) are widely reported to promote enhanced brain delivery of therapeutics. Here, we provide a comprehensive and unbiased biodistribution characterization of TfR and CD98hc antibody transport vehicles (ATVTfR and ATVCD98hc) compared to control IgG. Mouse whole-body tissue clearing reveals distinct organ localization for each molecule. In the brain, ATVTfR and ATVCD98hc achieve enhanced exposure and parenchymal distribution even when brain exposures are matched between ATV and control IgG in bulk tissue. Using a combination of cell sorting and single-cell RNAseq, we reveal that control IgG is nearly absent from parenchymal cells and is distributed primarily to brain perivascular and leptomeningeal cells. In contrast, ATVTfR and ATVCD98hc exhibit broad and unique parenchymal cell-type distribution. Finally, we profile in detail brain region-specific biodistribution of ATVTfR in cynomolgus monkey brain and spinal cord. Taken together, this in-depth multiscale characterization will guide platform selection for therapeutic targets of interest.

Large-scale transcriptomics analysis reveals a novel stress biomarker in CHO cells producing difficult to express mAbs

Monoclonal antibodies (mAbs) are considered one of the most game-changing products of the biopharmaceutical industry. The introduction of several diverse and complex formats consisting of several polypeptide chains and engineered with multiple antigen-binding domains has made the manufacturability process particularly challenging, especially in the context of assessing expression levels and yields of the formats. Here we present the largest and most diversified CHO transcriptomics analysis consisting of data derived from 892 different monoclonal cell lines, producing 11 different mAbs with various non-standard, highly complex formats. We apply three robust feature selection methods, one traditional differential expression analysis and two machine learning approaches to identify genes correlated to high product titer and quality. Cnpy3 gene is identified as a novel gene biomarker, showing a very strong negative correlation (Pearson r2 = 0.94) to the overall format productivity. These results were validated by a hold-out data set from cell lines expressing two different antibody formats. Additionally, the expression of Cnpy3 gene is positively correlated to the structural complexity of the examined mAbs. As complexity increases, cellular stress escalates leading to reduced productivity, implicating Cnpy3 as a strong CHO cell lines stress indicator. Thus, we conclude that Cnpy3 gene has the potential to be used as a screening biomarker for assessing format manufacturability and selecting formats and pools with a high potential to deliver subsequent higher productivity rates, resulting in a substantially smarter cell line and process development.

Experiences from Clinical Research and Routine Use of Florbetaben Amyloid PET-A Decade of Post-Authorization Insights

Florbetaben (FBB) is a radiopharmaceutical approved by the FDA and EMA in 2014 for the positron emission tomography (PET) imaging of brain amyloid deposition in patients with cognitive impairment who are being evaluated for Alzheimer's disease (AD) or other causes of cognitive decline. Initially, the clinical adoption of FBB PET faced significant barriers, including reimbursement challenges and uncertainties regarding its integration into diagnostic clinical practice. This review examines the progress made in overcoming these obstacles and describes the concurrent evolution of the diagnostic landscape. Advances in quantification methods have further strengthened the traditional visual assessment approach. Over the past decade, compelling evidence has emerged, demonstrating that amyloid PET has a strong impact on AD diagnosis, management, and outcomes across diverse clinical scenarios, even in the absence of amyloid-targeted therapies. Amyloid PET imaging has become essential in clinical trials and the application of new AD therapeutics, particularly for confirming eligibility criteria (i.e., the presence of amyloid plaques) and monitoring biological responses to amyloid-lowering therapies. Since its approval, FBB PET has transitioned from a purely diagnostic tool aimed primarily at excluding amyloid pathology to a critical component in AD drug development, and today, it is essential in the diagnostic workup and therapy management of approved AD treatments.

Emerging trends in virus and virus-like particle gene therapy delivery to the brain

Recent advances in gene therapy and gene-editing techniques offer the very real potential for successful treatment of neurological diseases. However, drug delivery constraints continue to impede viable therapeutic interventions targeting the brain due to its anatomical complexity and highly restrictive microvasculature that is impervious to many molecules. Realizing the therapeutic potential of gene-based therapies requires robust encapsulation and safe and efficient delivery to the target cells. Although viral vectors have been widely used for targeted delivery of gene-based therapies, drawbacks such as host genome integration, prolonged expression, undesired off-target mutations, and immunogenicity have led to the development of alternative strategies. Engineered virus-like particles (eVLPs) are an emerging, promising platform that can be engineered to achieve neurotropism through pseudotyping. This review outlines strategies to improve eVLP neurotropism for therapeutic brain delivery of gene-editing agents.

Advanced Noninvasive Strategies for the Brain Delivery of Therapeutic Proteins and Peptides

Recent years have witnessed rapid progress in the discovery of therapeutic proteins and peptides for the treatment of central nervous system (CNS) diseases. However, their clinical applications have been considerably hindered by challenges such as low biomembrane permeability, poor stability, short circulation time, and the formidable blood-brain barrier (BBB). Recently, substantial improvements have been made in understanding the dynamics of the BBB and developing efficient approaches for delivering proteins and peptides to the CNS, especially by using various nanoparticles. Herein, we present an overview of the up-to-date understanding of the BBB under physiological and pathological conditions, emphasizing their effects on brain drug delivery. We summarize advanced strategies and elucidate the underlying mechanisms for delivering proteins and peptides to the brain. We highlight the developments and applications of nanocarriers in treating CNS diseases via BBB crossing. We also provide critical opinions on the limitations and obstacles of the current strategies and put forward prospects for future research.

Monoclonal antibodies and aptamers: The future therapeutics for Alzheimer's disease

Alzheimer's disease (AD) is considered the most common and prevalent form of dementia of adult-onset with characteristic progressive impairment in cognition and memory. The cure for AD has not been found yet and the treatments available until recently were only symptomatic. Regardless of multidisciplinary approaches and efforts made by pharmaceutical companies, it was only in the past two years that new drugs were approved for the treatment of the disease. Amyloid beta (Aβ) immunotherapy is at the core of this therapy, which is one of the most innovative approaches looking to change the course of AD. This technology is based on synthetic peptides or monoclonal antibodies (mAb) to reduce Aβ levels in the brain and slow down the advance of neurodegeneration. Hence, this article reviews the state of the art about AD neuropathogenesis, the traditional pharmacologic treatment, as well as the modern active and passive immunization describing approved drugs, and drug prototypes currently under investigation in different clinical trials. In addition, future perspectives on immunotherapeutic strategies for AD and the rise of the aptamer technology as a non-immunogenic alternative to curb the disease progression are discussed.

The present and future of bispecific antibodies for cancer therapy

Bispecific antibodies (bsAbs) enable novel mechanisms of action and/or therapeutic applications that cannot be achieved using conventional IgG-based antibodies. Consequently, development of these molecules has garnered substantial interest in the past decade and, as of the end of 2023, 14 bsAbs have been approved: 11 for the treatment of cancer and 3 for non-oncology indications. bsAbs are available in different formats, address different targets and mediate anticancer function via different molecular mechanisms. Here, we provide an overview of recent developments in the field of bsAbs for cancer therapy. We focus on bsAbs that are approved or in clinical development, including bsAb-mediated dual modulators of signalling pathways, tumour-targeted receptor agonists, bsAb-drug conjugates, bispecific T cell, natural killer cell and innate immune cell engagers, and bispecific checkpoint inhibitors and co-stimulators. Finally, we provide an outlook into next-generation bsAbs in earlier stages of development, including trispecifics, bsAb prodrugs, bsAbs that induce degradation of tumour targets and bsAbs acting as cytokine mimetics.

Bispecific antibody shuttles targeting CD98hc mediate efficient and long-lived brain delivery of IgGs

The inability of antibodies to penetrate the blood-brain barrier (BBB) is a key limitation to their use in diverse applications. One promising strategy is to deliver IgGs using a bispecific BBB shuttle, which involves fusing an IgG to a second affinity ligand that engages a cerebrovascular endothelial target and facilitates transport across the BBB. Nearly all prior efforts have focused on shuttles that target transferrin receptor (TfR-1) despite inherent delivery and safety challenges. Here, we report bispecific antibody shuttles that engage CD98hc, the heavy chain of the large neutral amino acid transporter (LAT1), and efficiently transport IgGs into the brain. Notably, CD98hc shuttles lead to much longer-lived brain retention of IgGs than TfR-1 shuttles while enabling more specific targeting due to limited CD98hc engagement in the brain parenchyma, which we demonstrate for IgGs that either agonize a neuronal receptor (TrkB) or target other endogenous cell-surface proteins on neurons and astrocytes.

Enhancing Antibody Exposure in the Central Nervous System: Mechanisms of Uptake, Clearance, and Strategies for Improved Brain Delivery

Antibodies (mAbs) are attractive molecules for their application as a diagnostic and therapeutic agent for diseases of the central nervous system (CNS). mAbs can be generated to have high affinity and specificity to target molecules in the CNS. Unfortunately, only a very small number of mAbs have been specifically developed and approved for neurological indications. This is primarily attributed to their low exposure within the CNS, hindering their ability to reach and effectively engage their potential targets in the brain. This review discusses aspects of various barriers such as the blood-brain barrier (BBB) and blood-cerebrospinal fluid (CSF) barrier (BCSFB) that regulate the entry and clearance of mAbs into and from the brain. The roles of the glymphatic system on brain exposure and clearance are being described. We also discuss the proposed mechanisms of the uptake of mAbs into the brain and for clearance. Finally, several methods of enhancing the exposure of mAbs in the CNS were discussed, including receptor-mediated transcytosis, osmotic BBB opening, focused ultrasound (FUS), BBB-modulating peptides, and enhancement of mAb brain retention.

A novel strategy to increase the therapeutic potency of GBM chemotherapy via altering parenchymal/cerebral spinal fluid clearance rate

Patients with glioblastoma (GBM) face a poor prognosis with a median survival of less than two years. Escalating the dose of chemotherapy is often impossible due to patient comorbidities; thus, we focused on modulating brain clearance as a mechanism to enhance drug accumulation. Given the recently identified interconnectivity between brain parenchymal fluid and cerebral spinal fluid (CSF), we reasoned enhancing drug concentration in the CSF also increases drug concentration in the parenchyma where a GBM resides. To improve drug accumulation in the CSF, we impair the motility of ependymal cell cilia. We identified FDA-approved therapeutics that interact with cilia as a "side effect." Therapeutics that inhibit airway cilia also inhibit ependymal cilia. Multiple cilia-inhibiting drugs, when administered in combination with GBM chemotherapy temozolomide (TMZ), significantly improved the overall survival of mice bearing orthotopic GBM. Combining TMZ with lidocaine results in 100% of animals surviving tumor-free to the study endpoint. This treatment results in a ~ 40-fold increase in brain TMZ levels and is well-tolerated. Mice bearing MGMT methylated, human PDX orthotopic GBM also responded with 100% of animals surviving tumor-free to the study endpoint. Finally, even mice bearing TMZ-resistant, orthotopic GBM responded to the combination treatment with 40% of animals surviving tumor-free to the study endpoint, implying this strategy can sensitize TMZ-resistant GBM. These studies offer a new concept for treating malignant brain tumors by improving the accumulation of TMZ in the CNS. In the future, this regimen may also improve the treatment of additional encephalopathies treated by brain-penetrating therapeutics. SIGNIFICANCE: We exploit the interconnectivity of parenchymal and cerebral spinal fluid to enhance the amount of temozolomide that accumulates in the central nervous system to improve the survival of mice bearing brain tumors.

Alzheimer's Targeted Treatments: Focus on Amyloid and Inflammation

Alzheimer's disease (AD) is the major cause of dementia that is now threatening the lives of billions of elderly people on the globe, and recent progress in the elucidation of the pathomechanism of AD is now opening venue to tackle the disease by developing and implementing "disease-modifying therapies" that directly act on the pathophysiology and slow down the progression of neurodegeneration. A recent example is the success of clinical trials of anti-amyloid b antibody drugs, whereas other therapeutic targets, e.g., inflammation and tau, are being actively investigated. In this dual perspective session, we plan to have speakers from leading pharmas in the field representing distinct investments in the AD space, which will be followed by the comment from scientific leadership of the Alzheimer's Association who will speak on behalf of all stakeholders. Neuroscientists participating in the Society for Neuroscience may be able to gain insights into the cutting edge of the therapeutic approaches to AD and neurodegenerative disorders, and discuss future contribution of neuroscience to this field.

Toxicologic Neuropathology of Novel Biotherapeutics

Biotherapeutic modalities such as cell therapies, gene therapies, nucleic acids, and proteins are increasingly investigated as disease-modifying treatments for severe and life-threatening neurodegenerative disorders. Such diverse bio-derived test articles are fraught with unique and often unpredictable biological consequences, while guidance regarding nonclinical experimental design, neuropathology evaluation, and interpretation is often limited. This paper summarizes key messages offered during a half-day continuing education course on toxicologic neuropathology of neuro-targeted biotherapeutics. Topics included fundamental neurobiology concepts, pharmacology, frequent toxicological findings, and their interpretation including adversity decisions. Covered biotherapeutic classes included cell therapies, gene editing and gene therapy vectors, nucleic acids, and proteins. If agents are administered directly into the central nervous system, initial screening using hematoxylin and eosin (H&E)-stained sections of currently recommended neural organs (brain [7 levels], spinal cord [3 levels], and sciatic nerve) may need to expand to include other components (e.g., more brain levels, ganglia, and/or additional nerves) and/or special neurohistological procedures to characterize possible neural effects (e.g., cell type-specific markers for reactive glial cells). Scientists who evaluate the safety of novel biologics will find this paper to be a practical reference for preclinical safety testing and risk assessment.

CD98hc is a target for brain delivery of biotherapeutics

Brain exposure of systemically administered biotherapeutics is highly restricted by the blood-brain barrier (BBB). Here, we report the engineering and characterization of a BBB transport vehicle targeting the CD98 heavy chain (CD98hc or SLC3A2) of heterodimeric amino acid transporters (TVCD98hc). The pharmacokinetic and biodistribution properties of a CD98hc antibody transport vehicle (ATVCD98hc) are assessed in humanized CD98hc knock-in mice and cynomolgus monkeys. Compared to most existing BBB platforms targeting the transferrin receptor, peripherally administered ATVCD98hc demonstrates differentiated brain delivery with markedly slower and more prolonged kinetic properties. Specific biodistribution profiles within the brain parenchyma can be modulated by introducing Fc mutations on ATVCD98hc that impact FcγR engagement, changing the valency of CD98hc binding, and by altering the extent of target engagement with Fabs. Our study establishes TVCD98hc as a modular brain delivery platform with favorable kinetic, biodistribution, and safety properties distinct from previously reported BBB platforms.

Affibody Molecules Intended for Receptor-Mediated Transcytosis via the Transferrin Receptor

The development of biologics for diseases affecting the central nervous system has been less successful compared to other disease areas, in part due to the challenge of delivering drugs to the brain. The most well-investigated and successful strategy for increasing brain uptake of biological drugs is using receptor-mediated transcytosis over the blood-brain barrier and, in particular, targeting the transferrin receptor-1 (TfR). Here, affibody molecules are selected for TfR using phage display technology. The two most interesting candidates demonstrated binding to human TfR, cross-reactivity to the murine orthologue, non-competitive binding with human transferrin, and binding to TfR-expressing brain endothelial cell lines. Single amino acid mutagenesis of the affibody molecules revealed the binding contribution of individual residues and was used to develop second-generation variants with improved properties. The second-generation variants were further analyzed and showed an ability for transcytosis in an in vitro transwell assay. The new TfR-specific affibody molecules have the potential for the development of small brain shuttles for increasing the uptake of various compounds to the central nervous system and thus warrant further investigations.

Microglia mediate neurocognitive deficits by eliminating C1q-tagged synapses in sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a severe and frequent complication of sepsis causing delirium, coma, and long-term cognitive dysfunction. We identified microglia and C1q complement activation in hippocampal autopsy tissue of patients with sepsis and increased C1q-mediated synaptic pruning in a murine polymicrobial sepsis model. Unbiased transcriptomics of hippocampal tissue and isolated microglia derived from septic mice revealed an involvement of the innate immune system, complement activation, and up-regulation of lysosomal pathways during SAE in parallel to neuronal and synaptic damage. Microglial engulfment of C1q-tagged synapses could be prevented by stereotactic intrahippocampal injection of a specific C1q-blocking antibody. Pharmacologically targeting microglia by PLX5622, a CSF1-R inhibitor, reduced C1q levels and the number of C1q-tagged synapses, protected from neuronal damage and synapse loss, and improved neurocognitive outcome. Thus, we identified complement-dependent synaptic pruning by microglia as a crucial pathomechanism for the development of neuronal defects during SAE.

Long-term effects of immunotherapy with a brain penetrating Aβ antibody in a mouse model of Alzheimer's disease

BACKGROUND

Brain-directed immunotherapy is a promising strategy to target amyloid-β (Aβ) deposits in Alzheimer's disease (AD). In the present study, we compared the therapeutic efficacy of the Aβ protofibril targeting antibody RmAb158 with its bispecific variant RmAb158-scFv8D3, which enters the brain by transferrin receptor-mediated transcytosis.

METHODS

AppNL-G-F knock-in mice received RmAb158, RmAb158-scFv8D3, or PBS in three treatment regimens. First, to assess the acute therapeutic effect, a single antibody dose was given to 5 months old AppNL-G-F mice, with evaluation after 3 days. Second, to assess the antibodies' ability to halt the progression of Aβ pathology, 3 months old AppNL-G-F mice received three doses during a week, with evaluation after 2 months. Reduction of RmAb158-scFv8D3 immunogenicity was explored by introducing mutations in the antibody or by depletion of CD4+ T cells. Third, to study the effects of chronic treatment, 7-month-old AppNL-G-F mice were CD4+ T cell depleted and treated with weekly antibody injections for 8 weeks, including a final diagnostic dose of [125I]RmAb158-scFv8D3, to determine its brain uptake ex vivo. Soluble Aβ aggregates and total Aβ42 were quantified with ELISA and immunostaining.

RESULTS

Neither RmAb158-scFv8D3 nor RmAb158 reduced soluble Aβ protofibrils or insoluble Aβ1-42 after a single injection treatment. After three successive injections, Aβ1-42 was reduced in mice treated with RmAb158, with a similar trend in RmAb158-scFv8D3-treated mice. Bispecific antibody immunogenicity was somewhat reduced by directed mutations, but CD4+ T cell depletion was used for long-term therapy. CD4+ T cell-depleted mice, chronically treated with RmAb158-scFv8D3, showed a dose-dependent increase in blood concentration of the diagnostic [125I]RmAb158-scFv8D3, while concentration was low in plasma and brain. Chronic treatment did not affect soluble Aβ aggregates, but a reduction in total Aβ42 was seen in the cortex of mice treated with both antibodies.

CONCLUSIONS

Both RmAb158 and its bispecific variant RmAb158-scFv8D3 achieved positive effects of long-term treatment. Despite its ability to efficiently enter the brain, the benefit of using the bispecific antibody in chronic treatment was limited by its reduced plasma exposure, which may be a result of interactions with TfR or the immune system. Future research will focus in new antibody formats to further improve Aβ immunotherapy.

Bispecific antibody shuttles targeting CD98hc mediate efficient and long-lived brain delivery of IgGs

The inability of antibodies and other biologics to penetrate the blood-brain barrier (BBB) is a key limitation to their use in diagnostic, imaging, and therapeutic applications. One promising strategy is to deliver IgGs using a bispecific BBB shuttle, which involves fusing an IgG with a second affinity ligand that engages a cerebrovascular endothelial target and facilitates transport across the BBB. Nearly all prior efforts have focused on the transferrin receptor (TfR-1) as the prototypical endothelial target despite inherent delivery and safety challenges. Here we report bispecific antibody shuttles that engage CD98hc (also known as 4F2 and SLC3A2), the heavy chain of the large neutral amino acid transporter (LAT1), and efficiently transport IgGs into the brain parenchyma. Notably, CD98hc shuttles lead to much longer-lived brain retention of IgGs than TfR-1 shuttles while enabling more specific brain targeting due to limited CD98hc engagement in the brain parenchyma. We demonstrate the broad utility of the CD98hc shuttles by reformatting three existing IgGs as CD98hc bispecific shuttles and delivering them to the mouse brain parenchyma that either agonize a neuronal receptor (TrkB) or target other endogenous antigens on specific types of brain cells (neurons and astrocytes).

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.

Delivery of the Brainshuttle™ amyloid-beta antibody fusion trontinemab to non-human primate brain and projected efficacious dose regimens in humans

There are few treatments that slow neurodegeneration in Alzheimer's disease (AD), and while therapeutic antibodies are being investigated in clinical trials for AD treatment, their access to the central nervous system is restricted by the blood-brain barrier. This study investigates a bispecific modular fusion protein composed of gantenerumab, a fully human monoclonal anti- amyloid-beta (Aβ) antibody under investigation for AD treatment, with a human transferrin receptor 1-directed Brainshuttle™ module (trontinemab; RG6102, INN trontinemab). In vitro, trontinemab showed a similar binding affinity to fibrillar Aβ40 and Aβ plaques in human AD brain sections to gantenerumab. A single intravenous administration of trontinemab (10 mg/kg) or gantenerumab (20 mg/kg) to non-human primates (NHPs, Macaca fascicularis), was well tolerated in both groups. Immunohistochemistry indicated increased trontinemab uptake into the brain endothelial cell layer and parenchyma, and more homogeneous distribution, compared with gantenerumab. Brain and plasma pharmacokinetic (PK) parameters for trontinemab were estimated by nonlinear mixed-effects modeling with correction for tissue residual blood, indicating a 4-18-fold increase in brain exposure. A previously developed clinical PK/pharmacodynamic model of gantenerumab was adapted to include a brain compartment as a driver of plaque removal and linked to the allometrically scaled above model from NHP. The new brain exposure-based model was used to predict trontinemab dosing regimens for effective amyloid reduction. Simulations from these models were used to inform dosing of trontinemab in the first-in-human clinical trial.

Transcriptional signature in microglia isolated from an Alzheimer's disease mouse model treated with scanning ultrasound

Transcranial scanning ultrasound combined with intravenously injected microbubbles (SUS+MB) has been shown to transiently open the blood-brain barrier and reduce the amyloid-β (Aβ) pathology in the APP23 mouse model of Alzheimer's disease (AD). This has been accomplished through the activation of microglial cells; however, their response to the SUS treatment is incompletely understood. Here, wild-type (WT) and APP23 mice were subjected to SUS+MB, using nonsonicated mice as sham controls. After 48 h, the APP23 mice were injected with methoxy-XO4 to label Aβ aggregates, followed by microglial isolation into XO4+ and XO4- populations using flow cytometry. Both XO4+ and XO4- cells were subjected to RNA sequencing and transcriptome profiling. The analysis of the microglial cells revealed a clear segregation depending on genotype (AD model vs. WT mice) and Aβ internalization (XO4+ vs. XO4- microglia), but interestingly, no differences were found between SUS+MB and sham in WT mice. Differential gene expression analysis in APP23 mice detected 278 genes that were significantly changed by SUS+MB in the XO4+ cells (248 up/30 down) and 242 in XO- cells (225 up/17 down). Pathway analysis highlighted differential expression of genes related to the phagosome pathway and marked upregulation of cell cycle-related transcripts in XO4+ and XO4- microglia isolated from SUS+MB-treated APP23 mice. Together, this highlights the complexity of the microglial response to transcranial ultrasound, with potential applications for the treatment of AD.

Enhanced delivery of antibodies across the blood-brain barrier via TEMs with inherent receptor-mediated phagocytosis

BACKGROUND

The near impermeability of the blood-brain barrier (BBB) and the unique neuroimmune environment of the CNS prevents the effective use of antibodies in neurological diseases. Delivery of biotherapeutics to the brain can be enabled through receptor-mediated transcytosis via proteins such as the transferrin receptor, although limitations such as the ability to use Fc-mediated effector function to clear pathogenic targets can introduce safety liabilities. Hence, novel delivery approaches with alternative clearance mechanisms are warranted.

METHODS

Binders that optimized transport across the BBB, known as transcytosis-enabling modules (TEMs), were identified using a combination of antibody discovery techniques and pharmacokinetic analyses. Functional activity of TEMs were subsequently evaluated by imaging for the ability of myeloid cells to phagocytose target proteins and cells.

FINDINGS

We demonstrated significantly enhanced brain exposure of therapeutic antibodies using optimal transferrin receptor or CD98 TEMs. We found that these modules also mediated efficient clearance of tau aggregates and HER2+ tumor cells via a non-classical phagocytosis mechanism through direct engagement of myeloid cells. This mode of clearance potentially avoids the known drawbacks of FcγR-mediated antibody mechanisms in the brain such as the neurotoxic release of proinflammatory cytokines and immune cell exhaustion.

CONCLUSIONS

Our study reports a new brain delivery platform that harnesses receptor-mediated transcytosis to maximize brain uptake and uses a non-classical phagocytosis mechanism to efficiently clear pathologic proteins and cells. We believe these findings will transform therapeutic approaches to treat CNS diseases.

FUNDING

This research was funded by Janssen, Pharmaceutical Companies of Johnson & Johnson.

Antibody-Based In Vivo Imaging of Central Nervous System Targets-Evaluation of a Pretargeting Approach Utilizing a TCO-Conjugated Brain Shuttle Antibody and Radiolabeled Tetrazines

Bioorthogonal pretargeted imaging using the inverse-electron-demand Diels-Alder (IEDDA) reaction between a tetrazine (Tz) and a trans-cyclooctene (TCO) represents an attractive strategy for molecular imaging via antibodies. The advantages of using a pretargeted imaging approach are on the one hand the possibility to achieve a high signal-to-noise ratio and imaging contrast; on the other hand, the method allows the uncoupling of the biological half-life of antibodies from the physical half-life of short-lived radionuclides. A brain-penetrating antibody (mAb) specific for β-amyloid (Aβ) plaques was functionalized with TCO moieties for pretargeted labeling of Aβ plaques in vitro, ex vivo, and in vivo by a tritium-labeled Tz. The overall aim was to explore the applicability of mAbs for brain imaging, using a preclinical model system. In vitro clicked mAb-TCO-Tz was able to pass the blood-brain barrier of transgenic PS2APP mice and specifically visualize Aβ plaques ex vivo. Further experiments showed that click reactivity of the mAb-TCO construct in vivo persisted up to 3 days after injection by labeling Aβ plaques ex vivo after incubation of brain sections with the Tz in vitro. An attempted in vivo click reaction between injected mAb-TCO and Tz did not lead to significant labeling of Aβ plaques, most probably due to unfavorable in vivo properties of the used Tz and a long half-life of the mAb-TCO in the blood stream. This study clearly demonstrates that pretargeted imaging of CNS targets via antibody-based click chemistry is a viable approach. Further experiments are warranted to optimize the balance between stability and reactivity of all reactants, particularly the Tz.

Radiolabelling small and biomolecules for tracking and monitoring

Radiolabelling small molecules with beta-emitters has been intensively explored in the last decades and novel concepts for the introduction of radionuclides continue to be reported regularly. New catalysts that induce carbon/hydrogen activation are able to incorporate isotopes such as deuterium or tritium into small molecules. However, these established labelling approaches have limited applicability for nucleic acid-based drugs, therapeutic antibodies, or peptides, which are typical of the molecules now being investigated as novel therapeutic modalities. These target molecules are usually larger (significantly >1 kDa), mostly multiply charged, and often poorly soluble in organic solvents. However, in preclinical research they often require radiolabelling in order to track and monitor drug candidates in metabolism, biotransformation, or pharmacokinetic studies. Currently, the most established approach to introduce a tritium atom into an oligonucleotide is based on a multistep synthesis, which leads to a low specific activity with a high level of waste and high costs. The most common way of tritiating peptides is using appropriate precursors. The conjugation of a radiolabelled prosthetic compound to a functional group within a protein sequence is a commonly applied way to introduce a radionuclide or a fluorescent tag into large molecules. This review highlights the state-of-the-art in different radiolabelling approaches for oligonucleotides, peptides, and proteins, as well as a critical assessment of the impact of the label on the properties of the modified molecules. Furthermore, applications of radiolabelled antibodies in biodistribution studies of immune complexes and imaging of brain targets are reported.

Recent advances in drug delivery and targeting to the brain

Our body keeps separating the toxic chemicals in the blood from the brain. A significant number of drugs do not enter the central nervous system (CNS) due to the blood-brain barrier (BBB). Certain diseases, such as tumor growth and stroke, are known to increase the permeability of the BBB. However, the heterogeneity of this permeation makes it difficult and unpredictable to transport drugs to the brain. In recent years, research has been directed toward increasing drug penetration inside the brain, and nanomedicine has emerged as a promising approach. Active targeting requires one or more specific ligands on the surface of nanoparticles (NPs), which brain endothelial cells (ECs) recognize, allowing controlled drug delivery compared to conventional targeting strategies. This review highlights the mechanistic insights about different cell types contributing to the development and maintenance of the BBB and summarizes the recent advancement in brain-specific NPs for different pathological conditions. Furthermore, fundamental properties of brain-targeted NPs will be discussed, and the standard lesion features classified by neurological pathology are summarized.

Delivering the Promise of Gene Therapy with Nanomedicines in Treating Central Nervous System Diseases

Central Nervous System (CNS) diseases, such as Alzheimer's diseases (AD), Parkinson's Diseases (PD), brain tumors, Huntington's disease (HD), and stroke, still remain difficult to treat by the conventional molecular drugs. In recent years, various gene therapies have come into the spotlight as versatile therapeutics providing the potential to prevent and treat these diseases. Despite the significant progress that has undoubtedly been achieved in terms of the design and modification of genetic modulators with desired potency and minimized unwanted immune responses, the efficient and safe in vivo delivery of gene therapies still poses major translational challenges. Various non-viral nanomedicines have been recently explored to circumvent this limitation. In this review, an overview of gene therapies for CNS diseases is provided and describes recent advances in the development of nanomedicines, including their unique characteristics, chemical modifications, bioconjugations, and the specific applications that those nanomedicines are harnessed to deliver gene therapies.

Symptomatic and Disease-Modifying Therapy Pipeline for Alzheimer's Disease: Towards a Personalized Polypharmacology Patient-Centered Approach

Since 1906, when Dr. Alois Alzheimer first described in a patient "a peculiar severe disease process of the cerebral cortex", people suffering from this pathology have been waiting for a breakthrough therapy. Alzheimer's disease (AD) is an irreversible, progressive neurodegenerative brain disorder and the most common form of dementia in the elderly with a long presymptomatic phase. Worldwide, approximately 50 million people are living with dementia, with AD comprising 60-70% of cases. Pathologically, AD is characterized by the deposition of amyloid β-peptide (Aβ) in the neuropil (neuritic plaques) and blood vessels (amyloid angiopathy), and by the accumulation of hyperphosphorylated tau in neurons (neurofibrillary tangles) in the brain, with associated loss of synapses and neurons, together with glial activation, and neuroinflammation, resulting in cognitive deficits and eventually dementia. The current competitive landscape in AD consists of symptomatic treatments, of which there are currently six approved medications: three AChEIs (donepezil, rivastigmine, and galantamine), one NMDA-R antagonist (memantine), one combination therapy (memantine/donepezil), and GV-971 (sodium oligomannate, a mixture of oligosaccharides derived from algae) only approved in China. Improvements to the approved therapies, such as easier routes of administration and reduced dosing frequencies, along with the developments of new strategies and combined treatments are expected to occur within the next decade and will positively impact the way the disease is managed. Recently, Aducanumab, the first disease-modifying therapy (DMT) has been approved for AD, and several DMTs are in advanced stages of clinical development or regulatory review. Small molecules, mAbs, or multimodal strategies showing promise in animal studies have not confirmed that promise in the clinic (where small to moderate changes in clinical efficacy have been observed), and therefore, there is a significant unmet need for a better understanding of the AD pathogenesis and the exploration of alternative etiologies and therapeutic effective disease-modifying therapies strategies for AD. Therefore, a critical review of the disease-modifying therapy pipeline for Alzheimer's disease is needed.

AAV Vector-Mediated Antibody Delivery (A-MAD) in the Central Nervous System

In the last four decades, monoclonal antibodies and their derivatives have emerged as a powerful class of therapeutics, largely due to their exquisite targeting specificity. Several clinical areas, most notably oncology and autoimmune disorders, have seen the successful introduction of monoclonal-based therapeutics. However, their adoption for treatment of Central Nervous System diseases has been comparatively slow, largely due to issues of efficient delivery resulting from limited permeability of the Blood Brain Barrier. Nevertheless, CNS diseases are becoming increasingly prevalent as societies age, accounting for ~6.5 million fatalities worldwide per year. Therefore, harnessing the full therapeutic potential of monoclonal antibodies (and their derivatives) in this clinical area has become a priority. Adeno-associated virus-based vectors (AAVs) are a potential solution to this problem. Preclinical studies have shown that AAV vector-mediated antibody delivery provides protection against a broad range of peripheral diseases, such as the human immunodeficiency virus (HIV), influenza and malaria. The parallel identification and optimization of AAV vector platforms which cross the Blood Brain Barrier with high efficiency, widely transducing the Central Nervous System and allowing high levels of local transgene production, has now opened a number of interesting scenarios for the development of AAV vector-mediated antibody delivery strategies to target Central Nervous System proteinopathies.

Enhancing autophagy in Alzheimer's disease through drug repositioning

Alzheimer's disease (AD) is one of the biggest human health threats due to increases in aging of the global population. Unfortunately, drugs for treating AD have been largely ineffective. Interestingly, downregulation of macroautophagy (autophagy) plays an essential role in AD pathogenesis. Therefore, targeting autophagy has drawn considerable attention as a therapeutic approach for the treatment of AD. However, developing new therapeutics is time-consuming and requires huge investments. One of the strategies currently under consideration for many diseases is "drug repositioning" or "drug repurposing". In this comprehensive review, we have provided an overview of the impact of autophagy on AD pathophysiology, reviewed the therapeutics that upregulate autophagy and are currently used in the treatment of other diseases, including cancers, and evaluated their repurposing as a possible treatment option for AD. In addition, we discussed the potential of applying nano-drug delivery to neurodegenerative diseases, such as AD, to overcome the challenge of crossing the blood brain barrier and specifically target molecules/pathways of interest with minimal side effects.

Molecular architecture determines brain delivery of a transferrin receptor–targeted lysosomal enzyme

Delivery of biotherapeutics across the blood–brain barrier (BBB) is a challenge. Many approaches fuse biotherapeutics to platforms that bind the transferrin receptor (TfR), a brain endothelial cell target, to facilitate receptor-mediated transcytosis across the BBB. Here, we characterized the pharmacological behavior of two distinct TfR-targeted platforms fused to iduronate 2-sulfatase (IDS), a lysosomal enzyme deficient in mucopolysaccharidosis type II (MPS II), and compared the relative brain exposures and functional activities of both approaches in mouse models. IDS fused to a moderate-affinity, monovalent TfR-binding enzyme transport vehicle (ETV:IDS) resulted in widespread brain exposure, internalization by parenchymal cells, and significant substrate reduction in the CNS of an MPS II mouse model. In contrast, IDS fused to a standard high-affinity bivalent antibody (IgG:IDS) resulted in lower brain uptake, limited biodistribution beyond brain endothelial cells, and reduced brain substrate reduction. These results highlight important features likely to impact the clinical development of TfR-targeting platforms in MPS II and potentially other CNS diseases.

The amyloid hypothesis in Alzheimer disease: new insights from new therapeutics

Many drugs that target amyloid-β (Aβ) in Alzheimer disease (AD) have failed to demonstrate clinical efficacy. However, four anti-Aβ antibodies have been shown to mediate the removal of amyloid plaque from brains of patients with AD, and the FDA has recently granted accelerated approval to one of these, aducanumab, using reduction of amyloid plaque as a surrogate end point. The rationale for approval and the extent of the clinical benefit from these antibodies are under intense debate. With the aim of informing this debate, we review clinical trial data for drugs that target Aβ from the perspective of the temporal interplay between the two pathognomonic protein aggregates in AD - Aβ plaques and tau neurofibrillary tangles - and their relationship to cognitive impairment, highlighting differences in drug properties that could affect their clinical performance. On this basis, we propose that Aβ pathology drives tau pathology, that amyloid plaque would need to be reduced to a low level (~20 centiloids) to reveal significant clinical benefit and that there will be a lag between the removal of amyloid and the potential to observe a clinical benefit. We conclude that the speed of amyloid removal from the brain by a potential therapy will be important in demonstrating clinical benefit in the context of a clinical trial.

Current and Emerging Strategies for Enhancing Antibody Delivery to the Brain

For the treatment of neurological diseases, achieving sufficient exposure to the brain parenchyma is a critical determinant of drug efficacy. The blood-brain barrier (BBB) functions to tightly control the passage of substances between the bloodstream and the central nervous system, and as such poses a major obstacle that must be overcome for therapeutics to enter the brain. Monoclonal antibodies have emerged as one of the best-selling treatment modalities available in the pharmaceutical market owing to their high target specificity. However, it has been estimated that only 0.1% of peripherally administered antibodies can cross the BBB, contributing to the low success rate of immunotherapy seen in clinical trials for the treatment of neurological diseases. The development of new strategies for antibody delivery across the BBB is thereby crucial to improve immunotherapeutic efficacy. Here, we discuss the current strategies that have been employed to enhance antibody delivery across the BBB. These include (i) focused ultrasound in combination with microbubbles, (ii) engineered bi-specific antibodies, and (iii) nanoparticles. Furthermore, we discuss emerging strategies such as extracellular vesicles with BBB-crossing properties and vectored antibody genes capable of being encapsulated within a BBB delivery vehicle.

A highly-specific fully-human antibody and CAR-T cells targeting CD66e/CEACAM5 are cytotoxic for CD66e-expressing cancer cells in vitro and in vivo

Neuro-endocrine prostate cancer (NEPC) accounts for about 20% of lethal metastatic castration-resistant prostate cancer (CRPC). NEPC has the most aggressive biologic behavior of all prostate cancers and is associated with poor patient outcome. Effective treatment for NEPC is not available because NEPC exhibit distinct cell-surface expression profiles compared to other types of prostate cancer. Recently, the carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) (known as CEA or CD66e) was suggested to be a specific surface protein marker for NEPC. Therefore, we identified a new, fully-human anti-CEACAM5 monoclonal antibody, 1G9, which bound to the most proximal membrane domains, A3 and B3, of CEACAM5 with high affinity and specificity. It shows no off-target binding to other CEACAM family members, membrane distal domains of CEACAM5, or 5800 human membrane proteins. IgG1 1G9 exhibited CEACAM5-specific ADCC activity toward CEACAM5-positive prostate cancer cells in vitro and in vivo. Chimeric antigen receptor T cells (CAR-T) based on scFv 1G9 induced specific and strong antitumor activity in a mouse model of prostate cancer. Our results suggest that IgG1 and CAR-T cells based on 1G9 are promising candidate therapeutics for CEACAM5-positive NEPC and other cancers.

Rescue of a lysosomal storage disorder caused by Grn loss of function with a brain penetrant progranulin biologic

GRN mutations cause frontotemporal dementia (GRN-FTD) due to deficiency in progranulin (PGRN), a lysosomal and secreted protein with unclear function. Here, we found that Grn-/- mice exhibit a global deficiency in bis(monoacylglycero)phosphate (BMP), an endolysosomal phospholipid we identified as a pH-dependent PGRN interactor as well as a redox-sensitive enhancer of lysosomal proteolysis and lipolysis. Grn-/- brains also showed an age-dependent, secondary storage of glucocerebrosidase substrate glucosylsphingosine. We investigated a protein replacement strategy by engineering protein transport vehicle (PTV):PGRN-a recombinant protein linking PGRN to a modified Fc domain that binds human transferrin receptor for enhanced CNS biodistribution. PTV:PGRN rescued various Grn-/- phenotypes in primary murine macrophages and human iPSC-derived microglia, including oxidative stress, lysosomal dysfunction, and endomembrane damage. Peripherally delivered PTV:PGRN corrected levels of BMP, glucosylsphingosine, and disease pathology in Grn-/- CNS, including microgliosis, lipofuscinosis, and neuronal damage. PTV:PGRN thus represents a potential biotherapeutic for GRN-FTD.

Strategies for delivering therapeutics across the blood-brain barrier

Achieving sufficient delivery across the blood-brain barrier is a key challenge in the development of drugs to treat central nervous system (CNS) disorders. This is particularly the case for biopharmaceuticals such as monoclonal antibodies and enzyme replacement therapies, which are largely excluded from the brain following systemic administration. In recent years, increasing research efforts by pharmaceutical and biotechnology companies, academic institutions and public-private consortia have resulted in the evaluation of various technologies developed to deliver therapeutics to the CNS, some of which have entered clinical testing. Here we review recent developments and challenges related to selected blood-brain barrier-crossing strategies - with a focus on non-invasive approaches such as receptor-mediated transcytosis and the use of neurotropic viruses, nanoparticles and exosomes - and analyse their potential in the treatment of CNS disorders.

Therapeutic Advances in Diabetes, Autoimmune, and Neurological Diseases

Since 2015, 170 small molecules, 60 antibody-based entities, 12 peptides, and 15 gene- or cell-therapies have been approved by FDA for diverse disease indications. Recent advancement in medicine is facilitated by identification of new targets and mechanisms of actions, advancement in discovery and development platforms, and the emergence of novel technologies. Early disease detection, precision intervention, and personalized treatments have revolutionized patient care in the last decade. In this review, we provide a comprehensive overview of current and emerging therapeutic modalities developed in the recent years. We focus on nine diseases in three major therapeutics areas, diabetes, autoimmune, and neurological disorders. The pathogenesis of each disease at physiological and molecular levels is discussed and recently approved drugs as well as drugs in the clinic are presented.

Structural insights into the inhibition of glycine reuptake

The human glycine transporter 1 (GlyT1) regulates glycine-mediated neuronal excitation and inhibition through the sodium- and chloride-dependent reuptake of glycine^1-3. Inhibition of GlyT1 prolongs neurotransmitter signalling, and has long been a key strategy in the development of therapies for a broad range of disorders of the central nervous system, including schizophrenia and cognitive impairments⁴. Here, using a synthetic single-domain antibody (sybody) and serial synchrotron crystallography, we have determined the structure of GlyT1 in complex with a benzoylpiperazine chemotype inhibitor at 3.4 Å resolution. We find that the inhibitor locks GlyT1 in an inward-open conformation and binds at the intracellular gate of the release pathway, overlapping with the glycine-release site. The inhibitor is likely to reach GlyT1 from the cytoplasmic leaflet of the plasma membrane. Our results define the mechanism of inhibition and enable the rational design of new, clinically efficacious GlyT1 inhibitors.

Monoclonal Antibodies as Neurological Therapeutics

Over the last 30 years the role of monoclonal antibodies in therapeutics has increased enormously, revolutionizing treatment in most medical specialties, including neurology. Monoclonal antibodies are key therapeutic agents for several neurological conditions with diverse pathophysiological mechanisms, including multiple sclerosis, migraines and neuromuscular disease. In addition, a great number of monoclonal antibodies against several targets are being investigated for many more neurological diseases, which reflects our advances in understanding the pathogenesis of these diseases. Untangling the molecular mechanisms of disease allows monoclonal antibodies to block disease pathways accurately and efficiently with exceptional target specificity, minimizing non-specific effects. On the other hand, accumulating experience shows that monoclonal antibodies may carry class-specific and target-associated risks. This article provides an overview of different types of monoclonal antibodies and their characteristics and reviews monoclonal antibodies currently in use or under development for neurological disease.

Ten years in the making: application of CrossMab technology for the development of therapeutic bispecific antibodies and antibody fusion proteins

Bispecific antibodies have recently attracted intense interest. CrossMab technology was described in 2011 as novel approach enabling correct antibody light-chain association with their respective heavy chain in bispecific antibodies, together with methods enabling correct heavy-chain association using existing pairs of antibodies. Since the original description, CrossMab technology has evolved in the past decade into one of the most mature, versatile, and broadly applied technologies in the field, and nearly 20 bispecific antibodies based on CrossMab technology developed by Roche and others have entered clinical trials. The most advanced of these are the Ang-2/VEGF bispecific antibody faricimab, currently undergoing regulatory review, and the CD20/CD3 T cell bispecific antibody glofitamab, currently in pivotal Phase 3 trials. In this review, we introduce the principles of CrossMab technology, including its application for the generation of bi-/multispecific antibodies with different geometries and mechanisms of action, and provide an overview of CrossMab-based therapeutics in clinical trials.

Format chain exchange (FORCE) for high-throughput generation of bispecific antibodies in combinatorial binder-format matrices

Generation of bispecific antibodies (bsAbs) requires a combination of compatible binders in formats that support desired functionalities. Here, we report that bsAb-matrices can be generated by Format Chain Exchange (FORCE), enabling screening of combinatorial binder/format spaces. Input molecules for generation of bi/multi-valent bsAbs are monospecific entities similar to knob-into-hole half-antibodies, yet with complementary CH3-interface-modulated and affinity-tagged dummy-chains. These contain mutations that lead to limited interface repulsions without compromising expression or biophysical properties of educts. Mild reduction of combinations of educts triggers spontaneous chain-exchange reactions driven by partially flawed CH3-educt interfaces resolving to perfect complementarity. This generates large bsAb matrices harboring different binders in multiple formats. Benign biophysical properties and good expression yields of educts, combined with simplicity of purification enables process automation. Examples that demonstrate the relevance of screening binder/format combinations are provided as a matrix of bsAbs that simultaneously bind Her1/Her2 and DR5 without encountering binder or format-inflicted interferences.

Bispecific antibodies have been generated in many different formats and it is becoming clear that rational design alone cannot create optimal functionalities. Here the authors introduce the high throughput methodology, Format Chain Exchange (FORCE), to enable combinatorial generation of bispecific antibodies.

SPECT imaging of distribution and retention of a brain-penetrating bispecific amyloid-β antibody in a mouse model of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) immunotherapy with antibodies targeting amyloid-β (Aβ) has been extensively explored in clinical trials. The aim of this study was to study the long-term brain distribution of two radiolabeled monoclonal Aβ antibody variants - RmAb158, the recombinant murine version of BAN2401, which has recently demonstrated amyloid removal and reduced cognitive decline in AD patients, and the bispecific RmAb158-scFv8D3, which has been engineered for enhanced brain uptake via transferrin receptor-mediated transcytosis.

METHODS

A single intravenous injection of iodine-125 (¹²⁵I)-labeled RmAb158-scFv8D3 or RmAb158 was administered to AD transgenic mice (tg-ArcSwe). In vivo single-photon emission computed tomography was used to investigate brain retention and intrabrain distribution of the antibodies over a period of 4 weeks. Activity in blood and brain tissue was measured ex vivo and autoradiography was performed in combination with Aβ and CD31 immunostaining to investigate the intrabrain distribution of the antibodies and their interactions with Aβ.

RESULTS

Despite faster blood clearance, [¹²⁵I]RmAb158-scFv8D3 displayed higher brain exposure than [¹²⁵I]RmAb158 throughout the study. The brain distribution of [¹²⁵I]RmAb158-scFv8D3 was more uniform and coincided with parenchymal Aβ pathology, while [¹²⁵I]RmAb158 displayed a more scattered distribution pattern and accumulated in central parts of the brain at later times. Ex vivo autoradiography indicated greater vascular escape and parenchymal Aβ interactions for [¹²⁵I]RmAb158-scFv8D3, whereas [¹²⁵I]RmAb158 displayed retention and Aβ interactions in lateral ventricles.

CONCLUSIONS

The high brain uptake and uniform intrabrain distribution of RmAb158-scFv8D3 highlight the benefits of receptor-mediated transcytosis for antibody-based brain imaging. Moreover, it suggests that the alternative transport route of the bispecific antibody contributes to improved efficacy of brain-directed immunotherapy.

Acute and Chronic Dosing of a High-Affinity Rat/Mouse Chimeric Transferrin Receptor Antibody in Mice

Non-invasive brain delivery of neurotherapeutics is challenging due to the blood-brain barrier. The revived interest in transferrin receptor antibodies (TfRMAbs) as brain drug-delivery vectors has revealed the effect of dosing regimen, valency, and affinity on brain uptake, TfR expression, and Fc-effector function side effects. These studies have primarily used monovalent TfRMAbs with a human constant region following acute intravenous dosing in mice. The effects of a high-affinity bivalent TfRMAb with a murine constant region, without a fusion partner, following extravascular dosing in mice are, however, not well characterized. Here we elucidate the plasma pharmacokinetics and safety of a high-affinity bivalent TfRMAb with a murine constant region following acute and chronic subcutaneous dosing in adult C57BL/6J male mice. Mice received a single (acute dosing) 3 mg/kg dose, or were treated for four weeks (chronic dosing). TfRMAb and control IgG1 significantly altered reticulocyte counts following acute and chronic dosing, while other hematologic parameters showed minimal change. Chronic TfRMAb dosing did not alter plasma- and brain-iron measurements, nor brain TfR levels, however, it significantly increased splenic-TfR and -iron. Plasma concentrations of TfRMAb were significantly lower in mice chronically treated with IgG1 or TfRMAb. Overall, no injection related reactions were observed in mice.

Characterization of basigin monoclonal antibodies for receptor-mediated drug delivery to the brain

The brain uptake of biotherapeutics for brain diseases is hindered by the blood–brain barrier (BBB). The BBB selectively regulates the transport of large molecules into the brain and thereby maintains brain homeostasis. Receptor-mediated transcytosis (RMT) is one mechanism to deliver essential proteins into the brain parenchyma. Receptors expressed in the brain endothelial cells have been explored to ferry therapeutic antibodies across the BBB in bifunctional antibody formats. In this study, we generated and characterized monoclonal antibodies (mAbs) binding to the basigin receptor, which recently has been proposed as a target for RMT across the BBB. Antibody binding properties such as affinity have been demonstrated to be important factors for transcytosis capability and efficiency. Nevertheless, studies of basigin mAb properties' effect on RMT are limited. Here we characterize different basigin mAbs for their ability to associate with and subsequently internalize human brain endothelial cells. The mAbs were profiled to determine whether receptor binding epitope and affinity affected receptor-mediated uptake efficiency. By competitive epitope binning studies, basigin mAbs were categorized into five epitope bins. mAbs from three of the epitope bins demonstrated properties required for RMT candidates judged by binding characteristics and their superior level of internalization in human brain endothelial cells.