Current and Emerging Strategies for Enhancing Antibody Delivery to the Brain

Amyloid-β-targeting immunotherapies for Alzheimer's disease

Recent advances in clinical passive immunotherapy have provided compelling evidence that eliminating amyloid-β (Aβ) slows cognitive decline in Alzheimer's disease (AD). However, the modest benefits and side effects observed in clinical trials indicate that current immunotherapy therapy is not a panacea, highlighting the need for a deeper understanding of AD mechanisms and the significance of early intervention through optimized immunotherapy or immunoprevention. This review focuses on the centrality of Aβ pathology in AD and summarizes recent clinical progress in passive and active immunotherapies targeting Aβ, discussing their lessons and failures to inform future anti-Aβ biotherapeutics design. Various delivery strategies to optimize Aβ-targeting immunotherapies are outlined, highlighting their benefits and drawbacks in overcoming challenges such as poor stability and limited tissue accessibility of anti-Aβ biotherapeutics. Additionally, the perspectives and challenges of immunotherapy and immunoprevention targeting Aβ are concluded in the end, aiming to guide the development of next-generation anti-Aβ immunotherapeutic agents towards improved efficacy and safety.

Human-derived monoclonal autoantibodies as interrogators of cellular proteotypes in the brain

A major aim of neuroscience is to identify and model the functional properties of neural cells whose dysfunction underlie neuropsychiatric illness. In this article, we propose that human-derived monoclonal autoantibodies (HD-mAbs) are well positioned to selectively target and manipulate neural subpopulations as defined by their protein expression; that is, cellular proteotypes. Recent technical advances allow for efficient cloning of autoantibodies from neuropsychiatric patients. These HD-mAbs can be introduced into animal models to gain biological and pathobiological insights about neural proteotypes of interest. Protein engineering can be used to modify, enhance, silence, or confer new functional properties to native HD-mAbs, thereby enhancing their versatility. Finally, we discuss the challenges and limitations confronting HD-mAbs as experimental research tools for neuroscience.

Chitosan-Tricarbocyanine-Based Nanogels Were Able to Cross the Blood-Brain Barrier Showing Its Potential as a Targeted Site Delivery Agent

Targeting drugs to the central nervous system (CNS) is challenging due to the presence of the blood-brain barrier (BBB). The cutting edge in nanotechnology generates optimism to overcome the growing challenges in biomedical sciences through the effective engineering of nanogels. The primary objective of the present report was to develop and characterize a biocompatible natural chitosan (CS)-based NG that can be tracked thanks to the tricarbocyanine (CNN) fluorescent probe addition on the biopolymer backbone. FTIR shed light on the chemical groups involved in the CS and CNN interactions and between CNN-CS and tripolyphosphate, the cross-linking agent. Both in vitro and in vivo experiments were carried out to determine if CS-NGs can be utilized as therapeutic delivery vehicles directed towards the brain. An ionic gelation method was chosen to generate cationic CNN-CS-NG. DLS and TEM confirmed that these entities' sizes fell into the nanoscale. CNN-CS-NG was found to be non-cytotoxic, as determined in the SH-SY5Y neuroblastoma cell line through biocompatibility assays. After cellular internalization, the occurrence of an endo-lysosomal escape (a crucial event for an efficient drug delivery) of CNN-CS-NG was detected. Furthermore, CNN-CS-NG administered intraperitoneally to female CF-1 mice were detected in different brain regions after 2 h of administration, using fluorescence microscopy. To conclude, the obtained findings in the present report can be useful in the field of neuro-nanomedicine when designing drug vehicles with the purpose of delivering drugs to the CNS.

Exosome-mediated delivery platform of biomacromolecules into the brain: Cetuximab in combination with doxorubicin for glioblastoma therapy

Monoclonal antibodies (mAbs) have become the predominant treatment modality for various diseases due to their high affinity and specificity. Although antibodies also have great potential for neurological diseases, they couldn't fully meet the therapeutic requirements due to their high molecular weight and limitations in crossing the blood-brain barrier (BBB). Herein, an innovative strategy based on exosomes (Exos) platform was developed to enhance the delivery of cetuximab (CTX) into the brain, and in combination with doxorubicin (DOX) for the synergistic targeted therapy of glioblastoma (GBM). The in vitro/vivo experiments have shown that exosomes could effectively promote BBB penetration and increase the content of CTX in glioma cells and brain lesions. Cytotoxicity and wound healing experiments have shown that CTX-Exo-DOX could significantly inhibit the proliferation of tumor cells. Finally, in vivo results showed that CTX-Exo-DOX significantly prolonged the survival time of tumor-bearing rats to 28 days, which was 1.47 times that of the DOX group. In summary, exosomes could deliver more antibodies into the brain, and CTX-Exo-DOX is a promising co-delivery system for the treatment of GBM. The results of this study will also provide a prospective strategy for antibody drugs in the treatment of neurological diseases.

The solute carrier SLC7A1 may act as a protein transporter at the blood-brain barrier

Despite extensive research, targeted delivery of substances to the brain still poses a great challenge due to the selectivity of the blood-brain barrier (BBB). Most molecules require either carrier- or receptor-mediated transport systems to reach the central nervous system (CNS). These transport systems form attractive routes for the delivery of therapeutics into the CNS, yet the number of known brain endothelium-enriched receptors allowing the transport of large molecules into the brain is scarce. Therefore, to identify novel BBB targets, we combined transcriptomic analysis of human and murine brain endothelium and performed a complex screening of BBB-enriched genes according to established selection criteria. As a result, we propose the high-affinity cationic amino acid transporter 1 (SLC7A1) as a novel candidate for transport of large molecules across the BBB. Using RNA sequencing and in situ hybridization assays, we demonstrated elevated SLC7A1 gene expression in both human and mouse brain endothelium. Moreover, we confirmed SLC7A1 protein expression in brain vasculature of both young and aged mice. To assess the potential of SLC7A1 as a transporter for larger proteins, we performed internalization and transcytosis studies using a radiolabelled or fluorophore-labelled anti-SLC7A1 antibody. Our results showed that SLC7A1 internalised a SLC7A1-specific antibody in human colorectal carcinoma (HCT116) cells. Moreover, transcytosis studies in both immortalised human brain endothelial (hCMEC/D3) cells and primary mouse brain endothelial cells clearly demonstrated that SLC7A1 effectively transported the SLC7A1-specific antibody from luminal to abluminal side. Therefore, here in this study, we present for the first time the SLC7A1 as a novel candidate for transport of larger molecules across the BBB.

Nanoparticle-Based Combinational Strategies for Overcoming the Blood-Brain Barrier and Blood-Tumor Barrier

The blood-brain barrier (BBB) and blood-tumor barrier (BTB) pose substantial challenges to efficacious drug delivery for glioblastoma multiforme (GBM), a primary brain tumor with poor prognosis. Nanoparticle-based combinational strategies have emerged as promising modalities to overcome these barriers and enhance drug penetration into the brain parenchyma. This review discusses various nanoparticle-based combinatorial approaches that combine nanoparticles with cell-based drug delivery, viral drug delivery, focused ultrasound, magnetic field, and intranasal drug delivery to enhance drug permeability across the BBB and BTB. Cell-based drug delivery involves using engineered cells as carriers for nanoparticles, taking advantage of their intrinsic migratory and homing capabilities to facilitate the transport of therapeutic payloads across BBB and BTB. Viral drug delivery uses engineered viral vectors to deliver therapeutic genes or payloads to specific cells within the GBM microenvironment. Focused ultrasound, coupled with microbubbles or nanoparticles, can temporarily disrupt the BBB to increase drug permeability. Magnetic field-guided drug delivery exploits magnetic nanoparticles to facilitate targeted drug delivery under an external magnetic field. Intranasal drug delivery offers a minimally invasive avenue to bypass the BBB and deliver therapeutic agents directly to the brain via olfactory and trigeminal pathways. By combining these strategies, synergistic effects can enhance drug delivery efficiency, improve therapeutic efficacy, and reduce off-target effects. Future research should focus on optimizing nanoparticle design, exploring new combination strategies, and advancing preclinical and clinical investigations to promote the translation of nanoparticle-based combination therapies for GBM.

Targeting cerebral diseases with enhanced delivery of therapeutic proteins across the blood-brain barrier

INTRODUCTION

Cerebral diseases have been threatening public physical and psychological health in the recent years. With the existence of the blood-brain barrier (BBB), it is particularly hard for therapeutic proteins like peptides, enzymes, antibodies, etc. to enter the central nervous system (CNS) and function in diagnosis and treatment in cerebral diseases. Fortunately, the past decade has witnessed some emerging strategies of delivering macromolecular therapeutic proteins across the BBB.

AREAS COVERED

Based on the structure, functions, and substances transport mechanisms, various enhanced delivery strategies of therapeutic proteins were reviewed, categorized by molecule-mediated delivery strategies, carrier-mediated delivery strategies, and other delivery strategies.

EXPERT OPINION

As for molecule-mediated delivery strategies, development of genetic engineering technology, optimization of protein expression and purification techniques, and mature of quality control systems all help to realize large-scale production of recombinant antibodies, making it possible to apply to the clinical practice. In terms of carrier-mediated delivery strategies and others, although nano-carriers/adeno-associated virus (AAV) are also promising candidates for delivering therapeutic proteins or genes across the BBB, some issues still remain to be further investigated, including safety concerns related to applied materials, large-scale production costs, quality control standards, combination therapies with auxiliary delivery strategies like focused ultrasound, etc.

The Glioblastoma Landscape: Hallmarks of Disease, Therapeutic Resistance, and Treatment Opportunities

Malignant brain tumors are aggressive and difficult to treat. Glioblastoma is the most common and lethal form of primary brain tumor, often found in patients with no genetic predisposition. The median life expectancy for individuals diagnosed with this condition is 6 months to 2 years and there is no known cure. New paradigms in cancer biology implicate a small subset of tumor cells in initiating and sustaining these incurable brain tumors. Here, we discuss the heterogenous nature of glioblastoma and theories behind its capacity for therapy resistance and recurrence. Within the cancer landscape, cancer stem cells are thought to be both tumor initiators and major contributors to tumor heterogeneity and therapy evasion and such cells have been identified in glioblastoma. At the cellular level, disruptions in the delicate balance between differentiation and self-renewal spur transformation and support tumor growth. While rapidly dividing cells are more sensitive to elimination by traditional treatments, glioblastoma stem cells evade these measures through slow division and reversible exit from the cell cycle. At the molecular level, glioblastoma tumor cells exploit several signaling pathways to evade conventional therapies through improved DNA repair mechanisms and a flexible state of senescence. We examine these common evasion techniques while discussing potential molecular approaches to better target these deadly tumors. Equally important, the presented information encourages the idea of augmenting conventional treatments with novel glioblastoma stem cell-directed therapies, as eliminating these harmful progenitors holds great potential to modulate tumor recurrence.

The Dawn of a New Era: Targeting the "Undruggables" with Antibody-Based Therapeutics

The high selectivity and affinity of antibodies toward their antigens have made them a highly valuable tool in disease therapy, diagnosis, and basic research. A plethora of chemical and genetic approaches have been devised to make antibodies accessible to more "undruggable" targets and equipped with new functions of illustrating or regulating biological processes more precisely. In this Review, in addition to introducing how naked antibodies and various antibody conjugates (such as antibody-drug conjugates, antibody-oligonucleotide conjugates, antibody-enzyme conjugates, etc.) work in therapeutic applications, special attention has been paid to how chemistry tools have helped to optimize the therapeutic outcome (i.e., with enhanced efficacy and reduced side effects) or facilitate the multifunctionalization of antibodies, with a focus on emerging fields such as targeted protein degradation, real-time live-cell imaging, catalytic labeling or decaging with spatiotemporal control as well as the engagement of antibodies inside cells. With advances in modern chemistry and biotechnology, well-designed antibodies and their derivatives via size miniaturization or multifunctionalization together with efficient delivery systems have emerged, which have gradually improved our understanding of important biological processes and paved the way to pursue novel targets for potential treatments of various diseases.

CD33 isoforms in microglia and Alzheimer's disease: Friend and foe

Alzheimer's disease (AD) is the most common form of neurodegenerative disease and is considered the main cause of dementia worldwide. Genome-wide association studies combined with integrated analysis of functional datasets support a critical role for microglia in AD pathogenesis, identifying them as important potential therapeutic targets. The ability of immunomodulatory receptors on microglia to control the response to pathogenic amyloid-β aggregates has gained significant interest. Siglec-3, also known as CD33, is one of these immunomodulatory receptors expressed on microglia that has been identified as an AD susceptibility factor. Here, we review recent advances made in understanding the multifaceted roles that CD33 plays in microglia with emphasis on two human-specific CD33 isoforms that differentially correlate with AD susceptibility. We also describe several different therapeutic approaches for targeting CD33 that have been advanced for the purpose of skewing microglial cell responses.

Reconsidering the role of blood-brain barrier in Alzheimer's disease: From delivery to target

The existence of a selective blood-brain barrier (BBB) and neurovascular coupling are two unique central nervous system vasculature features that result in an intimate relationship between neurons, glia, and blood vessels. This leads to a significant pathophysiological overlap between neurodegenerative and cerebrovascular diseases. Alzheimer's disease (AD) is the most prevalent neurodegenerative disease whose pathogenesis is still to be unveiled but has mostly been explored under the light of the amyloid-cascade hypothesis. Either as a trigger, bystander, or consequence of neurodegeneration, vascular dysfunction is an early component of the pathological conundrum of AD. The anatomical and functional substrate of this neurovascular degeneration is the BBB, a dynamic and semi-permeable interface between blood and the central nervous system that has consistently been shown to be defective. Several molecular and genetic changes have been demonstrated to mediate vascular dysfunction and BBB disruption in AD. The isoform ε4 of Apolipoprotein E is at the same time the strongest genetic risk factor for AD and a known promoter of BBB dysfunction. Low-density lipoprotein receptor-related protein 1 (LRP-1), P-glycoprotein, and receptor for advanced glycation end products (RAGE) are examples of BBB transporters implicated in its pathogenesis due to their role in the trafficking of amyloid-β. This disease is currently devoid of strategies that change the natural course of this burdening illness. This unsuccess may partly be explained by our misunderstanding of the disease pathogenesis and our inability to develop drugs that are effectively delivered to the brain. BBB may represent a therapeutic opportunity as a target itself or as a therapeutic vehicle. In this review, we aim to explore the role of BBB in the pathogenesis of AD including the genetic background and detail how it can be targeted in future therapeutic research.

Ultrasonic-induced reversible blood–brain barrier opening: Safety evaluation into the cellular level

An important function of the blood–brain barrier (BBB) is to protect the central nervous system and maintain its homeostasis, but it is also a major barrier to the intervention and treatment of neurological diseases. Our study aimed at opening the BBB using a noninvasive method, focused ultrasound, screening for 16 different parameter combinations of frequency, peak voltage (Ppeak) and irradiation time. Comparing the results of hematoxylin–eosin staining, serum oxidative damage factor and TUNEL staining under various conditions, we obtained a parameter combination that did not lead to oxidative stress injury and apoptosis: 0.8 mHz + 900 mVpp + 90 s. It will be used as a safety parameter for BBB opening treatment of Parkinson’s disease in our subsequent experiments. In addition, the closing time after the BBB opening was verified in magnetic resonance imaging contrast examination and at the tissue level. It is worth mentioning that, different from previous studies, we focused on damage assessment at cellular and molecular levels.

Origin, activation, and targeted therapy of glioma-associated macrophages

The glioma tumor microenvironment plays a crucial role in the development, occurrence, and treatment of gliomas. Glioma-associated macrophages (GAMs) are the most widely infiltrated immune cells in the tumor microenvironment (TME) and one of the major cell populations that exert immune functions. GAMs typically originate from two cell types-brain-resident microglia (BRM) and bone marrow-derived monocytes (BMDM), depending on a variety of cytokines for recruitment and activation. GAMs mainly contain two functionally and morphologically distinct activation types- classically activated M1 macrophages (antitumor/immunostimulatory) and alternatively activated M2 macrophages (protumor/immunosuppressive). GAMs have been shown to affect multiple biological functions of gliomas, including promoting tumor growth and invasion, angiogenesis, energy metabolism, and treatment resistance. Both M1 and M2 macrophages are highly plastic and can polarize or interconvert under various malignant conditions. As the relationship between GAMs and gliomas has become more apparent, GAMs have long been one of the promising targets for glioma therapy, and many studies have demonstrated the therapeutic potential of this target. Here, we review the origin and activation of GAMs in gliomas, how they regulate tumor development and response to therapies, and current glioma therapeutic strategies targeting GAMs.

Ultrasound-mediated delivery of novel tau-specific monoclonal antibody enhances brain uptake but not therapeutic efficacy

Tau-specific immunotherapy is an attractive strategy for the treatment of Alzheimer's disease and other tauopathies. However, effectively targeting tau in the brain remains a considerable challenge due to the restrictive nature of the blood-brain barrier (BBB), which excludes an estimated >99% of peripherally administered antibodies. However, their transport across the BBB can be facilitated by a novel modality, low-intensity scanning ultrasound used in combination with intravenously injected microbubbles (SUS^+MB). We have previously shown that SUS^+MB-mediated delivery of a tau-specific antibody in a single-chain (scFv) format to tau transgenic mice enhanced brain and neuronal uptake and subsequently, reduced tau pathology and improved behavioural outcomes to a larger extent than either scFv or SUS^+MB on its own. Here we generated a novel tau-specific monoclonal antibody, RNF5, and validated it in its IgG format in the presence or absence of SUS^+MB by treating K369I tau transgenic K3 mice once weekly for 12 weeks. We found that both RNF5 and SUS^+MB treatments on their own significantly reduced tau pathology. In the combination group (RNF5 + SUS^+MB), however, despite increased antibody localization in the brain, there were no further reductions in tau pathology when compared to RNF5 treatment alone. Furthermore, following SUS^+MB, RNF5 accumulated heavily within cells across the pyramidal cell layer of the hippocampus, that were negative for MAP2 and p-tau, suggesting that SUS^+MB may not facilitate enhanced RNF5 engagement of intraneuronal tau. Overall, our new findings reveal the complexities of combining tau immunotherapy with SUS^+MB and challenge the view that this is a straight-forward approach.

A TNFR2-Specific TNF Fusion Protein With Improved In Vivo Activity

Tumor necrosis factor (TNF) receptor-2 (TNFR2) has attracted considerable interest as a target for immunotherapy. Indeed, using oligomeric fusion proteins of single chain-encoded TNFR2-specific TNF mutants (scTNF80), expansion of regulatory T cells and therapeutic activity could be demonstrated in various autoinflammatory diseases, including graft-versus-host disease (GvHD), experimental autoimmune encephalomyelitis (EAE) and collagen-induced arthritis (CIA). With the aim to improve the in vivo availability of TNFR2-specific TNF fusion proteins, we used here the neonatal Fc receptor (FcRn)-interacting IgG1 molecule as an oligomerizing building block and generated a new TNFR2 agonist with improved serum retention and superior in vivo activity.

Methods

Single-chain encoded murine TNF80 trimers (sc(mu)TNF80) were fused to the C-terminus of an in mice irrelevant IgG1 molecule carrying the N297A mutation which avoids/minimizes interaction with Fcγ-receptors (FcγRs). The fusion protein obtained (irrIgG1(N297A)-sc(mu)TNF80), termed NewSTAR2 (New selective TNF-based agonist of TNF receptor 2), was analyzed with respect to activity, productivity, serum retention and in vitro and in vivo activity. STAR2 (TNC-sc(mu)TNF80 or selective TNF-based agonist of TNF receptor 2), a well-established highly active nonameric TNFR2-specific variant, served as benchmark. NewSTAR2 was assessed in various in vitro and in vivo systems.

Results

STAR2 (TNC-sc(mu)TNF80) and NewSTAR2 (irrIgG1(N297A)-sc(mu)TNF80) revealed comparable in vitro activity. The novel domain architecture of NewSTAR2 significantly improved serum retention compared to STAR2, which correlated with efficient binding to FcRn. A single injection of NewSTAR2 enhanced regulatory T cell (Treg) suppressive activity and increased Treg numbers by > 300% in vivo 5 days after treatment. Treg numbers remained as high as 200% for about 10 days. Furthermore, a single in vivo treatment with NewSTAR2 upregulated the adenosine-regulating ectoenzyme CD39 and other activation markers on Tregs. TNFR2-stimulated Tregs proved to be more suppressive than unstimulated Tregs, reducing conventional T cell (Tcon) proliferation and expression of activation markers in vitro. Finally, singular preemptive NewSTAR2 administration five days before allogeneic hematopoietic cell transplantation (allo-HCT) protected mice from acute GvHD.

Conclusions

NewSTAR2 represents a next generation ligand-based TNFR2 agonist, which is efficiently produced, exhibits improved pharmacokinetic properties and high serum retention with superior in vivo activity exerting powerful protective effects against acute GvHD.