Comparison of blood-brain barrier transport of glial-derived neurotrophic factor (GDNF) and an IgG-GDNF fusion protein in the rhesus monkey

Treatment of Parkinson's disease with biologics that penetrate the blood-brain barrier via receptor-mediated transport

Parkinson's disease (PD) is characterized by neurodegeneration of nigral-striatal neurons in parallel with the formation of intra-neuronal α-synuclein aggregates, and these processes are exacerbated by neuro-inflammation. All 3 components of PD pathology are potentially treatable with biologics. Neurotrophins, such as glial derived neurotrophic factor or erythropoietin, can promote neural repair. Therapeutic antibodies can lead to disaggregation of α-synuclein neuronal inclusions. Decoy receptors can block the activity of pro-inflammatory cytokines in brain. However, these biologic drugs do not cross the blood-brain barrier (BBB). Biologics can be made transportable through the BBB following the re-engineering of the biologic as an IgG fusion protein, where the IgG domain targets an endogenous receptor-mediated transcytosis (RMT) system within the BBB, such as the insulin receptor or transferrin receptor. The receptor-specific antibody domain of the fusion protein acts as a molecular Trojan horse to ferry the biologic into brain via the BBB RMT pathway. This review describes the re-engineering of all 3 classes of biologics (neurotrophins, decoy receptor, therapeutic antibodies) for BBB delivery and treatment of PD. Targeting the RMT pathway at the BBB also enables non-viral gene therapy of PD using lipid nanoparticles (LNP) encapsulated with plasmid DNA encoding therapeutic genes. The surface of the lipid nanoparticle is conjugated with a receptor-specific IgG that triggers RMT of the LNP across the BBB in vivo.

VHHs as tools for therapeutic protein delivery to the central nervous system

Background

The blood brain barrier (BBB) limits the therapeutic perspective for central nervous system (CNS) disorders. Previously we found an anti-mouse transferrin receptor (TfR) VHH (Nb62) that was able to deliver a biologically active neuropeptide into the CNS in mice. Here, we aimed to test its potential to shuttle a therapeutic relevant cargo. Since this VHH could not recognize the human TfR and hence its translational potential is limited, we also aimed to find and validate an anti-human transferrin VHH to deliver a therapeutic cargo into the CNS.

Methods

Alpaca immunizations with human TfR, and subsequent phage selection and screening for human TfR binding VHHs was performed to find a human TfR specific VHH (Nb188). Its ability to cross the BBB was determined by fusing it to neurotensin, a neuropeptide that reduces body temperature when present in the CNS but is not able to cross the BBB on its own. Next, the anti–β-secretase 1 (BACE1) 1A11 Fab and Nb62 or Nb188 were fused to an Fc domain to generate heterodimeric antibodies (1A11AM-Nb62 and 1A11AM-Nb188). These were then administered intravenously in wild-type mice and in mice in which the murine apical domain of the TfR was replaced by the human apical domain (hAPI KI). Pharmacokinetic and pharmacodynamic (PK/PD) studies were performed to assess the concentration of the heterodimeric antibodies in the brain over time and the ability to inhibit brain-specific BACE1 by analysing the brain levels of Aβ_1–40.

Results

Selections and screening of a phage library resulted in the discovery of an anti-human TfR VHH (Nb188). Fusion of Nb188 to neurotensin induced hypothermia after intravenous injections in hAPI KI mice. In addition, systemic administration 1A11AM-Nb62 and 1A11AM-Nb188 fusions were able to reduce Aβ_1-40 levels in the brain whereas 1A11AM fused to an irrelevant VHH did not. A PK/PD experiment showed that this effect could last for 3 days.

Conclusion

We have discovered an anti-human TfR specific VHH that is able to reach the CNS when administered systemically. In addition, both the currently discovered anti-human TfR VHH and the previously identified mouse-specific anti-TfR VHH, are both able to shuttle a therapeutically relevant cargo into the CNS. We suggest the mouse-specific VHH as a valuable research tool in mice and the human-specific VHH as a moiety to enhance the delivery efficiency of therapeutics into the CNS in human patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-022-00374-4.

IgG Fusion Proteins for Brain Delivery of Biologics via Blood-Brain Barrier Receptor-Mediated Transport

The treatment of neurological disorders with large-molecule biotherapeutics requires that the therapeutic drug be transported across the blood–brain barrier (BBB). However, recombinant biotherapeutics, such as neurotrophins, enzymes, decoy receptors, and monoclonal antibodies (MAb), do not cross the BBB. These biotherapeutics can be re-engineered as brain-penetrating bifunctional IgG fusion proteins. These recombinant proteins comprise two domains, the transport domain and the therapeutic domain, respectively. The transport domain is an MAb that acts as a molecular Trojan horse by targeting a BBB-specific endogenous receptor that induces receptor-mediated transcytosis into the brain, such as the human insulin receptor (HIR) or the transferrin receptor (TfR). The therapeutic domain of the IgG fusion protein exerts its pharmacological effect in the brain once across the BBB. A generation of bifunctional IgG fusion proteins has been engineered using genetically engineered MAbs directed to either the BBB HIR or TfR as the transport domain. These IgG fusion proteins were validated in animal models of lysosomal storage disorders; acute brain conditions, such as stroke; or chronic neurodegeneration, such as Parkinson’s disease and Alzheimer’s disease. Human phase I–III clinical trials were also completed for Hurler MPSI and Hunter MPSII using brain-penetrating IgG-iduronidase and -iduronate-2-sulfatase fusion protein, respectively.

Altered levels of interleukins and neurotrophic growth factors in mood disorders and suicidality: an analysis from periphery to central nervous system

Interleukins and neurotrophins levels are altered in the periphery of patients with major depression and suicidal behavior, however it is not clear if similar abnormalities occur in the central nervous system. Our objective was to examine the association of IL-6, IL-1β, BDNF, and GDNF levels between postmortem plasma, cerebrospinal fluid (CSF), and brain tissue in a heterogeneous diagnostic subject groups including normal controls, mood disorders only, mood disorders with AUD/SUD (alcohol abuse disorder, substance abuse disorder), and AUD/SUD without mood disorders. To address these questions we collected postmortem plasma (n = 29), CSF (n = 28), and brain (BA10) (n = 57) samples from individuals with mood disorder, mood disorder with AUD/SUD, AUD/SUD and normal controls. These samples were analyzed using a multiplex based luminex assay with a customized 4-plex cytokine/interleukins- IL-6, IL-1β, BDNF, and GDNF human acute phase based on xMAP technology platform. Protein levels were determined using a Luminex 200 instrument equipped with Xponent-analyzing software. We observed IL-6 (p = 2.1e-07), and GDNF (p = 0.046) were significantly correlated between brain and CSF. In addition, IL-6 (p = 0.031), were significantly correlated between brain and plasma. Overall diagnostic group analysis showed a significant difference with brain GDNF, p = 0.0106. Pairwise comparisons showed that GDNF level is-39.9 ± 12 pg/ml, p = 0.0106, was significantly higher than in the brains derived from mood disorders compared to normal controls, -23.8 ± 5.5 pg/ml, p = 0.034. Brain BDNF was higher in suicide (p = 0.0023), males compared to females (p = 0.017), and psychiatric medication treated vs. non-treated (p = 0.005) individuals. Overall, we demonstrate that blood IL-6, GDNF and BDNF could be informative peripheral biomarkers of brain biology associated with mood disorders, substance disorders, and suicide.

Interplay of BDNF and GDNF in the Mature Spinal Somatosensory System and Its Potential Therapeutic Relevance

The growth factors BDNF and GDNF are gaining more and more attention as modulators of synaptic transmission in the mature central nervous system (CNS). The two molecules undergo a regulated secretion in neurons and may be anterogradely transported to terminals where they can positively or negatively modulate fast synaptic transmission. There is today a wide consensus on the role of BDNF as a pro-nociceptive modulator, as the neurotrophin has an important part in the initiation and maintenance of inflammatory, chronic, and/or neuropathic pain at the peripheral and central level. At the spinal level, BDNF intervenes in the regulation of chloride equilibrium potential, decreases the excitatory synaptic drive to inhibitory neurons, with complex changes in GABAergic/glycinergic synaptic transmission, and increases excitatory transmission in the superficial dorsal horn. Differently from BDNF, the role of GDNF still remains to be unraveled in full. This review resumes the current literature on the interplay between BDNF and GDNF in the regulation of nociceptive neurotransmission in the superficial dorsal horn of the spinal cord. We will first discuss the circuitries involved in such a regulation, as well as the reciprocal interactions between the two factors in nociceptive pathways. The development of small molecules specifically targeting BDNF, GDNF and/or downstream effectors is opening new perspectives for investigating these neurotrophic factors as modulators of nociceptive transmission and chronic pain. Therefore, we will finally consider the molecules of (potential) pharmacological relevance for tackling normal and pathological pain.

Drug Delivery Strategies to Overcome the Blood-Brain Barrier (BBB)

The brain capillary endothelium serves both as an exchange site for gases and solutes between blood and brain and as a protective fence against neurotoxic compounds from the blood. While this "blood-brain barrier" (BBB) function protects the fragile environment in the brain, it also poses a tremendous challenge for the delivery of drug compounds to the brain parenchyma. Paracellular brain uptake of drug compounds is limited by the physical tightness of the endothelium, which is tightly sealed with junction complexes. Transcellular uptake of lipophilic drug compounds is limited by the activity of active efflux pumps in the luminal membrane. As a result, the majority of registered CNS drug compounds are small lipophilic compounds which are not efflux transporter substrates. Small molecule CNS drug development therefore focuses on identifying compounds with CNS target affinity and modifies these in order to optimize lipophilicity and decrease efflux pump interactions. Since efflux pump activity is limiting drug uptake, it has been investigated whether coadministration of drug compounds with efflux pump inhibitors could increase drug uptake. While the concept works to some extent, a lot of challenges have been encountered in terms of obtaining efficient inhibition while avoiding adverse effects.Some CNS drug compounds enter the brain via nutrient transport proteins, an example is the levodopa, a prodrug of Dopamine, which crosses the BBB via the large neutral amino acid transporter LAT1. While carrier-mediated transport of drug compounds may seem attractive, the development of drugs targeting transporters is very challenging, since the compounds should have a good fit to the binding site, while still maintaining their CNS target affinity.Receptor-mediated transport of drug compounds, especially biotherapeutics, conjugated to a receptor-binding ligand has shown some promise, although the amounts transported are rather low. This also holds true for drug-conjugation to cell-penetrating peptides. Due to the low uptake of biotherapeutics, barrier-breaching approaches such as mannitol injections and focused ultrasound have been employed with some success to patient groups with no other treatment options.

A new technology for increasing therapeutic protein levels in the brain over extended periods

Effective delivery of protein therapeutics into the brain remains challenging because of difficulties associated with crossing the blood-brain barrier (BBB). To overcome this problem, many researchers have focused on antibodies binding the transferrin receptor (TfR), which is expressed in endothelial cells, including those of the BBB, and is involved in receptor-mediated transcytosis (RMT). RMT and anti-TfR antibodies provide a useful means of delivering therapeutics into the brain, but the anti-TfR antibody has a short half-life in blood because of its broad expression throughout the body. As a result, anti-TfR antibodies are only maintained at high concentrations in the brain for a short time. To overcome this problem, we developed a different approach which slows down the export of therapeutic antibodies from the brain by binding them to a brain-specific antigen. Here we report a new technology, named AccumuBrain, that achieves both high antibody concentration in the brain and a long half-life in blood by binding to myelin oligodendrocyte glycoprotein (MOG), which is specifically expressed in oligodendrocytes. We report that, using our technology, anti-MOG antibody levels in the brains of mice (Mus musculus) and rats (Rattus norvegicus) were increased several tens of times for a period of one month. The mechanism of this technology is different from that of RMT technologies like TfR and would constitute a breakthrough for central nervous system disease therapeutics.

Biologically-derived nanomaterials for targeted therapeutic delivery to the brain

Delivery of imaging agents and pharmaceutical payloads to the central nervous system (CNS) is essential for efficient diagnosis and treatment of brain diseases. However, therapeutic delivery is often restricted by the blood-brain barrier (BBB), which prevents transport of clinical compounds to their region of interest. This review discusses the methods that have been used to avoid or overcome this barrier, presenting the use of biologically-derived nanomaterial systems as an efficient strategy for the diagnosis and treatment of CNS diseases. Biological nanomaterials have many advantages over synthetic systems, including being biodegradable, biocompatible, easily surface functionalised for conjugation of targeting moieties, and are often able to self-assemble. These abilities are discussed in relation to various systems, including liposomes, dendrimers, and viral nanoparticles.

Biological hypotheses and biomarkers of bipolar disorder

The most common mood disorders are major depressive disorders and bipolar disorders (BD). The pathophysiology of BD is complex, multifactorial, and not fully understood. Creation of new hypotheses in the field gives impetus for studies and for finding new biomarkers for BD. Conversely, new biomarkers facilitate not only diagnosis of a disorder and monitoring of biological effects of treatment, but also formulation of new hypotheses about the causes and pathophysiology of the BD. BD is characterized by multiple associations between disturbed brain development, neuroplasticity, and chronobiology, caused by: genetic and environmental factors; defects in apoptotic, immune-inflammatory, neurotransmitter, neurotrophin, and calcium-signaling pathways; oxidative and nitrosative stress; cellular bioenergetics; and membrane or vesicular transport. Current biological hypotheses of BD are summarized, including related pathophysiological processes and key biomarkers, which have been associated with changes in genetics, systems of neurotransmitter and neurotrophic factors, neuroinflammation, autoimmunity, cytokines, stress axis activity, chronobiology, oxidative stress, and mitochondrial dysfunctions. Here we also discuss the therapeutic hypotheses and mechanisms of the switch between depressive and manic state.

The glial cell-line derived neurotrophic factor: a novel regulator of intestinal barrier function in health and disease

Regulation of the intestinal epithelial barrier is a differentiated process, which is profoundly deranged in inflammatory bowel diseases. Recent data provide evidence that the glial cell line-derived neurotrophic factor (GDNF) is critically involved in intestinal epithelial wound healing and barrier maturation and exerts antiapoptotic effects under certain conditions. Furthermore, not only the enteric nervous system, but also enterocytes synthesize GDNF in significant amounts, which points to a potential para- or autocrine signaling loop between enterocytes. Apart from direct effects of GDNF on enterocytes, an immunomodulatory role of this protein has been previously assumed because of a significant reduction of inflammation in a model of chronic inflammatory bowel disease after application of GDNF. In this review we summarize the current knowledge of GDNF on intestinal epithelial barrier regulation and discuss the novel role for GDNF as a regulator of intestinal barrier functions in health and disease.

Exercise-induced neuroprotective effects on neurodegenerative diseases: the key role of trophic factors

Age-related neurodegenerative disorders, like Alzheimer's or Parkinson's disease, are becoming a major issue to public health care. Currently, there is no effective pharmacological treatment to address cognitive impairment in these patients. Here, we aim to explore the role of exercise-induced trophic factor enhancement in the prevention or delay of cognitive decline in patients with neurodegenerative diseases. There is a significant amount of evidence from animal and human studies that links neurodegenerative related cognitive deficits with changes on brain and peripheral trophic factor levels. Several trials with elderly individuals and patients with neurodegenerative diseases report exercise induced cognitive improvements and changes on trophic factor levels including BDNF, IGF-I, among others. Further studies with healthy aging and clinical populations are needed to understand how diverse exercise interventions produce different variations in trophic factor signaling. Genetic profiles and potential confounders regarding trophic factors should also be addressed in future trials.

Insulin Receptor Antibody-α-N-Acetylglucosaminidase Fusion Protein Penetrates the Primate Blood-Brain Barrier and Reduces Glycosoaminoglycans in Sanfilippo Type B Fibroblasts

Mucopolysaccharidosis Type IIIB (MPSIIIB) is caused by mutations in the gene encoding the lysosomal enzyme, α-N-acetylglucosaminidase (NAGLU). MPSIIIB presents with severe disease of the central nervous system, but intravenous NAGLU enzyme replacement therapy has not been developed because the NAGLU enzyme does not cross the blood-brain barrier (BBB). A BBB-penetrating form of the enzyme was produced by re-engineering NAGLU as an IgG-enzyme fusion protein, where the IgG domain is a monoclonal antibody (mAb) against the human insulin receptor (HIR). The HIRMAb traverses the BBB via transport on the endogenous insulin receptor and acts as a molecular Trojan horse to ferry the fused NAGLU across the BBB from blood. The NAGLU was fused to the carboxyl terminus of each heavy chain of the HIRMAb via an extended 31-amino acid linker, and the fusion protein is designated HIRMAb-LL-NAGLU. The fusion protein retains high affinity binding to the HIR, and on a molar basis has an enzyme activity equal to that of recombinant human NAGLU. Treatment of MPSIIIB fibroblasts with the fusion protein normalizes intracellular NAGLU enzyme activity and reduces sulfate incorporation into intracellular glycosoaminoglycan. The fusion protein is targeted to the lysosomal compartment of the cells as shown by confocal microscopy. The fusion protein was radiolabeled with the [(125)I]-Bolton-Hunter reagent and injected intravenously in the adult Rhesus monkey. The fusion protein was rapidly cleared from plasma by all major peripheral organs. The high brain uptake of the fusion protein, 1% injected dose/brain, enables normalization of brain NAGLU enzyme activity with a therapeutic dose of 1 mg/kg. The HIRMAb-LL-NAGLU fusion protein is a new treatment of the brain in MPSIIIB, which can be administered by noninvasive intravenous infusion.

Tight junction modulation of the blood brain barrier: CNS delivery of small molecules

The blood brain barrier (BBB) represents a major obstacle for targeted drug delivery to the brain for the treatment of central nervous system (CNS) disorders. Significant advances in barrier research over the past decade has led to the discovery of an increasing number of structural and regulatory proteins in tight junctions (TJ) and adherens junctions (AJ). These discoveries are providing the framework for the development of novel TJ modulators which can act specifically and temporarily to alter BBB function and regulate paracellular uptake of molecules. TJ modulators that have shown therapeutic potential in preclinical models include claudin-5 and occludin siRNAs, peptides derived from zonula occludens toxin as well as synthetic peptides targeting the extracellular loops of TJs. Adding to the array of modulating agents are novel mechanisms of BBB regulation such as focused ultrasound (FUS). This review will give a succinct overview of BBB biology and TJ modulation in general. Novel insights into BBB regulation in health and disease will also be summarized.

Novel delivery methods bypassing the blood-brain and blood-tumor barriers

Glioblastoma (GBM) is the most common primary brain tumor and carries a grave prognosis. Despite years of research investigating potentially new therapies for GBM, the median survival rate of individuals with this disease has remained fairly stagnant. Delivery of drugs to the tumor site is hampered by various barriers posed by the GBM pathological process and by the complex physiology of the blood-brain and blood-cerebrospinal fluid barriers. These anatomical and physiological barriers serve as a natural protection for the brain and preserve brain homeostasis, but they also have significantly limited the reach of intraparenchymal treatments in patients with GBM. In this article, the authors review the functional capabilities of the physical and physiological barriers that impede chemotherapy for GBM, with a specific focus on the pathological alterations of the blood-brain barrier (BBB) in this disease. They also provide an overview of current and future methods for circumventing these barriers in therapeutic interventions. Although ongoing research has yielded some potential options for future GBM therapies, delivery of chemotherapy medications across the BBB remains elusive and has limited the efficacy of these medications.

GDNF-based therapies, GDNF-producing interneurons, and trophic support of the dopaminergic nigrostriatal pathway. Implications for Parkinson's disease

The glial cell line-derived neurotrophic factor (GDNF) is a well-established trophic agent for dopaminergic (DA) neurons in vitro and in vivo. GDNF is necessary for maintenance of neuronal morphological and neurochemical phenotype and protects DA neurons from toxic damage. Numerous studies on animal models of Parkinson’s disease (PD) have reported beneficial effects of GDNF on nigrostriatal DA neuron survival. However, translation of these observations to the clinical setting has been hampered so far by side effects associated with the chronic continuous intra-striatal infusion of recombinant GDNF. In addition, double blind and placebo-controlled clinical trials have not reported any clinically relevant effect of GDNF on PD patients. In the past few years, experiments with conditional Gdnf knockout mice have suggested that GDNF is necessary for maintenance of DA neurons in adulthood. In parallel, new methodologies for exogenous GDNF delivery have been developed. Recently, it has been shown that a small population of scattered, electrically interconnected, parvalbumin positive (PV+) GABAergic interneurons is responsible for most of the GDNF produced in the rodent striatum. In addition, cholinergic striatal interneurons appear to be also involved in the modulation of striatal GDNF. In this review, we summarize current knowledge on brain GDNF delivery, homeostasis, and its effects on nigrostriatal DA neurons. Special attention is paid to the therapeutic potential of endogenous GDNF stimulation in PD.

The role of neurotrophins in bipolar disorder

Bipolar disorder (BD) is a chronic psychiatric illness of which the pathophysiology remains partially unknown. Abnormalities of neurotrophins and other trophic factors orchestrate important alterations which could be implicated in the etiology of BD. Therefore, the main objective of this review is to examine the recent findings and critically evaluate the potential role of neurotrophins that may allow us to substantially improve the development of novel treatments. The most recently published findings highlight that brain-derived neurotrophic factor (BDNF), insulin-like growth factor (IGF-1) and vascular endothelial growth factor (VEGF) present distinct patterns in the different stages of BD, suggesting their potential in the identification of the BD subgroups and may ultimately advance treatment strategies.

Targeted delivery of protein and gene medicines through the blood-brain barrier

The development of biologic drugs (recombinant proteins, therapeutic antibodies, peptides, nucleic acid therapeutics) as new treatments of brain disorders has been difficult, and a major reason is the lack of transport through the blood-brain barrier (BBB) of these large molecule pharmaceuticals. Biologic drugs can be re-engineered as brain-penetrating neuropharmaceuticals using BBB molecular Trojan horse technology. Certain peptidomimetic monoclonal antibodies that target endogenous receptors on the BBB, such as the insulin or transferrin receptor, enable the re-engineering of biologic drugs that cross the BBB.

Targeting receptor-mediated transport for delivery of biologics across the blood-brain barrier

Biologics are an emerging class of medicines with substantial promise to treat neurological disorders such as Alzheimer's disease, stroke, and multiple sclerosis. However, the blood-brain barrier (BBB) presents a formidable obstacle that appreciably limits brain uptake and hence the therapeutic potential of biologics following intravenous administration. One promising strategy for overcoming the BBB to deliver biologics is the targeting of endogenous receptor-mediated transport (RMT) systems that employ vesicular trafficking to transport ligands across the BBB endothelium. If a biologic is modified with an appropriate targeting ligand, it can gain improved access to the brain via RMT. Various RMT-targeting strategies have been developed over the past 20 years, and this review explores exciting recent advances, emphasizing studies that show brain targeting in vivo.

A novel platform for engineering blood-brain barrier-crossing bispecific biologics

The blood-brain barrier (BBB) prevents the access of therapeutic antibodies to central nervous system (CNS) targets. The engineering of bispecific antibodies in which a therapeutic "arm" is combined with a BBB-transcytosing arm can significantly enhance their brain delivery. The BBB-permeable single-domain antibody FC5 was previously isolated by phenotypic panning of a naive llama single-domain antibody phage display library. In this study, FC5 was engineered as a mono- and bivalent fusion with the human Fc domain to optimize it as a modular brain delivery platform. In vitro studies demonstrated that the bivalent fusion of FC5 with Fc increased the rate of transcytosis (Papp) across brain endothelial monolayer by 25% compared with monovalent fusion. Up to a 30-fold enhanced apparent brain exposure (derived from serum and cerebrospinal fluid pharmacokinetic profiles) of FC5- compared with control domain antibody-Fc fusions after systemic dosing in rats was observed. Systemic pharmacological potency was evaluated in the Hargreaves model of inflammatory pain using the BBB-impermeable neuropeptides dalargin and neuropeptide Y chemically conjugated with FC5-Fc fusion proteins. Improved serum pharmacokinetics of Fc-fused FC5 contributed to a 60-fold increase in pharmacological potency compared with the single-domain version of FC5; bivalent and monovalent FC5 fusions with Fc exhibited similar systemic pharmacological potency. The study demonstrates that modular incorporation of FC5 as the BBB-carrier arm in bispecific antibodies or antibody-drug conjugates offers an avenue to develop pharmacologically active biotherapeutics for CNS indications.

Insulin receptor antibody-sulfamidase fusion protein penetrates the primate blood-brain barrier and reduces glycosoaminoglycans in Sanfilippo type A cells

Mutations in the lysosomal enzyme, N-sulfoglucosamine sulfohydrolase (SGSH), also called sulfamidase, cause accumulation of lysosomal inclusion bodies in the brain of children born with mucopolysaccharidosis type IIIA, also called Sanfilippo type A syndrome. Enzyme replacement therapy with recombinant SGSH does not treat the brain because the enzyme is a large molecule drug that does not cross the blood–brain barrier (BBB). A BBB-penetrating form of SGSH was produced by re-engineering the enzyme as an IgG fusion protein, where the IgG domain is a monoclonal antibody (mAb) against the human insulin receptor (HIR). The HIRMAb domain of the HIRMAb–SGSH fusion protein acts as a molecular Trojan horse to ferry the fused enzyme across the BBB. The HIRMAb–SGSH was produced in stably transfected host cells and purified to homogeneity by protein A chromatography. The fusion protein reacted with antibodies against either human IgG or SGSH on Western blotting. High affinity binding to the HIR was retained following SGSH fusion to the HIRMAb, with an EC₅₀ of 0.33 ± 0.05 nM in an HIR binding ELISA. The SGSH enzyme activity of the HIRMAb–SGSH fusion protein was 4712 ± 388 units/mg protein based on a two-step fluorometric enzyme assay. The HIRMAb–SGSH was taken up by lysosomes in MPSIIIA fibroblasts, and treatment of these cells with the fusion protein caused an 83% reduction in sulfate incorporation into lysosomal glycosoaminoglycans. The HIRMAb–SGSH fusion protein was radiolabeled with the [¹²⁵I]-Bolton–Hunter reagent and injected intravenously in the Rhesus monkey. The brain uptake of the fusion protein was high, ∼1% injected dose/brain. Calculations, based on this level of brain uptake, suggest normalization of brain SGSH enzyme activity is possible following administration of therapeutic doses of the fusion protein. These studies describe a novel IgG–SGSH fusion protein that is a new noninvasive treatment of the brain in MPS type IIIA.

Agile delivery of protein therapeutics to CNS

A variety of therapeutic proteins have shown potential to treat central nervous system (CNS) disorders. Challenge to deliver these protein molecules to the brain is well known. Proteins administered through parenteral routes are often excluded from the brain because of their poor bioavailability and the existence of the blood-brain barrier (BBB). Barriers also exist to proteins administered through non-parenteral routes that bypass the BBB. Several strategies have shown promise in delivering proteins to the brain. This review, first, describes the physiology and pathology of the BBB that underscore the rationale and needs of each strategy to be applied. Second, major classes of protein therapeutics along with some key factors that affect their delivery outcomes are presented. Third, different routes of protein administration (parenteral, central intracerebroventricular and intraparenchymal, intranasal and intrathecal) are discussed along with key barriers to CNS delivery associated with each route. Finally, current delivery strategies involving chemical modification of proteins and use of particle-based carriers are overviewed using examples from literature and our own work. Whereas most of these studies are in the early stage, some provide proof of mechanism of increased protein delivery to the brain in relevant models of CNS diseases, while in few cases proof of concept had been attained in clinical studies. This review will be useful to broad audience of students, academicians and industry professionals who consider critical issues of protein delivery to the brain and aim developing and studying effective brain delivery systems for protein therapeutics.

Blood-brain barrier molecular trojan horse enables imaging of brain uptake of radioiodinated recombinant protein in the rhesus monkey

Recombinant proteins are large molecule drugs that do not cross the blood-brain barrier (BBB). However, BBB-penetration of protein therapeutics is enabled by re-engineering the recombinant protein as IgG fusion proteins. The IgG domain is a monoclonal antibody (mAb) against an endogenous BBB receptor-mediated transport system, such as the human insulin receptor (HIR), and acts as a molecular Trojan horse to ferry the fused protein across the BBB. In the present study, a recombinant lysosomal enzyme, iduronate 2-sulfatase (IDS), is fused to the HIRMAb, and BBB penetration of the IDS alone vs the HIRMAb-IDS fusion protein is compared in the Rhesus monkey. Recombinant IDS and the HIRMAb-IDS fusion protein were radiolabeled with indirect iodination with the [(125)I]-Bolton-Hunter reagent and with direct iodination with Iodogen/[(125)I]-idodine. IDS and the HIRMAb-IDS fusion protein have comparable plasma pharmacokinetics and uptake by peripheral organs. IDS does not cross the BBB. The HIRMAb-IDS fusion protein crosses the BBB and the brain uptake is 1% of injected dose/brain. Brain imaging shows HIRMAb-IDS penetration to all parts of brain, and immunoprecipitation of brain radioactivity shows intact fusion protein in brain. The use of BBB molecular Trojan horses enables brain imaging of recombinant proteins that are re-engineered for BBB transport.

Combination stroke therapy in the mouse with blood-brain barrier penetrating IgG-GDNF and IgG-TNF decoy receptor fusion proteins

Stroke therapy may be optimized by combination therapy with both a neuroprotective neurotrophin and an anti-inflammatory agent. In the present work, the model neurotrophin is glial cell line-derived neurotrophic factor (GDNF), and the model anti-inflammatory agent is the type II tumor necrosis factor receptor (TNFR) decoy receptor. Both the GDNF and the TNFR are large molecules that do not cross the blood-brain barrier (BBB), which is intact in the early hours after stroke when neural rescue is still possible. The GDNF and the TNFR decoy receptor were re-engineered for BBB transport as IgG fusion proteins, wherein the GDNF or the TNFR are fused to the heavy chain of a chimeric monoclonal antibody (MAb) against the mouse transferrin receptor (TfR), and these fusion proteins are designated cTfRMAb-GDNF and cTfRMAb-TNFR, respectively. Mice were treated intravenously with (a) saline, (b) GDNF alone, (c) the cTfRMAb-GDNF fusion protein alone, or (d) the combined cTfRMAb-GDNF and cTfRMAb-TNFR fusion proteins, following a 1-h reversible middle cerebral artery occlusion (MCAO). The cTfRMAb-GDNF fusion protein alone caused a significant 25% and 30% reduction in hemispheric and cortical stroke volumes. Combined treatment with the cTfRMAb-GDNF and cTfRMAb-TNFR fusion proteins caused a significant 54%, 69% and 30% reduction in hemispheric, cortical and subcortical stroke volumes. Conversely, intravenous GDNF had no therapeutic effect. In conclusion, combination treatment with BBB penetrating IgG-GDNF and IgG-TNFR fusion proteins enhances the therapeutic effect of single treatment with the IgG-GDNF fusion protein following delayed intravenous administration in acute stroke.

Nanobiotechnology-based strategies for crossing the blood-brain barrier

The blood-brain barrier (BBB) is meant to protect the brain from noxious agents; however, it also significantly hinders the delivery of therapeutics to the brain. Several strategies have been employed to deliver drugs across this barrier and some of these may do structural damage to the BBB by forcibly opening it to allow the uncontrolled passage of drugs. The ideal method for transporting drugs across the BBB should be controlled and should not damage the barrier. Among the various approaches that are available, nanobiotechnology-based delivery methods provide the best prospects for achieving this ideal. This review describes various nanoparticle (NP)-based methods used for drug delivery to the brain and the known underlying mechanisms. Some strategies require multifunctional NPs combining controlled passage across the BBB with targeted delivery of the therapeutic cargo to the intended site of action in the brain. An important application of nanobiotechnology is to facilitate the delivery of drugs and biological therapeutics for brain tumors across the BBB. Although there are currently some limitations and concerns for the potential neurotoxicity of NPs, the future prospects for NP-based therapeutic delivery to the brain are excellent.

Pharmacokinetics and brain uptake in the rhesus monkey of a fusion protein of arylsulfatase a and a monoclonal antibody against the human insulin receptor

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder of the brain caused by mutations in the gene encoding the lysosomal sulfatase, arylsulfatase A (ASA). It is not possible to treat the brain in MLD with recombinant ASA, because the enzyme does not cross the blood-brain barrier (BBB). In the present investigation, a BBB-penetrating IgG-ASA fusion protein is engineered and expressed, where the ASA monomer is fused to the carboxyl terminus of each heavy chain of an engineered monoclonal antibody (MAb) against the human insulin receptor (HIR). The HIRMAb crosses the BBB via receptor-mediated transport on the endogenous BBB insulin receptor, and acts as a molecular Trojan horse to ferry the ASA into brain from blood. The HIRMAb-ASA is expressed in stably transfected Chinese hamster ovary cells grown in serum free medium, and purified by protein A affinity chromatography. The fusion protein retains high affinity binding to the HIR, EC50 = 0.34 ± 0.11 nM, and retains high ASA enzyme activity, 20 ± 1 units/mg. The HIRMAb-ASA fusion protein is endocytosed and triaged to the lysosomal compartment in MLD fibroblasts. The fusion protein was radio-labeled with the Bolton-Hunter reagent, and the [(125) I]-HIRMAb-ASA rapidly penetrates the brain in the Rhesus monkey following intravenous administration. Film and emulsion autoradiography of primate brain shows global distribution of the fusion protein throughout the monkey brain. These studies describe a new biological entity that is designed to treat the brain of humans with MLD following non-invasive, intravenous infusion of an IgG-ASA fusion protein.

Drug transport across the blood-brain barrier

The blood-brain barrier (BBB) prevents the brain uptake of most pharmaceuticals. This property arises from the epithelial-like tight junctions within the brain capillary endothelium. The BBB is anatomically and functionally distinct from the blood-cerebrospinal fluid barrier at the choroid plexus. Certain small molecule drugs may cross the BBB via lipid-mediated free diffusion, providing the drug has a molecular weight <400 Da and forms <8 hydrogen bonds. These chemical properties are lacking in the majority of small molecule drugs, and all large molecule drugs. Nevertheless, drugs can be reengineered for BBB transport, based on the knowledge of the endogenous transport systems within the BBB. Small molecule drugs can be synthesized that access carrier-mediated transport (CMT) systems within the BBB. Large molecule drugs can be reengineered with molecular Trojan horse delivery systems to access receptor-mediated transport (RMT) systems within the BBB. Peptide and antisense radiopharmaceuticals are made brain-penetrating with the combined use of RMT-based delivery systems and avidin-biotin technology. Knowledge on the endogenous CMT and RMT systems expressed at the BBB enable new solutions to the problem of BBB drug transport.

Periventricular leukomalacia long-term prognosis may be improved by treatment with UDP-glucose, GDNF, and memantine in neonatal rats

The therapeutic effects of UDP-glucose (UDPG), an endogenous agonist of GPR17 that may promote the self-repair of white matter, glial cell line-derived neurotrophic factor (GDNF), a neurotrophic factor correlated with the growth and survival of nerve cells, and memantine, an antagonist of NMDA receptors, were evaluated for functional improvement of neonatal rats with experimental periventricular leukomalacia (PVL). Five day-old neonatal rat pups were subjected to an ischemia-induced model of PVL. The pups were then randomly divided into sham, PVL, PVL plus UDPG, PVL plus GDNF, and PVL plus memantine groups. All pups were weighed and the age at first eye opening recorded. Pathological changes and myelin sheath formation in the white matter were assessed under both light and electron microscopy on day 7 and 21 after induction of PVL. Values of escape latency (EL) and swimming distance (SD) in Morris water maze test, and the modified inclined plane scores in Rivlin inclined plane test were recorded for rats on day 26. Pups in the PVL group were found to be significantly lower in weight (p<0.05), delayed in age at first eye opening (p<0.01), and impaired in their inclined plane (p<0.01) and Morris water maze (p<0.01) performance compared with those in the sham, UDPG, GDNF and memantine groups. Histopathological grading of the white matter classified all pups in the PVL group with significantly more severe injury (p<0.01), and the number and thickness of their myelin sheaths were significantly less (p<0.01), compared to the UDPG, GDNF, memantine, or sham groups. These results indicate that treatment with UDPG, GDNF, and memantine may significantly improve long-term prognosis in neonatal rats with cerebral white matter injury, characteristic of PVL.

Drug penetration across the blood-brain barrier: an overview

The brain is one of the most protected organs in the body. There are two key barriers that control the access of endogenous substances and xenobiotics (drugs or toxins) to the CNS. These physiological structures are the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier. The BBB represents the main determinant of the effective delivery of drugs to the CNS. Good access through the BBB is essential if the target site is located within the CNS or, in contrast, can be a disadvantage if adverse reactions occur at central level. The development of new drugs targeted to the CNS requires a better knowledge of the factors affecting BBB permeation as well as in vitro and in silico predictive tools to optimize screening, and to reduce the attrition rate at later stages of drug development. This review discusses the particular characteristics of the biology and physiology of the BBB with respect to the permeation and distribution of drugs into the brain. The factors affecting rate, extent and distribution into the brain are discussed and a brief description of the in silico, in vitro, in situ and in vivo methods used to measure BBB transport are presented. Finally, the lastest proposals and strategies to enhance transport across the BBB of new CNS drugs are summarized.

Drug delivery to the brain via the blood-brain barrier: a review of the literature and some recent patent disclosures

Delivery of drugs to the brain is challenging, not only for large biopharmaceutical molecules, but also for small organics, which are effluxed from the brain capillary endothelial cells. These cells constitute, in part, the selectively permeable blood-brain barrier. Progress is being made using delivery systems comprising a vector, a linker and cargo, which are purported to enter the brain via receptors on the luminal surface of the brain capillary endothelial cells. Unfortunately, from a delivery perspective, these receptors are not expressed only on brain capillary endothelial cells; so the approaches described in this review are for enhanced delivery to the brain, not for specific brain targeting. The inventions disclosed in patents relate to technologies to screen for new blood-brain barrier receptors and to identify new vectors, or describe systems that deliver cargoes to the brain via any blood-brain barrier receptor, or define specified peptide vectors that target a specific receptor. To date, only one of the technologies has reached early clinical trials and, as always, major challenges remain to be addressed.

A monoclonal antibody-GDNF fusion protein is not neuroprotective and is associated with proliferative pancreatic lesions in parkinsonian monkeys

Glial cell line derived neurotrophic factor (GDNF) is a neurotrophic factor that has neuroprotective effects in animal models of Parkinson’s disease (PD) and has been proposed as a PD therapy. GDNF does not cross the blood brain barrier (BBB), and requires direct intracerebral delivery to be effective. Trojan horse technology, in which GDNF is coupled to a monoclonal antibody (mAb) against the human insulin receptor (HIR), has been proposed to allow GDNF BBB transport (ArmaGen Technologies Inc.). In this study we tested the feasibility of HIRMAb-GDNF to induce neuroprotection in parkinsonian monkeys, as well as its tolerability and safety. Adult rhesus macaques were assessed throughout the study with a clinical rating scale, a computerized fine motor skills task and general health evaluations. Following baseline measurements, the animals received a unilateral intracarotid artery MPTP injection. Seven days later the animals were evaluated, matched according to disability and blindly assigned to receive twice a week iv. treatments (vehicle, 1 or 5 mg/kg HIRmAb-GDNF) for a period of three months. HIRmAb-GDNF did not improve parkinsonian motor symptoms and induced a dose-dependent hypersensitivity reaction. Quantification of dopaminergic striatal optical density and stereological nigral cell counts did not demonstrate differences between treatment groups. Focal pancreatic acinar to ductular metaplasia (ADM) was noted in four of seven animals treated with 1 mg/kg HIRmAb-GDNF; two of four with ADM also had focal pancreatic intraepithelial neoplasia 1B (PanIN-1B) lesions. Minimal to mild, focal to multifocal, nonsuppurative myocarditis was noted in all animals in the 5 mg/kg treatment group. Our results demonstrate that HIRmAb-GDNF dosing in a monkey model of PD is not an effective neuroprotective strategy and may present serious health risks that should be considered when planning future use of the IR antibody as a carrier, or of any systemic treatment of a GDNF-containing molecule.

Vascular Pathology as a Potential Therapeutic Target in SCI

Acute traumatic spinal cord injury (SCI) is characterized by a progressive secondary degeneration which exacerbates the loss of penumbral tissue and neurological function. Here, we first provide an overview of the known pathophysiological mechanisms involving injured microvasculature and molecular regulators that contribute to the loss and dysfunction of existing and new blood vessels. We also highlight the differences between traumatic and ischemic injuries which may yield clues as to the more devastating nature of traumatic injuries, possibly involving toxicity associated with hemorrhage. We also discuss known species differences with implications for choosing models, their relevance and utility to translate new treatments towards the clinic. Throughout this review, we highlight the potential opportunities and proof-of-concept experimental studies for targeting therapies to endothelial cell-specific responses. Lastly, we comment on the need for vascular mechanisms to be included in drug development and non-invasive diagnostics such as serum and cerebrospinal fluid biomarkers and imaging of spinal cord pathology.

Strategies for enhancing antibody delivery to the brain

Antibodies and antibody conjugates have emerged as important tools for cancer therapy. However, a major therapeutic challenge for the use of antibodies is their inability to cross the blood-brain barrier (BBB) to reach tumors localized in the central nervous system (CNS). Multiple methods have been developed to enhance antibody delivery to the CNS, including direct injection, mechanical or biochemical disruption of the BBB, conjugation to a 'molecular Trojan horse', cationization, encapsulation in nanoparticles and liposomes, and more recently, stem cell-mediated antibody delivery. In this review, we discuss each of these approaches, highlighting their successes and the obstacles that remain to be overcome.

Erythropoietin: recent developments in the treatment of spinal cord injury

Erythropoietin (EPO), originally identified for its critical function in regulating production and survival of erythrocytes, is a member of the type 1 cytokine superfamily. Recent studies have shown that EPO has cytoprotective effects in a wide variety of cells and tissues. Here is presented the analysis of EPO effects on spinal cord injury (SCI), considering both animal experiments concerning to mechanisms of neurodegeneration in SCI and EPO as a neuroprotective agent, and some evidences coming from ongoing clinical trials. The evidences underling that EPO could be a promising therapeutic agent in a variety of neurological insults, including trauma, are mounting. In particular, it is highlighted that administration of EPO or other recently generated EPO analogues such as asialo-EPO and carbamylated-EPO demonstrate interesting preclinical and clinical characteristics, rendering the evaluation of these tissue-protective agents imperative in human clinical trials. Moreover the demonstration of rhEPO and its analogues' broad neuroprotective effects in animal models of cord lesion and in human trial like stroke, should encourage scientists and clinicians to design clinical trials assessing the efficacy of these pharmacological compounds on SCI.

Chronic dosing of mice with a transferrin receptor monoclonal antibody-glial-derived neurotrophic factor fusion protein

Glial-derived neurotrophic factor (GDNF) is a potential neurotrophic factor treatment of brain disorders, including Parkinson's disease. However, GDNF does not cross the blood-brain barrier (BBB). A brain-penetrating form of GDNF, which is a fusion protein of human GDNF and a chimeric monoclonal antibody (MAb) against the mouse transferrin receptor (TfR), has been engineered for the mouse and is designated the cTfRMAb-GDNF fusion protein. The present study examined the potential toxic side effects and immune response after treatment of mice with twice-weekly cTfRMAb-GDNF fusion protein at a dose of 2 mg/kg i.v. for 12 consecutive weeks. Chronic treatment with the fusion protein caused no change in body weight, no change in 23 serum chemistry measurements, and no histologic changes in brain and cerebellum, kidney, liver, spleen, heart, or pancreas. Chronic treatment caused a low-titer immune response against the fusion protein, which was directed against the variable region of the antibody part of the fusion protein, with no immune response directed against either the constant region of the antibody or against GDNF. A pharmacokinetics and brain uptake study was performed at the end of the 12 weeks of treatment. There was no change in clearance of the fusion protein mediated by the TfR in peripheral organs, and there was no change in BBB permeability to the fusion protein mediated by the TfR at the BBB. The study shows no toxic side effects from chronic cTfRMAb-GDNF systemic treatment and the absence of neutralizing antibodies in vivo.

Expression in CHO cells and pharmacokinetics and brain uptake in the Rhesus monkey of an IgG-iduronate-2-sulfatase fusion protein

Sulfatases are potential therapeutic biopharmaceuticals, as mutations in sulfatase genes leads to inherited disease. Mucopolysaccharidosis (MPS) Type II is caused by mutations in the lysosomal enzyme, iduronate-2-sulfatase (IDS). MPS-II affects the brain and enzyme replacement therapy is ineffective for the brain, because IDS does not cross the blood-brain barrier (BBB). To deliver IDS across the human BBB, the sulfatase has been re-engineered as an IgG-sulfatase fusion protein with a genetically engineered monoclonal antibody (MAb) against the human insulin receptor (HIR). The HIRMAb part of the HIRMAb-IDS fusion protein acts as a molecular Trojan horse to ferry the fused IDS across the BBB. Chinese hamster ovary (CHO) cells were stably transfected to produce the HIRMAb-IDS fusion protein. The fusion protein was triaged to the lysosomal compartment of MPS-II fibroblasts based on confocal microscopy, and 300 ng/mL medium concentrations normalized IDS enzyme activity in the cells. The HIRMAb-IDS fusion protein was tritiated and injected intravenously into the adult Rhesus monkey at a low dose of 0.1 mg/kg. The IDS enzyme activity in plasma was elevated 10-fold above the endogenous level, and therapeutic plasma concentrations were generated in vivo. The uptake of the HIRMAb-IDS fusion protein in the brain was sufficiently high to produce therapeutic concentrations of IDS in the brain following IV administration of the fusion protein.

CHO cell expression, long-term stability, and primate pharmacokinetics and brain uptake of an IgG-paroxonase-1 fusion protein

Paraoxonase (PON)-1 is the most potent human organophosphatase known, but recombinant forms of human PON1 have been difficult to produce owing to poor secretion by host cells. In the present investigation, human PON1 is re-engineered as an IgG-PON1 fusion protein. The 355 amino acid human PON1 is fused to the carboxyl terminus of the heavy chain of a chimeric monoclonal antibody (MAb) against the human insulin receptor (HIR), and this fusion protein is designated HIRMAb-PON1. The HIRMAb part of the fusion protein enables brain penetration of the PON1, which was considered important, because organophosphate toxicity causes death via a central nervous system site of action. A high producing line of stably transfected Chinese hamster ovary (CHO) cells secreting the HIRMAb-PON1 fusion protein in the absence of serum or lipid acceptors was cloned. The bioreactor generated fusion protein was purified to homogeneity with low impurities by protein A affinity chromatography and anion exchange chromatography. The HIRMAb-PON1 fusion protein was stable as a sterile liquid formulation stored at 4°C for at least 1 year. The plasma pharmacokinetics (PK) of the HIRMAb-PON1 fusion protein was evaluated in Rhesus monkeys, which is the first PK evaluation of a recombinant PON1 protein. The fusion protein was rapidly removed from blood, primarily by the liver. The blood-brain barrier permeation of the HIRMAb-PON1 fusion protein was high and comparable to other HIRMAb fusion proteins. Re-engineering human PON1 as the HIRMAb fusion protein allows for production of a stable, field-deployable formulation of the enzyme that is brain-penetrating.

Brain-penetrating tumor necrosis factor decoy receptor in the mouse

Biologic tumor necrosis factor inhibitors (TNFIs) include TNF decoy receptors (TNFRs). TNFα plays a pathologic role in both acute and chronic brain disease. However, biologic TNFIs cannot be developed as brain therapeutics because these large molecule drugs do not cross the blood-brain barrier (BBB). To enable penetration of the brain via receptor-mediated transport, the human TNFR type II was re-engineered as an IgG fusion protein, where the IgG part is a chimeric monoclonal antibody (MAb) against the mouse transferrin receptor (TfR), and this fusion protein is designated cTfRMAb-TNFR. The cTfRMAb part of the fusion protein acts as a molecular Trojan horse to ferry the TNFR across the BBB via transport on the endogenous BBB TfR. cTfRMAb-TNFR was expressed by stably transfected Chinese hamster ovary cells and purified by affinity chromatography to homogeneity on electrophoretic gels. The fusion protein reacted with antibodies to both mouse IgG and the human TNFR and bound TNFα with high affinity (K(d) = 96 ± 34 pM). cTfRMAb-TNFR was rapidly transported into mouse brain in vivo after intravenous administration, and the brain uptake of the fusion protein was 2.8 ± 0.5% of injected dose per gram of brain, which is >45-fold higher than the brain uptake of an IgG that does not recognize the mouse TfR. This new IgG-TNFR fusion protein can be tested in mouse models of brain diseases in which TNFα plays a pathologic role.

Intravenous treatment of experimental Parkinson's disease in the mouse with an IgG-GDNF fusion protein that penetrates the blood-brain barrier

Glial-derived neurotrophic factor (GDNF) is a trophic factor for the nigra-striatal tract in experimental Parkinson's disease (PD). The neurotrophin must be administered by intra-cerebral injection, because GDNF does not cross the blood-brain barrier (BBB). In the present study, GDNF was re-engineered to enable receptor-mediated transport across the BBB following fusion of GDNF to the heavy chain of a chimeric monoclonal antibody (MAb) against the mouse transferrin receptor (TfR), and this fusion protein is designated cTfRMAb-GDNF. This fusion protein had been previously shown to retain low nM binding constants for both the GDNF receptor and the mouse TfR, and to rapidly enter the mouse brain in vivo following intravenous administration. Experimental PD in mice was induced by the intra-striatal injection of 6-hydroxydopamine, and mice were treated with either saline or the cTfRMAb-GDNF fusion protein every other day for 3 weeks, starting 1 h after toxin injection. Fusion protein treatment caused a 44% decrease in apomorphine-induced rotation, a 45% reduction in amphetamine-induced rotation, a 121% increase in the vibrissae-elicited forelimb placing test, and a 272% increase in striatal tyrosine hydroxylase (TH) enzyme activity at 3 weeks after toxin injection. Fusion protein treatment caused no change in TH enzyme activity in either the contralateral striatum or the frontal cortex. In conclusion, following fusion of GDNF to a BBB molecular Trojan horse, GDNF trophic effects in brain in experimental PD are observed following intravenous administration.

Biopharmaceutical drug targeting to the brain

Biopharmaceuticals are large molecule drugs that do not cross the blood-brain barrier (BBB). The limiting factor in the drug development of biopharmaceuticals as new drugs for the human brain is the engineering of effective brain drug targeting technology platforms. Recombinant proteins, enzymes, and monoclonal antibodies can be re-engineered for transport across the human BBB with the molecular Trojan horse technology. The most active BBB molecular Trojan horse is a monoclonal antibody to the human insulin receptor. The genetic engineering of IgG fusion proteins has been demonstrated for neurotrophic factors, decoy receptors, therapeutic enzymes, single chain Fv antibodies, and avidin. The IgG fusion proteins are not toxic on repeated administration in high doses to primates and do not interfere with glycemic control in plasma or brain. IgG fusion proteins contain amino acid sequences that induce immune tolerance, and show low immunogenicity in primates. The IgG fusion proteins are new bifunctional biopharmaceuticals that are both targeted to brain via transport on endogenous BBB receptors, and exert pharmacological effects in brain at the cognate receptor, ligand, or enzyme substrate.

Drug targeting of erythropoietin across the primate blood-brain barrier with an IgG molecular Trojan horse

Erythropoietin (EPO) is a neurotrophic factor that could be developed as a new drug for brain disorders. However, EPO does not cross the blood-brain barrier (BBB). In the present study, human EPO was re-engineered by fusion to the carboxyl terminus of the heavy chain of a chimeric monoclonal antibody (MAb) to the human insulin receptor (HIR). The HIRMAb acts as a molecular Trojan horse to ferry the EPO into the brain via receptor-mediated transport on the endogenous BBB insulin receptor. The HIRMAb-EPO fusion protein was immunoreactive with antibodies to both human IgG and EPO. The HIRMAb-EPO fusion protein bound with high affinity to the extracellular domain of both the HIR (ED(50) = 0.21 +/- 0.05 nM) and the EPO receptor (ED(50) = 0.30 +/- 0.01 nM) and activated thymidine incorporation into human TF-1 cells with an ED(50) of 0.1 nM. Differentially radiolabeled EPO and the HIRMAb-EPO fusion protein were injected intravenously into adult rhesus monkeys. Whereas EPO did not cross the primate BBB, the HIRMAb-EPO fusion protein was rapidly transported into brain, at levels that produce pharmacologic elevations in brain EPO at small systemic doses. The HIRMAb fusion protein selectively targeted the brain relative to peripheral organs. In conclusion, a novel IgG-EPO fusion protein has been engineered, expressed, and shown to be bifunctional with retention of high-affinity binding to both the insulin and EPO receptors. The IgG-EPO fusion protein represents a new class of EPO neurotherapeutics that has been specifically re-engineered to penetrate the human BBB.

IgG-single chain Fv fusion protein therapeutic for Alzheimer's disease: Expression in CHO cells and pharmacokinetics and brain delivery in the rhesus monkey

Monoclonal antibodies (MAb) directed against the Abeta amyloid peptide of Alzheimer's disease (AD) are potential new therapies for AD, since these antibodies disaggregate brain amyloid plaque. However, the MAb is not transported across the blood-brain barrier (BBB). To enable BBB transport, a single chain Fv (ScFv) antibody against the Abeta peptide of AD was re-engineered as a fusion protein with the MAb against the human insulin receptor (HIR). The HIRMAb acts as a molecular Trojan horse to ferry the ScFv therapeutic antibody across the BBB. Chinese hamster ovary (CHO) cells were stably transfected with a tandem vector encoding the heavy and light chains of the HIRMAb-ScFv fusion protein. A high secreting line was isolated following methotrexate amplification and dilutional cloning. The HIRMAb-ScFv fusion protein in conditioned serum-free medium was purified by protein A affinity chromatography. The fusion protein was stable as a liquid formulation, and retained high-affinity binding of both the HIR and the Abeta amyloid peptide. The HIRMAb-ScFv fusion protein was radiolabeled with the (125)I-Bolton-Hunter reagent, followed by measurement of the pharmacokinetics of plasma clearance and brain uptake in the adult Rhesus monkey. The HIRMAb-ScFv fusion protein was rapidly cleared from plasma and was transported across the primate BBB in vivo. In conclusion, the HIRMAb-ScFv fusion protein is a new class of antibody-based therapeutic for AD that has been specifically engineered to cross the human BBB.

Selective targeting of a TNFR decoy receptor pharmaceutical to the primate brain as a receptor-specific IgG fusion protein

Decoy receptors, such as the human tumor necrosis factor receptor (TNFR), are potential new therapies for brain disorders. However, decoy receptors are large molecule drugs that are not transported across the blood-brain barrier (BBB). To enable BBB transport of a TNFR decoy receptor, the human TNFR-II extracellular domain was re-engineered as a fusion protein with a chimeric monoclonal antibody (MAb) against the human insulin receptor (HIR). The HIRMAb acts as a molecular Trojan horse to ferry the TNFR therapeutic decoy receptor across the BBB. The HIRMAb-TNFR fusion protein was expressed in stably transfected CHO cells, and was analyzed with electrophoresis, Western blotting, size exclusion chromatography, and binding assays for the HIR and TNFalpha. The HIRMAb-TNFR fusion protein was radio-labeled by trititation, in parallel with the radio-iodination of recombinant TNFR:Fc fusion protein, and the proteins were co-injected in the adult Rhesus monkey. The TNFR:Fc fusion protein did not cross the primate BBB in vivo, but the uptake of the HIRMAb-TNFR fusion protein was high and 3% of the injected dose was taken up by the primate brain. The TNFR was selectively targeted to brain, relative to peripheral organs, following fusion to the HIRMAb. This study demonstrates that decoy receptors may be re-engineered as IgG fusion proteins with a BBB molecular Trojan horse that selectively targets the brain, and enables penetration of the BBB in vivo. IgG-decoy receptor fusion proteins represent a new class of human neurotherapeutics.