Intrathecal enzyme replacement therapy reduces lysosomal storage in the brain and meninges of the canine model of MPS I

Choroid plexus-targeted viral gene therapy for alpha-mannosidosis, a prototypical neurometabolic lysosomal storage disease

The choroid plexuses (CP) are highly vascularized structures that project into the ventricles of the vertebrate brain. The polarized epithelia of the CP produce cerebrospinal fluid by transporting water and ions into the ventricles from the blood and normally secrete a large number of proteins. We assessed the feasibility of selective CP transduction with recombinant adeno-associated virus (rAAV) gene therapy vectors for treatment of lysosomal storage disease (LSD), a broad category of neurometabolic illness associated with significant burdens to affected patients and their families. There are no ideal or complete therapeutic options currently available, especially for the central nervous system manifestations of LSDs. Alpha-mannosidosis (AMD) is an autosomal recessive prototypical LSD caused by deficiency of lysosomal alpha-mannosidase and characterized by cerebellar ataxia, neurocognitive disability, facial and skeletal abnormalities, hearing impairment, and mild immune deficiency. In a murine model of AMD, we compared the biochemical effects of CSF-directed rAAV serotypes 1, 4, 5, 6, and 9. Recombinant AAV1 and rAAV6, two closely related serotypes whose capsid sequences differ by only six amino acids, showed the most robust transduction of CP in mouse brain, consistent with their transduction of CPE in nonhuman primates and cats, as well as in other structures. We found restoration of LAMAN enzyme activity comparable to or higher than AMD heterozygote levels in the brain globally (olfactory bulb, cortex, cerebellum, brainstem). Further IND-generating preclinical experiments will advance rAAV6-LAMAN, which appears to be the most promising choroid plexus-targeting candidate serotype for future clinical translation to treat AMD.

Laronidase-loaded liposomes reach the brain and other hard-to-treat organs after noninvasive nasal administration

Mucopolysaccharidosis type I (MPS I) is caused by a lack of the lysosomal enzyme α-L-iduronidase (IDUA), responsible for the degradation of the glycosaminoglycans (GAGs) dermatan and heparan sulfate, leading to multisystemic signs and symptoms. Enzyme replacement therapy (ERT) is a treatment that consists of weekly intravenous administrations of laronidase, a recombinant version of IDUA. However, ERT has limited access to certain tissues, such as bone, cartilage, and brain, and laronidase fails to trespass the BBB. In this sense, this study reports the development and characterization of laronidase-loaded liposomes for the treatment of MPS I mice. Liposomal complexes were obtained by the thin film formation method followed by microfluidization. The main characterization results showed mean vesicle size of 103.0 ± 3.3 nm, monodisperse populations of vesicles, zeta potential around + 30.0 ± 2.1 mV, and mucoadhesion strength of 5.69 ± 0.14 mN. Treatment of MPS I mice fibroblasts showed significant increase in enzyme activity. Nasal administration of complexes to MPS I mice resulted in significant increase in laronidase activity in the brain cortex, heart, lungs, kidneys, eyes, and serum. The overall results demonstrate the feasibility of nasal administration of laronidase-loaded liposomes to deliver enzyme in difficult-to-reach tissues, circumventing ERT issues and bringing hope as a potential treatment for MPS I.

Targeting the central nervous system in lysosomal storage diseases: Strategies to deliver therapeutics across the blood-brain barrier

Lysosomal storage diseases (LSDs) are multisystem inherited metabolic disorders caused by dysfunctional lysosomal activity, resulting in the accumulation of undegraded macromolecules in a variety of organs/tissues, including the central nervous system (CNS). Treatments include enzyme replacement therapy, stem/progenitor cell transplantation, and in vivo gene therapy. However, these treatments are not fully effective in treating the CNS as neither enzymes, stem cells, nor viral vectors efficiently cross the blood-brain barrier. Here, we review the latest advancements in improving delivery of different therapeutic agents to the CNS and comment upon outstanding questions in the field of neurological LSDs.

Quantification of Glycosaminoglycans in Urine by Isotope-Dilution Liquid Chromatography-Electrospray Ionization Tandem Mass Spectrometry

Mucopolysaccharidoses (MPSs) are complex lysosomal storage disorders that result in the accumulation of glycosaminoglycans (GAGs) in urine, blood, and tissues. Lysosomal enzymes responsible for GAG degradation are defective in MPSs. GAGs including chondroitin sulfate (CS), dermatan sulfate (DS), heparan sulfate (HS), and keratan sulfate (KS) are disease-specific biomarkers for MPSs. This article describes a stable isotope dilution-tandem mass spectrometric method for quantifying CS, DS, and HS in urine samples. The GAGs are methanolyzed to uronic or iduronic acid-N-acetylhexosamine or iduronic acid-N-sulfo-glucosamine dimers and mixed with internal standards derived from deuteriomethanolysis of GAG standards. Specific dimers derived from HS, DS, and CS are separated by ultra-performance liquid chromatography (UPLC) and analyzed by electrospray ionization tandem mass spectrometry (MS/MS) using selected reaction monitoring for each targeted GAG product and its corresponding internal standard. This UPLC-MS/MS GAG assay is useful for identifying patients with MPS types I, II, III, VI, and VII. © 2023 Wiley Periodicals LLC. Basic Protocol: Urinary GAG analysis by ESI-MS/MS Support Protocol 1: Prepare calibration samples Support Protocol 2: Preparation of stable isotope-labeled internal standards Support Protocol 3: Preparation of quality controls for GAG analysis in urine Support Protocol 4: Optimization of the methanolysis time Support Protocol 5: Measurement of the concentration of methanolic HCl.

Transduction characteristics of alternative adeno-associated virus serotypes in the cat brain by intracisternal delivery

Multiple studies have examined the transduction characteristics of different AAV serotypes in the mouse brain, where they can exhibit significantly different patterns of transduction. The pattern of transduction also varies with the route of administration. Much less information exists for the transduction characteristics in large-brained animals. Large animal models have brains that are closer in size and organization to the human brain, such as being gyrencephalic compared to the lissencephalic rodent brains, pathway organization, and certain electrophysiologic properties. Large animal models are used as translational intermediates to develop gene therapies to treat human diseases. Various AAV serotypes and routes of delivery have been used to study the correction of pathology in the brain in lysosomal storage diseases. In this study, we evaluated the ability of selected AAV serotypes to transduce cells in the cat brain when delivered into the cerebrospinal fluid via the cisterna magna. We previously showed that AAV1 transduced significantly greater numbers of cells than AAV9 in the cat brain by this route. In the present study, we evaluated serotypes closely related to AAVs 1 and 9 (AAVs 6, AS, hu32) that may mediate more extensive transduction, as well as AAVs 4 and 5, which primarily transduce choroid plexus epithelial (CPE) and ependymal lining cells in the rodent brain. The related serotypes tended to have similar patterns of transduction but were divergent in some specific brain structures.

Large-Volume Intrathecal Administrations: Impact on CSF Pressure and Safety Implications

The increasing number of studies demonstrates the high potency of the intrathecal (IT) route for the delivery of biopharmaceuticals to the central nervous system (CNS). Our earlier data exhibited that both the infused volume and the infusion rate can regulate the initial disposition of the administered solute within the cerebrospinal fluid (CSF). This disposition is one of key factors in defining the subsequent transport of the solute to its intended target. On the other hand, fast additions of large volumes of liquid to the CSF inevitably raise the CSF pressure [a.k.a. intracranial pressure (ICP)], which may in turn lead to adverse reactions if the physiologically delimited threshold is exceeded. While long-term biological effects of elevated ICP (hydrocephalus) are known, the safety thresholds pertaining to short-term ICP elevations caused by IT administrations have not yet been characterized. This study aimed to investigate the dynamics of ICP in rats and non-human primates (NHPs) with respect to IT infusion rates and volumes. The safety regimes were estimated and analyzed across species to facilitate the development of translational large-volume IT therapies. The data revealed that the addition of a liquid to the CSF raised the ICP in a rate and volume-dependent manner. At low infusion rates (<0.12 ml/min in rats and <2 ml/min in NHPs), NHPs and rats displayed similar tolerance patterns. Specifically, safe accommodations of such added volumes were mainly facilitated by the accelerated pressure-dependent CSF drainage into the blood, with I stabilizing at different levels below the safety threshold of 28 ± 4 mm Hg in rats and 50 ± 5 mm Hg in NHPs. These ICPs were safely tolerated for extended durations (of at least 2–25 min). High infusion rates (including boluses) caused uncompensated exponential ICP elevations rapidly exceeding the safety thresholds. Their tolerance was species-dependent and was facilitated by the compensatory role of the varied components of craniospinal compliance while not excluding the possibility of other contributing factors. In conclusion, large volumes of liquids can safely be delivered via IT routes provided that ICP is monitored as a safety factor and cross-species physiological differences are accounted for.

Enzyme replacement combinational therapy: effective treatments for mucopolysaccharidoses

INTRODUCTION

Mucopolysaccharidoses (MPS), as a group of inherited lysosomal storage disorders (LSDs), are clinically heterogeneous and characterized by multi-systemic manifestations, such as skeletal abnormalities and neurological dysfunctions. The currently used enzyme replacement therapy (ERT) might be associated with several limitations including the low biodistribution of the enzymes into the main targets, immunological responses against foreign enzymes, and the high cost of the treatment procedure. Therefore, a suitable combination approach can be considered for the successful treatment of each type of MPS.

AREAS COVERED

In this review, we provide comprehensive insights into the ERT-based combination therapies of MPS by reviewing the published literature on PubMed and Scopus. We also discuss the recent advancements in the treatment of MPS and bring up the hopes and hurdles in the futuristic treatment strategies.

EXPERT OPINION

Given the complex pathophysiology of MPS and its involvement in different tissues, the ERT of MPS in combination with stem cell therapy or gene therapy is deemed to provide a personalized precision treatment modality with the highest therapeutic responses and minimal side effects. By the same token, new combinational approaches need to be evaluated by using drugs that target alternative and secondary pathological pathways.

Novel therapies for mucopolysaccharidosis type III

Mucopolysaccharidosis type III (MPS III) or Sanfilippo disease is an orphan inherited lysosomal storage disease and one of the most common MPS subtypes. The classical presentation is an infantile-onset neurodegenerative disease characterised by intellectual regression, behavioural and sleep disturbances, loss of ambulation, and early death. Unlike other MPS, no disease-modifying therapy has yet been approved. Here, we review the numerous approaches of curative therapy developed for MPS III from historical ineffective haematopoietic stem cell transplantation and substrate reduction therapy to the promising ongoing clinical trials based on enzyme replacement therapy or adeno-associated or lentiviral vectors mediated gene therapy. Preclinical studies are presented alongside the most recent translational first-in-man trials. In addition, we present experimental research with preclinical mRNA and gene editing strategies. Lessons from animal studies and clinical trials have highlighted the importance of an early therapy before extensive neuronal loss. A disease-modifying therapy for MPS III will undoubtedly mandate development of new strategies for early diagnosis.

Enzyme Replacement Therapy for Mucopolysaccharidosis IIID using Recombinant Human α-N-Acetylglucosamine-6-Sulfatase in Neonatal Mice

There is currently no cure or effective treatment available for mucopolysaccharidosis type IIID (MPS IIID, Sanfilippo syndrome type D), a lysosomal storage disorder (LSD) caused by the deficiency of α-N-acetylglucosamine-6-sulfatase (GNS). The clinical symptoms of MPS IIID, like other subtypes of Sanfilippo syndrome, are largely localized to the central nervous system (CNS), and any treatments aiming to ameliorate or reverse the catastrophic and fatal neurologic decline caused by this disease need to be delivered across the blood-brain barrier. Here, we report a proof-of-concept enzyme replacement therapy (ERT) for MPS IIID using recombinant human α-N-acetylglucosamine-6-sulfatase (rhGNS) via intracerebroventricular (ICV) delivery in a neonatal MPS IIID mouse model. We overexpressed and purified rhGNS from CHO cells with a specific activity of 3.9 × 10⁴ units/mg protein and a maximal enzymatic activity at lysosomal pH (pH 5.6), which was stable for over one month at 4 °C in artificial cerebrospinal fluid (CSF). We demonstrated that rhGNS was taken up by MPS IIID patient fibroblasts via the mannose 6-phosphate (M6P) receptor and reduced intracellular glycosaminoglycans to normal levels. The delivery of 5 μg of rhGNS into the lateral cerebral ventricle of neonatal MPS IIID mice resulted in normalization of the enzymatic activity in brain tissues; rhGNS was found to be enriched in lysosomes in MPS IIID-treated mice relative to the control. Furthermore, a single dose of rhGNS was able to reduce the accumulated heparan sulfate and β-hexosaminidase. Our results demonstrate that rhGNS delivered into CSF is a potential therapeutic option for MPS IIID that is worthy of further development.

Targeting the Choroid Plexuses for Protein Drug Delivery

Delivery of therapeutic agents to the central nervous system is challenged by the barriers in place to regulate brain homeostasis. This is especially true for protein therapeutics. Targeting the barrier formed by the choroid plexuses at the interfaces of the systemic circulation and ventricular system may be a surrogate brain delivery strategy to circumvent the blood-brain barrier. Heterogenous cell populations located at the choroid plexuses provide diverse functions in regulating the exchange of material within the ventricular space. Receptor-mediated transcytosis may be a promising mechanism to deliver protein therapeutics across the tight junctions formed by choroid plexus epithelial cells. However, cerebrospinal fluid flow and other barriers formed by ependymal cells and perivascular spaces should also be considered for evaluation of protein therapeutic disposition. Various preclinical methods have been applied to delineate protein transport across the choroid plexuses, including imaging strategies, ventriculocisternal perfusions, and primary choroid plexus epithelial cell models. When used in combination with simultaneous measures of cerebrospinal fluid dynamics, they can yield important insight into pharmacokinetic properties within the brain. This review aims to provide an overview of the choroid plexuses and ventricular system to address their function as a barrier to pharmaceutical interventions and relevance for central nervous system drug delivery of protein therapeutics. Protein therapeutics targeting the ventricular system may provide new approaches in treating central nervous system diseases.

Intravenous delivery for treatment of mucopolysaccharidosis type I: A comparison of AAV serotypes 9 and rh10

Mucopolysaccharidosis type I (MPS I) is an inherited metabolic disorder caused by deficiency of alpha-L-iduronidase (IDUA), resulting in accumulation of heparan and dermatan sulfate glycosaminoglycans (GAGs). Individuals with the most severe form of the disease (Hurler syndrome) suffer from neurodegeneration, intellectual disability, and death by age 10. Current treatments for this disease include allogeneic hematopoietic stem cell transplantation (HSCT) and enzyme replacement therapy (ERT). However, these treatments do not address CNS manifestations of the disease. In this study we compared the ability of intravenously administered AAV serotypes 9 and rh10 (AAV9 and AAVrh10) for delivery and expression of the IDUA gene in the CNS. Adult C57BL/6 MPS I mice were infused intravenously with either AAV9 or AAVrh10 vector encoding the human IDUA gene. Treated animals demonstrated supraphysiological levels and widespread restoration of IDUA enzyme activity in the plasma and all organs including the CNS. High levels of IDUA enzyme activity were observed in the plasma, brain and spinal cord ranging from 10 to 100-fold higher than heterozygote controls, while levels in peripheral organs were also high, ranging from 1000 to 10,000-fold higher than control animals. In general, levels of IDUA expression were slightly higher in peripheral organs for AAVrh10 administered animals although these differences were not significant except for the lung. Levels of IDUA expression between AAV 9 and rh10 were roughly equivalent in the brain. Urinary and tissue GAGs were significantly reduced starting at 3 weeks after vector infusion, with restoration of normal GAG levels by the end of the study in animals treated with either AAV9 or rh10. These results demonstrate that non-invasive intravenous AAV9 or AAVrh10-mediated IDUA gene therapy is a potentially effective treatment for both systemic and CNS manifestations of MPS I, with implications for the treatment of other metabolic and neurological diseases as well.

A deletion of IDUA exon 10 in a family of Golden Retriever dogs with an attenuated form of mucopolysaccharidosis type I

Background

Mucopolysaccharidosis type I (MPS‐I) is a lysosomal storage disorder caused by a deficiency of the enzyme α‐l‐iduronidase, leading to accumulation of undegraded dermatan and heparan sulfates in the cells and secondary multiorgan dysfunction. In humans, depending upon the nature of the underlying mutation(s) in the IDUA gene, the condition presents with a spectrum of clinical severity.

Objectives

To characterize the clinical and biochemical phenotypes, and the genotype of a family of Golden Retriever dogs.

Animals

Two affected siblings and 11 related dogs.

Methods

Family study. Urine metabolic screening and leucocyte lysosomal enzyme activity assays were performed for biochemical characterization. Whole genome sequencing was used to identify the causal mutation.

Results

The clinical signs shown by the proband resemble the human attenuated form of the disease, with a dysmorphic appearance, musculoskeletal, ocular and cardiac defects, and survival to adulthood. Urinary metabolic studies identified high levels of dermatan sulfate, heparan sulfate, and heparin. Lysosomal enzyme activities demonstrated deficiency in α‐l‐iduronidase activity in leucocytes. Genome sequencing revealed a novel homozygous deletion of 287 bp resulting in full deletion of exon 10 of the IDUA gene (NC_006585.3(NM_001313883.1):c.1400‐76_1521+89del). Treatment with pentosan polyphosphate improved the clinical signs until euthanasia at 4.5 years.

Conclusion and Clinical Importance

Analysis of the genotype/phenotype correlation in this dog family suggests that dogs with MPS‐I could have a less severe phenotype than humans, even in the presence of severe mutations. Treatment with pentosan polyphosphate should be considered in dogs with MPS‐I.

Canine Models of Inherited Musculoskeletal and Neurodegenerative Diseases

Mouse models of human disease remain the bread and butter of modern biology and therapeutic discovery. Nonetheless, more often than not mouse models do not reproduce the pathophysiology of the human conditions they are designed to mimic. Naturally occurring large animal models have predominantly been found in companion animals or livestock because of their emotional or economic value to modern society and, unlike mice, often recapitulate the human disease state. In particular, numerous models have been discovered in dogs and have a fundamental role in bridging proof of concept studies in mice to human clinical trials. The present article is a review that highlights current canine models of human diseases, including Alzheimer's disease, degenerative myelopathy, neuronal ceroid lipofuscinosis, globoid cell leukodystrophy, Duchenne muscular dystrophy, mucopolysaccharidosis, and fucosidosis. The goal of the review is to discuss canine and human neurodegenerative pathophysiologic similarities, introduce the animal models, and shed light on the ability of canine models to facilitate current and future treatment trials.

Large animal models contribute to the development of therapies for central and peripheral nervous system dysfunction in patients with lysosomal storage diseases

Lysosomal storage diseases (LSDs) are a group of 70 monogenic disorders characterized by the lysosomal accumulation of a substrate. As a group, LSDs affect ~1 in 5000 live births; however, each individual storage disease is rare, limiting the ability to perform natural history studies or to perform clinical trials. Perhaps in no other biomedical field have naturally occurring large animal (canine, feline, ovine, caprine, and bovine) models been so essential for understanding the fundamentals of disease pathogenesis and for developing safe and effective therapies. These models were critical for the development of hematopoietic stem cell transplantation in α- and β- mannosidosis, fucosidosis, and the mucopolysaccharidoses; enzyme replacement therapy for fucosidosis, the mucopolysaccharidoses, and neuronal ceroid lipofuscinosis; and small molecule therapy in Niemann-Pick type C disease. However, their most notable contributions to the biomedical field are in the development of gene therapy for LSDs. Adeno-associated viral vectors to treat nervous system disease have been evaluated in the large animal models of α-mannosidosis, globoid cell leukodystrophy, GM1 and GM2 gangliosidosis, the mucopolysaccharidoses, and neuronal ceroid lipofuscinosis. This review article will summarize the large animal models available for study as well as their contributions to the development of central and peripheral nervous system dysfunction in LSDs.

Evaluation of non-reducing end pathologic glycosaminoglycan detection method for monitoring therapeutic response to enzyme replacement therapy in human mucopolysaccharidosis I

Therapeutic development and monitoring require demonstration of effects on disease phenotype. However, due to the complexity of measuring clinically-relevant effects in rare multisystem diseases, robust biomarkers are essential. For the mucopolysaccharidoses (MPS), the measurement of glycosaminoglycan levels is relevant as glycosaminoglycan accumulation is the primary event that occurs due to reduced lysosomal enzyme activity. Traditional dye-based assays that measure total glycosaminoglycan levels have a high background, due to a normal, baseline glycosaminoglycan content in unaffected individuals. An assay that selectively detects the disease-specific non-reducing ends of heparan sulfate glycosaminoglycans that remain undegraded due to deficiency of a specific enzyme in the catabolic pathway avoids the normal background, increasing sensitivity and specificity. We evaluated glycosaminoglycan content by dye-based and non-reducing end methods using urine, serum, and cerebrospinal fluid from MPS I human samples before and after treatment with intravenous recombinant human alpha-l-iduronidase. We found that both urine total glycosaminoglycans and serum heparan sulfate derived non-reducing end levels were markedly decreased compared to baseline after 26 weeks and 52 weeks of therapy, with a significantly greater percentage reduction in serum non-reducing end (89.8% at 26 weeks and 81.3% at 52 weeks) compared to urine total glycosaminoglycans (68.3% at 26 weeks and 62.4% at 52 weeks, p < 0.001). Unexpectedly, we also observed a decrease in non-reducing end levels in cerebrospinal fluid in all five subjects for whom samples were collected (mean 41.8% reduction, p = 0.01). The non-reducing ends in cerebrospinal fluid showed a positive correlation with serum non-reducing end levels in the subjects (r² = 0.65, p = 0.005). Results suggest utility of the non-reducing end assay in evaluating a therapeutic response in MPS I.

Companion animal models of neurological disease

Clinical translation of novel therapeutics that improve the survival and quality of life of patients with neurological disease remains a challenge, with many investigational drug and device candidates failing in advanced stage clinical trials. Naturally occurring inherited and acquired neurological diseases, such as epilepsy, inborn errors of metabolism, brain tumors, spinal cord injury, and stroke occur frequently in companion animals, and many of these share epidemiologic, pathophysiologic and clinical features with their human counterparts. As companion animals have a relatively abbreviated lifespan and genetic background, are immunocompetent, share their environment with human caregivers, and can be clinically managed using techniques and tools similar to those used in humans, they have tremendous potential for increasing the predictive value of preclinical drug and device studies. Here, we review comparative features of spontaneous neurological diseases in companion animals with an emphasis on neuroimaging methods and features, illustrate their historical use in translational studies, and discuss inherent limitations associated with each disease model. Integration of companion animals with naturally occurring disease into preclinical studies can complement and expand the knowledge gained from studies in other animal models, accelerate or improve the manner in which research is translated to the human clinic, and ultimately generate discoveries that will benefit the health of humans and animals.

Current and Emerging Therapies for Mucopolysaccharidoses

Mucopolysaccharidoses (MPSs) are caused by deficiencies of specific lysosomal enzymes that affect the degradation of mucopolysaccharides or glycosaminoglycans (GAGs). Enzyme replacement therapies are available for an increasing number of MPSs since more than 15 years. Together with hematopoietic stem cell transplantation, these enzyme therapies are currently the gold standard of causal treatment in MPS. Both treatments can improve symptoms and prognosis, but they do not cure these severe conditions. The limitations of intravenous enzyme replacement and cell therapy can be summarized as the development of immune reactions against the therapeutic molecules/cells and failure to restore enduring and sufficient drug exposures in all relevant tissues. Thus innovative approaches include small molecules and encapsulated cells that do not induce immune reactions, gene therapy approaches that aim for sustained enzyme expression, and new enzymes that are able to penetrate barriers to drug distribution like the blood-brain barrier. This chapter provides an update on the state of development of these new therapies and highlights current challenges.

Targeted enzyme delivery systems in lysosomal disorders: an innovative form of therapy for mucopolysaccharidosis

Mucopolysaccharidoses (MPSs), which are inherited lysosomal storage disorders caused by the accumulation of undegraded glycosaminoglycans, can affect the central nervous system (CNS) and elicit cognitive and behavioral issues. Currently used enzyme replacement therapy methodologies often fail to adequately treat the manifestations of the disease in the CNS and other organs such as bone, cartilage, cornea, and heart. Targeted enzyme delivery systems (EDSs) can efficiently cross biological barriers such as blood-brain barrier and provide maximal therapeutic effects with minimal side effects, and hence, offer great clinical benefits over the currently used conventional enzyme replacement therapies. In this review, we provide comprehensive insights into MPSs and explore the clinical impacts of multimodal targeted EDSs.

Cell and Gene Therapies for Mucopolysaccharidoses: Base Editing and Therapeutic Delivery to the CNS

Although individually uncommon, rare diseases collectively account for a considerable proportion of disease impact worldwide. A group of rare genetic diseases called the mucopolysaccharidoses (MPSs) are characterized by accumulation of partially degraded glycosaminoglycans cellularly. MPS results in varied systemic symptoms and in some forms of the disease, neurodegeneration. Lack of treatment options for MPS with neurological involvement necessitates new avenues of therapeutic investigation. Cell and gene therapies provide putative alternatives and when coupled with genome editing technologies may provide long term or curative treatment. Clustered regularly interspaced short palindromic repeats (CRISPR)-based genome editing technology and, more recently, advances in genome editing research, have allowed for the addition of base editors to the repertoire of CRISPR-based editing tools. The latest versions of base editors are highly efficient on-targeting deoxyribonucleic acid (DNA) editors. Here, we describe a number of putative guide ribonucleic acid (RNA) designs for precision correction of known causative mutations for 10 of the MPSs. In this review, we discuss advances in base editing technologies and current techniques for delivery of cell and gene therapies to the site of global degeneration in patients with severe neurological forms of MPS, the central nervous system, including ultrasound-mediated blood-brain barrier disruption.

The Configuration of the Perivascular System Transporting Macromolecules in the CNS

Large blood vessels entering the CNS are surrounded by perivascular spaces that communicate with the cerebrospinal fluid and, at their termini, with the interstitial space. Solutes and particles can translocate along these perivascular conduits, reportedly in both directions. Recently, this prompted a renewed interest in the intrathecal therapy delivery route for CNS-targeted therapeutics. However, the extent of the CNS coverage by the perivascular system is unknown, making the outcome of drug administration to the CSF uncertain. We traced the translocation of model macromolecules from the CSF into the CNS of rats and non-human primates. Conduits transporting macromolecules were found to extend throughout the parenchyma from both external and internal (fissures) CNS boundaries, excluding ventricles, in large numbers, on average ca. 40 channels per mm² in rats and non-human primates. The high density and depth of extension of the perivascular channels suggest that the perivascular route can be suitable for delivery of therapeutics to parenchymal targets throughout the CNS.

The efficacy of intracerebroventricular idursulfase-beta enzyme replacement therapy in mucopolysaccharidosis II murine model: heparan sulfate in cerebrospinal fluid as a clinical biomarker of neuropathology

Mucopolysaccharidosis II (MPS II) is caused by a deficiency of iduronate-2-sulfatase that results in accumulation of glycosaminoglycans (GAG), including heparan sulfate (HS), which is considered to contribute to neuropathology. We examined the efficacy of intracerebroventricular (ICV) enzyme replacement therapy (ERT) of idursulfase-beta (IDS-β) and evaluated the usefulness of HS as a biomarker for neuropathology in MPS II mice. We first examined the efficacy of three different doses (3, 10, and 30 μg) of single ICV injections of IDS-β in MPS II mice. After the single-injection study, its long-term efficacy was elucidated with 30 μg of IDS-β ICV injections repeated every 4 weeks for 24 weeks. The efficacy was assessed by the HS content in the cerebrospinal fluid (CSF) and the brain of the animals along with histologic examinations and behavioral tests. In the single-injection study, the 30 μg of IDS-β ICV injection showed significant reductions of HS content in brain and CSF that were maintained for 28 days. Furthermore, HS content in CSF was significantly correlated with HS content in brain. In the long-term repeated-injection study, the HS content in the brain and CSF was also significantly reduced and correlated. The histologic examinations showed a reduction in lysosomal storage. A significant improvement in memory/learning function was observed in open-field and fear-conditioning tests. ICV ERT with 30 μg of IDS-β produced significant improvements in biochemical, histological, and functional parameters in MPS II mice. Furthermore, we demonstrate for the first time that the HS in the CSF had significant positive correlation with brain tissue HS and GAG levels, suggesting HS in CSF as a useful clinical biomarker for neuropathology.

A novel Blind Start study design to investigate vestronidase alfa for mucopolysaccharidosis VII, an ultra-rare genetic disease

BACKGROUND

Drug development for ultra-rare diseases is challenging because small sample sizes and heterogeneous study populations hamper the ability of randomized, placebo-controlled trials with a single primary endpoint to demonstrate valid treatment effects.

METHODS

To overcome these challenges, a novel Blind Start design was utilized in a study of vestronidase alfa in mucopolysaccharidosis VII (Sly syndrome), an ultra-rare lysosomal disease, that demonstrates the strengths of this approach in a challenging drug-development setting. Twelve subjects were randomized to 1 of 4 blinded groups, each crossing over to active treatment in a blinded fashion at different timepoints with efficacy analysis comparing the last assessment before cross over to after 24 weeks of treatment. Study assessments included: Percentage change from baseline in urinary GAG (uGAG); a Multi-Domain Responder Index (MDRI) using prespecified minimal important differences (6-Minute Walk Test, Forced Vital Capacity, shoulder flexion, visual acuity, and Bruininks-Oseretsky Test of Motor Proficiency); fatigue as assessed by the Pediatric Quality of Life Inventory™ Multidimensional Fatigue Scale; and safety.

RESULTS

Vestronidase alfa treatment for 24 weeks significantly reduced uGAG excretion (dermatan sulfate: 64.8%, p < 0.0001). Most subjects (10/12) had a clinically meaningful improvement in at least one MDRI domain with an overall mean change (±SD) of +0.5 (±0.8) at Treatment Week 24 (p = 0.0527). Exposure-adjusted incidence rates of adverse events were similar between groups.

CONCLUSIONS

The Blind Start study and MDRI design improve statistical power that enhances detection of a positive treatment effect in this rare heterogeneous disease and could be utilized for other ultra-rare diseases.

Treatment of brain disease in the mucopolysaccharidoses

The mucopolysaccharidosis (MPS) disorders are a group of lysosomal storage diseases caused by lysosomal enzyme deficits that lead to glycosaminoglycan accumulation, affecting various tissues throughout the body based on the specific enzyme deficiency. These disorders are characterized by their progressive nature and a variety of somatic manifestations and neurological symptoms. There are established treatments for some MPS disorders, but these mostly alleviate somatic and non-neurological symptoms and do not cure the disease. Patients with MPS I, II, III, and VII can present with neurological manifestations such as neurocognitive decline and behavioral problems. Treatment of these neurological manifestations remains challenging due to the blood-brain barrier (BBB) that limits delivery of therapeutic agents to the central nervous system (CNS). New therapies that circumvent this barrier and target brain disease in MPS are currently under development. They primarily focus on facilitating penetration of drugs through the BBB, delivery of recombinant enzyme to the brain by gene therapy, or direct CNS administration. This review summarizes existing and potential future treatment approaches that target brain disease in MPS. The information in this review is based on current literature and presentations and discussions during a closed meeting by an international group of experts with extensive experience in managing and treating MPS.

Transcranial pulsed ultrasound facilitates brain uptake of laronidase in enzyme replacement therapy for Mucopolysaccharidosis type I disease

Background

Mucopolysaccharidosis type I (MPS I) is a debilitating hereditary disease characterized by alpha-L-iduronidase (IDUA) deficiency and consequent inability to degrade glycosaminoglycans. The pathological accumulation of glycosaminoglycans systemically results in severe mental retardation and multiple organ dysfunction. Enzyme replacement therapy with recombinant human alpha-L-iduronidase (rhIDU) improves the function of some organs but not neurological deficits owing to its exclusion from the brain by the blood-brain barrier (BBB).

Methods

We divided MPS I mice into control group, enzyme replacement group with rhIDU 2.9 mg/kg injection, enzyme replacement with one-spot ultrasound treatment group, and enzyme replacement with two-spot ultrasound treatment group, and compare treatment effectiveness between groups. All ultrasound treatments were applied on left side brain. Evans blue was used to simulate the distribution of rhIDU in the brain.

Results

Transcranial pulsed weakly focused ultrasound combined with microbubbles facilitates brain rhIDU delivery in MPS I mice receiving systemic enzyme replacement therapy. With intravenously injected rhIDU 2.9 mg/kg, the IDUA enzyme activity on the ultrasound treated side of the cerebral hemisphere raised to 7.81-fold that on the untreated side and to 75.84% of its normal value. Evans blue simulation showed the distribution of the delivered drug was extensive, involving a large volume of the treated cerebral hemisphere. Two-spot ultrasound treatment scheme is more efficient for brain rhIDU delivery than one-spot ultrasound treatment scheme.

Conclusions

Transcranial pulsed weakly focused ultrasound can open BBB extensively and facilitates brain rhIDU delivery. This novel technology may provide a new MPS I treatment strategy.

Clearance of Heparan Sulfate and Attenuation of CNS Pathology by Intracerebroventricular BMN 250 in Sanfilippo Type B Mice

Sanfilippo syndrome type B (mucopolysaccharidosis IIIB), caused by inherited deficiency of α-N-acetylglucosaminidase (NAGLU), required for lysosomal degradation of heparan sulfate (HS), is a pediatric neurodegenerative disorder with no approved treatment. Intracerebroventricular (ICV) delivery of a modified recombinant NAGLU, consisting of human NAGLU fused with insulin-like growth factor 2 (IGF2) for enhanced lysosomal targeting, was previously shown to result in marked enzyme uptake and clearance of HS storage in the Naglu^−/− mouse brain. To further evaluate regional, cell type-specific, and dose-dependent biodistribution of NAGLU-IGF2 (BMN 250) and its effects on biochemical and histological pathology, Naglu^−/− mice were treated with 1–100 μg ICV doses (four times over 2 weeks). 1 day after the last dose, BMN 250 (100 μg doses) resulted in above-normal NAGLU activity levels, broad biodistribution, and uptake in all cell types, with NAGLU predominantly localized to neurons in the Naglu^−/− mouse brain. This led to complete clearance of disease-specific HS and reduction of secondary lysosomal defects and neuropathology across various brain regions lasting for at least 28 days after the last dose. The substantial brain uptake of NAGLU attainable by this highest ICV dosage was required for nearly complete attenuation of disease-driven storage accumulations and neuropathology throughout the Naglu^−/− mouse brain.

Slow, continuous enzyme replacement via spinal CSF in dogs with the paediatric-onset neurodegenerative disease, MPS IIIA

Intra-cerebrospinal fluid (CSF) injection of recombinant human lysosomal enzyme is a potential treatment strategy for several neurodegenerative lysosomal storage disorders including Sanfilippo syndrome (Mucopolysaccharidosis type IIIA; MPS IIIA). Here we have utilised the MPS IIIA Huntaway dog model to compare the effectiveness of the repeated intermittent bolus injection strategy being used in the trials with an alternate approach; slow, continual infusion of replacement enzyme (recombinant human sulphamidase; rhSGSH) into the spinal CSF using a SynchroMed II® pump attached to a spinal infusion cannula. The ability of each enzyme delivery strategy to ameliorate lesions in MPS IIIA brain was determined in animals treated from ∼three- to six-months of age. Controls received buffer or no treatment. Significant reductions in heparan sulphate (primary substrate) were observed in brain samples from dogs treated via either cisternal or lumbar spinal CSF bolus injection methods and also in slow intra-spinal CSF infusion-treated dogs. The extent of the reduction differed regionally. Pump-delivered rhSGSH was less effective in reducing secondary substrate (G_M3 ganglioside) in deeper aspects of cerebral cortex, and although near-amelioration of microglial activation was seen in superficial (but not deep) layers of cerebral cortex in both bolus enzyme-treated groups, pump-infusion of rhSGSH had little impact on microgliosis. While continual low-dose infusion of rhSGSH into MPS IIIA dog CSF reduces disease-based lesions in brain, it was not as efficacious as repeated cisternal or spinal CSF bolus infusion of rhSGSH over the time-frame of these experiments.

Intranasal Adeno-Associated Virus Mediated Gene Delivery and Expression of Human Iduronidase in the Central Nervous System: A Noninvasive and Effective Approach for Prevention of Neurologic Disease in Mucopolysaccharidosis Type I

Mucopolysaccharidosis type I (MPS I) is a progressive, multi-systemic, inherited metabolic disease caused by deficiency of α-L-iduronidase (IDUA). Current treatments for this disease are ineffective in treating central nervous system (CNS) disease due to the inability of lysosomal enzymes to traverse the blood-brain barrier. A noninvasive and effective approach was taken in the treatment of CNS disease by intranasal administration of an IDUA-encoding adeno-associated virus serotype 9 (AAV9) vector. Adult IDUA-deficient mice aged 3 months were instilled intranasally with AAV9-IDUA vector. Animals sacrificed 5 months post instillation exhibited IDUA enzyme activity levels that were up to 50-fold that of wild-type mice in the olfactory bulb, with wild-type levels of enzyme restored in all other parts of the brain. Intranasal treatment with AAV9-IDUA also resulted in the reduction of tissue glycosaminoglycan storage materials in the brain. There was strong IDUA immunofluorescence staining of tissue sections observed in the nasal epithelium and olfactory bulb, but there was no evidence of the presence of transduced cells in other portions of the brain. This indicates that reduction of storage materials most likely occurred as a result of enzyme diffusion from the olfactory bulb and the nasal epithelium into deeper areas of the brain. At 8 months of age, neurocognitive testing using the Barnes maze to assess spatial navigation demonstrated that treated IDUA-deficient mice were no different from normal control animals, while untreated IDUA-deficient mice exhibited significant learning and navigation deficits. This novel, noninvasive strategy for intranasal AAV9-IDUA instillation could potentially be used to treat CNS manifestations of human MPS I.

Drug delivery in overcoming the blood-brain barrier: role of nasal mucosal grafting

The blood-brain barrier (BBB) plays a fundamental role in protecting and maintaining the homeostasis of the brain. For this reason, drug delivery to the brain is much more difficult than that to other compartments of the body. In order to bypass or cross the BBB, many strategies have been developed: invasive techniques, such as temporary disruption of the BBB or direct intraventricular and intracerebral administration of the drug, as well as noninvasive techniques. Preliminary results, reported in the large number of studies on the potential strategies for brain delivery, are encouraging, but it is far too early to draw any conclusion about the actual use of these therapeutic approaches. Among the most recent, but still pioneering, approaches related to the nasal mucosa properties, the permeabilization of the BBB via nasal mucosal engrafting can offer new potential opportunities. It should be emphasized that this surgical procedure is quite invasive, but the implication for patient outcome needs to be compared to the gold standard of direct intracranial injection, and evaluated whilst keeping in mind that central nervous system diseases and lysosomal storage diseases are chronic and severely debilitating and that up to now no therapy seems to be completely successful.

Neonatal tolerance induction enables accurate evaluation of gene therapy for MPS I in a canine model

High fidelity animal models of human disease are essential for preclinical evaluation of novel gene and protein therapeutics. However, these studies can be complicated by exaggerated immune responses against the human transgene. Here we demonstrate that dogs with a genetic deficiency of the enzyme α-l-iduronidase (IDUA), a model of the lysosomal storage disease mucopolysaccharidosis type I (MPS I), can be rendered immunologically tolerant to human IDUA through neonatal exposure to the enzyme. Using MPS I dogs tolerized to human IDUA as neonates, we evaluated intrathecal delivery of an adeno-associated virus serotype 9 vector expressing human IDUA as a therapy for the central nervous system manifestations of MPS I. These studies established the efficacy of the human vector in the canine model, and allowed for estimation of the minimum effective dose, providing key information for the design of first-in-human trials. This approach can facilitate evaluation of human therapeutics in relevant animal models, and may also have clinical applications for the prevention of immune responses to gene and protein replacement therapies.

Emerging drugs for the treatment of mucopolysaccharidoses

INTRODUCTION

Despite being reported for the first time almost one century ago, only in the last few decades effective have treatments become available for the mucopolysaccharidoses (MPSs), a group of 11 inherited metabolic diseases that affect lysosomal function. These diseases are progressive, usually severe, and, in a significant number of cases, involve cognitive impairment.

AREAS COVERED

This review will not cover established treatments such as bone marrow/hematopoietic stem cell transplantation and classic intravenous enzyme replacement therapy (ERT), whose long-term outcomes have already been published (MPS I, MPS II, and MPS VI), but it instead focuses on emerging therapies for MPSs. That includes intravenous ERT for MPS IVA and VII, intrathecal ERT, ERT with fusion proteins, substrate reduction therapy, gene therapy, and other novel approaches.

EXPERT OPINION

The available treatments have resulted in improvements for several disease manifestations, but they still do not represent a cure for these diseases; thus, it is important to develop alternative methods to approach the unmet needs (i.e. bone disease, heart valve disease, corneal opacity, and central nervous system (CNS) involvement). The work in progress with novel approaches makes us confident that in 2017, when MPS will commemorate 100 years of its first report, we will be much closer to an effective cure for these challenging conditions.

Continual Low-Dose Infusion of Sulfamidase Is Superior to Intermittent High-Dose Delivery in Ameliorating Neuropathology in the MPS IIIA Mouse Brain

Mucopolysaccharidosis IIIA (MPS IIIA) is a neurodegenerative lysosomal storage disorder characterised by progressive loss of learned skills, sleep disturbance and behavioural problems. Reduced activity of lysosomal sulfamidase results in accumulation of heparan sulfate and secondary storage of glycolipids in the brain. Intra-cisternal sulfamidase infusions reduce disease-related neuropathology; however, repeated injections may subject patients to the risk of infection and tissue damage so alternative approaches are required. We undertook a proof-of-principle study comparing the ability of slow/continual or repeat/bolus infusion to ameliorate neuropathology in MPS IIIA mouse brain. Six-week-old MPS IIIA mice were implanted with subcutaneously located mini-osmotic pumps filled with recombinant human sulfamidase (rhSGSH) or vehicle, connected to lateral ventricle-directed cannulae. Pumps were replaced at 8 weeks of age. Additional MPS IIIA mice received intra-cisternal bolus infusions of the same amount of rhSGSH (or vehicle), at 6 and 8 weeks of age. Unaffected mice received vehicle via each strategy. All mice were euthanised at 10 weeks of age and the brain was harvested to assess the effect of treatment on neuropathology. Mice receiving pump-delivered rhSGSH exhibited highly significant reductions in lysosomal storage markers (lysosomal integral membrane protein-2, G_M3 ganglioside and filipin-positive lipids) and neuroinflammation (isolectin B4-positive microglia, glial fibrillary acidic protein-positive astroglia). MPS IIIA mice receiving rhSGSH via bolus infusion displayed reductions in these markers, but the effectiveness of the strategy was inferior to that seen with slow/pump-based delivery. Continual low-dose infusion may therefore be a more effective strategy for enzyme delivery in MPS IIIA.

Lysosomal storage diseases: from pathophysiology to therapy

Lysosomal storage diseases are a group of rare, inborn, metabolic errors characterized by deficiencies in normal lysosomal function and by intralysosomal accumulation of undegraded substrates. The past 25 years have been characterized by remarkable progress in the treatment of these diseases and by the development of multiple therapeutic approaches. These approaches include strategies aimed at increasing the residual activity of a missing enzyme (enzyme replacement therapy, hematopoietic stem cell transplantation, pharmacological chaperone therapy and gene therapy) and approaches based on reducing the flux of substrates to lysosomes. As knowledge has improved about the pathophysiology of lysosomal storage diseases, novel targets for therapy have been identified, and innovative treatment approaches are being developed.

Clinical Improvement of Alpha-mannosidosis Cat Following a Single Cisterna Magna Infusion of AAV1

Lysosomal storage diseases (LSDs) are debilitating neurometabolic disorders for most of which long-term effective therapies have not been developed. Gene therapy is a potential treatment but a critical barrier to treating the brain is the need for global correction. We tested the efficacy of cisterna magna infusion of adeno-associated virus type 1 (AAV1) expressing feline alpha-mannosidase gene in the postsymptomatic alpha-mannosidosis (AMD) cat, a homologue of the human disease. Lysosomal alpha-mannosidase (MANB) activity in the cerebrospinal fluid (CSF) and serum were increased above the control values in untreated AMD cats. Clinical neurological signs were delayed in onset and reduced in severity. The lifespan of the treated cats was significantly extended. Postmortem histopathology showed resolution of lysosomal storage lesions throughout the brain. MANB activity in brain tissue was significantly above the levels of untreated tissues. The results demonstrate that a single cisterna magna injection of AAV1 into the CSF can mediate widespread neuronal transduction of the brain and meaningful clinical improvement. Thus, cisterna magna gene delivery by AAV1 appears to be a viable strategy for treatment of the whole brain in AMD and should be applicable to many of the neurotropic LSDs as well as other neurogenetic disorders.

Safety of laronidase delivered into the spinal canal for treatment of cervical stenosis in mucopolysaccharidosis I

Enzyme replacement therapy with laronidase (recombinant human alpha-l-iduronidase) is successfully used to treat patients with mucopolysaccharidosis type I (MPS I). However, the intravenously-administered enzyme is not expected to treat or prevent neurological deterioration. As MPS I patients suffer from spinal cord compression due in part to thickened spinal meninges, we undertook a phase I clinical trial of lumbar intrathecal laronidase in MPS I subjects age 8 years and older with symptomatic (primarily cervical) spinal cord compression. The study faced significant challenges, including a heterogeneous patient population, difficulty recruiting subjects despite an international collaborative effort, and an inability to include a placebo-controlled design due to ethical concerns. Nine serious adverse events occurred in the subjects. All subjects reported improvement in symptomatology and showed improved neurological examinations, but objective outcome measures did not demonstrate change. Despite limitations, we demonstrated the safety of this approach to treating neurological disease due to MPS I.

Neonatal Systemic AAV Induces Tolerance to CNS Gene Therapy in MPS I Dogs and Nonhuman Primates

The potential host immune response to a nonself protein poses a fundamental challenge for gene therapies targeting recessive diseases. We demonstrate in both dogs and nonhuman primates that liver-directed gene transfer using an adeno-associated virus (AAV) vector in neonates induces a persistent state of immunological tolerance to the transgene product, substantially improving the efficacy of subsequent vector administration targeting the central nervous system (CNS). We applied this approach to a canine model of mucopolysaccharidosis type I (MPS I), a progressive neuropathic lysosomal storage disease caused by deficient activity of the enzyme α-l-iduronidase (IDUA). MPS I dogs treated systemically in the first week of life with a vector expressing canine IDUA did not develop antibodies against the enzyme and exhibited robust expression in the CNS upon intrathecal AAV delivery at 1 month of age, resulting in complete correction of brain storage lesions. Newborn rhesus monkeys treated systemically with AAV vector expressing human IDUA developed tolerance to the transgene, resulting in high cerebrospinal fluid (CSF) IDUA expression and no antibody induction after subsequent CNS gene therapy. These findings suggest that inducing tolerance to the transgene product during a critical period in immunological development can improve the efficacy and safety of gene therapy.

Experimental therapies in the neuronal ceroid lipofuscinoses

The neuronal ceroid lipofuscinoses represent a group of severe childhood lysosomal storage diseases. With at least 13 identified variants they are the most common cause of inherited neurodegeneration in children. These diseases share common pathological characteristics including motor problems, vision loss, seizures, and cognitive decline, culminating in premature death. Currently, no form of the disease can be treated or cured, with only palliative care to minimise discomfort. This review focuses on current and potentially ground-breaking clinical trials, including small molecule, enzyme replacement, stem cell, and gene therapies, in the development of effective treatments for the various disease subtypes. This article is part of a Special Issue entitled: "Current Research on the Neuronal Ceroid Lipofuscinoses (Batten Disease)".

Determination of the role of injection site on the efficacy of intra-CSF enzyme replacement therapy in MPS IIIA mice

MPS IIIA is an inherited neurodegenerative lysosomal storage disorder characterized by cognitive impairment, sleep-wake cycle disturbance, speech difficulties, eventual mental regression and early death. Neuropathological changes include accumulation of heparan sulfate and glycolipids, neuroinflammation and degeneration. Pre-clinical animal studies indicate that replacement of the deficient enzyme, sulfamidase, via intra-cerebrospinal fluid (CSF) injection is a clinically-relevant treatment approach, reducing neuropathological changes and improving symptoms. Given that there are several routes of administration of enzyme into the CSF (intrathecal lumbar, cisternal and ventricular), determining the effectiveness of each injection strategy is crucial in order to provide the best outcome for patients. We delivered recombinant human sulfamidase (rhSGSH) to a congenic mouse model of MPS IIIA via each of the three routes. Mice were euthanized 24h or one-week post-injection; the distribution of enzyme within the brain and spinal cord parenchyma was investigated, and the impact on primary substrate levels and other pathological lesions determined. Both ventricular and cisternal injection of rhSGSH enable enzyme delivery to brain and spinal cord regions, with the former mediating large, statistically significant decreases in substrate levels and reducing microglial activation. The single lumbar CSF infusion permitted more restricted enzyme delivery, with no reduction in substrate levels and little change in other disease-related lesions in brain tissue. While the ventricular route is the most invasive of the three methods, this strategy may enable the widest distribution of enzyme within the brain, and thus requires further exploration.

Ex vivo gene therapy using patient iPSC-derived NSCs reverses pathology in the brain of a homologous mouse model

Neural stem cell (NSC) transplantation is a promising strategy for delivering therapeutic proteins in the brain. We evaluated a complete process of ex vivo gene therapy using human induced pluripotent stem cell (iPSC)-derived NSC transplants in a well-characterized mouse model of a human lysosomal storage disease, Sly disease. Human Sly disease fibroblasts were reprogrammed into iPSCs, differentiated into a stable and expandable population of NSCs, genetically corrected with a transposon vector, and assessed for engraftment in NOD/SCID mice. Following neonatal intraventricular transplantation, the NSCs engraft along the rostrocaudal axis of the CNS primarily within white matter tracts and survive for at least 4 months. Genetically corrected iPSC-NSCs transplanted post-symptomatically into the striatum of adult Sly disease mice reversed neuropathology in a zone surrounding the grafts, while control mock-corrected grafts did not. The results demonstrate the potential for ex vivo gene therapy in the brain using human NSCs from autologous, non-neural tissues.

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Sly disease patient fibroblasts converted to iPSCs yield transplantable NSCs

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A PiggyBac transposon-based approach corrects the lysosomal enzyme deficiency

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Widespread migration of transplanted NSCs occurs in neonates, but not in adults

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Reversal of microglial pathology in a zone surrounding corrected grafts

Evaluation of enzyme dose and dose-frequency in ameliorating substrate accumulation in MPS IIIA Huntaway dog brain

Intracerebrospinal fluid (CSF) infusion of replacement enzyme is under evaluation for amelioration of disease-related symptoms and biomarker changes in patients with the lysosomal storage disorder mucopolysaccharidosis type IIIA (MPS IIIA; www.clinicaltrials.gov ; NCT#01155778; #01299727). Determining the optimal dose/dose-frequency is important, given the invasive method for chronically supplying recombinant protein to the brain, the main site of symptom generation. To examine these variables, we utilised MPS IIIA Huntaway dogs, providing recombinant human sulphamidase (rhSGSH) to young pre-symptomatic dogs from an age when MPS IIIA dog brain exhibits significant accumulation of primary (heparan sulphate) and secondary (glycolipid) substrates. Enzyme was infused into CSF via the cisterna magna at one of two doses (3 mg or 15 mg/infusion), with the higher dose supplied at two different intervals; fortnightly or monthly. Euthanasia was carried out 24 h after the final injection. Dose- and frequency-dependent reductions in heparan sulphate were observed in CSF and deeper layers of cerebral cortex. When we examined the amount of immunostaining of the general endo/lysosomal marker, LIMP-2, or quantified activated microglia, the higher fortnightly dose resulted in superior outcomes in affected dogs. Secondary lesions such as accumulation of GM3 ganglioside and development of GAD-reactive axonal spheroids were treated to a similar degree by both rhSGSH doses and dose frequencies. Our findings indicate that the lower fortnightly dose is sub-optimal for ameliorating existing and preventing further development of disease-related pathology in young MPS IIIA dog brain; however, increasing the dose fivefold but halving the frequency of administration enabled near normalisation of disease-related biomarkers.

Neuronopathic lysosomal storage disorders: Approaches to treat the central nervous system

Pharmacological research has always focused on developing new therapeutic strategies capable of modifying a disease's natural history and improving patients' quality of life. Despite recent advances within the fields of medicine and biology, some diseases still represent a major challenge for successful therapy. Neuronopathic lysosomal storage disorders, in particular, have high rates of morbidity and mortality and a devastating socio-economic effect. Many of the available therapies, such as enzyme replacement therapy, can reverse the natural history of the disease in peripheral organs but, unfortunately, are still unable to reach the central nervous system effectively because they cannot cross the blood-brain barrier that surrounds and protects the brain. Moreover, many lysosomal storage disorders are characterized by a number of blood-brain barrier dysfunctions, which may further contribute to disease neuropathology and accelerate neuronal cell death. These issues, and their context in the development of new therapeutic strategies, will be discussed in detail in this chapter.

Disease stage determines the efficacy of treatment of a paediatric neurodegenerative disease

Lysosomal storage disorders are a large group of inherited metabolic conditions resulting from the deficiency of proteins involved in lysosomal catabolism, with resulting accumulation of substrates inside the cell. Two-thirds of these disorders are associated with a neurodegenerative phenotype and, although few therapeutic options are available to patients at present, clinical trials of several treatments including lysosomal enzyme replacement are underway. Although animal studies indicate the efficacy of presymptomatic treatment, it is largely unknown whether symptomatic disease-related pathology and functional deficits are reversible. To begin to address this, we used a naturally-occurring mouse model with Sanfilippo syndrome (mucopolysaccharidosis type IIIA) to examine the effectiveness of intracisternal cerebrospinal fluid enzyme replacement in early, mid- and symptomatic disease stage mice. We observed a disease-stage-dependent treatment effect, with the most significant reductions in primary and secondary substrate accumulation, astrogliosis and protein aggregate accumulation seen in mucopolysaccharidosis type IIIA mice treated very early in the disease course. Affected mice treated at a symptomatic age exhibited little change in these neuropathological markers in the time-frame of the study. Microgliosis was refractory to treatment regardless of the age at which treatment was instigated. Although longer-term studies are warranted, these findings indicate the importance of early intervention in this condition.

Gene therapy for neurologic manifestations of mucopolysaccharidoses

INTRODUCTION

Mucopolysaccharidoses (MPS) are a family of lysosomal disorders caused by mutations in genes that encode enzymes involved in the catabolism of glycoaminoglycans. These mutations affect multiple organ systems and can be particularly deleterious to the nervous system. At the present time, enzyme replacement therapy and hematopoietic stem-cell therapy are used to treat patients with different forms of these disorders. However, to a great extent, the nervous system is not adequately responsive to current therapeutic approaches.

AREAS COVERED

Recent advances in gene therapy show great promise for treating MPS. This article reviews the current state of the art for routes of delivery in developing genetic therapies for treating the neurologic manifestations of MPS.

EXPERT OPINION

Gene therapy for treating neurological manifestations of MPS can be achieved by intraventricular, intrathecal, intranasal and systemic administrations. The intraventricular route of administration appears to provide the most widespread distribution of gene therapy vectors to the brain. The intrathecal route of delivery results in predominant distribution to the caudal areas of the brain. The systemic route of delivery via intravenous infusion can also achieve widespread delivery to the CNS; however, the distribution to the brain is greatly dependent on the vector system. Intravenous delivery using lentiviral vectors appear to be less effective than adeno-associated viral (AAV) vectors. Moreover, some subtypes of AAV vectors are more effective than others in crossing the blood-brain barrier. In summary, the recent advances in gene vector technology and routes of delivery to the CNS will facilitate the clinical translation of gene therapy for the treatment of the neurological manifestations of MPS.

Delivery of therapeutic protein for prevention of neurodegenerative changes: comparison of different CSF-delivery methods

Injection of lysosomal enzyme into cisternal or ventricular cerebrospinal fluid (CSF) has been carried out in 11 lysosomal storage disorder models, with each study demonstrating reductions in primary substrate and secondary neuropathological changes, and several reports of improved neurological function. Whilst acute studies in mucopolysaccharidosis (MPS) type II mice revealed that intrathecally-delivered enzyme (into thoraco-lumbar CSF) accesses the brain, the impact of longer-term treatment of affected subjects via this route is unknown. This approach is presently being utilized to treat children with MPS types I, II and III. Our aim was to determine the efficacy of repeated intrathecal injection of recombinant human sulfamidase (rhSGSH) on pathological changes in the MPS IIIA dog brain. The outcomes were compared with those in dogs treated via intra-cisternal or ventricular routes. Control dogs received buffer or no treatment. Significant reductions in primary/secondary substrate levels in brain were observed in dogs treated via all routes, although the extent of the reduction differed regionally. Treatment via all CSF access points resulted in large reductions in microgliosis in superficial cerebral cortex, but only ventricular injection enabled amelioration in deep cerebral cortex. Formation of glutamic acid decarboxylase-positive axonal spheroids in deep cerebellar nuclei was prevented by treatment delivered via any route. Anti-rhSGSH antibodies in the sera of some dogs did not reduce therapeutic efficacy. Our data indicates the capacity of intra-spinal CSF-injected rhSGSH to circulate within CSF-filled spaces, penetrate into brain and mediate a significant reduction in substrate accumulation and secondary pathology in the MPS IIIA dog brain.

Intra-articular enzyme replacement therapy with rhIDUA is safe, well-tolerated, and reduces articular GAG storage in the canine model of mucopolysaccharidosis type I

BACKGROUND

Treatment with intravenous enzyme replacement therapy and hematopoietic stem cell transplantation for mucopolysaccharidosis (MPS) type I does not address joint disease, resulting in persistent orthopedic complications and impaired quality of life. A proof-of-concept study was conducted to determine the safety, tolerability, and efficacy of intra-articular recombinant human iduronidase (IA-rhIDUA) enzyme replacement therapy in the canine MPS I model.

METHODS

Four MPS I dogs underwent monthly rhIDUA injections (0.58 mg/joint) into the right elbow and knee for 6 months. Contralateral elbows and knees concurrently received normal saline. No intravenous rhIDUA therapy was administered. Monthly blood counts, chemistries, anti-rhIDUA antibody titers, and synovial fluid cell counts were measured. Lysosomal storage of synoviocytes and chondrocytes, synovial macrophages and plasma cells were scored at baseline and 1 month following the final injection.

RESULTS

All injections were well-tolerated without adverse reactions. One animal required prednisone for spinal cord compression. There were no clinically significant abnormalities in blood counts or chemistries. Circulating anti-rhIDUA antibody titers gradually increased in all dogs except the prednisone-treated dog; plasma cells, which were absent in all baseline synovial specimens, were predominantly found in synovium of rhIDUA-treated joints at study-end. Lysosomal storage in synoviocytes and chondrocytes following 6 months of IA-rhIDUA demonstrated significant reduction compared to tissues at baseline, and saline-treated tissues at study-end. Mean joint synovial GAG levels in IA-rhIDUA joints were 8.62 ± 5.86 μg/mg dry weight and 21.6 ± 10.4 μg/mg dry weight in control joints (60% reduction). Cartilage heparan sulfate was also reduced in the IA-rhIDUA joints (113 ± 39.5 ng/g wet weight) compared to saline-treated joints (142 ± 56.4 ng/g wet weight). Synovial macrophage infiltration, which was present in all joints at baseline, was abolished in rhIDUA-treated joints only.

CONCLUSIONS

Intra-articular rhIDUA is well-tolerated and safe in the canine MPS I animal model. Qualitative and quantitative assessments indicate that IA-rhIDUA successfully reduces tissue and cellular GAG storage in synovium and articular cartilage, including cartilage deep to the articular surface, and eliminates inflammatory macrophages from synovial tissue.

CLINICAL RELEVANCE

The MPS I canine IA-rhIDUA results suggest that clinical studies should be performed to determine if IA-rhIDUA is a viable approach to ameliorating refractory orthopedic disease in human MPS I.

Intrathecal gene therapy corrects CNS pathology in a feline model of mucopolysaccharidosis I

Enzyme replacement therapy has revolutionized the treatment of the somatic manifestations of lysosomal storage diseases (LSD), although it has been ineffective in treating central nervous system (CNS) manifestations of these disorders. The development of neurotrophic vectors based on novel serotypes of adeno-associated viruses (AAV) such as AAV9 provides a potential platform for stable and efficient delivery of enzymes to the CNS. We evaluated the safety and efficacy of intrathecal delivery of AAV9 expressing α-l-iduronidase (IDUA) in a previously described feline model of mucopolysaccharidosis I (MPS I). A neurological phenotype has not been defined in these animals, so our analysis focused on the biochemical and histological CNS abnormalities characteristic of MPS I. Five MPS I cats were dosed with AAV9 vector at 4-7 months of age and followed for 6 months. Treated animals demonstrated virtually complete correction of biochemical and histological manifestations of the disease throughout the CNS. There was a range of antibody responses against IDUA in this cohort which reduced detectable enzyme without substantially reducing efficacy; there was no evidence of toxicity. This first demonstration of the efficacy of intrathecal gene therapy in a large animal model of a LSD should pave the way for translation into the clinic.

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.