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

Community consensus for Heparan sulfate as a biomarker to support accelerated approval in Neuronopathic Mucopolysaccharidoses

Mucopolysaccharidoses (MPS) disorders are a group of ultra-rare, inherited, lysosomal storage diseases caused by enzyme deficiencies that result in accumulation of glycosaminoglycans (GAGs) in cells throughout the body including the brain, typically leading to early death. Current treatments do not address the progressive cognitive impairment observed in patients with neuronopathic MPS disease. The rarity and clinical heterogeneity of these disorders as well as pre-existing brain disease in clinically diagnosed patients make the development of new therapeutics utilizing a traditional regulatory framework extremely challenging. Children with neuronopathic MPS disorders will likely sustain irreversible brain damage if randomized to a placebo or standard-of-care treatment arm that does not address brain disease. The United States Food and Drug Administration (FDA) recognized these challenges, and, in 2020, issued final guidance for industry on slowly progressive, low-prevalence, rare diseases with substrate deposition that result from single enzyme defects, outlining a path for generating evidence of effectiveness to support accelerated approval based on reduction of substrate accumulation [1]. Neuronopathic MPS disorders, which are characterized by the accumulation of the GAG heparan sulfate (HS) in the brain, fit the intended disease characteristics for which this guidance was written, but to date, this guidance has not yet been applied to any therapeutic candidate for MPS. In February 2024, the Reagan-Udall Foundation for the FDA convened a public workshop for representatives from the FDA, patient advocacy groups, clinical and basic science research, and industry to explore a case study of using cerebrospinal fluid (CSF) HS as a relevant biomarker to support accelerated approval of new therapeutics for neuronopathic MPS disorders. This review provides a summary of the MPS presentations at the workshop and perspective on the path forward for neuronopathic MPS disorders.

Intracerebroventricular dosing of N-sulfoglucosamine sulfohydrolase in mucopolysaccharidosis IIIA mice reduces markers of brain lysosomal dysfunction

Mucopolysaccharidosis type IIIA (MPS IIIA) is a lysosomal storage disorder caused by N-sulfoglucosamine sulfohydrolase (SGSH) deficiency. SGSH removes the sulfate from N-sulfoglucosamine residues on the nonreducing end of heparan sulfate (HS-NRE) within lysosomes. Enzyme deficiency results in accumulation of partially degraded HS within lysosomes throughout the body, leading to a progressive severe neurological disease. Enzyme replacement therapy has been proposed, but further evaluation of the treatment strategy is needed. Here, we used Chinese hamster ovary cells to produce a highly soluble and fully active recombinant human sulfamidase (rhSGSH). We discovered that rhSGSH utilizes both the CI-MPR and LRP1 receptors for uptake into patient fibroblasts. A single intracerebroventricular (ICV) injection of rhSGSH in MPS IIIA mice resulted in a tissue half-life of 9 days and widespread distribution throughout the brain. Following a single ICV dose, both total HS and the MPS IIIA disease-specific HS-NRE were dramatically reduced, reaching a nadir 2 weeks post dose. The durability of effect for reduction of both substrate and protein markers of lysosomal dysfunction and a neuroimmune response lasted through the 56 days tested. Furthermore, seven weekly 148 μg doses ICV reduced those markers to near normal and produced a 99.5% reduction in HS-NRE levels. A pilot study utilizing every other week dosing in two animals supports further evaluation of less frequent dosing. Finally, our dose-response study also suggests lower doses may be efficacious. Our findings show that rhSGSH can normalize lysosomal HS storage and markers of a neuroimmune response when delivered ICV.

Animal medical genetics: a historical perspective on more than 50 years of research into genetic disorders of animals at Massey University

Over the last 50 years, there have been major advances in knowledge and technology regarding genetic diseases, and the subsequent ability to control them in a cost-effective manner. This review traces these advances through research into genetic diseases of animals at Massey University (Palmerston North, NZ), and briefly discusses the disorders investigated during that time, with additional detail for disorders of major importance such as bovine α-mannosidosis, ovine ceroid-lipofuscinosis, canine mucopolysaccharidosis IIIA and feline hyperchylomicronaemia. The overall research has made a significant contribution to veterinary medicine, has provided new biological knowledge and advanced our understanding of similar disorders in human patients, including testing various specific therapies prior to human clinical trials.

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.

Temporospatial Development of Neuropathologic Findings in a Canine Model of Mucopolysaccharidosis IIIB

Mucopolysaccharidosis (MPS) IIIB is a neuropathic lysosomal storage disease characterized by the deficient activity of a lysosomal enzyme obligate for the degradation of the glycosaminoglycan (GAG) heparan sulfate (HS). The pathogenesis of neurodegeneration in MPS IIIB is incompletely understood. Large animal models are attractive for pathogenesis and therapeutic studies due to their larger size, outbred genetics, longer lifespan, and naturally occurring MPS IIIB disease. However, the temporospatial development of neuropathologic changes has not been reported for canine MPS IIIB. Here we describe lesions in 8 brain regions, cervical spinal cord, and dorsal root ganglion (DRG) in a canine model of MPS IIIB that includes dogs aged from 2 to 26 months of age. Pathological changes in the brain included early microscopic vacuolation of glial cells initially observed at 2 months, and vacuolation of neurons initially observed at 10 months. Inclusions within affected cells variably stained positively with PAS and LFB stains. Quantitative immunohistochemistry demonstrated increased glial expression of GFAP and Iba1 in dogs with MPS IIIB compared to age-matched controls at all time points, suggesting neuroinflammation occurs early in disease. Loss of Purkinje cells was initially observed at 10 months and was pronounced in 18- and 26-month-old dogs with MPS IIIB. Our results support the dog as a replicative model of MPS IIIB neurologic lesions and detail the pathologic and neuroinflammatory changes in the spinal cord and DRG of MPS IIIB-affected dogs.

Diagnosis of Mucopolysaccharidoses

The mucopolysaccharidoses (MPSs) include 11 different conditions caused by specific enzyme deficiencies in the degradation pathway of glycosaminoglycans (GAGs). Although most MPS types present increased levels of GAGs in tissues, including blood and urine, diagnosis is challenging as specific enzyme assays are needed for the correct diagnosis. Enzyme assays are usually performed in blood, with some samples (as leukocytes) providing a final diagnosis, while others (such as dried blood spots) still being considered as screening methods. The identification of variants in the specific genes that encode each MPS-related enzyme is helpful for diagnosis confirmation (when needed), carrier detection, genetic counseling, prenatal diagnosis (preferably in combination with enzyme assays) and phenotype prediction. Although the usual diagnostic flow in high-risk patients starts with the measurement of urinary GAGs, it continues with specific enzyme assays and is completed with mutation identification; there is a growing trend to have genotype-based investigations performed at the beginning of the investigation. In such cases, confirmation of pathogenicity of the variants identified should be confirmed by measurement of enzyme activity and/or identification and/or quantification of GAG species. As there is a growing number of countries performing newborn screening for MPS diseases, the investigation of a low enzyme activity by the measurement of GAG species concentration and identification of gene mutations in the same DBS sample is recommended before the suspicion of MPS is taken to the family. With specific therapies already available for most MPS patients, and with clinical trials in progress for many conditions, the specific diagnosis of MPS as early as possible is becoming increasingly necessary. In this review, we describe traditional and the most up to date diagnostic methods for mucopolysaccharidoses.

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.

A Cure for Sanfilippo Syndrome? A Summary of Current Therapeutic Approaches and their Promise

Mucopolysaccharidoses III (MPS III, Sanfilippo syndrome) is a subtype of the Mucopolysaccharidoses (MPS), a group of inherited lysosomal disorders caused by a deficiency of lysosomal enzymes responsible for catabolizing glycosaminoglycans (GAGs). Although MPS III is rare, MPS diseases as a group are relatively frequent with an overall incidence of approximately 1 in 20,000 - 25,000 births. MPS III are paediatric diseases, which cause learning difficulties, behavioural disorders and dementia, as well as skeletal deformities and ultimately result in premature death. There are currently no approved treatments for MPS III, but a number of therapeutic approaches are under development. In the past 30 years, research using cellular and animal models have led to clinical trials involving enzyme replacement therapy (ERT), substrate reduction therapy (SRT) and gene therapy, while stem cells approaches remain at the pre-clinical stage. Although safety and clinical efficacy in animal models have shown promise, the results of clinical trials have proved costly and shown limited therapeutic effects. In this review, we describe the most recent results from clinical trials. While ERT and gene therapy are the most developed therapies for MPS III, we highlight the work that needs to be done to bring us closer to a real treatment for these devastating diseases.

Synthetic Disaccharide Standards Enable Quantitative Analysis of Stored Heparan Sulfate in MPS IIIA Murine Brain Regions

Heparan sulfate (HS) is a complex polysaccharide from the glycosaminoglycan (GAG) family that accumulates in tissues in several neurological lysosomal storage diseases known as mucopolysaccharidosis (MPS) disorders. The quantitation of HS in biological samples is important for studying MPS disorders but is very challenging because of its high molecular weight and heterogeneity. Recently, acid-catalyzed butanolysis followed by LC-MS/MS analysis has emerged as a promising method for the determination of HS. Butanolysis of HS produces fully desulfated disaccharide cleavage products which are detected by LC-MS/MS. Herein we describe the synthesis of butylated HS disaccharide standards and their use for determining the identity of major product peaks in LC-MS chromatograms from butanolysis of HS as well as the related GAGs heparin and heparosan. Furthermore, synthesis of a d₉-labeled disaccharide internal standard enabled the development of a quantitative LC-MS/MS assay for HS. The assay was utilized for the analysis of MPS IIIA mouse brain tissues, revealing significant differences in abundance and in the regional accumulation of the various HS disaccharides in affected mice.

Neurobehavioral phenotypes of neuronopathic mucopolysaccharidoses

Mucopolysaccharidoses (MPS) are a group of lysosomal multisystemic, chronic, and progressive diseases characterized by the storage of glycosaminoglycans (GAGs) that may affect the central nervous system. Neuronopathic MPS such as MPS IH, MPS II, MPS IIIA–D, and MPS VII are characterized by neurocognitive regression. In severe MPS I (MPS IH, or Hurler syndrome) initial developmental trajectory is usually unremarkable but cognitive development shows a plateau by 2 to 4 years of age and then progressively regresses with aging. Patients with neuronopathic MPS II have a plateau of cognitive and adaptive development on average by 4 to 4.5 years of age, although there is significant variability, followed by progressive neurocognitive decline. In patients with classic MPS III, developmental trajectory reaches a plateau around 3 years of age, followed by regression. Sleep disturbances and behavioral problems occur early in MPS II and III with features of externalizing disorders. Acquired autism-like behavior is often observed in children with MPS III after 4–6 years of age. Impaired social and communication abilities do occur, but MPS III children do not have restricted and repetitive interests such as in autism spectrum disorder. MPS type VII is an ultra-rare neuronopathic MPS with a wide clinical spectrum from very severe with early mortality to milder phenotypes with longer survival into adolescence and adulthood. Most patients with MPS VII have intellectual disability and severely delayed speech development, usually associated with hearing impairment. Cognitive regression in neuronopathic MPS runs parallel to a significant decrease in brain tissue volume. Assessment of the developmental profile is challenging because of low cognitive abilities, physical impairment, and behavioral disturbances. Early diagnosis is crucial as different promising treatment approaches have been extensively studied in animal MPS models and are currently being applied in clinical trials.

Pentosan Polysulfate Treatment of Mucopolysaccharidosis Type IIIA Mice

Overall Goal: This study was designed to evaluate the impact of pentosan polysulfate (PPS) treatment on mice with mucopolysaccharidosis (MPS) type IIIA (Sanfilippo A syndrome; OMIM 252900). Protocol: Three groups of MPS IIIA mice were evaluated: 1-week-old mice treated with subcutaneous (subQ) PPS at 25 mg/kg once weekly for 31 weeks (group 1); 5-month-old mice treated with subQ PPS once weekly at 50 mg/kg for 12 weeks (group 2); and 5-week-old mice treated by continual intracerebroventricular (ICV) PPS infusion for 11 weeks (60 μg/kg/day). Treated MPS IIIA mice and controls were assessed by measuring plasma cytokine levels, histologic analyses of systemic organs, and analyses of various neuroinflammatory, neurodegenerative, and lysosomal disease markers in their brains. Neurobehavioral testing also was carried out. Results: As seen in other MPS animal models, subQ PPS treatment reduced plasma cytokine levels and macrophage infiltration in systemic tissues. ICV administration did not elicit these systemic effects. SubQ PPS administration also significantly impacted brain neuropathology, inflammation, and behavior. The effect of early subQ treatment was more significant than dose. Surprisingly, ICV PPS treatment had intermediate effects on most of these brain markers, perhaps due to the limited dose and/or duration of treatment. Consistent with these neuropathological findings, we also observed significant improvements in the hyperactivity/anxiety and learning behaviors of the MPS IIIA mice treated with early subQ PPS.

How close are we to therapies for Sanfilippo disease?

Sanfilippo disease is one of mucopolysaccharidoses (MPS), a group of lysosomal storage diseases characterized by accumulation of partially degraded glycosaminoglycans (GAGs). It is classified as MPS type III, though it is caused by four different genetic defects, determining subtypes A, B, C and D. In each subtype of MPS III, the primary storage GAG is heparan sulfate (HS), but mutations leading to A, B, C, and D subtypes are located in genes coding for heparan N-sulfatase (the SGSH gene), α-N-acetylglucosaminidase (the NAGLU gene), acetyl-CoA:α-glucosaminide acetyltransferase (the HGSNAT gene), and N-acetylglucosamine-6-sulfatase (the GNS gene), respectively. Neurodegenerative changes in the central nervous system (CNS) are major problems in Sanfilippo disease. They cause severe cognitive disabilities and behavioral disturbances. This is the main reason of a current lack of therapeutic options for MPS III patients, while patients from some other MPS types (I, II, IVA, and VI) can be treated with enzyme replacement therapy or bone marrow or hematopoietic stem cell transplantations. Nevertheless, although no therapy is available for Sanfilippo disease now, recent years did bring important breakthroughs in this aspect, and clinical trials are being conducted with enzyme replacement therapy, gene therapy, and substrate reduction therapy. These recent achievements are summarized and discussed in this review.

Synthesis and mass spectrometric analysis of disaccharides from methanolysis of heparan sulfate

Heparan sulfate (HS) disaccharides were synthesized to identify HS methanolysis products by LC-MS/MS with applications for mucopolysaccharidosis disorders.

Whole Body and CNS Biodistribution of rhHNS in Cynomolgus Monkeys after Intrathecal Lumbar Administration: Treatment Implications for Patients with MPS IIIA

Mucopolysaccharidosis III type A (MPS IIIA; Sanfilippo syndrome), a genetic lysosomal disorder causing a deficiency of heparan N-sulfatase (HNS), leads to progressive cognitive decline from an early age. An effective enzyme replacement therapy (ERT) for MPS IIIA requires central nervous system (CNS) biodistribution. Recombinant human heparan N-sulfatase (rhHNS), an investigatory ERT for MPS IIIA, has been formulated for intrathecal (IT) administration since intravenous (IV) administration cannot cross the blood brain barrier (BBB) in sufficient amounts to have a therapeutic effect. In this study, systemic and CNS distribution of rhHNS in cynomolgus monkeys following IV and IT administration was evaluated by quantitation of rhHNS in serum, cerebral spinal fluid (CSF) and various tissues, and positron emission tomography (PET) imaging of live animals. Following IV administration, rhHNS levels were low to non-detectable in the CSF, and systemic clearance was rapid (≤2 h). With IT administration, rhHNS was observable in CNS tissues in ≤1 h, with varying T_max (1-24 h). Appreciable systemic distribution was observed up to 7 days. This provides evidence that in this animal model, intrathecal administration of rhHNS delivers the replacement enzyme to therapeutically relevant tissues for the treatment of Sanfilippo Syndrome type A. Penetration into grey matter and cortex was 3-4 times greater than concentrations in white matter and deeper parenchymal regions, suggesting some limitations of this ERT strategy.

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.

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.

Sanfilippo syndrome: causes, consequences, and treatments

Sanfilippo syndrome, or mucopolysaccharidosis (MPS) type III, refers to one of five autosomal recessive, neurodegenerative lysosomal storage disorders (MPS IIIA to MPS IIIE) whose symptoms are caused by the deficiency of enzymes involved exclusively in heparan sulfate degradation. The primary characteristic of MPS III is the degeneration of the central nervous system, resulting in mental retardation and hyperactivity, typically commencing during childhood. The significance of the order of events leading from heparan sulfate accumulation through to downstream changes in the levels of biomolecules within the cell and ultimately the (predominantly neuropathological) clinical symptoms is not well understood. The genes whose deficiencies cause the MPS III subtypes have been identified, and their gene products, as well as a selection of disease-causing mutations, have been characterized to varying degrees with respect to both frequency and direct biochemical consequences. A number of genetic and biochemical diagnostic methods have been developed and adopted by diagnostic laboratories. However, there is no effective therapy available for any form of MPS III, with treatment currently limited to clinical management of neurological symptoms. The availability of animal models for all forms of MPS III, whether spontaneous or generated via gene targeting, has contributed to improved understanding of the MPS III subtypes, and has provided and will deliver invaluable tools to appraise emerging therapies. Indeed, clinical trials to evaluate intrathecally-delivered enzyme replacement therapy in MPS IIIA patients, and gene therapy for MPS IIIA and MPS IIIB patients are planned or underway.

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.