Biodistribution, kinetics, and efficacy of highly phosphorylated and non-phosphorylated beta-glucuronidase in the murine model of mucopolysaccharidosis VII

In vivo brain delivery of BBB-enabled iduronate 2-sulfatase in rats

BACKGROUND

Iduronate-2-sulfatase (IDS) deficiency (MPS II; Hunter syndrome) is a disorder that exhibits peripheral and CNS pathology. The blood brain barrier (BBB) prevents systemic enzyme replacement therapy (ERT) from alleviating CNS pathology. We aimed to enable brain delivery of systemic ERT by using molecular BBB-Trojans targeting endothelial transcytosis receptors.

METHODS

Single-domain antibody (sdAb)-enzyme fusion protein constructs were prepared in Yarrowia lipolytica. sdAb affinity and BBB permeability were characterized using SPR and an in vitro rodent BBB assay, respectively. In vivo pharmacokinetic (PK) analysis was performed in rats. Quantification of fusion protein amounts were performed using LC-MS.

RESULTS

Fusion proteins consisting of IDS and BBB-transmigrating sdAbs, albumin binding sdAbs or human serum albumin (HSA) were evaluated for their in vitro BBB permeability. IGF1R3H5-IDS was selected for in vivo PK analysis in rats. IDS and IGF1R3H5-IDS exhibited very short (< 10 min) serum half-life (t1/2α), while constructs containing either HSA or anti-serum albumin sdAbs (R28 or M79) showed 8-11 fold increases in the area under the curve (AUC) in serum. CSF analysis indicated that IGF1R3H5 increased brain exposure by 9 fold (AUC) and constructs containing HSA or R28 exhibited 42-52 fold increases. Quantitation of brain levels confirmed the increased and sustained delivery of IDS to the brain of HSA- and R28-containing constructs. Lastly, analysis of brain fractions demonstrated that the increases in brain tissue were due to parenchymal delivery without fusion protein accumulation in brain vessels.

CONCLUSIONS

These results demonstrate the utility of IGF1R-targeting sdAbs to effect brain delivery of lysosomal enzymes, as well as the utility of serum albumin-targeting sdAbs in t1/2 extension, to increase brain delivery of rapidly cleared enzymes.

Development of Lanzyme as the Potential Enzyme Replacement Therapy Drug for Fabry Disease

Fabry disease (FD) is a progressive multisystemic disease characterized by lysosomal enzyme deficiency. Enzyme replacement therapy (ERT) is one of the most significant advancements and breakthroughs in treating FD. However, limited resources and the high cost of ERT might prevent patients from receiving prompt and effective therapy, thereby resulting in severe complications. Future progress in ERT can uncover promising treatment options. In this study, we developed and validated a recombinant enzyme (Lanzyme) based on a CHO-S cell system to provide a new potential option for FD therapy. Our results indicated that Lanzyme was heavily glycosylated, and its highest activity was similar to a commercial enzyme (Fabrazyme®). Our pharmacokinetic assessment revealed that the half-life of Lanzyme was up to 11 min, which is nearly twice that of the commercial enzyme. In vivo experiments revealed that Lanzyme treatment sharply decreased the accumulation levels of Gb3 and lyso-Gb3 in various tissues of FD model mice, with superior or comparable therapeutic effects to Fabrazyme®. Based on these data, Lanzyme may represent a new and promising treatment approach for FD. Building this enzyme production system for ERT can offer additional choice, potentially with enhanced efficacy, for the benefit of patients with FD.

Urinary glycosaminoglycans as a potential biomarker for evaluating treatment efficacy in subjects with mucopolysaccharidoses

Accumulations of glycosaminoglycans (GAGs) that result from deficiencies in lysosomal hydrolases are characteristic of mucopolysaccharidoses (MPS). Enzyme replacement therapies (ERTs) are now available for several MPS diseases (MPS I, MPS II, MPS IVA, MPS VI, and MPS VII), but assessment of the efficacy of treatment can be challenging because these are rare, progressive, and highly heterogeneous diseases; because some clinical manifestations may be irreversible if treatment initiation is delayed; and because determining the benefits of a treatment to prevent those manifestations may take prolonged periods of time. In addition to accumulation of GAGs in tissues, elevated urinary GAG (uGAG) levels are evident and are reduced rapidly after initiation of ERT. Studies in MPS animal models and clinical studies in subjects with MPS diseases have revealed correlations between reductions of uGAG levels and clinical effects of ERTs. In this article, we review the growing body of evidence to support the potential for the use of uGAG levels as predictive biomarkers of treatment efficacy.

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.

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.

A Humoral Immune Response Alters the Distribution of Enzyme Replacement Therapy in Murine Mucopolysaccharidosis Type I

Antibodies against recombinant proteins can significantly reduce their effectiveness in unanticipated ways. We evaluated the humoral response of mice with the lysosomal storage disease mucopolysaccharidosis type I treated with weekly intravenous recombinant human alpha-l-iduronidase (rhIDU). Unlike patients, the majority of whom develop antibodies to recombinant human alpha-l-iduronidase, only approximately half of the treated mice developed antibodies against recombinant human alpha-l-iduronidase and levels were low. Serum from antibody-positive mice inhibited uptake of recombinant human alpha-l-iduronidase into human fibroblasts by partial inhibition compared to control serum. Tissue and cellular distributions of rhIDU were altered in antibody-positive mice compared to either antibody-negative or naive mice, with significantly less recombinant human alpha-l-iduronidase activity in the heart and kidney in antibody-positive mice. In the liver, recombinant human alpha-l-iduronidase was preferentially found in sinusoidal cells rather than in hepatocytes in antibody-positive mice. Antibodies against recombinant human alpha-l-iduronidase enhanced uptake of recombinant human alpha-l-iduronidase into macrophages obtained from MPS I mice. Collectively, these results imply that a humoral immune response against a therapeutic protein can shift its distribution preferentially into macrophage-lineage cells, causing decreased availability of the protein to the cells that are its therapeutic targets.

Pathogenesis and treatment of spine disease in the mucopolysaccharidoses

The mucopolysaccharidoses (MPS) are a family of lysosomal storage disorders characterized by deficient activity of enzymes that degrade glycosaminoglycans (GAGs). Skeletal disease is common in MPS patients, with the severity varying both within and between subtypes. Within the spectrum of skeletal disease, spinal manifestations are particularly prevalent. Developmental and degenerative abnormalities affecting the substructures of the spine can result in compression of the spinal cord and associated neural elements. Resulting neurological complications, including pain and paralysis, significantly reduce patient quality of life and life expectancy. Systemic therapies for MPS, such as hematopoietic stem cell transplantation and enzyme replacement therapy, have shown limited efficacy for improving spinal manifestations in patients and animal models. Therefore, there is a pressing need for new therapeutic approaches that specifically target this debilitating aspect of the disease. In this review, we examine how pathological abnormalities affecting the key substructures of the spine - the discs, vertebrae, odontoid process and dura - contribute to the progression of spinal deformity and symptomatic compression of neural elements. Specifically, we review current understanding of the underlying pathophysiology of spine disease in MPS, how the tissues of the spine respond to current clinical and experimental treatments, and discuss future strategies for improving the efficacy of these treatments.

Mannose receptor-mediated delivery of moss-made α-galactosidase A efficiently corrects enzyme deficiency in Fabry mice

Enzyme replacement therapy (ERT) is an effective treatment for several lysosomal storage disorders (LSDs). Intravenously infused enzymes are taken up by tissues through either the mannose 6-phosphate receptor (M6PR) or the mannose receptor (MR). It is generally believed that M6PR-mediated endocytosis is a key mechanism for ERT in treating LSDs that affect the non-macrophage cells of visceral organs. However, the therapeutic efficacy of MR-mediated delivery of mannose-terminated enzymes in these diseases has not been fully evaluated. We tested the effectiveness of a non-phosphorylated α-galactosidase A produced from moss (referred to as moss-aGal) in vitro and in a mouse model of Fabry disease. Endocytosis of moss-aGal was MR-dependent. Compared to agalsidase alfa, a phosphorylated form of α-galactosidase A, moss-aGal was more preferentially targeted to the kidney. Cellular localization of moss-aGal and agalsidase alfa in the heart and kidney was essentially identical. A single injection of moss-aGal led to clearance of accumulated substrate in the heart and kidney to an extent comparable to that achieved by agalsidase alfa. This study suggested that mannose-terminated enzymes may be sufficiently effective for some LSDs in which non-macrophage cells are affected, and that M6P residues may not always be a prerequisite for ERT as previously considered.

Pharmacologic manipulation of lysosomal enzyme transport across the blood-brain barrier

The adult blood-brain barrier, unlike the neonatal blood-brain barrier, does not transport lysosomal enzymes into brain, making enzyme replacement therapy ineffective in treating the central nervous system symptoms of lysosomal storage diseases. However, enzyme transport can be re-induced with alpha-adrenergics. Here, we examined agents that are known to alter the blood-brain barrier transport of large molecules or to induce lysosomal enzyme transport across the blood-brain barrier ((±)epinephrine, insulin, retinoic acid, and lipopolysaccharide) in 2-week-old and adult mice. In 2-week-old adolescent mice, all these pharmacologic agents increased brain and heart uptake of phosphorylated human β-glucuronidase. In 8-week-old adult mice, manipulations with (±)epinephrine, insulin, and retinoic acid were significantly effective on uptake by brain and heart. The increased uptake of phosphorylated human β-glucuronidase was inhibited by mannose 6-phosphate for the agents (±)epinephrine and retinoic acid and by L-NG-nitroarginine methyl ester for the agent lipopolysaccharide in neonatal and adult mice. An in situ brain perfusion study revealed that retinoic acid directly modulated the transport of phosphorylated human β-glucuronidase across the blood-brain barrier. The present study indicates that there are multiple opportunities to at least transiently induce phosphorylated human β-glucuronidase transport at the adult blood-brain barrier.

Evaluation of AAV-mediated Gene Therapy for Central Nervous System Disease in Canine Mucopolysaccharidosis VII

Mucopolysaccharidosis VII (MPS VII) is a lysosomal storage disease arising from mutations in β-d-glucuronidase (GUSB), which results in glycosaminoglycan (GAG) accumulation and a variety of clinical manifestations including neurological disease. Herein, MPS VII dogs were injected intravenously (i.v.) and/or intrathecally (i.t.) via the cisterna magna with AAV9 or AAVrh10 vectors carrying the canine GUSB cDNA. Although i.v. injection alone at 3 days of age resulted in normal cerebrospinal fluid (CSF) GUSB activity, brain tissue homogenates had only ~1 to 6% normal GUSB activity and continued to have elevated GAG storage. In contrast, i.t. injection at 3 weeks of age resulted in CSF GUSB activity 44-fold normal while brain tissue homogenates had >100% normal GUSB activity and reduced GAGs compared with untreated dogs. Markers for secondary storage and inflammation were eliminated in i.t.-treated dogs and reduced in i.v.-treated dogs compared with untreated dogs. Given that i.t.-treated dogs expressed higher levels of GUSB in the CNS tissues compared to those treated i.v., we conclude that i.t. injection of AAV9 or AAVrh10 vectors is more effective than i.v. injection alone in the large animal model of MPS VII.

Strategies for delivery of therapeutics into the central nervous system for treatment of lysosomal storage disorders

Lysosomal storage disorders (LSDs) are a group of about fifty life-threatening conditions caused by genetic defects affecting lysosomal components. The underscoring molecular deficiency leads to widespread cellular dysfunction through most tissues in the body, including peripheral organs and the central nervous system (CNS). Efforts during the last few decades have rendered a remarkable advance regarding our knowledge, medical awareness, and early detection of these genetic defects, as well as development of several treatment modalities. Clinical and experimental strategies encompassing enzyme replacement, gene and cell therapies, substrate reduction, and chemical chaperones are showing considerable potential in attenuating the peripheral pathology. However, a major drawback has been encountered regarding the suboptimal impact of these approaches on the CNS pathology. Particular anatomical and biochemical constraints of this tissue pose a major obstacle to the delivery of therapeutics into the CNS. Approaches to overcome these obstacles include modalities of local administration, strategies to enhance the blood-CNS permeability, intranasal delivery, use of exosomes, and those exploiting targeting of transporters and transcytosis pathways in the endothelial lining. The later two approaches are being pursued at the time by coupling therapeutic agents to affinity moieties and drug delivery systems capable of targeting these natural transport routes. This approach is particularly promising, as using paths naturally active at this interface may render safe and effective delivery of LSD therapies into the CNS.

Transplantation of human umbilical mesenchymal stem cells cures the corneal defects of mucopolysaccharidosis VII mice

Mucopolysaccharidosis (MPS) are a family of related disorders caused by a mutation in one of the lysosomal exoglycosidases which leads to the accumulation of glycosaminoglycans (GAGs). MPS VII, caused by a mutation in β-glucuronidase, manifests hepatomegaly, skeletal dysplasia, short stature, corneal clouding, and developmental delay. Current treatment regimens for MPS are not effective for treating corneal clouding and impaired mental development. We hypothesized that human umbilical mesenchymal stem cells (UMSCs) transplanted into the corneal stroma could participate in the catabolism of GAGs providing a means of cell therapy for MPS. For such treatment, human UMSCs were intrastromally transplanted into corneas of MPS VII mice. UMSC transplantation restored the dendritic and hexagonal morphology of host keratocytes and endothelial cells, respectively, and in vivo confocal microscopy (HRT-II) revealed reduced corneal haze. Immunohistochemistry using antibodies against heparan sulfate and chondroitin sulfate chains as well as lysosomal-associated membrane protein 2 revealed a decrease in GAG content and both lysosomal number and size in the treated corneas. Labeling UMSC intracellular compartments prior to transplantation revealed the distribution of UMSC vesicles throughout the corneal stroma and endothelium. An in vitro coculture assay between skin fibroblasts isolated from MPS VII mice and UMSC demonstrated that neutral vesicles released by the UMSC are taken up by the fibroblasts and proceed to fuse with the acidic lysosomes. Therefore, transplanted UMSCs participate both in extracellular GAG turnover and enable host keratocytes to catabolize accumulated GAG products, suggesting that UMSC could be a novel alternative for treating corneal defects associated with MPS and other congenital metabolic disorders.

Insulin-like growth factor II peptide fusion enables uptake and lysosomal delivery of α-N-acetylglucosaminidase to mucopolysaccharidosis type IIIB fibroblasts

Enzyme replacement therapy for MPS IIIB (mucopolysaccharidosis type IIIB; also known as Sanfilippo B syndrome) has been hindered by inadequate mannose 6 phosphorylation and cellular uptake of rhNAGLU (recombinant human α-N-acetylglucosaminidase). We expressed and characterized a modified rhNAGLU fused to the receptor-binding motif of IGF-II (insulin-like growth factor 2) (rhNAGLU-IGF-II) to enhance its ability to enter cells using the cation-independent mannose 6-phosphate receptor, which is also the receptor for IGF-II (at a different binding site). RhNAGLU-IGF-II was stably expressed in CHO (Chinese-hamster ovary) cells, secreted and purified to apparent homogeneity. The Km and pH optimum of the fusion enzyme was similar to those reported for rhNAGLU. Both intracellular uptake and confocal microscopy suggested that MPS IIIB fibroblasts readily take up the fusion enzyme via receptor-mediated endocytosis that was inhibited significantly (P<0.001) by the monomeric IGF-II peptide. Glycosaminoglycan storage was reduced by 60% (P<0.001) to near background levels in MPS IIIB cells after treatment with rhNAGLU-IGF-II, with half-maximal correction at concentrations of 3-12 pM. A similar cellular uptake mechanism via the IGF-II receptor was also demonstrated in two different brain tumour-derived cell lines. Fusion of rhNAGLU to IGF-II enhanced its cellular uptake while maintaining enzymatic activity, supporting its potential as a therapeutic candidate for treating MPS IIIB.

Enzyme replacement therapy for lysosomal diseases: lessons from 20 years of experience and remaining challenges

In 1964, Christian de Duve first suggested that enzyme replacement might prove therapeutic for lysosomal storage diseases (LSDs). Early efforts identified the major obstacles, including the inability to produce large quantities of the normal enzymes, the lack of animal models for proof-of-concept studies, and the potentially harmful immune responses to the "foreign" normal enzymes. Subsequently, the identification of receptor-mediated targeting of lysosomal enzymes, the cloning and overexpression of human lysosomal genes, and the generation of murine models markedly facilitated the development of enzyme replacement therapy (ERT). However, ERT did not become a reality until the early 1990s, when its safety and effectiveness were demonstrated for the treatment of type 1 Gaucher disease. Today, ERT is approved for six LSDs, and clinical trials with recombinant human enzymes are ongoing in several others. Here, we review the lessons learned from 20 years of experience, with an emphasis on the general principles for effective ERT and the remaining challenges.

Cerebellar alterations and gait defects as therapeutic outcome measures for enzyme replacement therapy in α-mannosidosis

α-Mannosidosis is a rare lysosomal storage disease with accumulation of undegraded mannosyl-linked oligosaccharides in cells throughout the body, most notably in the CNS. This leads to a broad spectrum of neurological manifestations, including progressive intellectual impairment, disturbed motor functions, and cerebellar atrophy. To develop therapeutic outcome measures for enzyme replacement therapy that could be used for human patients, a gene knockout model of α-mannosidosis in mice was analyzed for CNS pathology and motor deficits. In the cerebellar molecular layer, α-mannosidosis mice display clusters of activated Bergman glia, infiltration of phagocytic macrophages, and accumulation of free cholesterol and gangliosides (GM1), notably in regions lacking Purkinje cells. α-Mannosidosis brain lysates also displayed increased expression of Lamp1 and hyperglycosylation of the cholesterol binding protein NPC2. Detailed assessment of motor function revealed age-dependent gait defects in the mice that resemble the disturbed motor function in human patients. Short-term enzyme replacement therapy partially reversed the observed cerebellar pathology with fewer activated macrophages and astrocytes but unchanged levels of hyperglycosylated NPC2, gangliosides, and cholesterol. The present study demonstrates cerebellar alterations in α-mannosidosis mice that relate to the motor deficits and pathological changes seen in human patients and can be used as therapeutic outcome measures.

Guanidinylated neomycin mediates heparan sulfate-dependent transport of active enzymes to lysosomes

Guanidinylated neomycin (GNeo) can transport bioactive, high molecular weight cargo into the interior of cells in a process that depends on cell surface heparan sulfate proteoglycans. In this report, we show that GNeo-modified quantum dots bind to cell surface heparan sulfate, undergo endocytosis and eventually reach the lysosomal compartment. An N-hydroxysuccinimide activated ester of GNeo (GNeo-NHS) was prepared and conjugated to two lysosomal enzymes, beta-D-glucuronidase (GUS) and alpha-L-iduronidase. Conjugation did not interfere with enzyme activity and enabled binding of the enzymes to heparin-Sepharose and heparan sulfate on primary human fibroblasts. Cells lacking the corresponding lysosomal enzyme took up sufficient amounts of the conjugated enzymes to restore normal turnover of glycosaminoglycans. The high capacity of proteoglycan-mediated uptake suggests that this method of delivery might be used for enzyme replacement or introduction of foreign enzymes into cells.

Enhancement of drug delivery: enzyme-replacement therapy for murine Morquio A syndrome

Mucopolysaccharidosis IVA (MPS IVA, Morquio A disease) is an inherited lysosomal storage disorder that features skeletal chondrodysplasia caused by deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS). Human GALNS was bioengineered with the N-terminus extended by the hexaglutamate sequence (E6) to improve targeting to bone (E6-GALNS). We initially assessed blood clearance and tissue distribution. Next, to assess the effectiveness of storage clearance and reversal of pathological phenotype, a dose of 250 U/g of enzyme was given weekly to Morquio A mice (adults: 12 or 24 weeks, newborn: 8 weeks). Sulfatase modifier factor 1 (SUMF1) was co-transfected to activate the enzyme fully. The E6-GALNS tagged enzyme had markedly prolonged clearance from circulation, giving over 20 times exposure time in blood, compared to untagged enzyme. The tagged enzyme was retained longer in bone, with residual enzyme activity demonstrable at 48 hours after infusion. The pathological findings in adult mice treated with tagged enzyme showed substantial clearance of the storage materials in bone, bone marrow, and heart valves, especially after 24 weekly infusions. Mice treated from the newborn period showed marked reduction of storage materials in tissues investigated. These findings indicate the feasibility of using tagged enzyme to enhance delivery and pathological effectiveness in Morquio A mice.

New biotechnological and nanomedicine strategies for treatment of lysosomal storage disorders

This review discusses the multiple bio- and nanotechnological strategies developed in the last few decades for treatment of a group of fatal genetic diseases termed lysosomal storage disorders. Some basic foundation on the biomedical causes and social and clinical relevance of these diseases is provided. Several treatment modalities, from those currently available to novel therapeutic approaches under development, are also discussed; these include gene and cell therapies, substrate reduction therapy, chemical chaperones, enzyme replacement therapy, multifunctional chimeras, targeting strategies, and drug carrier approaches.

Improved retroviral vector design results in sustained expression after adult gene therapy in mucopolysaccharidosis I mice

BACKGROUND

Mucopolysaccharidosis I (MPS I) is a lysosomal storage disease due to alpha-L-iduronidase (IDUA) deficiency that results in the accumulation of glycosaminoglycans (GAG). Gene therapy can reduce most clinical manifestations, but mice that receive transfer as adults lose expression unless they receive immunosuppression. Increasing liver specificity of transgene expression has reduced immune responses to other genes.

METHODS

A gamma retroviral vector was generated with a liver-specific human alpha1-antitrypsin promoter and the canine IDUA cDNA inverted relative to the retroviral long-terminal repeat. Adult MPS I mice received the vector intravenously at 6 weeks of age and were assessed for expression via serial serum IDUA assays. Functional testing and organ analysis were performed at 8 months.

RESULTS

This vector resulted in high specificity of expression in liver, and serum IDUA activity was stable in 90% of animals. Although the average serum IDUA activity was relatively low at 12.6 +/- 8.1 units/ml in mice with stable expression, a relatively high percentage of enzyme contained the mannose 6-phosphorylation necessary for uptake by other cells. At 6.5 months after transduction, most organs had high IDUA activity and normalized GAG levels. There was complete correction of hearing and vision abnormalities and significant improvements in bone, although the aorta was refractory to treatment.

CONCLUSIONS

Stable expression of IDUA in adult MPS I mice can be achieved without immunosuppression by modifying the vector to reduce expression in the spleen. This approach may be effective in patients with MPS I or other lysosomal storage diseases.

Pompe's disease

Pompe's disease, glycogen-storage disease type II, and acid maltase deficiency are alternative names for the same metabolic disorder. It is a pan-ethnic autosomal recessive trait characterised by acid alpha-glucosidase deficiency leading to lysosomal glycogen storage. Pompe's disease is also regarded as a muscular disorder, but the generalised storage of glycogen causes more than mobility and respiratory problems. The clinical spectrum is continuous and broad. First symptoms can present in infants, children, and adults. Cardiac hypertrophy is a key feature of classic infantile Pompe's disease. For a long time, there was no means to stop disease progression, but the approval of enzyme replacement therapy has substantially changed the prospects for patients. With this new development, the disease is now among the small but increasing number of lysosomal storage disorders, for which treatment has become a reality. This review is meant to raise general awareness, to present and discuss the latest insights in disease pathophysiology, and to draw attention to new developments about diagnosis and care. We also discuss the developments that led to the approval of enzyme replacement therapy with recombinant human alpha-glucosidase from Chinese hamster ovary cells (alglucosidase alfa) by the US Food and Drug Administration and European Medicines Agency in 2006, and review clinical practice.

Immune tolerance improves the efficacy of enzyme replacement therapy in canine mucopolysaccharidosis I

Mucopolysaccharidoses (MPSs) are lysosomal storage diseases caused by a deficit in the enzymes needed for glycosaminoglycan (GAG) degradation. Enzyme replacement therapy with recombinant human alpha-L-iduronidase successfully reduces lysosomal storage in canines and humans with iduronidase-deficient MPS I, but therapy usually also induces antibodies specific for the recombinant enzyme that could reduce its efficacy. To understand the potential impact of alpha-L-iduronidase-specific antibodies, we studied whether inducing antigen-specific immune tolerance to iduronidase could improve the effectiveness of recombinant iduronidase treatment in canines. A total of 24 canines with MPS I were either tolerized to iduronidase or left nontolerant. All canines received i.v. recombinant iduronidase at the FDA-approved human dose or a higher dose for 9-44 weeks. Nontolerized canines developed iduronidase-specific antibodies that proportionally reduced in vitro iduronidase uptake. Immune-tolerized canines achieved increased tissue enzyme levels at either dose in most nonreticular tissues and a greater reduction in tissue GAG levels, lysosomal pathology, and urinary GAG excretion. Tolerized MPS I dogs treated with the higher dose received some further benefit in the reduction of GAGs in tissues, urine, and the heart valve. Therefore, immune tolerance to iduronidase improved the efficacy of enzyme replacement therapy with recombinant iduronidase in canine MPS I and could potentially improve outcomes in patients with MPS I and other lysosomal storage diseases.

Infused Fc-tagged beta-glucuronidase crosses the placenta and produces clearance of storage in utero in mucopolysaccharidosis VII mice

Glycosaminoglycan storage begins in prenatal life in patients with mucopolysaccharidosis (MPS). In fact, prenatal hydrops is a common manifestation of MPS VII because of beta-glucuronidase (GUS) deficiency. One way to address prenatal storage might be to deliver the missing enzyme across the placenta into the fetal circulation. Maternal IgG is transported across the placenta by the neonatal Fc receptor (FcRn), which recognizes the Fc domain of IgG and mediates transcytosis from maternal to fetal circulation. We hypothesized that we could exploit this process to deliver corrective enzyme to the fetus. To test this hypothesis, the C-terminal fusion protein, GUS-Fc, was compared with native, untagged, recombinant GUS for clearance from the maternal circulation, delivery to the fetus, and reduction of lysosomal storage in offspring of MPS VII mice. We observed that GUS-Fc, infused into pregnant mothers on embryonic days 17 and 18, was transported across the placenta. Similarly infused untagged GUS was not delivered to the fetus. GUS-Fc plasma enzyme activity in newborn MPS VII mice was 1,000 times that seen after administration of untagged GUS and approximately 100 times that of untreated WT newborns. Reduced lysosomal storage in heart valves, liver, and spleen provided evidence that in utero enzyme replacement therapy with GUS-Fc targeted sites of storage in the MPS VII fetus. We hypothesize that this noninvasive approach could deliver the missing lysosomal enzyme to a fetus with any lysosomal storage disease. It might also provide a method for inducing immune tolerance to the missing enzyme or another foreign protein.

Acidic amino acid tag enhances response to enzyme replacement in mucopolysaccharidosis type VII mice

We have tested an acidic oligopeptide-based targeting system for delivery of enzymes to tissues, especially bone and brain, in a murine mucopolysaccharidosis type VII (MPS VII) model. This strategy is based upon tagging a short peptide consisting of acidic amino acids (AAA) to N terminus of human beta-glucuronidase (GUS). The pharmacokinetics, biodistribution, and the pathological effect on MPS VII mouse after 12 weekly infusions were determined for recombinant human untagged and tagged GUS. The tagged GUS was taken up by MPS VII fibroblasts in a mannose 6-phosphate receptor-dependent manner. Intravenously injected AAA-tagged enzyme had five times more prolonged blood clearance compared with the untagged enzyme. The tagged enzyme was delivered effectively to bone, bone marrow, and brain in MPS VII mice and was effective in reversing the storage pathology. The storage in osteoblasts was cleared similarly with both enzyme types. However, cartilage showed a little response to any of the enzymes. The tagged enzyme reduced storage in cortical neurons, hippocampus, and glia cells. A highly sensitive method of tandem mass spectrometry on serum indicated that the concentration of serum dermatan sulfate and heparan sulfate in mice treated with the tagged enzyme decreased more than the untagged enzyme. These preclinical studies suggest that this AAA-based targeting system may enhance enzyme-replacement therapy.

Non-inhibitory antibodies impede lysosomal storage reduction during enzyme replacement therapy of a lysosomal storage disease

Enzyme replacement therapy is a treatment option for several lysosomal storage disorders. We reported previously that treatment of a knockout mouse model of the sphingolipid storage disease metachromatic leukodystrophy (MLD) by intravenous injection of recombinant human arylsulfatase A (rhASA) reduces sulfatide storage and improves nervous system pathology and function. Here, we show that treated mice can develop anti-rhASA antibodies, which impede sulfatide clearance without inhibiting enzyme activity. The neutralizing effect of antibodies was reproduced in cell culture models of MLD by demonstrating that mouse immune serum reduces the ability of rhASA to clear sulfatide from cultured ASA-deficient Schwann and kidney cells. We show that reduced clearance is due to an antibody-mediated blockade of mannose 6-phosphate receptor-dependent enzyme uptake, retargeting of rhASA from sulfatide-storing cells to macrophages, intracellular misrouting of rhASA, and reduction of enzyme stability. Induction of immunotolerance to rhASA by transgenic expression of an active site mutant of human ASA restores sulfatide clearance in mice. The data indicate that the influence of non-inhibitory antibodies must be more intensively considered in evaluating the therapeutic efficacy of enzyme replacement in lysosomal storage disorders in general and in patients without cross-reacting material specifically.

Epinephrine enhances lysosomal enzyme delivery across the blood brain barrier by up-regulation of the mannose 6-phosphate receptor

Delivering therapeutic levels of lysosomal enzymes across the blood-brain barrier (BBB) has been a pivotal issue in treating CNS storage diseases, including the mucopolysaccharidoses. An inherited deficiency of beta-glucuronidase (GUS) causes mucopolysaccharidosis type VII that is characterized by increased systemic and CNS storage of glycosaminoglycans. We previously showed that the neonate uses the mannose 6-phosphate (M6P) receptor to transport phosphorylated GUS (P-GUS) across the BBB and that this transporter is lost with maturation. Induction of expression of this BBB transporter would make enzyme replacement therapy in the adult possible. Here, we tested pharmacological manipulation with epinephrine to restore functional transport of P-GUS across the adult BBB. Epinephrine (40 nmol) coinjected i.v. with (131)I-P-GUS induced the transport across the BBB in 8-week-old mice. The brain influx rate of (131)I-P-GUS (0.29 mul/g per min) returned to the level seen in neonates. Capillary depletion showed that 49% of the (131)I-P-GUS in brain was in brain parenchyma. No increases of influx rate or the vascular space for (125)I-albumin, a vascular marker, was observed with epinephrine (40 nmol), showing that enhanced passage was not caused by disruption of the BBB. Brain uptake of (131)I-P-GUS was significantly inhibited by M6P in a dose-dependent manner, whereas epinephrine failed to increase brain uptake of nonphosphorylated GUS. Thus, the effect of epinephrine on the transport of (131)I-P-GUS was ligand specific. These results indicate that epinephrine restores the M6P receptor-mediated functional transport of (131)I-P-GUS across the BBB in adults to levels seen in the neonate.

Lysosomal Enzyme Replacement of the Brain with Intravenous Non-Viral Gene Transfer

PURPOSE

The delivery of non-viral plasmid DNA to brain across the blood-brain barrier (BBB) with intravenous administration of non-viral plasmid DNA encoding a lysosomal enzyme, beta-glucuronidase (GUSB), was examined in GUSB null mice, a model of type VII mucopolysaccharidosis.

METHODS

The plasmid, designated pCMV-GUSB, is encapsulated in Trojan horse liposomes, which are targeted across the BBB, and the brain cell membrane, with a monoclonal antibody to the mouse transferrin receptor.

RESULTS

The GUSB enzyme activity was increased >50-fold in cell culture of fibroblasts obtained from GUSB null mice, following application of the antibody-targeted liposomes carrying the pCMV-GUSB, and enzyme activity remained high for >2 weeks. Adult GUSB null mice were treated with a single intravenous administration of 0.2 ml of Trojan horse liposomes carrying the pCMV-GUSB at a dose of 10 mug/mouse of plasmid DNA. The GUSB enzyme activity was increased greater than tenfold in brain, liver, spleen, lung, and kidney, but not in heart.

CONCLUSIONS

Intravenous Trojan horse liposome administration increased brain GUSB enzyme activity to the therapeutic range of brain GUSB enzyme activity. These studies show it is possible to deliver non-viral plasmid DNA encoding lysosomal enzymes to the brain following intravenous administration of receptor-specific Trojan horse liposomes.

Characterization and pharmacokinetic study of recombinant human N-acetylgalactosamine-6-sulfate sulfatase

Mucopolysaccharidosis IVA (MPS IVA) is an autosomal recessive disorder caused by a deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS). The aims of this study were to establish Chinese hamster ovary (CHO) cells overexpressing recombinant human GALNS (rhGALNS) and to assess pharmacokinetics and tissue distribution of purified enzymes by using MPS IVA knock-out mouse (Galns(-/-)). The CHO-cell derived rhGALNS was purified from the media by a two-step affinity chromatography procedure. The rhGALNS was administered intravenously to 3-month-old Galns(-/-) mice at a single dose of 250U/g of body weight. The treated mice were examined by assaying the GALNS activity at baseline and up to 240min to assess clearance of the enzyme from blood circulation. The mice were sacrificed 4h after infusion of the enzyme to study the enzyme distribution in tissues. The rhGALNS was purified 1317-fold with 71% yield. The enzyme was taken up by Galns(-/-) chondrocytes (150U/mg/15h). The uptake was inhibited by mannose-6-phosphate. The enzyme activity disappeared from circulation with a half-life of 2.9min. After enzyme infusion, the enzyme was taken up and detected in multiple tissues (40.7% of total infused enzymes in liver). Twenty-four hours after a single infusion of the fluorescence-labeled enzymes into MPS IVA mice, biodistribution pattern showed the amount of tagged enzyme retained in bone, bone marrow, liver, spleen, kidney, and heart. In conclusion, we have shown that the phosphorylated rhGALNS is delivered to multiple tissues, including bone, and that it functions bioactively in Galns(-/-) chondrocytes implying a potential enzyme replacement treatment.

Clinical response to persistent, low-level beta-glucuronidase expression in the murine model of mucopolysaccharidosis type VII

Mucopolysaccharidosis type VII (MPS VII) is a lysosomal storage disease caused by beta-glucuronidase (GUSB) deficiency. This disease exhibits a broad spectrum of clinical signs including skeletal dysplasia, retinal degeneration, cognitive deficits and hearing impairment. Sustained, high-level expression of GUSB significantly improves the clinical course of the disease in the murine model of MPS VII. Low levels of enzyme expression (1-5% of normal) can significantly reduce the biochemical and histopathological manifestations of MPS VII. However, it has not been clear from previous studies whether persistent, low levels of circulating GUSB lead to significant improvements in the clinical presentation of this disease. We generated a rAAV2 vector that mediates persistent, low-level GUSB expression in the liver. Liver and serum levels of GUSB were maintained at approximately 5% and approximately 2.5% of normal, respectively, while other tissue ranged from background levels to 0.9%. This level of activity significantly reduced the secondary elevations of alpha-galactosidase and the levels of glycosaminoglycans in multiple tissues. Interestingly, this level of GUSB was also sufficient to reduce lysosomal storage in neurons in the brain. Although there were small but statistically significant improvements in retinal function, auditory function, skeletal dysplasia, and reproduction in rAAV-treated MPS VII mice, the clinical deficits were still profound and there was no improvement in lifespan. These data suggest that circulating levels of GUSB greater than 2.5% will be required to achieve substantial clinical improvements in MPS VII.

Enzyme therapy in mannose receptor-null mucopolysaccharidosis VII mice defines roles for the mannose 6-phosphate and mannose receptors

Enzyme replacement therapy (ERT) is available for several lysosomal storage diseases. Except for Gaucher disease, for which an enzyme with exposed mannosyl residues targets mannose receptors (MR) on macrophages, ERT targets primarily the mannose 6-phosphate receptor (MPR). Most recombinant lysosomal enzymes contain oligosaccharides with both terminal mannosyl and mannose 6-phosphate residues. Effective MPR-mediated delivery may be compromised by rapid clearance of infused enzyme by the MR on fixed tissue macrophages, especially Kupffer cells. To evaluate the impact of this obstacle to ERT, we introduced the MR-null mutation onto the mucopolysaccharidosis type VII (MPS VII) background and produced doubly deficient MR-/- MPS VII mice. The availability of both MR+/+ and MR-/- mice allowed us to study the effects of eliminating the MR on MR- and MPR-mediated plasma clearance and tissue distribution of infused phosphorylated (P) and nonphosphorylated (NP) forms of human beta-glucuronidase (GUS). In MR+/+ MPS VII mice, the MR clearance system predominated at doses up to 6.4 mg/kg P-GUS. Genetically eliminating the MR slowed plasma clearance of both P- and NP-GUS and enhanced the effectiveness of P-GUS in clearing storage in kidney, bone, and retina. Saturating the MR clearance system by high doses of enzyme also improved targeting to MPR-containing tissues such as muscle, kidney, heart, and hepatocytes. Although ablating the MR clearance system genetically is not practical clinically, blocking the MR-mediated clearance system with high doses of enzyme is feasible. This approach delivers a larger fraction of enzyme to MPR-expressing tissues, thus enhancing the effectiveness of MPR-targeted ERT.

Reversibility of cellular and organ pathology in enzyme replacement trials in animal models of lysosomal storage diseases

Enzyme replacement therapy (ERT) has now become a feasible treatment option for several lysosomal storage diseases (LSDs). Although the rationale behind this approach is straightforward, there are many factors that may influence the efficacy of treatment. The reversibility of cellular and organ pathology depends on several factors including the particular organ targeted, the dose and biodistribution of enzyme, the accessibility of the target cell to the infused enzyme, the abundance of receptors for mannose-6-phosphate and other ligands in the target tissue and the activity of endocytosis. In addition, each lysosomal enzyme is unique and its ability to reverse pathology must be individually determined according to source, glycosylation and phosphorylation status. The extent to which cellular pathology may be corrected depends upon the delivery of sufficient enzyme to the diseased tissues.

CONCLUSION

Studies in animal models have identified numerous factors that influence the therapeutic efficacy of ERT. This would suggest that in patients affected by LSDs rigorous evaluation of each therapeutic preparation will be needed.

Lysosomal enzyme delivery by ICAM-1-targeted nanocarriers bypassing glycosylation- and clathrin-dependent endocytosis

Enzyme replacement therapy, a state-of-the-art treatment for many lysosomal storage disorders, relies on carbohydrate-mediated binding of recombinant enzymes to receptors that mediate lysosomal delivery via clathrin-dependent endocytosis. Suboptimal glycosylation of recombinant enzymes and deficiency of clathrin-mediated endocytosis in some lysosomal enzyme-deficient cells limit delivery and efficacy of enzyme replacement therapy for lysosomal disorders. We explored a novel delivery strategy utilizing nanocarriers targeted to a glycosylation- and clathrin-independent receptor, intercellular adhesion molecule (ICAM)-1, a glycoprotein expressed on diverse cell types, up-regulated and functionally involved in inflammation, a hallmark of many lysosomal disorders. We targeted recombinant human acid sphingomyelinase (ASM), deficient in types A and B Niemann-Pick disease, to ICAM-1 by loading this enzyme to nanocarriers coated with anti-ICAM. Anti-ICAM/ASM nanocarriers, but not control ASM or ASM nanocarriers, bound to ICAM-1-positive cells (activated endothelial cells and Niemann-Pick disease patient fibroblasts) via ICAM-1, in a glycosylation-independent manner. Anti-ICAM/ASM nanocarriers entered cells via CAM-mediated endocytosis, bypassing the clathrin-dependent pathway, and trafficked to lysosomes, where delivered ASM displayed stable activity and alleviated lysosomal lipid accumulation. Therefore, lysosomal enzyme targeting using nanocarriers targeted to ICAM-1 bypasses defunct pathways and may improve the efficacy of enzyme replacement therapy for lysosomal disorders, such as Niemann-Pick disease.

Short-term, high dose enzyme replacement therapy in sialidosis mice

Given the success of enzyme replacement therapy (ERT) in treating the systemic manifestations in a number of lysosomal storage disorders (LSDs), we evaluated the effect of ERT on the mouse model of sialidosis. This glycoproteinosis, which affects primarily the reticuloendothelial (RE) system, is caused by deficiency of lysosomal neuraminidase (NEU1) and consequent accumulation of sialylated glycoconjugates. NEU1 lacks a functional mannose-6-phosphate recognition marker and is not endocytosed by mammalian cells. However, the enzyme produced in insect cells has features that allow its effective uptake by RE cells and macrophages via the mannose receptor, and therefore represent an alternative method of therapy. In this study we tested the therapeutic efficacy of baculovirus (BV) expressed mouse neuraminidase (Neu1) in sialidosis mice. Four-week-old Neu1-/- mice were first injected intravenously with a single dose of the recombinant enzyme for assessment of the half-life of mannosylated Neu1 in vivo. Afterwards, a short-term ERT with a total of five enzyme injections over a 2-week period was performed for evaluation of phenotype correction. Neu1 infused alone or co-administered with its associated protein, protective protein/cathepsin A (PPCA) was effectively taken up by resident macrophages in many tissues. Restored Neu1 activity persisted for up to 4 days, depending on the tissue, and resulted in a significant reduction of lysosomal storage. However, beyond 2 weeks of treatment, ERT mice developed a severe immune response towards the exogenous Neu1 enzyme. These results may have important implications for ERT in sialidosis patients.

Enzyme replacement improves nervous system pathology and function in a mouse model for metachromatic leukodystrophy

A deficiency of arylsulfatase A (ASA) causes the lysosomal storage disease metachromatic leukodystrophy, which is characterized by accumulation of the sphingolipid 3-O-sulfogalactosylceramide (sulfatide). Sphingolipid storage results in progressive demyelination and severe neurologic symptoms. The disease is lethal, and curative therapy is not available. To assess the therapeutic potential of enzyme replacement therapy (ERT), ASA knockout mice were treated by intravenous injection of recombinant human ASA. Plasma levels of ASA declined with a half-time of approximately 40 min, and enzyme was detectable in tissues within minutes after injection. The uptake of injected enzyme was high into liver, moderate into peripheral nervous system (PNS) and kidney and very low into brain. The apparent half-life of endocytosed enzyme was approximately 4 days. A single injection led to a time- and dose-dependent decline of the excess sulfatide in PNS and kidney by up to 70%, but no reduction was seen in brain. Four weekly injections with 20 mg/kg body weight not only reduced storage in peripheral tissues progressively, but also were surprisingly effective in reducing sulfatide storage in brain and spinal cord. The histopathology of kidney and central nervous system was ameliorated. Improved neuromotor coordination capabilities and normalized peripheral compound motor action potential demonstrate the benefits of ERT on the nervous system function. Enzyme replacement may therefore be a promising therapeutic option in this devastating disease.

Conjugation of Mannose 6-Phosphate-containing Oligosaccharides to Acid α-Glucosidase Improves the Clearance of Glycogen in Pompe Mice

Clinical studies of enzyme replacement therapy for Pompe disease have indicated that relatively high doses of recombinant human acid alpha-glucosidase (rhGAA) may be required to reduce the abnormal glycogen storage in cardiac and skeletal muscles. This may be because of inefficient cation-independent mannose 6-phosphate receptor (CI-MPR)-mediated endocytosis of the enzyme by the affected target cells. To address this possibility, we examined whether the addition of a high affinity ligand to rhGAA would improve its delivery to these cells. Chemical conjugation of high mannose oligosaccharides harboring mono- and bisphosphorylated mannose 6-phosphates onto rhGAA (neo-rhGAA) significantly improved its uptake characteristics by muscle cells in vitro. Infusion of neo-rhGAA into Pompe mice also resulted in greater delivery of the enzyme to muscle tissues when compared with the unmodified enzyme. Importantly, this increase in enzyme levels was associated with significantly improved clearance of glycogen ( approximately 5-fold) from the affected tissues. These results suggest that CI-MPR-mediated endocytosis of rhGAA is an important pathway by which the enzyme is delivered to the affected lysosomes of Pompe muscle cells. Hence, the generation of rhGAA containing high affinity ligands for the CI-MPR represents a strategy by which the potency of rhGAA and therefore the clinical efficacy of enzyme replacement therapy for Pompe disease may be improved.

Developmentally regulated mannose 6-phosphate receptor-mediated transport of a lysosomal enzyme across the blood-brain barrier

Mucopolysaccharidosis type VII is a lysosomal storage disorder resulting from inherited deficiency of beta-glucuronidase (GUS). Mucopolysaccharidosis type VII is characterized by glycosaminoglycan storage in most tissues, including brain. In these disorders, enzyme delivery across the blood-brain barrier (BBB) is the main obstacle to correction of lysosomal storage in the CNS. Prior studies suggested mouse brain is accessible to GUS in the first 2 weeks of life but not later. To explore a possible role for the mannose 6-phosphate/insulin-like growth factor II receptor in GUS transport across the BBB in neonatal mice, we compared brain uptake of phosphorylated GUS (P-GUS) and nonphosphorylated GUS (NP-GUS) in newborn and adult mice. (131)I-P-GUS was transported across the BBB after i.v. injection in 2-day-old mice. The brain influx rate (K(in)) of (131)I-P-GUS in 2-day-old mice was 0.21 microl/g.min and decreased with age. By 7 weeks of age, transport of (131)I-P-GUS was not significant. Capillary depletion revealed that 62% of the (131)I-P-GUS in brain was in brain parenchyma in 2-day-old mice. In addition, uptake of (131)I-P-GUS into brain was significantly reduced by coinjection of unlabeled P-GUS or M6P in a dose-dependent manner. In contrast, the K(in) of (131)I-NP-GUS (0.04 microl/g.min) was significantly lower than (131)I-P-GUS in 2-day-old mice. Transcardiac brain perfusion confirmed that neither (131)I-P-GUS nor (131)I-NP-GUS crossed the BBB in adult mice. These results indicate that (131)I-P-GUS transport into brain parenchyma in early postnatal life is mediated by the mannose 6-phosphate/insulin-like growth factor II receptor. This receptor-mediated transport is not observed in adult mice.

Lipoprotein Receptor Binding, Cellular Uptake, and Lysosomal Delivery of Fusions between the Receptor-associated Protein (RAP) and α-l-Iduronidase or Acid α-Glucosidase

Enzyme replacement therapy for lysosomal storage disorders depends on efficient uptake of recombinant enzyme into the tissues of patients. This uptake is mediated by oligosaccharide receptors including the cation-independent mannose 6-phosphate receptor and the mannose receptor. We have sought to exploit alternative receptor systems that are independent of glycosylation but allow for efficient delivery to the lysosome. Fusions of the human lysosomal enzymes alpha-l-iduronidase or acid alpha-glucosidase with the receptor-associated protein were efficiently endocytosed by lysosomal storage disorder patient fibroblasts, rat C6 glioma cells, mouse C2C12 myoblasts, and recombinant Chinese hamster ovary cells expressing individual members of the low-density lipoprotein receptor family. Uptake of the fusions exceeded that of phosphorylated enzyme in all cases, often by an order of magnitude or greater. Uptake was specifically mediated by members of the low-density lipoprotein receptor protein family and was followed by delivery of the fusions to the lysosome. The advantages of the lipoprotein receptor system over oligosaccharide receptor systems include more efficient cellular delivery and the potential for transcytosis of ligands across tight endothelia, including the blood-brain barrier.

Numerous transcriptional alterations in liver persist after short-term enzyme-replacement therapy in a murine model of mucopolysaccharidosis type VII

The lysosomal storage disease MPS VII (mucopolysaccharidosis type VII) is caused by a deficiency in beta-glucuronidase activity, and results in the accumulation of partially degraded glycosaminoglycans in many cell types. Although MPS VII is a simple monogenetic disorder, the clinical presentation is complex and incompletely understood. ERT (enzyme replacement therapy) is relatively effective at improving the clinical course of the disease; however, some pathologies persist. In order to clarify the molecular events contributing to the disease phenotype and how ERT might impact upon them, we analysed liver tissue from untreated and treated MPS VII mice at both 2 and 5 months of age using biochemical assays and microarray analysis. Overall, as the disease progresses, more genes have altered expression and, at either age, numerous transcriptional changes in multiple pathways appear to be refractory to therapy. With respect to the primary site of disease, both transcriptional and post-transcriptional mechanisms are involved in the regulation of lysosomal enzymes and other lysosome-associated proteins. Many of the changes observed in both lysosome-associated mRNAs and proteins are normalized by enzyme replacement. In addition, gene expression changes in seemingly unrelated pathways may account for the complex metabolic phenotype of the MPS VII mouse. In particular, beta-glucuronidase deficiency appears to induce physiological malnutrition in MPS VII mice. Malnutrition may account for the pronounced adipose storage deficiency observed in this animal. Studying the molecular response to lysosomal storage, especially those changes recalcitrant to therapy, has revealed additional targets that may improve the efficacy of existing therapies.

Long-term intravenous treatment of Pompe disease with recombinant human alpha-glucosidase from milk

OBJECTIVE

Recent reports warn that the worldwide cell culture capacity is insufficient to fulfill the increasing demand for human protein drugs. Production in milk of transgenic animals is an attractive alternative. Kilogram quantities of product per year can be obtained at relatively low costs, even in small animals such as rabbits. We tested the long-term safety and efficacy of recombinant human -glucosidase (rhAGLU) from rabbit milk for the treatment of the lysosomal storage disorder Pompe disease. The disease occurs with an estimated frequency of 1 in 40,000 and is designated as orphan disease. The classic infantile form leads to death at a median age of 6 to 8 months and is diagnosed by absence of alpha-glucosidase activity and presence of fully deleterious mutations in the alpha-glucosidase gene. Cardiac hypertrophy is characteristically present. Loss of muscle strength prevents infants from achieving developmental milestones such as sitting, standing, and walking. Milder forms of the disease are associated with less severe mutations and partial deficiency of alpha-glucosidase.

METHODS

In the beginning of 1999, 4 critically ill patients with infantile Pompe disease (2.5-8 months of age) were enrolled in a single-center open-label study and treated intravenously with rhAGLU in a dose of 15 to 40 mg/kg/week.

RESULTS

Genotypes of patients were consistent with the most severe form of Pompe disease. Additional molecular analysis failed to detect processed forms of alpha-glucosidase (95, 76, and 70 kDa) in 3 of the 4 patients and revealed only a trace amount of the 95-kDa biosynthetic intermediate form in the fourth (patient 1). With the more sensitive detection method, 35S-methionine incorporation, we could detect low-level synthesis of -glucosidase in 3 of the 4 patients (patients 1, 2, and 4) with some posttranslation modification from 110 kDa to 95 kDa in 1 of them (patient 1). One patient (patient 3) remained totally deficient with both detection methods (negative for cross-reactive immunologic material [CRIM negative]). The alpha-glucosidase activity in skeletal muscle and fibroblasts of all 4 patients was below the lower limit of detection (<2% of normal). The rhAGLU was tolerated well by the patients during >3 years of treatment. Anti-rhAGLU immunoglobulin G titers initially increased during the first 20 to 48 weeks of therapy but declined thereafter. There was no consistent difference in antibody formation comparing CRIM-negative with CRIM-positive patients. Muscle alpha-glucosidase activity increased from <2% to 10% to 20% of normal in all patients during the first 12 weeks of treatment with 15 to 20 mg/kg/week. For optimizing the effect, the dose was increased to 40 mg/kg/week. This resulted, 12 weeks later, in normal alpha-glucosidase activity levels, which were maintained until the last measurement in week 72. Importantly, all 4 patients, including the patient without any endogenous alpha-glucosidase (CRIM negative), revealed mature 76- and 70-kDa forms of -glucosidase on Western blot. Conversion of the 110-kDa precursor from milk to mature 76/70-kDa alpha-glucosidase provides evidence that the enzyme is targeted to lysosomes, where this proteolytic processing occurs. At baseline, patients had severe glycogen storage in the quadriceps muscle as revealed by strong periodic acid-Schiff--positive staining and lacework patterns in hematoxylin and eosin--stained tissue sections. The muscle pathology correlated at each time point with severity of signs. Periodic acid-Schiff intensity diminished and number of vacuoles increased during the first 12 weeks of treatment. Twelve weeks after dose elevation, we observed signs of muscle regeneration in 3 of the 4 patients. Obvious improvement of muscular architecture was seen only in the patient who learned to walk. Clinical effects were significant. All patients survived beyond the age of 4 years, whereas untreated patients succumb at a median age of 6 to 8 months. The characteristic cardiac hypertrophy present at start of treatment diminished significantly. The left ventricular mass index decreased from 171 to 599 g/m2 (upper limit of normal 86.6 g/m2 for infants from 0 to 1 year) to 70 to 160 g/m2 during 84 weeks of treatment. In addition, we found a significant change of slope for the diastolic thickness of the left ventricular posterior wall against time at t = 0 for each separate patient. Remarkably, the younger patients (patients 1 and 3) showed no significant respiratory problems during the first 2 years of life. One of the younger patients recovered from a life-threatening bronchiolitis at the age of 1 year without sequelae, despite borderline oxygen saturations at inclusion. At the age of 2, however, she became ventilator dependent after surgical removal of an infected Port-A-Cath. She died at the age of 4 years and 3 months suddenly after a short period of intractable fever of >42 degrees C, unstable blood pressure, and coma. The respiratory course of patient 1 remained uneventful. The 2 older patients, who both were hypercapnic (partial pressure of carbon dioxide: 10.6 and 9.8 kPa; normal range: 4.5-6.8 kPa) at start of treatment, became ventilator dependent before the first infusion (patient 2) and after 10 weeks of therapy (patient 4). Patient 4 was gradually weaned from the ventilator after 1 year of high-dose treatment and was eventually completely ventilator-free for 5 days, but this situation could not be maintained. Currently, both patients are completely ventilator dependent. The most remarkable progress in motor function was seen in the younger patients (patients 1 and 3). They achieved motor milestones that are unmet in infantile Pompe disease. Patient 1 learned to crawl (12 months), walk (16 months), squat (18 months), and climb stairs (22 months), and patient 3 learned to sit unsupported. The Alberta Infant Motor Scale score for patients 2, 3, and 4 remained far below p5. Patient 1 followed the p5 of normal.

CONCLUSION

Our study shows that a safe and effective medicine can be produced in the milk of mammals and encourages additional development of enzyme replacement therapy for the several forms of Pompe disease. Restoration of skeletal muscle function and prevention of pulmonary insufficiency require dosing in the range of 20 to 40 mg/kg/week. The effect depends on residual muscle function at the start of treatment. Early start of treatment is required.

Expression of lysosomal protective protein/cathepsin A in a stably transformed human neuroblastoma cell line during bi-directional differentiation into neuronal and Schwannian cells

Human neuroblastoma GOTO cell lines were established that stably express recombinant human lysosomal protective protein/cathepsin A (PPCA) cDNA by transfection. Intracellular cathepsin A (acid serine carboxypeptidase) activity increased four-fold compared with in those of the parent and mock-transfected cell lines. The immunoreactive 54 kDa precursor/zymogen and mature 32/20 kDa two-chain forms were produced in the cells. The amount of the latter form expressed in the GOTO cells was significantly larger than those in the PPCA-overexpressing CHO cell lines previously established. The intracellular proteins showed a typical lysosomal granular distribution and the glycosylated 54 kDa precursor was secreted into the culture medium without the addition of an alkalizing agent. The PPCA-overexpressing cell lines also retained the ability to differentiate bi-directionally as well as the parent cells; into neuronal cells on induction by dibutyryl cAMP in serum-free medium and into Schwannian cells on induction by bromodeoxyuridine. During the course of differentiation into neuronal and Schwannian cells, the intracellular cathepsin A activity further increased two and five times, respectively, which was associated with an increase in the expression of the 32/20 kDa two-chain form. The glycosylated precursor proteins were taken up via the mannose 6-phosphate receptors, and the cathepsin A, alpha-neuraminidase and beta-galactosidase (beta-Gal) activities deficient in the fibroblasts derived from a patient with PPCA deficiency (galactosialidosis) were restored. These results suggest that the bi-directional differentiation of GOTO cell lines stably expressing the recombinant human PPCA gene could be a model system for analyzing the functions of PPCA in peripheral neuronal cells and Schwannian cells as well as the recombinant PPCA could be a useful source for enzyme replacement therapy (ERT) for galactosialidosis patients.

Targeting macrophages with baculovirus-produced lysosomal enzymes: implications for enzyme replacement therapy of the glycoprotein storage disorder galactosialidosis

Lysosomal storage diseases (LSDs) are monogenic disorders of metabolism caused by deficiency of hydrolytic enzymes. In several LSDs, cells of the reticuloendothelial (RE) system are the primary targets of the disease. Exogenous administration of recombinant enzymes overproduced in mammalian cells has proved effective for treating the systemic phenotype in nonneuropathic patients with LSDs. However, for the treatment of diseases with primary involvement of the RE system, the production of the therapeutic enzyme in insect cells could be an alternative and advantageous method because glycoproteins expressed in insect cells carry carbohydrates of the pauci-mannose or core-type. These recombinant enzymes are in principle already poised to be internalized by cells that express mannose receptors, including macrophages. Here, we demonstrate that three baculovirus-expressed enzymes, protective protein/cathepsin A (PPCA), neuraminidase (Neu1), and beta-glucosidase, were readily taken up and restored lysosomal function in enzyme-deficient mouse macrophages. The capacity of recombinant PPCA and Neu1 to clear the lysosomal storage in target cells was assessed in PPCA-/- mice, a model of galactosialidosis. Intravenously injected PPCA-/- mice efficiently internalized the corrective enzymes in resident macrophages of many organs. In addition, treated mice showed overall clearance of lysosomal storage in the most affected systemic organs, kidney, liver, and spleen. Our results suggest that ERT with baculovirus-expressed enzymes might be an effective treatment for nonneuropathic patients with galactosialidosis and possibly for others with LSDs that primarily involve the RE system.

Glycosylation-independent targeting enhances enzyme delivery to lysosomes and decreases storage in mucopolysaccharidosis type VII mice

Enzyme-replacement therapy is an established means of treating lysosomal storage diseases. Infused therapeutic enzymes are targeted to lysosomes of affected cells by interactions with cell-surface receptors that recognize carbohydrate moieties, such as mannose and mannose 6-phosphate, on the enzymes. We have tested an alternative, peptide-based targeting system for delivery of enzymes to lysosomes in a murine mucopolysaccharidosis type VII (MPS VII) model. This strategy depends on the interaction of a fragment of insulin-like growth factor II (IGF-II), with the IGF-II binding site on the bifunctional, IGF-II cation-independent mannose 6-phosphate receptor. A chimeric protein containing a portion of mature human IGF-II fused to the C terminus of human beta-glucuronidase was taken up by MPS VII fibroblasts in a mannose 6-phosphate-independent manner, and its uptake was inhibited by the addition of IGF-II. Furthermore, the tagged enzyme was delivered effectively to clinically significant tissues in MPS VII mice and was effective in reversing the storage pathology. The tagged enzyme was able to reduce storage in glomerular podocytes and osteoblasts at a dose at which untagged enzyme was much less effective. This peptide-based, glycosylation-independent lysosomal targeting system may enhance enzyme-replacement therapy for certain human lysosomal storage diseases.

Mannose 6-Phosphate Receptor-mediated Uptake Is Defective in Acid Sphingomyelinase-deficient Macrophages

Progressive accumulation of lipid-laden macrophages is a hallmark of the acid sphingomyelinase (ASM)-deficient forms of Niemann-Pick disease (i.e. Types A and B NPD). To investigate the mechanisms underlying enzyme replacement therapy for this disorder, we studied the uptake of recombinant, human ASM (rhASM) by alveolar macrophages from ASM knock-out (ASMKO) mice. The recombinant enzyme used for these studies was produced in Chinese hamster ovary cells and contained complex type, N-linked oligosaccharides. Binding of radiolabeled, rhASM to the ASMKO macrophages was enhanced as compared with normal macrophages, consistent with their larger size and increased surface area. However, internalization of the enzyme by the ASMKO cells was markedly reduced when compared with normal cells. Studies using receptor-specific ligands to inhibit enzyme uptake revealed that in normal cells rhASM was taken up by a combination of mannose and mannose 6-phosphate receptors (MR and M6PR, respectively), whereas in the ASMKO cells the M6PR had a minimal role in rhASM uptake. Expression of M6PR mRNA was normal in the ASMKO cells, although Western blotting revealed more receptors in these cells when compared with normal. We therefore hypothesized that lipid accumulation in ASMKO macrophages led to abnormalities in M6PR trafficking and/or degradation, resulting in reduced enzyme uptake. Consistent with this hypothesis, we also found that, when rhASM was modified to expose terminal mannose residues and target mannose receptors, the uptake of this modified enzyme form by ASMKO cells was approximately 10-fold greater when compared with the "complex" type rhASM. These findings have important implications for NPD enzyme replacement therapy, particularly in the lung.

Enzyme replacement and enhancement therapies for lysosomal diseases

Although first suggested by de Duve in 1964, enzyme replacement therapy (ERT) for lysosomal storage diseases did not become a reality until the early 1990s when its safety and effectiveness were demonstrated in type 1 Gaucher disease. Today, ERT is a reality for Gaucher disease, Fabry disease and mucopolysaccharidosis type I (MPS I), and clinical trials with recombinant human enzymes are ongoing in Pompe disease, MPS II and MPS VI, and are about to begin in Neimann-Pick B disease. In addition to ERT, enzyme enhancement therapy (EET) offers a novel therapeutic strategy to increase the residual function of mutant proteins. EET employs small molecules as 'pharmacological chaperones' to rescue misfolded and/or unstable mutant enzymes or proteins that have residual function. EET also offers the possibility of treating neurodegenerative lysosomal disorders since these small therapeutic molecules may cross the blood-brain barrier. The current status of ERT and the prospects for EET for lysosomal storage diseases are reviewed.