Alpha-L-iduronidase and enzyme replacement therapy for mucopolysaccharidosis I

Challenges, approaches and enablers: effectively triangulating towards dose selection in pediatric rare diseases

Dose selection is an integral part of a molecule's journey to become medicine. On top of typical challenges faced in dose selection for more common diseases, pediatric rare disease has additional unique challenges due to the combination of 'rare' and 'pediatric' populations. Using the central theme of maximizing 'relevant' information to overcome information paucity, dose selection strategy in pediatric rare diseases is discussed using a triangulation concept involving challenges, approaches and very importantly, enablers. Using actual examples, unique scenarios are discussed where specific enablers allowed certain approaches to be used to overcome the challenges. The continued need for model-informed drug development is also discussed using examples of where modeling and simulation tools have been successfully used in bridging available information to select pediatric doses in rare disease. Additionally, challenges with translation and associated dose selection of new modalities such as gene therapy in rare diseases are examined with the lens of continuous learning and knowledge development that will enable pediatric dose selection of these modalities with confidence.

Novel approach to idursulfase and laronidase desensitization in type 2 and type 1 S mucopolysaccharidosis (MPS)

BACKGROUND

Idursulfase and laronidase are drugs used to treat Hunter syndrome (mucopolysaccharidosis type 2) and Scheie syndrome (mucopolysaccharidosis type 1 S), respectively. These are rare lysosomal storage disorders, leading to accumulation of glycosaminoglycans within lysosomes. Failure of early recognition of the disease and/or delay in starting the appropriate treatment result in severe clinical impairment and death. For almost 20 years, enzyme replacement therapy with recombinant proteins has represented the first line therapeutic option. However, administration of idursulfase and laronidase is associated with infusion-related hypersensitivity reactions, in approx. 20% of patients. In these patients, rapid desensitization by intravenous administration protocols has been used in order to avoid treatment discontinuation. This approach proved effective and safe. However, long-term tolerance could not be achieved. Thus, we decided to combine rapid desensitization with allergen immunotherapy-like desensitization.

RESULTS

Two patients with Hunter syndrome and one patient with Scheie syndrome developed severe allergy to idursulfase and laronidase, respectively, preventing them from continuing the otherwise indispensable therapy. In all three patients, the possible IgE-mediated nature of the reactions suffered was suggested by positive skin tests with the two enzymes, respectively. By devising 12-step, 3-dilution rapid desensitization protocols, we resumed the enzyme replacement therapy. However, the prolonged time required for administration (a not negligible pitfall, since therapy should be given weekly for life) and the persistent occurrence of reactions (mild but still requiring anti-allergic medication at full dosage) led us to combine rapid desensitization with a compact 11-step, 24-day allergen immunotherapy-like desensitization protocol. Thus, idursulfase and laronidase were injected subcutaneously, with a 500-fold increase from step 1 to step 11 for idursulfase and a 222-fold increase for laronidase. This strategy led to restoration of long-term tolerance, allowing weekly intravenous therapy administration under standard conditions, according to the manufacturer instructions, in the absence of side effects and with only precautionary low-dose premedication.

CONCLUSION

Rapid desensitization is a suitable and safe option in the case of idursulfase and laronidase allergy. Combination with subcutaneous allergen immunotherapy-like desensitization afforded restoration of enzyme replacement therapy given by the normal administration schedule, by inducing sustained tolerance.

Enzyme Therapy: Current Challenges and Future Perspectives

In recent years, enzymes have risen as promising therapeutic tools for different pathologies, from metabolic deficiencies, such as fibrosis conditions, ocular pathologies or joint problems, to cancer or cardiovascular diseases. Treatments based on the catalytic activity of enzymes are able to convert a wide range of target molecules to restore the correct physiological metabolism. These treatments present several advantages compared to established therapeutic approaches thanks to their affinity and specificity properties. However, enzymes present some challenges, such as short in vivo half-life, lack of targeted action and, in particular, patient immune system reaction against the enzyme. For this reason, it is important to monitor serum immune response during treatment. This can be achieved by conventional techniques (ELISA) but also by new promising tools such as microarrays. These assays have gained popularity due to their high-throughput analysis capacity, their simplicity, and their potential to monitor the immune response of patients during enzyme therapies. In this growing field, research is still ongoing to solve current health problems such as COVID-19. Currently, promising therapeutic alternatives using the angiotensin-converting enzyme 2 (ACE2) are being studied to treat COVID-19.

Enzyme Replacement Therapy for Genetic Disorders Associated with Enzyme Deficiency

Mutations in human genes might lead to loss of functional proteins, causing diseases. Among these genetic disorders, a large class is associated with the deficiency in metabolic enzymes, resulting in both an increase in the concentration of substrates and a loss in the metabolites produced by the catalyzed reactions. The identification of therapeutic actions based on small molecules represents a challenge to medicinal chemists because the target is missing. Alternative approaches are biology-based, ranging from gene and stem cell therapy, CRISPR/Cas9 technology, distinct types of RNAs, and enzyme replacement therapy (ERT). This review will focus on the latter approach that since the 1990s has been successfully applied to cure many rare diseases, most of them being lysosomal storage diseases or metabolic diseases. So far, a dozen enzymes have been approved by FDA/EMA for lysosome storage disorders and only a few for metabolic diseases. Enzymes for replacement therapy are mainly produced in mammalian cells and some in plant cells and yeasts and are further processed to obtain active, highly bioavailable, less degradable products. Issues still under investigation for the increase in ERT efficacy are the optimization of enzymes interaction with cell membrane and internalization, the reduction in immunogenicity, and the overcoming of blood-brain barrier limitations when neuronal cells need to be targeted. Overall, ERT has demonstrated its efficacy and safety in the treatment of many genetic rare diseases, both saving newborn lives and improving patients' life quality, and represents a very successful example of targeted biologics.

Enzyme enhancement therapeutics for lysosomal storage diseases: Current status and perspective

Small-molecule- enzyme enhancement therapeutics (EETs) have emerged as attractive agents for the treatment of lysosomal storage diseases (LSDs), a broad group of genetic diseases caused by mutations in genes encoding lysosomal enzymes, or proteins required for lysosomal function. The underlying enzyme deficiencies characterizing LSDs cause a block in the stepwise degradation of complex macromolecules (e.g. glycosaminoglycans, glycolipids and others), such that undegraded or partially degraded substrates progressively accumulate in lysosomal and non-lysosomal compartments, a process leading to multisystem pathology via primary and secondary mechanisms. Missense mutations underlie many of the LSDs; the resultant mutant variant enzyme hydrolase is often impaired in its folding and maturation making it subject to rapid disposal by endoplasmic reticulum (ER)-associated degradation (ERAD). Enzyme deficiency in the lysosome is the result, even though the mutant enzyme may retain significant catalytic functioning. Small molecule modulators - pharmacological chaperones (PCs), or proteostasis regulators (PRs) are being identified through library screens and computational tools, as they may offer a less costly approach than enzyme replacement therapy (ERT) for LSDs, and potentially treat neuronal forms of the diseases. PCs, capable of directly stabilizing the mutant protein, and PRs, which act on other cellular elements to enhance protein maturation, both allow a proportion of the synthesized variant protein to reach the lysosome and function. Proof-of-principle for PCs and PRs as therapeutic agents has been demonstrated for several LSDs, yet definitive data of their efficacy in disease models and/or in downstream clinical studies in many cases has yet to be achieved. Basic research to understand the cellular consequences of protein misfolding such as perturbed organellar crosstalk, redox status, and calcium balance is needed. Likewise, an elucidation of the early in cellulo pathogenic events underlying LSDs is vital and may lead to the discovery of new small molecule modulators and/or to other therapeutic approaches for driving proteostasis toward protein rescue.

N-glycan structures and downstream mannose-phosphorylation of plant recombinant human alpha-L-iduronidase: toward development of enzyme replacement therapy for mucopolysaccharidosis I

Arabidopsis N-glycan processing mutants provide the basis for tailoring recombinant enzymes for use as replacement therapeutics to treat lysosomal storage diseases, including N-glycan mannose phosphorylation to ensure lysosomal trafficking and efficacy. Functional recombinant human alpha-L-iduronidase (IDUA; EC 3.2.1.76) enzymes were generated in seeds of the Arabidopsis thaliana complex-glycan-deficient (cgl) C5 background, which is deficient in the activity of N-acetylglucosaminyl transferase I, and in seeds of the Arabidopsis gm1 mutant, which lacks Golgi α-mannosidase I (GM1) activity. Both strategies effectively prevented N-glycan maturation and the resultant N-glycan structures on the consensus sites for N-glycosylation of the human enzyme revealed high-mannose N-glycans of predominantly Man₅ (cgl-IDUA) or Man_6-8 (gm1-IDUA) structures. Both forms of IDUA were equivalent with respect to their kinetic parameters characterized by cleavage of the artificial substrate 4-methylumbelliferyl-iduronide. Because recombinant lysosomal enzymes produced in plants require the addition of mannose-6-phosphate (M6P) in order to be suitable for lysosomal delivery in human cells, we characterized the two IDUA proteins for their amenability to downstream in vitro mannose phosphorylation mediated by a soluble form of the human phosphotransferase (UDP-GlcNAc: lysosomal enzyme N-acetylglucosamine [GlcNAc]-1-phosphotransferase). Gm1-IDUA exhibited a slight advantage over the cgl-IDUA in the in vitro M6P-tagging process, with respect to having a better affinity (i.e. lower K _m) for the soluble phosphotransferase. This may be due to the greater number of mannose residues comprising the high-mannose N-glycans of gm1-IDUA. Our elite cgl- line produces IDUA at > 5.7% TSP (total soluble protein); screening of the gm1 lines showed a maximum yield of 1.5% TSP. Overall our findings demonstrate the relative advantages and disadvantages associated with the two platforms to create enzyme replacement therapeutics for lysosomal storage diseases.

Aminoglycoside-Induced Premature Stop Codon Read-Through of Mucopolysaccharidosis Type I Patient Q70X and W402X Mutations in Cultured Cells

The premature stop codon mutations, Q70X and W402X, are the most common α-L-iduronidase gene (IDUA) mutations in mucopolysaccharidosis type I (MPS I) patients. Read-through drugs have been used to suppress premature stop codons, and this can potentially be used to treat patients who have this type of mutation. We examined the effects of aminoglycoside treatment on the IDUA mutations Q70X and W402X in cultured cells and show that 4,5-disubstituted aminoglycosides induced more read-through for the W402X mutation, while 4,6-disubstituted aminoglycosides promoted more read-through for the Q70X mutation: lividomycin (4,5-disubstituted) induced a 7.8-fold increase in α-L-iduronidase enzyme activity for the W402X mutation; NB54 (4,5-disubstituted) induced a 3.7 fold increase in the amount of α-L-iduronidase enzyme activity for the W402X mutation, but had less effect on the Q70X mutation, whereas gentamicin (4,6-disubstituted) had the reverse effect on read-through for both mutations. The predicted mRNA secondary structural changes for both mutations were markedly different, which may explain these different effects on read-through for these two premature stop codons.

Production of α-L-iduronidase in maize for the potential treatment of a human lysosomal storage disease

Lysosomal storage diseases are a class of over 70 rare genetic diseases that are amenable to enzyme replacement therapy. Towards developing a plant-based enzyme replacement therapeutic for the lysosomal storage disease mucopolysaccharidosis I, here we expressed α-L-iduronidase in the endosperm of maize seeds by a previously uncharacterized mRNA-targeting-based mechanism. Immunolocalization, cellular fractionation and in situ RT-PCR demonstrate that the α-L-iduronidase protein and mRNA are targeted to endoplasmic reticulum (ER)-derived protein bodies and to protein body-ER regions, respectively, using regulatory (5'- and 3'-UTR) and signal-peptide coding sequences from the γ-zein gene. The maize α-L-iduronidase exhibits high activity, contains high-mannose N-glycans and is amenable to in vitro phosphorylation. This mRNA-based strategy is of widespread importance as plant N-glycan maturation is controlled and the therapeutic protein is generated in a native form. For our target enzyme, the N-glycan structures are appropriate for downstream processing, a prerequisite for its potential as a therapeutic protein.

Suppression of premature termination codons as a therapeutic approach

In this review, we describe our current understanding of translation termination and pharmacological agents that influence the accuracy of this process. A number of drugs have been identified that induce suppression of translation termination at in-frame premature termination codons (PTCs; also known as nonsense mutations) in mammalian cells. We discuss efforts to utilize these drugs to suppress disease-causing PTCs that result in the loss of protein expression and function. In-frame PTCs represent a genotypic subset of mutations that make up ~11% of all known mutations that cause genetic diseases, and millions of patients have diseases attributable to PTCs. Current approaches aimed at reducing the efficiency of translation termination at PTCs (referred to as PTC suppression therapy) have the goal of alleviating the phenotypic consequences of a wide range of genetic diseases. Suppression therapy is currently in clinical trials for treatment of several genetic diseases caused by PTCs, and preliminary results suggest that some patients have shown clinical improvements. While current progress is promising, we discuss various approaches that may further enhance the efficiency of this novel therapeutic approach.

Musculoskeletal manifestations of lysosomal storage disorders

Lysosomal storage disorders (LSDs), a heterogeneous group of inborn metabolic disorders, are far more common than most doctors presume. Although patients with a severe LSD subtype are often readily diagnosed, the more attenuated subtypes are frequently missed or diagnosis is significantly delayed. The presenting manifestations often involve the bones and/or joints and therefore these patients are frequently under specialist care by (paediatric) rheumatologists, receiving inadequate treatment. Since effective disease-specific treatments, including enzyme replacement therapy and stem cell transplantation, have become available for certain LSDs and timely initiation of these treatments is necessary to prevent the development of severe, disabling and irreversible manifestations, early diagnosis has become essential. The challenge is to raise awareness for better recognition of the presenting signs and symptoms of LSDs by all doctors who may encounter these patients, including rheumatologists.

Uptake of a recombinant human alpha-L-iduronidase (laronidase) by cultured fibroblasts and osteoblasts

To examine the uptake of a recombinant human alpha-L-iduronidase (laronidase) by cultured fibroblasts from a patient with mucopolysaccharidosis I (MPS I) and its effect on the cleavage of accumulated substrates, we performed enzymological, Western blotting, immunocytochemical and morphological studies. Laronidase was incorporated into the MPS I cells dose-dependently mainly via mannose 6-phosphate (M6P) receptors. Then the incorporated enzyme was transported to lysosomes and processed to the mature form, the pathological changes of the cells being improved. Furthermore, we compared the uptake of laronidase by cultured mouse osteoblasts with that by cultured mouse fibroblasts. The enzyme was incorporated into the cultured mouse osteoblasts mainly via M6P receptors, although mannose (Man) receptors were partially involved in the uptake of the enzyme, as in the cultured fibroblasts. But the uptake by the former was apparently lower than that by the latter. The administration of a high dose of the enzyme or development of a recombinant alpha-L-iduronidase containing many M6P residues is required for further improvement of enzyme replacement therapy for skeletal disorders caused by MPS I.

Structural study on mutant alpha-L-iduronidases: insight into mucopolysaccharidosis type I

To elucidate the basis of mucopolysaccharidosis type I (MPS I), we constructed structural models of mutant alpha-L: -iduronidases (IDUAs) resulting from 33 amino acid substitutions that lead to MPS I (17 severe, eight intermediate, and eight attenuated). Then, we examined the structural changes in the enzyme protein by calculating the number of atoms affected and determined the root-mean-square distance (RMSD) and the solvent-accessible surface area (ASA). In the severe MPS I group, the number of atoms influenced by a mutation and the average RMSD value were larger than those in the attenuated group, and the residues associated with the mutations identified in the severe group tended to be less solvent accessible than those in the attenuated group. The clinically intermediate phenotype group exhibited intermediate values for the numbers of atoms affected, RMSD, and ASA between those in the severe group and those in the attenuated group. The results indicated that large structural changes had occurred in the core region in the severe MPS I group and small ones on the molecular surface in the attenuated MPS I group. Color imaging revealed the distributions and degrees of the structural changes caused by representative mutations for MPS I. Thus, structural analysis is useful for elucidating the basis of MPS I. As there was a difference in IDUA structural change between the severe MPS I group and the attenuated one, except for a couple of mutations, structural analysis can help predict the clinical outcome of the disease.

The first 5 years of clinical experience with laronidase enzyme replacement therapy for mucopolysaccharidosis I

Mucopolysaccharidosis I (MPS I, McKusick 25280) is caused by the deficiency or absence of the lysosomal enzyme, alpha-L-iduronidase (EC 3.2.1.76). This inherited disease causes progressive cellular, tissue and organ damage across the entire phenotypic spectrum. Disabling, multi-organ disease is the rule, and generally results in death between the first and fourth decades of life. Recently, laronidase (Aldurazyme) [Genzyme], a specific recombinant human alpha-L-iduronidase) became commercially available as long-term enzyme replacement therapy. Results from the Phase I/II and III extended clinical studies have shown that laronidase safely and effectively alleviates many systemic signs and symptoms of this progressive multisystemic disease. Clinically meaningful and sustained improvements in pulmonary function and functional capacity have been observed in Phase III study patients. Significant and sustained reductions in urinary glysosaminoglycan (GAG) excretion and hepatomegaly have also been observed. Improvements in sleep apnoea and joint range of motion occurred in patients with the most severe symptoms at baseline. Improvements in Disability Index scores as measured using the CHAQ and HAQ questionnaires were modest, which may have been related to the fact that these disability measuring tools are not disease-specific. Anecdotal reports of improvements in the performance of daily activities further add to the therapeutic benefits, as do case histories pointing at stabilisation or improvement of symptomatology in various organs, such as the eyes, heart, and muscles. With the availability of specific treatment, the importance of early recognition of the disease and appropriate therapeutic intervention has increased. The variability in clinical symptomatology is reviewed in detail and may allow for a better understanding of the diagnostic and therapeutic challenges. Results of the clinical trials and their initial extension periods, as well as the anecdotal experiences of physicians with laronidase in non-study settings, are discussed.

Clinical presentation and follow-up of patients with the attenuated phenotype of mucopolysaccharidosis type I

AIM

To review the heterogeneity and severity of the clinical features at the attenuated end of the mucopolysaccharidosis (MPS) type I disease spectrum.

METHODS

The course of disease in 29 patients with attenuated mucopolysaccharidosis I who attended the MPS clinic in Manchester, UK, was reviewed.

RESULTS

For more than half of the patients, onset of symptoms was in the first 2 y of life, and the age at diagnosis ranged from 15 mo to 40 y. Joint stiffness, corneal clouding, umbilical hernia and recurrent ear, nose and throat symptoms were the commonest features at presentation. Patients experienced significant morbidity during the course of this inherited disease. Skeletal problems predominated and cardiac valve pathology, upper airway obstruction and hearing deficits were detected in a notable number of patients. Nerve decompression for carpal tunnel syndrome, cervical cord decompression, and grommet insertion for serous otitis media were the most frequent surgical interventions.

CONCLUSION

Clinical presentation of attenuated ("non-Hurler") mucopolysaccharidosis type I is heterogeneous in time of onset and types of clinical features. A better understanding of the spectrum of disease and of the related disease progression will contribute to more accurate diagnosis, and patients will benefit from early intervention.

Evolución de dos pacientes con síndrome de Hurler en tratamiento con enzima recombinante humana α-L-iduronidasa

We performed a prospective study of two patients with Hurler's syndrome (aged 4.8 years and 17 months at the beginning of the intervention) under enzyme replacement therapy with human recombinant alpha-L-iduronidase for 452 and 28 weeks respectively. The aim of this study was to analyze the safety and efficacy of the intervention during the treatment periods. Several diagnostic imaging tests, clinical examinations, and serial laboratory determinations were performed to demonstrate the effectiveness of the therapy in both patients. In patient 1 (a boy aged 4.8 years, homozygote W402X), the treatment was always intended to be palliative because of the advanced stage of the disease. In patient 2 (a 17-month-old girl, heterozygote W402X) the treatment was initiated early with subsequent clinical stabilization without acquisition of regressive factors. Bone marrow transplantation from an unrelated donor was successful. Currently, because of the lack of histocompatible bone marrow donors, transplantation of hematopoietic stem cells from umbilical cord blood or peripheral blood are being performed with satisfactory results. In the future, gene therapy may be able to prevent the diseases associated with Hurler's syndrome and halt the neurocognitive deterioration characteristic of these patients.

Gene therapy of metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a lysosomal storage disease that is caused by a deficiency of arylsulfatase A (ASA). The deficiency results in the intralysosomal accumulation of the acidic sphingolipid 3-O-sulfogalactosyl-ceramide (sulfatide). Patients suffer from progressive demyelination and die from multiple neurological deficits. Curative treatment is not available. ASA bears mannose 6-phosphate residues which function as recognition markers in endosome/lysosome-specific targeting pathways. The endocytic targeting route can be exploited to deliver exogenous ASA to the lysosomes of ASA-deficient cells. ASA knockout mice, which develop a disorder related to MLD, have therefore been treated by ex vivo and in vivo gene therapy. Following transplantation of bone marrow cells overexpressing ASA from a retroviral vector, donor-type cells secrete ASA, which is endocytosed by recipient cells. The enzyme transfer results in the metabolic cross-correction of recipient cells and the improvement of biochemical, histological and clinical parameters. For the transfer of the ASA cDNA to non-dividing cells, adenovirus, adeno-associated virus and lentivirus vectors have been constructed. Such vectors might be particularly advantageous for direct ASA gene delivery to the brain, which is the main site of disease in MLD.

Evaluation of reliability for urine mucopolysaccharidosis screening by dimethylmethylene blue and Berry spot tests

BACKGROUND

The mucopolysaccharidosis (MPS) are a group of inherited metabolic disorders resulting from the deficiency of the enzyme responsible for intralysosomal catabolism of glycosaminoglycans (GAGs). GAGs are progressively accumulated in multiple tissues and released into the corporal fluids. The first laboratory approximation to MPS diagnosis is the identification of an increased urinary GAG excretion. For this, several semiquantitative and quantitative methods have been developed. The aim of this retrospective statistical study was to evaluate the reliability of MPS urine screening for the semiquantitative Berry spot test (BST) and the quantitative dimethylmethylene blue test (DMB).

METHODS

The 24-h-urine samples (n = 246) were tested through BST, DMB, and for GAG excretion pattern by one-dimensional electrophoresis or thin layer chromatography.

RESULTS

the 204 samples that demonstrated a normal GAG excretion pattern were considered as non-MPS samples. Forty-two samples presented an abnormal GAG excretion pattern. Enzyme analysis was available for 31 out of 42 patients (31/42), confirming that all were affected by MPS. Urinary GAG concentrations of MPS patients by DMB were increased 1.04- to 7.1-folds, compared to age-related normal levels. The sensitivity was 100% for DMB and 93.6% for BST. DMB demonstrated a specificity of 74.5%, while BST a specificity of 53.9%. The specificity of MPS screening increased to 84.3%, considering conjunctly DMB and BST.

CONCLUSION

The DMB is a sensitive method, however, inclusion of BST could increase the specificity of MPS urine screening.