Efficacy and Safety of Avalglucosidase Alfa in Patients With Late-Onset Pompe Disease After 97 Weeks: A Phase 3 Randomized Clinical Trial

Quantitative Systems Pharmacology-Based Digital Twins Approach Supplements Clinical Trial Data for Enzyme Replacement Therapies in Pompe Disease

Pompe disease is a rare, progressive neuromuscular disease caused by deficient lysosomal glycogen degradation, and includes both late-onset (LOPD) and severe infantile-onset (IOPD) phenotypes. Due to very small patient numbers in IOPD and the high phenotypic heterogeneity observed in this population, a quantitative systems pharmacology (QSP)-based "digital twin" approach was developed to perform an in silico comparison of the efficacy of avalglucosidase alfa vs. the standard of care, in a virtual population of IOPD patients. A QSP model was developed that represents key elements of Pompe disease pathophysiology, including tissue glycogen accumulation and the elevation of the biomarker urine Hex4 in both LOPD and IOPD patients. In this approach, the QSP model was used to generate digital twins of each IOPD patient enrolled in the avalglucosidase alfa clinical program, considering their respective disease burden, demographics, and treatment history. This virtual cohort supplemented clinical observations by simulating and comparing tissue glycogen and urine Hex4 following avalglucosidase alfa treatment vs. the standard of care. The digital twin analysis supports the interpretation that the enhanced reduction in urine Hex4 observed following avalglucosidase alfa treatment is attributable to greater tissue glycogen clearance. Overall, this study provides mechanism-based insight into avalglucosidase alfa efficacy across the phenotypic spectrum of Pompe disease and demonstrates the value of applying a QSP-based digital twin analysis to support rare disease drug development.

Prenatal Delivery of Enzyme Replacement Therapy to Fetuses Affected by Early-Onset Lysosomal Storage Diseases

The expansion of prenatal genetic screening and diagnosis warrants the evaluation of approved postnatal therapies that may be safely and feasibly translated to prenatal administration to a fetus affected by monogenic disease. For lysosomal storage diseases (LSDs), enzyme replacement therapy (ERT) often represents the main therapeutic approach. In utero enzyme replacement therapy (IUERT) has several potential benefits compared to postnatal therapy, such as: (1) delivering enzyme before the onset of irreversible organ damage; (2) developing tolerance toward the recombinant enzyme; and (3) targeting the central nervous system through a more permeable blood-brain barrier. In this review, we examine the general and disease-specific rationale for IUERT, and provide an overview of the main elements of our current clinical trial for the prenatal treatment of early-onset lysosomal storage diseases. Trial Registration: IUERT clinical trial: NCT04532047; Alpha thalassemia clinical trial: NCT02986698.

Clinical Reasoning: A 65-Year-Old Woman With Isolated Macroglossia as the Initial Presentation of a Rare Disease

Macroglossia can be seen in multiple conditions, but its evaluation becomes more challenging when approached as an isolated presenting symptom. This is a case of a 65-year-old patient with isolated progressive tongue hypertrophy of unclear etiology for 5 years. We navigate the causes of macroglossia and discuss the clinical and diagnostic procedures that helped us narrow the differential diagnoses for our patient. We emphasize searching for evidence of more systemic involvement and the use of appropriate genetic testing to change the course of the disease and avoid therapeutic delay.

Advances in Disease-Modifying Therapeutics for Chronic Neuromuscular Disorders

Neuromuscular disorders can cause respiratory impairment by affecting the muscle fibers, neuromuscular junction, or innervation of respiratory muscles, leading to significant morbidity and mortality. Over the past few years, new disease-modifying therapies have been developed and made available for treating different neuromuscular disorders. Some of these therapies have remarkable effectiveness, resulting in the prevention and reduction of respiratory complications. For myasthenia gravis (MG), efgartigimod, ravulizumab, rozanolixizumab, and zilucoplan have been Food and Drug Administration (FDA)-approved for the treatment of acetylcholine receptor (AChR) antibody-positive generalized MG in the past 2 years. Rozanolixiumab is also approved for treating MG caused by muscle-specific tyrosine kinase (MuSK) antibodies. The new MG therapeutics target the complement system or block the neonatal fragment crystallizable (Fc) receptors (FcRn), leading to significant clinical improvement. For spinal muscular atrophy (SMA), nusinersen (intrathecal route) and risdiplam (oral route) modify the splicing of the SMN2 gene, increasing the production of normal survival motor neuron (SMN) protein. Onasemnogene abeparvovec is a gene replacement therapy that encodes a functional SMN protein. All SMA medications, particularly onasemnogene abeparvovec, have led to clinically meaningful improvement. For late-onset Pompe disease (LOPD), avalglucosidase alfa has shown a greater improvement in respiratory function, ambulation, and functional outcomes in comparison to alglucosidase alfa, and cipaglucosidase alfa combined with miglustat has shown improvement in respiratory and motor function in a cohort of enzyme replacement therapy-experienced LOPD patients. Amyotrophic lateral sclerosis (ALS) remains a challenge. The two most recent FDA-approved medications, namely sodium phenylbutyrate and tofersen, may slow down the disease by a few months in a selected population but do not stop the progression of the disease.

Clinical modeling of motor function to predict treatment efficacy and enable in silico treatment comparisons in infantile-onset Pompe disease

Infantile-onset Pompe disease (IOPD) is a rare, deadly, quickly-progressing degenerative disease. Even with life-sustaining treatment (e.g., alglucosidase alfa [ALGLU]), many patients experience continued motor impairment. The Mini-COMET trial evaluated avalglucosidase alfa (AVAL) versus ALGLU on motor and other outcomes in IOPD. However, treatment groups were imbalanced at baseline and the trial was not powered to directly compare treatments. To supplement this limited data, we developed a modeling and simulation approach to compare AVAL versus ALGLU head-to-head in in silico (i.e., computer-simulated) trials. We first developed a longitudinal clinical model to establish the relationship between changes in motor function and changes in urinary hexose tetrasaccharide (uHex4), an established biomarker in IOPD. This model was based on pooled data from Mini-COMET (n = 21) and COMET trials (n = 100 patients with late-onset Pompe disease, LOPD). We then conducted in silico trials mimicking Mini-COMET. Simulated trials were informed by motor data generated from the clinical model and uHex4 profiles simulated in a quantitative systems pharmacology model. The virtual IOPD population was based on observed Mini-COMET baseline characteristics but engineered to have well-balanced baseline characteristics across treatment cohorts. In silico trials showed that patients with IOPD would have the greatest improvements in motor function with AVAL 40 mg/kg every other week (Q2W), suboptimal improvement with ALGLU 40 mg/kg Q2W, and no improvement with ALGLU 20 mg/kg Q2W. This study provides information on the relative efficacy of IOPD treatments and mitigates the confounding effects of imbalanced treatment cohorts. Our approach could also be applied in other rare diseases.

The European reference network for metabolic diseases (MetabERN) clinical pathway recommendations for Pompe disease (acid maltase deficiency, glycogen storage disease type II)

Clinical pathway recommendations (CPR) are based on existing guidelines and deliver a short overview on how to deal with a specific diagnosis, resulting therapy and follow-up. In this paper we propose a methodology for developing CPRs for Pompe disease, a metabolic myopathy caused by deficiency of lysosomal acid alpha-glucosidase. The CPR document was developed within the activities of the MetabERN, a non-profit European Reference Network for Metabolic Diseases established by the European Union. A working group was selected among members of the MetabERN lysosomal storage disease subnetwork, with specific expertise in the care of Pompe disease, and patient support group representatives. The working strategy was based on a systematic literature search to develop a database, followed by quality assessment of the studies selected from the literature, and by the development of the CPR document according to a matrix provided by MetabERN. Quality assessment of the literature and collection of citations was conducted according to the AGREE II criteria and Grading of Recommendations, Assessment, Development and Evaluation methodology. General aspects were addressed in the document, including pathophysiology, genetics, frequency, classification, manifestations and clinical approach, laboratory diagnosis and multidisciplinary evaluation, therapy and supportive measures, follow-up, monitoring, and pregnancy. The CPR document that was developed was intended to be a concise and easy-to-use tool for standardization of care for patients among the healthcare providers that are members of the network or are involved in the care for Pompe disease patients.

Advances in Pompe Disease Treatment: From Enzyme Replacement to Gene Therapy

Pompe disease is a neuromuscular disorder caused by a deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA), hydrolyzing glycogen to glucose. Pathological glycogen storage, the hallmark of the disease, disrupts the metabolism and function of various cell types, especially muscle cells, leading to cardiac, motor, and respiratory dysfunctions. The spectrum of Pompe disease manifestations spans two main forms: classical infantile-onset (IOPD) and late-onset (LOPD). IOPD, caused by almost complete GAA deficiency, presents at birth and leads to premature death by the age of 2 years without treatment. LOPD, less severe due to partial GAA activity, appears in childhood, adolescence, or adulthood with muscle weakness and respiratory problems. Since 2006, enzyme replacement therapy (ERT) has been approved for Pompe disease, offering clinical benefits but not a cure. However, advances in early diagnosis through newborn screening, recognizing disease manifestations, and developing improved treatments are set to enhance Pompe disease care. This article reviews recent progress in ERT and ongoing translational research, including the approval of second-generation ERTs, a clinical trial of in utero ERT, and preclinical development of gene and substrate reduction therapies. Notably, gene therapy using intravenous delivery of adeno-associated virus (AAV) vectors is in phase I/II clinical trials for both LOPD and IOPD. Promising data from LOPD trials indicate that most participants met the criteria to discontinue ERT several months after gene therapy. The advantages and challenges of this approach are discussed. Overall, significant progress is being made towards curative therapies for Pompe disease. While several challenges remain, emerging data are promising and suggest the potential for a once-in-a-lifetime treatment.

Cipaglucosidase alfa plus miglustat: linking mechanism of action to clinical outcomes in late-onset Pompe disease

Enzyme replacement therapy (ERT) is the only approved disease-modifying treatment modality for Pompe disease, a rare, inherited metabolic disorder caused by a deficiency in the acid α-glucosidase (GAA) enzyme that catabolizes lysosomal glycogen. First-generation recombinant human GAA (rhGAA) ERT (alglucosidase alfa) can slow the progressive muscle degeneration characteristic of the disease. Still, most patients experience diminished efficacy over time, possibly because of poor uptake into target tissues. Next-generation ERTs aim to address this problem by increasing bis-phosphorylated high mannose (bis-M6P) N-glycans on rhGAA as these moieties have sufficiently high receptor binding affinity at the resultant low interstitial enzyme concentrations after dosing to drive uptake by the cation-independent mannose 6-phosphate receptor on target cells. However, some approaches introduce bis-M6P onto rhGAA via non-natural linkages that cannot be hydrolyzed by natural human enzymes and thus inhibit the endolysosomal glycan trimming necessary for complete enzyme activation after cell uptake. Furthermore, all rhGAA ERTs face potential inactivation during intravenous delivery (and subsequent non-productive clearance) as GAA is an acid hydrolase that is rapidly denatured in the near-neutral pH of the blood. One new therapy, cipaglucosidase alfa plus miglustat, is hypothesized to address these challenges by combining an enzyme enriched with naturally occurring bis-M6P N-glycans with a small-molecule stabilizer. Here, we investigate this hypothesis by analyzing published and new data related to the mechanism of action of the enzyme and stabilizer molecule. Based on an extensive collection of in vitro, preclinical, and clinical data, we conclude that cipaglucosidase alfa plus miglustat successfully addresses each of these challenges to offer meaningful advantages in terms of pharmacokinetic exposure, target-cell uptake, endolysosomal processing, and clinical benefit.

Non-invasive optoacoustic imaging of glycogen-storage and muscle degeneration in late-onset Pompe disease

Pompe disease (PD) is a rare autosomal recessive glycogen storage disorder that causes proximal muscle weakness and loss of respiratory function. While enzyme replacement therapy (ERT) is the only effective treatment, biomarkers for disease monitoring are scarce. Following ex vivo biomarker validation in phantom studies, we apply multispectral optoacoustic tomography (MSOT), a laser- and ultrasound-based non-invasive imaging approach, in a clinical trial (NCT05083806) to image the biceps muscles of 10 late-onset PD (LOPD) patients and 10 matched healthy controls. MSOT is compared with muscle magnetic resonance imaging (MRI), ultrasound, spirometry, muscle testing and quality of life scores. Next, results are validated in an independent LOPD patient cohort from a second clinical site. Our study demonstrates that MSOT enables imaging of subcellular disease pathology with increases in glycogen/water, collagen and lipid signals, providing higher sensitivity in detecting muscle degeneration than current methods. This translational approach suggests implementation in the complex care of these rare disease patients.

Avalglucosidase alfa in infantile-onset Pompe disease: A snapshot of real-world experience in Italy

Introduction

Infantile-onset Pompe disease (IOPD) is due to mutations in the GAA gene leading to profound deficiency of the lysosomal enzyme α-1,4-glucosidase. The disease is characterized by severe hypotonia, hypertrophic cardiomyopathy, macroglossia, and liver enlargement with onset in the first months of life. In the late-onset form (LOPD), muscle signs predominate with a clinical picture resembling muscle dystrophies. Enzyme replacement therapy with alglucosidase alfa (rhGAA) has been available since 2006 and patients treated with the enzyme show improved outcomes. Nevertheless, there is evidence that some patients have a suboptimal response or, after an initial improvement, reach a plateau with stabilization of the clinical picture. Thus, a new enzyme formulation, avalglucosidase alfa (neoGAA), with a higher degree of mannosylation, was developed.

Methods

We conducted a multicenter survey that collected data on four patients with IOPD, aged 6 to 16 years, who were switched to neoGAA thanks to a compassionate use program, after being treated for an average of 11.5 years with rhGAA. Follow-up data, including biochemical parameters and clinical features, were analyzed to determine clinical outcomes and the safety profile after a mean of 9 months.

Results

Patients with IOPD who were treated with neoGAA showed a positive change in biomarker levels. Moreover, the clinical picture revealed improved motor performance and cardiac parameters in patients who previously responded poorly.

Conclusion

This study highlights the improved efficacy of neoGAA, as a next generation enzyme replacement therapy, in 4 Italian patients with IOPD. Several clinical parameters showed a positive response to the new formulation suggesting that, if used at diagnosis, neoGAA may result in better outcomes for patients with IOPD.

Start, switch and stop (triple-S) criteria for enzyme replacement therapy of late-onset Pompe disease: European Pompe Consortium recommendation update 2024

BACKGROUND AND PURPOSE

Two novel enzyme replacement therapies (ERTs), studied in phase 3 trials in late-onset Pompe patients, reached marketing authorization by the European Medicines Agency in 2022 and 2023. The European Pompe Consortium (EPOC) updates and extends the scope of the 2017 recommendations for starting, switching and stopping ERT.

METHODS

The European Pompe Consortium consists of 25 neuromuscular and metabolic experts from eight European countries. This update was performed after an in-person meeting, three rounds of discussion and voting to provide a consensus recommendation.

RESULTS

The patient should be symptomatic, that is, should have skeletal muscle weakness or respiratory muscle involvement. Muscle magnetic resonance imaging findings showing substantial fat replacement can support the decision to start in a patient-by-patient scenario. Limited evidence supports switching ERT if there is no indication that skeletal muscle and/or respiratory function have stabilized or improved during standard ERT of 12 months or after severe infusion-associated reactions. Switching of ERT should be discussed on a patient-by-patient shared-decision basis. If there are severe, unmanageable infusion-associated reactions and no stabilization in skeletal muscle function during the first 2 years after starting or switching treatment, stopping ERT should be considered. After stopping ERT for inefficacy, restarting ERT can be considered. Six-monthly European Pompe Consortium muscle function assessments are recommended.

CONCLUSIONS

The triple-S criteria on ERT start, switch and stop include muscle magnetic resonance imaging as a supportive finding and the potential option of home infusion therapy. Six-monthly long-term monitoring of muscle function is highly recommended to cover insights into the patient's trajectory under ERT.

Response to Comments on "Increasing Enzyme Mannose-6-Phosphate Levels but Not Miglustat Coadministration Enhances the Efficacy of Enzyme Replacement Therapy in Pompe Mice"

We thank Dr. Weimer and her colleagues for their comments related to our recent work (Anding et al., 2023) and are grateful for the opportunity to further discuss the importance of efficient lysosomal targeting of enzyme-replacement therapies (ERT) for the treatment of Pompe disease. Patients with Pompe disease have mutations in the gene that encodes for acid α glucosidase (GAA), a lysosomal enzyme necessary for the breakdown of glycogen. The first-generation ERT, alglucosidase alfa, provides a lifesaving therapy for the severe form of the disease (infantile onset Pompe disease) and improves or stabilizes respiratory and motor function in patients with less severe disease (late onset Pompe disease). Despite these gains, significant unmet need remains, particularly in patients who display respiratory and motor decline following years of treatment. Poor tissue uptake and lysosomal targeting via inefficient binding of the cation-independent mannose-6-phosphate (M6P) receptor (CIMPR) in skeletal muscle contributed to this suboptimal treatment response, prompting the development of new ERTs with increased levels of M6P.

Therapeutic Peptides, Proteins and their Nanostructures for Drug Delivery and Precision Medicine

Peptide and protein nanostructures with tunable structural features, multifunctionality, biocompatibility and biomolecular recognition capacity enable development of efficient targeted drug delivery tools for precision medicine applications. In this review article, we present various techniques employed for the synthesis and self-assembly of peptides and proteins into nanostructures. We discuss design strategies utilized to enhance their stability, drug-loading capacity, and controlled release properties, in addition to the mechanisms by which peptide nanostructures interact with target cells, including receptor-mediated endocytosis and cell-penetrating capabilities. We also explore the potential of peptide and protein nanostructures for precision medicine, focusing on applications in personalized therapies and disease-specific targeting for diagnostics and therapeutics in diseases such as cancer.

Long-term safety and efficacy of cipaglucosidase alfa plus miglustat in individuals living with Pompe disease: an open-label phase I/II study (ATB200-02)

Cipaglucosidase alfa plus miglustat (cipa + mig) is a novel, two-component therapy for Pompe disease. We report data from the Phase I/II ATB200-02 study for up to 48 months of treatment. Four adult cohorts, including one non-ambulatory ERT-experienced (n = 6) and three ambulatory cohorts, (two enzyme replacement therapy [ERT]-experienced cohorts [2-6 years (n = 11) and ≥ 7 years (n = 6)]), one ERT-naïve cohort (n = 6), received 20 mg/kg intravenous-infused cipa plus 260 mg oral mig biweekly. Change from baseline (CFBL) for multiple efficacy endpoints at 12, 24, 36, and 48 months, pharmacodynamics, pharmacokinetics, safety, and immunogenicity data were assessed. Six-minute walking distance (% predicted) improved at 12, 24, 36, and 48 months: pooled ambulatory ERT-experienced cohorts, mean(± standard deviation [SD]) CFBL: 6.1(± 7.84), n = 16; 5.4(± 10.56), n = 13; 3.4(± 14.66), n = 12; 5.9(± 17.36), n = 9, respectively; ERT-naïve cohort: 10.7(± 3.93), n = 6; 11.0(± 5.06), n = 6; 9.0(± 7.98), n = 5; 11.7(± 7.69), n = 4, respectively. Percent predicted forced vital capacity was generally stable in ERT-experienced cohorts, mean(± SD) CFBL - 1.2(± 5.95), n = 16; 1.0(± 7.96), n = 13; - 0.3(± 6.68), n = 10; 1.0(± 6.42), n = 6, respectively, and improved in the ERT-naïve cohort: 3.2(± 8.42), n = 6; 4.7(± 5.09), n = 6; 6.2(± 3.35), n = 5; 8.3(± 4.50), n = 4, respectively. Over 48 months, CK and Hex4 biomarkers improved in ambulatory cohorts. Overall, cipa + mig was well tolerated with a safety profile like alglucosidase alfa. ATB200-02 results show the potential benefits of cipa + mig as a long-term treatment option for Pompe disease. Trial registration number: NCT02675465 January 26, 2016.

Evaluating avalglucosidase alfa for the management of late-onset Pompe disease

INTRODUCTION

Glycogenosis type II (GSDII) is a rare autosomal disorder that is caused by the deficiency of alpha-glucosidase, a lysosomal enzyme that hydrolyzes glycogen to glucose. Autophagy dysregulation plays a critical role. Importantly, since 2006, both patients with infantile (classic Pompe disease) and adult GSDII (late-onset Pompe disease or LOPD) have been treated with enzyme replacement therapy (ERT). To support this use, several double-blind and observational studies including large cohorts of GSDII patients have been undertaken and have shown ERT to be effective in modifying the natural course of disease. Indeed, most LOPD cases improve in the first 20 months of treatment in a six-minute walk test (6MWT), while those who are untreated do not; instead, their response declines over time.

AREAS COVERED

The author reviews avalglucosidase alpha, a therapy approved by both the FDA and European regulatory agencies. Herein, the author considers the pathophysiological approaches such as the role of enzyme entry, autophagy, and the response to ERT treatment of motor and respiratory components.

EXPERT OPINION

There has been a notable drive toward the research of various aspects of this disease regarding the role of new enzyme penetration and immune adverse events. Consequently, avalglucosidase alpha might be a further step forward.

Real-world evidence study finds no new-onset diabetes or drug-related hyperglycemia in Pompe disease patients treated with avalglucosidase alfa

Avalglucosidase alfa therapy for Pompe disease is diluted in dextrose 5% solution in water (D5W) for infusion, which raises questions about the potential for hyperglycemia or worsening diabetes. Using United States insurance claims data, we assessed the impact of biweekly infusions on hyperglycemia, new-onset diabetes mellitus, insulin resistance, and prediabetes in patients with Pompe disease. After starting avalglucosidase alfa treatment, 1 of 26 patients had one claim for hyperglycemia, which was attributed to acute pancreatitis.

Real-world outcomes from a series of patients with late onset Pompe disease who switched from alglucosidase alfa to avalglucosidase alfa

Introduction: Pompe disease is an inherited, progressive neuromuscular disorder caused by deficiency of lysosomal acid α-glucosidase and accumulation of glycogen in tissues, resulting in cellular dysfunction, muscle damage, and functional disabilities. Enzyme replacement therapy with alglucosidase alfa (Myozyme/Lumizyme) has led to better outcomes, but many patients have plateaued or declined despite treatment. The second-generation ERT avalglucosidase alfa (Nexviazyme) was designed to have enhanced cellular uptake via the conjugation of additional bis-mannose-6-phosphate residues. There have been trials comparing the efficacy of alglucosidase and avalglucosidase, but there remains a need for more real-world data on patients who switched from alglucosidase to avalglucosidase. Methods: A chart review was conducted on n = 15 patients with late-onset Pompe disease followed at a single center who switched from alglucosidase to avalglucosidase and continued for at least 6 months. Results: A total of n = 8/15 patients received alglucosidase for more than 3 years prior to switching, and n = 7/15 received it for more than 5 years prior to switching. There were statistically significant improvements in CK, Hex4, and AST with mean differences of -104.8 U/L, -3.0 mmol/molCr, and -14.7 U/L, respectively, post-switch. 6-Minute Walk Test; comfortable gait speed; Gait, Stairs, Gower, Chair; and Quick Motor Function Test scores improved or stabilized in most patients post-switch (n = 8/12, n = 11/12, n = 9/12, n =7/11, respectively). Of n = 7 patients with pulmonary function testing, n = 4/7 had improved upright FVC. Patient-reported outcomes revealed improvements in dyspnea (n = 4/4), physical function (n = 3/4), fatigue (n = 2/3), and lower back pain (n = 3/3). Avalglucosidase was well tolerated without infusion-associated reactions, and all n = 7 patients on home infusions continued receiving ERT at home. Anti-drug antibodies were seen in n = 9/10 of patients on alglucosidase and n = 8/13 of those on avalglucosidase, with titers below 12,800 in a majority of patients. We also present the first outcome data for a patient with LOPD who is non-ambulatory and a full-time wheelchair user; she demonstrated meaningful improvements in quality of life and motor function with the switch. Discussion: In summary, improved outcomes were seen in most patients, with a subset whose decline persisted. This study presents evidence that switching from alglucosidase to avalglucosidase may be associated with improved outcomes in certain patients with LOPD.

Targeted protein degradation through site-specific antibody conjugation with mannose 6-phosphate glycan

Recent developments in targeted protein degradation have provided great opportunities to eliminating extracellular protein targets using potential therapies with unique mechanisms of action and pharmacology. Among them, Lysosome-Targeting Chimeras (LYTACs) acting through mannose 6-phosphate receptor (M6PR) have been shown to facilitate degradation of several soluble and membrane-associated proteins in lysosomes with high efficiency. Herein we have developed a novel site-specific antibody conjugation approach to generate antibody mannose 6-phosphate (M6P) conjugates. The method uses a high affinity synthetic M6P glycan, bisM6P, that is coupled to an Fc-engineered antibody NNAS. This mutant without any effector function was generated by switching the native glycosylation site from position 297 to 298 converting non-sialylated structures to highly sialylated N-glycans. The sialic acid of the glycans attached to Asn298 in the engineered antibody was selectively conjugated to bisM6P without chemoenzymatic modification, which is often used for site-specific antibody conjugation through glycans. The conjugate is mainly homogeneous by analysis using mass spectrometry, typically with one or two glycans coupled. The M6P-conjugated antibody against a protein of interest (POI) efficiently internalized targeted soluble proteins, such as human tumor necrosis factor (TNF), in both cancer cell lines and human immune cells, through the endo-lysosomal pathway as demonstrated by confocal microscopy and flow cytometry. TNF in cell culture media was significantly depleted after the cells were incubated with the M6P-conjugated antibody. TNF internalization is mediated through M6PR, and it is correlated well with cell surface expression of cation-independent M6PR (CI-MPR) in immune cells. A significant amount of CI-MPR remains on the cell surface, while internalized TNF is degraded in lysosomes. Thus, the antibody-M6P conjugate is highly efficient in inducing internalization and subsequent lysosome-mediated protein degradation. Our platform provides a unique method for producing biologics-based degraders that may be used to treat diseases through event-driven pharmacology, thereby addressing unmet medical needs.

Current avenues of gene therapy in Pompe disease

PURPOSE OF REVIEW

Pompe disease is a rare, inherited, devastating condition that causes progressive weakness, cardiomyopathy and neuromotor disease due to the accumulation of glycogen in striated and smooth muscle, as well as neurons. While enzyme replacement therapy has dramatically changed the outcome of patients with the disease, this strategy has several limitations. Gene therapy in Pompe disease constitutes an attractive approach due to the multisystem aspects of the disease and need to address the central nervous system manifestations. This review highlights the recent work in this field, including methods, progress, shortcomings, and future directions.

RECENT FINDINGS

Recombinant adeno-associated virus (rAAV) and lentiviral vectors (LV) are well studied platforms for gene therapy in Pompe disease. These products can be further adapted for safe and efficient administration with concomitant immunosuppression, with the modification of specific receptors or codon optimization. rAAV has been studied in multiple clinical trials demonstrating safety and tolerability.

SUMMARY

Gene therapy for the treatment of patients with Pompe disease is feasible and offers an opportunity to fully correct the principal pathology leading to cellular glycogen accumulation. Further work is needed to overcome the limitations related to vector production, immunologic reactions and redosing.

Glycogen storage diseases

Glycogen storage diseases (GSDs) are a group of rare, monogenic disorders that share a defect in the synthesis or breakdown of glycogen. This Primer describes the multi-organ clinical features of hepatic GSDs and muscle GSDs, in addition to their epidemiology, biochemistry and mechanisms of disease, diagnosis, management, quality of life and future research directions. Some GSDs have available guidelines for diagnosis and management. Diagnostic considerations include phenotypic characterization, biomarkers, imaging, genetic testing, enzyme activity analysis and histology. Management includes surveillance for development of characteristic disease sequelae, avoidance of fasting in several hepatic GSDs, medically prescribed diets, appropriate exercise regimens and emergency letters. Specific therapeutic interventions are available for some diseases, such as enzyme replacement therapy to correct enzyme deficiency in Pompe disease and SGLT2 inhibitors for neutropenia and neutrophil dysfunction in GSD Ib. Progress in diagnosis, management and definitive therapies affects the natural course and hence morbidity and mortality. The natural history of GSDs is still being described. The quality of life of patients with these conditions varies, and standard sets of patient-centred outcomes have not yet been developed. The landscape of novel therapeutics and GSD clinical trials is vast, and emerging research is discussed herein.

Hypertrophic Cardiomyopathy versus Storage Diseases with Myocardial Involvement

One of the main causes of heart failure is cardiomyopathies. Among them, the most common is hypertrophic cardiomyopathy (HCM), characterized by thickening of the left ventricular muscle. This article focuses on HCM and other cardiomyopathies with myocardial hypertrophy, including Fabry disease, Pompe disease, and Danon disease. The genetics and pathogenesis of these diseases are described, as well as current and experimental treatment options, such as pharmacological intervention and the potential of gene therapies. Although genetic approaches are promising and have the potential to become the best treatments for these diseases, further research is needed to evaluate their efficacy and safety. This article describes current knowledge and advances in the treatment of the aforementioned cardiomyopathies.