Global CNS correction in a large brain model of human alpha-mannosidosis by intravascular gene therapy

Widespread correction of brain pathology in feline alpha-mannosidosis by dose escalation of intracisternal AAV vector injection

Alpha-mannosidosis is caused by a genetic deficiency of lysosomal alpha-mannosidase, leading to the widespread presence of storage lesions in the brain and other tissues. Enzyme replacement therapy is available but is not approved for treating the CNS, since the enzyme does not penetrate the blood-brain barrier. However, intellectual disability is a major manifestation of the disease; thus, a complimentary treatment is needed. While enzyme replacement therapy into the brain is technically feasible, it requires ports and frequent administration over time that are difficult to manage medically. Infusion of adeno-associated viral vectors into the cerebrospinal fluid is an attractive route for broadly targeting brain cells. We demonstrate here the widespread post-symptomatic correction of the globally distributed storage lesions by infusion of a high dose of AAV1-feline alpha-mannosidase (fMANB) into the CSF via the cisterna magna in the gyrencephalic alpha-mannosidosis cat brain. Significant improvements in clinical parameters occurred, and widespread global correction was documented pre-mortem by non-invasive magnetic resonance imaging. Postmortem analysis demonstrated high levels of MANB activity and reversal of lysosomal storage lesions throughout the brain. Thus, CSF treatment by adeno-associated viral vector gene therapy appears to be a suitable complement to systemic enzyme replacement therapy to potentially treat the whole patient.

Dose-dependent delivery of genes to the cerebral cortex via the nasal route

The use of nucleic acids to treat various brain diseases could offer new therapeutic modalities, providing the nucleic acids may be effectively delivered to areas of the brain using non-toxic vectors. In this study, we present evidence that genes may be successfully delivered in a dose-dependent manner via the nose, primarily to the cerebral cortex using a 6-O-glycolchitosan (GC) formulation of plasmid DNA. Positively charged (zeta potential = +13 - + 25 mV) GC-DNA nanoparticles of 100-500 nm in diameter with favourable cell biocompatibility were shown to deliver the reporter Green Fluorescent Protein (GFP) plasmid to the U87MG cell line and the resulting protein expression was not significantly different from that obtained with Lipofectamine 2000. On intranasal delivery of GC-luciferase-plasmid nanoparticles to Balb/ C mice at 4 doses, ranging from 0.02 to 0.1 mg/ kg, luciferase activity was observed qualitatively in intact mouse brains, 48 h after intranasal, using the IV-VIS visualisation. In further confirmation of brain delivery, dose-dependent protein expression was quantified in multiple brain areas 48 h after dosing; with protein expression seen mainly in the cerebral cortex and striatum and following expression levels: cerebral cortex = olfactory bulb > striatum > brain stem > mid brain = cerebellum. No protein expression was observed in the liver and lungs of dosed animals. GC-DNA protein expression was not significantly different to that observed with Lipofectamine 2000. These results demonstrate that GC-DNA nanoparticles are able to deliver genes preferably to specific brain regions such as the cerebral cortex and striatum; offering the possibility of using genes to treat a range of neurological disorders using a non-invasive method of dosing.

Gene therapy for lysosomal storage diseases: Current clinical trial prospects

Lysosomal storage diseases (LSDs) are a group of metabolic inborn errors caused by defective enzymes in the lysosome, resulting in the accumulation of undegraded substrates. LSDs are progressive diseases that exhibit variable rates of progression depending on the disease and the patient. The availability of effective treatment options, including substrate reduction therapy, pharmacological chaperone therapy, enzyme replacement therapy, and bone marrow transplantation, has increased survival time and improved the quality of life in many patients with LSDs. However, these therapies are not sufficiently effective, especially against central nerve system abnormalities and corresponding neurological and psychiatric symptoms because of the blood-brain barrier that prevents the entry of drugs into the brain or limiting features of specific treatments. Gene therapy is a promising tool for the treatment of neurological pathologies associated with LSDs. Here, we review the current state of gene therapy for several LSDs for which clinical trials have been conducted or are planned. Several clinical trials using gene therapy for LSDs are underway as phase 1/2 studies; no adverse events have not been reported in most of these studies. The administration of viral vectors has achieved good therapeutic outcomes in animal models of LSDs, and subsequent human clinical trials are expected to promote the practical application of gene therapy for LSDs.

Die α-Mannosidose: eine seltene, aber unterdiagnostizierte Erkrankung?

Bei der α‑Mannosidose handelt es sich um eine seltene lysosomale Speichererkrankung, bedingt durch eine autosomal-rezessiv vererbte Defizienz der α‑Mannosidase. Die Erkrankung weist ein breites klinisches Spektrum mit chronisch progredientem Verlauf auf. Charakteristische klinische Zeichen in den ersten Lebensjahren sind Hörminderung, Entwicklungsverzögerung, rezidivierende Infekte und/oder faziale Dysmorphie. Im weiteren Verlauf der Erkrankung manifestieren sich zunehmende skeletale Probleme und eine Ataxie, beide zu Immobilität führend. Im Gegensatz zu anderen lysosomalen Speichererkrankungen zeigt sich nach dem 20. Lebensjahr meist kein weiterer Verlust kognitiver Fähigkeiten. Ab dem Alter von 15 Jahren entwickeln ca. 25 % der Patienten psychiatrische Symptome. Aufgrund der Seltenheit der Erkrankung werden viele Patienten verspätet, z. T. erst im Erwachsenenalter, diagnostiziert.

Mittlerweile stehen 2 Therapieoptionen zur Behandlung der α‑Mannosidose zur Verfügung. Bei frühzeitiger Diagnosestellung ist die hämatopoetische Stammzelltransplantation eine wichtige therapeutische Option mit potenziell positivem Effekt auf die neurokognitive Entwicklung. Die Enzymersatztherapie mit Velmanase alfa ist seit 2018 in Europa zugelassen und eine therapeutische Option zur Behandlung der nichtneurologischen Manifestationen bei α‑Mannosidose. Sie hat jedoch keinen Einfluss auf neurologische Manifestationen der Erkrankung.

Zur Verbesserung der Diagnostik von Kindern und Jugendlichen mit der seltenen Erkrankung α‑Mannosidose möchte dieser Beitrag das Wissen um und das Bewusstsein für diese Erkrankung schärfen. Die frühe Diagnose einer α‑Mannosidose erspart nicht nur den Familien einen jahrelangen diagnostischen Leidensweg, sondern ermöglicht auch den betroffenen Patienten ein verbessertes Auskommen durch einen frühen Therapiestart.

Brain Gene Silencing with Cationic Amino-Capped Poly(ethylene glycol) Polyplexes

Therapeutic gene silencing in the brain is usually achieved using highly invasive intracranial administration methods and/or comparatively toxic vectors. In this work, we use a relatively biocompatible vector: poly(ethylene glycol) star-shaped polymer capped with amine groups (4APPA) via the nose to brain route. 4APPA complexes anti- itchy E3 ubiquitin protein ligase (anti-ITCH) siRNA to form positively charged (zeta potential +15 ± 5 mV) 150 nm nanoparticles. The siRNA-4APPA polyplexes demonstrated low cellular toxicity (IC50 = 13.92 ± 6 mg mL⁻¹) in the A431 cell line and were three orders of magnitude less toxic than Lipofectamine 2000 (IC50 = 0.033 ± 0.04 mg mL⁻¹) in this cell line. Cell association and uptake of fluorescently labelled siRNA bound to siRNA-4APPA nanoparticles was demonstrated using fluorescent activated cell sorting (FACS) and confocal laser scanning microscopy (CLSM), respectively. Gene silencing of the ITCH gene was observed in vitro in the A431 cell line (65% down regulation when compared to the use of anti-ITCH siRNA alone). On intranasal dosing with fluorescently labelled siRNA-4APPA polyplexes, fluorescence was seen in the cells of the olfactory bulb, cerebral cortex and mid-brain regions. Finally, down regulation of ITCH was seen in the brain cells (54 ± 13% ITCH remaining compared to untreated controls) in a healthy rat model, following intranasal dosing of siRNA-4APPA nanoparticles (0.15 mg kg⁻¹ siRNA twice daily for 3 days). Gene silencing in the brain may be achieved by intranasal administration of siRNA- poly(ethylene glycol) based polyplexes.

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

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

A Multifaceted Approach to Optimizing AAV Delivery to the Brain for the Treatment of Neurodegenerative Diseases

Despite major advancements in gene therapy technologies, there are no approved gene therapies for diseases which predominantly effect the brain. Adeno-associated virus (AAV) vectors have emerged as the most effective delivery vector for gene therapy owing to their simplicity, wide spread transduction and low immunogenicity. Unfortunately, the blood-brain barrier (BBB) makes IV delivery of AAVs, to the brain highly inefficient. At IV doses capable of widespread expression in the brain, there is a significant risk of severe immune-mediated toxicity. Direct intracerebral injection of vectors is being attempted. However, this method is invasive, and only provides localized delivery for diseases known to afflict the brain globally. More advanced methods for AAV delivery will likely be required for safe and effective gene therapy to the brain. Each step in AAV delivery, including delivery route, BBB transduction, cellular tropism and transgene expression provide opportunities for innovative solutions to optimize delivery efficiency. Intra-arterial delivery with mannitol, focused ultrasound, optimized AAV capsid evolution with machine learning algorithms, synthetic promotors are all examples of advanced strategies which have been developed in pre-clinical models, yet none are being investigated in clinical trials. This manuscript seeks to review these technological advancements, and others, to improve AAV delivery to the brain, and to propose novel strategies to build upon this research. Ultimately, it is hoped that the optimization of AAV delivery will allow for the human translation of many gene therapies for neurodegenerative and other neurologic diseases.

Improved systemic AAV gene therapy with a neurotrophic capsid in Niemann-Pick disease type C1 mice

Niemann-Pick C1 disease (NPC1) is a rare, fatal neurodegenerative disease caused by mutations in NPC1, which encodes the lysosomal cholesterol transport protein NPC1. Disease pathology involves lysosomal accumulation of cholesterol and lipids, leading to neurological and visceral complications. Targeting the central nervous system (CNS) from systemic circulation complicates treatment of neurological diseases with gene transfer techniques. Selected and engineered capsids, for example, adeno-associated virus (AAV)-PHP.B facilitate peripheral-to-CNS transfer and hence greater CNS transduction than parental predecessors. We report that systemic delivery to Npc1 m1N/m1N mice using an AAV-PHP.B vector ubiquitously expressing NPC1 led to greater disease amelioration than an otherwise identical AAV9 vector. In addition, viral copy number and biodistribution of GFP-expressing reporters showed that AAV-PHP.B achieved more efficient, albeit variable, CNS transduction than AAV9 in Npc1 m1N/m1N mice. This variability was associated with segregation of two alleles of the putative AAV-PHP.B receptor Ly6a in Npc1 m1N/m1N mice. Our data suggest that robust improvements in NPC1 disease phenotypes occur even with modest CNS transduction and that improved neurotrophic capsids have the potential for superior NPC1 AAV gene therapy vectors.

Intravenous delivery of adeno-associated viral gene therapy in feline GM1 gangliosidosis

GM1 gangliosidosis is a fatal neurodegenerative disease caused by a deficiency of lysosomal β-galactosidase. In its most severe form, GM1 gangliosidosis causes death by 4 years of age, and no effective treatments exist. Previous work has shown that injection of the brain parenchyma with an adeno-associated viral vector provides pronounced therapeutic benefit in a feline GM1 model. To develop a less invasive treatment for the brain and increase systemic biodistribution, intravenous injection of AAV9 was evaluated. AAV9 expressing feline β-galactosidase was intravenously administered at 1.5x1013 vector genomes/kilogram body weight to six GM1 cats at approximately 1 month of age. The animals were divided into two cohorts: 1) a long-term group, which was followed to humane endpoint, and 2) a short-term group, which was analyzed 16-weeks post treatment. Clinical assessments included neurological exams, cerebrospinal fluid and urine biomarkers, and 7-Telsa magnetic resonance imaging and spectroscopy. Postmortem analysis included β-galactosidase and virus distribution, histological analysis, and ganglioside content. Untreated GM1 animals survived 8.0 ± 0.6 months while intravenous treatment increased survival to an average of 3.5 years (n = 2) with substantial improvements in quality of life and neurologic function. Neurological abnormalities, which in untreated animals progress to the inability to stand and debilitating neurological disease by 8 months of age, were mild in all treated animals. Cerebrospinal fluid biomarkers were normalized, indicating decreased central nervous system cell damage in the treated animals. Urinary glycosaminoglycans decreased to normal levels in the long-term cohort. Magnetic resonance imaging and spectroscopy showed partial preservation of the brain in treated animals, which was supported by postmortem histological evaluation. β-galactosidase activity was increased throughout the central nervous system, reaching carrier levels in much of the cerebrum and normal levels in the cerebellum, spinal cord and cerebrospinal fluid. Ganglioside accumulation was significantly reduced by treatment. Peripheral tissues such as heart, skeletal muscle, and sciatic nerve also had normal β-galactosidase activity in treated GM1 cats. GM1 histopathology was largely corrected with treatment. There was no evidence of tumorigenesis or toxicity. Restoration of β-galactosidase activity in the central nervous system and peripheral organs by intravenous gene therapy led to profound increases in lifespan and quality of life in GM1 cats. This data supports the promise of intravenous gene therapy as a safe, effective treatment for GM1 gangliosidosis.

Emerging Concepts in Vector Development for Glial Gene Therapy: Implications for Leukodystrophies

Central Nervous System (CNS) homeostasis and function rely on intercellular synchronization of metabolic pathways. Developmental and neurochemical imbalances arising from mutations are frequently associated with devastating and often intractable neurological dysfunction. In the absence of pharmacological treatment options, but with knowledge of the genetic cause underlying the pathophysiology, gene therapy holds promise for disease control. Consideration of leukodystrophies provide a case in point; we review cell type – specific expression pattern of the disease – causing genes and reflect on genetic and cellular treatment approaches including ex vivo hematopoietic stem cell gene therapies and in vivo approaches using adeno-associated virus (AAV) vectors. We link recent advances in vectorology to glial targeting directed towards gene therapies for specific leukodystrophies and related developmental or neurometabolic disorders affecting the CNS white matter and frame strategies for therapy development in future.

White matter alteration and cerebellar atrophy are hallmarks of brain MRI in alpha-mannosidosis

OBJECTIVE

Despite profound neurological symptomatology there are only few MRI studies focused on the brain abnormalities in alpha-mannosidosis (AM). Our aim was to characterize brain MRI findings in a large cohort of AM patients along with clinical manifestations.

METHODS

Twenty-two brain MRIs acquired in 13 untreated AM patients (8 M/5F; median age 17 years) were independently assessed by three experienced readers and compared to 16 controls.

RESULTS

Focal and/or diffuse hyperintense signals in the cerebral white matter were present in most (85%) patients. Cerebellar atrophy was common (62%), present from the age of 5 years. Progression was observed in two out of 6 patients with follow-up scans. Cortical atrophy (62%) and corpus callosum thinning (23%) were already present in a 13-month-old child. The presence of low T₂ signal intensity in basal ganglia and thalami was excluded by the normalized signal intensity profiling. The enlargement of perivascular spaces in white matter (38%), widening of perioptic CSF spaces (62%), and enlargement of cisterna magna (85%) were also observed. Diploic space thickening (100%), mucosal thickening (69%) and sinus hypoplasia (54%) were the most frequent non-CNS abnormalities.

CONCLUSION

White matter changes and cerebellar atrophy are proposed to be the characteristic brain MRI features of AM. The previously reported decreased T₂ signal intensity in basal ganglia and thalami was not detected in this quantitative study. Rather, this relative MR appearance seems to be related to the diffuse high T₂ signal in the adjacent white matter and not the gray matter iron deposition that has been hypothesized.

Gene therapy for global brain diseases: one small step for mice, one giant leap for humans

This scientific commentary refers to ‘Global CNS correction in a large brain model of human alpha-mannosidosis by intravascular gene therapy’, by Yoon et al. (doi:10.1093/brain/awaa161).