A Preclinical Study Evaluating AAVrh10-Based Gene Therapy for Sanfilippo Syndrome.

Mucopolysaccharidosis type IIIA (MPS IIIA) is predominantly a disorder of the central nervous system, caused by a deficiency of sulfamidase (SGSH) with subsequent storage of heparan sulfate-derived oligosaccharides. No widely available therapy exists, and for this reason, a mouse model has been utilized to carry out a preclinical assessment of the benefit of intraparenchymal administration of a gene vector (AAVrh10-SGSH-IRES-SUMF1) into presymptomatic MPS IIIA mice. The outcome has been assessed with time, measuring primary and secondary storage material, neuroinflammation, and intracellular inclusions, all of which appear as the disease progresses. The vector resulted in predominantly ipsilateral distribution of SGSH, with substantially less detected in the contralateral hemisphere. Vector-derived SGSH enzyme improved heparan sulfate catabolism, reduced microglial activation, and, after a time delay, ameliorated GM3 ganglioside accumulation and halted ubiquitin-positive lesion formation in regions local to, or connected by projections to, the injection site. Improvements were not observed in regions of the brain distant from, or lacking connections with, the injection site. Intraparenchymal gene vector administration therefore has therapeutic potential provided that multiple brain regions are targeted with vector, in order to achieve widespread enzyme distribution and correction of disease pathology.

Continual Low-Dose Infusion of Sulfamidase Is Superior to Intermittent High-Dose Delivery in Ameliorating Neuropathology in the MPS IIIA Mouse Brain.

Mucopolysaccharidosis IIIA (MPS IIIA) is a neurodegenerative lysosomal storage disorder characterised by progressive loss of learned skills, sleep disturbance and behavioural problems. Reduced activity of lysosomal sulfamidase results in accumulation of heparan sulfate and secondary storage of glycolipids in the brain. Intra-cisternal sulfamidase infusions reduce disease-related neuropathology; however, repeated injections may subject patients to the risk of infection and tissue damage so alternative approaches are required. We undertook a proof-of-principle study comparing the ability of slow/continual or repeat/bolus infusion to ameliorate neuropathology in MPS IIIA mouse brain. Six-week-old MPS IIIA mice were implanted with subcutaneously located mini-osmotic pumps filled with recombinant human sulfamidase (rhSGSH) or vehicle, connected to lateral ventricle-directed cannulae. Pumps were replaced at 8 weeks of age. Additional MPS IIIA mice received intra-cisternal bolus infusions of the same amount of rhSGSH (or vehicle), at 6 and 8 weeks of age. Unaffected mice received vehicle via each strategy. All mice were euthanised at 10 weeks of age and the brain was harvested to assess the effect of treatment on neuropathology. Mice receiving pump-delivered rhSGSH exhibited highly significant reductions in lysosomal storage markers (lysosomal integral membrane protein-2, GM3 ganglioside and filipin-positive lipids) and neuroinflammation (isolectin B4-positive microglia, glial fibrillary acidic protein-positive astroglia). MPS IIIA mice receiving rhSGSH via bolus infusion displayed reductions in these markers, but the effectiveness of the strategy was inferior to that seen with slow/pump-based delivery. Continual low-dose infusion may therefore be a more effective strategy for enzyme delivery in MPS IIIA.

Determination of the role of injection site on the efficacy of intra-CSF enzyme replacement therapy in MPS IIIA mice.

MPS IIIA is an inherited neurodegenerative lysosomal storage disorder characterized by cognitive impairment, sleep-wake cycle disturbance, speech difficulties, eventual mental regression and early death. Neuropathological changes include accumulation of heparan sulfate and glycolipids, neuroinflammation and degeneration. Pre-clinical animal studies indicate that replacement of the deficient enzyme, sulfamidase, via intra-cerebrospinal fluid (CSF) injection is a clinically-relevant treatment approach, reducing neuropathological changes and improving symptoms. Given that there are several routes of administration of enzyme into the CSF (intrathecal lumbar, cisternal and ventricular), determining the effectiveness of each injection strategy is crucial in order to provide the best outcome for patients. We delivered recombinant human sulfamidase (rhSGSH) to a congenic mouse model of MPS IIIA via each of the three routes. Mice were euthanized 24h or one-week post-injection; the distribution of enzyme within the brain and spinal cord parenchyma was investigated, and the impact on primary substrate levels and other pathological lesions determined. Both ventricular and cisternal injection of rhSGSH enable enzyme delivery to brain and spinal cord regions, with the former mediating large, statistically significant decreases in substrate levels and reducing microglial activation. The single lumbar CSF infusion permitted more restricted enzyme delivery, with no reduction in substrate levels and little change in other disease-related lesions in brain tissue. While the ventricular route is the most invasive of the three methods, this strategy may enable the widest distribution of enzyme within the brain, and thus requires further exploration.

Helper-dependent canine adenovirus vector-mediated transgene expression in a neurodegenerative lysosomal storage disorder.

Mucopolysaccharidosis type IIIA (MPS-IIIA) is a severe neurodegenerative lysosomal storage disorder caused by a deficiency of N-sulfoglucosamine sulfohydrolase (SGSH) activity with subsequent accumulation of partially-degraded heparan sulfate and other glycolipids. In this study, we have evaluated a gene therapy approach using a helper-dependent canine adenovirus vector that expresses human SGSH as a means of delivering sustained transgene expression to the brain. Initial testing in a mixed neural cell culture model demonstrated that the vector could significantly increase SGSH activity in transduced cells, resulting in near-normalization of heparan sulfate-derived fragments. While administration of vector by direct injection into the brain of adult MPS-IIIA mice enabled transgene expression for at least 8.5 months post-treatment, it was only in discrete areas of brain. Heparan sulfate storage was reduced in some regions following treatment, however there was no improvement in secondary neuropathological changes. These data demonstrate that helper-dependent canine adenovirus vectors are capable of neural transduction and mediate long-term transgene expression, but increased SGSH expression throughout the brain is likely to be required in order to effectively treat all aspects of the MPS-IIIA phenotype.

Examination of intravenous and intra-CSF protein delivery for treatment of neurological disease.

Mucopolysaccharidosis type IIIA is a neurodegenerative lysosomal storage disorder characterized by progressive loss of learned skills, sleep disturbance and behavioural problems. Absent or greatly reduced activity of sulphamidase, a lysosomal protein, results in intracellular accumulation of heparan sulphate. Subsequent neuroinflammation and neurodegeneration typify this and many other lysosomal storage disorders. We propose that intra-cerebrospinal fluid protein delivery represents a potential therapeutic avenue for treatment of this and other neurodegenerative conditions; however, technical restraints restrict examination of its use prior to adulthood in mice. We have used a naturally-occurring Mucopolysaccharidosis type IIIA mouse model to determine the effectiveness of combining intravenous protein replacement (1 mg/kg) from birth to 6 weeks of age with intra-cerebrospinal fluid sulphamidase delivery (100 microg, fortnightly from 6 weeks) on behaviour, the level of heparan sulphate-oligosaccharide storage and other neuropathology. Mice receiving combination treatment exhibited similar clinical improvement and reduction in heparan sulphate storage to those only receiving intra-cerebrospinal fluid enzyme. Reductions in micro- and astrogliosis and delayed development of ubiquitin-positive lesions were seen in both groups. A third group of intravenous-only treated mice did not exhibit clinical or neuropathological improvements. Intra-cerebrospinal fluid injection of sulphamidase effectively, but dose-dependently, treats neurological pathology in Mucopolysaccharidosis type IIIA, even when treatment begins in mice with established disease.