Clearance of Heparan Sulfate and Attenuation of CNS Pathology by Intracerebroventricular BMN 250 in Sanfilippo Type B Mice

Abstract

Sanfilippo syndrome type B (mucopolysaccharidosis IIIB), caused by inherited deficiency of α-N-acetylglucosaminidase (NAGLU), required for lysosomal degradation of heparan sulfate (HS), is a pediatric neurodegenerative disorder with no approved treatment. Intracerebroventricular (ICV) delivery of a modified recombinant NAGLU, consisting of human NAGLU fused with insulin-like growth factor 2 (IGF2) for enhanced lysosomal targeting, was previously shown to result in marked enzyme uptake and clearance of HS storage in the Naglu−/− mouse brain. To further evaluate regional, cell type-specific, and dose-dependent biodistribution of NAGLU-IGF2 (BMN 250) and its effects on biochemical and histological pathology, Naglu−/− mice were treated with 1–100 μg ICV doses (four times over 2 weeks). 1 day after the last dose, BMN 250 (100 μg doses) resulted in above-normal NAGLU activity levels, broad biodistribution, and uptake in all cell types, with NAGLU predominantly localized to neurons in the Naglu−/− mouse brain. This led to complete clearance of disease-specific HS and reduction of secondary lysosomal defects and neuropathology across various brain regions lasting for at least 28 days after the last dose. The substantial brain uptake of NAGLU attainable by this highest ICV dosage was required for nearly complete attenuation of disease-driven storage accumulations and neuropathology throughout the Naglu−/− mouse brain.

Genetically Corrected iPSC-Derived Neural Stem Cell Grafts Deliver Enzyme Replacement to Affect CNS Disease in Sanfilippo B Mice

“…The lysosomal hexosaminidase enzyme is upregulated as a result of lysosomal dysfunction. 32 , 33 As expected, hexosaminidase was elevated in vehicle-injected Naglu −/− mice compared with unaffected mice in all sections ( Figure 5 D). Following engraftment in Naglu −/− mice, a partial reduction of hexosaminidase was achieved in the pool of sections 1 and 2, with a significant 1.2-fold reduction (p = 0.0127), in section 3, with a reduction of 1.2-fold (p = 0.0166), and a 1.3-fold reduction in section 4 (p < 0.0001), but no difference was observed for sections 5 and 6, which are farther away from the site of graft placement ( Figure 5 D).…”

Assessment of predicted enzymatic activity of α‐ N ‐acetylglucosaminidase variants of unknown significance for CAGI 2016

“…The age of onset of Sanfilippo Type B is 1-4 years (Andrade, Aldámiz-Echevarría, Llarena, & Couce, 2015) and the estimate for lifetime risk at birth (number of patients per 100,000 live births) varies substantially in European populations from 0.05 in Sweden to 0.78 in Greece (Zelei, Csetneki, Vokó, & Siffel, 2018). To date, no effective treatment for Sanfilippo syndrome exists although several promising approaches are being developed, including enzyme replacement therapy, gene therapy, bone marrow stem cell transplantation and small molecules (Aoyagi-Scharber et al, 2017;Gaffke, Pierzynowska, Piotrowska, & Węgrzyn, 2018). Because newborns are asymptomatic at birth, early diagnosis is critical for improved management and outcome of therapeutic trials.…”

How close are we to therapies for Sanfilippo disease?

“…A combination of the two methods described above, i.e. construction of the fusion protein and direct administration of the enzyme into CNS, has been applied recently (Aoyagi-Scharber et al 2017 ). Human α-N-acetylglucosaminidase has been fused with insulin-like growth factor 2 (which ensures more efficient lysosomal targeting) and administered intracerebroventriculary to MPS IIIB mice.…”

“…Human α-N-acetylglucosaminidase has been fused with insulin-like growth factor 2 (which ensures more efficient lysosomal targeting) and administered intracerebroventriculary to MPS IIIB mice. Broad distribution of the fusion protein was observed in the brain, which was accompanied with normalization of HS levels and significant reduction of secondary storage (Aoyagi-Scharber et al 2017 ).…”