Preliminary findings of a twenty-six week or longer intracerebroventricular infusion study of BMN 250 administered once every 2 weeks in a canine model of mucopolysaccharidosis type IIIB

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Abstracts / Molecular Genetics and Metabolism 120 (2016) S17–S145

Classic infantile Pompe disease is a rare metabolic myopathy that leads to death in the first year if untreated. In 1999, we pioneered enzyme replacement therapy (ERT) with recombinant human alphaglucosidase. Although ERT has significantly improved patients’ survival, cardiac hypertrophy and motor functioning, it cannot pass the bloodbrain barrier, while glycogen storage occurs in the brain as well. The few studies of cognitive development involved patients no older than 12 years of age. To date, the consequence of glycogen storage have seemed limited, with mild periventricular white-matter abnormalities and cognition ranging from normal to mildly delayed. As our oldest patients are now on the threshold of adulthood, we need to understand the impact of glycogen storage in the brain. Using neuropsychological tests and brain MRI, we prospectively assessed a large cohort of 11 classic infantile Pompe patients aged up to 17 years. From age 2.7 onwards, brain MRI showed involvement of the periventricular white matter and centrum semiovale. After age 8, additional white-matter abnormalities occurred in the corpus callosum, internal and external capsule, and subcortical areas. From age 11, white-matter abnormalities were found in the brainstem as well. Although there seems to be a characteristic pattern of involvement over time, there are also considerable variations between patients, which are reflected in neuropsychological development. While cognition in some patients is stable and normal, a decline in others reached the level of intellectual disabilities. A specific profile is emerging with problems in processing speed, performance intelligence, attention and working memory. As our patient population matures towards adulthood, a new challenge is taking shape with regard to classic infantile Pompe disease. In our view, it is extremely important to focus on the brain in future research and to include the central nervous system as an additional target in the development of next-generation therapeutic strategies. doi:10.1016/j.ymgme.2016.11.088

80 Preliminary findings of a twenty-six week or longer intracerebroventricular infusion study of BMN 250 administered once every 2 weeks in a canine model of mucopolysaccharidosis type IIIB N. Matthew Ellinwooda, Bethann Valentinea, Andrew S Hessa, Jackie K Jensa, Elizabeth M Snellaa, Wendy A Warea, Shannon J Hostettera, Gil Ben-Shlomoa, Nicholas D Jefferya, Sina Safayia, Jodi D Smitha, Suzanne T Millmana, Rebecca L Parsonsa, Mark Buttb, Jonathan Cooperc,d, Igor Nestrasile, Heather Prillf, Xiao Liuf, Roger Lawrencef, Brett E Crawfordf, Anita Groverf, Andrew Meltonf, Anu Cherukurif, Jill C.M. Waitf, Jason Pinkstafff, aIowa State University, Ames, IA, United States, b Tox Path Specialists, LLC, Frederick, MD, United States, cKing College, London, United Kingdom, dLos Angeles Biomedical Research Institute, Torrance, CA, United States, eUniversity of Minnesota, Minneapolis, MN, United States, fBioMarin Pharmaceutical Inc., San Rafael, CA, United States Mucopolysaccharidosis type IIIB (MPS IIIB) is an untreatable fatal autosomal recessive pediatric disease caused by deficient activity of alpha-N-acetyl-D-glucosaminidase (NAGLU). NAGLU-deficient dogs are a relevant MPS IIIB model with pathologic heparan sulfate (HS) accumulation in tissue and clinical signs presenting at 18-24 months of age. Progressive neurological decline in dogs involves severe cerebellar atrophy, Purkinje cell loss, cytoplasmic vacuolization, and humane euthanasia at 3-5 years. BMN 250 is a recombinant fusion protein of human NAGLU and insulin-like growth factor 2 (IGF2) developed as an enzyme replacement therapy for MPS IIIB to be delivered to the CNS via intracerebroventricular (ICV) infusions. This canine model study evaluated safety, pharmacodynamics, and efficacy of BMN 250 in MPS IIIB (n = 12) and wild-type dogs (n = 12). Each group was subdivided

into 3 groups of 4 dogs treated with vehicle, 12 mg or 48 mg of BMN 250 administered every two weeks via ICV catheters. In-life studies are completed, and analyses continue. Safety evaluations (clinical pathology, ophthalmology, neurology, cardiology and histopathology) identified no safety concerns with BMN 250. Catheter complications in the dogs were distributed between vehicle and BMN 250 groups. Pharmacodynamics and efficacy endpoints indicate benefit of BMN 250 treatment. Total HS and disease specific HS non-reducing end assays showed a reduction to normal or near normal levels in all BMN 250 treated dogs. Signs of cerebellar dysfunction (positional nystagmus and ataxia) were observed only in affected, untreated dogs, and cognitive testing showed improvement in treated affected animals. These preliminary results demonstrate that ICV administration of BMN 250 appears safe, is able to reduce HS storage and improves clinical and functional signs of canine MPS IIIB.

doi:10.1016/j.ymgme.2016.11.089

81 Cardiovascular manifestations of feline Sandhoff disease after intravenous AAV gene therapy Lauren E Ellisa, Randolph Winterb, Heather L Gray-Edwardsa, Stacy Maitlandc,d, Ashley E Randlea, Robert Edwardse, Miguel Sena-Estevesc,d, Douglas R Martina, Raymond Y Wangf, aScott-Ritchey Research Center, College of Veterinary Medicine, Auburn University, Auburn, AL, United States, bDepartment of Clinical Sciences, College of Veterinary Medicine, Auburn University, Auburn, AL, United States, cGene Therapy Center, University of Massachusetts Medical School, Worcester, MA, United States, d Department of Neurology, University of Massachusetts Medical School, Worcester, MA, United States, eUniversity of California-Irvine School of Medicine, Department of Pathology, Orange, CA, United States, fCHOC Children's Hospital, Orange, CA, United States GM2 gangliosidosis is a fatal neurodegenerative disorder caused by a deficiency of lysosomal β-N-acetylhexosaminidase (Hex) and includes both Tay-Sachs and Sandhoff diseases. Feline models of Sandhoff disease recapitulate the human condition and are utilized to assess safety and efficacy of adeno-associated viral (AAV) gene therapy. A monocistronic AAVrh8 vector encoding the Hex β subunit (deficient in Sandhoff disease) was delivered intravenously at a dose of 5×1012 v.g./ kg body weight. Despite attenuation of neurologic disease, treated cats demonstrated valvular dysplasia, dilatation of the aorta and skeletal deformities. Cardiovascular manifestations in treated cats were further investigated. Myocardium, carotid artery, ascending/descending aorta, and mitral/aortic valves were obtained at necropsy from normal (n=2; 2.1 months), untreated GM2 (n=6; 1.4 months), and AAV-treated GM2 cats (GM2+AAV) (n=2; 4.8 months). Paraffin-embedded tissues were stained with hematoxylin & eosin or Verhoeff-Van Gieson (for elastin). Vascular intima-media thicknesses were measured using ImageJ. Data are reported as (mean±SD). Carotid artery thickness of GM2 (0.034± 0.0072 μm) and GM2+AAV (0.039±0.00044 μm) cats was increased compared to normal (0.023±0.00044 μm). Ascending aorta thickness of GM2 (0.12±0.020 μm) and GM2+AAV (0.092±0.022 μm) cats was decreased compared to normal (0.167±0.004 μm). Descending aorta measurements were lowest in GM2+AAV cats (0.075±0.014 μm), while untreated GM2 cats (0.13±0.023 μm) and normal cats (0.11± 0.028 μm) were comparable. Arterial media of GM2 cats contained ‘clear cells’ with prominent storage, causing widening of the spaces between elastin laminae. Focal areas of elastin fragmentation were noted in the untreated GM2 aortas. Abnormalities of the arterial tunica media, also reported in human mucopolysaccharidoses, may explain aortic dilatation in GM2+AAV cats. GM2 cats had increased carotid