Endocrine Abstracts

Objectives: Hypophosphatasia (HPP) is an inborn error of metabolism resulting from loss of function mutations in the tissue-nonspecific alkaline phosphatase (TNAP) gene. Asfotase alfa is an approved enzyme replacement therapy for HPP, while effective, it requires chronic multiple injections up to 6 times per week. We have developed a one-time gene therapy drug (ARU-2801: an adeno-associated viral vector expressing TNAP-D₁₀) for HPP and examined the safety and efficacy of ARU-2801 in Alpl^-/- HPP mice. To develop the ARU-2801 for clinical use, we evaluate the efficacy and safety of ARU-2801 in non-Human primates.

Methods: Juvenile WT macaques were injected intramuscularly with either saline or 5.0E12, 1.0E13, 2.0E13, and 4.0E13 vector genome/kg dose levels of ARU-2801. Blood samples were collected from anesthetized animals and assessed for plasma ALP enzymatic activity and clinical chemistry evaluation. Deeply anesthetized primates were sacrificed and tissues were collected for histopathology and examination of the biodistribution of ARU-2801. Toxicities of chronic exposure to TNAP-D₁₀ were evaluated using Von Kossa staining and CT scan.

Results: Following treatment with a single dose of ARU-2801, durable high plasma ALP levels (100-10,000 U/l) were achievable with normal physical activity and a healthy appearance. The clinical chemistry parameters of these animals did not show signs of liver toxicity, which is consistent with histopathology examination. ARU-2801 DNA was detected in only injected side muscle but not other organs by quantitative PCR analysis. Von Kossa staining and CT scan of the animal sacrificed at 9 months did not show any ectopic calcification.

Conclusion: Durable transgenic plasma ALP levels without any toxicities are achievable with ARU-2801 in NHPs, at levels that potentially could be efficacious in the clinic. ARU-2801, which can be administered as a single dose, has the potential to improve the quality of life for HPP patients by eliminating chronic administration.