An Open Label Phase 2 Study of ManNAc in Subjects With GNE Myopathy

GNE myopathy is a rare genetic (autosomal recessive) disorder that causes progressive skeletal muscle atrophy and weakness. The disease presents in young adults typically between the ages of 20 and 40 years, and includes foot drop and difficulty walking. The disease progresses to involve all skeletal muscles, eventually leading to the use of a wheelchair and, in some cases, dependence on a caregiver. The causative gene, GNE, encodes the rate-limiting enzyme in the biosynthesis of CMP-sialic acid. While the exact pathophysiology of GNE myopathy remains unknown, decreased sialic acid production and subsequent hyposialylation of muscle glycoproteins are thought to be key factors leading to muscle deterioration in GNE myopathy. This hypothesis is supported by prevention of disease after administration of oral N-acetyl-D-mannosamine (ManNAc) in mouse models of GNE myopathy. A first-in-human, Phase 1 single ascending dose study evaluated the safety, pharmacokinetics, and pharmacodynamics of a single dose of 3, 6, or 10 g of oral ManNAc in subjects with GNE myopathy (ClinicalTrials.gov NCT01634750; IND No.78,091). ManNAc was safe and well-tolerated in all subjects who participated in this study. In this Phase 2, open-label, single-center study ManNAc will be administered orally to 12 subjects. The objectives of the study are to assess the long-term safety, tolerability, pharmacokinetics, and biochemical efficacy of oral ManNAc in GNE myopathy subjects. In the first phase of pharmacokinetic assessment, two cohorts of 6 subjects will receive ManNAc at doses of 3 g twice a day (6 g per day) or 6 g twice a day (12 g per day) for 7 days to assess safety and PK. In the second phase of the study, all subjects will receive treatment with ManNAc at a dose of 6 g twice daily (12 g per day) for the remainder of the study. The study was extended to include follow-up evaluations at 6, 12, 18, 24 and 30 months. During the 30 month visit, PK of 4 g three times daily was assessed. Biochemical efficacy was assessed by change in the sialylation of proteins at 3 months compared to baseline. To evaluate the effect of ManNAc on clinical measures of GNE myopathy, a battery of clinical assessments was performed at every visit to identify clinical endpoints suitable for subsequent clinical trials.