Novel recombinant human acid α-glucosidase with optimal glycosylation is significantly better than standard of care enzyme replacement for glycogen clearance in skeletal muscles of GAA knock-out mice

Abstract

Pompe disease is an inherited lysosomal disorder that results from a deficiency in acid α-glucosidase (GAA), and is characterized by progressive accumulation of lysosomal glycogen in cardiac and skeletal muscles. Enzyme replacement therapy (ERT) using recombinant human GAA (rhGAA) is the only approved treatment available for Pompe disease. This ERT requires the specialized carbohydrate mannose 6-phosphate (M6P) for cellular uptake and subsequent delivery to lysosomes via cell surface cation-independent M6P receptors (CI-MPRs). However, the current rhGAA ERT contains low amounts of M6P that limit drug targeting and efficacy in diseaserelevant tissues. We have developed a proprietary production cell line and manufacturing process that yield a novel rhGAA (designated as ATB200) with optimal glycosylation and higher M6P content, particularly the high-affinity bis-M6P N-glycan structure, for improved drug targeting. ATB200 binds the CI-MPR with high affinity (KD ~ 2–4 nM) and was efficiently internalized by Pompe fibroblasts and skeletal muscle myoblasts (Kuptake ~ 7–14 nM). ATB200 was evaluated in vivo and shown to be much more effective for clearing accumulated glycogen in skeletal muscles of Gaa KO mice than the current rhGAA ERT. Our results indicate that bi-weekly administrations of 5 mg/kg ATB200 were equivalent to 20 mg/kg rhGAA for reducing glycogen, while substantially greater glycogen clearance was observed with 20 mg/kg ATB200 compared to 20 mg/kg rhGAA in key skeletal muscles. These results were confirmed by histological examination. The addition of a pharmacological chaperone (PC) enhanced glycogen reduction by ATB200. Taken together, these data demonstrate that the higher M6P content of ATB200 results in better lysosomal targeting and substrate reduction, which can be further improved by combination with a PC, thus warranting further investigation of this next-generation treatment for Pompe disease.