Barry J. Byrne ^1* Giancarlo Parenti ^2,3 Benedikt Schoser ⁴ Ans T. van der Ploeg ⁵ Hung Do ⁶ Brian Fox ⁷ Mitchell Goldman ⁷ Franklin K. Johnson ⁷ Jia Kang ⁸ Nickita Mehta ⁷ John Mondick ⁹ M. O. Sheikh ⁷ Sheela Sitaraman Das ⁷ Steve Tuske ⁷ Jon Brudvig ⁷ Jill M. Weimer ⁷ Tahseen Mozaffar ¹⁰

• ¹ University of Florida, Gainesville, FL, United States
• ² Metabolic Unit, Department of Translational Medical Sciences, University of Naples Federico II, Naples, Italy
• ³ Telethon Institute of Genetics and Medicine, Pozzuoli, Italy
• ⁴ Friedrich-Baur-Institute, Department of Neurology, LMU University Clinic, LMU Munich, Munich, Germany
• ⁵ Erasmus MC University Medical Center, Rotterdam, Netherlands
• ⁶ Independent researcher, St Louis, MO, United States
• ⁷ Amicus Therapeutics, Inc., Princeton, United States
• ⁸ Metrum Research Group, Tariffville, CT, United States
• ⁹ Independent researcher, Ann Arbor, MI, United States
• ¹⁰ Department of Neurology, University of California, Irvine, CA, United States

Enzyme replacement therapy (ERT) is the only approved disease-modifying treatment modality for Pompe disease, a rare, inherited metabolic disorder caused by a deficiency in the acid α-glucosidase (GAA) enzyme that catabolizes lysosomal glycogen. First-generation recombinant human GAA (rhGAA) ERT (alglucosidase alfa) can slow the progressive muscle degeneration characteristic of the disease. Still, most patients experience diminished efficacy over time, possibly because of poor uptake into target tissues. Next-generation ERTs aim to address this problem by increasing bisphosphorylated high mannose (bis-M6P) N-glycans on rhGAA as these moieties have sufficiently high receptor binding affinity at the resultant low interstitial enzyme concentrations after dosing to drive uptake by the cation-independent mannose 6-phosphate receptor on target cells. However, some approaches introduce bis-M6P onto rhGAA via non-natural linkages that cannot be hydrolyzed by natural human enzymes and thus inhibit the endolysosomal glycan trimming necessary for complete enzyme activation after cell uptake. Furthermore, all rhGAA ERTs face potential inactivation during intravenous delivery (and subsequent non-productive clearance) as GAA is an acid hydrolase that is rapidly denatured in the near-neutral pH of the blood. One new therapy, cipaglucosidase alfa plus miglustat, is hypothesized to address these challenges by combining an enzyme enriched with naturally occurring bis-M6P N-glycans with a small-molecule stabilizer. Here, we investigate this hypothesis by analyzing published and new data related to the mechanism of action of the enzyme and stabilizer molecule. Based on an extensive collection of in vitro, preclinical, and clinical data, we conclude that cipaglucosidase alfa plus miglustat successfully addresses each of these challenges to offer meaningful advantages in terms of pharmacokinetic exposure, target-cell uptake, endolysosomal processing, and clinical benefit.