Engineering of a lysosomal-targeted GAA enzyme.

Pompe disease is a tissue glycogen disorder caused by genetic insufficiency of the GAA enzyme. GAA enzyme replacement therapies for Pompe disease have been limited by poor lysosomal trafficking of the recombinant GAA molecule through the native mannose-6-phosphate-mediated pathway. Here, we describe the successful rational engineering of a chimeric GAA enzyme that utilizes the binding affinity of a modified IGF-II moiety to its native receptor to bypass the mannose-6-phosphate-mediated lysosomal trafficking pathway, conferring a significant increase in cellular uptake of the GAA enzyme. We also demonstrate the ablation of binding between our modified IGF-II tag and two off-target receptors: IGF-I receptor and insulin receptor, as well as preserved enzymatic activity of the chimeric GAA molecule.