Abstract
Clinical studies of enzyme replacement therapy for Pompe disease have indicated that relatively high doses of recombinant human acid alpha-glucosidase (rhGAA) may be required to reduce the abnormal glycogen storage in cardiac and skeletal muscles. This may be because of inefficient cation-independent mannose 6-phosphate receptor (CI-MPR)-mediated endocytosis of the enzyme by the affected target cells. To address this possibility, we examined whether the addition of a high affinity ligand to rhGAA would improve its delivery to these cells. Chemical conjugation of high mannose oligosaccharides harboring mono- and bisphosphorylated mannose 6-phosphates onto rhGAA (neo-rhGAA) significantly improved its uptake characteristics by muscle cells in vitro. Infusion of neo-rhGAA into Pompe mice also resulted in greater delivery of the enzyme to muscle tissues when compared with the unmodified enzyme. Importantly, this increase in enzyme levels was associated with significantly improved clearance of glycogen ( approximately 5-fold) from the affected tissues. These results suggest that CI-MPR-mediated endocytosis of rhGAA is an important pathway by which the enzyme is delivered to the affected lysosomes of Pompe muscle cells. Hence, the generation of rhGAA containing high affinity ligands for the CI-MPR represents a strategy by which the potency of rhGAA and therefore the clinical efficacy of enzyme replacement therapy for Pompe disease may be improved.
Highlights
Clinical studies of enzyme replacement therapy for Pompe disease have indicated that relatively high doses of recombinant human acid ␣-glucosidase may be required to reduce the abnormal glycogen storage in cardiac and skeletal muscles
mannose 6-phosphate (M6P)-containing oligosaccharides were derivatized to glycosylhydrazines and conjugated to Recombinant human GAA (rhGAA), the sialic acids of which had been oxidized with periodate to aldehydes
Using phosphopentamannose-hydrazine as a model ligand, we demonstrated that its conjugation onto rhGAA did not affect the hydrolytic activity of the enzyme
Summary
Vol 279, No 48, Issue of November 26, pp. 50336 –50341, 2004 Printed in U.S.A. Conjugation of Mannose 6-Phosphate-containing Oligosaccharides to Acid ␣-Glucosidase Improves the Clearance of Glycogen in Pompe Mice*. Clinical studies of enzyme replacement therapy for Pompe disease have indicated that relatively high doses of recombinant human acid ␣-glucosidase (rhGAA) may be required to reduce the abnormal glycogen storage in cardiac and skeletal muscles. This may be because of inefficient cation-independent mannose 6-phosphate receptor (CI-MPR)-mediated endocytosis of the enzyme by the affected target cells. We showed that the modified rhGAA (neo-rhGAA) containing a higher content of M6P residues displayed improved uptake characteristics into myoblasts in vitro and facilitated greater clearance of glycogen from the muscles of Pompe mice These observations are consistent with the importance of the CI-MPR in lysosomal enzyme trafficking and support the continued evaluation of similar approaches to improve the targeting of the enzyme to Pompe-affected tissues
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