Glycoengineered acid alpha-glucosidase with improved efficacy at correcting the metabolic aberrations and motor function deficits in a mouse model of Pompe disease

Abstract

Improving the delivery of therapeutics to disease-affected tissues can increase their efficacy and safety. Here, we show that chemical conjugation of a synthetic oligosaccharide harboring mannose 6-phosphate (M6P) residues onto recombinant human acid alpha-glucosidase (rhGAA) via oxime chemistry significantly improved its affinity for the cation-independent mannose 6-phosphate receptor (CI-MPR) and subsequent uptake by muscle cells. Administration of the carbohydrate-remodeled enzyme (oxime-neo-rhGAA) into Pompe mice resulted in an approximately fivefold higher clearance of lysosomal glycogen in muscles when compared to the unmodified counterpart. Importantly, treatment of immunotolerized Pompe mice with oxime-neo-rhGAA translated to greater improvements in muscle function and strength. Treating older, symptomatic Pompe mice also reduced tissue glycogen levels but provided only modest improvements in motor function. Examination of the muscle pathology suggested that the poor response in the older animals might have been due to a reduced regenerative capacity of the skeletal muscles. These findings lend support to early therapeutic intervention with a targeted enzyme as important considerations in the management of Pompe disease.

Figure 1

Structure of the synthetic oligosaccharide ligand and scheme for its conjugation to rhGAA. (a) Design of the synthetic oligosaccharide used in the conjugations studies. (b) Scheme used to conjugate the synthetic glycan to rhGAA. The sialic acids on the enzyme were oxidized with periodate before reacting with the reactive group (aminooxy) on the synthetic glycan to generate oxime-neo-rhGAA. Symbols in diagram: open circle, mannose; open square, N-acetylglucosamine; open diamond, galactose; open triangle, sialic acid. GAA, acid α-glucosidase; M6P, mannose 6-phosphate; rhGAA, recombinant human acid α-glucosidase.

Figure 2

Biochemical characteristics of the unmodified and glycoengineered enzymes. (a) Chromatography of oxime-neo-rhGAA (open circle) and rhGAA (closed circle) over a CI-MPR column. Approximately 5 µg of the different enzymes were loaded onto a 2 ml column. After washing the column with binding buffer, the bound material was eluted (starting at fraction 11) with binding buffer containing 5 mmol/l M6P. Fractions (2 ml) were collected and assayed for GAA activity. (b) Uptake of the enzymes by L6 myoblasts in culture. Increasing amounts of either oxime-neo-rhGAA (open circle) or rhGAA (closed circle) were added to L6 myoblasts and incubated at 37 °C for 18 hours. After washing, the cells were lysed and the enzyme activity in the lysates assayed using the fluorogenic substrate, 4-methylumbelliferyl-α-D-glucopyranoside. Enzyme activity was expressed in relative units (RU). (c) Stability of oxime-neo-rhGAA at 4 °C (open square) and 25 °C (closed triangle). The modified enzyme was incubated at the respective temperatures for the times indicated after which they were subjected to analysis to determine the level of M6P. CI-MPR, cation-independent mannose 6-phosphate receptor; GAA, acid α-glucosidase; M6P, mannose 6-phosphate; rhGAA, recombinant human acid α-glucosidase.

Figure 3

Relative abilities of unmodified and modified rhGAA to reduce tissue glycogen levels in young Pompe mice. (a) Cohorts of 5-month-old Pompe mice were administered increasing amounts of either rhGAA or oxime-neo-rhGAA. The mice (8 animals/group) were treated with four weekly doses of enzyme and killed 2 weeks after the last treatment. Tissues were collected and assayed for glycogen levels using the Amplex Red glucose assay. Data are expressed as means ± SD. (b) Sections of the heart and quadriceps were stained with PAS and then analyzed by high resolution light microscopy. Representative sections from the heart of Pompe mice treated with vehicle (i), 20 mg/kg rhGAA (iii) and 20 mg/kg oxime-neo-rhGAA (v) are shown, as are quadriceps of animals treated with vehicle (ii), 20 mg/kg rhGAA (iv) and 20 mg/kg oxime-neo-rhGAA (vi). Glycogen is visualized as purple-beaded structures within the myocytes. PAS, periodic acid-Schiff; rhGAA, recombinant human acid α-glucosidase.

Figure 4

Assessment of motor coordination and muscle strength after enzyme therapy of young Pompe mice. Pompe mice (4.5 months old) were first administered 5E11 drp of AAV8/DC190-GAA_D404N to induce immunotolerance to human GAA. One month after dosing with the viral vector, the mice were treated biweekly with injections of different doses of rhGAA or oxime-neo-rhGAA for 8 months. (a) At the end of the study, the mice were killed and their tissues analyzed for glycogen levels. Data are expressed as means ± SD (n = 10 animals per group). Throughout the study, the animals (both wild type and Pompe mice) were subjected to (b) rocking rotarod and (c) wire-hang tests. Age-matched wild type mice (closed square) and Pompe mice treated with vehicle (closed circle), 20 mg/kg rhGAA (closed triangle), 100 mg/kg rhGAA (closed diamond), and 20 mg/kg oxime-neo-rhGAA (open circle) were tested monthly. Statistical analyses were performed between vehicle and enzyme-treated groups (vehicle versus 20 mg/kg oxime-neo-rhGAA, *P < 0.05, **P < 0.01, and ***P < 0.001; vehicle versus 100 mg/kg rhGAA, ⁺P < 0.05, ⁺⁺P < 0.01, ⁺⁺⁺P < 0.001), as well as between oxime-neo-rhGAA- and rhGAA-treated groups (^‡P < 0.01)) for each time point. Data are presented as means ± SEM. drp, DNase resistant particle; rhGAA, recombinant human acid α-glucosidase.

Figure 5

Assessment of motor coordination and muscle strength after enzyme therapy of older, symptomatic Pompe mice. Pompe mice (10 months old) were first immunotolerized to human GAA by administering 7E11 drp AAV8/DC190-GAA_D404N and after 1 month they were subjected to weekly injections with varying doses of either rhGAA or oxime-neo-rhGAA for 5 months. (a) At the end of the study, the mice were killed and their tissues analyzed for glycogen levels. Data are expressed as means ± SD (n = 10 animals per group). Throughout the study, the animals were subjected to (b) rocking rotarod and (c) wire-hang tests. Pompe mice treated with vehicle (closed circle), 40 mg/kg rhGAA (closed triangle), 100 mg/kg rhGAA (closed diamond), and 40 mg/kg oxime-neo-rhGAA (open circle) were tested monthly. drp, DNase resistant particle; GAA, acid α-glucosidase; rhGAA, recombinant human acid α-glucosidase.

Figure 6

Histopathological analysis of skeletal muscles of Pompe mice. Representative sections of quadriceps from Pompe mice of different ages and after enzyme therapy were fixed in 10% neutral buffer formalin and stained with hematoxylin and eosin. The extent of glycogen accumulation (visualized as white deposits) and centronucleation was noted in tissues obtained from representative tissues (×20 magnification) of (a) 3-month-old wild type mouse, (b) 3-month-old Pompe mouse, (c) 5-month-old Pompe mouse and (d) 10-month-old Pompe mouse. Panel (e) was sectioned from a 13.5-month-old Pompe mouse treated with vehicle for 8 months; (f) was from a 13.5-month-old Pompe mouse that received 20 mg/kg rhGAA beginning at 5.5 months of age for a total of 8 months; panel (g) was obtained from a Pompe mouse that received 100 mg/kg rhGAA for 8 months and panel (h) from one that received 20 mg/kg oxime-neo-rhGAA for 8 months. Arrows denote the location of myofibers with centronucleation. rhGAA, recombinant human acid α-glucosidase.

Figure 7

Extent of degeneration and regeneration in Pompe mouse muscles treated at different ages. Hematoxylin and eosin stained sections from three animals of each treatment group (at each time point) was scored for the number of myofibers harboring a centralized nuclei. For each animal, 1,000–3,500 muscle fibers from different fields were examined. The results illustrated in a were from Pompe mice that were treated with biweekly infusions of enzyme starting at 5.5 months of age, and those in (b) were from Pompe mice treated weekly with enzyme infusions starting when they were 11 months old. Data are presented as means ± SD. Dashed lines represent the time periods the animals were treated.