Adjunctive β ₂ ‐agonist treatment reduces glycogen independently of receptor‐mediated acid α‐glucosidase uptake in the limb muscles of mice with Pompe disease

Abstract

Enzyme or gene replacement therapy with acid α-glucosidase (GAA) has achieved only partial efficacy in Pompe disease. We evaluated the effect of adjunctive clenbuterol treatment on cation-independent mannose-6-phosphate receptor (CI-MPR)-mediated uptake and intracellular trafficking of GAA during muscle-specific GAA expression with an adeno-associated virus (AAV) vector in GAA-knockout (KO) mice. Clenbuterol, which increases expression of CI-MPR in muscle, was administered with the AAV vector. This combination therapy increased latency during rotarod and wirehang testing at 12 wk, in comparison with vector alone. The mean urinary glucose tetrasaccharide (Glc4), a urinary biomarker, was lower in GAA-KO mice following combination therapy, compared with vector alone. Similarly, glycogen content was lower in cardiac and skeletal muscle following 12 wk of combination therapy in heart, quadriceps, diaphragm, and soleus, compared with vector alone. These data suggested that clenbuterol treatment enhanced trafficking of GAA to lysosomes, given that GAA was expressed within myofibers. The integral role of CI-MPR was demonstrated by the lack of effectiveness from clenbuterol in GAA-KO mice that lacked CI-MPR in muscle, where it failed to reverse the high glycogen content of the heart and diaphragm or impaired wirehang performance. However, the glycogen content of skeletal muscle was reduced by the addition of clenbuterol in the absence of CI-MPR, as was lysosomal vacuolation, which correlated with increased AKT signaling. In summary, β2-agonist treatment enhanced CI-MPR-mediated uptake and trafficking of GAA in mice with Pompe disease, and a similarly enhanced benefit might be expected in other lysosomal storage disorders.

Synergistic Efficacy from Gene Therapy with Coreceptor Blockade and a β2-Agonist in Murine Pompe Disease

“…15 We observed the same phenomenon in the current study; however, the greatest clearance of the accumulated glycogen in heart was observed by adding anti-CD4 mAb treatment to suppress anti-GAA formation. A synergistic effect on glycogen clearance was demonstrated after triple therapy in the heart, diaphragm, and quadriceps, which reduced glycogen content to the lowest concentration observed in each of these muscles (Fig.…”

“…11 However, a muscle-specific GAA expression vector, AAV2/8-MHCK7hGAApA, did not clear accumulated glycogen from the heart and skeletal muscles despite a large increase in the observed GAA activity. 15 We observed this phenomenon again in the current study (Fig. 1).…”

“…As previously demonstrated, clenbuterol alone reduced glycogen content in skeletal muscle in the absence of GAA replacement by AAV vector administration in GAA-KO mice. 15 Treatment with a b 2 -agonist was well tolerated and efficacious in an open label clinical trial in combination with ERT, 27 and this adjunctive therapy would be feasible in the context of gene therapy. Furthermore, the reduction of glycogen in cardiac muscle was dependent on immune tolerance induction with anti-CD4 mAb.…”

“…13 The AAV vector containing a muscle-specific promoter, AAV2/8-MHCK7hGAApA, expressed GAA in both cardiac and skeletal muscle. 15 Combined anti-CD4 mAb and clenbuterol with AAV2/8-MHCK7hGAApA, termed triple therapy, revealed a synergistic therapeutic effect on biochemical correction in cardiac and skeletal muscle, as well as improved muscle strength, after AAV vector administration in GAA-KO mice.…”

Profile of alglucosidase alfa in the treatment of Pompe disease: safety, efficacy, and patient acceptability

“…69 Notably, Albuterol-reduced muscular glycogen even independently from receptor-mediated GAA uptake in the murine model. 70 Another strategy is the use of small molecules known as pharmacological chaperones, which bind to the mutant enzyme and recover its lysosomal activity by correcting the protein folding. 71,72 However, the presence of a misfolded enzyme with recoverable function is essential for an effect of this class of drug.…”