β2 Agonists enhance the efficacy of simultaneous enzyme replacement therapy in murine Pompe disease

Abstract

Enzyme replacement therapy (ERT) with recombinant human acid α-glucosidase (rhGAA) has improved clinical outcomes in patients with Pompe disease; however, the response of skeletal muscle and the central nervous system to ERT has been attenuated. The poor response of skeletal muscle to ERT has been attributed to the low abundance of the cation-independent mannose-6-phosphate receptor (CI-MPR), which mediates receptor-mediated uptake of rhGAA. Hence the ability of adjunctive therapy with β2-agonists to increase CI-MPR expression in skeletal muscle was evaluated during ERT in murine Pompe disease with regard to reversal of neuromuscular involvement. Mice with Pompe disease were treated with weekly rhGAA injections (20 mg/kg) and a selective β2-agonist, either albuterol (30 mg/l in drinking water) or low-dose clenbuterol (6 mg/l in drinking water). Biochemical correction was enhanced by β2-agonist treatment in both muscle and the cerebellum, indicating that adjunctive therapy could enhance efficacy from ERT in Pompe disease with regard to neuromuscular involvement. Intriguingly, clenbuterol slightly reduced muscle glycogen content independent of CI-MPR expression, as demonstrated in CI-MPR knockout/GAA knockout mice that were otherwise resistant to ERT. Thus, adjunctive therapy with β2 agonists might improve the efficacy of ERT in Pompe disease and possibly other lysosomal storage disorders through enhancing receptor-mediated uptake of recombinant lysosomal enzymes.

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

“…11,13 In this study, clenbuterol significantly increased the expression of CI-MPR in skeletal muscle (Fig. 3), including the quadriceps ( p < 0.01) and gastrocnemius ( p < 0.05).…”

“…We previously found that receptor-mediated uptake of GAA could be enhanced via increased CI-MPR expression, using b 2 -agonists including clenbuterol and albuterol. 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.…”

“…[11][12][13] The underlying mechanism of the therapeutic action of clenbuterol might be related to insulin-like growth factor (IGF)-1-mediated muscle hypertrophy, which has been correlated with increased CI-MPR (also known as IGF-2 receptor) expression. 14 In the present study, we evaluated a combination of anti-CD4 mAb and clenbuterol to induce immune tolerance and to increase CI-MPR-mediated uptake and trafficking of GAA, respectively.…”

Pharmacologic manipulation of lysosomal enzyme transport across the blood–brain barrier

“…We showed the successful re-induction of CI-M6P receptor-mediated transport for [ 131 I]P-GUS in the brain and heart in 2-and 8-week-old mice. In related experiments, Koeberl et al 9 recently showed enhanced uptake of activity of acid alphaglucosidase by chronic treatment with adrenergic agents in the brain and muscle, and also found that the effect of b 2 -adrenergics in enhancing the efficacy of the ERT in Pompe disease model mice was, at least in part, mediated through adrenergic-induced, increased expression of CI-M6P receptors in the brain. There was about a 1.4-fold increase in the CI-M6P receptor level by clenbuterol in the cerebellum.…”

“…Further studies confirming the effectiveness of these pharmacological manipulations in higher vertebrates are needed. Also, chronic multiple dosing studies such as those of Koeberl et al 9 are necessary to determine which of these pharmacological manipulations might potentially have clinical application to enhancing enzyme delivery to brain.…”