Salmeterol enhances the cardiac response to gene therapy in Pompe disease

Abstract

Enzyme replacement therapy (ERT) with recombinant human (rh) acid α-glucosidase (GAA) has prolonged the survival of patients. However, the paucity of cation-independent mannose-6-phosphate receptor (CI-MPR) in skeletal muscle, where it is needed to take up rhGAA, correlated with a poor response to ERT by muscle in Pompe disease. Clenbuterol, a selective β2 receptor agonist, enhanced the CI-MPR expression in striated muscle through Igf-1 mediated muscle hypertrophy, which correlated with increased CI-MPR (also the Igf-2 receptor) expression. In this study we have evaluated 4 new drugs in GAA knockout (KO) mice in combination with an adeno-associated virus (AAV) vector encoding human GAA, 3 alternative β2 agonists and dehydroepiandrosterone (DHEA). Mice were injected with AAV2/9-CBhGAA (1E+11 vector particles) at a dose previously found to be partially effective at clearing glycogen storage from the heart. Heart GAA activity was significantly increased by either salmeterol (p<0.01) or DHEA (p<0.05), in comparison with untreated mice. Furthermore, glycogen content was reduced in the heart by treatment with DHEA (p<0.001), salmeterol (p<0.05), formoterol (p<0.01), or clenbuterol (p<0.01) in combination with the AAV vector, in comparison with untreated GAA-KO mice. Wirehang testing revealed that salmeterol and the AAV vector significantly increased performance in comparison with the AAV vector alone (p<0.001). Similarly, salmeterol with the vector increased performance significantly more than any of the other drugs. The most effective individual drugs had no significant effect in absence of vector, in comparison with untreated mice. Thus, salmeterol should be further developed as adjunctive therapy in combination with either ERT or gene therapy for Pompe disease.

Salmeterol with Liver Depot Gene Therapy Enhances the Skeletal Muscle Response in Murine Pompe Disease

“…This observation was consistent with previous studies showing that AAV vector-mediated expression of GAA increased CI-MPR expression in skeletal muscle without concurrent b2 agonist administration. 12,14 We further analyzed a marker for autophagosome clearance p62, which is increased in the muscle of Pompe patients and normalized by treatment with ERT. 30 Salmeterol treatment significantly decreased p62 in the quadriceps, either alone or in combination with AAV vector administration (Fig.…”

“…[8][9][10]33,35 Previously, salmeterol was evaluated with an AAV vector that expressed GAA ubiquitously with a chicken b-actin promoter and cytomegalovirus enhancer, and only the cardiac response was improved by salmeterol administration. 12 That earlier study failed to demonstrate biochemical correction of skeletal muscle. The correction of skeletal muscle was currently achieved by combining salmeterol and liver depot gene therapy with an AAV vector that induced immune tolerance and continuously secreted GAA into the circulating blood, thereby achieving partial biochemical correction of skeletal muscle.…”

“…The AAV vector was prepared as described and administered intravenously to 4 month-old GAA-KO mice with a C57BL/6 background. 12,21 The liver-specific regulatory cassette in the vector contains a thyroid hormone-binding globulin promoter sequence downstream from 2 copies of a a1-microglobulin/bikunin enhancer sequence. 16 Rotarod testing was performed as described.…”

“…11 Another b2 agonist, salmeterol, increased the efficacy of an adeno-associated virus (AAV) vector expressing GAA from a ubiquitous promoter by increasing muscle strength of GAA-KO mice, although it only improved biochemical correction in the heart. 12 Previous studies revealed the importance of immune tolerance induction during gene therapy in mice with Pompe disease, [13][14][15] which has been achieved by liver-specific expression of GAA with an AAV vector as described. [16][17][18] In contrast, constitutive expression with a ubiquitous promoter provoked immune responses in GAA-KO mice 16 that might complicate gene therapy in crossreactive immune material-negative patients with Pompe disease, who do not express any residual GAA protein.…”

Advancements in AAV-mediated Gene Therapy for Pompe Disease

“…This strategy increased CI-MPR expression in skeletal tissue, enhanced the uptake and trafficking of GAA to the lysosomes, and improved the efficacy of ERT. In the second approach, salmeterol, a selective ␤ 2 agonist, was used to increase the efficacy of AAV mediated therapies when administered alongside AAV2/9-CBhGAApA [121]. Both strategies showed promise in enhancing GAA activity and glycogen clearance in skeletal muscle.…”