G.P.11.05 The pharmacological chaperone AT2220 increases trafficking, processing, and cellular activity of acid α-glucosidase and is a potential new treatment for Pompe disease

Abstract

Pompe disease is an inherited disorder caused by a deficiency in acid alpha-glucosidase (GAA) activity, which reduces lysosomal glycogen turnover and results in progressive skeletal muscle weakness, reduced cardiac function, and respiratory insufficiency. As a potential treatment for Pompe disease, we are developing the pharmacological chaperone AT2220 (1-deoxynojirimycin-HCl), a molecule that directly binds to and stabilizes GAA. To determine the mechanism of action for AT2220, we examined its effect on mutant GAA trafficking, processing, and activity. GAA is synthesized as a precursor protein that trafficks from the endoplasmic reticulum (ER) to lysosomes. In lysosomes, GAA is proteolytically processed into mature forms that have higher affinity for the natural substrate, glycogen. Patient-derived GAA-P545L fibroblasts contain mainly the precursor form and have low levels of enzyme activity, indicative of reduced trafficking and processing of mutant GAA. Incubation of cells with AT2220 increases GAA-P545L trafficking out of the ER, as shown by pulse-chase, glycosidase sensitivity, and lectin affinity experiments. Moreover, AT2220 incubation increases GAA-P545L levels in lysosomes, as evidenced by increased amounts of mature protein, elevated enzyme activity in lysosomal fractions, and increased affinity for glycogen. These results indicate that AT2220 improves mutant GAA trafficking and processing that ultimately leads to increased lysosomal enzyme activity. AT2220 treatment of wild type rodents and monkeys increases mature GAA protein and enzyme activity levels in disease-relevant tissues, including gastrocnemius, heart, and diaphragm. The finding that wild type GAA levels can be increased suggests that AT2220 may increase GAA activity in patients with the common IVS1 (−13 t → g) splice variant that produces low levels of wild type enzyme. Collectively, these data indicate that AT2220 merits further evaluation as a treatment for Pompe disease.