Pharmacological Enhancement of alpha-Glucosidase by the Allosteric Chaperone N-acetylcysteine

Pompe disease (PD) is a metabolic myopathy due to the deficiency of the
lysosomal enzyme alpha-glucosidase (GAA). The only approved treatment
for this disorder, enzyme replacement with recombinant human GAA
(rhGAA), has shown limited therapeutic efficacy in some PD patients.
Pharmacological chaperone therapy (PCT), either alone or in combination
with enzyme replacement, has been proposed as an alternative therapeutic
strategy. However, the chaperones identified so far also are active
site-directed molecules and potential inhibitors of target enzymes. We
demonstrated that N-acetylcysteine (NAC) is a novel allosteric chaperone
for GAA. NAC improved the stability of rhGAA as a function of pH and
temperature without disrupting its catalytic activity. A computational
analysis of NAC-GAA interactions confirmed that NAC does not interact
with GAA catalytic domain. NAC enhanced the residual activity of mutated
GAA in cultured PD fibroblasts and in COS7 cells overexpressing mutated
GAA. NAC also enhanced rhGAA efficacy in PD fibroblasts. In cells
incubated with NAC and rhGAA, GAA activities were 3.7-8.7-fold higher
than those obtained in cells treated with rhGAA alone. In a PD mouse
model the combination of NAC and rhGAA resulted in better correction of
enzyme activity in liver, heart, diaphragm and gastrocnemia, compared to
rhGAA alone. Received 12 May 2012; accepted 3 July 2012; advance online
publication 18 September 2012. doi:10.1038/mt.2012.152