Further improvements in efficacy were achieved by using

a scAAV8 vector expressing human G6Pase-α from a minimal human G6Pase promoter. A complete normalization of biochemical parameters for up to 1 year postvector administration was achieved in G6pc−/− mice, despite the use of a 600-fold lower dose than in previous studies.12 Prolonged survival for up to 1 year and sustained correction of hypoglycemia subsequent to AAV8 gene transfer was also demonstrated in GSD-Ia dogs.12 Further comparison with AAV7 and AAV9 vectors in G6pc−/− mice showed that AAV9 is more efficient in transducing Rapamycin in vivo kidney because of its broad tropism, and partial correction of renal failure was achieved.13 The use of human G6Pase promoter regions regulates G6Pases-α expression in response to glucose, dexamethasone, and insulin levels, therefore preventing potential overexpression of the enzyme as observed in animals treated with high vector doses.12, 14 They also

bypass the limitations of liver-specific promoters, which have limited or no expression in kidney, or the problems of ubiquitous promoters, which are associated with cytotoxic T-cell response and rapid clearance of vector in the liver of young GSD-Ia mice.14 G6pc−/− mice treated with an AAV8 vector expressing the human G6Pase-α driven by the human G6PC promoter/enhancer (GPE) showed MAPK Inhibitor Library cost improved G6Pase-α expression and complete normalization of G6Pase-α deficiency in the liver for 24 weeks.14 Another challenge faced by gene therapy for GSD-Ia and for many other metabolic diseases that manifest soon after birth is the loss of efficacy and persistence after neonatal gene transfer resulting from the loss of episomal vector genomes caused by hepatocyte proliferation and liver growth. In addition, ongoing liver damage related to glycogen storage and hypoglycemia might accelerate the loss of vector

genomes in liver. Two strategies were attempted to overcome this problem. selleck In G6pc−/− mice, delaying the injection age from 2 days to 2 weeks significantly improved long-term efficacy.14 In GSD-Ia dogs, readministration with vector of a different serotype after the initial neonatal vector treatment restored long-term efficacy (prevention of hypoglycemia and marked reduction of glycogen storage in liver) and prolonged survival for up to 5 years.15 The advances made through these preclinical studies significantly prolonged the life of GSD-Ia animals, therefore allowing one to address the long-term efficacy of gene therapy. In GSD-Ia patients, one of the most significant chronic risks is hepatocellular adenoma (HCA), which develops in 70%-80% of GSD-I patients over 25 years of age.16, 17 In 10% of GSD-Ia patients, HCAs undergo malignant transformation to HCC. It is hard to assess HCA in the existing GSD-Ia dogs and G6pc−/− mice because of their short lifespan.