Chances and shortcomings of adenovirus-mediated ATP7B gene transfer in Wilson disease: Proof of principle demonstrated in a pilot study with LEC rats

Background & Aims: Wilson disease (WD) is an autosomal recessively inherited copper storage disease due to mutations in the ATP7B gene. It results in impaired biliary copper excretion followed by liver injury leading to cirrhosis. In parallel, copper accumulates in other tissues e. g. basal ganglia of the brain inducing motoric disorders. Phenotypical cure of Wilson disease by liver transplantation raised the question whether gene therapy may represent a successful alternative treatment procedure. To examine the principle feasibility of this approach we investigated the effects of gene transfer using an adenoviral vector construct expressing the human ATP7B cDNA in an established rodent model for WD, the Long-Evans Cinnemon rat (LEC). Methods: Transduction efficiency was assessed by RT-PCR, Western blot and immunofluorescence analysis. The therapeutic effect was estimated by analyzing holoceruloplasmin and its ferroxidase activity in serum, and the copper content of excrements. Changes in copper homeostasis were determined by positron emission tomography (PET). Results: Successful, but temporary gene transfer was clearly detectable on RNA and protein levels. In parallel the temporary therapeutic effect was documented by restoration of serum holoceruloplasmin and of its ferroxidase activity. Additionally the Ad-ATP7B treated LEC rat revealed a higher Cu-64 content in stool. PET was able to visualize differences in Cu-64 distribution between wild type and LEC rats, indicating its principle usefulness as analytical tool. Conclusion: The data demonstrate proof of principle of successful gene therapy in an experimental model of WD. As a consequence of successful but only transient therapeutic effect of adenoviral gene transfer we can now focus more efficient and permanent gene transfer strategies.