Community Research and Development Information Service - CORDIS


GLYCODIS3 Report Summary

Project ID: 658712
Funded under: H2020-EU.1.3.2.

Periodic Reporting for period 1 - GLYCODIS3 (Genetic correction of glycogen debranching enzyme deficiency in Glycogen Storage disease III: a proof of concept study)

Reporting period: 2016-01-01 to 2017-12-31

Summary of the context and overall objectives of the project

Glycogen storage disease III (GSDIII) is a rare (1:100,000) autosomal recessive disorder resulting from the deficiency of glycogen debranching enzyme (GDE) the enzyme that hydrolyzes glycogen branches in the cytosol. The disease manifestation occurs in two phases. Early symptoms of the disease includes hepatomegaly, hypoglycemia, failure to thrive and recurrent illness. After adolescence, the metabolic impairment becomes less evident and a generalized muscle weakness appears. A dietary treatment with frequent meals high in carbohydrates, slows the progression of the pathology that is however inevitable and severely affecting the quality of life of affected individuals.
At present, no cure is available for GSDIII and the disease represents an unmet medical need.
GLYCODIS3 had the overall aim to obtain a proof-of-concept of an adeno-associated virus (AAV) vector-mediated gene therapy for the treatment of GSDIII. AAV gene therapy has been successfully used for the correction of several genetic diseases in animal models and humans. GLYCODIS3 had also, as an accessory aim, the development of human induced pluripotent stem cells (iPSc) derived from GSDIII patients.
AAV are the vectors of choice for in vivo genetic correction of monogenic disorders. Human trials of liver gene transfer for hemophilia A and B and eye gene transfer for congenital blindness have unveiled the therapeutic potential of this viral vector platform. Follow-up data of subjects treated with AAV vectors is showing sustained correction of the disease phenotype for several years after gene transfer, and recent data confirmed that AAV vectors can drive expression of a transgene in humans for >10 years. Despite these advantages, one limitation of AAV vectors is that they cannot package vector genomes significantly larger than 5kb inside their capsid. Due to the length of the sequence of the GDE enzyme (4.6 Kb), a transgene expression cassette for the efficient expression of GDE in both muscle and liver, hardly fit in a single AAV vector. To overcome this limitation, we engineered a dual-vector system with a recombinogenic bridging DNA sequence to drive reconstitution of the full-length GDE sequence within a cell. GDE-knockout mice treated with dual vectors showed an efficient expression of the protein in both muscle and liver and the rescue of the muscle weakness and the metabolic impairment associated with the disease.
In conclusion, data obtained in the frame of the GLYCODIS3 project, constitute a fundamental step in the translation of this approach to patients and represent an important advance over the state of the art as:
1) No gene therapy approach has been tested in vivo in models of GSDIII, so far only symptomatic treatments were attempted based on diet or conventional drugs administration. The paper showed that gene therapy can be used to express GDE and correct the actual disease.
2) Low levels of GDE expression are needed to revert the disease. This is a very important point when devising strategies based on gene therapy to treat the disease.
3) Concomitant correction of both liver and muscle phenotype has been achieved with gene transfer for GDE
4) Previous reports showed that recombinant GAA, a lysosomal enzyme, has the potential to reduce glycogen accumulation in human myoblasts from GSDIII patients. This approach has been proposed to treat patients. Here, we tested the approach in vivo and we demonstrated that the approach is efficient in clearing glycogen from liver (thus confirming that a lysosomal enzyme can clear cytosolic glycogen). However, no long-lasting effect is seen in muscle.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The main objective of the GLYOCODIS3 proposal was to develop a therapeutic strategy for GSDIII. During the two years of the grant, Dr. Ronzitti characterized a mouse model of GSDIII that was then used for the development of an AAV-based gene therapy for GSDIII. The challenges of this project were related to the expression of a transgene larger than the AAV encapsidation limit and the fact that the disease involves two different organs, liver and muscle. Dr. Ronzitti demonstrated that de-novo AAV-mediated expression of GDE was able to clear glycogen from muscle, rescue the muscle weakness associated and partially restore glycemia. The biggest limitation of the approach was that a high dose of the vector was needed to rescue the phenotype. The translation of this proof of concept to the clinic will therefore require an optimization of the approach aimed at the reduction of the therapeutic dose and the simultaneous targeting of the two tissues involved. These two aspects constitute the core of the experimental activity of Dr. Ronzitti for the next years. Importantly, the improvement of the gene transfer efficacy and the targeting of multiple tissues are primary goals in the AAV gene therapy field. More in general, innovations derived from the project of Dr. Ronzitti will contribute to the advancement of the AAV gene therapy for neuromuscular diseases involving large proteins.
Exploitation and dissemination:
Dr. Ronzitti participated in the preparation of 9 scientific publication, 1 review and 1 commentary on the development of AAV-mediated gene therapy. Of note, three publications focused on GSDs and in two of them, Dr. Ronzitti was co-corresponding author. Three oral presentations and 2 posters about GSDs were presented at international meetings. In addition to that, Dr. Ronzitti is member of the trainee committee of the American Society for Gene and Cell Therapy created to increase the visibility of the trainee and to inform the community on the scientific activity of the society.
Dr. Ronzitti authored 5 patents about GSDs, two of them on the development of AAV gene therapy for GSDIII (one in preparation). Finally last year Dr. Ronzitti has been invited as speaker at ‘’Family days’’ of the French, Spanish and English Glycogenosis associations to present his results on GSDs.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The main impact of GLYCODIS3 was the development of a proof-of concept of AAV gene therapy approach for GSDIII. More in general, the research activities performed in the frame of this project will be instrumental not only for GSDIII but also for the development of gene therapy for other neuromuscular diseases that require the expression of proteins larger than the AAV size limit. In addition to that, data generated during GLYCODIS3 were used to obtain grants from ANR (Agence Nationale de Recherche) and AFG (Association Francophone contre le Glycogenoses) to continue the development of the AAV gene therapy approach for GSDIII toward the clinic. This clearly demonstrates the commitment of Dr. Ronzitti, in pursuing the development of a therapeutic approach for GSDIII, at present a neglected disease.

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