Novel synthetic zinc finger proteins delivered to the brain through the use of viral vectors, efficiently and selectively repress the mutant huntingtin gene in a mouse model of Huntington’s disease long term after a single intervention, and successfully restore the motor coordination to levels comparable to those in healthy controls in an acute model of the disease.
The invention can be applicable to the treatment by gene therapy of Huntington’s disease and other, still incurable neurodegenerative disorders associated with expanded CAG repeats.
Huntington's disease (HD) is a dominantly inherited neurodegenerative disorder caused by expanded CAG (polyglutamine) repeats in the huntingtin (HTT) gene, which currently has no cure. Lowering mutant Htt reverses the disease phenotype in animals and several approaches are in development that target the RNA or the mutated huntingtin protein, but none has yet proved to be effective and selective enough. Researchers at CRG and Imperial College London have developed and validated in vitro and in vivo a new approach that induces selective repression of the mutant HTT gene using synthetic zinc fingers proteins (ZFP) delivered to the brain using adeno-associated viral vectors (AAV2). A first generation ZF construct mediates acute dose-dependent repression in vivo upon striatal injection in R6/2 mice, resulting in protein aggregate reduction and improvement of animal functional behavior (reduced decline in rotarod performance, and alleviation of clasping). A third generation ZF construct optimized for increased expression and persistence of the ZFP in the brain mediates long-term mutant HTT repression in vivo (up to 77% in whole brain, and still 25% after 6 months of single intraventricular injection in R6/1 mice!).
- Therapy based on proprietary ZFPs - the best established, and to date the only clinically validated class of engineered DNA-binding proteins
- Specific – the ZFPs bind specifically to CAG/CTG repeats
- Selective for mutant HTT gene with no signs of repression of wild type HTT and limited risk of toxicity. Leave the normal and other, unrelated genes unaffected
- Potentially more effective than other therapeutic approaches in development (e.g. antisense) – it tackles the problem of trinucleotide expansion at the source (i.e. the defect at the DNA level)
- Tested for gene therapy in mice using well-established and clinically validated adeno-associated viral (AAV2/1) vectors, although it can potentially be implemented in other vector systems
- Sustained repression of mutant HTT observed from a single dose, suggesting potential for long-term curative treatment
- Potentially applicable to other polyglutamine (polyQ) disorders
Garriga-Canut et al. (2012) Synthetic zinc finger repressors reduce mutant huntingtin expression in the brain of R6/2 mice. PNAS, 109(45):E3136-45.
Agustín-Pavón et al. (2016) Deimmunization for gene therapy: host matching of synthetic zinc finger constructs enables long-term mutant Huntingtin repression in mice. Mol Neurodegener. 11(1):64.