Exosome-based Gene Therapy for Huntington's Disease

Huntington's disease (HD) is a devastating neurodegenerative disease that is comparatively rare (compared with Parkinson's and Alzheimer's diseases) but which nevertheless affects 1 in 10,000 people in the UK. HD is a chronic, slowly progressive inherited disorder caused by mutations in a single gene (the huntingtin gene) that leave patients demented and bedridden typically 20 years after the onset of symptoms. This disease represents an immense burden on patients and their families. Currently there is no cure for HD available due largely in part to the inability of therapeutic compounds to cross the blood brain barrier and enter affected parts of the brain at sufficient levels for clinical benefit. Symptoms and signs are managed relatively well by a combination of medical treatments, but none of these treatments halts the devastating progression of the disease.

While therapeutic compounds are being actively developed to treat HD, the delivery of these into the brain is the major impediment to their successful development into treatments that could be widely used. In this application we plan to develop an entirely new SOLUTION to this major problem. Over the course of 36 months we will develop a new treatment that can switch off the mutant huntingtin gene AND that can successfully cross the blood brain barrier to enter the brain using small, natural particles called exosomes. Exosomes are very small, fat encapsulated particles that are generated naturally by all cells of the body and that we have exploited for the delivery of drugs into the brain by modifying them in such a way that they display small molecules on their surface that allow them to home into the brain following their injection into a vein in the body. This will open the door to testing many compounds that have been proven to reduce the levels of the mutant Huntingtin gene. If we are able to do this successfully for HD this will open the door to the application of the exosome methods to treat many other currently incurable neurodegenerative diseases.

During the course of this work we aim to achieve the following:
1. To produce an optimised exosome particle containing the drug to switch off the Huntingtin gene and to test this initially in cells in culture.
2. To then test whether this optimised exosome drug can reach the parts of the brain affected by HD, and to understand what doses of exosome drug are required in order to achieve the required levels of drug activity in the brain. This work will be carried out in healthy mice.
3. Having put all of the necessary methods and information in place we will then test the exosome drug in mice which carry the Huntingtin gene mutation and we will evaluate this new therapy for its ability to prevent or reverse the development of the disease process in the mice.

Huntington's disease (HD) is a monogenic, autosomal dominant disorder affecting 1 in 10,000 people caused by a pathological CAG repeat expansion mutation in exon 1 of the Huntingtin gene (Htt). This is translated into a polyglutamine protein that aggregates into toxic inclusions within neurons leading to neural dysfunction then neurodegeneration, progressive motor dysfunction, cognitive decline and death on average within 20-25 years. Drugs currently only allow symptomatic management. Due to the toxic gain-of-function of mutant Htt, a rational therapeutic strategy is to suppress expression of the mutant protein by RNA interference, an approach that would be APPLICABLE TO ALL HD patients. This has been investigated using antisense oligonucleotides, siRNA and viral vectors expressing shRNA given via local administration into the brain. From a clinical therapeutic perspective, given that Htt is ubiquitously expressed and that HD pathology affects a number of brain regions and has peripheral non-nervous system manifestations, it would be highly advantageous to systemically deliver these silencing agents. However, delivery across the blood brain barrier (BBB) remains a major hurdle. Our PROPOSED SOLUTION is the use biological membrane vesicles termed exosomes for delivery of therapeutic agents systemically to the brain. Exosomes naturally transport RNA and protein between cells and our recent research has shown that they can be targeted to the brain following systemic injection to deliver macromolecular siRNA drugs across the BBB. More recently we have demonstrated that exosome-delivered siRNA significantly decreases alpha-synuclein levels in a transgenic mouse model of Parkinson's disease highlighting the potential of this technology. This project will develop brain-targeted exosome technology for targeted reduction of Htt expression in vivo and to demonstrate efficacy and safety in an HD mouse model.

The present project aims to develop novel exosome nanotechnology for the treatment of Huntington's disease (HD). There thus is likely to be high impact with numerous individuals, groups and organisations likely to gain significant benefit:

ACADEMIC BENEFICIARIES include the PI, the Project Team, the PI's and Co-I's UK collaborators (e.g. the MDEX Consortium, EU IMI COMPACT Consortium,TRANSEURO Consortium) and non-UK international collaborators. Other academic beneficiaries will include groups working in the HD and related neurodegenerative disease fields, the siRNA and oligonucleotide therapeutics field, and those working in relation to macromolecular drug delivery to the brain.

NON-ACADEMIC BENEFICIARIES will include HD patients, their families and charitable organisations that support HD patients and research, and those in the biotechnology, pharmaceutical and investment sectors that have interests in relation to HD, nanotechnology for drug delivery, siRNA and oligonucleotide therapeutics and to those interested in the therapy of rare diseases more generally.

ACADEMIC BENEFICIARIES will benefit in the short term from direct knowledge of outputs of the present project including publications and other forms of research communication. Knowledge gained will inform future research directions, future funding applications, future research ideas and projects, and future collaborative opportunities. For example, knowledge gained in relation to brain-targeted nanotechnology with utility for targeted delivery of siRNAs to brain will provide insight into understanding of mechanisms (leading to future improvements), utility for application to other diseases (e.g. other neurological diseases) and to delivery of other drug cargoes (e.g. therapeutic oligonucleotides, miRNAs). Such specific knowledge will not be restricted to the PI and Co-Is although these groups are likely to benefit soonest. Longer-term, success in this project will provide fundamental knowledge in relation to the treatment of neurological disorders and will likely lead directly and indirectly to numerous long-term academic beneficiaries exploiting this knowledge in relation to other neurodegenerative diseases in particular and neurological diseases more generally.

NON-ACADEMIC BENEFICIARIES especially HD patients will benefit directly from an advanced exosome drug delivery technology, which could be available for clinical testing in approximately 5 years and offer disease modification and improved quality of life for HD patients. HD families will benefit immediately because such research is crucial to maintaining the morale of the HD community. In the medium term, families of HD patients will benefit directly from a therapeutic agent (i.e. a product) that can be tested on relatives offering the prospect of disease modification. HD charities and foundations play a crucial role in supporting families and funding early stage research. Such organisations will benefit from encouraging results as they play a key role in supporting, informing and motivating HD patients and their families. In the medium term such organisations will benefit as they play a critical stakeholder role during clinical testing and in guiding the development and application of new therapies, including in relation to research, ethical and commercial issues. Finally, non-academic beneficiaries in the commercial sector are likely to benefit directly in the medium term through opportunities to acquire licences to intellectual property in relation to aspects of the technology - either specifically in relation to clinical development of the lead compound for HD or more generally in relation to the platform exosome nanotechnology that could have broad application. This is likely to lead to further development, a range of possible products and a range of possible commercial benefits for companies in the biotechnology or pharmaceutical sectors and/or investors in relation to such companies.