Continuous L-DOPA secretion by AAV gene therapy to improve the treatment of Parkinson's disease

• Main Author: Antunes, Andre Saraiva Leao Marcelo
• Format: Dissertation
• Language: English
• Published: King's College London 2016

Parkinson's disease (PD) is characterised by progressive degeneration of the dopaminergic neurons in the substantia nigra leading to severe motor complications. Standard oral treatment with L-DOPA provides powerful symptomatic relief, but disabling side effects eventually develop due to the pulsatile stimulation of the dopamine receptors. In this thesis, two gene therapy strategies were evaluated as potential treatments to diminish the fluctuations inherent to oral medication. In the first project, I evaluated a proof-of-concept for AAV-mediated continuous L-DOPA synthesis in the periphery. I could show that, in healthy mice, hepatic L-DOPA production and release can be achieved by the delivery of tyrosine hydroxylase (TH) and GTP-cyclohydrolase-1 (GCH1), but to achieve plasma L-DOPA levels that approximate those achieved with oral treatment additional organs may need to be targeted. Therefore a tricistronic vector was generated that encoded TH, GCH1 and 6-pyrovoyltetrahydopterin synthase (PTPS) under the control of a ubiquitous promoter to achieve L-DOPA synthesis in muscle and liver. Preclinical studies are currently ongoing to test the potential of this vector. The second project builds on strong preclinical data generated in a rat model of PD and assesses safety and efficacy of an AAV vector harbouring TH and GCH1 delivered to the brain of MPTP-lesioned non-human primates (NHP). I show that intervention is safe and leads to symptomatic improvement without worsening pre-established dyskinesia. However, it was discovered that vector production invariably leads to the formation of two vector species due to recombination between identical promoter sequences. Alternative vectors were designed with the goal to further improve transgene expression and clinical effect, and to avoid the generation of additional vector species. However, these did not prove to be superior in animal models of PD. The data indicate that (1) AAV-mediated continuous L-DOPA delivery in the periphery is feasible but requires further optimisation and assessment in animal models to fully demonstrate proof-of-concept, (2) AAV-mediated continuous L- DOPA delivery has clinical relevance but may require improved vector design and the achievement of stronger preclinical efficacy data to warrant progression to clinical trials.