Hughes, Michael; (2017) The development of gene therapy for Niemann-Pick Type C disease. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Niemann-Pick Type C (NP-C) is a lysosomal storage disorder with neurological and visceral pathology, for which there is currently no major disease modifying treatment. Loss of NPC1 function, a late endosomal transmembrane protein, leads to systemic intracellular lipid accumulation. The subsequent premature death is usually associated with neurological manifestations, such as neurodegeneration and neuroinflammation. This project focuses on the development and preclinical evaluation of gene therapy for NP-C in a mouse model using an adeno-associated viral (AAV) vector. The vector would be capable of delivering and expressing human NPC1 in the mouse brain and providing therapeutic benefit. AAV vectors exhibit efficient and widespread gene delivery throughout the brain, however their limited packaging capacity can be a constraint for larger genes. In this project extensive construct modifications were carried out to incorporate the relatively large NPC1 cDNA into a functional AAV serotype 9 vector, where NPC1 is controlled by a constitutively active neuronal promoter. Initial in vivo testing demonstrated successful NPC1 over-expression in administered mouse brains, compared to endogenous NPC1 levels in unadministered controls. No indications of toxicity were observed as a result of exogenous NPC1 overexpression in vivo. A series of preclinical proof of concept survival studies were subsequently carried out on the Npc1-/- model, where newborn Npc1-/- mice were administered with 4.6 x 109 vector genomes of AAV9-NPC1 via intracerebroventricular injections. Treated Npc1-/- mice exhibited an increased lifespan (median survival - 116.5 days) compared to untreated Npc1-/- mice (median survival - 75.5 days). Low dose treated mice exhibited permanent normalisation of locomotor function and significant neuronal rescue in all brain regions analysed. A subsequent study with a 65-fold dose increase resulted in an additional significant extension of lifespan, along with improved weight maintenance. Combined, these results demonstrate the potential beneficial use of gene therapy for NP-C and support the further development of this approach.

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