611. Promoter Evaluation of AAV Gene Therapy in the Central Nervous System for Feline Niemann-Pick Type C Disease

Niemann-Pick type C1 (NPC1) disease is characterized by progressive cerebellar ataxia, dementia, and death in adolescence. It is caused by mutations that result in deficient function of lysosomal, membrane-bound NPC1, resulting in the intralysosomal accumulation of cholesterol and sphingolipids. There are no FDA-approved therapies for NPC1 disease, however, we have previously shown that administration of 2-hydroxypropyl-beta-cyclodextrin (HPsCD) via the cerebromedullary cistern (CBMC) in presymptomatic cats with NPC1 disease prevented the onset of cerebellar tremor and resulted in Purkinje cell (PC) survival and near normal concentrations of cerebral cortex and cerebellar cholesterol and sphingolipids. Remarkably, these cats remained alive for greater than three years of age, in contrast to untreated NPC1 cats that died before six months of age. This therapy has advanced to clinical trials where patients receive biweekly HPsCD. In an attempt to both reduce the number of HPsCD injections and to treat uncorrected brain regions, we studied the feasibility of viral gene therapy, providing a one-time injection, in NPC1 cats. Preliminary studies utilized administration of an adeno-associated virus serotype 9 carrying the feline NPC1 transgene (fNPC1) via the CBMC of pre-symptomatic NPC1 cats. These treated cats showed reduced ataxia compared to untreated cats. Histologic evaluation of the brains revealed that NPC1 expression had been restored to some PCs and that this was associated with increased PC survival. This initial success prompted us to further explore the potential of various promoters to express functional NPC1 protein in the brain. In this study we evaluated the ability of four different promoters, three ubiquitous (CB7, GUSB, and JeTi) and one neuron-specific (CamKII), to drive GFP expression in the central nervous system of normal cats. Our preliminary therapeutic studies used the GUSB promoter (pGUSB) to mediate fNPC1 expression. Expression of both fNPC1 and a GFP reporter under pGUSB were low in PCs, and in cerebrocortical neurons and astrocytes. Overall, the CB7 promoter drove the highest level of expression in similar regions; however, this large promoter (~970bp) limits transgene size (where NPC is ~4.3Kbp) and led us to examine a smaller exogenous promoter based on CB7, termed JeTi. This promoter was similar in expression levels to the pGUSB, leading to low-level expression at our limit of detection using DAB-based immunohistochemistry. Interestingly, a six-month therapeutic study using the JeTi promoter had a similar outcome as pGUSB where treated cats had reduced clinical signs at the end of study. Expression driven by the neuron-specific promoter CamKII produced levels similar to the CB7 promoter, although PCs of the cerebellum had low to undetectable expression levels. These data and preliminary therapeutic data in AAV-treated NPC1 cats will be further explained in this presentation.