Novel gene therapy strategies for Canavan disease

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DESCRIPTION (provided by applicant): Canavan disease (CD) is a rare, inherited, and fatal, childhood leukodystrophy caused by autosomal recessive mutations in the aspartoacylase gene (ASPA). Although CD has been found in a wide range of ethnic groups, it is especially prevalent in the Ashkenazi Jewish population, affecting one in 6,400 - 13,500 people in this group. ASPA deficiency in Canavan patients leads to accumulation of N-Acetyl-Aspartic Acid (NAA), resulting in swelling and spongy degeneration of white matter in the brain. The clinical manifestations of this fatal disease includ psychomotor retardation, hypotonia, macrocephaly, head lag, and early death. NAA is synthesized in the mitochondria of neurons by N-acetyltransferase (NAT1) and hydrolyzed in oligodendrocytes (OLs) by ASPA. Pathogenic mechanism(s) of ASPA deficiency in the CNS and contributions of ASPA deficits in PTs to the pathophysiology of CD are not well studied. Currently, there is no effective clinical intervention available for CD. ASPA gene replacement therapy is an attractive strategy for the treatment of CD. Earlier gene therapy efforts based on the first generation of AAV serotype 2-derived vector offered no clinical benefit. That was likely due to inadequate transduction efficiency of rAAV2 and limitations of localized intraparenchymal vector delivery. Recent advances in AAV vectorology produced some novel recombinant AAVs (rAAVs), such as rAAV9 reported by Kaspar et al., and rAAVrh.8 and rh.10 identified by our lab, that are highly efficient in transducing large areas of the brain and spinal cord by crossing the blood-brain-barrier (BBB) after intravenous (IV) injection. Here, we hypothesize that using these novel vectors and route of administration, we can develop safe, effective, and sustained gene therapy strategies that will correct the metabolic defect, alleviate the disease phenotype, and prolong survival of CD mice without causing significant toxicity. Specifically, this project will further our understanding of the pathophysiology of CD, particularly in the PTs and the mechanism of rAAV-mediated CD gene therapy after intravenous delivery. We will compare the BBB permeability between wild type (Wt) and ASPA Knockout (ASPA-/-) mice, and define the latest therapeutic window for CD. We will optimize the transgene cassette to express hASPA more efficiently and safely. We will compare our 3 lead vectors (i.e. rAAV9, rh.8, and rh.10) in ASPA-/- mice for minimum effective dose, the latest therapeutic window, long lasting therapeutic outcomes, immunotoxicity, and biodistribution profiles. To facilitate future clinical development, we will also compare these 3 vectors for sero- prevalence in the CD patient population and study impact of pre-existing immunity on CNS gene therapy by adoptively transferring capsid immunities to ASPA-/- mice. These proposed studies will significantly advance our current understanding of CD, and serve as the basis for the development of safe and effective rAAV gene therapeutics for CD patients. PUBLIC HEALTH RELEVANCE: Cavanan disease (CD) is a rare, inherited, and fatal, childhood neurodegenerative disorder caused by autosomal recessive mutations in the aspartoacylase gene (ASPA). It affects a wide range of ethnic groups, but is especially prevalent among the Ashkenazi Jewish population. Currently, there is no effective clinical intervention for CD. Adeno-associated virus (AAV) vector-based ASPA gene replacement therapy is a promising strategy for the treatment of CD; however, a previous gene therapy attempt with the vector based on AAV serotype 2 met with limited success. Here we propose to develop novel AAV-based, efficacious, and safe gene therapeutics to treat CD in the mouse model of CD. Our studies will open avenues leading to the eventual cure of Canavan patients.