Drug Discovery for Spinocerebellar Ataxia Type 2 (SCA2)

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DESCRIPTION (provided by applicant): Neurodegenerative diseases represent an ever-increasing societal and economic burden with WHO estimates indicating that they will replace cancer as the 2nd leading cause of death by 2040. In neurodegenerative disease research, a wealth of pathways has been uncovered, but their direct and primary relevance to the respective human disease have been difficult to prove and pathways have remained difficult to target. For polyglutamine diseases, there is clear evidence that expression levels of the respective genes affect the phenotype and shutting-off expression in mouse models reverses already established motor phenotypes. We have chosen an autosomal dominant polyglutamine (polyQ) disease to demonstrate the proof-of-principle that small molecules can be used to downregulate expression of a disease gene at the transcriptional or mRNA stability level. Spinocerebellar ataxia type 2 (SCA2) is a multisystem neurodegenerative disease caused by a dominantly-acting mutation leading to expansion of a polyQ domain in the ataxin-2 protein. SCA2 patients develop progressive ataxia and later lose function in other neuronal systems. Prominent parkinsonian signs develop in some. Similar to many neurodegenerative disorders, no symptomatic or disease-modifying treatments are known. The primary objective of the proposed research is to identify compounds inhibiting ATXN2 expression and to test them for efficacy in SCA2 mouse models. To this end, we have developed a cell-based assay paired with an in vivo mouse model using identical luciferase expression constructs. This will allow us to progress compounds rapidly from a high-throughput screen conducted at NIH Chemical Genomics Center (NCGC) to efficacy and toxicity testing in mice. Four specific aims are proposed: 1) HTS with 300,000 compounds at the NCGC, 2) In vitro testing of compounds in SCA2 patient lymphoblasts, 3) In vivo testing of compounds in ATXN2-luciferase transgenic mice, and 4) testing the ability for compounds to ameliorate an ATXN2 phenotype in a humanized SCA2 mouse BAC model. Our approach takes advantage of an ATXN2-luciferase transgene with luciferase gene flanked by the upstream and downstream portions of the ATXN2 gene. Mouse models are in place to test rapidly the efficacy of compounds in vivo including passage of the blood brain barrier, and further progression of compounds to test in mouse models with morphological, biochemical, and motor phenotypes replicating human SCA2. The proposed work will break new ground for treatment of neurodegenerative diseases by demonstrating feasibility of targeting dominant-acting mutated genes with compounds. We aim to identify small molecules not only targeting gene expression levels, but also mRNA stability via the 3'-UTR. Our focus is on small molecules and extensive and rapid post HTS-testing in a number of rodent models as well as human cell lines. PUBLIC HEALTH RELEVANCE: Neurodegenerative diseases are not only a major worldwide health problem, but owing to the large number affected and long course of illness, a significant economic threat. We are using SCA2, a debilitating and terminal disorder, as a model to examine novel approaches to identify disease-modifying compounds. Our approach of tightly coupling in vitro and in vivo screens can used to target other neurodegenerative diseases caused by dominant-acting gene mutations.