Genetic and pathologic evidence in 'pure' tauopathies such as Progressive Supranuclear Palsy (PSP), Corticobasilar Degeneration (CBD) and some cases of Fronto-temporal Dementia (FTD) directly implicate tau as causing neuronal cell death, while in Alzheimer?s Disease (AD) tau accumulation correlates with development and progression of cognitive impairment. Because of failure (to date) of drugs targeting amyloid beta, tau has now emerged as 'the next best' therapeutic target in the search for disease modifying drugs. There are currently 2 active phase 2 clinical studies using anti-tau antibodies in both AD and PSP underway, with additional tau targeting agents under development. Here, we propose a novel, alternative strategy to ameliorate neuronal tau toxicity by targeting MSUT2 gene expression. The body of knowledge supporting this approach includes amelioration of tau toxicity in vivo when MSUT2 is knocked out in transgenic animals expressing a pathologic tau species and in vitro where siRNA's that knock down MSUT2 are cytoprotective. Effective in vivo delivery of siRNA conjugates that lower MSUT2 levels will provide a distinct means of intervening against tauopathy with the advantage of having a viable pathway forward for development of a human therapeutic. We hypothesize that siRNA-mediated reduction of MSUT2 levels will protect against and potentially reverse in vivo neurodegeneration driven by tau accumulation. DTx Pharma has created a novel, proprietary fatty acid motif that delivers siRNA in vivo into multiple cells/tissues, including CNS neurons, allowing efficient target gene knockdown. Here we outline the initial steps of a collaborative drug discovery program with Brian Kraemer that uses the DTx motif to deliver MSUT2 specific siRNA to neurons in vivo to test whether knockdown of MSUT2 is neuro-protective in a well-characterized mouse model of tau-mediated degeneration. If successful, this approach would be advanced to generate lead, fatty acid-modified, MSUT2 siRNAs for potential therapeutic application in tauopathies. We propose 3 specific aims: SA1, generation and screening of MSUT2 siRNAs for gene knockdown activity in MSUT2 expressing cells. Conjugation of the most active siRNAs to the DTx fatty acid motif for evaluation of knockdown efficiency in cell lines and primary neurons. SA2, in vivo experiments to optimize dosing, evaluate duration of activity and assess for potential toxicities of DTx-conjugated MSUT2 siRNAs in wildtype mice. SA3, a potent, safe and efficacious siRNA identified in SA2 will be used to treat mutant tau expressing mice (PS19) in a therapeutic trial. Analyses will include the measurement of memory function, accumulation of phosphorylated tau, deposition of aggregated/oligomeric tau, neuroinflammation, and neurofibrillary degeneration. We will compare the effect of siRNA mediated MSUT2 knockdown on tau pathology with prior results in the same mouse model using anti-tau antibodies (C2N/Abbvie) and tau-targeted antisense oligonucleotides (Ionis/Biogen) that supported advancement of novel therapeutics that are currently in phase 2 clinical trials. If we have similar or better activity?we will seek to advance a lead MSUT2 targeted siRNA.
Statement Accumulation of misfolded tau protein is associated with cognitive decline and neuronal cell loss in several devastating neurodegenerative disorders including Alzheimer's disease, Progressive Supranuclear Palsy and additional rare disorders for which there currently do not exist disease modifying drugs or meaningful preventive measures. In this application we outline the initial steps in making a drug to treat tau-mediated diseases by reducing the activity of MSUT2, a gene that serves as a modulator of tau toxicity. The proposed work, if successful, will validate a new drug delivery approach being developed by DTx Pharma that uses fatty acid conjugates to deliver siRNA to relevant target cells in the CNS, and will outline a pathway whereby knockdown of MSUT2 can be tested as a potential disease modifying therapy for Alzheimer?s disease and related tauopathies.
