Reversal of Tau Pathology with MSUT2 siRNA Conjugates

Project Summary
Genetic and pathologic evidence in andapos;pureandapos; 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 andapos;the next bestandapos; 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 siRNAandapos;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.Narrative Statement
Accumulation of misfolded tau protein is associated with cognitive decline and neuronal cell loss in several
devastating neurodegenerative disorders including Alzheimerandapos;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.