Design of an Orally Bioavailable Small Molecule That Modulates the Microtubule-Associated Protein Tau’s Pre-mRNA Splicing

Frontotemporal dementia
with parkinsonism linked to chromosome
17 (FTDP-17) is caused by the aberrant alternative pre-mRNA splicing
of microtubule-associated protein tau (MAPT) exon
10, the inclusion of which encodes a toxic tau protein harboring four
microtubule domains (4R tau). Here, we describe the design of an RNA-targeted
small molecule that thermodynamically stabilizes the structure of
a pre-mRNA splicing regulator element in the MAPT pre-mRNA exon 10-intron 10 junction to reduce the inclusion of exon
10 and hence 4R tau abundance. Structure-guided drug design was used
to obtain compounds that form a network of specific interactions to
the RNA, including multiple interactions between a single nucleotide
(nt) A-bulge and the Hoogsteen face of a closing GC base pair, the
latter of which was enabled by the design of base triple interactions.
A battery of assays revealed that the compound binds the target in vitro and in cells and affects pre-mRNA splicing in various
cellular models, including primary neurons from a human tau (htau)
knock-in mouse model. The orally bioavailable compound was administered per os (p.o.), where treatment diminished
exon 10 inclusion and reduced the 4R tau protein isoform. Further,
the molecule mitigated cellular pathologies and behavioral phenotypes
observed in the htau transgenic mouse model. This study provides a
potentially general pipeline to design compounds that target RNAs,
affect disease pathways, and deliver compounds that have oral bioavailability
and blood–brain barrier penetrance.