MAPT Splicing Modulators as a Therapeutic Strategy for Tauopathies

ABSTRACT Tauopathies are neurodegenerative diseases characterized by the abnormal accumulation of microtubule-associated protein tau (MAPT) in the brain. These disorders, like frontotemporal dementia (FTD-Tau), currently lack effective therapies and can occur sporadically or be inherited when associated with MAPT gene mutations. The MAPT gene region encompassing exon 10 and adjacent introns is a hotspot for pathogenic variants, including splicing mutations that enhance exon 10 inclusion and increase 4R tau expression, and gain-of-function mutations that generate aggregation-prone mutant 4R tau protein. For these 4R-specific tauopathies, a targeted mRNA splicing approach that promotes exon 10 exclusion may offer therapeutic benefit. In this study, we discovered novel splicing modulator compounds (SMCs) that promote MAPT exon 10 exclusion, and demonstrated their efficacy in FTD patient-derived neuronal models carrying the tau-P301L gain-of-function mutation or the tau-S305N splicing mutation. Treatment with SMC reduced 4R tau expression and decreased the accumulation of hyperphosphorylated tau (pTau), oligomeric and insoluble tau, thereby rescuing tau-associated neuronal toxicity. Importantly, our lead SMC corrected the 3R/4R splice ratio in vivo and significantly reduced pTau in the brain of a gene- replacement (GR) mouse model expressing the human tau-N279K splicing mutation. These findings support the therapeutic potential of this class of small molecules and establish MAPT pre- mRNA splicing modulation as a promising strategy for the treatment of 4R tauopathies. One Sentence Summary Discovery of SMCs that correct MAPT splicing, reduce 4R tau, and rescue pathology in patient- derived neuronal and in vivo models of 4R tauopathies. Competing Interest Statement MCS is a paid consultant to Proximity Therapeutics Inc. MCS has received funding as sponsored research from Proximity Therapeutics and AstraZeneca. JL, YY, CM, MA, SJB, KS, MD, AM, NZ, JN, MW, CRT, MW, EW, KD, and JT are/were employees of PTC Therapeutics, Inc. In connection with such employment, the authors receive salary, benefits and stock-based compensation, including stock options, restricted stock, other stock-related grants, and the right to purchase discounted stock through PTC's employee stock purchase plan. EM serves on the scientific advisory board (SAB) of Revir Therapeutics and is an inventor on an International Patent Application Number PCT/US2021/012103, assigned to Massachusetts General Hospital and PTC Therapeutics entitled "RNA Splicing Modulation" related to the use of BPN-15477 in modulating splicing. SJH serves on the scientific advisory board (SAB) of Proximity Therapeutics, Psy Therapeutics, Sensorium Therapeutics, 4M Therapeutics, Ilios Therapeutics, Entheos Labs, and Birdwood Therapeutics, none of whom were involved in the present study. SJH. has also received speaking or consulting fees from Amgen, AstraZeneca, Biogen, Merck, Regenacy Pharmaceuticals, Syros Pharmaceuticals, Juvenescence Life, as well as sponsored research or gift funding from AstraZeneca, JW Pharmaceuticals, Lexicon Pharmaceuticals, Vesigen Therapeutics, Compass Pathways, Atai Life Sciences, and Stealth Biotherapeutics. All other authors declare no competing interests.