Development of a novel oral treatment that rescues gait ataxia and retinal degeneration in a phenotypic mouse model of familial dysautonomia.

Familial Dysautonomia (FD) is a rare neurodegenerative disease caused by a splicing mutation in the Elongator complex protein 1 gene (ELP1). This mutation leads to the skipping of exon 20 and a tissue-specific reduction of ELP1 protein, mainly in the central and peripheral nervous systems. FD is a complex neurological disorder accompanied by severe gait ataxia and retinal degeneration. There is currently no effective treatment to restore ELP1 protein expression in individuals with FD, and the disease is ultimately fatal. After identifying kinetin as a small molecule able to correct the ELP1 splicing defect, we worked on its optimization to generate novel splicing modulator compounds (SMCs) that can be used in patients. Here, we optimize the potency, efficacy, and bio-distribution of second-generation kinetin derivatives to develop an oral treatment for FD that can efficiently pass the blood-brain barrier and correct the ELP1 splicing defect in the nervous system. We demonstrate that the novel compound, PTC258, efficiently restores correct ELP1 splicing in mouse tissues, including brain, and most importantly, prevents the progressive neuronal degeneration that is characteristic of FD. Postnatal oral administration of PTC258 to the phenotypic mouse model TgFD9;Elp1 delta20/flox increases full-length ELP1 transcript in a dose-dependent manner and leads to a two-fold increase in functional ELP1 protein in the brain. Remarkably, PTC258 treatment improves survival, gait ataxia, and retinal degeneration in the phenotypic FD mice. Our findings highlight the great therapeutic potential of this novel class of small molecules as an oral treatment for FD. ### Competing Interest Statement The authors declare competing financial interests. Jana Narasimhan, Vijayalakshmi Gabbeta, Shivani Grover, Amal Dakka, Anna Mollin, Stephen Jung, Xin Zhao, Nanjing Zhang, Sophie Zhang, Michael Arnold, Matthew G. Woll, Nikolai A. Naryshkin, Marla Weetall are/were employees of PTC Therapeutics, Inc., a biotechnology company. 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. Funding: Research support from PTC Therapeutics, Inc. (S.A.S. and E.M.). Personal financial interests: Susan A. Slaugenhaupt is a paid consultant to PTC Therapeutics and is an inventor on several U.S. and foreign patents and patent applications assigned to the Massachusetts General Hospital, including U.S Patents 8,729,025 and 9,265,766, both entitled: Methods for altering mRNA splicing and treating familial dysautonomia by administering benzyladenine, filed on August 31, 2012 and May 19, 2014 and related to use of kinetin; and U.S. Patent 10,675,475 entitled: Compounds for improving mRNA splicing, filed on July 14, 2017 and related to use of BPN-15477. Elisabetta Morini, Vijayalakshmi Gabbeta, Amal Dakka, Nikolai A. Naryshkin, and Susan A. Slaugenhaupt are inventors on an International Patent Application Number PCT/US2021/012103, assigned to Massachusetts General Hospital and PTC Therapeutics entitled: RNA Splicing Modulation, related to use of BPN-15477 in modulating splicing. All other authors declare no competing interests.