Development of a SYF2 antisense oligonucleotide treatment for ALS and FTD

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Development of a SYF2 antisense oligonucleotide treatment for ALS and FTD Project Summary Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are complex diseases that result from many diverse genetic etiologies. Although therapeutic strategies that target specific causal mutations (e.g. C9ORF72 antisense oligonucleotides (ASOs)) may prove effective against individual forms of ALS or FTD, these approaches cannot address the vast majority of cases that have unknown genetic etiology. Moreover, given the large number of different genes that likely contribute to ALS and FTD and the fact that each genetic form is relatively rare, this strategy may be difficult to implement for all cases. Thus, there is a pressing need for new therapeutic strategies that rescue multiple forms of ALS and FTD, particularly those with unknown genetic etiologies. A hallmark pathological feature of ALS and FTD is the depletion of TAR DNA-binding protein 43 (TDP-43) from the nucleus of neurons in the brain and spinal cord to the cytoplasm where it aggregates into insoluble inclusion bodies in >95% of ALS cases and ~45% of FTD cases post mortem. While studies suggest that these neuronal TDP-43 aggregates drive neurodegeneration58, reduction in TDP-43 from the nucleus also alters the splicing or expression levels of more than 1,500 RNAs9, including disease hallmarks such as STMN2. Thus, both the loss of TDP-43 from the nucleus and its aggregation in the cytoplasm contribute to neurodegeneration, and it is critical to develop treatments that address both aspects of this challenging pathology. We found that suppressing the gene encoding the spliceosome-associated factor SYF2 alleviates TDP-43 aggregation and mislocalization, improves TDP-43 activity, and rescues C9ORF72 and sporadic ALS survival. Moreover, Syf2 suppression ameliorates neurodegeneration, neuromuscular junction loss, and motor dysfunction in TDP-43 mice. Mice with one loss-of-function copy of Syf2 are healthy and humans carrying a loss-of-function SYF2 allele are not affected by pediatric diseases or known to be affected by disease in adulthood. Thus, suppression of spliceosome-associated factors such as SYF2 is a promising and broadly-effective genetic target for ALS and FTD. Antisense oligonucleotides (ASOs) are an attractive approach for genetic targets in the central nervous system (CNS) like SYF2 because they can be injected directly into the spinal cord, achieve sustained target engagement throughout the CNS, and are less likely to cause peripheral toxicity. Leveraging our proprietary ASO design software, we assessed all possible SYF2 ASO sequences in silico and prioritized several hundred leads predicted to have enhanced stability and manufacturability, and reduced immunogenicity and off-target effects. The objective of this Direct to Phase 2 project is to identify a bona fide development candidate SYF2 ASO from among these leads for advancement in investigational new drug (IND)-enabling toxicity studies. The broad aims of the project are to establish the therapeutic index of Syf2 suppression in TDP-43 mice, assess SYF2 leads for potency, efficacy and tolerability in a large panel of ALS patient-derived neurons and a bacterial artificial chromosome human SYF2 transgenic mouse, and lastly to assess the leads in an exploratory toxicity study in rodents.