Recent breakthroughs in antisense oligonucleotide (ASO) therapy have demonstrated that the damaging effects of some disease-causing mutations can be corrected in vivo. Briefly, an ASO is a short strand of synthetic DNA that is designed to bind to a specific messenger RNA (mRNA) sequence. ASOs can be used to block specific regulatory sites on the mRNA or to target a mutant transcript for degradation. To date, antisense therapies have followed two approaches: (1) restoring the production of a functional protein by blocking an aberrant splice event (e.g., Spinraza® [nusinersen] for the treatment of spinal muscular atrophy) or by skipping a mutant exon (e.g., Exondys 51® [eteplirsen] for Duchenne muscular dystrophy and STK-001 for Dravet syndrome); or (2) eliminating a toxic mRNA or protein by targeting the mutant allele for degradation (e.g., Tofersen [formerly IONIS-SOD1Rx] for amyotrophic lateral sclerosis).
Detection of de novo genetic mutations in autism spectrum disorder (ASD) has identified more than one hundred ASD susceptibility genes with high confidence. These discoveries have created new opportunities to develop targeted therapies for rare conditions within the autism spectrum. However, ASD susceptibility genes that are implicated by de novo mutations consist predominantly of dominant ‘haploinsufficiencies’ (DHIs), in which biallelic expression of a gene is required for proper development, and as such, the loss or inactivation of one copy carries significant risk for ASD. DHIs are associated with a wide spectrum of risk alleles, most of which are not amenable to the ASO designs described above.
For DHIs, a more broadly applicable therapeutic strategy would be one that is not allele-specific but instead boosts the overall expression of genes. The goal of this pilot study is to demonstrate an approach to antisense therapy that is effective for ramping up the expression of specific ASD genes. The therapeutic approach being untaken by Jonathan Sebat and colleagues is to develop ASOs that increase expression of specific genes by blocking ribosomal binding sites that negatively regulate translation initiation. As a proof-of-concept, the researchers propose to develop molecules that block ribosomal binding to upstream open reading frames (ORFs), regulatory sites in mammalian mRNAs that have been shown to repress translation of the protein coding ORF. The Sebat lab will develop ASOs that block ribosomal binding to upstream ORFs that have been identified within 20 high-confidence ASD genes. ASOs will be designed, synthesized and tested for activity in HeLa cells. Lead molecules that have the desired activity will then be tested in patient-derived cell lines to determine whether ASOs can normalize the expression level of the functional protein. Successful completion of these aims will generate lead molecules and provide a basis of knowledge and a scientific rationale for their further clinical development.