Nusinersen

Nusinersen is a survival motor neuron-2 (SMN2)-directed antisense oligonucleotide (ASO) designed to treat SMA caused by mutations in chromosome 5q that lead to SMN protein deficiency. Using in vitro assays and studies in transgenic animal models of SMA, nusinersen was shown to increase exon 7 inclusion in SMN2 messenger ribonucleic acid (mRNA) transcripts and production of full-length SMN protein. Nusinersen acts to replace the SMN protein deficit which causes SMA, by increasing the splicing efficiency of the SMN2 pre- mRNA. More specifically, nusinersen in an 18-mer 2’-MOE phosphorothioate antisense oligonucleotide that acts as a splice-altering oligonucleotide. Nusinersen was designed to pair with a specific target sequence on the SMN2 pre-mRNA to displace heterogeneous ribonucleoproteins (hnRNPs) at the intronic splice silencing site-1 (ISS-1) between exons 7 and 8 to allow for more complete translation of SMN protein from the paralogous gene SMN2. Further reinforcing this concept, SMA phenotype is closely tied to SMN2 copy number. SMN2 serves to produce SMN protein, however at a greatly reduced rate because of differential splicing caused by the binding of the hnRNPs at the ISS-1.