SMN2 splice modulators enhance U1–pre-mRNA association and rescue SMA mice

A high-throughput screen identified a small molecule that promoted inclusion of SMN2 exon 7, increased SMN2 protein levels and extended survival in a SMA mouse model through stabilization of the interaction between SMN2 pre-mRNA and U1 snRNP complex. Spinal muscular atrophy (SMA), which results from the loss of expression of the survival of motor neuron-1 ( SMN1 ) gene, represents the most common genetic cause of pediatric mortality. A duplicate copy ( SMN2 ) is inefficiently spliced, producing a truncated and unstable protein. We describe herein a potent, orally active, small-molecule enhancer of SMN2 splicing that elevates full-length SMN protein and extends survival in a severe SMA mouse model. We demonstrate that the molecular mechanism of action is via stabilization of the transient double-strand RNA structure formed by the SMN2 pre-mRNA and U1 small nuclear ribonucleic protein (snRNP) complex. The binding affinity of U1 snRNP to the 5′ splice site is increased in a sequence-selective manner, discrete from constitutive recognition. This new mechanism demonstrates the feasibility of small molecule–mediated, sequence-selective splice modulation and the potential for leveraging this strategy in other splicing diseases.