RESUMEN
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.
Asunto(s)
Empalme Alternativo , Atrofia Muscular Espinal/tratamiento farmacológico , ARN Bicatenario/agonistas , Ribonucleoproteína Nuclear Pequeña U1/agonistas , Bibliotecas de Moléculas Pequeñas/farmacología , Proteína 2 para la Supervivencia de la Neurona Motora/metabolismo , Animales , Sitios de Unión , Modelos Animales de Enfermedad , Femenino , Expresión Génica , Humanos , Ratones , Ratones Transgénicos , Modelos Moleculares , Atrofia Muscular Espinal/metabolismo , Atrofia Muscular Espinal/mortalidad , Atrofia Muscular Espinal/patología , Unión Proteica/efectos de los fármacos , Estabilidad Proteica/efectos de los fármacos , Proteolisis , Precursores del ARN/agonistas , Precursores del ARN/química , Precursores del ARN/metabolismo , ARN Bicatenario/química , ARN Bicatenario/metabolismo , Ribonucleoproteína Nuclear Pequeña U1/química , Ribonucleoproteína Nuclear Pequeña U1/metabolismo , Bibliotecas de Moléculas Pequeñas/síntesis química , Bibliotecas de Moléculas Pequeñas/metabolismo , Análisis de Supervivencia , Proteína 2 para la Supervivencia de la Neurona Motora/química , Proteína 2 para la Supervivencia de la Neurona Motora/genéticaRESUMEN
Spinal muscular atrophy (SMA), a rare neuromuscular disorder, is the leading genetic cause of death in infants and toddlers. SMA is caused by the deletion or a loss of function mutation of the survival motor neuron 1 (SMN1) gene. In humans, a second closely related gene SMN2 exists; however it codes for a less stable SMN protein. In recent years, significant progress has been made toward disease modifying treatments for SMA by modulating SMN2 pre-mRNA splicing. Herein, we describe the discovery of LMI070/branaplam, a small molecule that stabilizes the interaction between the spliceosome and SMN2 pre-mRNA. Branaplam (1) originated from a high-throughput phenotypic screening hit, pyridazine 2, and evolved via multiparameter lead optimization. In a severe mouse SMA model, branaplam treatment increased full-length SMN RNA and protein levels, and extended survival. Currently, branaplam is in clinical studies for SMA.