A SMN2 splicing modifier rescues the disease phenotypes in an in vitro human spinal muscular atrophy model.

Spinal muscular atrophy (SMA) is caused by the mutation or deletion of the survival motor neuron 1 (SMN1) gene. Only approximately 10 % of the products of SMN2, a paralogue of SMN1, are functional full-length SMN proteins, whereas SMN2 primarily produces alternatively spliced transcripts lacking exon 7. Reduced SMN protein levels in SMA patients lead to progressive degeneration of spinal motor neurons (MNs). Here, we report an advanced platform based on an SMN2 splicing-targeting approach for SMA drug screening and validation by using an SMN2 splicing reporter cell line and an in vitro human SMA model via induced pluripotent stem cell (iPSC) technology. Through drug screening using a robust cell-based luciferase assay to quantitatively measure SMN2 splicing, the small-molecule candidate compound rigosertib was identified as an SMN2 splicing modulator that led to enhanced SMN protein expression. The therapeutic potential of the candidate compound was validated in motor neuron progenitors differentiated from SMA patient-derived iPSCs (SMA iPSC-pMNs) as an in vitro human SMA model, which recapitulated the biochemical and molecular phenotypes of SMA, including lower levels of full-length SMN transcripts and protein, enhanced cell death, and reduced neurite length. The candidate compound exerted strong splicing correction activity for SMN2 and potently alleviated the disease-related phenotypes of SMA iPSC-pMNs by modulating various cellular and molecular abnormalities. Our combined screening platform representing a pMN model of human SMA provides an efficient and reliable drug screening system and is a promising resource for drug evaluation and the exploration of drug modes of action.