Antisense Oligonucleotides for the Treatment of Spinal Muscular Atrophy

Abstract

Spinal muscular atrophy (SMA) is an autosomal recessive disease affecting *1 in 10,000 live births. The most striking component is the loss of a-motor neurons in the ventral horn of the spinal cord, resulting in progressive paralysis and eventually premature death. There is no current treatment paradigm other than supportive care, though the past 15 years has seen a striking advancement in understanding of both SMA genetics and molecular mechanisms. A variety of disease-modifying interventions are rapidly bridging the translational gap from the laboratory to clinical trials, including the application of antisense oligonucleotide (ASO) therapy for the correction of aberrant RNA splicing characteristic of SMA. Survival motor neuron (SMN) is a ubiquitously expressed 38-kD protein. Humans have two genes that produce SMN, SMN1 and SMN2, the former of which is deleted or nonfunctional in the majority of patients with SMA. These two genes are nearly identical with one exception, a C to T transition (C6T) within exon 7 of SMN2. C6T disrupts a modulator of splicing, leading to the exclusion of exon 7 from *90% of the mRNA transcript. The resultant truncated D7SMN protein does not oligomerize efficiently and is rapidly degraded. SMA can therefore be considered a disease of too little SMN protein. A number of cis-acting splice modifiers have been identified in the region of exon 7, the steric block of which enhances the retention of the exon and a resultant full-length mRNA sequence. ASOs targeted to these splice motifs have shown impressive phenotype rescue in multiple SMA mouse models.

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“…Woo et al also studied the effect of LNA-modified oligos against SMN-AS1 in combination with other previously described ASOs participating in SMN2 splicing correction [73]. It was established that treatment of cells with two antisense oligonucleotides vs. one splicing corrector leads to a 2-fold increase in the amount of full-length mRNA SMN2.…”

Newborn Blood Spot Screening Test Using Multiplexed Real-Time PCR to Simultaneously Screen for Spinal Muscular Atrophy and Severe Combined Immunodeficiency

“…Several potential therapies for SMA are in development (1,4 ), 2 of which are undergoing clinical trials in symptomatic children with some encouraging results (5, 6 ). Because of the early onset and rapid progression of infantile SMA, evaluation of these therapies in presymptomatic infants will require prompt detection.…”

Assays for the Identification and Prioritization of Drug Candidates for Spinal Muscular Atrophy

“…The snRNP assembly assay has been described for both cell extracts, 44,47,48 as well as tissue homogenates. [30][31][32][33][34][35]37,54,55,205 In addition, a version of the protocol compatible with high-throughput screening has been developed. 206 The method includes the following main steps: (i) preparation of a cell extract or tissue homogenate and incubation with a synthetic radiolabeled U snRNA (typically at 10,000 cpm or between 100 pM and 1 nM RNA in a 20 mL reaction) in the presence of a test compound, (ii) immunoprecipitation against a protein component of the snRNP (typically using the anti-Sm antibody Y12), (iii) denaturation to release the RNA, and (iv) gel electrophoretic separation followed by autoradiography.…”