Cooperative lead development program for treatment of spinal muscular atrophy

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DESCRIPTION (provided by applicant): Spinal Muscular Atrophy (SMA) is a common form of muscular dystrophy and the leading genetic cause of infant mortality. This autosomal recessive disorder is characterized by progressive muscle weakness due to loss of motor neuron function. SMA is caused by insufficient levels of the survival motor neuron (SMN) protein, usually from homozygous mutation of the SMN1 gene. A nearly identical copy gene, SMN2, fails to protect from development of SMA because its mRNA undergoes alternative splicing of exon 7. About 10% of SMN2 RNA transcripts include exon 7 and encode the same SMN protein as SMN1. We implemented a novel lead discovery program to identify drug-like compounds that increase intracellular SMN protein levels. Using a new and improved cell-based reporter assay, we completed three high-throughput screens of large chemical diversity libraries in collaborations with the Laboratory of Drug Discovery in Neurodegeneration, the Genomics Institute of Novartis Foundation, and the NIH Chemical Genomics Center. These screens have identified drug-like activators of SMN protein expression that have been confirmed in secondary assays. The first aim of this three-year grant is to design and synthesize more potent compounds based on the active scaffolds we have identified. We will then investigate the pharmacokinetics and acute toxicology of the leads that emerge. A medicinal chemistry program will modify these compounds for improved absorption and maintenance of adequate tissue levels and prepare formulations for their administration in animals. The second aim is to test the most active and pharmacologically suitable compounds in SMA mouse models for efficacy in raising SMN protein levels in vivo and to determine whether the severity of disease can be ameliorated. This proposal unites the experience and talents of six teams with expertise in molecular biology and pre-clinical drug development in SMA with leaders in design of novel medicines for neurodegenerative diseases. The predicted outcome of this proposal is identification of pharmacologically suitable drug-like compounds that increase SMN levels and restore motor activity in SMA model mice that can be rapidly advanced to human trials. The ultimate goal is to develop an effective drug treatment of spinal muscular atrophy. PUBLIC HEALTH RELEVANCE: Spinal muscular atrophy (SMA), a form of muscular dystrophy, is the leading genetic cause of infant death, and in less devastating forms leads to symptomatic muscle weakness in children and adults. All forms of SMA result from insufficient levels of the protein called SMN. There is no treatment for SMA. We used a strategy to test very large collections of chemical compounds for ability to increase SMN protein levels in cells. This grant application requests funds for maximizing the potency and drug-like properties of these compounds. We will then test their efficacy in mice genetically engineered to reproduce SMA and measure their SMN levels and effects. Discovery of a medicine that increases SMN levels and improves SMA mouse survival would represent an important milestone for advancement to human clinical trials.