Discovery and Development of Small Molecule Sarcospan Enhancers for Duchenne Muscular Dystrophy
- Author(s): Shu, Cynthia
- Advisor(s): Crosbie, Rachelle H.
- et al.
Duchenne muscular dystrophy (DMD) is a progressive muscle wasting disorder that affects 1 in every 5,700 males. Individuals with DMD experience muscle degeneration beginning in early childhood, wheelchair reliance by age 10-12, and succumb to cardiac or respiratory failure by the third decade of life. DMD is caused by mutations in the gene encoding for the dystrophin protein, which normally connects the muscle cell membrane to the extracellular matrix (ECM). Loss of this connection renders the membrane vulnerable to contraction-induced damage, resulting in muscle inflammation and degeneration. Restoring the adhesion between the cell and the ECM is a critical target in the development of urgently needed therapies for DMD.
The Crosbie group previously established that transgenic overexpression of the integral membrane protein sarcospan (SSPN) in murine models of DMD prevents muscle disease by increasing membrane localization of adhesion complexes that compensate for dystrophin. In this thesis work, we describe the identification and development of chemical modulators of SSPN for the treatment of DMD. To develop a platform to efficiently screen large chemical libraries, we first created fluorescent and luminescent reporter cell lines to quantify SSPN gene activation. We created high-throughput cell-based assays and conducted a proof-of-concept screen on FDA approved drugs. The assay is capable of identifying drugs that increase SSPN gene and protein expression in dystrophin-deficient murine muscle cells. To identify compounds that could be developed into new chemical entities, we screened over 200,000 small molecules from curated libraries of lead-like drugs. We identified lead compounds that increased SSPN gene and protein expression in both dystrophin-deficient mouse and human DMD myotubes. The lead compound OT-9 improved in vitro membrane stability of dystrophin-deficient mouse and human myotubes. Knockdown of SSPN reduced the ability of OT-9 to increase membrane stability, demonstrating that OT-9 improved membrane stability through SSPN. In vivo studies revealed that OT-9 increased SSPN gene expression in the muscle of the murine model of DMD, indicating its therapeutic potential in a relevant animal model. Optimization of the lead compounds through structure-activity relationship analysis resulted in the creation of new chemical entities with improved solubility and activity. Future studies will focus on target identification and further optimization of the new chemical entities. In summary, this thesis work sets the path for the development of pharmacological modulators of SSPN for the treatment of DMD.