P.194 Development of a novel, EEV-Conjugated PMO for Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a rare, X-linked neuromuscular disorder caused by frameshift mutations in the DMD gene resulting in a lack of functional dystrophin. Antisense phosphorodiamidate morpholino oligomer (PMO) mediated exon skipping therapies have been approved for several mutations but produce only a very modest amount of dystrophin in skeletal muscle, likely due to poor distribution to target tissues and a limited ability to escape the target cell endosome. To overcome limitations of unconjugated PMOs, we designed a family of proprietary cyclic cell-penetrating peptides that form the core of our endosomal escape vehicle (EEV™) technology. To evaluate our EEV in DMD, we administered an exon 23 splice modulating conjugate (EEV-PMO-23) to D2-mdx mice. These mice have been generated by backcrossing the spontaneous DMDmdx mice on to the DBA/2J background thereby producing a severe DMD phenotype. Four monthly intravenous (IV) doses of EEV-PMO-23 resulted in enhanced exon skipping, broad dystrophin expression, and restoration of muscle integrity in both skeletal and cardiac muscle. Significant improvement in muscle function (wire hang and grip strength) were also observed and creatine kinase levels were corrected to wild-type levels. These results illustrate significant therapeutic potential of the EEV-PMO delivery system for the treatment of DMD. Based on these findings, we examined the therapeutic potential of a DMD exon 44 splice modulating EEV-PMO (ENTR-601-44). Single IV doses of ENTR-601-44 led to dose-dependent exon skipping in cardiac and skeletal muscle in human dystrophin-expressing (hDMD) mice. Additionally, ENTR-601-44 demonstrated robust exon skipping in skeletal muscle and the heart of nonhuman primates. Together, these findings suggest potential for further study of ENTR-601-44 in patients with DMD amenable to exon 44 skipping.