Efficient Downregulation of in Skeletal Muscle After Systemic Treatment with Conjugated siRNAs in a Mouse Model for Duchenne Muscular Dystrophy.

Downregulation of genes involved in the secondary pathology of Duchenne muscular dystrophy, for example, inflammation, fibrosis, and adiposis, is an interesting approach to ameliorate degeneration of muscle and replacement by fibrotic and adiposis tissue. Small interfering RNAs (siRNAs) are able to downregulate target genes, however, delivery of siRNAs to skeletal muscle still remains a challenge. We investigated delivery of fully chemically modified, cholesterol-conjugated siRNAs targeting , a nontherapeutic target that is expressed highly in muscle. We observed that a single intravenous or intraperitoneal (IP) injection of 10 mg/kg resulted in significant downregulation of mRNA expression in skeletal muscles in both wild-type and mice. Treatment with multiple IP injections of 10 mg/kg led to an overall reduction of expression, reaching significance in tibialis anterior (39.7% ± 6.2%), diaphragm (32.7% ± 5.8%), and liver (41.3% ± 29.9%) in mice. Doubling of the siRNA dose did not further increase mRNA silencing in muscles of mice. The chemically modified conjugated siRNAs used in this study are very promising for delivery to both nondystrophic and dystrophic muscles and could have major implications for treatment of muscular dystrophy pathology.