Allele-Selective LNA Gapmers for the Treatment of Fibrodysplasia Ossificans Progressiva Knock Down the Pathogenic ACVR1 R206H Transcript and Inhibit Osteogenic Differentiation.

Fibrodysplasia ossificans progressiva (FOP) is a rare autosomal dominant disorder characterized by episodic heterotopic ossification. The median life span of people with this disorder is ∼40 years, and currently, there is no effective treatment available. More than 95% of cases are caused by a recurrent mutation (c.617G>A; R206H) of Activin A receptor, type I (ACVR1)/Activin receptor-like kinase-2 (ALK2), a bone morphogenetic protein type I receptor. The mutation renders ACVR1 responsive to activin A, which does not activate wild-type ACVR1. Ectopic activation of ACVR1 R206H by activin A induces heterotopic ossification. Since ACVR1 R206H is a hyperactive receptor, a promising therapeutic strategy is to decrease the activity of mutated ACVR1. To accomplish this goal, we developed locked nucleic acid (LNA) gapmers. These are short DNA oligonucleotides with LNA modification at both ends. They induce targeted mRNA degradation and specific knockdown of gene expression. We demonstrated that some of these gapmers efficiently knocked down ACVR1 R206H expression at RNA levels, while ACVR1 WT was mostly unaffected in human FOP fibroblasts. Also, the gapmers suppressed osteogenic differentiation induced by ACVR1 R206H and activin A. These gapmers may be promising drug candidates for FOP. This novel strategy will also pave the way for antisense-mediated therapy of other autosomal dominant disorders.