High throughput screening for modulators of ACVR1 transcription potentially applicable to the treatment of Fibrodysplasia Ossificans Progressiva

Abstract

ACVR1 gene encodes a type I receptor of Bone Morphogenetic Proteins (BMPs). Activating mutations in ACVR1 are responsible for Fibrodysplasia Ossificans Progressiva (FOP), a rare disease characterized by congenital toe malformation and progressive heterotopic endochondral ossification leading to severe and cumulative disability. Until now, no therapy is available to prevent soft tissue swelling (flare ups) that trigger the ossification process. With the aim to find a new therapeutic strategy for FOP, we developed a High Throughput Screening (HTS) assay to identify inhibitors of ACVR1 gene expression among drugs already approved for the therapy of other diseases. The screening, based on an ACVR1 promoter assay, was followed by in vitro and in vivo test to validate and characterize candidate molecules. Among compounds that modulate the ACVR1 promoter activity, we selected the one showing highest inhibitory effect, dipyridamole, a drug that is currently used as platelet anti-aggregant. The inhibitory effect was detectable on ACVR1 gene expression, on the whole Smad-dependent BMP signaling and on chondrogenic and osteogenic differentiation processes by in vitro cellular assays. Moreover, dipyridamole reduced the process of heterotopic bone formation in vivo. Our drug repositioning strategy has led to the identification of dipyridamole as a possible therapeutic tool for the treatment of FOP. Furthermore, our study has also defined a pipeline of assays that will be useful for the evaluation of other pharmacological inhibitors of heterotopic ossification.