Compound KTI-2338 Inhibits ACVR1 Receptor Signaling in Fibrodysplasia Ossificans Progressiva

Background/Objectives: Fibrodysplasia Ossificans Progressiva (FOP) is a rare genetic bone disorder, leading to progressive immobilization through the formation of bone in muscles, tendons, and ligaments. A variant in the ACVR1 gene results in a constitutively overactive ALK2 receptor, leading to the aberrant activation of the SMAD1/5/9 pathway. This activation occurs not only in response to Activin A, which does not normally activate this pathway, but also through heightened sensitivity to BMP ligands and even in the absence of ligand binding. This dysregulated signaling ultimately drives the formation of heterotopic ossification. The inhibition of the altered ALK2 receptor holds promise as a potential treatment strategy that is currently being investigated in several trials. In this study, we performed an in vitro characterization of novel kinase inhibitor KTI-2338 with high selectivity for the ALK2 receptor. Methods: Dermal human FOP and control fibroblasts were cultured in osteogenic medium with and without the inhibitor to assess the effect on transdifferentiation into osteoblast-like cells. Results: Compound KTI-2338 elicited effects consistent with inhibiting aberrant Activin A signaling and receptor sensitization, through reductions in osteogenic markers and pSMAD1/5/9 expression levels. In line with this, a pattern of reduced Alizarin Red staining was observed following treatment with the compound, indicating reduced mineralization. Conclusions: These findings indicate that kinase inhibitor KTI-2338 disrupts the pathological processes underlying FOP and may offer a new therapeutic option for this devastating disease.