ldn-193189 and Myositis-Ossificans

Fibrodysplasia ossificans progressiva (FOP) is a rare autosomal dominant disorder characterized by progressive heterotopic bone formation in skeletal muscle tissue. In 2007, FOP was authorized as one of the Intractable Disorders by the Ministry of Health, Labour and Welfare of Japan. The Research Committee on FOP is working on the molecular mechanisms underlying heterotopic bone formation and the development of new treatments for FOP.

Topics: Activin Receptors, Type I; Bone Morphogenetic Proteins; Drug Discovery; Genes, Dominant; Humans; Molecular Targeted Therapy; Mutation; Myositis Ossificans; Pyrazoles; Pyrimidines; Signal Transduction; Transforming Growth Factor beta

There are currently no effective therapies for fibrodysplasia ossificans progressiva (FOP), a debilitating and progressive heterotopic ossification disease caused by activating mutations of ACVR1 encoding the BMP type I receptor kinase ALK2. Recently, a subset of these same mutations of ACVR1 have been identified in diffuse intrinsic pontine glioma (DIPG) tumors. Here we describe the structure-activity relationship for a series of novel ALK2 inhibitors based on the 2-aminopyridine compound K02288. Several modifications increased potency in kinase, thermal shift, or cell-based assays of BMP signaling and transcription, as well as selectivity for ALK2 versus closely related BMP and TGF-β type I receptor kinases. Compounds in this series exhibited a wide range of in vitro cytotoxicity that was not correlated with potency or selectivity, suggesting mechanisms independent of BMP or TGF-β inhibition. The study also highlights a potent 2-methylpyridine derivative 10 (LDN-214117) with a high degree of selectivity for ALK2 and low cytotoxicity that could provide a template for preclinical development. Contrary to the notion that activating mutations of ALK2 might alter inhibitor efficacy due to potential conformational changes in the ATP-binding site, the compounds demonstrated consistent binding to a panel of mutant and wild-type ALK2 proteins. Thus, BMP inhibitors identified via activity against wild-type ALK2 signaling are likely to be of clinical relevance for the diverse ALK2 mutant proteins associated with FOP and DIPG.

Topics: Activin Receptors, Type I; Aminopyridines; Humans; Mutation; Myositis Ossificans; Phenols; Protein Kinase Inhibitors; Structure-Activity Relationship

Fibrodysplasia ossificans progressiva (FOP) is a rare congenital disorder characterized by progressive ossification of soft tissues. FOP is caused by mutations in activin receptor-like kinase 2 (ALK2) that cause its constitutive activation and result in dysregulation of BMP signaling. Here, we show that generation of induced pluripotent stem cells (iPSCs) from FOP-derived skin fibroblasts is repressed because of incomplete reprogramming and inhibition of iPSC maintenance. This repression was mostly overcome by specific suppression of ALK2 expression and treatment with an ALK2 inhibitor, indicating that the inhibition of iPSC generation and maintenance observed in FOP-derived skin fibroblasts results from constitutive activation of ALK2. Using this system, we identified an ALK2 inhibitor as a potential candidate for future drug development. This study highlights the potential of the inhibited production and maintenance of iPSCs seen in diseases as a useful phenotype not only for studying the molecular mechanisms underlying iPS reprogramming but also for identifying drug candidates for future therapies.

Topics: Activin Receptors, Type I; Animals; Cell Differentiation; Cell Lineage; Cells, Cultured; Coculture Techniques; Drug Evaluation, Preclinical; Enzyme Activation; Fibroblasts; Humans; Induced Pluripotent Stem Cells; Mice; Mutation, Missense; Myositis Ossificans; Phenotype; Protein Kinase Inhibitors; Pyrazoles; Pyrimidines; Signal Transduction; Skin; Transcriptome