The bone morphogenetic protein (BMP) signaling pathway has essential functions in

The bone morphogenetic protein (BMP) signaling pathway has essential functions in development, homeostasis, and in the normal and pathophysiologic remodeling of tissues. and type II receptors, although there is considerable functional redundancy among ligands and receptors (5). Biological context is provided by the spatiotemporally regulated expression of ligands and their cognate receptors in target tissues (6). The diversity of upstream ligand and receptors signals, and their pleiotropic downstream effects raises questions of how specificity is recognized and translated into biological 118288-08-7 supplier outcome in this pathway (7). Targeting individual ligands and receptors by genetic epistasis has yielded important insights into function, but their interpretation is limited again by redundancy as well as embryonic effects. Pharmacologic strategies for modulating BMP and TGF- signaling have emerged as a promising strategy for elucidating function and specificity in these pathways. These strategies include small molecule kinase inhibitors and recombinant protein ligand-traps (3). A common challenge to the development of selective ATP competitive small molecule kinase inhibitors is the structural homology of highly conserved ATP binding domains (8). Structural homology is particularly high between the type I receptors of the BMP and TGF- signaling pathways. For example, the ALK3 kinase domain possesses 66% SLC39A6 sequence identity with that of ALK5 (9). Even greater kinase domain sequence identity is found between homologues within the BMP 118288-08-7 supplier or TGF- families, such as ALK1 and ALK2 (79%), ALK3 and ALK6 (86%), and ALK4 and ALK5 (90%). The high degree of structural homology between receptors poses serious challenges for the development of highly selective small molecules that can discriminate between the individual members of the TGF- or BMP receptor families. Highly selective inhibitors could be useful 118288-08-7 supplier as therapeutics for diseases mediated by inappropriate signaling of an individual type I receptor, exemplified best by fibrodysplasia ossificans progressiva (FOP), an extremely rare genetic disease with a worldwide prevalence of 1 1 in 2 million (10). FOP manifests generally within the first decade of life with episodic soft tissue lesions that progress to ectopic endochrondral bone within skeletal muscles, ligaments and fascia, resulting in severely impaired mobility and shortened life expectancy (11). The majority of FOP cases are caused by a highly conserved missense mutation in encoding the BMP type I receptor ALK2 (c.617G>A; p.R206H) (10). Crystal structures of ALK2 have revealed that FOP mutations affecting the glycine-serine (GS-) rich regulatory domain disrupt stabilizing interactions with the regulatory protein FKBP12, rendering the kinase constitutively active with inappropriate downstream signaling.(12, 13) Possessing a constitutively-active intracellular kinase, ALK2R206H is unlikely to be affected by endogenous antagonists of BMP signaling such as chordin or noggin, which sequester BMP ligands, or 118288-08-7 supplier similar ligand-traps. ALK2R206H thus represents an ideal therapeutic target for a highly selective small molecule kinase inhibitor as a treatment for FOP. We previously described the identification of a small molecule BMP inhibitor, dorsomorphin, and the development of a highly potent derivative, LDN-193189, based on the same pyrazolo[1,5-a]pyrimidine core structure (14, 15). LDN-193189 reduced heterotopic ossification (HO) in a 118288-08-7 supplier mouse model of FOP with an inducible constitutively active mutant ALK2Q207D (caALK2) transgene (16). LDN-193189 is a potent inhibitor of BMP signaling, but exhibits TGF- receptor inhibition at higher concentrations. Previously well-described small molecule inhibitors of the TGF- type I receptor kinases, such as A-83-01 and SB-505124, have both high potency and high ( 3 log) selectivity for TGF- versus BMP signaling (17, 18). While TGF- signaling inhibitors had potential utility as therapeutic agents, preclinical animal studies have associated the administration of highly potent ALK5 inhibitors with bone physeal abnormalities in immature animals, and hemorrhagic necrosis of heart valves in adult animals (19, 20). Clinically.