title: A small molecule targeting ALK1 prevents Notch cooperativity and inhibits functional angiogenesis.
abstract: Activin receptor-like kinase 1 (ALK1, encoded by the gene ACVRL1) is a type I BMP/TGF-β receptor that mediates signalling in endothelial cells via phosphorylation of SMAD1/5/8. During angiogenesis, sprouting endothelial cells specialise into tip cells and stalk cells. ALK1 synergises with Notch in stalk cells to induce expression of the Notch targets HEY1 and HEY2 and thereby represses tip cell formation and angiogenic sprouting. The ALK1-Fc soluble protein fusion has entered clinic trials as a therapeutic strategy to sequester the high-affinity extracellular ligand BMP9. Here, we determined the crystal structure of the ALK1 intracellular kinase domain and explored the effects of a small molecule kinase inhibitor K02288 on angiogenesis. K02288 inhibited BMP9-induced phosphorylation of SMAD1/5/8 in human umbilical vein endothelial cells to reduce both the SMAD and the Notch-dependent transcriptional responses. In endothelial sprouting assays, K02288 treatment induced a hypersprouting phenotype reminiscent of Notch inhibition. Furthermore, K02288 caused dysfunctional vessel formation in a chick chorioallantoic membrane assay of angiogenesis. Such activity may be advantageous for small molecule inhibitors currently in preclinical development for specific BMP gain of function conditions, including diffuse intrinsic pontine glioma and fibrodysplasia ossificans progressiva, as well as more generally for other applications in tumour biology.
authors.affiliation: Structural Genomics Consortium, University of Oxford, Old Road Campus Research Building, Roosevelt Drive, Headington, Oxford, OX3 7DQ, UK.
authors.forename: Georgina
authors.initials: G
authors.lastname: Kerr
authors.forename: Helen
authors.initials: H
authors.lastname: Sheldon
authors.forename: Apirat
authors.initials: A
authors.lastname: Chaikuad
authors.forename: Ivan
authors.initials: I
authors.lastname: Alfano
authors.forename: Frank
authors.initials: F
authors.lastname: von Delft
authors.forename: Alex N
authors.initials: AN
authors.lastname: Bullock
authors.forename: Adrian L
authors.initials: AL
authors.lastname: Harris
mesh_terms: D030301:Activin Receptors, Type II / Q000187:drug effects* / Q000378:metabolism; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D002642:Chick Embryo; D055427:Growth Differentiation Factor 2; D055412:Growth Differentiation Factors / Q000378:metabolism; D061307:Human Umbilical Vein Endothelial Cells; D006801:Humans; D018919:Neovascularization, Physiologic / Q000187:drug effects*; D010636:Phenols / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D051880:Receptors, Notch / Q000378:metabolism*
chemical_list: C584410:3-(6-amino-5-(3,4,5-trimethoxyphenyl)pyridin-3-yl)phenol; D000631:Aminopyridines; C525887:GDF2 protein, human; D055427:Growth Differentiation Factor 2; D055412:Growth Differentiation Factors; D010636:Phenols; D047428:Protein Kinase Inhibitors; D051880:Receptors, Notch; C425364:ACVRL1 protein, human; D030301:Activin Receptors, Type II