Angiopoietin 1 (ANG-1) and ANG-2, two growth factors that regulate angiogenesis by a complex signaling system involving two tunica interna endothelial (TIE) receptor tyrosine kinases, TIE1 and TIE2. The two angiopoietins are expressed in different locations: ANG-1, in perivascular cells, and ANG-2 in endothelial cells. Both bind TIE2, stimulating the maturation and stabilization of blood vessels. ANG-2, however, which is upregulated in many human cancers, binds to TIE2 less strongly than to ANG-1. Blocking ANG2-TIE2 signaling in mice with a conditional loss of TIE1 function (gene knockouts of TIE1, TIE2 or ANG-1 are embryonically lethal) led to a pronounced anti-tumor effect, which was not repeated when VEGF was inhibited.
Sheridan C. Amgen's angiopoietin blocker fails in ovarian cancer[J]. 2015.