Blockade of specific NOTCH ligands: a new promising approach in cancer therapy.

SUMMARY: The signaling specificity conveyed by distinct combination of NOTCH receptors/ligands has remained elusive. In this issue of Cancer Discovery, through the development of ligand-specific NOTCH inhibitors, Kangsamaksin and colleagues uncovered unique signaling outcomes downstream of DLL- and JAG-receptor activation and demonstrated their effects in the suppression of tumor angiogenesis.

NOTCH decoys that selectively block DLL/NOTCH or JAG/NOTCH disrupt angiogenesis by unique mechanisms to inhibit tumor growth.

UNLABELLED: A proangiogenic role for Jagged (JAG)-dependent activation of NOTCH signaling in the endothelium has yet to be described. Using proteins that encoded different NOTCH1 EGF-like repeats, we identified unique regions of Delta-like ligand (DLL)-class and JAG-class ligand-receptor interactions, and developed NOTCH decoys that function as ligand-specific NOTCH inhibitors. N110-24 decoy blocked JAG1/JAG2-mediated NOTCH1 signaling, angiogenic sprouting in vitro, and retinal angiogenesis, demonstrating that JAG-dependent NOTCH signal activation promotes angiogenesis. In tumors, N110-24 decoy reduced angiogenic sprouting, vessel perfusion, pericyte coverage, and tumor growth. JAG-NOTCH signaling uniquely inhibited expression of antiangiogenic soluble (s) VEGFR1/sFLT1. N11-13 decoy interfered with DLL1-DLL4-mediated NOTCH1 signaling and caused endothelial hypersprouting in vitro, in retinal angiogenesis, and in tumors. Thus, blockade of JAG- or DLL-mediated NOTCH signaling inhibits angiogenesis by distinct mechanisms. JAG-NOTCH signaling positively regulates angiogenesis by suppressing sVEGFR1-sFLT1 and promoting mural-endothelial cell interactions. Blockade of JAG-class ligands represents a novel, viable therapeutic approach to block tumor angiogenesis and growth. SIGNIFICANCE: This is the first report identifying unique regions of the NOTCH1 extracellular domain that interact with JAG-class and DLL-class ligands. Using this knowledge, we developed therapeutic agents that block JAG-dependent NOTCH signaling and demonstrate for the first time that JAG blockade inhibits experimental tumor growth by targeting tumor angiogenesis.