Inhibition of Dll4 signalling inhibits tumour growth by deregulating angiogenesis

Blood line VEGF, or vascular endothelial growth factor, is the best-characterized inducer of tumour angiogenesis, and the blockade of VEGF has become an important tool in cancer therapy. But VEGF blockade is not effective against all tumours, so the search for alternative approaches continues. Two groups this week report that one such alternative could be blockade of Dll4, Delta-like ligand 4. This transmembrane molecule is part of the Notch signalling pathway. It was known to be essential for normal development of blood vessels in the embryo: the new work shows that it is also required for tumour angiogenesis. It may be a viable — and potentially well tolerated — alternative in patients with solid tumours that are resistant to anti-VEGF therapy. One of two papers showing that inhibition of Dll4-mediated Notch signalling inhibits tumour growth by deregulation of tumour angiogenesis. Haploinsufficiency of Dll4, a vascular-specific Notch ligand, has shown that it is essential for embryonic vascular development and arteriogenesis 1 , 2 , 3 . Mechanistically, it is unclear how the Dll4-mediated Notch pathway contributes to complex vascular processes that demand meticulous coordination of multiple signalling pathways. Here we show that Dll4-mediated Notch signalling has a unique role in regulating endothelial cell proliferation and differentiation. Neutralizing Dll4 with a Dll4-selective antibody rendered endothelial cells hyperproliferative, and caused defective cell fate specification or differentiation both in vitro and in vivo . In addition, blocking Dll4 inhibited tumour growth in several tumour models. Remarkably, antibodies against Dll4 and antibodies against vascular endothelial growth factor (VEGF) had paradoxically distinct effects on tumour vasculature. Our data also indicate that Dll4-mediated Notch signalling is crucial during active vascularization, but less important for normal vessel maintenance. Furthermore, unlike blocking Notch signalling globally, neutralizing Dll4 had no discernable impact on intestinal goblet cell differentiation 4 , 5 , supporting the idea that Dll4-mediated Notch signalling is largely restricted to the vascular compartment. Therefore, targeting Dll4 might represent a broadly efficacious and well-tolerated approach for the treatment of solid tumours.