Abstract LB-311: Inhibition of angiopoietin and Dll4 signaling in the tumor vasculature leads to increased efficacy in mouse tumor xenograft models
Authors: Coxon Angela , Kaplan-Lefko Paula , Kaufman Stephen , Moriguchi Jodi , Sun Jan , Ziegler Beth , Wayne William , Estrada Juan , Lavallee Jenni , Park Cindy , Arora Taruna , Burgess Teresa , Jun Toni 
Published: August 2012

Abstract
Inhibition of angiogenesis is a proven cancer treatment strategy as an adequate blood supply is critical for tumor growth. Two of the key pathways regulating tumor angiogenesis are angiopoietin/Tie2 and Dll4/Notch. Inhibition of the angiopoietin/Tie2 pathway has been shown to reduce blood vessel density and inhibit tumor growth in mouse xenograft models. Inhibition of Dll4 also prevents tumor xenograft growth but does so by promoting a non-productive vascular network via excessive endothelial branching and sprouting. In this study, we examined the effects of combined inhibition of these pathways in models of angiogenesis and tumor growth. To inhibit the angiopoietin pathway we used AMG 386, a selective angiopoietin 1/2-neutralizing peptibody that prevents the interaction between these two angiopoietins and the Tie2 receptor. To inhibit Dll4 we used a neutralizing monoclonal antibody. The combination of AMG 386 and anti-Dll4 led to enhanced antitumor activity compared with either agent alone in four xenograft models (U-87 glioma, Calu-6 lung, Colo205 colorectal and MiaPaca pancreatic tumors). All treatments were well tolerated and no weight loss was observed. Histological analysis of U-87 tumors following one week of treatment revealed an increase in vessel area with anti-Dll4 alone and the combined treatment with AMG 386 showed a similar increase. At these same doses, AMG 386 reduced anti-Dll4-induced tumor associated endothelial cell proliferation following 24 hours of treatment. We also examined AMG 386/anti-Dll4 treatment in models of angiogenesis. In the rat cornea, individual anti-Dll4 and AMG 386 treatment had distinct morphological effects on VEGF-induced vessel formation. Vessel number and area were decreased following AMG 386 treatment, whereas vessel cross-branching and terminal tufting were observed following anti-Dll4 treatment. After combined treatment, vessels were truncated but the branching/tufting phenotype was preserved. Similar effects were seen in the mouse neonatal retina, where AMG 386 and anti-Dll4 treatment alone resulted in the expected distinct vascular phenotypes; AMG 386 treatment reduced vessel density and inhibited radial expansion, while anti-Dll4 treatment resulted in marked branching and thickening, and showed full radial expansion. In this model, combined treatment led to clear evidence of both mechanisms of action: increased branching and reduced radial expansion were observed in all retinas examined. Taken together, these data suggest that combined inhibition of the angiopoietin/Tie2 and Dll4/Notch pathways does not interfere with their individual mechanisms of action and furthermore, leads to enhanced efficacy in preclinical models. Therefore, the combination of these agents may have the potential to provide an expanded therapeutic opportunity to inhibit tumor angiogenesis beyond either individual agent alone.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-311. doi:1538-7445.AM2012-LB-311