Angiopoietin-2 Interferes with Anti-VEGFR2–Induced Vessel Normalization and Survival Benefit in Mice Bearing Gliomas

Abstract

Purpose: In brain tumors, cerebral edema is a significant source of morbidity and mortality. Recent studies have shown that inhibition of vascular endothelial growth factor (VEGF) signaling induces transient vascular normalization and reduces cerebral edema, resulting in a modest survival benefit in glioblastoma patients. During anti-VEGF treatment, circulating levels of angiopoietin (Ang)-2 remained high after an initial minor reduction. It is not known, however, whether Ang-2 can modulate anti-VEGF treatment of glioblastoma. Here, we used an orthotopic glioma model to test the hypothesis that Ang-2 is an additional target for improving the efficacy of current anti-VEGF therapies in glioma patients. Experimental Design: To recapitulate high levels of Ang-2 in glioblastoma patients during anti-VEGF treatment, Ang-2 was ectopically expressed in U87 glioma cells. Animal survival and tumor growth were assessed to determine the effects of Ang-2 and anti–VEGF receptor 2 (VEGFR2) treatment. We also monitored morphologic and functional vascular changes using multiphoton laser scanning microscopy and immunohistochemistry. Results: Ectopic expression of Ang-2 had no effect on vascular permeability, tumor growth, or survival, although it resulted in higher vascular density, with dilated vessels and reduced mural cell coverage. On the other hand, when combined with anti-VEGFR2 treatment, Ang-2 destabilized vessels without affecting vessel regression and compromised the survival benefit of VEGFR2 inhibition by increasing vascular permeability. VEGFR2 inhibition normalized tumor vasculature whereas ectopic expression of Ang-2 diminished the beneficial effects of VEGFR2 blockade by inhibiting vessel normalization. Conclusion: Cancer treatment regimens combining anti-VEGF and anti-Ang-2 agents may be an effective strategy to improve the efficacy of current anti-VEGF therapies. Clin Cancer Res; 16(14); 3618–27. ©2010 AACR.

Dual inhibition of Ang-2 and VEGF receptors normalizes tumor vasculature and prolongs survival in glioblastoma by altering macrophages

“…We treated mice bearing orthotopic Gl261 or U87 tumors with control IgG, MEDI3617, cediranib, or cediranib+MEDI3617 dual therapy. Consistent with our previous experience in GBM (10,11,27), treatment with cediranib alone significantly increased survival of Gl261-bearing mice compared with control (median 24 d vs. 20 d). MEDI3617 treatment also increased median survival (24 d).…”

“…In both clinical and preclinical GBM studies, Ang-2 levels decline temporarily following inhibition of the VEGF pathway but later rebound as tumors become resistant to therapy (10,12). We have shown that ectopic expression of Ang-2 in a GBM animal model compromised the survival benefit of VEGF-signaling inhibition by impairing vessel normalization and edema control (27). Moreover, tumor autopsy tissues from rGBM patients treated with anti-VEGF therapy showed abnormally high levels of Ang-2 (28), and the Ang-1/Ang-2 ratio correlated positively with survival (29) and vascular normalization (12).…”

Improved tumor oxygenation and survival in glioblastoma patients who show increased blood perfusion after cediranib and chemoradiation

“…Preclinical and clinical studies in a number of solid tumors, including recurrent GBM (rGBM), have demonstrated that after the administration of antiangiogenic therapies a subset of rGBM patients experience a transient period of vascular normalization characterized by increased perfusion, reduced vessel diameter and permeability, specific circulating biomarker changes, reduction in tumor interstitial pressure, and improved tumor oxygenation (10)(11)(12)(13)(14)(15)(16). These parameters can be used to generate a "vascular normalization index" to help identify rGBM patients most likely to benefit from antiangiogenic therapy (17,18).…”

Vascular Normalization as a Therapeutic Strategy for Malignant and Nonmalignant Disease

“…Preclinical studies have used a number of approaches including (1) specific VEGF blockade with agents that interfere with VEGF binding to its receptors (including antihuman VEGF antibodies such as A4.6.1 and bevacizumab), antimurine VEGF antibodies, and the "VEGF-Trap" aflibercept; (2) inhibition of VEGFR2 function (using anti-VEGFR2 antibodies such as DC101 or receptor tyrosine kinase inhibitors [TKIs] which inhibit the kinase domain of VEGFRs). In addition, elegant preclinical work examining the role of Yuan et al 1996;Tong et al 2004;Dickson et al 2007b;Taguchi et al 2008;Falcon et al 2009;Juan et al 2009;Kamoun et al 2009;Chae et al 2010;Koh et al 2010;Primo et al 2010. b Jain et al 1998;Izumi et al 2002;Delmas et al 2003;Qayum et al 2009. d Inai et al 2004;Tong et al 2004;Nakahara et al 2006;Dickson et al 2007b;Dings et al 2007;Fischer et al 2007;Zhou et al 2008;Falcon et al 2009;Juan et al 2009;Kamoun et al 2009;Ohta et al 2009;Zhou and Gallo 2009;Chae et al 2010;Primo et al 2010.…”

“…In addition, elegant preclinical work examining the role of Yuan et al 1996;Tong et al 2004;Dickson et al 2007b;Taguchi et al 2008;Falcon et al 2009;Juan et al 2009;Kamoun et al 2009;Chae et al 2010;Koh et al 2010;Primo et al 2010. b Jain et al 1998;Izumi et al 2002;Delmas et al 2003;Qayum et al 2009. d Inai et al 2004;Tong et al 2004;Nakahara et al 2006;Dickson et al 2007b;Dings et al 2007;Fischer et al 2007;Zhou et al 2008;Falcon et al 2009;Juan et al 2009;Kamoun et al 2009;Ohta et al 2009;Zhou and Gallo 2009;Chae et al 2010;Primo et al 2010. Lee et al 2000;Winkler et al 2004;Dings et al 2007;Fischer et al 2007;Eichhorn et al 2008;Batra et al 2009;Skuli et al 2009;McGee et al 2010.…”