Requisite endothelial reactivation and effective siRNA nanoparticle targeting of Etv2/Er71 in tumor angiogenesis.

Ashraf Ul Kabir,Lihua Yang,Samantha Hamilton,Karen Krchma,Robert P Mecham,Hua Pan,Tae-Jin Lee,Kyunghee Choi,Jun Wu,Hee-Kyoung Kang,Kristina Hinman,Samuel A Wickline,Deborah J Veis,Jeffrey C Berry,Mark J Miller,Qingyu Zhou,Fang Liu

doi:10.1172/jci.insight.97349

Abstract

Angiogenesis, new blood vessel formation from preexisting vessels, is critical for solid tumor growth. As such, there have been efforts to inhibit angiogenesis as a means to obstruct tumor growth. However, antiangiogenic therapy faces major challenges to the selective targeting of tumor-associated-vessels, as current antiangiogenic targets also disrupt steady-state vessels. Here, we demonstrate that the developmentally critical transcription factor Etv2 is selectively upregulated in both human and mouse tumor-associated endothelial cells (TAECs) and is required for tumor angiogenesis. Two-photon imaging revealed that Etv2-deficient tumor-associated vasculature remained similar to that of steady-state vessels. Etv2-deficient TAECs displayed decreased Flk1 (also known as Vegfr2) expression, FLK1 activation, and proliferation. Endothelial tube formation, proliferation, and sprouting response to VEGF, but not to FGF2, was reduced in Etv2-deficient ECs. ROS activated Etv2 expression in ECs, and ROS blockade inhibited Etv2 expression in TAECs in vivo. Systemic administration of Etv2 siRNA nanoparticles potently inhibited tumor growth and angiogenesis without cardiovascular side effects. These studies highlight a link among vascular oxidative stress, Etv2 expression, and VEGF response that is critical for tumor angiogenesis. Targeting the ETV2 pathway might offer a unique opportunity for more selective antiangiogenic therapies.

Highlights

Angiogenesis is an important process for successful embryogenesis, postinjury tissue repair and regeneration, and progression of many pathologic conditions, including cancer
As Etv2 was required for endothelial cells (ECs) undergoing active angiogenesis [32], we assessed whether Etv2 plays a role in tumor angiogenesis
Since tumor cells and ECs in nonmalignant vessels do not express Etv2 (Figure 1, A–D, and Supplemental Figure 1A), we conclude that Etv2 expression is induced in tumor-associated endothelial cells (TAECs)

Summary

Introduction

Angiogenesis is an important process for successful embryogenesis, postinjury tissue repair and regeneration, and progression of many pathologic conditions, including cancer. Anti-VEGF therapies, considered to be most prevalent in inhibiting tumor angiogenesis, have severe shortcomings in targeting tumor-associated vessels undergoing neoangiogenesis [4, 5], as VEGF is required for physiological steady-state vessels [6, 7]. Considering these limitations, it would be crucial to identify molecular marker(s) and signaling pathways uniquely functioning in tumor-associated vessels that can be exclusively targeted.

Methods

Results

Conclusion