Rapid vascular regrowth in tumors after reversal of VEGF inhibition
Michael R. Mancuso, … , Dana D. Hu-Lowe, Donald M. McDonald
Michael R. Mancuso, … , Dana D. Hu-Lowe, Donald M. McDonald
Published October 2, 2006
Citation Information: J Clin Invest. 2006;116(10):2610-2621. https://doi.org/10.1172/JCI24612.
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Research Article Oncology

Rapid vascular regrowth in tumors after reversal of VEGF inhibition

Abstract

Inhibitors of VEGF signaling can block angiogenesis and reduce tumor vascularity, but little is known about the reversibility of these changes after treatment ends. In the present study, regrowth of blood vessels in spontaneous RIP-Tag2 tumors and implanted Lewis lung carcinomas in mice was assessed after inhibition of VEGF receptor signaling by AG-013736 or AG-028262 for 7 days. Both agents caused loss of 50%–60% of tumor vasculature. Empty sleeves of basement membrane were left behind. Pericytes also survived but had less α–SMA immunoreactivity. One day after drug withdrawal, endothelial sprouts grew into empty sleeves of basement membrane. Vessel patency and connection to the bloodstream followed close behind. By 7 days, tumors were fully revascularized, and the pericyte phenotype returned to baseline. Importantly, the regrown vasculature regressed as much during a second treatment as it did in the first. Inhibition of MMPs or targeting of type IV collagen cryptic sites by antibody HUIV26 did not eliminate the sleeves or slow revascularization. These results suggest that empty sleeves of basement membrane and accompanying pericytes provide a scaffold for rapid revascularization of tumors after removal of anti-VEGF therapy and highlight their importance as potential targets in cancer therapy.

Authors

Michael R. Mancuso, Rachel Davis, Scott M. Norberg, Shaun O’Brien, Barbara Sennino, Tsutomu Nakahara, Virginia J. Yao, Tetsuichiro Inai, Peter Brooks, Bruce Freimark, David R. Shalinsky, Dana D. Hu-Lowe, Donald M. McDonald

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Figure 1

Regression and regrowth of tumor vessels after VEGF inhibition.

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Regression and regrowth of tumor vessels after VEGF inhibition. Confocal...
Confocal micrographs of RIP-Tag2 tumors compare the dense vascularity of an untreated tumor (A) with the sparse vascularity after AG-013736 treatment for 7 days (B). Tumor vessels that survived treatment had a more uniform caliber and less branching than those in untreated tumors. At 2 days after the treatment ended, vascular sprouts (C, arrows) marked the beginning of vascular regrowth. The projections from vessels were confirmed as sprouts by examining multiple optical sections in the stack of confocal images from the 80-μm-thick cryostat section. (D) By 7 days, normalized vessels were replaced by typical tumor vessels. Vascularity of Lewis lung carcinoma (E) was similarly reduced by AG-013736 treatment for 7 days (F). (G) By 7 days after the treatment, vascularity of Lewis lung carcinoma was back to baseline. Bar graphs illustrate changes in area density of CD31-positive vessels in RIP-Tag2 tumors (H) and Lewis lung carcinomas (I) after 7 days of treatment (0 days withdrawal) and after the treatment ended. Treatment reduced tumor vascularity in the 2 models by 61% and 50%, respectively. After AG-013736 treatment was stopped, tumor vascularity was back to baseline by 7 days but from day 7–14 did not increase beyond that present in untreated tumors (H). *P < 0.05 compared with the untreated group. Scale bar (applies to all images): 115 μm (A–D); 55 μm (E–G).