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 3

Reduction in intensity of VEGFR-2 immunofluorescence in RIP-Tag2 tumor vessels after AG-013736 treatment (i.p. injection) for 7 days and during vascular regrowth.

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Reduction in intensity of VEGFR-2 immunofluorescence in RIP-Tag2 tumor v...
Fluorescence micrographs comparing the intense VEGFR-2 immunofluorescence and high vascular density in an untreated tumor (A) with the faint VEGFR-2 immunofluorescence and sparse vasculature in a tumor after 7 days of AG-013736 treatment (B). (C) At 7 days after the treatment ended, both VEGFR-2 immunofluorescence and vascular density returned to baseline. (D–F) Changes in height of peaks in surface plots illustrate the reduction in VEGFR-2 immunofluorescence after 7-day treatment and rebound 7 days thereafter (F). (G) Measurements of VEGFR-2 immunofluorescence show the magnitude of the changes. Comparison of VEGFR-2 immunofluorescence and area density of CD31-positive tumor vessels (both values expressed as percent of corresponding untreated baseline value) suggests that the increase in VEGFR-2 expression preceded the increase in vascular density. (H) Further experiments showed that a second round of AG-013736 reduced tumor vascularity as much as the first round, indicating that much of the regrown tumor vasculature was VEGF dependent. *P < 0.05 compared with corresponding baseline value. †P < 0.05, CD31 compared with VEGFR-2. Scale bar: 60 μm (A–C).