Abstract 3279: Effects of the isoforms of the angiogenic growth factor VEGF on neo-vascularization and tumor response to the tyrosine kinase inhibitor cediranib
Authors: Daniel Rachel A. , Fisher Matthew , Flores-Merino Miriam V. , Battaglia Giuseppe , Ryan Anderson J. , Blakey David C. , Tozer Gillian M. 
Published: June 2012

Functional vasculature is required to supply tissues with oxygen and metabolic needs. A complex network of angiogenic growth factors directs blood vessel growth and maturation. This work investigated the role of VEGF-A isoforms in the mechanism of action of the pan-VEGF receptor inhibitor cediranib, currently in clinical trials.

Recombinant VEGF-A isoforms (VEGF120, 164, 189) were encapsulated in polyvinylpyrrolidone (PVP) hydrogel and effects on blood vessel development were determined using dorsal skin-fold window chambers surgically implanted into SCID mice. Intravital microscopy was used to monitor vasculature in vivo. In separate experiments, mouse fibrosarcoma cell lines expressing individual mouse VEGF-A isoforms (120, 164, 188) or all three isoforms (WT) were implanted into window chambers, and mice treated with cediranib (6 mg/kg/day p.o.) or vehicle for 4 days. Mice bearing single VEGF-A isoform-expressing subcutaneous tumors were treated with cediranib/vehicle once daily, as above, but continuing until tumors reached 15mm diameter in one dimension or a mean of 12.5mm. Pericyte (α-SMA, PDGFRβ) and endothelial cell (PECAM) marker expression were determined by real time PCR.

A reversible vascular ‘blurriness’ (VEGF189&lt;VEGF164&lt;VEGF120), indicative of edema, occurred 1 day after hydrogel implant. VEGF164 increased neovascular development immediately adjacent to implants whilst VEGF120 stimulated vascular extension/widening at a distance from hydrogels within the window chamber tissue area. VEGF120 and VEGF189 tended to increase vessel tortuosity. In the fibrosarcoma window chamber experiments, cediranib had little effect on VEGF188-driven tumor vasculature except a transient reduction in vessel width up to 6 h after the first dose. PCR data showed VEGF188-induced vasculature was associated with higher levels of pericyte marker expression than vessels from VEGF120-driven tumors although pericyte marker expression increased in both tumor types with cediranib treatment. WT and VEGF120-induced vessels appeared smoother and wider after cediranib treatment in the window chamber with the greatest growth-inhibition being seen with VEGF120-expressing subcutaneous tumors.

Our preliminary results support the hypothesis that VEGF188/9 promotes development of more mature vessels insensitive to vascular pruning by VEGFR signalling inhibition, whereas VEGF120 promotes the formation of more immature vessels susceptible to vascular pruning. Our data suggest that vascular responsiveness to cediranib treatment may decrease as pericyte coverage increases.

Funding: BBSRC/AstraZeneca

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3279. doi:10.1158/1538-7445.AM2011-3279