Abstract 5296: The role of VEGF receptors 1 and 2 on tumor vascularization and progression in single VEGF isoform expressing tumors

Abstract

Abstract Background Murine fibrosarcoma cell lines that express single VEGF isoforms (VEGF120 VEGF165 and VEGF188) and a wild-type control (VEGFWT) have been developed. The most extreme differences in vascular properties are observed between VEGF120 and VEGF188 tumors, with VEGF120 tumors developing more immature vessels. These differences impact on therapeutic outcome. We hypothesised that differential signaling through VEGF receptors 1 and 2 underlie the isoform-specific differences. Methods VEGFWT, VEGF120 and VEGF164 tumors were implanted sub-cutaneously (s/c), and VEGF188 tumors s/c or in dorsal skin-flap window-chambers (WC) in SCID mice. Mice were treated with ImClone neutralizing antibodies against VEGFR-1 (MF-1) or VEGFR-2 (DC101). Excised s/c tumors were stained for blood vessels (CD31), pericytes (αSMA), necrosis (H&E) or apoptosis (Caspase III). Tumor vascular development in WCs was imaged using intra-vital microscopy. Results VEGFWT and VEGF188 tumors were most sensitive to growth inhibition following treatment with DC101, whereas MF-1 had no effect on growth of any tumor type. In vitro, DC101 had no effect on proliferation of any tumor cell types. Immunohistochemical studies showed no changes in necrosis or apoptosis in VEGF120 tumors, but a significant decrease in vascular area with DC101. VEGF188 tumors showed no change in apoptosis, but both treatments increased necrosis. Vascular area was significantly reduced post DC101 treatment but significantly increased post MF-1 treatment. Both antibodies significantly increased αSMA staining, primarily due to myofibroblast infiltration. WC studies using VEGF188 tumors supported the effects observed with DC101, showing a significantly reduced blood vessel number and length. Furthermore, MF-1 treatment (either immediately post tumor implantation or to established tumors) resulted in more hemorrhagic tumors with large peripheral feeder vessels. Early DC101 treatment impaired tumor development, and once tumors developed on cessation of treatment, the vessels were highly chaotic. Conclusions DC101-induced tumor growth retardation, and corresponding vascular effects in VEGF188 tumors, confirms a role for VEGFR2 signaling in tumor progression and vascular development. However, the lack of growth effect in VEGF120 and VEGF164 tumors following treatment with either antibody suggests a level of receptor redundancy. MF-1 increased angiogenesis in VEGF188 tumors, despite no change in growth rate, and these neo-vessels appeared hemorrhagic, implying increased permeability. These data suggest a role for VEGFR-1 in tumor angiogenesis, involving vascular maturation, at least where VEGF188 is highly expressed. This may occur via specific VEGFR-1 signaling and/or sequestration of VEGF to control signaling via VEGFR-2. Acknowledgements Supported by CR-UK We thank ImClone Systems for providing MF-1 and DC101. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5296. doi:1538-7445.AM2012-5296