Abstract 3634: Selective targeting of tumor-associated angiogenic tip and stalk cells with immunoliposomes (ILs) directed against VEGFR-2 and VEGFR-3 expressing cells
Authors: Wicki Andreas , Rochlitz Christoph , Orleth Annette , Ritschard Reto , Alitalo Kari , Herrmann Richard , Christofori Gerhard , Mamot Christoph 
Published: June 2012

Abstract
Angiogenesis is a key process in tumor progression. Angiogenic sprouting involves specification of subpopulations of endothelial cells into tip cells that respond to vascular endothelial growth factor (VEGF) guidance cues, and stalk cells that proliferate to form the vascular network. While angiogenic stalk cells mainly express VEGFR-2, the tip cells express VEGFR-3. Up to now, therapeutic approaches have mainly been aimed against VEGFR-2 activity. Bevacizumab, a monoclonal antibody against VEGF-A, has been used with some success in different treatment regimens of metastatic bowel and breast cancer. However, it remains unclear to which extend VEGFR-2 expressing stalk and VEGFR-3 expressing tip cells contribute to tumor-associated angiogenesis in vivo. While anti-VEGF-A antibodies inhibit angiogenesis by blocking VEGFR-2 expressing stalk cells, they do not interfere with VEGFR-3 signalling.
Until recently, it was not possible to directly target different populations of endothelial cells involved in neoangiogenesis. This has changed since new technologies based on liposomes allow for the transport of pharmacological compounds to selected cells in vivo. In our lab we have established a method of transportation based on immunoliposomes (ILs), i.e., liposomes coated with antibodies directed against cell surface antigens. DC101 anti-mouse VEGFR-2 and AFL4 anti-mouse VEGFR-3 antibodies were utilized to target liposomes to VEGFR-2 or -3 expressing endothelial cells in vivo. Using this technology, we are able to selectively deplete VEGFR-2 or VEGFR-3 expressing cells from the angiogenic endothelial cell pool and thereby study the functional role of these cell populations.
In this study we have investigated doxorubicin-containing ILs coated with anti-VEGFR-2 or anti-VEGFR-3 antibodies in two transgenic mouse models (the Rip1Tag2 model of human insulinoma and the MMTV-PyMT model of human breast cancer) and one xenograft model (the human colon cancer cell line HT29 in nude mice). In all three models, doxorubicin-containing ILs against VEGFR-2- or VEGFR-3-positive cells were effective in suppressing tumor growth. Both were more powerful than untargeted liposomes containing the same dose of doxorubicin. Combined anti-VEGFR-2 and -3 therapy was significantly more potent than targeting anti-VEGFR-2 expressing endothelial cells alone. In the Rip1Tag2 model, tumor burden after 2 weeks of therapy was 14.4 ± 7.9 mm3 (mean ± standard deviation) in the empty liposome group, 5.4 ± 4.7 mm3 in the untargeted liposomal doxorubicin group, 2.1 ± 2.5 mm3 in the anti-VEGFR-2 ILs group, 1.1 ± 1.5 mm3 in the anti-VEGFR-3 ILs and 0.3 ± 0.4 mm3 in the combined anti-VEGFR-2 and -3 ILs group. Thus, delivery of cytotoxic drugs to different angiogenic tumor-associated cells is feasible and may be more promising than focusing on a single entity of endothelial cells.
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 3634. doi:10.1158/1538-7445.AM2011-3634