A Placental Growth Factor Variant Unable to Recognize VEGFR-1 Inhibits VEGF-Dependent Angiogenesis via Heterodimerization

Abstract

Purpose: : Two members of VEGF family, VEGF-A and PlGF, which are able to heterodimerize if co-expressed in the same cell, are both required for pathological angiogenesis. Here we report that co-expression of the PlGF-DE variant (D72-A, E73-A), unable to bind VEGFR-1 but still able to heterodimerize with VEGF, in tumor cells, strongly inhibits VEGF-dependent angiogenesis. Due to the main role of VEGF in choroidal neovascularization (CNV), gene therapy approach with PlGF-DE in experimental CNV model will be evaluated.

Methods: : Intratumoral injection of AdV-PlGF-DE (MOI 10:1) has been performed in xenograft tumors generated in nude mice with human lung and ovarian carcinoma cell lines. IHC analysis for vessel density, vessel stabilization and monocyte-macrophage infiltration were performed with anti -CD31, -SMA, and -F4/80 antibodies. Adeno-Associated viruses expressing PlGF-DE, and as control, PlGF wild type or LacZ (serotype 2) have been generated. CNV will be induced by laser injury, AAV delivered by sub-retinal injection, and volumes measured 7 days later by confocal evaluation of Isolectin B4 staining of RPE-choroid flat mounts.

Results: : Intratumoral injection of AdV-PlGF-DE (MOI 10:1) strongly reduced tumor growth (75%) and neoangiogenesis (71%). The over-expression of PlGF-DE induced a significant reduction of large vessels, vessel stabilization and monocyte-macrophage infiltration. The effects of AAV-PlGF-DE delivery in laser-induced CNV model will be presented.

Conclusions: : Data obtained with ADV-PlGF-DE in tumor angiogenesis strongly indicate that the property of VEGF and PlGF to generate heterodimer may represent a successful strategy to reduce the VEGF-driven angiogenesis by inhibiting the production of active VEGF homodimer via heterodimerization mechanism. These results suggest that the PlGF-DE variant may be a candidate for gene therapy in CNV.

Keywords: choroid: neovascularization • vascular endothelial growth factor • gene transfer/gene therapy