Soluble VEGF receptor 1 (sFLT1) induces non-apoptotic death in ovarian and colorectal cancer cells

In a previous study1,2,3,4, we developed a mouse model of preeclampsia by overexpressing placenta-specific human sFLT1 (hsFLT1). In these mice, only transduction of sFLT1 decreased placental weight. To study the relationship between rapidly growing cells and sFLT1 overexpression, we have focused here on the effect of sFLT1 on highly proliferative tumour cells. Vascular Endothelial Growth Factor (VEGF) and its soluble receptors are associated with endothelial dysfunction, vascular remodelling, and endothelial repair and regeneration mechanisms2,5,6,7. Soluble FLT1 is produced by a variety of tissues such as the placenta, endothelial cells and peripheral blood mononuclear cells8,9,10. Recently, several studies have demonstrated proliferative suppression by sFLT1 which caused apoptosis in an endothelial cell line11 and suppressed vascular development in the labyrinthine layer in a preeclampsia mouse model4. Moreover, systemic administration of AdV-sFLT1 led to reduced tumour growth, tumour vascularity, and ascites formation in ovarian cancer xenografts12,13. A monoclonal antibody to VEGF, bevacizumab, is now clinically used as an antiangiogenic therapeutic for ovarian cancer, colorectal cancer and others14,15,16. To the best of our knowledge, there is no literature clarifying the direct mechanism of cell injury by sFLT1. Previous reports11,12,13 have examined the secondary effects of anti-angiogenesis by sFLT1 in vivo. In the present study, we probed the mechanism of cell injury induced by sFLT1 by investigating the following four factors: 1) changes in cell morphology, 2) effects on cell proliferation signalling pathways, 3) effects on apoptosis, and 4) effects on non-apoptotic cell death. Furthermore, considering future therapies, we evaluated cytotoxicity in two ways: 1) transfection of LV-sFLT1 into cells, and 2) exogenous administration of rVEGFR1 to culture media of four cell lines (HEK293T, SKOV3, HeyA8 and HT-29). Finally, we investigated the anti-tumour effect of exogenous rVEGFR1, endogenous sFLT1, and bevacizumab using mice transplanted with SKOV3 cells.