Fig. 5.

The endothelial Dll4 over expression effects on RT2 insulinoma kinetics and vascular response. Dll4 over-expression in endothelial cells was induced in 9.5-week old RT2 Tie2-rtTA TetO7-Dll4 mice, maintained for 4 weeks by doxycycline p.o. application and assessed as a potential therapeutic strategy in comparison with non-induced RT2 Tie2-rtTA TetO7-Dll4 littermates. Increased endothelial Dll4 expression was demonstrated to be a powerful tumor-suppressor intervention in RT2 mice recapitulating the vascular phenotype previously observed in grafted and autochthonous skin tumors. a Number of tumors per mouse, mean tumor volume (b) and over-all tumor burden per mouse (c), calculated as the sum of tumor volumes developed by a mouse, in 13.5-week old RT2 D4BE vs. RT2 D4OE mice. d Double immunostaining to PECAM/SMA indicating reduced microvessel density (e) and increased mural cell recruitment (f) in RT2 D4OE vs. RT2 D4BE insulinomas (left). g Vascular functionality was examined by mouse lectin perfusion. Simultaneous immunostaining to PECAM and biotinylated lectin visualization with Streptavidin-Alexa 488 demonstrate increased portion of perfused vessels in RT2 D4OE vs. RT2 D4BE tumors (h). Percentage of PECAM-positive area co-localized with lectin signals was measured to quantify the portion of competent vessels within pancreatic tumors (h). The images presented in panels D and G were captured and processed as described in Fig. 1. Error bars represent SEM. *, P < 0.05 was considered statistically significant. Results are representative of n = 10 per mice group