Effects of adenoviral VEGFR3-Ig fusion protein on growth and metastasis of orthotopic PC-3 tumors. Mice were treated with recombinant adenoviruses expressing the VEGFR3-Ig fusion protein (R3) or β-galactosidase (lacZ). Tumor occurrence was 68% (n = 15/22) in the VEGFR3-Ig group and 91% (n = 21/23) in the control (lacZ-Ig) group. Blocking of VEGFR3 decreased tumor volume compared with those in control vector treated mice (A, VEGFR3-Ig 77 ± 6 mm3, n = 15 vs. lacZ-Ig 120 ± 8 mm3, n = 21, p < 0.05). No major differences in morphology were detected in H&E-stained sections of tumors from the VEGFR3-Ig (B) vs. lacZ-Ig treated mice (C). Histomorphometric analysis of tumor sections immunostained with m-LYVE-1 antibody demonstrated that blocking of VEGFR3 decreased the density of lymphatic capillaries (D, VEGFR3-Ig 69 ± 19 μm/mm2, n = 15 vs. E and F, lacZ-Ig 130 ± 18 μm/mm2, n = 21, p < 0.05). Immunohistochemical staining of tumor sections with CD34 antibody showed that blocking of VEGFR3 decreased the density of blood capillaries, arrows (G, VEGFR3-Ig 24 ± 5 μm/mm2, n = 15 vs. H and I, lacZ-Ig 67 ± 8 μm/mm2, n = 21, p < 0.05). The incidence of metastasis (arrows) in prostate-draining lymph nodes was 0% (n = 0 out of 15 tumor bearing mice) in the VEGFR3-Ig group and 19% (n = 4 of 21 tumor bearing mice, p < 0.001) in the control group (J-L). The occurrence of metastasis in lungs was 0% in both groups (data not shown). Bar 500 μm.