VEGF₁₆₅, but not VEGF₁₈₉, stimulates vasculogenesis and bone marrow cell migration into Ewing's sarcoma tumors in vivo

We previously showed that bone marrow stem cells participate in the tumor vessel expansion that supports the growth of Ewing's sarcoma tumors in vivo. The purpose of this study was to determine the relative importance of two isoforms of vascular endothelial growth factor (VEGF) in tumor vessel expansion and recruitment of bone marrow-derived cells during tumor growth. We injected VEGF₁₆₅-siRNA-transfected cells (TCsi/7-1), control siRNA-transfected cells (TC/si-control), or TC71 parental Ewing's sarcoma cells into nude mice. The TCsi/7-1 tumors were then treated with adenoviral vectors expressing VEGF₁₆₅ (Ad-VEGF₁₆₅), VEGF₁₈₉ (Ad-VEGF ₁₈₉), or β-galactosidase (Ad-β-gal). Bone marrow cells labeled with fluorescent tracker dye were injected into the mice 3 weeks later. The TCsi/7-1 tumors were significantly smaller (P < 0.05), had decreased vessel density, and showed significantly lower bone marrow cell migration than did TC71 parental and TC/si-control tumors. Treatment with Ad-VEGF ₁₆₅, but not Ad-VEGF₁₈₉ or Ad-β-gal, resulted in a significant increase in bone marrow cell infiltration, tumor vessel density, and tumor growth. Immunohistochemical staining revealed that the injected bone marrow cells migrated to and incorporated into the expanding CD31⁺ tumor vessel network. Taken together, these data show that VEGF₁₆₅ is a chemoattractant that recruits bone marrow cells into the tumor area. These data provide a mechanism by which Ewing's sarcoma cells induce vasculogenesis.