Mammalian tumor xenografts induce neovascularization in zebrafish embryos.

The zebrafish (Danio rerio)/tumor xenograft model represents
a powerful new model system in cancer. Here, we describe a
novel exploitation of the zebrafish model to investigate tumor
angiogenesis, a pivotal step in cancer progression and target
for antitumor therapies. Human and murine tumor cell lines
that express the angiogenic fibroblast growth factor (FGF) 2
and/or vascular endothelial growth factor (VEGF) induce the
rapid formation of a new microvasculature when grafted close
to the developing subintestinal vessels of zebrafish embryos at
48 h postfertilization. Instead, no angiogenic response was
exerted by related cell clones defective in the production of
these angiogenic growth factors. The newly formed blood
vessels sprout from the subintestinal plexus of the zebrafish
embryo, penetrate the tumor graft, and express the transcripts
for the zebrafish orthologues of the early endothelial markers
Fli-1, VEGF receptor-2 (VEGFR2/KDR), and VE-cadherin.
Accordingly, green fluorescent protein–positive neovessels
infiltrate the graft when tumor cells are injected in transgenic
VEGFR2:G-RCFP zebrafish embryos that express green fluorescent
protein under the control of the VEGFR2/KDR
promoter. Systemic exposure of zebrafish embryos immediately
after tumor cell injection to prototypic antiangiogenic
inhibitors, including the FGF receptor tyrosine kinase inhibitor
SU5402 and the VEGFR2/KDR tyrosine kinase inhibitor
SU5416, suppresses tumor-induced angiogenesis without
affecting normal blood vessel development. Accordingly,
VE-cadherin gene inactivation by antisense morpholino
oligonucleotide injection inhibits tumor neovascularization
without affecting the development of intersegmental and
subintestinal vessels. These data show that the zebrafish/
tumor xenograft model represents a novel tool for investigating
the neovascularization process exploitable for drug
discovery and gene targeting in tumor angiogenesis.