Human umbilical vein endothelial cells (HUVEC) and human microvascular endothelial cells (HMVEC) have been the standards for cell-based assays in the field of angiogenesis research and in antiangiogenic
drug discovery. These normal mature endothelial cells may not be most representative of human
tumor endothelial cells. Human AC133+/CD34+ bone marrow progenitor cells were established in cell
culture media containing
vascular endothelial growth factor,
basic fibroblast growth factor (bFGF), and
heparin to drive differentiation toward the endothelial phenotype. The resulting cells designated endothelial precursor cells (
EPC) have many of the same functional properties as mature endothelial cells represented by HUVEC and HMVEC. By SAGE analysis, the genes expressed by
EPC are more similar to the genes expressed by endothelial cells isolated from fresh surgical specimens of human
tumors than are the genes expressed by HUVEC and HMVEC. Analysis of several cell surface markers by flow cytometry showed that
EPC, HUVEC, and HMVEC have similar expression of P1H12,
vascular endothelial growth factor 2, and
endoglin but that
EPC have much lower expression of ICAM1, ICAM2, VCAM1, and
thrombomodulin than do HUVEC and HMVEC. The
EPC generated can form tubes/networks on
Matrigel, migrate through porous membranes, and invade through thin layers of
Matrigel similarly to HUVEC and HMVEC. However, in a coculture assay using human SKOV3
ovarian cancer cell clusters in
collagen as a stimulus for invasion through
Matrigel,
EPC were able to invade into the malignant cell cluster, whereas HMVEC were not able to invade the malignant cell cluster. In vivo, a
Matrigel plug assay where human
EPC were suspended in the
Matrigel allowed tube/network formation by human
EPC to be carried out in a murine host.
EPC may be a better model of human
tumor endothelial cells than HUVEC and HMVEC and, thus, may provide an improved cell-based model for second generation
antineoplastic antiangiogenic
drug discovery.