The role of VEGF pathways in human physiologic and pathologic angiogenesis.
BACKGROUND
In preclinical models, VEGF is a potent stimulant of both physiologic and pathologic angiogenesis. Conversely, anti-VEGF regimens have successfully inhibited angiogenesis both in vitro and in vivo. We hypothesized that VEGF would stimulate both physiologic and pathologic angiogenesis in a human-based fibrin-thrombin clot angiogenesis assay. We further speculated that anti-VEGF regimens would inhibit angiogenesis in this assay.


METHODS
To test these hypotheses, discs of human placental veins (physiologic model) and fragments of human tumors (pathologic model) were embedded in fibrin-thrombin clots and treated with either VEGF-A165 (VEGF) or anti-VEGF pathway reagents including bevacizumab, IMC-18F1, IMC-1121, and PTK787 (n=30 wells per treatment group, multiple concentrations tested in each specimen). Angiogenic responses were assessed visually using a previously validated grading scheme. The percent of tissue explants that developed angiogenic invasion into the clot (% I) as well as the extent of angiogenic growth (AI) via a semi-quantitative scale were assessed at set intervals.


RESULTS
VEGF failed to stimulate angiogenesis in both the physiologic and the pathologic model. While anti-VEGF reagents that targeted only one element of the VEGF pathway failed to consistently inhibit angiogenesis, PTK787, a receptor tyrosine kinase inhibitor that targets multiple VEGF and non-VEGF receptors, profoundly inhibited both physiologic and pathologic angiogenesis.


CONCLUSIONS
These results suggest that VEGF-related pathways may not be solely responsible for stimulating angiogenesis in humans. Targeting the VEGF pathway in combination with elements of other growth factor pathways may provide a more effective means of inhibiting angiogenesis than targeting VEGF alone.
Lyons
John M
JM
Louisiana State University Health Sciences Center Department of Surgery, Section of Surgical Oncology and Section of Surgical Endocrinology, Kenner, Louisiana 70065, USA.
Schwimer
Joshua E
JE
Anthony
Catherine T
CT
Thomson
Jessica L
JL
Cundiff
Jason D
JD
Casey
Douglas T
DT
Maccini
Cynthia
C
Kucera
Paul
P
Wang
Yi-Zarn
YZ
Boudreaux
J Philip
JP
Woltering
Eugene A
EA
D002478:Cells, Cultured; D042783:Endothelial Cells / Q000378:metabolism; D005337:Fibrin; D006801:Humans; D066298:In Vitro Techniques; D009389:Neovascularization, Pathologic; D018919:Neovascularization, Physiologic; D015398:Signal Transduction; D013917:Thrombin; D042461:Vascular Endothelial Growth Factor A / Q000037:antagonists & inhibitors / Q000378:metabolism*
C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; D005337:Fibrin; D013917:Thrombin