Angiogenesis in pancreatic ductal
adenocarcinomas depends on the presence of angiogenic factors such as
vascular endothelial growth factor (
VEGF) and
basic fibroblast growth factor (bFGF) and is thought to be stimulated by
hypoxia. We tested the angiogenic potential of 9 cell lines of
pancreatic ductal carcinoma origin by screening
mRNA and
protein expression of
VEGF and bFGF and the release of
VEGF into culture medium under normoxic and hypoxic (5% or 0.2% O2) conditions. Angiogenic activity was determined using 2- and 3-D endothelial cell assays. Furthermore,
VEGF expression and
tumor vascularization were studied in human
pancreatic carcinoma tissues from orthotopic xenografts and resection specimens. All cell lines expressed (
mRNA,
protein) and secreted
VEGF, whereas bFGF was only found in 3 cell lines and was secreted into the medium in low concentrations. In addition to the dominant
isoforms VEGF121,VEGF165 and VEGF189, 2
isoforms described recently, VEGF145 and VEGF183, were detected. Severe
hypoxia (0.2% O2), but not moderate
hypoxia (5% O2) raised
VEGF mRNA expression and
protein secretion in 7/9 and 5/9 cell lines, respectively.
Conditioned media from 7/9, 6/9, 8/9 and 7/9 cell lines stimulated endothelial cell proliferation under normoxic (24 and 48 hr) or hypoxic (24 hr, 0.2% and 48 hr 5% O2) conditions, respectively.
Conditioned media from 4/9 cell lines also induced capillary-like sprouting under normoxic conditions and from 6/9 under hypoxic (0.2% O2) conditions. In xenografted
carcinoma tissues microvessel density was found not to be increased around areas of ischemic
necrosis. In resected
ductal carcinomas showing
tumor necrosis VEGF expression and microvessel density were only increased in 3/12 and 2/13 cases, respectively. In conclusion, in vitro most
pancreatic ductal carcinomas show a distinct
VEGF related angiogenic potential, as demonstrated by 2- and 3-D endothelial cell proliferation, which may be promoted by severe
hypoxia. Surprisingly, perinecrotic
tumor areas, which are supposed to be hypoxic, only rarely showed the expected increase in microvessel density and
VEGF expression.