Radiation-enhanced vascular endothelial growth factor (VEGF) secretion in glioblastoma multiforme cell lines--a clue to radioresistance?
OBJECTIVE
Postoperative radiotherapy is standard treatment for patients with a glioblastoma multiforme (GBM). However, a GBM is radioresistant and almost always recurs, even after a high dose of radiation. A GBM is characterized by its extensive neo-angiogenesis, which can be attributed to the high levels of vascular endothelial growth factor (VEGF). The scope of this study is to investigate the VEGF secretion by GBM cells with different radiosensitivity after irradiation.


METHODS
Three human GBM cell lines (U251, U251-NG2 and U87) were irradiated with single doses of 0, 5, 10 and 20 Gy of gamma-rays from a (137)Cs source. VEGF levels in medium were measured by ELISA at 24, 48 and 72 h after radiation. Cell survival was measured by the XTT assay 7 days after irradiation.


RESULTS
Following single dose radiation, the VEGF levels showed a dose dependent increase in U251, U251-NG2 and U87 glioma cells. Both base-line and radiation-enhanced VEGF levels were about 10-fold higher in U87 compared to U251 and U251-NG2 cells. In addition, in the XTT assay, the U87 was more radioresistant than both U251 and U251-NG2 cell lines (dose modifying factor (DMF) = 1.6 and 1.7 resp).


CONCLUSIONS
Irradiation enhanced VEGF secretion in all three tested glioma cell lines (up to eight times basal levels). It is tempting to associate the radiation-enhanced VEGF secretion with an increased angiogenic potential of the tumor, which may be a factor in radioresistance.
Hovinga
K E
KE
Department of Radiotherapy, Academic Medical Centre, University of Amsterdam, 1100 DD Amsterdam, The Netherlands.
Stalpers
L J A
LJ
van Bree
C
C
Donker
M
M
Verhoeff
J J C
JJ
Rodermond
H M
HM
Bosch
D A
DA
van Furth
W R
WR
D001932:Brain Neoplasms / Q000378:metabolism / Q000532:radiotherapy*; D049109:Cell Proliferation / Q000528:radiation effects; D002588:Cesium Radioisotopes; D004307:Dose-Response Relationship, Radiation; D005909:Glioblastoma / Q000378:metabolism / Q000532:radiotherapy*; D006801:Humans; D011836:Radiation Tolerance; D011839:Radiation, Ionizing; D014407:Tumor Cells, Cultured; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*
D002588:Cesium Radioisotopes; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A