Vascular endothelial growth factor expression is independent of hypoxia in human malignant glioma spheroids and tumours

Abstract

Among the various adaptive responses to cell and tissue hypoxia is that of neoangiogenesis. This process occurs under physiological and pathophysiological conditions. It is becoming apparent that primary brain tumours of astrocytic lineage, especially glioblastoma multiforme, exhibit hypoxia-induced neoangiogenesis in vivo through induction of the endothelial cell-specific mitogen, vascular endothelial growth factor (VEGF) (Shweiki et al, 1992;Plate et al, 1992Plate et al, , 1994. A strong correlation was found between intense VEGF expression and severe hypoxia in situ in HT29 and EMT-6 spheroids (Waleh et al, 1995).Recently we have observed variable presence of hypoxia adjacent to necrosis in some xenografted glioma lines and spheroids (Parliament et al, 1997;Franko et al, 1998). The results were interpreted in terms of regional variations in oxygen consumption, based on the concept of modulation of oxygen consumption in regions of oxygen and nutrient deprivation in solid tumours (Hochachka et al, 1996). We were interested in determining the pattern of VEGF expression in situ, particularly in the nutrientdeprived regions of viable cells adjoining necrosis, which may or may not be severely hypoxic in human glioma spheroids and xenografts. We recently showed that the M006XLo line has elevated expression of VEGF under aerobic conditions, with modest hypoxic induction compared to the M006X line (AllalunisTurner et al, 1999). In this report we have examined the oxygen dependence of VEGF mRNA expression in the M006X line undergoing mild hypoxic stress (6% oxygen (O 2 )), and we have also examined VEGF expression in spheroids of both M006X and M006XLo lines and in xenograft tumours of the M059K, M006 and M010b lines. We also sought to independently validate the presence of radiobiologically hypoxic cells in situ in M006 tumours using the comet assay of in-situ DNA damage (Olive et al, 1997(Olive et al, , 1998.Finally, we have performed preliminary experiments to assess the presence of tumour-cell VEGF receptor (Vaisman et al, 1990) expression which has previously been seen in melanoma and ovarian carcinoma lines (Boocock et al, 1995;Liu et al, 1995), suggesting autocrine/paracrine growth stimulation.  Cell lines, spheroids and xenograftsDetails of the origin and characterization of the glioma cell lines used in this study have been previously published (Parliament et al, 1997;Allalunis-Turner et al, 1991 Summary We recently showed that severe hypoxia was not universally present adjacent to necrosis in human glioma xenografts and spheroids established from the M059K, M006, M006X, M006XLo and M010b cell lines. Using these glioma models, we wished to test whether oxygen serves as a regulator of cellular VEGF expression in situ. In situ hybridization (ISH) and immunohistochemistry (IHC) were used to detect vascular endothelial growth factor (VEGF) mRNA and protein expression in sections of glioma xenografts and spheroids in which hypoxic regions and regions with well-oxygenated necrosis were identifie...

Regional Hypoxia in Glioblastoma Multiforme Quantified with [18F]Fluoromisonidazole Positron Emission Tomography before Radiotherapy: Correlation with Time to Progression and Survival

“…Anaplastic progression was associated with regional expression of VEGF. However, there may well be variations among and within gliomas in the VEGF response to hypoxia (41,42).…”

Expression and hypoxic up‐regulation of neuroglobin in human glioblastoma cells

“…The cellular response to hypoxia has been characterized in five of the cell lines: M006x, M006xLo, M059K are hypoxiatolerant whereas M010B and M059J are hypoxia-sensitive (Allalunis-Turner et al, 1999;Parliament et al, 2000;Turcotte et al, 2002). M006xLo cells are of particular interest as they were selected from the M006x parental line following culture for 2 weeks under reduced oxygen and glucose conditions, and accordingly, are exceptionally tolerant of low oxygen conditions.…”

Vascular Transdifferentiation in the CNS: A Focus on Neural and Glioblastoma Stem‐Like Cells

“…Both mechanisms employ common molecular effectors involved during physiological sprouting angiogenesis ( Section 2 ), such as Angiopoietins/Tie2 [ 67 , 69 , 70 ]; VEGF [ 71 ]; Ephrins [ 72 ]; Dll4-Notch1 [ 73 ]; PDGF-B/PDGFR β [ 74 ]; and SDF1-CXCR4 signaling pathways [ 75 , 76 ]. Angiogenesis in gliomas has also been shown to be either hypoxia dependent [ 70 ] or hypoxia independent [ 70 , 77 – 79 ]. Vasculogenesis, which involves recruitment and differentiation of circulating bone marrow-derived cells or endothelial progenitor cells (EPCs) [ 80 ], has also been demonstrated in glioma [ 81 ] but is currently disputed and controversial, mainly because of the debate on EPC identification markers.…”