A quantitative analysis of the reduction in oxygen levels required to induce up-regulation of vascular endothelial growth factor (VEGF) mRNA in cervical cancer cell lines

The presence of hypoxia (low oxygen concentrations) in solid tumours correlates with poor prognosis, increased metastasis, and resistance to radiotherapy and some forms of chemotherapy. Malignant cells produce an angiogenesis factor, vascular endothelial growth factor (VEGF), which may increase metastatic ability and is up-regulated in the presence of hypoxia. Clinical data for cancers of the cervix and head and neck relate oxygen levels in the tumour to treatment outcome. This suggests the possibility that the presence of VEGF mRMA might be used as a marker for relevant levels of hypoxia. Suspension cultures of three human cervical cancer cell lines, SiHa, ME-180 and HeLa, were used to investigate up-regulation of VEGF mRNA levels following exposure to precisely defined oxygen concentrations for 2 or 4 h. An oxygen sensor was used to confirm the actual levels of dissolved oxygen present. The oxygen concentrations which caused half-maximal upregulation (the K-m value) of VEGF mRNA level in the three cell lines were similar except for one instance (K-m at 4 h: SiHa 27.0 +/- 5.7 mu M, ME-180 16.8 +/- 3.3 mu M, HeLa 13.0 +/- 1.8 mu M, SiHa and HeLa P = 0.01). The K-m values for the HeLa cell line as measured at 2 h (24.9 +/- 0.8 mu M) and 4 h (13.0 +/- 1.8 mu M) were significantly different (P < 0.0001). VEGF mRNA half-lives measured in air were consistent with values in the literature (SiHa 59.8 +/- 5.8 min, ME-180 44.4 +/- 7.2 min, HeLa 44.5 +/- 6.3 min). Differences in oxygen consumption at low oxygen concentrations were noted between the different cell lines. Stirring in suspension culture was found to induce VEGF mRNA in SiHa cells; The presence of VEGF mRNA may be a marker for radiobiologic hypoxia.