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

Abstract

Regions of hypoxia, or low oxygen tension, are known to exist within tumours (Raleigh et al, 1996;Brown and Giaccia, 1998;Dewhirst, 1998). Since radiotherapy and some forms of chemotherapy are less effective at killing cancer cells in hypoxic environments, much effort has been directed toward identifying tumours containing such regions. Measurement of oxygen tension by needle electrodes in lymph node metastasis of cancer of the head and neck found that radiation was less effective at inducing regression when the lymph nodes were hypoxic (Gatenby et al, 1988) and such measurements have been reported to identify patients with poor locoregional tumour control (Nordsmark et al, 1996). Similar work in advanced cancer of the uterine cervix (Hockel et al, 1993(Hockel et al, , 1996Fyles et al, 1998;Hockel and Vaupel, 1998) showed that increased levels of hypoxia in the primary tumour mass correlated with poorer treatment outcome. These results suggested that hypoxia in cervical cancers correlated with a greater likelihood of both local failure and nodal metastasis. Metastases were also found to be more frequent in patients with the most hypoxic soft tissue sarcoma of the extremities (Brizel et al, 1996). Furthermore, exposure of cancer cells to hypoxia (Young et al, 1988;Jang and Hill, 1997) and hypoxia-induced increases in vascular endothelial growth factor (VEGF) secretion have been associated with an increased metastatic ability (Danielsen and Rofstad, 1998).VEGF is the most selective vascular endothelial cell mitogen known . In cancer cells, the four VEGF isoforms which have been most frequently described contain 121, 165, 189 and 206 amino acids (Tischer et al, 1991). In some studies, increased intra-tumoural VEGF mRNA and protein has been associated with poor prognosis (Berger et al, 1995;Toi et al, 1995), increased metastasis Takahashi et al, 1995), and increased microvessel density Toi et al, 1995;Fontini et al, 1997). Antibodies directed towards VEGF can inhibit angiogenesis and the proliferation of cancer cells in vivo (Kim et al, 1993;Kondo et al, 1993). Cancer cells constitutively produce VEGF and can up-regulate its expression under hypoxic stress (Shweiki et al, 1992) via the transcription factor hypoxia-inducible factor 1 (Forsythe et al, 1996) and by stabilization of the mRNA (Levy et al, 1996(Levy et al, , 1998. The qualitative relationship between oxygen level and VEGF up-regulation has been examined in a variety of different tumour systems but has not been quantitatively documented in most of the studies performed (Shweiki et al, 1992;Minchenko et al, 1994;Leith and Michelson, 1995;Mukhapadhyay et al, 1995). The purpose of the present work was to examine the relationship between VEGF mRNA level and oxygen concentration in detail and to determine the extent of its variation between different tumour cells of similar histopathological type. Cell lines derived from human cancer of the uterine cervix were chosen for the study based on the abundance of clinical data relating tumour A quantitative analysis ...

Evidence that involucrin, a marker for differentiation, is oxygen regulated in human squamous cell carcinomas

“…A similarly steep dependence has been reported for VEGF mRNA induction in a number of cell lines (Chiarotto and Hill, 1999). This steepness of response is reminiscent of synergistic interactions and it is tempting to speculate that these might involve interactions between hypoxia and calcium ions reported for the case of VEGF (Salnikow et al, 2002).…”

“…This steepness of response is reminiscent of synergistic interactions and it is tempting to speculate that these might involve interactions between hypoxia and calcium ions reported for the case of VEGF (Salnikow et al, 2002). Involucrin induction is further distinguished from pimonidazole binding in that the K m (15 mmHg) is similar to that for VEGF (Leith and Michelson, 1995;Chiarotto and Hill, 1999) and, therefore, ca 40 times higher than that for pimonidazole binding (0.4 mmHg). The rapid rate of induction, steep pO 2 dependence and high K m could be important in understanding immunostaining patterns for involucrin in squamous cell carcinomas.…”

“…Many oxygen-regulated processes are half maximally induced at oxygen partial pressures (K m ¼ 6 -20 mmHg) (Leith and Michelson, 1995;Jiang et al, 1996;Chiarotto and Hill, 1999;Wykoff et al, 2000) that would strongly inhibit the binding of nitroimidazole hypoxia markers such as pimonidazole, EF5 and misonidazole (K m ¼ 0.8 -2.0 mmHg) (Franko et al, 1987;Arteel et al, 1995;Gross et al, 1995;Koch et al, 1995). This could account for the immunostaining patterns for Glut-1 and CAIX.…”

Hypoxia-activated cytotoxic agent tirapazamine enhances hepatic artery ligation-induced killing of liver tumor in HBx transgenic mice

“…The proof-of-principle of the induction of hypoxia in the HCC of this animal model was accomplished by using the combined OxyLite/OxyFlo probes to continuously monitor blood flow and pO 2 . The average pO 2 of HCC in the HBx transgenic mouse model is 10 mmHg, which is equivalent to 15 μM O 2 (1 mmHg = 1.5 μM O 2 ) (20). A reduction in the blood flow to <25% of the baseline can induce hypoxia in HCC, with an average pO 2 of 0.75 mmHg during the period of HAL.…”

The Natural Progression of Microvasculature in Primary Tumor and Lymph Node Metastases in a Breast Carcinoma Model: Relationship between Microvessel Density, Vascular Endothelial Growth Factor Expression and Metastatic Invasion

“…[20][21][22] Since hypoxic areas are commonly present in tumors, upregulation of VEGF leads to angiogenesis and provides a mechanism for tumors to maintain a vascular supply insuring oxygen and nutrients. 23 The transition from a quiescent tumor to an invasive tumor, reflecting a change in the balance between cell death and proliferation, is accompanied by the acquisition of angiogenic properties. 24 This so-called angiogenic switch requires not only upregulation of promoters of angiogenesis, but also downregulation of suppressors.…”