Dependence of misonidazole binding on factors associated with hypoxic metabolism

Activation of the heat shock transcription factor by hypoxia in normal and tumor cell lines in vivo and in vitro

Cells exposed to hypoxia increase their synthesis of a specific set of proteins called oxygen regulated proteins. Recently, three of these proteins have been identified as hemoxygenase, Glucose Regulated Protein 78 kilodaltons and Glucose Regulated Protein 94 kilodaltons. In contrast, reoxygenation from hypoxic conditions increases the synthesis of the heat shock proteins. Although the molecular signals required for regulation of both sets of proteins by hypoxia and reoxygenation are still under investigation, it is known that their expression is regulated at the transcriptional level. This finding suggests that these stresses work either singularly or together to control the activation of nuclear transcription factors which bind distinct regulatory sequences in the promoter region of these genes. One possible nuclear transcription factor which could act as a transcriptional regulator for both hypoxia and reoxygenation gene transcription is the heat shock transcription factor. In this report, we focused on the kinetics of HSF activation by hypoxia in normal and tumor cell lines of murine and human origins. In cell culture, both the normal diploid cell line AG1522 and the tumor cell line JSQ-3 possess the same kinetics of HSF activation (binding to the heat shock element) by hypoxia, with maximal induction at or after 3 hr. We have also shown that the activation of HSF occurs in the SCCVII tumor in vivo without clamping, but not in SCCVII cells grown in monolayers. When SCCVII tumors are dissociated and allowed to reoxygenate in cell culture, HSF binding decreased in 5 hr, and was undetectable after 18 hr. Furthermore, one human tumor biopsy tested for the presence of hypoxia by both the pO2 histograph (Eppendorf, Germany) and HSF binding showed good agreement for both techniques. These results suggest that HSF binding may be a useful marker for monitoring the tumor hypoxia.

Tumor hypoxia, reoxygenation and oxygenation strategies: possible role in photodynamic therapy

The concept of hypoxia and its role in tumor therapy are currently under re-evaluation. Poor oxygenation is no longer visualized as an independent feature promoting necrosis and resistance to treatments, but rather as one of the several interdependent microenvironmental parameters associated with impaired blood perfusion. Tumor cells display several survival strategies and remain clonogenic for long periods in nutrient-deprived situations. Reoxygenation may cause lethal damage, improve the response to therapy, or else allow the cell variants adapted to hypoxia to resume proliferation with enhanced aggressiveness and resistance to treatment. The blood supply parameters, oxygenation status and metabolism of malignant cells are discussed here from the standpoint of tumor photodynamic therapy. The role of the tumor interstitial fluid as oxygen- and sensitizer-carrier is discussed. Techniques for assessing tumor oxygenation and for mapping hypoxic territories are described. Strategies for locally improving the oxygenation levels or for selectively destroying the hypoxic populations are outlined.

Radiation response of E. coli after combined treatment with misonidazole and WR-2721 at various oxygen concentrations

It has been reported that the aminothiol compound WR-2721 is a promising radioprotective agent and in combination with misonidazole (MISO) seems to be of therapeutic benefit. Since the radiomodification is oxygen-dependent, the actual oxygen status of cells and the surrounding media is an important factor influencing their effectiveness. Escherichia coli B/r radioresponse was studied either alone or in combination with these compounds at various oxygen concentrations ranging from anoxia to high oxygen content. WR-2721 had a protective effect under anoxic conditions and gave overall protection when oxygen was present. The maximum protection was seen at 3.2% O2 in N2 (PF 2.08). In combination with MISO the hypoxic sensitization of MISO was completely abolished by WR-2721, resulting in radioprotection under hypoxic conditions as well. Under euoxic conditions MISO was able to reduce the protective effect of WR-2721 by about 21%. According to our results MISO and WR-2721 influence each other in their radiomodifying effect in either fixation or repair of the radiation-induced damage.

Temperature dependence of binding of a fluorescent hypoxia probe

The rate of binding of a fluorescent probe for hypoxia, AF-2, is dependent upon cell temperature as well as oxygenation. Aerobic cells bind AF-2 about 5 times less rapidly at 37 degrees C than at 45 degrees C. Below 42 degrees C, the rate of AF-2 binding by aerobic cells increases by a factor of about two for each 10 degrees C, but above 42 degrees C, the rate increases 10-fold for each additional 10 degrees C. However, for cells incubated under nitrogen, these biphasic kinetics were not observed, and the rate of metabolism and binding increased only two-fold per 10 degrees C from 28 degrees to 45 degrees C. These differences in binding kinetics cannot be explained by a decrease in the rate of auto-oxidation of the nitro anion radical, but might involve differences in the available reducing equivalents in cells heated under air or nitrogen. The possibility of using fluorescent probes to measure temperatures of individual tumor cells during hyperthermic treatment is discussed.

Reducing the hypoxic fraction of a tumour model by growth in low glucose

The question of whether growth under low glucose conditions leads to a reduced amount of cell hypoxia was investigated using an in vitro tumour analogue, the sandwich system. In this multicellular system, the interplay between diffusion and consumption of oxygen and nutrients results in spatial gradients of these environmental factors. Gradients in the environment lead to biological heterogeneity within the cell population. A necrotic centre, surrounded by a viable cell border, subsequently develops. Cells adjacent to the necrotic centre in sandwiches are hypoxic and are in an environment somewhat analogous to that of cells adjacent to necrotic regions in solid tumours. Using sandwiches of the 9L and V79 cell lines, the effects of growth under low glucose conditions on the degree of hypoxia in regions adjacent to the necrotic centre were investigated. Per-cell binding of 3H-misonidazole, assessed by autoradiography, was used as an indicator of oxygen deprivation. It was found that the extent of the hypoxic region and the severity of hypoxia were considerably reduced by growing sandwiches in a glucose concentration of 0.6 mM rather than 6.5 mM. This reduction was found in conjunction with a smaller viable border; it occurred despite the fact that the average per-cell oxygen consumption is higher in the low glucose sandwiches. The data are qualitatively consistent with a joint oxygen-glucose deprivation model for cell necrosis.