Cell inactivation by combined low dose-rate irradiation and intermittent hypoxia

Differential expression of NPM, GSTA3, and GNMT in mouse liver following long-term in vivo irradiation by means of uranium tailings

Uranium tailings (UT) are formed as a byproduct of uranium mining and are of potential risk to living organisms. In the present study, we sought to identify potential biomarkers associated with chronic exposure to low dose rate γ radiation originating from UT. We exposed C57BL/6J mice to 30, 100, or 250 μGy/h of gamma radiation originating from UT samples. Nine animals were included in each treatment group. We observed that the liver central vein was significantly enlarged in mice exposed to dose rates of 100 and 250 μGy/h, when compared with nonirradiated controls. Using proteomic techniques, we identified 18 proteins that were differentially expressed (by a factor of at least 2.5-fold) in exposed animals, when compared with controls. We chose glycine N-methyltransferase (GNMT), glutathione S-transferase A3 (GSTA3), and nucleophosmin (NPM) for further investigations. Our data showed that GNMT (at 100 and 250 μGy/h) and NPM (at 250 μGy/h) were up-regulated, and GSTA3 was down-regulated in all of the irradiated groups, indicating that their expression is modulated by chronic gamma radiation exposure. GNMT, GSTA3, and NPM may therefore prove useful as biomarkers of gamma radiation exposure associated with UT. The mechanisms underlying those changes need to be further studied.

Low dose-rate irradiation with [3H]-labelled valine to selectively target hypoxic cells in a human colorectal cancer xenograft model

BACKGROUND

Earlier in vitro studies show that irradiation with an ultra-low dose-rate of 15 mGy/h delivered with [³H]-valine leads to loss of clonogenicity in hypoxic T-47D cells. Here, the aim was to determine if [³H]-valine could be used to deliver low dose-rate irradiation in a colorectal cancer model.

METHODS

Clonogenicity was measured in cultured cancer cell line HT29 irradiated with 15 mGy/h combined with intermittent hypoxia. Mice with HT29 xenografts were irradiated by repeated injections of [³H]-valine intravenously. The activity in the tumor tissue was measured by scintillation counting and tumor growth, hypoxic fraction and tritium distribution within tumors were assessed by pimonidazole staining and autoradiography.

RESULTS

Ultra-low dose-rate irradiation decreased clonogenicity in hypoxic colorectal cancer cells. In vivo, the tumor growth, hypoxic fraction and weight of the mice were similar between the treated and untreated group. Autoradiography showed no [³H]-valine uptake in hypoxic tumor regions in contrast to aerobic tissue.

CONCLUSION

Continuous low-dose-rate irradiation was well tolerated by aerobic tissue. This indicates a potential use of low dose-rate irradiation to target hypoxic tumor cells in combination with high dose-rate irradiation to eradicate the well oxygenated tumor regions. However, [³H]-valine is not the appropriate method to deliver ultra-low dose-rate irradiation in vivo.

Separation of two sub-groups with different DNA content after treatment of T-47D breast cancer cells with low dose-rate irradiation and intermittent hypoxia

Background Previous studies have shown that combined treatment with internal ultra-low dose-rate irradiation selectively inactivated hypoxic T-47D breast cancer cells after three to five weeks of treatment. However, 2-3% of the hypoxic cells were found to survive and restart proliferation upon re-oxygenation. Purpose To investigate the metastatic potential and characteristics of radiosensitivity of these surviving cells, named T - 47 D_S. Material and Methods The T - 47 D_S cells were grown in ambient air without irradiation. A cloning experiment identified two sub-groups with different DNA content ([Formula: see text] and [Formula: see text]). Furthermore, radiosensitivity and presence of hyper-radiosensitivity (HRS) was measured by Co-60 challenge irradiation and relative migration was determined by scratch assays. Results The two subpopulations of T - 47 D_S had different DNA content; one had abnormally high DNA content ([Formula: see text]) and one had DNA content similar to wild-type T-47D cells ([Formula: see text]). HRS was surprisingly present in cells of the cloned population [Formula: see text], but was absent in cells of both [Formula: see text] and T - 47 D_S. The radio response of T - 47 D_S, [Formula: see text] at higher radiation doses were similar to that of T-47D cells, and neither subpopulation showed increased migration compared with wild-type T-47D. Conclusion No increase in the risk of metastasis was found and only slight changes in radiosensitivity in response to conventional clinical doses was observed. Thus, the data suggest that if ultra-low dose-rate irradiation is used for targeting the hypoxic tumor fraction, conventional high dose-rate irradiation can be used to eradicate eventual surviving cells as well as cells in the well oxygenated areas of the tumor.