The relationship between radiation response of human squamous carcinoma cells and specific metabolic changes induced by chronic hypoxia.

Chronic hypoxia can cause a range of metabolic changes within cells, such as increasing the synthesis rate of a group of proteins, oxygen regulated proteins (ORPs) and reducing glutathione (GSH) content. We are currently interested in the radiation responses of cells during recovery after chronic hypoxia in relation to these metabolic changes. Experiments have therefore been carried out on the influence of hypoxic pretreatment to gamma rays of two human squamous carcinoma cell lines, A431 (vulva) and CaSki (cervix), in exponential and plateau growth phases. In both cell lines, the synthesis rate of ORPs reached to a maximum level after 12 hr of hypoxia and during the same time, the cellular GSH content reduced by about 50%, but both returned to the control levels by 12 hr of reoxygenation. After 12 hr of hypoxic incubation at 37 degrees C, cells were allowed to reoxygenate in air for 10 min (on ice) or 12 hr at 37 degrees C before irradiation. Clonogenic assays were performed immediately after irradiation. Compared to the aerobic control, the radiosensitivity of both cell lines reoxygenated for 10 min after hypoxia increased significantly and later returned to the aerobic control level by 12 hr of reoxygenation. Since aerobic A431 cells treated with 10 mM buthionine sulfoximine for 12 hr did not increase the radiosensitivity, the enhanced aerobic radiosensitivity observed after chronic hypoxia was unlikely to be directly related to decreased GSH content. Further investigations of ORPs and other associated metabolic changes caused by chronic hypoxia have been in progress to determine their possible role in this enhanced radiation sensitivity.