HYPOXIA-INDUCED CHANGES IN RADIATION SENSITIVITY IN HUMAN-MELANOMA CELLS - IMPORTANCE OF OXYGEN-REGULATED PROTEINS, ADENYLATE ENERGY-CHARGEAND CELL-CYCLE DISTRIBUTION

Background and purpose: The effects of transient hypoxia on the radiat ion sensitivity of human tumour cells have so far been investigated on ly to a limited extent, and only up to 12 h after reoxygenation. We ir radiated cells shortly after reoxygenation (<1 h) or at prolonged time s after reoxygenation (24 h and 38 h) in order to examine possible rel ationships between changes in radiation sensitivity on the one hand an d changes in rates of synthesis of oxygen-regulated proteins, changes in energy metabolism and changes in cell cycle distribution on the oth er. Materials and Methods: Four human melanoma cell lines (A-07, D-12, R-18 and U-25) were included in the study. After hypoxia treatment (4 h or 16 h) and reoxygenation, cells were either irradiated as monolay ers at a dose rate of 2.0 cGy/min or prepared for protein analysis, en ergy charge measurements or flow cytometric measurements of DNA. Resul ts: U-25 was the only line that showed increased radiation sensitivity shortly after reoxygenation, possibly because of extensive energy dep letion. A-07 was the only line that showed increased radiation sensiti vity at prolonged times after reoxygenation, possibly because of hypox ia-induced changes in the cell cycle distribution. The rates of synthe sis of oxygen-regulated proteins (GRP78, GRP94, HSP70 and HSP90) were transiently perturbed to a similar extent in all lines after hypoxia t reatment. Conclusion: The radiation sensitivity of the human melanoma cell lines was changed only to a minor extent by transient exposure to hypoxia. (C) 1997 Elsevier Science Ireland Ltd.