Response of extremely hypoxic cells to hyperthermia: survival and oxygen enhancement ratios.

Chinese hamster V79 cells and mouse EMT6 cells were made extremely hypoxic with a chamber technique that relies upon gas exchange rather than respiration-assisted oxygen depletion. Cells in these chambers were treated with heat (43degrees C) or heat plus x-irradiation, and colony-forming ability was determined. Hyperthermia: (a) kills exponentially growing V79 cells more efficiently than plateau-phase cells; (b) kills euoxic and extremely hypoxic cells equally; and (c) radiosensitizes euoxic and extremely hypoxic cells to the same degree, leaving the oxygen enhancement ratio unchanged.