The Enhanced Killing of Irradiated HeLa Cells in Synchronous Culture by Hyperthermia

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Abstract
Mitotically synchronized cultures of HeLa S-3 [human cervical cancer] cells were subjected to radiation (400 rad), hyperthermia (43.degree. C) and a combination of both at different phases of the division cycle. Radioresistance was most pronounced in the mid G-1 and late S phases, while thermal resistance was greatest in the early G-1 phase and steadily decreased as cells entered the S phase. Cells in the late S and early G-2 phases were most sensitive to hyperthermia. Sequential treatment of radiation immediately followed by hyperthermia resulted in enhanced cell killing throughout the cell cycle with a marked synergism occurring in cells in the late S phase. The age-response function of the combined treatment was more similar to that of the thermal age response.