Differential radiosensitivity of two mammalian cell lines after hyperthermic pretreatment

Hyperthermia in combination with 60Co-gamma-therapy not only increases the radiosensitivity of mammalian cells, it also can create a greater selectivity between individual cell populations. Tw established Chinese hamster cell lines (V79 and B14F28) showed a similar radiosensitivity at 37 degrees C, but exhibited a marked difference in their response to 60Co-gamma-rays when they were pretreated with mild hyperthermia (1 hour at 42 degrees C): About 50% of each cell type survived a dose of 400 rad 60Co-gamma-rays alone, while the same dose delivered in combination with hyperthermia was survived by 40% of the B14F28 cells and by only 2.4% of the V79 cells. Heat alone also caused cell death and cell cycle changes (as measured by flow-microfluorometry) to a different extent: 4 hours at 42 degrees C decreased survival of V79 cells to 1.3% while 70% of the B14F28 cells formed colonies. This differential response to hyperthermic killing and thermal radiosensitization is similar to the different RBE-values for survival of both cell lines after high LET pion irradiation.