Oncogenic potential of hyperthermia in combination with radiation.

The C3H 10T1/2 mouse embryo cell line was used to determine the effect of hyperthermia on the in vitro oncogenic transforming potential of radiation. Heat exposures at 45 degrees C/15 min or at 43 degrees C/60 min administered alone yielded no significant transformation as previously reported. However, our recent results repeat our earlier findings that there is an increase in the in vitro transformation frequency after the combined treatment of hyperthermia and radiation, if foci/flask or foci/surviving cell are used to calculate transformation frequency, if high temperature exposures are used (e.g. 43 degrees C/60 min or 45 degrees C/15 min) and if the time between the combined treatments of hyperthermia and 200 cGy of 60Co radiation is < or = 5 min at ambient temperature. As can be seen in this and past reports whether the combination of hyperthermia and radiation show an increase, a decrease, or no change in in vitro oncogenic transformation, a number of factors are critical. These critical factors are (1) temperature/exposure time and radiation dose as expected; (2) stage of the cell cycle and growth conditions at each exposure; (3) time between treatments; and (4) method of data analysis, i.e. whether the transformation frequency was based on the foci/viable cells, foci/flask or the foci/total cells at risk (total cells plated x plating efficiency of the untreated cells). Recent publications have shown that the position of cells in the cell cycle determine the frequency of cell transformation (Cao et al. 1992, Miller et al. 1992). Factors 1-3 affect the cells position in the cell cycle.(ABSTRACT TRUNCATED AT 250 WORDS)