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 r adiation. Heat exposures at 45-degrees-C/15 min or at 43-degrees-C/60 min administered alone yielded no significant transformation as previo usly reported. However, our recent results repeat our earlier findings that there is an increase in the in vitro transformation frequency af ter the combined treatment of hyperthermia and radiation, if foci/flas k or foci/surviving cell are. used to calculate transformation frequen cy, if high temperature exposures are used (e.g. 43-degrees-C/60 min o r 45-degrees-C/ 15 min) and if the time between the combined treatment s of hyperthermia and 200 cGy of Co-60 radiation is less-than-or-equal -to 5 min at ambient temperature. As can be seen in this and past repo rts whether the combination of hyperthermia and radiation show an incr ease, a decrease, or no change in in vitro oncogenic transformation, a number of factors are critical. These critical factors are (1) temper ature/exposure time and radiation dose as expected; (2) stage of the c ell cycle and growth conditions at each exposure; (3) time between tre atments; and (4) method of data analysis, i.e. whether the transformat ion frequency was based on the foci/viable cells, foci/flask or the fo ci/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 transformatio n (Cao et al. 1992, Miller et al. 1992). Factors 1-3 affect the cells position in the cell cycle. Factor 4 is critical if the concern is wit h possible treatment-induced secondaries.