Stability of heating temperature on cytotoxicity

Abstract

Chinese hamster V79 cells were used to test the cytotoxic effect of heat which alternates between high and low temperatures during the treatment period. This type of temperature fluctuation is often encountered in clinical hyperthermia. Two sets of heating protocols were used in the experiments: Temperature alternates (a) between 42 and 43° and (b) between 42 and 44° in cycle with equal total “thermal dose,” that is heating temperature × heating time. The effectiveness of these heating protocols expressed in average percentage of cell survival depend on the initial temperature attained and the length of the time of this temperature alternation. If the period of temperature change is short such as every 5 or 10 minutes, the cytotoxicity shows very little difference whether the initial treatment temperature is low or high. However, when the period is longer than 20 minutes, the difference in cell survival between the initial temperature at 42° and at higher temperatures is substantial. Cells obtained from logarithmic or plateau phases of growth yield the same result. This difference is likely resulted from a combination of thermotolerance and step-down heating mechanisms. In addition, the effects of heating temperature fluctuation on cytotoxicity is not altered by a 500 cGy of gamma-ray radiation applied either immediately before or after the heat treatment.