Thermosensitization by Sulfhydryl Compounds of Exponentially Growing Chinese Hamster Cells1

The effect of various sulfhydryl compounds on the survival of exponentially growing monolayer cultures of Chinese ham ster cells (HA1 ) heated to temperatures of 37-43° was exam ined. Concentrations of cysteamine which were nontoxic or minimally toxic at room temperature or 37° became increas ingly toxic at elevated temperatures, greatly potentiating the killing produced by heat alone in the absence of cysteamine. This enhancement of hyperthermia-induced cell killing in creased with increasing cysteamine concentration, increasing duration of cysteamine exposure, and increasing temperature. Studies with synchronized Chinese hamster cells heated at 43° for 1 hr in the presence of 16 rnw cysteamine demonstrated that the potentiation of heat killing occurred in all phases of the cell cycle. Similarly, enhancement of hyperthermia-induced cell killing was seen for asynchronous cells exposed to 2-aminoethylisothiourium bromide and cysteine, but the magnitude of the effect differed for the various sulfhydryl compounds.