The effect of various sulfhydryl compounds on the survival of exponentially growing monolayer cultures of Chinese hamster cells (HA1) heated to temperatures of 37–43° was examined. Concentrations of cysteamine which were nontoxic or minimally toxic at room temperature or 37° became increasingly toxic at elevated temperatures, greatly potentiating the killing produced by heat alone in the absence of cysteamine.

This enhancement of hyperthermia-induced cell killing increased 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 mm 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.

1

Preliminary results have been presented at the Twenty-sixth Annual Meeting of the Radiation Research Society, Toronto, Canada, 1978 (22). This work was supported by USPHS Research Grants CA-06519 and CA-15769.

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