Cytotoxicity of perillyl alcohol against cancer cells is potentiated by hyperthermia

Purpose: Perillyl alcohol (POH) (4-isopropenyl-cyclohexenecarbinol) is a member of the monoterpenes, which are present in various fruits and vegetables. POH has been demonstrated to be cytotoxic against a variety of experimental cancer cells in vitro and in vivo. Phase I clinical trials have indicated that POH may be useful for human tumor treatment. The purpose of our study was to reveal whether the anticancer effect of POH could be enhanced by hyperthermia. Methods and Materials: SCK mammary carcinoma cells of A/J mice were used. The effects of POH or hyperthermia alone were studied by incubating the cells during exponential growth phase in culture with 0.25-1.0 mM of POH at 37°C for varying lengths of time or heating cells at 41-43°C for varying lengths of time. The combined effect of POH and hyperthermia was investigated by heating the cells with 1 mM of POH at 41-43°C for varying lengths of time. The effects of the treatments were evaluated using the clonogenic cell survival assay and three types of apoptosis assays. Results: An incubation of SCK cells with 1 mM of POH at 37°C for 60 min or hyperthermia at 43°C for 1 h decreased clonogenic cell survival to 40% and 60%, respectively. When the cells were heated at 43°C for 1 h in the presence of 1 mM of POH, clonogenic cell survival decreased to 0.2%, indicating that hyperthermia potentiated the effect of POH to cause clonogenic cell death. Hyperthermia also markedly increased the degree of POH-induced apoptosis. Conclusion: Hyperthermia synergistically potentiates the cytotoxicity of naturally occurring POH against cancer cells.