Potentiation of bleomycin cytotoxicity toward cultured mouse cells by hyperthermia and ethanol

Abstract

The effects of hyperthermia and ethanol on bleomycin cytotoxicity toward mouse mammary carcinoma FM3A cells in culture were followed in terms of clonal growth in a soft agar medium. Heating the cells at 43 degrees during or before bleomycin treatment sensitized them to bleomycin. Heat treatment after drug treatment was less effective. Bleomycin cytotoxicity was also greatly potentiated by exposing the cells to ethanol at a concentration of more than 4% (v/v) at 37 degrees before or after drug treatment. However, when the cells were exposed to ethanol during bleomycin treatment, the potentiation of cytotoxicity was reduced, and a higher concentration of ethanol was required for inducing equivalent sensitization. The cytoxicity of pepleomycin, a potent antitumor agent derived from bleomycin, was also greatly potentiated by hyperthermia and ethanol. The cellular uptake of 3H-pepleomycin was not increased by either treatment, and thus the increased cytotoxicity was not correlated with a change in membrane permeability to the drug. The sensitizing effect of hyperthermia or ethanol was maximum when the drug treatment was carried out immediately after the cells were exposed to heat or ethanol. Sensitization decreased linearly as the time interval between the two treatments was increased, and after a 6 hr interval the sensitizing effect of either agent disappeared. This recovery from the sensitized state was not inhibited by cycloheximide or by incubation in phosphate-buffered saline instead of complete growth medium, but it was reversibly inhibited at 0 degrees. It is suggested that the modes of action of hyperthermia and ethanol in inducing cell sensitization of bleomycin are similar.