Modulation of adriamycin transport by hyperthermia as measured by fluorescence-activated cell sorting

Heat-induced (45.5 degrees C) modification of adriamycin uptake and efflux were measured by flow cytometry in CHO cells in vitro. Administration of adriamycin with simultaneous 15-min or 30-min heat treatment increased drug uptake in a dose-dependent manner. Fluorescence-activated cell sorting showed that cytotoxicity to adriamycin was correlated with relative cellular concentration (fluorescence) for both unheated cells and those heated and simultaneously treated with adriamycin. However, if adriamycin administration followed the heat treatment, accumulation was significantly reduced, primarily as a result of decreased passive drug diffusion (rather than increased efflux) in the heated cells. Cells made heat-tolerant by prior heating also exhibited reduced adriamycin uptake 12 h later, and further heating did not increase uptake. Cell sorting experiments indicated that cytotoxicity of adriamycin was not necessarily correlated with intracellular drug levels when drug administration followed the heat treatment. Also, heat-sterilized cells exhibited a two-fold increase in adriamycin uptake over surviving cells, as assessed by simultaneous measurement of dansyl lysine and adriamycin content. These results indicate that sensitization to adriamycin by simultaneous heat treatment is probably due to increased drug uptake. The decreased sensitization observed when drug administration is followed by heating is probably the result of both decreased uptake and decreased drug DNA accessibility.