Laser flow cytometric studies on the intracellular accumulation of anthracyclines when combined with heat

The effects of heat on intracellular accumulation of anthracyclines were investigated by laser flow cytometry analysis. Sarcoma-180 cells were exposed to Adriamycin (ADM), epirubicin (EPIR), daunomycin (DM), THP-Adriamycin (THP), ME-2303 (ME) and KRN-8602 (KRN) at 37 degrees C and at higher temperatures. There was a dose-dependent increase in the fluorescence intensity of all drugs at 37 degrees C, but heat varied the fluorescence intensity of each drug. At 43 degrees C the cellular fluorescence of ADM and EPIR increased by approximately 200%, but for DM the increase was 110-130%. The cellular fluorescence of THP and ME was little affected by heat, and heat reduced that of KRN to 80-90%. Each drug showed was unique in the relationship between drug exposure time and the fluorescence intensity at 37 degrees C and 43 degrees C. Cytotoxicity determined by the MTT assay was enhanced with heat in the cases of ADM and EPIR, but not with DM, THP, ME, or KRN. Thus, ADM and EPIR are expected to show enhanced antitumor activities when given in combination with hyperthermia.