Anthracycline-induced Inhibition of Membrane Permeability Functions Dependent on Metabolic Energy

The influence of anthracyclines on membrane permeability functions has been investigated in HeLa cells by monitoring the efflux of fluorescein. Release of the fluorescent dye, dependent on the metabolic energy supply, occurs after the intracellular accumulation and enzymatic hydrolysis of the non-fluorescent substrate fluorescein diacetate (FDA). Flow cytometric evaluation of the efflux kinetics showed that adriamycin (ADR), N-trifluoroacetyladriamycin-14-valerate (AD-32) and daunorubicin (DNR) inhibited the permeability process. The degree of inhibition was dependent, though to different extent, on the intracellular concentration of each drug. An increase in the efflux rate was always observed when the cells were treated with the drugs in the presence of 20 mM glucose. Relationship of these effects with energetic metabolism was supported by the finding that ATP levels were lowered by the drugs and increased by glucose. Evaluation of the cytotoxicity induced by each drug showed that the intracellular amount necessary to inhibit cell survival by 50% was of the same order of magnitude as that which decreases to 50% membrane permeability to fluorescein. These results indicate a correspondence in the concentrations of anthracyclines required for inducing cytotoxicity and for inhibiting membrane permeability functions dependent on the metabolic energy supply.