Reduction by Caffeine of Adriamycin-induced Cell Killing and DNA Damage in Chinese Hamster Cells: Correlation with Modulation in Intracellular Adriamycin Content¹

The effect of caffeine, at concentrations between 10 µm and 20 mm was studied on Adriamycin-induced cytotoxicity and DNA damage in exponentially growing Chinese hamster V79 cells. Simultaneous administration of caffeine with 0.4 µg/ml (0.69 µm) Adriamycin for 1 h resulted in a concentration-dependent reduction in cell killing. The surviving fraction increased from 0.001 for cells treated with Adriamycin alone to 0.14 for cells treated in the presence of 1 mm caffeine and to 0.8 for cells treated at caffeine concentrations higher than 6 mm. A significant reduction in Adriamycin-induced cell killing was also caused by caffeine at micromolar comcentrations where the surviving fraction increased from 0.00076 to 0.0014 (2-fold) after treatment with 10 µm, to 0.0038 (5-fold) after treatment with 20 µm and to 0.01 (13-fold) after treatment with 100 µm caffeine. Treatment of cells with caffeine for 1 h immediately after Adriamycin exposure (0.4 µg/ml, 1 h) resulted in a dose-dependent increase in survival as well, but the effect was smaller than that observed after simultaneous administration (increase in the surviving fraction from 0.003 to about 0.05 at concentrations higher than 5 mm). The reduction of Adriamycin-induced cytotoxicity by caffeine was reflected by a decrease in the slope of the survival curve, and it was similar over the entire range of Adriamycin and caffeine concentrations examined. The ability of cells to accumulate Adriamycin was reduced by caffeine from 43 mg/10⁶ cells after treatment for 1 h in the presence of 0.5 µg/ml Adriamycin to 16 mg/10⁶ cells for cells treated in the presence of 2 mm and to 8 ng/10⁶ cells for cells treated in the presence of 10 mm caffeine. Induction by Adriamycin of DNA breaks, as assayed by the alkaline filter elution technique, was linear with concentration and was decreased in the presence of caffeine. The response to caffeine of Adriamycin-induced killing and DNA damage was similar, and it was only slightly different from the modulation induced in intracellular Adriamycin content. Compared to the effect of caffeine on cells exposed to ionizing radiations or other cytotoxic compounds, the results indicate an entirely different mode of caffeine action with anthracyclines. In addition, the results suggest caffeine-induced modulations in intracellular drug accumulation as an important determinant for the effect and may have useful implications in the clinical application of these compounds.