Differential reduction by caffeine of adriamycin induced cell killing and cell cycle delays in chinese hamster v79 cells

Abstract

Exponentially growing Chinese-hamster V79-cells were treated with various doses of adriamycin (ADR) for 1 hr in the presence or absence of 2 mM caffeine and were subsequently incubated for 24 hr in fresh medium with or without caffeine (2 mM) before plating to assay for survival. The results indicated a reduction in killing when caffeine was present during treatment with ADR (e.g., reduction in killing from 0.03 to 0.3 after exposure to 0.5 μ/ml ADR). This reduction in killing was even more pronounced after a 24 hr treatment with ADR in the presence of caffeine (e.g, reduction from 0.005 to OS after exposure to 0.08 μg/ml ADR). Incubation with caffeine after ADR treatment (1 hr) caused only a comparably small increase in cell survival. Presence of caffeine either simultaneously or after treatment with ADR caused a reduction of the inhibition of growth and mean-cell-volume increase, and a reduction of the accumulation of cells in G2-phase. Qualitatively similar results were also obtained after continuous treatment with ADR in the presence or absence of caffeine. Reduction in growth inhibition and accumulation of cells in G2-phase was observed under conditions only slightly affecting cell survival, thus suggesting that caffeine may affect these two phenomena by independent mechanisms. Flow cytometry measurement of the intracellular ADR content indicated a reduction in the presence of caffeine. Furthermore, post-treatment incubation with caffeine was found to increase the rate of decay of ADR-related fluorescence. Quantitative comparison between the effect of caffeine in the intracellular ADR accumulation and cell survival suggested that the observed reduction in killing could be attributed to a decrease in the intracellular drug levels. The reduction by caffeine of the ADR-induced cell cycle delays is attributed to either the decrease in the intracellular ADR dose in the presence of caffeine, or to an effect of caffeine similar to that exerted after exposure of cells to ionizing radiation. Trifluoperazine, which had only a small effect on cell survival of cells treated with ADR alone, potentiated killing when cells were treated with ADR in the presence of caffeine. This effect can be partly attributed to the observed modification in the intracellular ADR content under these conditions but, as a quantitative comparison suggests, other effects might also be involved.