Intracellular accumulation of free calcium in mouse tumor cells exposed to anticancer drugs

Alterations in concentrations of intracellular free calcium ([Ca²⁺]i) were examined in mouse sarcoma S-180 cells exposed to cisplatin, mitomycin C and adriamycin, as related to cell viability. The [Ca²⁺i was measured using the fluorescent Ca²⁺ indicator, fura-2. During the first 24 hr of incubation of the cells in vitro, in the presence of the drugs, the [Ca²⁺]i began to increase at a time when the cell viability was reduced to 50% of the controls, and finally exceeded 1 μM with reduction to 10%. The increase in [Ca²⁺]i was reciprocal to the loss of cell viability. Changes in Ca²⁺ concentrations in the medium did not alter the results. These findings suggest that in the presence of anticancer drugs there is an accumulation of free Ca²⁺ with a release of this ion from internal stores and that cell death follows disruption in the homeostasis of intracellular Ca²⁺.