Co-application of arsenic trioxide (As2O3) and cisplatin (CDDP) on human SY-5Y neuroblastoma cells has differential effects on the intracellular calcium concentration ([Ca2+]i) and cytotoxicity.

Arsenic trioxide (As(2)O(3)) and cisplatin (CDDP) are clinically relevant chemotherapeutics which modulate the intracellular calcium concentration ([Ca(2+)](i)) by different mechanisms: As(2)O(3) depletes intracellular calcium stores while CDDP triggers an influx of Ca(2+). We investigate whether co-application of As(2)O(3) and CDDP has an effect on [Ca(2+)](i) homeostasis, resulting in an increase of cytotoxicity/apoptosis in human SY-5Y neuroblastoma cells. Confocal imaging with Ca(2+)-sensitive dye (fluo-4) was used for investigating [Ca(2+)](i) dynamics. The induction of cell death was assayed using Trypan blue exclusion and Hoechst 33347 staining. Application of As(2)O(3) (1microM) or CDDP (1microM) increased [Ca(2+)](i). The largest elevation was observed when the basic [Ca(2+)](i) concentration was low. Both, transient and sustained [Ca(2+)](i)-increases were observed in response to a single application of As(2)O(3) or CDDP. Sustained increase showed clear additive effects when both drugs were co-applied. The magnitude of the [Ca(2+)](i)-increase depends on the order of application; the most pronounced effect occurred when the cells were preincubated with CDDP followed by a co-application with As(2)O(3). The sustained [Ca(2+)](i) elevations resulted in increased cytotoxicity and apoptosis. Therefore, co-treatment with CDDP and As(2)O(3) may be a more effective anti-cancer therapy then either agent alone.