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+)) 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+) 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+) 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+). The largest elevation was observed when the basic Ca(2+) concentration was low. Both, transient and sustained Ca(2+)-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+)-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+) 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.