Arsenic trioxide (As2O3) induced calcium signals and cytotoxicity in two human cell lines: SY-5Y neuroblastoma and 293 embryonic kidney (HEK)

Arsenic trioxide (As(2)O(3)) has anticancer properties; however, its use also leads to neuro-, hepato- or nephro-toxicity, and therefore, it is important to understand the mechanism of As(2)O(3) toxicity. We studied As(2)O(3) influence on intracellular calcium ([Ca(2+)](i)) homeostasis of human neuroblastoma SY-5Y and embryonic kidney cells (HEK 293).We also relate the As(2)O(3) induced [Ca(2+)](i) modifications with cytotoxicity. We used Ca(2+) sensitive dyes (fluo-4 and rhod-2) combined with laser scanning microscopy or fluorescence activated cell sorting to measure Ca(2+) changes during the application of As(2)O(3) and we approach evaluation of cytotoxicity. As(2)O(3) (1 microM) increased [Ca(2+)](i) in SY-5Y and HEK 293 cells. Three forms of [Ca(2+)](i)-elevations were found: (1) steady-state increases, (2) transient [Ca(2+)](i)-elevations and (3) Ca(2+)-spikes. [Ca(2+)](i) modifications were independent from extracellular Ca(2+) but dependent on internal calcium stores. The effect was not reversible. Inositol triphosphate (IP(3)) and ryanodine (Ry) receptors are involved in regulation of signals induced by As(2)O(3). 2-APB and dantrolene significantly reduced the [Ca(2+)](i)-rise (p<0.001, t-test) but did not completely abolish [Ca(2+)](i)-elevation or spiking. This indicates that other Ca(2+) regulating mechanisms are involved. In cytotoxicity tests As(2)O(3) significantly reduced cell viability in both cell types. Staining with Hoechst 33342 showed occurrence of apoptosis and DNA damage. Our data suggest that [Ca(2+)](i) is an important messenger in As(2)O(3) induced cell death.