Background:

Auranofin, a gold complex used for the treatment of rheumatoid arthritis, also possesses antitumor properties. Here we investigate the effect of Auranofin in modulating the intracellular calcium concentration ([Ca²⁺]_i) and its correlation to cell death and apoptosis.

Objectives:

a) to investigate whether Auranofin modulates [Ca²⁺]_i, b) to determine the concentration response, c) to identify the source of [Ca²⁺]_i, d) to correlate the changes of [Ca²⁺]_i to its apoptotic effects.

Methods:

[Ca²⁺]_i was recorded using florescence microscopy with the calcium sensitive dye Fluo-4 AM. Cytotoxicity for 3hr and 24hr treatment was evaluated by MTS assay. Fluorescent dyes SR-FLICA and 7-AAD were used to determine total cytotoxicity with flow cytometry. To investigate whether calcium enters from the extracellular space or is released from the stores 2-APB (50µM), nimodipine (10µM) and caffeine (10mM) were applied while monitoring [Ca²⁺]_i.

Results:

A sustained increase in [Ca²⁺]_i by Auranofin occurred in a concentration dependent manner. With 10µM, the highest concentration used [Ca²⁺]_i was increased to 90%. Neither of the blockers used (2-APB, nimodipine or caffeine) significantly change this increase. Viability after 3hr and 24hr treatment decreased in a similar manner as [Ca²⁺]_i increased. Flow cytometry revealed an increase of apoptotic cells from 6% to 98% within a concentration range between 0.78µM to 100µM (with less than 16% necrotic cells).

Conclusion:

As Auranofin increases [Ca²⁺]_i in a concentration dependent manner, accompanied by an increase of apoptosis and cell death, modulating [Ca²⁺]_i could be a crucial factor to induce cell death in cancer cells.

Figure 1